業績情報

• 水表面の和周波発生分光の実験と計算　　　　　　　　　　　　　　　
  山口祥一
  フォトニクスニュース, 巻：10, 号：3, 2025年03月, ［査読有り］, ［招待有り］, ［筆頭著者］
  研究論文（学術雑誌）
• A macroscopically homogeneous lipid phase exhibits leaflet-specific lipid diffusion in a glass-supported lipid bilayer
  Takuhiro Otosu; Miyuki Sakaguchi; Shoichi Yamaguchi
  Physical Chemistry Chemical Physics, 巻：27, 号：9, 開始ページ：4944, 終了ページ：4949, 2025年03月, ［査読有り］
  Leaflet-specific lipid diffusion analysis revealed that the strength of interleaflet coupling is sensitive to the lipid composition even in the region where macroscopically homogeneous phase is observed.
  Royal Society of Chemistry (RSC), 研究論文（学術雑誌）
  DOI：https://doi.org/10.1039/d5cp00203f
  DOI ID：10.1039/d5cp00203f, ISSN：1463-9076, eISSN：1463-9084
• A new rigid non-polarizable model for semi-heavy water: TIP4P/2005-SHW
  Tetsuyuki Takayama; Takuhiro Otosu; Shoichi Yamaguchi
  The Journal of Chemical Physics, 巻：161, 号：23, 2024年12月, ［査読有り］
  In molecular dynamics (MD) simulations of water, rigid non-polarizable models are still valuable and widely used because of their low computational cost and excellent performance. Most of such models have been for light water (H2O) for a long time, and a few have recently been reported for heavy water (D2O). The specific models of D2O are needed because of its notably slower dynamics and stronger hydrogen bond than H2O. To our knowledge, no models of semi-heavy water (HOD) were made, although HOD is the most abundant and, therefore, most important chemical species in isotopically diluted water (IDW) prepared by mixing equal amounts of H2O and D2O. For precise MD simulations of IDW, a specific model of HOD is definitely needed. Here, we report the development of a new rigid non-polarizable model of HOD, TIP4P/2005-SHW, on the basis of the most popular H2O model, TIP4P/2005, and its D2O counterpart, TIP4P/2005-HW. We show the details of the development and demonstrate the high reproducibility of TIP4P/2005-SHW in terms of the density, the temperature of maximum density, the viscosity, and the diffusion coefficient.
  AIP Publishing, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/5.0240271
  DOI ID：10.1063/5.0240271, ISSN：0021-9606, eISSN：1089-7690
• Diffusion of Multiple Species Resolved by Fluorescence Lifetime Recovery after Photobleaching (FLRAP)
  Ikumi Mori; Shun Terasaka; Shoichi Yamaguchi; Takuhiro Otosu
  Analytical Chemistry, 巻：96, 号：12, 開始ページ：4854, 終了ページ：4859, 2024年04月, ［査読有り］
  American Chemical Society (ACS), 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/acs.analchem.3c05181
  DOI ID：10.1021/acs.analchem.3c05181, ISSN：0003-2700, eISSN：1520-6882
• Theoretical and experimental OD-stretch vibrational spectroscopy of heavy water
  Tetsuyuki Takayama; Takuhiro Otosu; Shoichi Yamaguchi
  The Journal of Chemical Physics, 巻：160, 号：10, 2024年04月, ［査読有り］
  In view of the current situation in which the OD-stretch vibrational spectra have been scarcely computed with non-polarizable rigid D2O models, we investigate the IR and Raman spectra of D2O by using a newly-reported model TIP4P/2005-HW. From the comparison between the calculations and experimental data, we find the excellent performance of TIP4P/2005-HW for vibrational spectroscopy of D2O in the same manner as TIP4P/2005 for H2O, although one may still conveniently employ an alternative method that regards OH as putative OD to calculate the OD-stretch spectra with similar quality from TIP4P/2005 trajectories. We also demonstrate that the appropriate setting for the spectral simulation of D2O under the time-averaging approximation reflects the slower dynamics (i.e., slower motion of translation and rotation due to the heavier mass and stronger hydrogen bond) of D2O than H2O. Moreover, we show from the theoretical calculations that the established interpretation of the OH-stretch spectra of H2O is finely applicable to the OD-stretch of D2O.
  AIP Publishing, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/5.0200623
  DOI ID：10.1063/5.0200623, ISSN：0021-9606, eISSN：1089-7690
• 振動分光の実験と理論計算による結晶氷の分子構造研究　　　　　　　　　　　　　　　
  高山哲侑; 山口祥一
  日本結晶成長学会誌, 巻：51, 開始ページ：1, 終了ページ：10, 2024年04月, ［招待有り］
  研究論文（学術雑誌）
• Peripheral adsorption of polylysine on one leaflet of a lipid bilayer reduces the lipid diffusion of both leaflets
  Kosei Shimizu; Miyuki Sakaguchi; Shoichi Yamaguchi; Takuhiro Otosu
  Physical Chemistry Chemical Physics, 巻：26, 号：11, 開始ページ：8873, 終了ページ：8878, 2024年04月, ［査読有り］
  Leaflet-specific lipid diffusion analysis revealed that polylysine adsorption on one leaflet of a lipid bilayer is sensed by the opposite leaflet.
  Royal Society of Chemistry (RSC), 研究論文（学術雑誌）
  DOI：https://doi.org/10.1039/d3cp04882a
  DOI ID：10.1039/d3cp04882a, ISSN：1463-9076, eISSN：1463-9084
• Complex phase of the nonresonant background in sum frequency generation spectroscopy
  Korenobu Matsuzaki; Shoichi Yamaguchi; Tahei Tahara
  The Journal of Chemical Physics, 巻：159, 号：22, 2023年12月
  Sum frequency generation (SFG) spectroscopy is an interface-selective spectroscopic technique that enables us to selectively observe the vibrational or electronic resonances of molecules within a very thin interface layer. The interfacial properties probed by SFG are contained in a complex quantity called the second-order nonlinear susceptibility (χ2). It is usually believed that the imaginary part of χ2 (Im χ2) exhibits the resonant responses of the system, whereas the nonresonant responses appear solely in the real part of χ2 (Re χ2). However, it was recently theoretically pointed out that a portion of the nonresonant responses actually contributes to the observed Im χ2 spectra when the finite thickness of the interface layer is taken into account. In this study, by considering a simple air/liquid interface without any solutes as a model system, we theoretically evaluate the nonresonant contribution to experimentally accessible Im χ2 as well as to Re χ2, from which the complex phase of the nonresonant background is estimated. It is shown that the deviation of the complex phase from 0° or 180° is less than 1° even if the thickness of the interface layer is taken into account. This means that the nonresonant contribution to Im χ2 is practically negligible, and it is a very good approximation to think that the nonresonant background appears solely in Re χ2 in the case of air/liquid interfaces. This result implies that Im χ2 practically contains only the resonant responses of the system, and molecular resonances at the interface can be conveniently studied using Im χ2 spectra at such interfaces.
  AIP Publishing, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/5.0169712
  DOI ID：10.1063/5.0169712, ISSN：0021-9606, eISSN：1089-7690
• Appraisal of TIP4P-type models at water surface
  Shoichi Yamaguchi; Tetsuyuki Takayama; Takuhiro Otosu
  The Journal of Chemical Physics, 巻：159, 号：17, 2023年11月
  In view of the current situation in which non-polarizable rigid water models have been scarcely examined against surface-specific properties, we appraise TIP4P-type models at the liquid water surface on the basis of heterodyne-detected sum frequency generation (HD-SFG) spectroscopy. We find in the HD-SFG spectrum of the water surface that the peak frequency of the hydrogen-bonded OH band, the half width at half maximum of the hydrogen-bonded OH band, and the full width at half maximum of the free OH band are best reproduced by TIP4P, TIP4P/Ew, and TIP4P/Ice, respectively, whereas it is already well known that TIP4P/2005 best reproduces the surface tension. These TIP4P-type models perform better at the water surface in terms of the present appraisal items than some polarizable models in the literature.
  AIP Publishing, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/5.0171999
  DOI ID：10.1063/5.0171999, ISSN：0021-9606, eISSN：1089-7690
• Transferability of vibrational spectroscopic map from TIP4P to TIP4P-like water models
  Tetsuyuki Takayama; Takuhiro Otosu; Shoichi Yamaguchi
  The Journal of Chemical Physics, 巻：158, 号：13, 2023年04月
  We computed the IR, Raman, and sum frequency generation spectra of water in the OH-stretch region by employing the quantum/classical mixed approach that consists of a vibrational spectroscopic map and molecular dynamics (MD) simulation. We carried out the MD simulation with the TIP4P, TIP4P/2005, and TIP4P/Ice models and applied the map designed for TIP4P by Skinner et al. to each MD trajectory. Although the map is not tuned for TIP4P-like models, TIP4P/2005 and TIP4P/Ice provide the best reproduction of the experimental vibrational spectra of liquid water and crystalline ice, respectively. This result demonstrates the transferability of the map from TIP4P to TIP4P/2005 and TIP4P/Ice, meaning that one can choose an appropriate TIP4P-like model to calculate the vibrational spectra of an aqueous system without rebuilding the map.
  AIP Publishing, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/5.0146084
  DOI ID：10.1063/5.0146084, ISSN：0021-9606, eISSN：1089-7690
• Experimental and Theoretical Heterodyne-Detected Sum Frequency Generation Spectroscopy of Isotopically Pure and Diluted Water Surfaces　　　　　　　　　　　　　　　
  Shoichi Yamaguchi; Tetsuyuki Takayama; Yuki Goto; Takuhiro Otosu; Takuma Yagasaki
  The Journal of Physical Chemistry Letters, 2022年10月, ［査読有り］
  研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/acs.jpclett.2c02533
  DOI ID：10.1021/acs.jpclett.2c02533, ORCID：120487669
• Experimental and Theoretical Raman Spectroscopy of Isotopically Pure and Diluted Ice VI　　　　　　　　　　　　　　　
  Tetsuyuki Takayama; Kota Kishi; Takuhiro Otosu; Takuma Yagasaki; Shoichi Yamaguchi
  The Journal of Physical Chemistry C, 2022年10月, ［査読有り］
  研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/acs.jpcc.2c05133
  DOI ID：10.1021/acs.jpcc.2c05133, ORCID：120088265
• Raman spectroscopy of isotopically pure and diluted high‐ and low‐density amorphous ices
  Senri Ishihara; Tetsuyuki Takayama; Miyuki Sakaguchi; Takuhiro Otosu; Takuma Yagasaki; Yoshiharu Suzuki; Shoichi Yamaguchi
  Journal of Raman Spectroscopy, 2022年02月
  Wiley, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1002/jrs.6322
  DOI ID：10.1002/jrs.6322, ISSN：0377-0486, eISSN：1097-4555
• DNA-Induced Reorganization of Water at Model Membrane Interfaces Investigated by Heterodyne-Detected Vibrational Sum Frequency Generation Spectroscopy　　　　　　　　　　　　　　　
  Prashant Chandra Singh; Mohammed Ahmed; Satoshi Nihonyanagi; Shoichi Yamaguchi; Tahei Tahara
  JOURNAL OF PHYSICAL CHEMISTRY B, 巻：126, 号：4, 開始ページ：840, 終了ページ：846, 2022年02月
  Lipid-DNA complexes are important nonviral vectors to be used in gene therapy, which is one of the promising strategies for the cure of many diseases. Although interfacial water is expected to play a significant role in lipid-DNA complexation, a molecular-level understanding about the role of interfacial water in the DNA-lipid complexation is still sparse. In this study, the structure and orientation of water at cationic and zwitterionic lipid monolayer/water interfaces in the presence of DNA are studied by the use of interface-selective heterodyne-detected vibrational sum frequency generation (HD-VSFG) spectroscopy. It is found that the adsorption of DNA at a cationic lipid interface drastically decreases the orientation of interfacial water reflecting the neutralization of the positively charged interface, whereas the adsorption of DNA at a zwitterionic lipid interface makes interfacial water become more "H-up", indicating that the originally zwitterionic interface becomes negatively charged due to the DNA adsorption. Furthermore, interfacial water having relatively strong hydrogen bonds is observed at both the cationic and zwitterionic lipid interfaces in the presence of DNA.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/acs.jpcb.1c08581
  DOI ID：10.1021/acs.jpcb.1c08581, ISSN：1520-6106, eISSN：1520-5207, Web of Science ID：WOS:000746682000001
• Heterodyne-Detected Sum Frequency Generation Spectroscopic Study of Weakly Hydrogen-Bonded Water at Charged Lipid Interfaces, Revisited
  Yuki Nojima; Shoichi Yamaguchi
  The Journal of Physical Chemistry C, 巻：125, 号：42, 開始ページ：23483, 終了ページ：23489, 2021年10月
  American Chemical Society (ACS), 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/acs.jpcc.1c07173
  DOI ID：10.1021/acs.jpcc.1c07173, ISSN：1932-7447, eISSN：1932-7455
• Progress in phase-sensitive sum frequency generation spectroscopy
  Shoichi Yamaguchi; Takuhiro Otosu
  Physical Chemistry Chemical Physics, 巻：23, 号：34, 開始ページ：18253, 終了ページ：18267, 2021年
  Representative methods of surface-selective phase-sensitive sum frequency generation spectroscopy are reviewed in terms of interferometer implementation for optical heterodyne detection.
  Royal Society of Chemistry (RSC), 研究論文（学術雑誌）
  DOI：https://doi.org/10.1039/d1cp01994e
  DOI ID：10.1039/d1cp01994e, ISSN：1463-9076, eISSN：1463-9084
• Resolving the Controversy over Dipole versus Quadrupole Mechanism of Bend Vibration of Water in Vibrational Sum Frequency Generation Spectra　　　　　　　　　　　　　　　
  Mohammed Ahmed; Satoshi Nihonyanagi; Achintya Kundu; Shoichi Yamaguchi; Tahei Tahara
  JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 巻：11, 号：21, 開始ページ：9123, 終了ページ：9130, 2020年11月
  Recently, there has been controversy over whether the HOH bend signal of water in the vibrational sum frequency generation (VSFG) spectrum arises from the conventional dipole mechanism or the quadrupole mechanism. Here, we show that the Im chi((2)) (the imaginary part of the second-order nonlinear susceptibility) spectra of the HOH bend mode of water at oppositely charged monolayer/water interfaces all exhibit positive bands, irrespective of the difference in the sign of the charge at the interface. Furthermore, it is found that the peak frequency of the HOH bend band substantially changes depending on the chemical structure of the charged headgroup located at the interface. These results demonstrate that the VSFG signal of the HOH bend vibration is generated from interfacial water with the interfacial quadrupole mechanism that is associated with the large field gradient of incident lights localized in a very thin region at the interface.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/acs.jpclett.0c02644
  DOI ID：10.1021/acs.jpclett.0c02644, ISSN：1948-7185, Web of Science ID：WOS:000589920000029
• Structure of water and polymer at the buried polymer/water interface unveiled using heterodyne-detected vibrational sum frequency generation　　　　　　　　　　　　　　　
  Anton Myalitsin; Sanat Ghosh; Shu-hei Urashima; Satoshi Nihonyanagi; Shoichi Yamaguchi; Takashi Aoki; Tahei Tahara
  PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 巻：22, 号：29, 開始ページ：16527, 終了ページ：16531, 2020年08月
  The structure of the prototypical acrylic polymer (poly(methyl methacrylate): PMMA)/water interface is elucidated at the molecular level using heterodyne-detected sum-frequency generation. Two distinct OH groups of interfacial water are found at the interface: one forms hydrogen bonds with the carbonyl group and the other weakly interacts with the ester methyl group of the polymer surface.
  ROYAL SOC CHEMISTRY, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1039/d0cp02618b
  DOI ID：10.1039/d0cp02618b, ISSN：1463-9076, eISSN：1463-9084, Web of Science ID：WOS:000556485900003
• Hydrogen order at the surface of ice Ih revealed by vibrational spectroscopy　　　　　　　　　　　　　　　
  Yuki Nojima; Yuki Shioya; Hajime Torii; Shoichi Yamaguchi
  Chem. Commun., 巻：56, 号：33, 開始ページ：4563, 終了ページ：4566, 2020年03月, ［査読有り］
  英語, 研究論文（学術雑誌）
• Effect of electrostatic interaction on the leaflet-specific diffusion in a supported lipid bilayer revealed by fluorescence lifetime correlation analysis　　　　　　　　　　　　　　　
  Takuhiro Otosu; Shoichi Yamaguchi
  PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 巻：22, 号：3, 開始ページ：1242, 終了ページ：1249, 2020年01月
  A supported lipid bilayer (SLB) is now an indispensable tool to analyze the dynamical properties of biomembranes. However, the effect of a solid support on the leaflet-specific lipid dynamics in a SLB remains elusive, which hampers the further application of the SLB as a model biomembrane. Here, we performed the leaflet-specific lipid diffusion analysis by means of two-dimensional fluorescence lifetime correlation spectroscopy to elucidate the effect of the electrostatic interaction between lipid headgroups and a glass surface on the lipid diffusion in each leaflet of the SLB. The results clearly showed the correlation between the strength of the electrostatic interaction and the lipid diffusion in the proximal leaflet of the SLB facing a glass surface. In particular, the electrostatic attraction between the cationic lipids and a negatively charged glass surface enhanced the lipid diffusion in the proximal leaflet of the SLB, providing important implications for the lipid dynamics not only in the SLB but also in biomembranes.
  ROYAL SOC CHEMISTRY, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1039/c9cp05833h
  DOI ID：10.1039/c9cp05833h, ISSN：1463-9076, eISSN：1463-9084, Web of Science ID：WOS:000509371400030
• Quadrupolar mechanism for vibrational sum frequency generation at air/liquid interfaces: Theory and experiment
  Korenobu Matsuzaki; Satoshi Nihonyanagi; Shoichi Yamaguchi; Takashi Nagata; Tahei Tahara
  The Journal of Chemical Physics, 巻：151, 号：6, 開始ページ：064701, 終了ページ：064701, 2019年08月
  AIP Publishing, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/1.5088192
  DOI ID：10.1063/1.5088192, ISSN：0021-9606, eISSN：1089-7690
• Reduction of glass-surface charge density slows the lipid diffusion in the proximal leaflet of a supported lipid bilayer　　　　　　　　　　　　　　　
  Takuhiro Otosu; Shoichi Yamaguchi
  JOURNAL OF CHEMICAL PHYSICS, 巻：151, 号：2, 2019年07月
  Understanding the effect of a solid support on the dynamical properties of a supported lipid bilayer (SLB) is a prerequisite for the applications of SLB as a model biomembrane. Here, we applied two-dimensional fluorescence lifetime correlation spectroscopy to examine the effect of solution pH on the diffusion of lipids in the proximal/distal leaflets of a zwitterionic SLB. Leaflet-specific diffusion analyses at various pH revealed that the diffusion of lipids in the proximal leaflet facing a glass surface becomes slower by decreasing pH with the transition pH of similar to 7.4. We attributed it to the reduction of the surface charge density of a glass support. Furthermore, the data clearly showed that the lipid diffusion in the distal leaflet facing a bulk solution is insensitive to the change in the diffusion property of the proximal leaflet. This reflects a weak interleaflet coupling between the proximal and distal leaflets of the SLB. Published under license by AIP Publishing.
