Koichi Itoh

Observation and Analysis of Molecular Vibration Modes in Polylactide at Terahertz Frequencies

Terahertz (THz) spectra were obtained for polylactide, and they were analyzed by numerical calculations based on density functional theory. An absorption band was observed at approximately 50 cm-1, which becomes larger when the THz electric field is parallel to the sample drawing direction. An absorption peak with a similar directional dependence appears at approximately 40 cm-1 in the simulation, which is due to normal-mode molecular vibrations parallel to the molecular helix. Since the 50 cm-1 absorption decreases with an increase in crystallinity and the permittivity shows a step-like decrease, the molecular vibrations responsible for the 50 cm-1 band seem to be subjected to strong damping in amorphous regions. On the other hand, another absorption peak at 65 cm-1 with a positive absorption dependence on the samples crystallinity is likely to be due to lattice vibration, since it does not appear in the calculations, which only deal with intramolecular vibration.

Electrochemical processes of meso-tetrakis (4-sulfonatophenyl) porphine at a silver electrode studied by surface-enhanced resonance Raman spectroscopy

Abstract The potential dependence of surface-enhanced resonance Roman spectra of meso-tetrakis (4-sulfonatophenyl) porphine (TSPP) in 0.05 M H 2 SO 4 reveals two electrochemical processes at a silver electrode surface. One which begins around −0.3 V is interpreted as dissociation of aggregated TSPP to monomers. The other which occurs near −0.4 V is ascribed to a partial Ag incorporation of TSPP molecules.

A theoretical approach to the dielectric relaxation of liquid alcohols

The dielectric relaxation mechanism of liquid alcohols was studied by assuming the association equilibrium between hydrogen‐bonded chain multimers. The dipole inversion arising from the cooperative rotation of the OH groups of the multimers was considered to be the main mechanism of the dipole relaxation. The stochastic model of one‐dimensional random walk was introduced to explain the dipole inversion process and it was found that the dipole relaxation time of an n‐mer is proportional to n+1. Based on this result and the stoichiometry of the association equilibrium, we calculated the dielectric constants and losses of liquid alcohols as a function of ω, which are in fair agreement with the experimental results.

Surface-enhanced resonance raman spectra of meso-tetraphenylporphine and its metal complexes in a layered structure having an Ag/sample/CaF2-roughened-substrate configuration

Abstract Surface-enhanced resonance Raman scattering spectra were measured for meso-tetraphenylporphine (TPP) and its Ag(II), Mg and Zn complexes in a layered structure, having an Ag/sample/CaF 2 -roughened-substrate configuration. The structural data of SERS-active species give information about and Ag incorporation and/or a metal-exchange reaction of TPP and MgTPP during the Ag deposition process.

Surface-enhanced raman scattering study on the structure of 2,2′-bipyridine adsorbed on an Ag electrode

Abstract The surface-enhanced Raman scattering (SERS) spectra were measured for 5 m M 2,2′-bipyridine+0.1 M KX (X = CI, Br or I) and the assignments of the bands were discussed by comparing the surface spectra with the Raman and infrared spectra of Ag(I)(bpy)2NO3 and bpy itself. As the electrode potential was changed from +0.05 to −1.1 V (vs. Ag/AgCl), the SERS spectra showed a sequence of changes in their features indicating that a series of transformations are taking place between at least four kinds of molecular states (Type I, II, III and IV) of adsorbed bpy molecules on silver electrode surfaces. Near +0.05 V in the KCI electrolyte solution the adsorbates take on a structure of type I which gives a SERS spectrum almost identical with the Raman spectrum of Ag(I)(bpy)2NO3. A study of the effect of illumination by a 514.5 nm laser indicated that the type I adsorbate is a reaction product from bpy molecules and Ag atoms which were created by photoreduction of an AgCl layer produced during the anodization process of the electrode. When the electrode potential was changed to a more negative region (−0.2, −0.4 and −0.5 V for the KCl, KBr and KI electrolytes, respectively), the silver halide layers were electrochemically reduced forming a fresh Ag layer. On adsorbing on this layer the bpy molecules always assume a structure of type II, where the molecules again take on coordination and backbone structures similar to those of the argentous complex. In this state some of the out-of-plane vibrations of the pyridine moieties are observed to be specifically enhanced, which suggests that the molecular plane of the ligands lies almost flat on the electrode surface. On sweeping the electrode potential to more negative values, the type II adsorbate is generally converted to a type III species, which is characterized by its breathing vibration observed at 1025 cm−1. It was suggested that in this state the nitrogen atoms of the pyridine moieties are strongly chemisorbed to a silver atom on the electrode surface, forming a Lewis acid coordination structure. In the KCl and KBr electrolyte solutions the type III species is converted to a type IV adsorbate when the electrode potential approaches the pzc of the Ag electrode (about −0.91 V). In the latter species the adsorbed bpy molecules give rise to the breathing vibration near 1005 cm−1 suggesting that the molecules exist in a physisorbed state.

