Vibrational spectroscopy of interfaces was developed by taking advantage of fourth- and third-order Raman processes. An example making use of the fourth-order Raman process is interface-specific vibrational spectroscopy using only visible light. An oxazine dye at an air-solution interface was irradiated with visible 16-fs pump and probe pulses. The fourth-order signal as a function of the pump-probe delay represents the Raman-active nuclear motion. The Fourier transform of the motion provided the vibrational spectrum from 0 to 1000 cm-1 for the dye at the interface. An example making use of the third-order Raman process is vibrational spectroscopy of molecular films of submonolayer coverage. For a cresyl-violet dye of submonolayer coverage (4 × 1013 molecules cm-2) on a fused silica, the observation of time-resolved reflectance due to the third-order Raman process provided the sensitivity six times higher than in time-resolved transmittance. The vibrational spectrum of the dye at the interface was obtained from 0 to 1000 cm-1 by the Fourier transform of the reflection signal.
The intramolecular charge-transfer (ICT) reaction is characterized by intra- and inter-molecular structural changes. A well-known example of the former is a twist around the single bond between the charge accepting and donating groups of the reactant itself. The latter is a reorientation of solvent molecules against the reactant to stabilize the energy of the system. Detailed information about such structural change should provide us with an insight for a well understanding of the ICT reaction. Thus, we have carried out transient infrared (IR) absorption spectroscopy of jet-cooled (p-cyanophenyl) pentamethyldisilane (CPDS) and its solvated clusters. We have succeeded in observing transient IR spectra of the CT state, exhibiting very distinct patterns compared with those of the electronic ground state. Combined with results of quantum chemical calculations, we determined the equilibrium structure of the CT state of CPDS monomer. Our result is clear evidence that the twist occurs in the ICT process, as expected. In addition, we found a step-wise process in the case of solvated clusters based on our transient IR spectra. This process was related to the solvent reorientation in the ICT reaction. The observed spectra enabled us to determine very precise information about the reorientation process such as the initial and final orientations of the solvent molecule(s). These findings should provide us with a deep insight for understanding the ICT reaction.
'Cluster impact', collision of a cluster onto a solid surface, induces specific many-body phenomena leading to splitting of a chemical bond by impulsive force, quasi-equilibrium at temporal ultrahigh temperature and pressure, formation of monatomic-layered clusters on a solid surface, etc. Specificities of the cluster impact originate from many-body multiple collision, which results in localization of energies within hundreds femtoseconds and subsequent formation of the quasi-equilibrium in the following several to tens picoseconds. This account presents essence of such a new field of science in combination with tailored instrumentation for the cluster impact.
Time-resolved transient grating spectroscopy has been applied to the study of the vibrational energy relaxation process in solution. The vibrationally hot azulene molecule in the ground state was produced by the photo-excitation of the S1 ← S0 electronic transition and the successive rapid internal conversion process. The vibrational energy dissipation process was detected by the propagation of the acoustic wave of the transient grating (TG) signal. By comparing the solvent temperature rise time determined by the TG method with the energy dissipation process of azulene determined by the transient absorption spectroscopy, the mechanism of the vibrational energy dissipation process was discussed. This spectroscopic method has been applied to the other molecules e.g., p-nitroaniline and N,N-dimethyl-p-nitroaniline, and solvated electron.
Water is a mother liquid of life. To understand why water is indispensable to life, I have been investigating the structures and interactions at protein-water interface, i.e. the hydration structures of proteins, by cryogenic X-ray crystallography and molecular dynamics simulation. Through developing devices and experimental techniques in cryogenic X-ray diffraction experiments, I realized that cryogenic X-ray crystallography is one of techniques effectively observe hydration structures of proteins surface. In addition, the author developed a novel calculation codes to characterize systematically hydration structures of the protein structures determined at around 100 K, as to the amount of water molecules, the hydrogen-bond geometries, the local and the global distribution of them on the surface of proteins. The standard tetrahedral hydrogen bonds of water molecules in bulk water were retained in the hydration structures and contributed to extend three-dimensional network of hydrogen bonds among hydration water molecules and oxygen and nitrogen atoms of protein surface. In cryo-crystallography of multi-subunit or multi-domain proteins, the reorganization of hydration structure occurred with the dynamical motions of proteins. In that, water molecules act as inhibitors for protein motions, glue to stabilize the higher-order structures or lubricant to realize conformational changes by utilizing its tetrahedral arms of hydrogen bonds. Thus, hydration water molecules must have great influences on the dynamics and functions of proteins in aqueous solution.
Peptide aptamers are artificially created short peptide sequences that have specific recognition abilities. The technique to create peptide aptamers has been developed in biology field and many peptides that bind to various biomolecules including enzymes, receptors etc. have been isolated since 1990. Recently, this methodology has been applied to create artificial peptides that specifically bind to the surfaces of inorganic materials. Here I introduce our studies on peptide aptamers against titanium and carbon nanohorns, and discuss on the "specificity" that is required for bionanotechnology.
History of the research of molecular conductors is well described as development of highly conducting materials, and actually produced organic metals and superconductors. Study of organic superconductors led us to the physics of correlated electrons such as Mott insulators and charge order. A charge-ordered material exhibited remarkable nonlinear conductivity and functions as an electronic device, and is called an organic thyristor. Together with the recent development of organic transistors, these findings bring about new research activities of organic conductors.
Recent progress of experimental studies on the gas-phase reaction dynamics of transition metal (TM) atoms carried out in our laboratory are presented. Reactions of transition metal atoms have provided an important class of systems for the study of reaction dynamics. Because TM atoms usually have several low lying electronic states, the interactions of the potential energy surfaces evolved from these states play important roles in their reactions. In order to clarify these interactions, preparation of the TM atoms in a selected electronic state and detection of products in a specific electronic state are necessary from the experimental viewpoint. The single collision condition is also essential. Crossed-beam laser-induced fluorescence technique has been applied for several oxidation reactions of metal atoms. The laser-vaporization TM beam source combined with several carrier gases is used to generate a single electronic state or their combination with known populations. They enable us to extract noble information about the reactivities of the specific electronic states. The analysis of Doppler profiles of product, O(3PJ), is also useful to determine branching ratios of products in different electronic states.
Resonant enhanced multiphoton ionization spectroscopy with a supersonic jet is an established method for molecular science. This familiar tool has an another possibility for chemical analysis by its resonant effect; real-time, highly sensitive analysis without pretreatment. The real-time chemical analysis is demonstrated for benzene in the automobile exhaust gas. Further extension to the history analyzer for a single suspended particulate matter is also introduced briefly.