  AMER INST PHYSICS, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/1.5103221
  DOI ID：10.1063/1.5103221, ISSN：0021-9606, eISSN：1089-7690, Web of Science ID：WOS:000486055700034
• Perspective on sum frequency generation spectroscopy of ice surfaces and interfaces　　　　　　　　　　　　　　　
  Shoichi Yamaguchi; Yudai Suzuki; Yuki Nojima; Takuhiro Otosu
  CHEMICAL PHYSICS, 巻：522, 開始ページ：199, 終了ページ：210, 2019年06月
  This perspective is focused on surfaces and interfaces of crystalline ice studied with sum frequency generation (SFG) spectroscopy by several research groups within these twenty years. The intrinsic interface selectivity of SFG has already enabled one to determine structural aspects of the ice surfaces and interfaces through vibrational signatures of the OH stretch. Here we describe why SFG is suitable for ice surface science and how SFG has revealed the structure and dynamics of dangling bonds, quasi-liquid layer, hydrogen-bond network, and ordered protons at the ice surfaces, ice/substrate interfaces, and ice films on metal surfaces. In particular, we compare SFG spectra of ice reported by different groups to examine consistency between their experiments. We elaborate current controversies on a few SFG studies of ice before presenting future outlook for ice surface science by SFG. Additionally in the appendix we briefly explain some technical issues that may help us resolve conflicts and make progress in the right way.
  ELSEVIER SCIENCE BV, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1016/j.chemphys.2019.03.005
  DOI ID：10.1016/j.chemphys.2019.03.005, ISSN：0301-0104, eISSN：1873-4421, Web of Science ID：WOS:000466713000027
• Quantifying the Diffusion of Lipids in the Proximal/Distal Leaflets of a Supported Lipid Bilayer by Two-Dimensional Fluorescence Lifetime Correlation Spectroscopy　　　　　　　　　　　　　　　
  Takuhiro Otosu; Shoichi Yamaguchi
  JOURNAL OF PHYSICAL CHEMISTRY B, 巻：122, 号：45, 開始ページ：10315, 終了ページ：10319, 2018年11月
  A supported lipid bilayer (SLB) is a versatile platform for examining the dynamical properties of biomembranes. However, the effect of a prerequisite solid substrate on the dynamics of a SLB remains very elusive. Especially, it is not clarified how the diffusivity of each leaflet in a SLB is affected by the SLB solid substrate interaction. In this study, we applied two-dimensional fluorescence lifetime correlation spectroscopy to a SLB for elucidating the diffusion of lipids in the proximal and distal leaflets of a SLB. We find that the autocorrelation curve of a fluorescent lipid in the proximal leaflet decays more slowly than that in the distal leaflet, meaning that the proximal leaflet is less diffusive. This result indicates stronger interaction between the proximal leaflet and a solid substrate.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/acs.jpcb.8b08614
  DOI ID：10.1021/acs.jpcb.8b08614, ISSN：1520-6106, Web of Science ID：WOS:000451101100006
• Total Internal Reflection Two-Dimensional Fluorescence Lifetime Correlation Spectroscopy　　　　　　　　　　　　　　　
  Takuhiro Otosu; Shoichi Yamaguchi
  Journal of Physical Chemistry B, 巻：122, 号：22, 開始ページ：5758, 終了ページ：5764, 2018年06月, ［査読有り］
  Fluorescence lifetime correlation analysis is becoming a powerful tool to understand the conformational heterogeneity of biomolecules and their dynamics with an unprecedented detection sensitivity and time resolution. However, its application to the study of biomembranes is very limited. Here, we report on two-dimensional fluorescence lifetime correlation spectroscopy (2D FLCS) in combination with total internal reflection (TIR) microscopy (TIR 2D-FLCS). High depth resolution in TIR microscopy and species-specific correlation analysis in 2D FLCS give us the opportunity to selectively analyze molecules in or on a supported lipid bilayer, a model biomembrane formed on the glass surface. Feasibility experiments performed in this study clearly demonstrated that TIR 2D-FLCS has a potential to selectively analyze the diffusion and the conformational dynamics of proteins peripherally bound on the membrane in the presence of substantial amounts of unbound molecules in the bulk phase.
  American Chemical Society, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/acs.jpcb.8b01176
  DOI ID：10.1021/acs.jpcb.8b01176, ISSN：1520-5207, SCOPUS ID：85048247541
• Local pH at the surface of hen egg white lysozyme　　　　　　　　　　　　　　　
  Takuhiro Otosu; Kaito Kobayashi; Shoichi Yamaguchi
  Chemical Physics Letters, 巻：693, 開始ページ：165, 終了ページ：169, 2018年02月, ［査読有り］
  The microenvironment at the surface of hen-egg-white lysozyme (HEWL) was examined by analyzing the change in pKa of fluorescein isothiocyanate (FITC) upon binding to the N-terminus of HEWL. The result showed that the local pH at the HEWL surface is higher than the bulk pH. Furthermore, the data showed that the difference between the local and bulk pH becomes larger with decreasing pH, suggesting HEWL repels more protons at lower pH. Because the local pH affects the protonation states of functional amino-acids at the protein surface, the results provide the fundamental insight into the microenvironment at the protein surface.
  Elsevier B.V., 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1016/j.cplett.2018.01.026
  DOI ID：10.1016/j.cplett.2018.01.026, ISSN：0009-2614, SCOPUS ID：85040701289
• Cooperative Hydrogen-Bond Dynamics at a Zwitterionic Lipid/Water Interface Revealed by 2D HD-VSFG Spectroscopy　　　　　　　　　　　　　　　
  Ken-ichi Inoue; Prashant C. Singh; Satoshi Nihonyanagi; Shoichi Yamaguchi; Tahei Tahara
  JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 巻：8, 号：20, 開始ページ：5160, 終了ページ：5165, 2017年10月, ［査読有り］
  Molecular-level elucidation of hydration at biological membrane interfaces is of great importance for understanding biological processes. We studied ultrafast hydrogen-bond dynamics at a zwitterionic phosphatidylcholine/water interface by two-dimensional heterodyne-detected vibrational sum frequency generation (2D HD-VSFG) spectroscopy. The obtained 2D spectra confirm that the anionic phosphate and cationic choline sites are individually hydrated at the interface. Furthermore, the data show that the dynamics of water at the zwitterionic lipid interface is not a simple sum of the dynamics of the water species that hydrate to the separate phosphate and choline. The center line slope (CLS) analysis of the 2D spectra reveals that ultrafast hydrogen bond fluctuation is not significantly suppressed around the phosphate at the zwitterionic lipid interface, which makes the hydrogen-bond dynamics look similar to that of the bulk water. The present study indicates that the hydrogen-bond dynamics at membrane interfaces is not determined only by the hydrogen bond to a specific site of the interface but is largely dependent on the water dynamics in the vicinity and other nearby moieties, through the hydrogen-bond network.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/acs.jpclett.7b02057
  DOI ID：10.1021/acs.jpclett.7b02057, ISSN：1948-7185, Web of Science ID：WOS:000413798300030
• Proton Order toward the Surface of Ice I-h Revealed by Heterodyne-Detected Sum Frequency Generation Spectroscopy　　　　　　　　　　　　　　　
  Yuki Nojima; Yudai Suzuki; Misato Takahashi; Shoichi Yamaguchi
  JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 巻：8, 号：20, 開始ページ：5031, 終了ページ：5034, 2017年10月, ［査読有り］
  Using heterodyne-detected sum frequency generation (HD-SFG) spectroscopy, we investigated surface proton order at the basal, primary prism, and secondary prism faces of single-crystalline ice I-h at ca. 130 K. The complex phase of the obtained spectra clearly indicates that second-order nonlinear polarization from which the HD-SFG signal arises is generated exclusively at the surfaces. This suggests surface proton ordering along the normal, whereas the bulk remains proton-disordered, as is well known for ice I-h. A strong positive peak observed in the HD-SFG spectra enables us to determine the "direction" of the surface proton order as "H-up", that is, the hydrogen atom of the OH group pointing away from the bulk, irrespective of the ice faces. Reliable HD-SFG measurements carried out in the present study have greatly advanced our understanding of surface structure of ice I-h.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/acs.jpclett.7b02198
  DOI ID：10.1021/acs.jpclett.7b02198, ISSN：1948-7185, ORCID：40809659, Web of Science ID：WOS:000413798300010
• Communication: Development of standing evanescent-wave fluorescence correlation spectroscopy and its application to the lateral diffusion of lipids in a supported lipid bilayer　　　　　　　　　　　　　　　
  Takuhiro Otosu; Shoichi Yamaguchi
  JOURNAL OF CHEMICAL PHYSICS, 巻：147, 号：4, 2017年07月, ［査読有り］
  We present standing evanescent-wave fluorescence correlation spectroscopy (SEW-FCS). This technique utilizes the interference of two evanescent waves which generates a standing evanescent-wave. Fringe-pattern illumination created by a standing evanescent-wave enables us to measure the diffusion coefficients of molecules with a super-resolution corresponding to one fringe width. Because the fringe width can be reliably estimated by a simple procedure, utilization of fringes is beneficial to quantitatively analyze the slow diffusion of molecules in a supported lipid bilayer (SLB), a model biomembrane formed on a solid substrate, with the timescale relevant for reliable FCS analysis. Furthermore, comparison of the data between SEW-FCS and conventional total-internal reflection FCS, which can also be performed by the SEW-FCS instrument, effectively eliminates the artifact due to afterpulsing of the photodiode detector. The versatility of SEW-FCS is demonstrated by its application to various SLBs. Published by AIP Publishing.
  AMER INST PHYSICS, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/1.4985871
  DOI ID：10.1063/1.4985871, ISSN：0021-9606, eISSN：1089-7690, ORCID：36223899, Web of Science ID：WOS:000406347200002
• Heterodyne-detected sum frequency generation spectroscopy of aqueous interfaces　　　　　　　　　　　　　　　
  Yamaguchi Shoichi
  ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 巻：253, 2017年04月, ［査読有り］
  ISSN：0065-7727, Web of Science ID：WOS:000430569106683
• Vibrational Coupling at the Topmost Surface of Water Revealed by Heterodyne-Detected Sum Frequency Generation Spectroscopy　　　　　　　　　　　　　　　
  Yudai Suzuki; Yuki Nojima; Shoichi Yamaguchi
  JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 巻：8, 号：7, 開始ページ：1396, 終了ページ：1401, 2017年04月, ［査読有り］
  Unraveling vibrational coupling is the key to consistently interpret vibrational spectra of complex molecular systems. The vibrational spectrum of the water surface heavily suffers from vibrational coupling, which hinders complete understanding of the molecular structure and dynamics of the water surface. Here we apply heterodyne detected sum frequency generation spectroscopy to the water surface and accomplish the assignment of a weak vibrational band located at the lower energy side of the free OH stretch. We find that this band is due to a combination mode of the hydrogen-bonded OH stretch and a low-frequency intermolecular vibration, and this combination band appears in the surface vibrational spectrum through anharmonic vibrational coupling that takes place exclusively at the topmost surface.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/acs.jpclett.7b00312
  DOI ID：10.1021/acs.jpclett.7b00312, ISSN：1948-7185, ORCID：36223900, Web of Science ID：WOS:000398884800012
• Weakly Hydrogen-Bonded Water Inside Charged Lipid Monolayer Observed with Heterodyne-Detected Vibrational Sum Frequency Generation Spectroscopy　　　　　　　　　　　　　　　
  Yuki Nojima; Yudai Suzuki; Shoichi Yamaguchi
  JOURNAL OF PHYSICAL CHEMISTRY C, 巻：121, 号：4, 開始ページ：2173, 終了ページ：2180, 2017年02月, ［査読有り］
  Many biological processes such as photosynthesis and signal transduction proceed at lipid/water interfaces. Although water molecules inside lipid membranes are considered to have a critical role in these processes, it has been difficult to experimentally observe those water molecules with high selectivity. Here, we measure the Im chi((2)) (imaginary part of second-order nonlinear optical susceptibility) spectra of water at anionic lipid (1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol, DPPG) and cationic lipid (1,2-dipalmitoyl-3trimethylammonium-propane, DPTAP) interfaces with single-channel heterodyne-detected sum frequency generation spectroscopy and investigate the structure of water molecules at the lipid interfaces. The presence of weakly hydrogen-bonded water molecules located above the lipid head group is clearly identified. The Im chi((2)) spectra indicate that water molecules above the head group are oriented oppositely to those below the head group and they donate hydrogen bonds to the carbonyl and glycerol groups of the lipids. It is likely that water molecules inside the lipid monolayers can freely flip without terminating the weak hydrogen bonds.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/acs.jpcc.6b09229
  DOI ID：10.1021/acs.jpcc.6b09229, ISSN：1932-7447, ORCID：31195802, Web of Science ID：WOS:000393443200017
• Comment on "Phase reference in phase-sensitive sum-frequency vibrational spectroscopy" [J. Chem. Phys. 144, 244711 (2016)]　　　　　　　　　　　　　　　
  Shoichi Yamaguchi
  JOURNAL OF CHEMICAL PHYSICS, 巻：145, 号：16, 2016年10月, ［査読有り］
  AMER INST PHYSICS, 英語
  DOI：https://doi.org/10.1063/1.4965437
  DOI ID：10.1063/1.4965437, ISSN：0021-9606, eISSN：1089-7690, ORCID：29445417, Web of Science ID：WOS:000387586200058
• Femtosecond Hydrogen Bond Dynamics of Bulk-like and Bound Water at Positively and Negatively Charged Lipid Interfaces Revealed by 2D HD-VSFG Spectroscopy　　　　　　　　　　　　　　　
  Prashant Chandra Singh; Ken-ichi Inoue; Satoshi Nihonyanagi; Shoichi Yamaguchi; Tahei Tahara
  ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 巻：55, 号：36, 開始ページ：10621, 終了ページ：10625, 2016年08月, ［査読有り］
  Interfacial water in the vicinity of lipids plays an important role in many biological processes, such as drug delivery, ion transportation, and lipid fusion. Hence, molecular-level elucidation of the properties of water at lipid interfaces is of the utmost importance. We report the two-dimensional heterodyne-detected vibrational sum frequency generation (2D HD-VSFG) study of the OH stretch of HOD at charged lipid interfaces, which shows that the hydrogen bond dynamics of interfacial water differ drastically, depending on the lipids. The data indicate that the spectral diffusion of the OH stretch at a positively charged lipid interface is dominated by the ultrafast (<approximate to 100fs) component, followed by the minor sub-picosecond slow dynamics, while the dynamics at a negatively charged lipid interface exhibit sub-picosecond dynamics almost exclusively, implying that fast hydrogen bond fluctuation is prohibited. These results reveal that the ultrafast hydrogen bond dynamics at the positively charged lipid-water interface are attributable to the bulk-like property of interfacial water, whereas the slow dynamics at the negatively charged lipid interface are due to bound water, which is hydrogen-bonded to the hydrophilic head group.
  WILEY-V C H VERLAG GMBH, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1002/anie.201603676
  DOI ID：10.1002/anie.201603676, ISSN：1433-7851, eISSN：1521-3773, ORCID：29445418, Web of Science ID：WOS:000383473600014
• Bend Vibration of Surface Water Investigated by Heterodyne-Detected Sum Frequency Generation and Theoretical Study: Dominant Role of Quadrupole　　　　　　　　　　　　　　　
  Achintya Kundu; Shogo Tanaka; Tatsuya Ishiyama; Mohammed Ahmed; Ken-ichi Inoue; Satoshi Nihonyanagi; Hiromi Sawai; Shoichi Yamaguchi; Akihiro Morita; Tahei Tahara
  JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 巻：7, 号：13, 開始ページ：2597, 終了ページ：2601, 2016年07月, ［査読有り］
  Heterodyne-detected vibrational sum frequency generation spectroscopy was applied to the water surface for measuring the imaginary part of second-order nonlinear susceptibility (Im chi((2))) spectrum in the bend frequency region for the first time. The observed Im chi((2)) spectrum shows an overall positive band around 1650 cm(-1), contradicting former theoretical predictions. We further found that the Im chi((2))) spectrum of NaI aqueous solution exhibits an even larger positive band, which is apparently contrary to the flip-flop orientation of surface water. These unexpected observations are elucidated by calculating quadrupole contributions beyond the conventional dipole approximation. It is indicated that the Im chi((2)) spectrum in the bend region has a large quadrupole contribution from the bulk water.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/acs.jpclett.6b00657
  DOI ID：10.1021/acs.jpclett.6b00657, ISSN：1948-7185, ORCID：28499888, Web of Science ID：WOS:000379457400052
• Partially Hydrated Electrons at the Air/Water Interface Observed by UV-Excited Time-Resolved Heterodyne-Detected Vibrational Sum Frequency Generation Spectroscopy　　　　　　　　　　　　　　　
  Korenobu Matsuzaki; Ryoji Kusaka; Satoshi Nihonyanagi; Shoichi Yamaguchi; Takashi Nagata; Tahei Tahara
  JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 巻：138, 号：24, 開始ページ：7551, 終了ページ：7557, 2016年06月, ［査読有り］
  Hydrated electrons are the most fundamental anion species, consisting only of electrons and surrounding water molecules. Although hydrated electrons have been extensively studied in the bulk aqueous solutions, even their existence is still controversial at the water surface. Here, we report the observation and characterization of hydrated electrons at the air/water interface using new time-resolved interface-selective nonlinear vibrational spectroscopy. With the generation of electrons at the air/water interface by ultraviolet photoirradiation, we observed the appearance of a strong transient band in the OH stretch region by heterodyne-detected vibrational sum-frequency generation. Through the comparison with the time-resolved spectra at the air/indole solution interface, the transient band was assigned to the vibration of water molecules that solvate electrons at the interface. The analysis of the frequency and decay of the observed transient band indicated that the electrons are only partially hydrated at the water surface, and that they escape into the bulk within 100 ps.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/jacs.6b02171
  DOI ID：10.1021/jacs.6b02171, ISSN：0002-7863, ORCID：28499890, Web of Science ID：WOS:000378584600026
• Water Structure at the Buried Silica/Aqueous Interface Studied by Heterodyne-Detected Vibrational Sum-Frequency Generation　　　　　　　　　　　　　　　
  Anton Myalitsin; Shu-hei Urashirna; Satoshi Nihonyanagi; Shoichi Yamaguchi; Tahei Tahara
  JOURNAL OF PHYSICAL CHEMISTRY C, 巻：120, 号：17, 開始ページ：9357, 終了ページ：9363, 2016年05月, ［査読有り］
  Complex chi((2)) spectra of buried silica/isotopically diluted water (HOD-D2O) interfaces were measured using multiplex heterodyne-detected vibrational sum frequency generation spectroscopy to elucidate the hydrogen bond structure and up/down orientation of water at the silica/water interface at different pHs. The data show that-vibrational coupling (inter- and/or intrarnolecular coupling) plays a significant role in determining the chi((2)) spectral feature of silica/H2O interfaces and indicate that the doublet feature in the H2O spectra does not represent two distinct water structures (i.e., the ice and liquid-like structures) at the silica/water interface. The observed pH dependence of the imaginary chi((2)) spectra is explained by (1) H-up oriented water donating a hydrogen bond to the oxygen atom of silanolate, which is accompanied by H-up water oriented by the electric field created by the negative charge of silanolate, (2) H-up oriented water which donates a hydrogen bond to the neutral silanol oxygen, and (3) H-down oriented water which accepts hydrogen bonds from the neutral silanol and donates hydrogen bonds to bulk water molecules. The broad continuum of the OH stretch band of HOD-D2O and a long tail in the low frequency region represent a wide distribution of strong hydrogen bonds at the silica/water interface, particularly at the low pH.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/acs.jpcc.6b03275
  DOI ID：10.1021/acs.jpcc.6b03275, ISSN：1932-7447, ORCID：28499891, Web of Science ID：WOS:000375631100042
• Efficient Spectral Diffusion at the Air/Water Interface Revealed by Femtosecond Time-Resolved Heterodyne-Detected Vibrational Sum Frequency Generation Spectroscopy　　　　　　　　　　　　　　　
  Ken-ichi Inoue; Tatsuya Ishiyama; Satoshi Nihonyanagi; Shoichi Yamaguchi; Akihiro Morita; Tahei Tahara
  JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 巻：7, 号：10, 開始ページ：1811, 終了ページ：1815, 2016年05月, ［査読有り］
  Femtosecond vibrational dynamics at the air/water interface is investigated by time-resolved heterodyne-detected vibrational sum frequency generation (TR-HD-VSFG) spectroscopy and molecular dynamics (MD) simulation. The low- and high-frequency sides of the hydrogen-bonded (HB) OH stretch band at the interface are selectively excited with special attention to the bandwidth and energy of the pump pulses. Narrow bleach is observed immediately after excitation of the high-frequency side of the HB OH band at similar to 3500 cm(-1), compared to the broad bleach observed with excitation of the low-frequency side at similar to 3300 cm(-1). However, the time-resolved spectra observed with the two different excitations become very similar at 0.5 ps and almost indistinguishable by 1.0 ps. This reveals that efficient spectral diffusion occurs regardless of the difference of the pump frequency. The experimental observations are well-reproduced by complementary MD simulation. There is no experimental and theoretical evidence that supports extraordinary slow dynamics in the high-frequency side of the FIB OH band, which was reported before.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/acs.jpclett.6b00701
  DOI ID：10.1021/acs.jpclett.6b00701, ISSN：1948-7185, ORCID：28499889, Web of Science ID：WOS:000376421200010
• Femtosecond Ultrafast Water Dynamics at Charged Lipid Interfaces Revealed by 2D Heterodyne-Detected Vibrational Sum Frequency Generation
  Satoshi Nihonyanagi; Prashant C. Singh; Ken-ichi Inoue; Shoichi Yamaguchi; Tahei Tahara
  International Conference on Ultrafast Phenomena, 2016年, ［査読有り］
  OSA, 研究論文（国際会議プロシーディングス）
  DOI：https://doi.org/10.1364/up.2016.uth1a.3
  DOI ID：10.1364/up.2016.uth1a.3
• Accurate determination of complex chi((2)) spectrum of the air/water interface　　　　　　　　　　　　　　　
  Satoshi Nihonyanagi; Ryoji Kusaka; Ken-ichi Inoue; Aniruddha Adhikari; Shoichi Yamaguchi; Tahei Tahara
  JOURNAL OF CHEMICAL PHYSICS, 巻：143, 号：12, 2015年09月, ［査読有り］
  Discussion on the structure of the water surface relies on accurate determination of the chi((2)) spectrum. For obtaining accurate chi((2)) spectrum of the air/water interface in the OH stretch region, we performed heterodyne-detected vibrational sum-frequency generation measurements with a high phase accuracy, and also examined the validity of the phase and amplitude calibration using different non-resonant materials. In contrast to the previous reports, it was concluded that the imaginary part of the chi((2)) spectrum of the air/water interface does not exhibit noticeable positive resonance in the low frequency region within the experimental error. This result urges us to reconsider the structure of the air/water interface based on the accurate chi((2)) spectrum. (C) 2015 AIP Publishing LLC.
