Tomobumi Mishina

Pressure dependence of local structure in liquid carbon disulfide

High pressure x-ray diffraction measurements on liquid carbon disulfide up to 1.2 GPa are performed by using an energy dispersion method. The results are compared with a molecular dynamics calculation with usual Lennard-Jones potential. They give very good agreement for all pressures measured. It becomes clear that the liquid structure changes like hard core liquid up to the pressure just below crystallizing point. The relation between structural change and optical response at high pressure is discussed.

OPTICAL KERR EFFECT IN CARBON DISULFIDE UNDER HIGH PRESSURE

The optical heterodyne spectroscopy of optical Kerr effect (OKE) in liquid carbon disulfide (CS2) was performed under various high pressures using a diamond anvil cell (DAC). The relaxation time of orientation was determined up to 1.20 GPa at 295 K using OKE signals. It increased from 1.6 ps at atmospheric pressure to 10.7ps at 1.20 GPa. Low-frequency light scattering (LFLS) spectra were measured in order to compare the intermolecular dynamical processes in liquid CS2 with those of crystalline CS2. A damped oscillation in OKE is found as a precursor of librational motion observed in crystalline state. This change shows that the intermolecular dynamical processes in the liquid vary gradually to that in crystal with increasing pressures.

Hierarchical viscosity of aqueous solution of tilapia scale collagen investigated via dielectric spectroscopy between 500 MHz and 2.5 THz

Aqueous solutions of biomolecules such as proteins are very important model systems for understanding the functions of biomolecules in actual life processes because interactions between biomolecules and the surrounding water molecules are considered to be important determinants of biomolecules’ functions. Globule proteins have been extensively studied via dielectric spectroscopy; the results indicate three relaxation processes originating from fluctuations in the protein molecule, the bound water and the bulk water. However, the characteristics of aqueous solutions of collagens have rarely been investigated. In this work, based on broadband dielectric measurements between 500u2009MHz and 2.5u2009THz, we demonstrate that the high viscosity of a collagen aqueous solution is due to the network structure being constructed of rod-like collagen molecules surrounding free water molecules and that the water molecules are not responsible for the viscosity. We determine that the macroscopic viscosity is related to the mean lifetime of the collagen-collagen interactions supporting the networks and that the local viscosity of the water surrounded by the networks is governed by the viscosity of free water as in the bulk. This hierarchical structure in the dynamics of the aqueous solution of biomolecules has been revealed for the first time.

High-Freqency Dielectric Response of Hydrogen-Bonded Liquids Between 0.2 and 2.5 THz

Using terahertz (THz) time-domain spectroscopy, we measured the complex permittivity of monohydric alcohols and diols in the frequency range of 0.2–2.5 THz at temperatures from 253 to 323 K. The complex permittivities of both monohydric alcohols and diols contain the following three components: (i) a high-frequency tail of dielectric relaxation processes, (ii) a broad vibration mode around 0.5–2.0 THz, and (iii) a low-frequency side of an intermolecular stretching mode located above 2.5 THz. At low temperatures, the dielectric relaxation processes substantially shifted to a low-frequency range. On the other hand, the broad vibration mode around 0.5–2.0 THz was independent of temperature and showed a clear peak in the dielectric loss spectra. Based on the experimental results, it is considered that the broad vibration mode originates from the vibration dynamics of the OH group. The spectral shape and intensity of the broad vibration mode were strongly influenced by both the number and position of the OH groups and the structure of the carbon chain.