An application of laser Raman spectroscopy to the study of a hereditary cataractous lens; on the Raman band for a diagnostic marker of cataractous signatures

Raman spectra were measured for cac-strain mouse (Nakano mouse) lenses in the various stages of cataract formation. The spectra were compared with those of normal mouse lenses of the corresponding ages. A significant difference was observed in the intensity of the Raman band due to an OH stretching mode of lens water (3390 cm-1) between the spectra of cataractous lenses and those of normal lenses. The difference was already obvious in the very incipient stage of hereditary cataract and became more pronounced with cataract development. These observations clearly show that changes in lens water occur during cataractogenesis. We propose in this communication that the intensity change of the Raman band at 3390 cm-1 may be very useful for the diagnostic marker of cataractous signatures.

Direct measurement of Raman spectra of intact lens in a whole eyeball

The Raman spectrum of an intact rabbit and rat lens was measured intraocularly without taking it out of a whole eyeball. The Raman spectrum was identical to that of an excised lens. There was no evidence for Raman bands from cornea, aqueous humor, or other ocular tissue in the spectrum of intact lens in the eyeball. The result is an important step toward the clinical application of Raman spectroscopy in the field of cataract research.

Resonance raman and absorption spectroscopic studies on the electrochemical oxidation processes of 3,3′,5,5′-tetramethylbenzidine

Abstract Resonance raman scattering (RRS) and absorption spectroscopies were applied to elucidate one- and two-electron oxidation processes of 3,3′,5,5′-tetramethylbenzidine (TMB) in organic solvents such as n-butyronitrile. The RRS spectra of a charge-transfer (CT) complex and a dication (TMB2+) were characterized. The CT-complex was found to give a CH out-of-plane bending band near 955 cm−1, which is absent in the RRS spectrum of the dication. A structural model was proposed for the CT-complex, in which the dication is converted to a neutral state through deprotonation and operates as an electron acceptor. RRS spectral changes observed during one-electron oxidation in n-butyronitrile at 0.60 V (vs. Ag|Ag+) were analyzed in order to propose a reaction scheme, which leads to the formation of the CT-complex. When a sample solution was flowed through a thin-layer electrochemical cell at 0.95 V (vs. Ag|Ag+), an electrodeposition process takes place, forming a CT-complex film at the electrode surface. On the other hand, when the solution was not flowed through the cell, an oxidation reaction occurs in the solution, resulting in the formation of the dication.

Raman Spectroscopic Study of Cataract Formation: Emory Mouse Cataract

Raman spectra of Emory mouse lenses at various stages of cataract formation have been measured and compared with those of normal lenses from ICR-strain mice. The relative intensity of an OH stretching mode of lens water was considerably stronger for the Emory mouse lenses, even in a precataractous stage, suggesting that lens hydration is deeply implicated in the initiation of Emory mouse cataract. The rate of 2SH → S-S conversion, estimated from the intensity decrease of a SH stretching mode, was similar between the Emory and ICR-strain mouse lenses. Accordingly, it seems unlikely that the conversion is a predominant factor for forming large protein aggregates which lead to lens opacification. A significant change was observed for the intensity ratio of a tyrosine doublet near 840 cm−1 during the cataract development, suggesting that the strength of the hydrogen bonding of some tyrosine residues alters upon the formation of the large protein aggregates. Comparison of the Raman spectral changes observed for Emory mouse cataract with those for normal lens aging and other cataract formation leads us to the conclusion that the microenvironmental change of tyrosine residues is only one common specific feature for lens opacification.

Raman scattering study on electrochemical reduction products of magnesium, zinc and copper tetraphenylporphines

The electrochemical reduction processes of magnesium, zinc and copper tetraphenylporphines in dimethylformamide were studied by resonance Raman spectroscopy with the combined use of cyclic voltammetry and absorption spectroscopy. The CV measurement indicates that all the metalloporphines exhibit a reversible one-electron process forming a stable π-anion radical with the half-wave potential vs. an Ag/AgCl reference electrode; −1.35 V for MgTPP, −1.28 V for ZnTPP and −1.12 V for CuTPP. In more negative potential regions the anion radicals are reduced to the corresponding dianions through a reversible one-electron reduction process. The dianions, however, are not stable in DMF and are readily converted to the phlorin monoanions via a protonation to one of the meso-carbon atoms of the porphine ring. By using the same electrochemical cell as that used for the CV measurement, the resonance Raman spectra of the reduction products, the π-anion radicals of MgTPP and ZnTPP and the phlorin monoanions of MgTPP, ZnTPP and CuTPP, were measured with the 457.9 nm excitation of an Ar+ laser. Assignments were given to observed Raman bands by comparing the spectra with those of the metalloporphines themselves. Possible electronic structural and geometrical changes accompanied by the conversions of the metalloporphines to the π-anion radicals and the phlorin anions were discussed based on the frequency shifts of Raman bands caused by the reduction processes.