  AMER INST PHYSICS, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/1.4931485
  DOI ID：10.1063/1.4931485, ISSN：0021-9606, eISSN：1089-7690, ORCID：28499893, Web of Science ID：WOS:000362568100045
• Development of single-channel heterodyne-detected sum frequency generation spectroscopy and its application to the water/vapor interface　　　　　　　　　　　　　　　
  Shoichi Yamaguchi
  JOURNAL OF CHEMICAL PHYSICS, 巻：143, 号：3, 2015年07月, ［査読有り］
  Single-channel heterodyne-detected sum frequency generation (HD-SFG) spectroscopy for selectively measuring vibrational spectra of liquid interfaces is presented. This new methodology is based on optical interference between sum frequency signal light from a sample interface and phase-controlled local oscillator light. In single-channel HD-SFG, interferometric and spectrometric measurements are simultaneously carried out with an input IR laser scanned in a certain wavenumber range, which results in a less task than existing phase-sensitive sum frequency spectroscopy. The real and imaginary parts of second-order nonlinear optical susceptibility (chi((2))) of interfaces are separately obtained with spectral resolution as high as 4 cm(-1) that is approximately six times better than existing multiplex HD-SFG. In this paper, the experimental procedure and theoretical background of single-channel HD-SFG are explicated, and its application to the water/vapor interface is demonstrated, putting emphasis on the importance of a standard for the complex phase of chi((2)). (C) 2015 AIP Publishing LLC.
  AMER INST PHYSICS, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/1.4927067
  DOI ID：10.1063/1.4927067, ISSN：0021-9606, eISSN：1089-7690, ORCID：28499896, Web of Science ID：WOS:000358429800013
• Development of Electronic Sum Frequency Generation Spectroscopies and Their Application to Liquid Interfaces　　　　　　　　　　　　　　　
  Shoichi Yamaguchi; Tahei Tahara
  JOURNAL OF PHYSICAL CHEMISTRY C, 巻：119, 号：27, 開始ページ：14815, 終了ページ：14828, 2015年07月, ［査読有り］
  This feature article describes our recent work on the development of interface-selective second-order nonlinear electronic spectroscopies and their application to molecular structure and dynamics at liquid interfaces. We describe three methods that measure electronically resonant second-order nonlinear optical susceptibility (chi((2))) of interfacial molecules without contribution from the bulk: electronic sum-frequency generation (ESFG) provides high-quality interfacial electronic spectra by employing the combination of narrow-band and broad-band visible/near-infrared femtosecond pulses. Time-resolved ESFG (TR-ESFG) is the extension of ESFG to time-resolved measurements and provides femtosecond time-resolved electronic spectra at interfaces. Heterodyne-detected ESFG (HD-ESFG) is the ultimate second-order nonlinear electronic spectroscopy that directly provides the real and imaginary parts of chi((2)). In particular, the imaginary chi((2)) spectra obtained with HD-ESFG can be directly compared to the absorption spectra of bulk solution, and their signs contain information about the absolute orientation of the interfacial molecules. These interface-selective electronic spectroscopies enable rigorous comparison between the electronic spectra of liquid interfaces and those of bulk liquids, and the application to the following topic is discussed in this article: effective polarity at the air/water interface, interfacial ultrafast dynamics, absolute alignment of interfacial molecules, pH of the air/water interface, and the origin of nonresonant background. These studies reveal unique properties of molecules at air/liquid interfaces, which is markedly different from that in the bulk from a microscopic viewpoint.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/acs.jpcc.5b02375
  DOI ID：10.1021/acs.jpcc.5b02375, ISSN：1932-7447, ORCID：28499895, Web of Science ID：WOS:000357964900001
• 2D heterodyne-detected sum frequency generation study on the ultrafast vibrational dynamics of H2O and HOD water at charged interfaces　　　　　　　　　　　　　　　
  Ken-ichi Inoue; Satoshi Nihonyanagi; Prashant C. Singh; Shoichi Yamaguchi; Tahei Tahara
  JOURNAL OF CHEMICAL PHYSICS, 巻：142, 号：21, 2015年06月, ［査読有り］
  Two-dimensional heterodyne-detected vibrational sum-frequency generation (2D HD-VSFG) spectroscopy is applied to study the ultrafast vibrational dynamics of water at positively charged aqueous interfaces, and 2D HD-VSFG spectra of cetyltrimethylammonium bromide (CTAB)/water interfaces in the whole hydrogen-bonded OH stretch region (3000 cm(-1) <= omega(pump) <= 3600 cm(-1)) are measured. 2D HD-VSFG spectrum of the CTAB/isotopically diluted water (HOD-D2O) interface exhibits a diagonally elongated bleaching lobe immediately after excitation, which becomes round with a time constant of similar to 0.3 ps due to spectral diffusion. In contrast, 2D HD-VSFG spectrum of the CTAB/H2O interface at 0.0 ps clearly shows two diagonal peaks and their cross peaks in the bleaching region, corresponding to the double peaks observed at 3230 cm(-1) and 3420 cm(-1) in the steady-state HD-VSFG spectrum. Horizontal slices of the 2D spectrum show that the relative intensity of the two peaks of the bleaching at the CTAB/H2O interface gradually change with the change of the pump frequency. We simulate the pump-frequency dependence of the bleaching feature using a model that takes account of the Fermi resonance and inhomogeneity of the OH stretch vibration, and the simulated spectra reproduce the essential features of the 2D HD-VSFG spectra of the CTAB/H2O interface. The present study demonstrates that heterodyne detection of the time-resolved VSFG is critically important for studying the ultrafast dynamics of water interfaces and for unveiling the underlying mechanism. (C) 2015 AIP Publishing LLC.
  AMER INST PHYSICS, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/1.4918644
  DOI ID：10.1063/1.4918644, ISSN：0021-9606, eISSN：1089-7690, ORCID：28499892, Web of Science ID：WOS:000355931800035
• Anomalous effective polarity of an air/liquid-mixture interface: a heterodyne-detected electronic and vibrational sum frequency generation study　　　　　　　　　　　　　　　
  Sudip Kumar Mondal; Ken-ichi Inoue; Shoichi Yamaguchi; Tahei Tahara
  PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 巻：17, 号：37, 開始ページ：23720, 終了ページ：23723, 2015年, ［査読有り］
  We study the effective polarity of an air/liquid-mixture interface by using interface-selective heterodyne-detected electronic sum frequency generation (HD-ESFG) and vibrational sum frequency generation (HD-VSFG) spectroscopies. With water and N,N-dimethyl-formamide (DMF) chosen as two components of the liquid mixture, the bulk polarity of the mixture is controlled nearly arbitrarily by the mixing ratio. The effective polarity of the air/mixture interface is evaluated by HD-ESFG with a surface-active solvatochromic molecule used as a polarity indicator. Surprisingly, the interfacial effective polarity of the air/mixture interface increases significantly, when the bulk polarity of the mixture decreases (i.e. when the fraction of DMF increases). Judging from the hydrogen-bond structure at the air/mixture interface clarified by HD-VSFG, this anomalous change of the interfacial effective polarity is attributed to the interface-specific solvation structure around the indicator molecule at the air/mixture interface.
  ROYAL SOC CHEMISTRY, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1039/c5cp04264j
  DOI ID：10.1039/c5cp04264j, ISSN：1463-9076, eISSN：1463-9084, ORCID：28499894, Web of Science ID：WOS:000361543200004
• Interfacial water in the vicinity of a positively charged interface studied by steady-state and time-resolved heterodyne-detected vibrational sum frequency generation　　　　　　　　　　　　　　　
  Prashant Chandra Singh; Satoshi Nihonyanagi; Shoichi Yamaguchi; Tahei Tahara
  JOURNAL OF CHEMICAL PHYSICS, 巻：141, 号：18, 2014年11月, ［査読有り］
  To investigate the properties of water in the close vicinity of a positively charged surfactant/water interface, steady-state and femtosecond time-resolved interfacial vibrational spectra were measured in the presence of excess alkali halide salts. The steady-state Im chi((2)) spectra show a drastic intensity decrease with excess salts, indicating that the thickness of the probed water layer is substantially reduced. Fluoride salts do not noticeably affect spectral features in the OH stretch region whereas the chloride and bromide salts induce significant blue shifts of the OH stretch frequency. Femtosecond time-resolved Delta Im chi((2)) spectra obtained with fluoride salts exhibit a very broad bleach even at 0 fs as observed without excess salts, while chloride and bromide salts give rise to a narrow spectral hole burning. These results indicate that the excess chloride and bromide ions strongly interact with interfacial water in the vicinity of the charged interface and it suppresses intramolecular coupling (i.e., Fermi resonance) that causes spectral broadening. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
  AMER INST PHYSICS, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/1.4897265
  DOI ID：10.1063/1.4897265, ISSN：0021-9606, eISSN：1089-7690, ORCID：28499899, Web of Science ID：WOS:000344847600071
• Counterion Effect on Interfacial Water at Charged Interfaces and Its Relevance to the Hofmeister Series　　　　　　　　　　　　　　　
  Satoshi Nihonyanagi; Shoichi Yamaguchi; Tahei Tahara
  JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 巻：136, 号：17, 開始ページ：6155, 終了ページ：6158, 2014年04月, ［査読有り］
  Specific counterion effects represented by Hofmeister series are important for a variety of phenomena such as protein precipitations, surface tensions of electrolytes solutions, phase transitions of surfactants, etc. We applied heterodyne-detected vibrational sum-frequency generation spectroscopy to study the counterion effect on the interfacial water at charged interfaces and discussed the observed effect with relevance to the Hofmeister series. Experiments were carried out for model systems of positively charged cetyltrimethylammonium monolayer/electrolyte solution interface and negatively charged dodecylsulfate monolayer/electrolyte interface. At the positively charged interface, the intensity of the OH band of the interfacial water decreases in the order of the Hofmeister series, suggesting that the adsorbability of halide anions onto the interface determines the Hofmeister order as previously proposed by Zhang and Cremer (Curr. Opin. Chem. Biol. 2006, 10, 658-663). At the negatively charged interfaces, on the other hand, the OH band intensity does not depend significantly on the countercation, whereas variation in the hydrogen-bond strength of the interfacial water is well correlated with the Hofmeister order of the cation effect. These results provide new insights into the molecular level mechanisms of anionic and cationic Hofmeister effects.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/ja412952y
  DOI ID：10.1021/ja412952y, ISSN：0002-7863, ORCID：28499897, Web of Science ID：WOS:000335369200002
• Evaluation of pH at Charged Lipid/Water Interfaces by Heterodyne-Detected Electronic Sum Frequency Generation　　　　　　　　　　　　　　　
  Achintya Kundu; Shoichi Yamaguchi; Tahei Tahara
  JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 巻：5, 号：4, 開始ページ：762, 終了ページ：766, 2014年02月, ［査読有り］
  Although the interface pH at a biological membrane is important for biological processes at the membrane, there has been no systematic study to evaluate it. We apply novel interface-selective nonlinear spectroscopy to the evaluation of the pH at model biological membranes (lipid/water interfaces). It is clearly shown that the pH at the charged lipid/water interfaces is substantially deviated from the bulk pH. The pH at the lipid/water interface is higher than that in the bulk when the head group of the lipid is positively charged, whereas the pH at the lipid/water interface is lower when the lipid has a negatively charged head group.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/jz500107e
  DOI ID：10.1021/jz500107e, ISSN：1948-7185, ORCID：28499898, Web of Science ID：WOS:000331860900021
• Ultrafast vibrational dynamics of water at a zwitterionic lipid/water interface revealed by two-dimensional heterodyne-detected vibrational sum frequency generation (2D HD-VSFG)　　　　　　　　　　　　　　　
  Ken-Ichi Inoue; Prashant Chandra Singh; Satoshi Nihonyanagi; Shoichi Yamaguchi; Tahei Tahara
  Optics InfoBase Conference Papers, 2014年
  2D HD-VSFG is applied to the study of ultrafast vibrational dynamics at a zwitterionic lipid/water interface for the first time. The 2D spectrum reveals spectral diffusion of three distinct water species existing at the interface. Ultrafast Phenomena 2014 © 2014 OSA.
  Optical Society of America (OSA), 英語, 研究論文（国際会議プロシーディングス）
  DOI：https://doi.org/10.1364/up.2014.07.mon.p1.27
  DOI ID：10.1364/up.2014.07.mon.p1.27, ISSN：2162-2701, SCOPUS ID：85087192595
• Communication: Ultrafast vibrational dynamics of hydrogen bond network terminated at the air/water interface: A two-dimensional heterodyne-detected vibrational sum frequency generation study　　　　　　　　　　　　　　　
  Prashant Chandra Singh; Satoshi Nihonyanagi; Shoichi Yamaguchi; Tahei Tahara
  JOURNAL OF CHEMICAL PHYSICS, 巻：139, 号：16, 2013年10月, ［査読有り］
  Ultrafast vibrational dynamics of hydrogen bond network at the air/water interface is revealed by two-dimensional heterodyne-detected vibrational sum frequency generation (2D HD-VSFG) spectroscopy. Three diagonal peaks are clearly observed in the 2D HD-VSFG spectrum, which correspond to the negative and positive hydrogen-bonded OH stretch bands and the positive "free" OH stretch band in the steady-state HD-VSFG spectrum. A diagonally elongated bleaching lobe of the hydrogen-bonded OH at 0 ps indicates that it is partly inhomogeneously broadened. This diagonal elongation vanishes in a few hundred femtoseconds, implying the ultrafast spectral diffusion in the hydrogen-bonded OH band. Off-diagonal cross peaks between each OH oscillator are clearly observed instantaneously within the time resolution of 0.2 ps, suggesting that they are vibrationally coupled through anharmonicity and/or energy transfer. (C) 2013 AIP Publishing LLC.
  AMER INST PHYSICS, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/1.4826095
  DOI ID：10.1063/1.4826095, ISSN：0021-9606, eISSN：1089-7690, ORCID：28499901, Web of Science ID：WOS:000326637500001
• Vibrational Sum Frequency Generation by the Quadrupolar Mechanism at the Nonpolar Benzene/Air Interface　　　　　　　　　　　　　　　
  Korenobu Matsuzaki; Satoshi Nihonyanagi; Shoichi Yamaguchi; Takashi Nagata; Tahei Tahara
  JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 巻：4, 号：10, 開始ページ：1654, 終了ページ：1658, 2013年05月, ［査読有り］
  The interface selectivity of vibrational sum frequency generation (VSFG) spectroscopy is explained under the dipole approximation as resulting from the breakdown of inversion symmetry at the interface. From this viewpoint, VSFG is not expected to occur at the interface consisting of centrosymmetric molecules, because the inversion symmetry is preserved even at the interface. In reality, however, VSFG at the nonpolar benzene/air interface has been observed with traditional homodyne-detected VSFG. Here we report a heterodyne-detected VSFG study of the benzene/air interface. The result strongly indicates that VSFG at this interface cannot be explained within the framework of the dipole approximation. The selection rule and polarization dependence of the observed VSFG signal show that the quadrupole transition plays an essential role because of the field discontinuity at the interface. This finding implies the applicability of interface-selective VSFG to the nonpolar interfaces comprising centrosymmetric molecules, which opens a new possibility of VSFG spectroscopy.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/jz400829k
  DOI ID：10.1021/jz400829k, ISSN：1948-7185, ORCID：28499905, Web of Science ID：WOS:000321793800013
• Agreement between Experimentally and Theoretically Estimated Orientational Distributions of Solutes at the Air/Water Interface　　　　　　　　　　　　　　　
  Achintya Kundu; Hidekazu Watanabe; Shoichi Yamaguchi; Tahei Tahara
  JOURNAL OF PHYSICAL CHEMISTRY C, 巻：117, 号：17, 開始ページ：8887, 終了ページ：8891, 2013年05月, ［査読有り］
  Linear and nonlinear polarization-sensitive spectroscopic techniques are employed to determine the orientational distributions of solute molecules adsorbed at the air/water interface. Each solute molecule shows very broad orientational distribution with a standard deviation ranging from 16 degrees to 21 degrees. The experimentally determined orientational distributions are well reproduced by classical molecular dynamics simulations. The good agreement between experimental results and theoretical calculations enables us to elucidate how the orientational distribution at the air/water interface is controlled by the chemical structure of the solute molecules.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/jp402674u
  DOI ID：10.1021/jp402674u, ISSN：1932-7447, ORCID：28499900, Web of Science ID：WOS:000318536600034
• Computational analysis of the quadrupole contribution in the second-harmonic generation spectroscopy for the water/vapor interface (vol 138, 064704, 2013)　　　　　　　　　　　　　　　
  Kazuya Shiratori; Shoichi Yamaguchi; Tahei Tahara; Akihiro Morita
  JOURNAL OF CHEMICAL PHYSICS, 巻：138, 号：15, 2013年04月, ［査読有り］
  AMER INST PHYSICS, 英語
  DOI：https://doi.org/10.1063/1.4802916
  DOI ID：10.1063/1.4802916, ISSN：0021-9606, ORCID：28499903, Web of Science ID：WOS:000317814900047
• Computational analysis of the quadrupole contribution in the second-harmonic generation spectroscopy for the water/vapor interface　　　　　　　　　　　　　　　
  Shiratori Kazuya; Shoichi Yamaguchi; Tahei Tahara; Akihiro Morita
  JOURNAL OF CHEMICAL PHYSICS, 巻：138, 号：6, 2013年02月, ［査読有り］
  Second-order susceptibility for water/vapor interface is calculated theoretically using molecular dynamics simulation, which considers both the dipole and quadrupole contributions. We find that the nonresonant second harmonic generation (SHG) signal is dominated by the quadrupole contribution from the bulk. We also elucidate the fact that the nonresonant susceptibility tends to be negative in general, irrespective of the molecular orientation. The present argument for SHG is commonly applicable to the nonresonant vibrational sum-frequency generation (SFG) spectra, and should be valid for other liquid interfaces. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4790407]
  AMER INST PHYSICS, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/1.4790407
  DOI ID：10.1063/1.4790407, ISSN：0021-9606, eISSN：1089-7690, ORCID：28499902, Web of Science ID：WOS:000315054400035
• Structure and Dynamics of Interfacial Water Studied by Heterodyne-Detected Vibrational Sum-Frequency Generation　　　　　　　　　　　　　　　
  Satoshi Nihonyanagi; Jahur A. Mondal; Shoichi Yamaguchi; Tahei Tahara
  ANNUAL REVIEW OF PHYSICAL CHEMISTRY, VOL 64, 巻：64, 開始ページ：579, 終了ページ：603, 2013年, ［査読有り］
  Vibrational sum-frequency generation (VSFG) spectroscopy is a powerful tool to study interfaces. Recently, multiplex heterodyne-detected VSFG (HD-VSFG) has been developed, which enables the direct measurement of complex second-order nonlinear susceptibility [chi((2))]. HD-VSFG has remarkable advantages over conventional VSFG. For example, the imaginary part of chi((2)) [Im chi((2))] obtained with this interferometric technique is the direct counterpart to the infrared [Im chi((1))] and Raman [Im chi((3))] spectra in the bulk, and it is free from the spectral deformation inevitable in conventional VSFG [vertical bar chi((2)vertical bar 2)] spectra. The Im chi((2)) signal is obtained with a sign that contains unambiguous information about the up/down orientation of interfacial molecules. Furthermore, HD-VSFG can be straightforwardly extended to time-resolved measurements when combined with photoexcitation. In this review, we describe the present status of experiments and applications of multiplex HD-VSFG spectroscopy, in particular with regard to the orientation and structure of interfacial water at charged, neutral, and biorelevant water interfaces.
  ANNUAL REVIEWS, 英語, 論文集(書籍)内論文
  DOI：https://doi.org/10.1146/annurev-physchem-040412-110138
  DOI ID：10.1146/annurev-physchem-040412-110138, ISSN：0066-426X, ORCID：28499904, Web of Science ID：WOS:000321771600026
• Communication: Quantitative estimate of the water surface pH using heterodyne-detected electronic sum frequency generation　　　　　　　　　　　　　　　
  Shoichi Yamaguchi; Achintya Kundu; Pratik Sen; Tahei Tahara
  JOURNAL OF CHEMICAL PHYSICS, 巻：137, 号：15, 2012年10月, ［査読有り］
  Most chemical reactions in water are very sensitive to pH. Many environmentally important chemical reactions are known to take place at the water surface (i.e., air/water interface). However, the pH of the water surface is still controversial. Spectroscopic experiments and theoretical calculations indicate that the water surface is more acidic than the bulk, whereas electrophoretic experiments provide a contrary view. Here, we report that a novel nonlinear optical experiment with a surface-active pH indicator can quantitatively evaluate the pH of the water surface. The result clearly shows that the pH of the water surface is lower than that of the bulk by 1.7. This is the first study to apply a principle of bulk pH measurements to the water surface, and therefore provides a reliable experimental estimate for the pH difference between the water surface and bulk. It is considered that the higher acidity of the water surface plays a key role in marine and atmospheric chemical reactions. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4758805]
  AMER INST PHYSICS, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/1.4758805
  DOI ID：10.1063/1.4758805, ISSN：0021-9606, ORCID：28499906, Web of Science ID：WOS:000310307100001
• Ultrafast vibrational dynamics of water at a charged interface revealed by two-dimensional heterodyne-detected vibrational sum frequency generation　　　　　　　　　　　　　　　
  Prashant Chandra Singh; Satoshi Nihonyanagi; Shoichi Yamaguchi; Tahei Tahara
  JOURNAL OF CHEMICAL PHYSICS, 巻：137, 号：9, 2012年09月, ［査読有り］
  Two-dimensional heterodyne-detected vibrational sum frequency generation (2D HD-VSFG) spectroscopy is performed for an aqueous interface for the first time. The 2D HD-VSFG spectra in the OH stretch region are obtained from a positively charged surfactant/water interface with isotopically diluted water (HOD/D2O) to reveal the femtosecond vibrational dynamics of water at the charged interface. The 2D HD-VSFG spectrum is diagonally elongated immediately after photoexcitation, clearly demonstrating inhomogeneity in the interfacial water. This elongation almost disappears at 300 fs owing to the spectral diffusion. Interestingly, the 2D HD-VSFG spectrum at the 0 fs shows an oppositely asymmetric shape to the corresponding 2D IR spectrum in bulk water: The bandwidth of the bleach signal gets narrower when the pump wavenumber becomes higher. This suggests that the dynamics and mechanism of the hydrogen bond rearrangement at the charged interface are significantly different from those in bulk water. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4747828]
  AMER INST PHYSICS, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/1.4747828
  DOI ID：10.1063/1.4747828, ISSN：0021-9606, eISSN：1089-7690, ORCID：28499909, Web of Science ID：WOS:000309092000045
• Ultrafast Vibrational Dynamics of a Charged Aqueous Interface by Femtosecond Time-Resolved Heterodyne-Detected Vibrational Sum Frequency Generation　　　　　　　　　　　　　　　
  Satoshi Nihonyanagi; Prashant C. Singh; Shoichi Yamaguchi; Tahei Tahara
  BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN, 巻：85, 号：7, 開始ページ：758, 終了ページ：760, 2012年07月, ［査読有り］
  Newly developed time-, frequency-, and phase-resolved heterodyne-detected vibrational sum frequency generation (TR-HD-VSFG) spectroscopy opens a new door to explore ultrafast vibrational dynamics of interfacial water. Here, we present the first observation of TR-HD-VSFG spectra of water at a charged monolayer/aqueous solution interface.
  CHEMICAL SOC JAPAN, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1246/bcsj.20120051
  DOI ID：10.1246/bcsj.20120051, ISSN：0009-2673, eISSN：1348-0634, ORCID：28499908, Web of Science ID：WOS:000307797100004
• Three Distinct Water Structures at a Zwitterionic Lipid/Water Interface Revealed by Heterodyne-Detected Vibrational Sum Frequency Generation　　　　　　　　　　　　　　　
  Jahur A. Mondal; Satoshi Nihonyanagi; Shoichi Yamaguchi; Tahei Tahara
  JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 巻：134, 号：18, 開始ページ：7842, 終了ページ：7850, 2012年05月, ［査読有り］
  Lipid/water interfaces and associated interfacial water are vital for various biochemical reactions, but the molecular-level understanding of their property is very limited. We investigated the water structure at a zwitterionic lipid, phosphatidylcholine, monolayer/water interface using heterodyne-detected vibrational sum frequency generation spectroscopy. Isotopically diluted water was utilized in the experiments to minimize the effect of intra/intermolecular couplings. It was found that the OH stretch band in the Im chi((2)) spectrum of the phosphatidylcholine/water interface exhibits a characteristic double-peaked feature. To interpret this peculiar spectrum of the zwitterionic lipid/water interface, Im chi((2)) spectra of a zwitterionic surfactant/water interface and mixed lipid/water interfaces were measured, The Im chi((2)) spectrum of the zwitterionic surfactant/water interface clearly shows both positive and negative bands in the OH stretch region, revealing that multiple water structures exist at the interface. At the mixed lipid/water interfaces, while gradually varying the fraction of the anionic and cationic lipids, we observed a drastic change in the Im chi((2)) spectra in which spectral features similar to those of the anionic, zwitterionic, and cationic lipid/water interfaces appeared successively. These observations demonstrate that, when the positive and negative charges coexist at the interface, the H-down-oriented water structure and H-up-oriented water structure appear in the vicinity of the respective charged sites. In addition, it was found that a positive Im chi((2)) appears around 3600 cm(-1) for all the monolayer interfaces examined, indicating weakly interacting water species existing in the hydrophobic region of the monolayer at the interface. On the basis of these results, we concluded that the characteristic Im chi((2)) spectrum of the zwitterionic lipid/water interface arises from three different types of water existing at the interface: (1) the water associated with the negatively charged phosphate, which is strongly H-bonded and has a net H-up orientation, (2) the water around the positively charged choline, which forms weaker H-bonds and has a net H-down orientation, and (3) the water weakly interacting with the hydrophobic region of the lipid, which has a net H-up orientation.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/ja300658h
  DOI ID：10.1021/ja300658h, ISSN：0002-7863, ORCID：28499907, Web of Science ID：WOS:000303696200045
• "Up" versus "down" alignment and hydration structures of solutes at the air/water interface revealed by heterodyne-detected electronic sum frequency generation with classical molecular dynamics simulation　　　　　　　　　　　　　　　
  Shoichi Yamaguchi; Hidekazu Watanabe; Sudip Kumar Mondal; Achintya Kundu; Tahei Tahara
  JOURNAL OF CHEMICAL PHYSICS, 巻：135, 号：19, 2011年11月, ［査読有り］
  We unambiguously demonstrate the "up" versus "down" alignment of a pair of prototypical solute molecules adsorbed at the air/water interface for the first time using heterodyne-detected electronic sum frequency generation spectroscopy. This molecular alignment is also reproduced by classical molecular dynamics (MD) simulation theoretically. Furthermore, the MD simulation indicates distinctly different interface-specific hydration structures around the two solute molecules, which dictate the molecular alignment at the interface. It is concluded that the hydrophilicity difference between the terminal functional groups of the solute governs the molecular orientation and surrounding hydration structures at the interface. (C) 2011 American Institute of Physics. [doi:10.1063/1.3662136]
  AMER INST PHYSICS, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/1.3662136
  DOI ID：10.1063/1.3662136, ISSN：0021-9606, ORCID：28499910, Web of Science ID：WOS:000297473300038
• Unified Molecular View of the Air/Water Interface Based on Experimental and Theoretical chi((2)) Spectra of an Isotopically Diluted Water Surface　　　　　　　　　　　　　　　
  Satoshi Nihonyanagi; Tatsuya Ishiyama; Touk-kwan Lee; Shoichi Yamaguchi; Mischa Bonn; Akihiro Morita; Tahei Tahara
  JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 巻：133, 号：42, 開始ページ：16875, 終了ページ：16880, 2011年10月, ［査読有り］
  The energetically unfavorable termination of the hydrogen-bonded network of water molecules at the air/water interface causes molecular rearrangement to minimize the free energy. The long-standing question is how water minimizes the surface free energy. The combination of advanced, surface-specific nonlinear spectroscopy and theoretical simulation provides new insights. The complex chi((2)) spectra of isotopically diluted water surfaces obtained by heterodyne-detected sum frequency generation spectroscopy and molecular dynamics simulation show excellent agreement, assuring the validity of the microscopic picture given in the simulation. The present study indicates that there is no ice-like structure at the surface in other words, there is no increase of tetrahedrally coordinated structure compared to the bulk but that there are water pairs interacting with a strong hydrogen bond at the outermost surface. Intuitively, this can be considered a consequence of the lack of a hydrogen bond toward the upper gas phase, enhancing the lateral interaction at the boundary. This study also confirms that the major source of the isotope effect on the water chi((2)) spectra is the intramolecular anharmonic coupling, i.e., Fermi resonance.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/ja2053754
  DOI ID：10.1021/ja2053754, ISSN：0002-7863, ORCID：28499914, Web of Science ID：WOS:000296678200035
• Electric quadrupole contribution to the nonresonant background of sum frequency generation at air/liquid interfaces　　　　　　　　　　　　　　　
  Shoichi Yamaguchi; Kazuya Shiratori; Akihiro Morita; Tahei Tahara
  JOURNAL OF CHEMICAL PHYSICS, 巻：134, 号：18, 開始ページ：7, 2011年05月, ［査読有り］
  We study an electric quadrupole contribution to sum frequency generation (SFG) at air/liquid interfaces in an electronically and vibrationally nonresonant condition. Heterodyne-detected electronic sum frequency generation spectroscopy of air/liquid interfaces reveals that nonresonant chi((2)) (second-order nonlinear susceptibility) has a negative sign and nearly the same value for all eight liquids studied. This result is rationalized on the basis of the theoretical expressions of chi((2)) with an electric quadrupole contribution taken into account. It is concluded that the nonresonant background of SFG is predominantly due to interfacial nonlinear polarization having a quadrupole contribution. Although this nonlinear polarization is localized at the interface, it depends on quadrupolar chi((2)) in the bulk as well as that at the interface. It means that the sign of nonresonant chi((2)) bears no relation to the "up" versus "down" alignment of interfacial molecules, because nonresonant chi((2)) has a quadrupolar origin. (C) 2011 American Institute of Physics. [doi:10.1063/1.3586811]
  AMER INST PHYSICS, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/1.3586811
  DOI ID：10.1063/1.3586811, ISSN：0021-9606, ORCID：28499912, Web of Science ID：WOS:000290589900037
• Acid-Base Equilibrium at an Aqueous Interface: pH Spectrometry by Heterodyne-Detected Electronic Sum Frequency Generation　　　　　　　　　　　　　　　
  Shoichi Yamaguchi; Kankan Bhattacharyya; Tahei Tahara
  JOURNAL OF PHYSICAL CHEMISTRY C, 巻：115, 号：10, 開始ページ：4168, 終了ページ：4173, 2011年03月, ［査読有り］
  We applied interface-selective heterodyne-detected electronic sum frequency generation (HD-ESFG) to the pH Spectrometry of an air/cationic surfactant/water interface in order to obtain insight into an acid - base equilibrium at the interface. We used an indicator molecule adsorbed at the interface to probe local pH and local effective polarity. We obtained unprecedentedly high quality spectral data of the interfacial pH spectrometry, which clearly indicates that this interface has higher pH than the bulk owing to the positive charge of the head group of the surfactant. In addition, we found that the air/surfactant/water interface and the micelle interface of the Same surfactant are essentially equivalent in local pH and local effective polarity.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/jp1113174
  DOI ID：10.1021/jp1113174, ISSN：1932-7447, eISSN：1932-7455, ORCID：28499911, Web of Science ID：WOS:000288113400042
• Molecules at the Air/Water Interface Experience a More Inhomogeneous Solvation Environment than in Bulk Solvents: A Quantitative Band Shape Analysis of Interfacial Electronic Spectra Obtained by HD-ESFG　　　　　　　　　　　　　　　
  Sudip Kumar Mondal; Shoichi Yamaguchi; Tahei Tahara
  JOURNAL OF PHYSICAL CHEMISTRY C, 巻：115, 号：7, 開始ページ：3083, 終了ページ：3089, 2011年02月, ［査読有り］
  To evaluate the inhomogeneity of the solvation environment at the air/water interface, we quantitatively analyzed the shape of the electronic spectra at the air/water interface for the first time. We measured the interface-selective electronic chi((2)) (second-order nonlinear susceptibility) spectra of solvatochromic coumarin molecules at the air/water interface by heterodyne-detected electronic sum frequency generation (HD-ESFG) spectroscopy. The observed imaginary chi((2)) (Im[chi((2))]) spectra were well reproduced by the convolution of a line shape function with a Gaussian distribution of a frequency shift, which enabled us to quantitatively determine the peal: position and bandwidth of the Im[chi((2))] spectra. The effective polarity of the air/water interface, which was determined by the peak position, was found to be dependent on each coumarin, which agreed with our previous homodyne-detected ESFG study. Interestingly, the spectra at the air/water interface showed substantially broader bandwidths than those in equally polar bulk solvents or even bulk water, indicating that the solvation environment at the air/water interface is more inhomogeneous than that in bulk solvents. At the air/water interface, the stabilization energy of the solvation not only changes with the change of the position and orientation of the surrounding solvents but also varies with the change of the position and orientation of the solute at the interface. We consider that this unique situation arising from the anisotropy along interface normal brings about a broader distribution of the stabilization energy of solvation at the air/water interface. The present work showed that the air/water interface provides a more inhomogeneous solvation environment than equally polar bulk solvents because of this broader distribution of the local solvation structure at the interface.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/jp110456t
  DOI ID：10.1021/jp110456t, ISSN：1932-7447, ORCID：28499913, Web of Science ID：WOS:000287338100023
• Physisorption Gives Narrower Orientational Distribution than Chemisorption on a Glass Surface: A Polarization-Sensitive Linear and Nonlinear Optical Study　　　　　　　　　　　　　　　
  Shoichi Yamaguchi; Haruko Hosoi; Megumi Yamashita; Pratik Sen; Tahei Taharat
  JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 巻：1, 号：18, 開始ページ：2662, 終了ページ：2665, 2010年09月, ［査読有り］
  Linear and nonlinear polarization-sensitive spectroscopic techniques were employed to determine the orientational distribution of a probe molecule physisorbed and chemisorbed On a fused-silica glass surface.. The chemisorption was through a well-known specific reaction between the maleimide group of the probe molecule and the thiol group of the surface. In the physisorption, the molecule was bound-to the surface by the weaker van der Waals forces, dipole-dipole interaction, or both. Despite the absence of the strong interaction between the molecule and the surface in the physisorption, it was found that the physisorption gives narrower orientational distribution than the chemisorption. The strong covalent bond in the chemisorption is not effective to increase the orientational order. It is highly likely that the present conclusion is applicable to a variety of probe molecules having a functional group for a specific reaction of chemisorption.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/jz101142m
  DOI ID：10.1021/jz101142m, ISSN：1948-7185, ORCID：28499916, Web of Science ID：WOS:000282017400008
• Structure and Orientation of Water at Charged Lipid Monolayer/Water Interfaces Probed by Heterodyne-Detected Vibrational Sum Frequency Generation Spectroscopy　　　　　　　　　　　　　　　
  Jahur A. Mondal; Satoshi Nihonyanagi; Shoichi Yamaguchi; Tahei Tahara
  JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 巻：132, 号：31, 開始ページ：10656, 終了ページ：10657, 2010年08月, ［査読有り］
  Cell membrane/water interfaces provide a unique environment for many biochemical reactions, and associated interfacial water is an integral part of such reactions. A molecular level understanding of the structure and orientation of water at lipid/water interfaces is required to realize the complex chemistry at biointerfaces. Here we report the heterodyne-detected vibrational sum frequency generation (HD-VSFG) studies of lipid monolayer/water interfaces. At charged lipid/water interfaces, the orientation of interfacial water is governed by the net charge on the lipid head-group; at an anionic lipid/water interface, water is in the hydrogen-up orientation, and at the cationic lipid/water interface, water is in the hydrogen-down orientation. At the cationic and anionic lipid/water interfaces, interfacial water has comparable hydrogen bond strength, and it is analogous to the bulk water.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/ja104327t
  DOI ID：10.1021/ja104327t, ISSN：0002-7863, ORCID：28499917, Web of Science ID：WOS:000280692200015
• Water Hydrogen Bond Structure near Highly Charged Interfaces Is Not Like Ice　　　　　　　　　　　　　　　
  Satoshi Nihonyanagi; Shoichi Yamaguchi; Tahei Tahara
  JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 巻：132, 号：20, 開始ページ：6867, 終了ページ：+, 2010年05月, ［査読有り］
  Imaginary x((2)) spectra of HOD at air/charged surfactant/aqueous interfaces highly resemble the IR spectrum of the bulk liquid HOD, showing no indication of the "ice-like" structure. Clearly, the hydrogen bond structures at highly charged interfaces are not like ice but very similar to the structure in the bulk.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/ja910914g
  DOI ID：10.1021/ja910914g, ISSN：0002-7863, ORCID：28499919, Web of Science ID：WOS:000277999700001
• Half hydration' at the air/water interface revealed by HD-ESFG spectroscopy, polarization SHG, and MD simulation　　　　　　　　　　　　　　　
  Hidekazu Watanabe; Shoichi Yamaguchi; Sobhan Sen; Akihiro Morita; Tahei Tahara
  J. Chem. Phys., 巻：132, 号：14, 開始ページ：144701, 2010年04月, ［査読有り］
  英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/1.3372620
  DOI ID：10.1063/1.3372620
• "Half-hydration" at the air/water interface revealed by heterodyne-detected electronic sum frequency generation spectroscopy, polarization second harmonic generation, and molecular dynamics simulation　　　　　　　　　　　　　　　
  Hidekazu Watanabe; Shoichi Yamaguchi; Sobhan Sen; Akihiro Morita; Tahei Tahara
  JOURNAL OF CHEMICAL PHYSICS, 巻：132, 号：14, 開始ページ：9, 2010年04月, ［査読有り］
  A solute-solvent interaction at the air/water interface was investigated both experimentally and theoretically, by studying a prototypical surface-active polarity indicator molecule, coumarin 110 (C110), adsorbed at the air/water interface with heterodyne-detected electronic sum frequency generation (HD-ESFG) spectroscopy, polarization second harmonic generation (SHG), and a molecular dynamics (MD) simulation. The second-order nonlinear optical susceptibility (chi((2))) tensor elements of C110 at the air/water interface were determined experimentally by HD-ESFG and polarization SHG, and information on "intermediate" polarity sensed by C110 at the interface was obtained by HD-ESFG. An MD simulation and a time-dependent density functional theory calculation were used to theoretically evaluate the chi((2)) tensor elements, which were in good agreement with the experimental results of HD-ESFG and polarization SHG. The microscopic "half-hydration" structure around C110 at the water surface was visualized on the basis of the MD simulation data, with which we can intuitively understand the microscopic origin of the surface activity of C110 and the intermediate polarity sensed by C110 at the air/water interface.
  AMER INST PHYSICS, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/1.3372620
  DOI ID：10.1063/1.3372620, ISSN：0021-9606, ORCID：28499915, Web of Science ID：WOS:000276973500028
• Ultrafast dynamics of malachite green at the air/water interface studied by femtosecond time-resolved electronic sum frequency generation (TR-ESFG): an indicator for local viscosity　　　　　　　　　　　　　　　
  Pratik Sen; Shoichi Yamaguchi; Tahei Tahara
  FARADAY DISCUSSIONS, 巻：145, 開始ページ：411, 終了ページ：428, 2010年, ［査読有り］
  The ultrafast excited-state dynamics of malachite green (MG) at the air/water interface was studied with a newly-developed interface-selective nonlinear optical technique: femtosecond time-resolved electronic sum frequency generation (TR-ESFG) spectroscopy. MG is known as a viscosity indicator because of its well-known viscosity-dependent dynamics in bulk solution. Femtosecond time-resolved electronic spectra of MG at the interface were obtained with nearly the same quality as that of conventional time-resolved absorption spectra in the bulk. The time constants of the ground-state recovery at the air/water interface were determined and compared with those in bulk glycerol-water mixtures. It was found that the ground-state recovery of MG at the air/water interface is much slower than that in bulk water and almost equivalent to that in the glycerol-water mixture containing glycerol volume fractions as high as 65-80%. This result indicates higher local viscosity at the interface than in bulk water. However, it is possible that changes of the molecular properties, e.g. a change of shape of the potential energy surface, of MG at the interface also contribute to the apparently very large viscosity values evaluated. On the basis of the present results, we discuss the applicability of probe molecules to evaluate the physicochemical properties of the liquid interface and note the importance of the extrinsic and intrinsic factors that make the chemical process at liquid interfaces different from that in bulk solution.
  ROYAL SOC CHEMISTRY, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1039/b908097j
  DOI ID：10.1039/b908097j, ISSN：1364-5498, ORCID：28499918, Web of Science ID：WOS:000273708000022
• Direct evidence for orientational flip-flop of water molecules at charged interfaces: A heterodyne-detected vibrational sum frequency generation study　　　　　　　　　　　　　　　
  Satoshi Nihonyanagi; Shoichi Yamaguchi; Tahei Tahara
  JOURNAL OF CHEMICAL PHYSICS, 巻：130, 号：20, 開始ページ：5, 2009年05月, ［査読有り］
  Complex chi((2)) spectra of air/water interfaces in the presence of charged surfactants were measured by heterodyne-detected broadband vibrational sum frequency generation spectroscopy for the first time. In contrast to the neat water surface, the signs of chi((2)) for two broad OH bands are the same in the presence of the charged surfactants. The obtained chi((2)) spectra clearly showed flip-flop of the interfacial water molecules which is induced by the opposite charge of the head group of the surfactants. With the sign of beta((2)) theoretically obtained, the absolute orientation, i.e., up/down orientation, of water molecules at the charged aqueous surfaces was uniquely determined by the relation between the sign of chi((2)) and the molecular orientation angle. Water molecules orient with their hydrogen up at the negatively charged aqueous interface whereas their oxygen up at the positively charged aqueous interface.
  AMER INST PHYSICS, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/1.3135147
  DOI ID：10.1063/1.3135147, ISSN：0021-9606, eISSN：1089-7690, ORCID：28499921, Web of Science ID：WOS:000266500200043
• Ultrafast Dynamics at Liquid Interfaces Investigated with Femtosecond Time-Resolved Multiplex Electronic Sum-Frequency Generation (TR-ESFG) Spectroscopy　　　　　　　　　　　　　　　
  Kentaro Sekiguchi; Shoichi Yamaguchi; Tahei Tahara
  ULTRAFAST PHENOMENA XVI, 巻：92, 開始ページ：520, 終了ページ：522, 2009年, ［査読有り］
  We developed a new nonlinear spectroscopy, femtosecond time-resolved electronic sum-frequency generation (TR-ESFG) spectroscopy, to investigate ultrafast dynamics at liquid interfaces. Transient electronic spectra at the air/water interface were obtained for the first time.
  SPRINGER-VERLAG BERLIN, 英語, 研究論文（国際会議プロシーディングス）
  ISSN：0172-6218, Web of Science ID：WOS:000282108000169
• Different Molecules Experience Different Polarities at the Air/Water Interface　　　　　　　　　　　　　　　
  Sobhan Sen; Shoichi Yamaguchi; Tahei Tahara
  ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 巻：48, 号：35, 開始ページ：6439, 終了ページ：6442, 2009年, ［査読有り］
  WILEY-V C H VERLAG GMBH, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1002/anie.200901094
  DOI ID：10.1002/anie.200901094, ISSN：1433-7851, ORCID：28499920, Web of Science ID：WOS:000269239700012
• Coherent acoustic phonons in a thin gold film probed by femtosecond surface plasmon resonance　　　　　　　　　　　　　　　
  Shoichi Yamaguchi; Tahei Tahara
  JOURNAL OF RAMAN SPECTROSCOPY, 巻：39, 号：11, 開始ページ：1703, 終了ページ：1706, 2008年11月, ［査読有り］
  We report on coherent phonon detection in a thin gold film by a new femtosecond pump-probe surface plasmon resonance (SPR) technique. Acoustic coherent phonons are generated impulsively in the gold film on a prism, and they are detected in the time domain through the reflectivity modulation for probe pulses that satisfy the SPR condition. We observed not only the fundamental vibration of a longitudinal acoustic phonon but also the overtones up to the fourth. Copyright (C) 2008 John Wiley & Sons, Ltd.
  JOHN WILEY & SONS LTD, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1002/jrs.2078
  DOI ID：10.1002/jrs.2078, ISSN：0377-0486, ORCID：28499922, Web of Science ID：WOS:000261206200027
• New Insight into the Surface Denaturation of Proteins: Electronic Sum Frequency Generation Study of Cytochrome c at Water Interfaces　　　　　　　　　　　　　　　
  Pratik Sen; Shoichi Yamaguchi; Tahei Tahara
  JOURNAL OF PHYSICAL CHEMISTRY B, 巻：112, 号：43, 開始ページ：13473, 終了ページ：13475, 2008年10月, ［査読有り］
  In situ characterization of Surface denaturation of a protein was realized by newly developed interface-selective multiplex electronic sum frequency generation spectroscopy. The observed electronic spectra of cytochrome c at the air/water interface exhibited a broad feature, which demonstrated coexistence of the nativelike and denatured protein at the interface. This situation of the mixed conformation at the air/water interface did not change in the acidic condition of pH = 2 where the protein was completely denatured in the bulk water. In sharp contrast, only native spectrum was observed at the silica/water interface.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/jp8061288
  DOI ID：10.1021/jp8061288, ISSN：1520-6106, ORCID：28499926, Web of Science ID：WOS:000260357700002
• Heterodyne-detected electronic sum frequency generation: "Up" versus "down" alignment of interfacial molecules　　　　　　　　　　　　　　　
  Shoichi Yamaguchi; Tahei Tahara
  JOURNAL OF CHEMICAL PHYSICS, 巻：129, 号：10, 2008年09月, ［査読有り］
  Heterodyne-detected electronic sum frequency generation (HD-ESFG) spectroscopy is newly developed to obtain complex electronic chi((2)) spectra of interfaces for a simultaneous detection bandwidth broader than 100 nm. HD-ESFG provides linear chi((2)) spectra that have unambiguous information on the "up" versus "down" alignment of interfacial molecules. It is demonstrated for p-nitroaniline, a prototypical molecule of nonlinear optical materials, that the up versus down alignment at an air/fused silica interface is critically influenced by a fine modification of the molecule. (c) 2008 American Institute of Physics.
  AMER INST PHYSICS, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/1.2981179
  DOI ID：10.1063/1.2981179, ISSN：0021-9606, Web of Science ID：WOS:000259883600002
• Heterodyne-detected electronic sum frequency generation: "Up" versus "down" alignment of interfacial molecules　　　　　　　　　　　　　　　
  Shoichi Yamaguchi; Tahei Tahara
  JOURNAL OF CHEMICAL PHYSICS, 巻：129, 号：10, 開始ページ：4, 2008年09月, ［査読有り］
  Heterodyne-detected electronic sum frequency generation (HD-ESFG) spectroscopy is newly developed to obtain complex electronic chi((2)) spectra of interfaces for a simultaneous detection bandwidth broader than 100 nm. HD-ESFG provides linear chi((2)) spectra that have unambiguous information on the "up" versus "down" alignment of interfacial molecules. It is demonstrated for p-nitroaniline, a prototypical molecule of nonlinear optical materials, that the up versus down alignment at an air/fused silica interface is critically influenced by a fine modification of the molecule. (c) 2008 American Institute of Physics.
  AMER INST PHYSICS, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/1.2981179
  DOI ID：10.1063/1.2981179, ISSN：0021-9606, ORCID：28499924, Web of Science ID：WOS:000259883600002
• PHYS 27-Hidden electronic excited state of enhanced green fluorescent protein (eGFP) by new multiplex two-photon absorption spectroscopy　　　　　　　　　　　　　　　
  Haruko Hosoi; Shoichi Yamaguchi; Hideaki Mizuno; Atsushi Miyawaki; Tahei Tahara
  ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 巻：235, 2008年04月, ［査読有り］
  AMER CHEMICAL SOC, 英語
  ISSN：0065-7727, Web of Science ID：WOS:000271775108798
• Novel interface-selective even-order nonlinear spectroscopy　　　　　　　　　　　　　　　
  Shoichi Yamaguchi; Tahei Tahara
  LASER & PHOTONICS REVIEWS, 巻：2, 号：1-2, 開始ページ：74, 終了ページ：82, 2008年04月, ［査読有り］
  New interface-selective second- (chi((2))) and fourth-order (chi ((4))) nonlinear spectroscopic techniques have been developed. chi((2)) electronic sum frequency generation (ESFG) spectroscopy enables us to obtain interfacial electronic spectra with an unprecedented high signal-to-noise ratio and dense wavelength data points. Frequency-domain chi((4)) Raman spectroscopy provides vibrational spectra of interfaces for a very wide wavenumber range covering the whole fingerprint region. Because these new even-order electronic and vibrational nonlinear spectroscopies utilize only visible and/or near-infrared laser pulses, they are applicable to a variety of "buried" interfaces that are not readily accessed by the other existing methods.
  WILEY-V C H VERLAG GMBH, 英語
  DOI：https://doi.org/10.1002/lpor.200710027
  DOI ID：10.1002/lpor.200710027, ISSN：1863-8880, ORCID：28499927, Web of Science ID：WOS:000255328600005
• Hidden electronic excited state of enhanced green fluorescent protein　　　　　　　　　　　　　　　
  Haruko Hosoi; Shoichi Yamaguchi; Hideaki Mizuno; Atsushi Miyawaki; Tahei Tahara
  JOURNAL OF PHYSICAL CHEMISTRY B, 巻：112, 号：10, 開始ページ：2761, 終了ページ：2763, 2008年03月, ［査読有り］
  Precise two-photon absorption spectra of the green fluorescent protein (GFP) and the mutants sapphire-GFP (T203I) and enhanced GFP (S65T/F64L), as well as a model compound for the chromophore, 4'-hydroxybenzylidene-2,3-dimethylimidazolinone (HBDI) were measured by multiplex two-photon absorption spectroscopy. The observed TPA bands of the anionic forms of enhanced GFP and HBDI were significantly shifted to the higher energy compared with the lowest-energy bands in one-photon absorption spectra. This result indicated the existence of a hidden electronic excited state in the vicinity of the lowest excited singlet (S I) state of the anionic form of the GFP chromophore, which is the origin of the blue shift of the two-photon absorption spectra as well as two-photon fluorescence excitation spectra.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/jp711628u
  DOI ID：10.1021/jp711628u, ISSN：1520-6106, ORCID：28499925, Web of Science ID：WOS:000253784700002
• Femtosecond time-resolved electronic sum-frequency generation spectroscopy: A new method to investigate ultrafast dynamics at liquid interfaces　　　　　　　　　　　　　　　
  Kentaro Sekiguchi; Shoichi Yamaguchi; Tahei Tahara
  JOURNAL OF CHEMICAL PHYSICS, 巻：128, 号：11, 開始ページ：8, 2008年03月, ［査読有り］
  We developed a new surface-selective time-resolved nonlinear spectroscopy, femtosecond time-resolved electronic sum-frequency generation (TR-ESFG) spectroscopy, to investigate ultrafast dynamics of molecules at liquid interfaces. Its advantage over conventional time-resolved second harmonic generation spectroscopy is that it can provide spectral information, which is realized by the multiplex detection of the transient electronic sum-frequency signal using a broadband white light continuum and a multichannel detector. We studied the photochemical dynamics of rhodamine 800 (R800) at the air/water interface with the TR-ESFG spectroscopy, and discussed the ultrafast dynamics of the molecule as thoroughly as we do for the bulk molecules with conventional transient absorption spectroscopy. We found that the relaxation dynamics of photoexcited R800 at the air/water interface exhibited three characteristic time constants of 0.32 ps, 6.4 ps, and 0.85 ns. The 0.32 ps time constant was ascribed to the lifetime of dimeric R800 in the lowest excited singlet (S(1)) state (S(1) dimer) that is directly generated by photoexcitation. The S(1) dimer dissociates to a monomer in the S(1) state (S(1) monomer) and a monomer in the ground state with this time constant. This lifetime of the S(1) dimer was ten times shorter than the corresponding lifetime in a bulk aqueous solution. The 6.4 ps and 0.85 ns components were ascribed to the decay of the S(1) monomer (as well as the recovery of the dimer in the ground state). For the 6.4 ps time constant, there is no corresponding component in the dynamics in bulk water, and it is ascribed to an interface-specific deactivation process. The 0.85 ns time constant was ascribed to the intrinsic lifetime of the S(1) monomer at the air/water interface, which is almost the same as the lifetime in bulk water. The present study clearly shows the feasibility and high potential of the TR-ESFG spectroscopy to investigate ultrafast dynamics at the interface.
  AMER INST PHYSICS, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/1.2841023
  DOI ID：10.1063/1.2841023, ISSN：0021-9606, ORCID：28499923, Web of Science ID：WOS:000254292500065
• New interface-selective even-order nonlinear spectroscopy　　　　　　　　　　　　　　　
  Shoichi Yamaguchi; Tahei Tahara
  2007 PACIFIC RIM CONFERENCE ON LASERS AND ELECTRO-OPTICS, VOLS 1-4, 開始ページ：851, 終了ページ：852, 2007年, ［査読有り］
  New interface-selective second- (chi((2))) and fourth-order (chi((4))) nonlinear spectroscopies were developed. The chi((2)) electronic sum frequency generation spectroscopy provides precise interfacial electronic spectra. Vibrational spectra of buried interfaces are acquired in the whole fingerprint region by the chi((4)) Raman spectroscopy.
  IEEE, 英語, 研究論文（国際会議プロシーディングス）
  DOI：https://doi.org/10.1109/CLEOPR.2007.4391513
  DOI ID：10.1109/CLEOPR.2007.4391513, Web of Science ID：WOS:000256956600429
• chi((4)) Raman spectroscopy for buried water interfaces　　　　　　　　　　　　　　　
  Shoichi Yamaguchi; Tahei Tahara
  ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 巻：46, 号：40, 開始ページ：7609, 終了ページ：7612, 2007年, ［査読有り］
  WILEY-V C H VERLAG GMBH, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1002/anie.200701609
  DOI ID：10.1002/anie.200701609, ISSN：1433-7851, eISSN：1521-3773, ORCID：28499928, Web of Science ID：WOS:000250249300013
• Determining electronic spectra at interfaces by electronic sum frequency generation: One- and two-photon double resonant oxazine 750 at the air/water interface　　　　　　　　　　　　　　　
  Shoichi Yamaguchi; Tahei Tahara
  JOURNAL OF CHEMICAL PHYSICS, 巻：125, 号：19, 開始ページ：8, 2006年11月, ［査読有り］
  The second-order nonlinear electronic spectra were measured for a dye oxazine 750 (OX750) adsorbed at the air/water interface using the multiplex electronic sum frequency generation (ESFG) spectroscopy recently developed by our group. The excitation-wavelength dependence of the ESFG spectrum was investigated, and a global fitting analysis was performed to separate contributions of one- and two-photon resonances. The analysis yielded linear interface electronic spectra in the one- and two-photon resonance regions, which can be directly compared to bulk absorption spectra. A two-dimensional plot of the linear interface electronic spectra is newly proposed to graphically represent all the essential information on the electronic structure of interfacial molecules. On this new analytical basis of the ESFG spectroscopy, the spectroscopic properties of OX750 at the interface are discussed. (c) 2006 American Institute of Physics.
  AMER INST PHYSICS, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/1.2375093
  DOI ID：10.1063/1.2375093, ISSN：0021-9606, ORCID：28499929, Web of Science ID：WOS:000242181800074
• Formation and dissociation of rhodamine 800 dimers in water: Steady-state and ultrafast spectroscopic study　　　　　　　　　　　　　　　
  K Sekiguchi; S Yamaguchi; T Tahara
  JOURNAL OF PHYSICAL CHEMISTRY A, 巻：110, 号：8, 開始ページ：2601, 終了ページ：2606, 2006年03月, ［査読有り］
  We investigated the fundamental photophysics and photochemistry of a cationic dye rhodamine 800 (R800) in water using steady-state and ultrafast time-resolved spectroscopies. In the ground state, the monomer and dimer coexist in equilibrium, which causes significant concentration dependence of UV-visible (vis) absorption spectra. We determined the equilibrium constant as well as the molar absorption spectra of the monomer and dimer from a global fitting analysis of the UV-vis spectra. The obtained pure dimer spectrum indicates that it is a nonparallel H-dimer. In contrast to the absorption spectra, the steady-state fluorescence spectra do not show any noticeable concentration dependence. The fluorescence lifetime was determined as 0.73 ns regardless of the concentration, and the fluorescence of R800 in water was solely attributed to the monomer. In femtosecond time-resolved absorption measurements, we observed the S-n <- S-1 absorption bands of the monomer and the dimer, as well as the ground-state bleaching signals. It was found that the S-1 dimer dissociates to produce the S-1 monomer (and the S-0 monomer) or relaxes to the So dimer with a time constant of as short as 3.0 ps, which brings about the absence of dimer fluorescence.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/jp055027p
  DOI ID：10.1021/jp055027p, ISSN：1089-5639, ORCID：28499930, Web of Science ID：WOS:000235943700005
• Multiplex electronic sum frequency generation spectroscopy of dye molecules at the air/water interface　　　　　　　　　　　　　　　
  Shoichi Yamaguchi; Kentaro Sekiguchi; Tahei Tahara
  Femtochemistry VII, 開始ページ：245, 終了ページ：248, 2006年, ［査読有り］
  This chapter describes multiplex electronic sum frequency generation spectroscopy and its application to the studies of static and dynamic properties of dye molecules adsorbed at the air-water interface. Second-order nonlinear spectroscopy is a powerful tool to study the structure and dynamics of molecules at interfaces that are very important in fundamental science and industrial application. Vibrational spectra of interfacial molecules are measured by IR-visible sum frequency generation (SFG) spectroscopy. The sensitivity of the IR-vis SFG spectroscopy has improved by using broadband IR pulses and multichannel detectors. High-quality IR-vis SFG spectra can be measured nowadays. On the other hand, second-order nonlinear susceptibility data of interfacial molecules are measured by the resonance second harmonic generation (SHG) method. In the spectral measurements, the SHG light intensity is recorded point by point with scanning the fundamental excitation wavelength. It is difficult to measure high-quality electronic spectra of interfacial molecules by the conventional scanning method. © 2006 Elsevier B.V. All rights reserved.
  Elsevier, 英語, 論文集(書籍)内論文
  DOI：https://doi.org/10.1016/B978-044452821-6/50036-8
  DOI ID：10.1016/B978-044452821-6/50036-8, SCOPUS ID：84882502327
• Interface-specific chi((4)) coherent Raman spectroscopy in the frequency domain　　　　　　　　　　　　　　　
  S Yamaguchi; T Tahara
  JOURNAL OF PHYSICAL CHEMISTRY B, 巻：109, 号：51, 開始ページ：24211, 終了ページ：24214, 2005年12月, ［査読有り］
  We demonstrate interface-specific fourth-order (chi((4))) coherent Raman spectroscopy in the frequency domain for the first time. Because the chi((4)) Raman spectroscopy uses only visible (vis) or near-IR light, it is expected to be a potential alternative to the widely utilized IR-vis sum frequency generation spectroscopy that cannot be applied to interfaces buried in thick IR absorbers such as water. We present the vibrational vertical bar chi((4))vertical bar(2) spectrum of rhodamine 800 at the air/water interface in a wide spectral range 100-3600 cm(-1). Comparison of the vertical bar chi((4))vertical bar(2) spectrum with the vertical bar chi((3))vertical bar(2) spectrum leads us to conclude that the present chi((4)) spectroscopy successfully probes the interface distinguished clearly from the bulk.
  AMER CHEMICAL SOC, 英語
  DOI：https://doi.org/10.1021/jp0542064
  DOI ID：10.1021/jp0542064, ISSN：1520-6106, ORCID：28499932, Web of Science ID：WOS:000234259900001
• Relaxation dynamics of the hydrated electron: Femtosecond time-resolved resonance Raman and luminescence study　　　　　　　　　　　　　　　
  M Mizuno; S Yamaguchi; T Tahara
  JOURNAL OF PHYSICAL CHEMISTRY A, 巻：109, 号：24, 開始ページ：5257, 終了ページ：5265, 2005年06月, ［査読有り］
  Femtosecond time-resolved resonance Raman measurements were carried out to examine the relaxation process of the hydrated electron in water. The rise of the intra- and intermolecular vibrational Raman bands of the solvating water molecules was successfully time-resolved with a time resolution as high as 250 fs. The temporal intensity change of Raman bands, as well as that of luminescence background, was compared with the time evolution of the transient absorption signal. It was found that (1) the Raman and luminescence signals exhibited the same temporal behavior, (2) the rise time of the Raman bands is faster than the appearance of the equilibrated hydrated electron, indicating that the precursor state also gives rise to resonance Raman signals, and (3) the rise of the transient Raman band is slower than that of the transient absorption at the probe wavelength of 800 nm. Because it has been shown that the Raman intensity enhancement arises from the resonance with the s -> p transition, fact 2 implies that the precursor state is the nonequilibrated s-state electron. The delayed rise of the Raman signal compared to the absorption was explained in terms of the temporal change of the resonance condition. In very early time when the absorption is largely red-shifted, the probe at 800 nm is resonant with the high energy part of the absorption that provides little resonance Raman enhancement. This explanation was consistent with the probe wavelength dependence of the temporal behavior of the Raman signal: the Raman bands measured with the higher energy probe (600 nm) rose even more slowly. The resonance Raman signal in the anti-Stokes side was also examined, but no anti-Stokes band was observable. It suggests that the temperature increase of the solvation structure around the nonequilibrated hydrated electron is less than 100 K.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/jp050828d
  DOI ID：10.1021/jp050828d, ISSN：1089-5639, ORCID：28499933, Web of Science ID：WOS:000229866900003
• Host to guest energy transfer in a self-assembled supramolecular nanocage observed by picosecond fluorescence quenching　　　　　　　　　　　　　　　
  H Hosoi; S Yamaguchi; T Tahara
  CHEMISTRY LETTERS, 巻：34, 号：4, 開始ページ：618, 終了ページ：619, 2005年04月, ［査読有り］
  The host-guest energy transfer process in a self-assembled system was investigated by picosecond time-resolved fluorescence spectroscopy. A self-assembled coordination nanocage (Pd6L4) was photoexcited and the appearance of the fluorescence from an encapsulated guest acridine dye molecule was observed. The time constant (1.3 ns) as well as the efficiency (9%) of the energy transfer from the nanocage to the guest molecule was determined.
  CHEMICAL SOC JAPAN, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1246/cl.2005.618
  DOI ID：10.1246/cl.2005.618, ISSN：0366-7022, eISSN：1348-0715, ORCID：28499931, Web of Science ID：WOS:000228541600081
• Precise electronic X-(2) spectra of molecules adsorbed at an interface measured by multiplex sum frequency generation　　　　　　　　　　　　　　　
  S Yamaguchi; T Tahara
  JOURNAL OF PHYSICAL CHEMISTRY B, 巻：108, 号：50, 開始ページ：19079, 終了ページ：19082, 2004年12月, ［査読有り］
  We have developed a new technique to obtain a second-order nonlinear (chi((2))) electronic spectrum of molecules adsorbed at an interface. This technique is based on multiplex sum frequency generation that utilizes femtosecond near-infrared pulses and white light continuum. We obtained the \X-(2)\(2) spectra of a dye Nile Blue (NB) at the air/water interface with an unprecedented high signal-to-noise ratio and dense wavelength data points. Fitting analyses with an exact chi((2)) expression were performed for the spectra, and detailed information about the electronic structure of NB at the interface was obtained.
  AMER CHEMICAL SOC, 英語
  DOI：https://doi.org/10.1021/jp045306x
  DOI ID：10.1021/jp045306x, ISSN：1520-6106, ORCID：28499935, Web of Science ID：WOS:000225695100001
• Observation of an optically forbidden state of C-60 by nondegenerate two-photon absorption spectroscopy　　　　　　　　　　　　　　　
  S Yamaguchi; T Tahara
  CHEMICAL PHYSICS LETTERS, 巻：390, 号：1-3, 開始ページ：136, 終了ページ：139, 2004年05月, ［査読有り］
  Two-photon absorption (TPA) spectra of C-60 in toluene were measured for it wide wavelength region from 270 to 680 nm by femtosecond pump-probe nondegenerate TPA spectroscopy. A distinct TPA band peaked at 314 nm was observed, and its intensity was evaluated to be 80 GM. The depolarization ratio of the TPA band was found to be zero within the experimental uncertainty, which indicates that this band is due to a totally symmetric (A(g)) two-photon allowed excited state. The energy of the observed A(g) state is about 1 eV below a prediction based on the theoretically calculated pi-electron energies. (C) 2004 Elsevier B.V. All rights reserved.
  ELSEVIER SCIENCE BV, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1016/j.cplett.2004.03.146
  DOI ID：10.1016/j.cplett.2004.03.146, ISSN：0009-2614, ORCID：28499934, Web of Science ID：WOS:000221628400025
• Femtosecond dynamics of the solvated electron in water studied by time-resolved Raman spectroscopy　　　　　　　　　　　　　　　
  M Mizuno; S Yamaguchi; T Tahara
  FEMTOCHEMISTRY AND FEMTOBIOLOGY: ULTRAFAST EVENTS IN MOLECULAR SCIENCE, 開始ページ：225, 終了ページ：228, 2004年, ［査読有り］
  ELSEVIER SCIENCE BV, 英語, 研究論文（国際会議プロシーディングス）
  Web of Science ID：WOS:000222945300044
• Two-photon absorption spectrum of all-trans retinal　　　　　　　　　　　　　　　
  S Yamaguchi; T Tahara
  CHEMICAL PHYSICS LETTERS, 巻：376, 号：1-2, 開始ページ：237, 終了ページ：243, 2003年07月, ［査読有り］
  The nondegenerate two-photon absorption spectrum of all-traps retinal in a nonpolar solvent at room temperature has been measured for the first time. The multichannel detection utilizing the technique of femtosecond time-resolved pump-probe absorption spectroscopy has enabled us to obtain precise two-photon absorption spectra. It was found that the two-photon absorption maximum of all-traps retinal is located at 376 nm, which is 7 nm longer than the one-photon absorption peak. This peak wavelength difference indicates the 500-cm(-1) energy gap between the S-3 (B-u) state and the S-2 (A(g)) state. On the basis of the obtained two-photon absorption data and the available fluorescence data, we determined the 0-0 position of the S-2 state to be 2.47 x 10(4) cm(-1). (C) 2003 Elsevier B.V. All rights reserved.
  ELSEVIER SCIENCE BV, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1016/S0009-2614(03)00984-9
  DOI ID：10.1016/S0009-2614(03)00984-9, ISSN：0009-2614, ORCID：28499936, Web of Science ID：WOS:000184315600037
• Oxidative cyclization of bis(biaryl)acetylenes: Synthesis and photophysics of dibenzo[g,p]chrysene-based fluorescent polymers　　　　　　　　　　　　　　　
  S Yamaguchi; TM Swager
  JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 巻：123, 号：48, 開始ページ：12087, 終了ページ：12088, 2001年12月, ［査読有り］
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/ja016692o
  DOI ID：10.1021/ja016692o, ISSN：0002-7863, Web of Science ID：WOS:000172591000031
• Spectroscopic determination of very low quantum yield of singlet oxygen formation photosensitized by industrial dyes　　　　　　　　　　　　　　　
  S Yamaguchi; Y Sasaki
  JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY, 巻：142, 号：1, 開始ページ：47, 終了ページ：50, 2001年08月, ［査読有り］
  We have measured the quantum yield Q(Delta) of (1)Delta (g) molecular oxygen (singlet oxygen, O-1(2)) formation photosensitized by some industrial dyes. As regards dyes and pigments for practical uses, it is widely believed that O-1(2) is a key intermediate in their photofading processes. Q(Delta) for practical dyes, however, is generally very low, and it has been difficult to determine accurately Q(Delta) for them. We have made a highly sensitive spectrometer for 1.27 mum O-1(2) phosphorescence detection, and determined Q(Delta) for an azo dye as low as (2.2 +/- 1.5) X 10(-5). This is the first demonstration of Q(Delta) lower than 10(-4). (C) 2001 Elsevier Science B.V. All rights reserved.
  ELSEVIER SCIENCE SA, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1016/S1010-6030(01)00470-1
  DOI：https://doi.org/10.1016/s1010-6030(01)00470-1
  DOI ID：10.1016/S1010-6030(01)00470-1, ISSN：1010-6030, ORCID：28499937, Web of Science ID：WOS:000170672600007
• Effect of water on primary photocarrier-generation process in Y-form titanyl phthalocyanine　　　　　　　　　　　　　　　
  S Yamaguchi; Y Sasaki
  JOURNAL OF PHYSICAL CHEMISTRY B, 巻：104, 号：39, 開始ページ：9225, 終了ページ：9229, 2000年10月, ［査読有り］
  We have studied the effect of adsorbed water on the primary photocarrier-generation process in Y-form titanyl phthalocyanine (Y-TiOPc) by using ground:state absorption and time-resolved fluorescence spectroscopy. The water adsorption is the unique feature of Y-TiOPc, which is not observed in the other polymorphs of TiOPc. We report for the first time the water-induced change of the absorption spectrum, that is, the hydrochromism of Y-TiOPc. The fluorescence lifetimes and amplitudes of Y-TiOPc are greatly influenced by adsorbed water. We have found that the mechanism of the fluorescence quenching of Y-TiOPc caused by water adsorption is the same as that by an electric field. Adsorbed water enhances the photocarrier generation of Y-TiOPc in the same way as an electric field does in the picosecond time regime.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/jp0019557
  DOI ID：10.1021/jp0019557, ISSN：1089-5647, ORCID：28499939, Web of Science ID：WOS:000089712900023
• Construction of electric-field-modulated picosecond time-resolved fluorescence spectrometer　　　　　　　　　　　　　　　
  S Yamaguchi; Y Sasaki
  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 巻：39, 号：10, 開始ページ：6107, 終了ページ：6108, 2000年10月, ［査読有り］
  We have developed a new electric-field-modulated picosecond time-resolved fluorescence spectrometer using a streak scope. We can obtain an electric-field-induced change of a fluorescence lifetime and that of an amplitude as low as 1% without losing the two-dimensional multichannel advantage of the streak scope. The spectrometer enabled us to observe electric-field-induced fluorescence quenching of titanyl phthalocyanine and obtain valuable information on the mechanism of photocarrier generation.
  INST PURE APPLIED PHYSICS, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1143/JJAP.39.6107
  DOI ID：10.1143/JJAP.39.6107, ISSN：0021-4922, ORCID：28499938, Web of Science ID：WOS:000090139000076
• Primary carrier-generation process in Y-form and phase I titanyl phthalocyanines　　　　　　　　　　　　　　　
  S Yamaguchi; Y Sasaki
  CHEMICAL PHYSICS LETTERS, 巻：323, 号：1-2, 開始ページ：35, 終了ページ：42, 2000年06月, ［査読有り］
  We have studied the primary process of the photocarrier generation in Y-form and phase I titanyl phthalocyanine (TiOPc) microcrystallites using the electric-field-modulated picosecond time-resolved fluorescence spectroscopy. The electric-field dependence of the fluorescence amplitudes and lifetimes of TiOPcs leads to a detailed understanding of excited-state charge-transfer (CT) character. We have concluded that only the shorter-lifetime singlet exciton of the Y-form has significant CT character. We regard the CT exciton as a key to the high photocarrier-generation quantum yield of the Y-form. The lack of a CT state in phase I TiOPc causes its low photosensitivity. (C) 2000 Elsevier Science B.V. All rights reserved.
  ELSEVIER SCIENCE BV, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1016/S0009-2614(00)00475-9
  DOI：https://doi.org/10.1016/s0009-2614(00)00475-9
  DOI ID：10.1016/S0009-2614(00)00475-9, ISSN：0009-2614, ORCID：28499940, Web of Science ID：WOS:000087538200006
• Ultrafast electronic relaxation and hydrogen-bond-formation/dissociation dynamics of photoexcited all-trans retinal in protic solvents　　　　　　　　　　　　　　　
  S Yamaguchi; H Hamaguchi
  JOURNAL OF PHYSICAL CHEMISTRY A, 巻：104, 号：18, 開始ページ：4272, 終了ページ：4279, 2000年05月, ［査読有り］
  The ultrafast electronic relaxation and the hydrogen-bond-formation/dissociation dynamics of photoexcited all-trans retinal in 1-butanol/cyclohexane mixed solvents have been studied by femtosecond time-resolved visible absorption spectroscopy. Four transient absorption bands, which can be assigned to the S-3, S-2, S-1, and T-1 states, were observed in neat cyclohexane. The shapes and the dynamics of these absorption bands agree very well with those reported previously for all-trans retinal in hexane. In contrast, only three transient absorption bands, which can be assigned to the S-3, S-2, and T-1 states, were identified in the mixed solvents. The band assigned to the S-2 State showed a time-dependent peak shift, which is attributed to solvent reorganization on a picosecond time scale. A kinetic analysis of the three transient absorption bands has led to the conclusion that no state-ordering change of the (n, pi*) and (pi, pi*) states takes place in the excited singlet manifold upon hydrogen-bond formation. The l-butanol concentration dependence of the absorption spectra shows that the free and hydrogen-bonded species coexist in the S-3 and T-1 states, but that all of the retinal molecules are hydrogen-bonded in the S-2 state. These observations indicate that an ultrafast hydrogen bond-formation reaction takes place during or just after the S-3 --> S-2 internal conversion and is complete within a time scale much shorter than the S-2 lifetime. Dissociation of the hydrogen bonding is most likely to take place during or after the S-1 --> T-1 intersystem crossing and is complete within a time scale much shorter than the T-1 lifetime. The observed longer lifetime of the hydrogen-bonded S-2 State is consistent with the higher isomerization quantum yield in protic solvents than in aprotic nonpolar solvents.
  AMER CHEMICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1021/jp993551o
  DOI ID：10.1021/jp993551o, ISSN：1089-5639, ORCID：28499941, Web of Science ID：WOS:000087003100019
• Primary process of photocarrier generation in Y-form titanyl phthalocyanine studied by electric-field-modulated picosecond time-resolved fluorescence spectroscopy　　　　　　　　　　　　　　　
  S Yamaguchi; Y Sasaki
  JOURNAL OF PHYSICAL CHEMISTRY B, 巻：103, 号：33, 開始ページ：6835, 終了ページ：6838, 1999年08月, ［査読有り］
  We have investigated the primary process of the carrier generation in Y-form titanyl phthalocyanine (Y-TiOPc) microcrystallites by means of newly developed electric-field-modulated picosecond time-resolved fluorescence spectroscopy. Two singlet excitons have been identified in the fluorescence decay curves of Y-TiOPc. We have inferred from the field-dependence of the fluorescence amplitudes and lifetimes that the shorter-lifetime exciton of intramolecular charge transfer (CT) character is a primary intermediate in the carrier generation process. It has been found that the internal conversion from the CT exciton to the Frenkel exciton is decelerated by the electric field.
  AMER CHEMICAL SOC, 英語
  DOI：https://doi.org/10.1021/jp991892w
  DOI ID：10.1021/jp991892w, ISSN：1089-5647, ORCID：28499942, Web of Science ID：WOS:000082335600001
• Two distinct solvated structures of para-nitroaniline in acetonitrile and their dissociation and reassociation dynamics　　　　　　　　　　　　　　　
  K Mohanalingam; S Yamaguchi; H Hamaguchi
  LASER CHEMISTRY, 巻：19, 号：1-4, 開始ページ：329, 終了ページ：333, 1999年, ［査読有り］
  We have measured the femtosecond time-resolved absorption spectra of para-nitroaniline in acetonitrile just after the photoexcitation to the lowest excited singlet state. The Singular Value Decomposition (SVD) analysis shows that two temporal evolutions follow the photoexcitation. The fast component (0.7 ps time constant) describes the dissociation of the 1:2 associated form to generate the 1:0 form followed by its reassociation with AN molecules. A slower temporal evolution of 10 ps is most likely to represent the cooling down process of the whole system.
  TAYLOR & FRANCIS LTD, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1155/1999/63925
  DOI ID：10.1155/1999/63925, ISSN：0278-6273, ORCID：28499943, Web of Science ID：WOS:000081370000058
• Femtosecond ultraviolet-visible absorption study of all-trans -> 13-cis center dot 9-cis photoisomerization of retinal　　　　　　　　　　　　　　　
  S Yamaguchi; H Hamaguchi
  JOURNAL OF CHEMICAL PHYSICS, 巻：109, 号：4, 開始ページ：1397, 終了ページ：1408, 1998年07月, ［査読有り］
  The all-trans --> 13-cis.9-cis photoisomerization reaction of retinal in aerated nonpolar solvents has been studied by femtosecond time-resolved ultraviolet-visible (UV-VIS) absorption spectroscopy. The excited-state absorption spectra in the wavelength region 400-800 nm indicate that there is no all-trans --> 13-cis.9-cis isomerization reaction pathway that is complete in the electronic excited singlet manifold of S-1, S-2, and S-3. The ground-state bleaching recovery of all-trans retinal monitored in the near UV (ultraviolet) wavelength region 310-390 nm shows that a perpendicular excited singlet state (p*) takes part in the all-trans --> 13-cis.9-cis isomerization reaction. The lifetime of p* is about 7 ps, and the precursor of p* is most probably the S-2 state. The isomerization quantum yield derived from the femtosecond UV absorption data agrees well with those determined by the HPLC analysis of the photoproduct. The temperature dependence of the isomerization quantum yield indicates the existence of a potential-energy barrier as high as (1.2 +/- 0.6) x 10(3) cm(-1) on the reaction pathway from the S-2 state to the p* state. (C) 1998 American Institute of Physics.
  AMER INST PHYSICS, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/1.476692
  DOI ID：10.1063/1.476692, ISSN：0021-9606, ORCID：28499944, Web of Science ID：WOS:000075255600025
• Femtosecond visible absorption study of excited-state dynamics of 9-cis retinal　　　　　　　　　　　　　　　
  S Yamaguchi; H Hamaguchi
  CHEMICAL PHYSICS LETTERS, 巻：287, 号：5-6, 開始ページ：694, 終了ページ：700, 1998年05月, ［査読有り］
  Femtosecond time-resolved pump-probe absorption spectroscopy has been used to study the photophysics and photochemistry of 9-cis retinal in aerated hexane. Three excited singlet states (S-3, S-2, S-1) and the lowest tripler start (T-1) have been identified by the SVD analysis of the observed time-resolved absorption spectra. No evidence has been obtained for a 9-cis --> all-trans isomerization reaction pathway that completes in the excited singlet manifold. (C) 1998 Elsevier Science B.V. All rights reserved.
  ELSEVIER SCIENCE BV, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1016/S0009-2614(98)00234-6
  DOI：https://doi.org/10.1016/s0009-2614(98)00234-6
  DOI ID：10.1016/S0009-2614(98)00234-6, ISSN：0009-2614, ORCID：28499945, Web of Science ID：WOS:000073718500035
• Femtosecond time-resolved absorption spectroscopy of all-trans-retinal in hexane　　　　　　　　　　　　　　　
  S Yamaguchi; HO Hamaguchi
  JOURNAL OF MOLECULAR STRUCTURE, 巻：379, 開始ページ：87, 終了ページ：92, 1996年06月, ［査読有り］
  We have carried out femtosecond time-resolved absorption measurements of all-trans-retinal in hexane. The S-n <-- S-2 and the T-n <-- T-1 absorption spectra with corresponding temporal evolutions have been obtained by a kinetic analysis based on singular value decomposition (SVD).
  ELSEVIER SCIENCE BV, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1016/0022-2860(95)09178-5
  DOI ID：10.1016/0022-2860(95)09178-5, ISSN：0022-2860, ORCID：28499947, Web of Science ID：WOS:A1996UQ82400010
• Exciton dynamics in poly(p-pyridyl vinylene)　　　　　　　　　　　　　　　
  JW Blatchford; SW Jessen; LB Lin; JJ Lih; TL Gustafson; AJ Epstein; DK Fu; MJ Marsella; TM Swager; AG MacDiarmid; S Yamaguchi; H Hamaguchi
  PHYSICAL REVIEW LETTERS, 巻：76, 号：9, 開始ページ：1513, 終了ページ：1516, 1996年02月, ［査読有り］
  We present results of picosecond photoinduced absorption (PA) and time-resolved photoluminescence studies on solid and solution forms of poly(p-pyridyl vinylene). The nearly identical PA response of all forms of the polymer reflects the generation of the same primary photoexcitation, a Couloumbically bound intrachain singlet exciton, and the absence of exotic species such as interchain excimers. The time dependence of the PA points to direct intersystem crossing as the origin of triplet excitons, ruling out generation of free carriers as a precursor to exciton formation.
  AMERICAN PHYSICAL SOC, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1103/PhysRevLett.76.1513
  DOI ID：10.1103/PhysRevLett.76.1513, ISSN：0031-9007, ORCID：28499946, Web of Science ID：WOS:A1996TW70000028
• CONVENIENT METHOD OF MEASURING THE CHIRP STRUCTURE OF FEMTOSECOND WHITE-LIGHT CONTINUUM PULSES　　　　　　　　　　　　　　　
  S YAMAGUCHI; HO HAMAGUCHI
  APPLIED SPECTROSCOPY, 巻：49, 号：10, 開始ページ：1513, 終了ページ：1515, 1995年10月, ［査読有り］
  We have developed a convenient method of measuring the temporal chirp structure of white-light continuum pulses used in femtosecond time-resolved absorption spectroscopy. This method, based on the nonresonant optical Kerr effect, is superior in many respects to the existing one that uses the sum or difference frequency generation by a nonlinear crystal.
  SOC APPLIED SPECTROSCOPY, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1366/0003702953965434
  DOI ID：10.1366/0003702953965434, ISSN：0003-7028, ORCID：28499948, Web of Science ID：WOS:A1995TD15400018
• ULTRAFAST VIBRATIONAL-RELAXATION IN PHOTOGENERATED S(1) ALPHA-TERTHIOPHENE IN SOLUTION BY FEMTOSECOND TIME-RESOLVED ABSORPTION EMISSION AND PICOSECOND TIME-RESOLVED RAMAN-SPECTROSCOPY　　　　　　　　　　　　　　　
  S YAMAGUCHI; H HAMAGUCHI
  CHEMICAL PHYSICS LETTERS, 巻：227, 号：3, 開始ページ：255, 終了ページ：260, 1994年09月, ［査読有り］
  Ultrafast vibrational population redistribution dynamics and subsequent cooling processes have been identified and quantified for photogenerated S1 alpha-terthiophene in solution by using femtosecond time-resolved absorption/emission spectroscopy combined with picosecond time-resolved Raman spectroscopy. The population redistribution among the S1 vibrational levels dominates the dynamics for the first few picoseconds after the photoexcitation. The cooling of the solvent-solute system then takes place in the time scale of a few tens of picoseconds.
  ELSEVIER SCIENCE BV, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1016/0009-2614(94)00832-9
  DOI ID：10.1016/0009-2614(94)00832-9, ISSN：0009-2614, eISSN：1873-4448, ORCID：28499949, Web of Science ID：WOS:A1994PF45600004
• Picosecond dynamics of photoexcited transient species of p-phenylenes; Population decay and structural chance　　　　　　　　　　　　　　　
  S YAMAGUCHI; H HAMAGUCHI
  FOURTEENTH INTERNATIONAL CONFERENCE ON RAMAN SPECTROSCOPY, 開始ページ：496, 終了ページ：497, 1994年, ［査読有り］
  JOHN WILEY & SONS LTD, 英語, 研究論文（国際会議プロシーディングス）
  Web of Science ID：WOS:A1994BD55D00225
• CONSTRUCTION OF A TRANSFORM-LIMITED PICOSECOND TIME-RESOLVED RAMAN SPECTROMETER　　　　　　　　　　　　　　　
  K IWATA; S YAMAGUCHI; H HAMAGUCHI
  REVIEW OF SCIENTIFIC INSTRUMENTS, 巻：64, 号：8, 開始ページ：2140, 終了ページ：2146, 1993年08月, ［査読有り］
  A pump-probe picosecond time-resolved Raman spectrometer has been constructed using a dye laser synchronously pumped by a cw mode-locked Nd:YAG laser and a high repetition rate (2 kHz) dye amplifier pumped by the frequency doubled output from a cw Nd:YAG regenerative amplifier. Transform-limited picosecond pulses with 3.5 cm-1 wave number width and 3.2 ps temporal width are obtained at the wavelength of 588 nm. The second harmonic of these pulses is generated at 294 nm and is used for pumping, while the remaining visible pulses are used for probing. resonance Raman scattering. The cross-correlation time between the pump and probe pulses is 4.1 ps. The temporal profile of the laser pulse is found to be very close to the sech2 shape. The wave number resolution of the system is estimated to be 3.5 cm-1 according to the Tailor criterion. The time resolution is estimated to be 2.2 ps using a criterion newly proposed in the present paper. Time-resolved Raman spectra of S1 trans-stilbene and S1 p-terphenyl are presented to demonstrate the capability of the constructed spectrometer.
  AMER INST PHYSICS, 英語, 研究論文（学術雑誌）
  DOI：https://doi.org/10.1063/1.1143951
  DOI ID：10.1063/1.1143951, ISSN：0034-6748, ORCID：28499950, Web of Science ID：WOS:A1993LR97900006

• Leaflet-specific Lipid Diffusion Revealed by Fluorescence Lifetime Correlation Analyses　　　　　　　　　　　　　　　
  Takuhiro Otosu; Shoichi Yamaguchi
  巻：49, 号：12, 開始ページ：1473, 終了ページ：1480, 2020年12月
  Cell membranes are fluidic, and the fluidic properties give unique biological functions to the membranes. Here, we review the application of fluorescence lifetime correlation analyses to elucidate the leaflet-specific lipid diffusion in a model cell membrane supported on a glass surface. Utilization of fluorescence lifetime enables us to discriminate the signals from each leaflet of the lipid bilayer and to analyze the lipid diffusion in a leaflet-specific manner. The results showed that the lipid diffusion in a proximal leaflet facing a glass surface is sensitive to the strength of the electrostatic interaction between the lipid headgroup and the glass surface whereas that in the distal one is insensitive to it. This clearly indicates that the interleaflet coupling is negligible. Because the strength of the interleaflet coupling is highly relevant to the cooperative formation of functional domains across the bilayer, this work provides an important insight into the lipid dynamics in cell membranes.
  英語, 書評論文,書評,文献紹介等
  DOI：https://doi.org/10.1246/cl.200539
  DOI ID：10.1246/cl.200539, ISSN：0366-7022, eISSN：1348-0715, Web of Science ID：WOS:000598377200011
• Comment on "Phase-sensitive sum frequency vibrational spectroscopic study of air/water interfaces: H2O, D2O, and diluted isotopic mixtures" [J. Chem. Phys. 150, 144701 (2019)]　　　　　　　　　　　　　　　
  Mohammed Ahmed; Yuki Nojima; Satoshi Nihonyanagi; Shoichi Yamaguchi; Tahei Tahara
  巻：152, 号：23, 2020年06月
  英語, その他
  DOI：https://doi.org/10.1063/1.5126062
  DOI ID：10.1063/1.5126062, ISSN：0021-9606, eISSN：1089-7690, Web of Science ID：WOS:000542728800001
• Two-Dimensional Fluorescence Lifetime Correlation Spectroscopy: Concepts and Applications　　　　　　　　　　　　　　　
  Takuhiro Otosu; Shoichi Yamaguchi
  巻：23, 号：11, 2018年11月
  We review the basic concepts and recent applications of two-dimensional fluorescence lifetime correlation spectroscopy (2D FLCS), which is the extension of fluorescence correlation spectroscopy (FCS) to analyze the correlation of fluorescence lifetime in addition to fluorescence intensity. Fluorescence lifetime is sensitive to the microenvironment and can be a "molecular ruler" when combined with FRET. Utilization of fluorescence lifetime in 2D FLCS thus enables us to quantify the inhomogeneity of the system and the interconversion dynamics among different species with a higher time resolution than other single-molecule techniques. Recent applications of 2D FLCS to various biological systems demonstrate that 2D FLCS is a unique and promising tool to quantitatively analyze the microsecond conformational dynamics of macromolecules at the single-molecule level.
  英語, 書評論文,書評,文献紹介等
  DOI：https://doi.org/10.3390/molecules23112972
  DOI ID：10.3390/molecules23112972, eISSN：1420-3049, Web of Science ID：WOS:000451641900244
• Ultrafast Dynamics at Water Interfaces Studied by Vibrational Sum Frequency Generation Spectroscopy　　　　　　　　　　　　　　　
  Satoshi Nihonyanagi; Shoichi Yamaguchi; Tahei Tahara
  巻：117, 号：16, 開始ページ：10665, 終了ページ：10693, 2017年08月
  We present an overview of studies on the ultrafast dynamics of water at aqueous interfaces carried out by time-resolved vibrational sum frequency generation (VSFG) spectroscopies. This research field has been growing rapidly, stimulated by technical developments achieved recently. In this review, first, the principles and instrumentations are described for conventional VSFG, heterodyne-detected VSFG, and various IR-pump/VSFG-probe techniques, namely, time-resolved conventional VSFG, time-resolved heterodyne-detected VSFG, and their extension to two-dimensional spectroscopy. Second, the applications of these time-resolved VSFG techniques to the study of the femtosecond vibrational dynamics of water at various interfaces are discussed, in the order of silica/water, charged monolayer/water, and the air/water interfaces. These studies demonstrate that there exists water dynamics specific to the interfaces and that time-resolved VSFG spectroscopies can unambiguously detect such unique dynamics in an interface-selective manner. In particular, the most recent time-resolved heterodyne detected VSFG and two-dimensional heterodyne-detected VSFG unveil the inhomogeneity of the hydrogen bond arid relevant vibrational dynamics of interfacial water through unambiguous observation of hole-burning in the OH stretch band, as well as the subsequent spectral diffusion in the femtosecond time region. These time-resolved VSFG studies have also left several issues for discussion. We describe not only the obtained conclusive physical insights into interfacial water dynamics but also the points left unclear or controversial. A new type of experiment that utilizes UV excitation is also described briefly. Lastly, the summary and some future perspectives of time-resolved VSFG spectroscopies are given.
  英語, 書評論文,書評,文献紹介等
  DOI：https://doi.org/10.1021/acs.chemrev.6b00728
  DOI ID：10.1021/acs.chemrev.6b00728, ISSN：0009-2665, eISSN：1520-6890, Web of Science ID：WOS:000408519200003
• Standing evanescent-wave fluorescence correlation spectroscopy for analyzing the translational diffusion in bio-membranes　　　　　　　　　　　　　　　
  Takuhiro Otosu; Shoichi Yamaguchi
  巻：252, 2016年08月
  英語, 研究発表ペーパー・要旨（国際会議）
  ISSN：0065-7727, Web of Science ID：WOS:000431460201108
• Ultrafast Vibrational Dynamics of Water at a Zwitterionic Lipid/Water Interface Revealed by Two-Dimensional Heterodyne-Detected Vibrational Sum Frequency Generation (2D HD-VSFG)　　　　　　　　　　　　　　　
  Inoue Ken-ichi; Singh Prashant Chandra; Nihonyanagi Satoshi; Yamaguchi Shoichi; Tahara Tahei
  ULTRAFAST PHENOMENA XIX, 巻：162, 開始ページ：309, 終了ページ：312, 2015年, ［査読有り］
  DOI：https://doi.org/10.1007/978-3-319-13242-6_75
  DOI ID：10.1007/978-3-319-13242-6_75, ISSN：0930-8989, Web of Science ID：WOS:000357738800075
• 時間分解ヘテロダイン検出振動和周波発生分光法を用いた水界面の超高速振動ダイナミクスの研究　　　　　　　　　　　　　　　
  井上 賢一; SINGH Prashant C; 二本柳 聡史; 山口 祥一; 田原 太平
  表面科学, 巻：35, 号：12, 開始ページ：662, 終了ページ：667, 2014年
  Molecular-level understanding of interfaces is of crucial importance in many fundamental and applied sciences. Vibrational sum frequency generation (VSFG) spectroscopy has intrinsic interface-selectivity and has been widely utilized to study molecular structures and dynamics at interfaces. However, conventional VSFG spectroscopy measures the intensity of the signal, providing only information about the square of second-order nonlinear susceptibility, |<I>χ</I>⁽²⁾|². Recently, we developed multiplex heterodyne-detected (HD-) VSFG spectroscopy. This HD-VSFG spectroscopy enables us to measure the imaginary part of <I>χ</I>⁽²⁾, Im<I>χ</I>⁽²⁾, which can be directly compared to infrared absorption and Raman spectra. Moreover, we have extended the HD-VSFG spectroscopy to time-resolved (TR-) HD-VSFG spectroscopy and two-dimensional (2D) HD-VSFG spectroscopy by combining with the pump-probe technique. This review describes development of these time-resolved HD-VSFG methods and their applications to the water interfaces.
  The Surface Science Society of Japan, 日本語
  DOI：https://doi.org/10.1380/jsssj.35.662
  DOI ID：10.1380/jsssj.35.662, ISSN：0388-5321, CiNii Articles ID：130004785031
• 新しい非線形分光で明らかになる液体界面の局所分子構造 : 和周波発生光のヘテロダイン検出　　　　　　　　　　　　　　　
  二本柳 総史; 山口 祥一; Mondal Jahur A.; 田原 太平
  光学, 巻：40, 号：8, 開始ページ：415, 終了ページ：420, 2011年08月10日
  応用物理学会分科会日本光学会, 日本語
  ISSN：0389-6625, CiNii Articles ID：10029467817, CiNii Books ID：AN00080324
• PHYS 351-Ultrafast dynamics at the air/water interface investigated with time-resolved electronic sum-frequency generation (TR-ESFG) spectroscopy　　　　　　　　　　　　　　　
  Kentaro Sekiguchi; Shoichi Yamaguchi; Tahei Tahara
  巻：235, 2008年04月
  英語, 研究発表ペーパー・要旨（国際会議）
  ISSN：0065-7727, Web of Science ID：WOS:000271775109234
• Novel even-order nonlinear spectroscopy for liquid interfaces: Interface-specific hydrogen bonds and interfacial polarity　　　　　　　　　　　　　　　
  Shoichi Yamaguchi; Sobhan Sen; Tahei Tahara
  巻：233, 2007年03月
  英語, 研究発表ペーパー・要旨（国際会議）
  ISSN：0065-7727, Web of Science ID：WOS:000207722807310
• Precise two-photon absorption measurements of biomolecules using femtosecond broadband pulses.　　　　　　　　　　　　　　　
  S Yamaguchi; T Tahara
  巻：226, 開始ページ：U333, 終了ページ：U333, 2003年09月
  英語, 研究発表ペーパー・要旨（国際会議）
  ISSN：0065-7727, Web of Science ID：WOS:000187062501700

• Applications of Theoretical Methods in Vibrational Spectroscopy　　　　　　　　　　　　　　　
  Shoichi Yamaguchi, ［単著］
  Springer Singapore, 2025年06月
  ISBN：9789819646272

• 水/水，水/氷，氷/氷界面の構造とダイナミクス　　　　　　　　　　　　　　　
  日本学術振興会, 科学研究費助成事業, 基盤研究(B), 2022年04月01日 - 2027年03月31日
  山口 祥一, 埼玉大学
  配分額（総額）：17290000, 配分額（直接経費）：13300000, 配分額（間接経費）：3990000
  課題番号：22H02027
• アミロイド形成を促す脂質‐蛋白質間相互作用の分子機構解明　　　　　　　　　　　　　　　
  日本学術振興会, 科学研究費助成事業, 基盤研究(B), 2019年04月01日 - 2023年03月31日
  乙須 拓洋; 山口 祥一, 埼玉大学
  配分額（総額）：15600000, 配分額（直接経費）：12000000, 配分額（間接経費）：3600000
  本研究ではモデル生体膜を用い，脂質二重膜上で促進されるアミロイド形成の分子機構理解を目的としている．2021年度はアミロイド形成蛋白質として知られているIAPPを用い，アミロイド感受性色素であるチオフラビンTを用いた凝集過程の追跡，ならびに蛍光ラベルしたIAPPを用いたIAPP拡散速度変化の追跡を行った．前者の実験の結果，IAPPはアミロイド形成開始後約70分間はアミロイドの形成は起こらず，その後加速度的にアミロイド形成が促進することが明らかとなった．
  この点についてより詳細に調べるために，蛍光ラベルしたIAPPを用いて，アミロイド形成開始後異なる経過時間での蛍光相関分光法によるIAPP拡散速度計測を行った．IAPPの拡散速度はIAPPの凝集サイズに敏感であることから，この測定により開始後70分間の間にどのような構造変化，またオリゴマーへの転移が起こっているかを調べることが可能となる．計測の結果，IAPPの拡散速度は70分の間ほとんど変化が見られなかった．この結果は，IAPPがアミロイド形成に至る前に形成するオリゴマーの分子サイズ（流体力学的半径）はモノマーとほとんど区別ができないことを示唆するものとなった．IAPPが構造変化を伴わずにオリゴマーとなった場合流体力学的半径の変化が起こることから，今回の結果はIAPPオリゴマーにおいてIAPPはモノマー時よりもよりコンパクトは構造へと転移している事を示唆する結果となった．
  課題番号：19H02669
• 単結晶氷Ihの界面の構造とダイナミクスの研究　　　　　　　　　　　　　　　
  日本学術振興会, 科学研究費助成事業, 基盤研究(B), 2018年04月01日 - 2022年03月31日
  山口 祥一; 野嶋 優妃, 埼玉大学
  配分額（総額）：17160000, 配分額（直接経費）：13200000, 配分額（間接経費）：3960000
  氷の数ある結晶相の中で，Ih相は大気圧下72K以上では最も安定である．氷Ih相のバルクにおける水分子の配向は，長距離秩序を持たない統計的なものであることがよく知られている．しかし，氷Ihの表面における水の配向秩序はこれまで謎に包まれていた．我々は同位体希釈した氷Ihの表面に非線形光学分光法と理論モデリングを適用し，H-up配向に起因するOH伸縮振動を観測した．さらにこの水素秩序は，バルクよりも表面の方が微視的環境が不均一であるにもかかわらず起こることを見いだした．この結果は，バルクでは起こらない水素秩序化を可能にする表面の重要な役割を示唆している．
  課題番号：18H01934
• 新規界面選択的偶数次非線形レーザー分光法による界面分子の化学反応の遷移状態の解明　　　　　　　　　　　　　　　
  日本学術振興会, 科学研究費助成事業, 基盤研究(B), 2015年07月10日 - 2018年03月31日
  山口 祥一, 埼玉大学
  配分額（総額）：18070000, 配分額（直接経費）：13900000, 配分額（間接経費）：4170000
  氷Ihのバルクの結晶構造は完全に解明されている．水分子の配向には長距離秩序が存在せず，これはプロトン無秩序性と呼ばれている．果たして氷Ihの表面もバルク同様にプロトン無秩序の状態にあるのか，あるいは表面では何らかの秩序が実現しているのか，まだ明らかになっていない．我々はヘテロダイン検出和周波発生分光法を単結晶氷Ihの表面に適用し，OH伸縮領域の振動スペクトルを測定した．同様の測定はオランダのグループからも報告されたが，彼我の結果は位相がπ/2異なり，全く相容れないものとなった．我々の結果は，水分子が水素を空気側に向けた“上向き”の配向を優勢とするプロトン秩序が表面に存在することを示唆している．
  課題番号：15KT0056
• 先端的な超高速分光と非線形分光による多自由度複雑分子系の研究　　　　　　　　　　　　　　　
  日本学術振興会, 科学研究費助成事業, 新学術領域研究(研究領域提案型), 2013年06月28日 - 2018年03月31日
  田原 太平; 竹内 佐年; 石井 邦彦; 山口 祥一; 須藤 雄気; 二本柳 聡史; 倉持 光, 国立研究開発法人理化学研究所
  配分額（総額）：141050000, 配分額（直接経費）：108500000, 配分額（間接経費）：32550000
  最高の分光計測を開発・駆使して多自由度複雑分子系の研究を行った。領域の研究者との共同研究を強力に進めながら多くの研究成果をあげた。特に（１）超高速分光では独自の時間分解インパルシブ誘導ラマン分光法の極限化を推し進めるとともに、種々の生体分子、超分子、機能性分子の超高速過程を解明した。（２）界面選択的非線形分光では、我々が開発したヘテロダイン検出振動和周波発生分光法を駆使して界面水構造を解明し、また二次元分光法や紫外励起時間分解測定に発展させて界面のダイナミクス研究を実現した。（３）単分子分光では、独自の二次元蛍光寿命相関分光法を開発してタンパク質の折り畳み過程を研究し、新しい重要な知見を得た。
  課題番号：25104005
• シングルチャンネル・ヘテロダイン検出和周波発生分光法の開発と応用　　　　　　　　　　　　　　　
  日本学術振興会, 科学研究費助成事業, 挑戦的萌芽研究, 2015年04月01日 - 2017年03月31日
  山口 祥一, 埼玉大学
  配分額（総額）：3900000, 配分額（直接経費）：3000000, 配分額（間接経費）：900000
  液体や固体の表面の振動スペクトルを選択的に測定するための新しい方法，シングルチャンネルヘテロダイン検出和周波発生(HD-SFG)分光法を開発した．この方法ではサンプルの表面からの和周波信号光と位相制御された局部発振器光との間の光干渉を利用する．シングルチャンネルHD-SFGでは干渉測定と分光測定がIRレーザーを特定の波数範囲でスキャンすることで同時に実行される．これにより既存の位相敏感和周波発生分光法に比べて測定に要する時間が大幅に短縮される．また，既存のマルチプレックスHD-SFGより約6倍優れた 4 cm-1という高い波数分解能を達成した．
  課題番号：15K13616
• 埋もれた界面のヘテロダイン検出和周波発生の開発と応用　　　　　　　　　　　　　　　
  日本学術振興会, 科学研究費助成事業, 基盤研究(B), 2013年04月01日 - 2016年03月31日
  山口 祥一
  配分額（総額）：18850000, 配分額（直接経費）：14500000, 配分額（間接経費）：4350000
  SFG分光法は，界面の分子のスペクトルを選択的に与える方法として広く用いられている．従来のSFGは和周波光の強度を測定する方法である．私は従来法の欠点を克服する新しい方法，HD-SFG分光法を開発し報告した．HD-SFGによって従来法では分からなかった界面の物理化学が次々に明らかにされている．HD-SFGのこれまでの適用範囲は，界面を挟む2つのバルク相のうちの1つが空気または真空である“埋もれていない”界面に限られていた．今回，新しい方法を開発して，等方的な固体と液体のバルクに挟まれた埋もれた界面のχ(2)スペクトルの決定に初めて成功した．
  課題番号：25288014
• 新しい界面選択的超高速分光の開発と液体界面ダイナミクス研究への応用　　　　　　　　　　　　　　　
  日本学術振興会, 科学研究費助成事業, 基盤研究(A), 2012年04月01日 - 2015年03月31日
  田原 太平; 山口 祥一; 石山 達也, 独立行政法人理化学研究所
  配分額（総額）：46150000, 配分額（直接経費）：35500000, 配分額（間接経費）：10650000
  界面はきわめて広範な科学・技術分野で大切な役割を果たしており、その分子論的理解は本質的に重要である。液体界面での分子の超高速ダイナミクスを研究するために、フェムト秒光パルスによる光励起とわれわれが開発したヘテロダイン検出振動和周波分光法とを組み合わせ、一群の新しい界面選択的な時間分解非線形振動分光計測法を開発した。開発した新しい計測法を用いて光励起された界面水分子のフェムト~ピコ秒ダイナミクスを研究し、界面水のOH伸縮振動バンドのホールバーニングとスペクトル拡散を数100フェムト秒の時間分解能で観測することに成功するなど、水界面の基礎的分子ダイナミクスについて初めての観測を実現した。
  課題番号：24245006
• 二次非線形分光によるタンパク質の高次構造解析　　　　　　　　　　　　　　　
  日本学術振興会, 科学研究費助成事業, 基盤研究(B), 2010年 - 2012年
  山口 祥一; 細井 晴子, 独立行政法人理化学研究所
  配分額（総額）：19890000, 配分額（直接経費）：15300000, 配分額（間接経費）：4590000
  新しいタンパク質高次構造解析法によってセグメントの配向を決定出来ることを,モデルタンパク質を用いて実際に証明した.モデルタンパク質の一つの残基をシステインに変異させて,マレイミド基を有する色素分子を導入した.その色素分子の電子遷移に共鳴する二次非線形感受率をヘテロダイン検出和周波発生法によって測定した.二次非線形感受率の符号によって,ガラス表面上のモデルタンパク質の上下の向きを決定できることを示した.
  課題番号：22350014
• 極限的分光計測による複雑系高次分子機能の研究　　　　　　　　　　　　　　　
  日本学術振興会, 科学研究費助成事業, 特定領域研究, 2007年 - 2011年
  田原 太平; 竹内 佐年; 山口 祥一; 石井 邦彦; 細井 晴子; 森田 明弘; 浅野 素子, 独立行政法人理化学研究所
  配分額（総額）：81600000, 配分額（直接経費）：81600000
  極限的な分子計測を駆使して複雑分子系の研究を推進した。超高速分光では、シススチルベン異性化の多次元的反応座標の解明、銅（I）錯体の超高速構造変化機構の解明、シアニン色素の異性化座標に沿った核波束運動の追跡など、多原子分子の反応初期過程の研究を行った。界面選択的非線形分光では、電子和周波発生と振動和周波発生のヘテロダイン検出を実現し、生体膜モデル界面を含む水界面での基本現象に関する多くの新しい知見を得た。相関分光では、蛍光寿命測定と蛍光相関測定を組み合わせ、生体高分子の構造揺らぎの研究に高いポテンシャルをもつ新しい方法を開発した。
  課題番号：19056009
• 新規な非線形分光計測による新しい界面分子科学の開拓　　　　　　　　　　　　　　　
  日本学術振興会, 科学研究費助成事業, 基盤研究(A), 2007年 - 2009年
  田原 太平; 山口 祥一; 石井 邦彦; 渡邉 秀和, 独立行政法人理化学研究所
  配分額（総額）：47970000, 配分額（直接経費）：36900000, 配分額（間接経費）：11070000
  われわれが独自に開発した電子和周波発生(ESFG)分光をベースに、さらにフェムト秒時間分解ESFG(TR-ESFG)分光、振動数領域の4次のラマン分光(X^<(4)>ラマン分光)、ヘテロダイン検出ESFG(HD-ESFG)分光、ヘテロダイン検出振動和周波(HD-VSFG)分光など、一群の新しい界面選択的非線形分光を開発した。これらを用いて水界面の基本的問題を研究し空気/水界面の実効的極性、タンパクの表面変性、界面における超高速緩和現象、水界面特有の水素結合、表面荷電の変化による水分子の配向の逆転現象などを明らかにした。
  課題番号：19205005
• DNAの二次構造転移の観測　　　　　　　　　　　　　　　
  日本学術振興会, 科学研究費助成事業, 若手研究(B), 2003年 - 2005年
  山口 祥一, 独立行政法人理化学研究所
  配分額（総額）：3800000, 配分額（直接経費）：3800000
  本年度は,若手研究(B)「DNAの二次構造転移の観測」(3年間)の最終年度であり,研究の総仕上げを行った.
  まず,昨年度までに開発した,マルチチャンネル二光子吸収測定法とマルチプレックス界面電子和周波測定法に加えて,今年度は新たに界面4次振動分光法を開発した.この新方法は,界面選択的な振動スペクトルを得るための方法で,特に,従来法では不可能であった"埋もれた界面"の測定が可能である点が重要な特徴である.埋もれた界面とは,液体や固体など高濃度のバルクに両側を挟まれた界面のことで,赤外-可視和周波分光法という従来法では,赤外光がバルクに吸収されてしまうことがその適用を不可能にしていた.実際に,本研究課題であるDNAなどの生体高分子は,水や細胞膜などに埋もれた界面に存在するケースが非常に多く,そのような界面にあるがままの生体高分子の振動スペクトルは,これまで測定不可能だった.今回の界面4次振動分光法は,可視・近赤外光のみを用いる方法であるため,赤外吸収の問題が回避され,より広い系に適用可能となる.最初の測定例として,水/ガラス界面,水/空気界面に吸着したプローブ色素分子の振動スペクトルを測定して,まず,この方法の界面選択性がナノメートルからサブナノメートルのオーダーの厚みであることを確認した.また,バルク水溶液中には見られないタイプの水素結合が界面に存在することを示唆する重要な結果が得られた.
  以上のような強力な3つの分光手法を用いて,DNAの二次構造転移の観測を試みている.DNAからの信号は大変弱く,測定は困難を極めている.今年度内に明快な結果を得ることは難しい状況だが,今後も研究を継続できる予定である.
  これまでの研究成果は,昨年末のPacifichem 2005で発表し,内外の研究者から大変好評を博した.
  課題番号：15750023
• 最適化極短パルスを用いた凝縮相光化学ダイナミクスの実時間観測と制御　　　　　　　　　　　　　　　
  日本学術振興会, 科学研究費助成事業, 基盤研究(B), 2001年 - 2003年
  田原 太平; 山口 祥一; 竹内 佐年
  配分額（総額）：14200000, 配分額（直接経費）：14200000
  超高速分光をベースに、電子状態に対する分光、振動状態に対する分光、核波束運動を実時間観測する分光、の3つを駆使して凝縮相光化学ダイナミクスに対する総合的研究を行い、以下の主たる成果を得た。
  1.極限的短パルス光を用いたポンプ-プローブ分光によってジフェニルシクロプロペノンの超高速光解離反応を研究した。反応前駆体であるS_2電子励起状態の核波束運動を観測し、その運動形と反応座標との連関を議論した。また、ポンプ-プローブ法と時間領域ラマン分光を組み合わせた時間分解時間領域ラマン分光法を開発し、トランススチルベン、ビナフチルの電子励起状態のテラヘルツ低波数領域のラマン活性振動を実時間で観測することに成功した。
  2.フェムト秒時間分解分光によって、基本反応である7-アザインドール二量体の光プロトン移動反応およびトランス-アゾベンゼンの光異性化反応を研究し、その反応メカニズムを明らかにした。またGFPの発色団のモデル分子の超高速蛍光ダイナミクスを観測し、その無輻射緩和過程について議論した。
  3.ピコ秒時間分解ラマン分光によって、溶媒和電子の電子吸収に共鳴させてラマン散乱を測定すると、共鳴効果によって電子に溶媒和した水分子の振動スペクトルが選択的に観測されることを発見した。
  4.フェムト秒アップコンバージョン顕微鏡を開発した。この装置によってサブミクロン微小領城からの蛍光を世界で初めてフェムト秒の時間分解能で測定できるようになった。また、時間分解蛍光信号を時間-波長の2次元像として一度に観測するフェムト秒蛍光イメージング法を開発した。さらにフェムト秒白色光を利用して、二光子吸収スペクトルをマルチチャンネル測定する非縮退二光子吸収測定法を開発し、レチナール分子およびC_<60>の精密な二光子吸収スペクトルを測定した。
  課題番号：13440183
• 熱による誘電場操作と化学反応の制御　　　　　　　　　　　　　　　
  日本学術振興会, 科学研究費助成事業, 基盤研究(A), 1996年 - 1998年
  濱口 宏夫; 山口 祥一, 東京大学
  配分額（総額）：35000000, 配分額（直接経費）：35000000
  溶液中の化学反応に大きな影響を及ぼす溶媒/溶質相互作用の本質、とくに溶媒の極性の役割を明らかにし、かつ溶媒の極性を光でコントロールすることができれば、最終的に化学反応を光で制御する道が開ける。本研究では、広範に溶媒/溶質相互作用の本質を探ることを目的として、以下の項目1から3の研究を行った。
  1)ミクロスコピックな視点から見た溶媒効果:アセトニトリル/四塩化炭素混合溶媒中のp-ニトロアニリンの3種の異なる溶媒和構造とその超高速解離、再結合ダイナミクスアセトニトリル/四塩化炭素混合溶媒中で、3つの異なるpNAの溶媒和構造、1:2型、1:1型、1:0型が存在することを、紫外吸収およびラマンスペクトルの特異値解析により明らかにした。
  2)溶液中のレチナールの光異性化反応の溶媒効果
  フェムト秒時間分解可視・紫外吸収分光を用いて、S2状態を経由した新しい異性化反応経路の存在を明らかにした。このS2状態が溶媒分子と水素結合を形成することが、レチナールの光異性化反応が顕著な溶媒効果示す理由であることを明らかにした。
  3)溶媒誘起動的分極構造と振動位相緩和、化学反応速度
  分子動力学と分子軌道計算を組み合わせた理論的研究により、「動的分極」モデルが溶液中のアセトン分子の振動位相緩和を良く説明することを明らかにした。
  課題番号：08404038
• フェムト秒円2色分光計の製作とその軸性不斉分子の光ラセミ化測定への応用　　　　　　　　　　　　　　　
  日本学術振興会, 科学研究費助成事業, 奨励研究(A), 1996年 - 1996年
  山口 祥一, 東京大学
  配分額（総額）：1200000, 配分額（直接経費）：1200000
  今回考案した実験の原理は、要約すると次のようであった。すなわち、基底状態において光学異性体であるR体とS体が等量存在するビフェニルを円偏光の超短パルス紫外ポンプ光で励起して、励起状態におけるR体、S体の量に円2色性に由来する差を生じさせる。その差を超短パルス可視プローブ光の偏光回転によって検出する。ポンプ光とプローブ光の時間差によって時間分解して、励起状態でのラセミ化の時定数を得る。
  この方法においては、プローブ光が試料のS_n←S_1吸収に共鳴していて、円2色性が共鳴による増大を受けることが必要であった。ビフェニルのS_n←S_1吸収は650nm付近に存在し、その点では問題はなかったが、共鳴による増大が期待ほどには大きくないためか、信号を得ることは出来なかった。
  そこで、1,1'-ビ-2-ナフトールを試料とすることを試みた。1,1'-ビ-2-ナフトールはそもそも光学分割がなされており、基底状態ではほとんどラセミ化しないものの、励起状態においては速いラセミ化が起こる可能性がある。光学分割がなされているという点で、ビフェニルの場合よりも大きな信号が期待された。実験においては、まず、光学分割がなされていないラセミ化の安価な1,1'-ビ-2-ナフトールを試料として、S_n←S_1吸収の波長を確かめようとしたのであるが、吸収信号はほとんど得られなかった。従って共鳴による増大もほとんど期待できない状態であった。結果として円2色性の信号は得られなかった。
  この実験の最も重要な意義は、ごく短い時間しか存在しない光学活性体を捉える、という点にあり、非常に興味深い問題であるから、今後は新たな試料の探索と更なるレーザーの安定化によって研究を続ける予定である。
  課題番号：08740447