Yuichi Seshimo

Trehalose Bioprotective Effects in Lysozyme Aqueous Solution Studied by Brillouin Scattering and Calorimetric Measurements

The bioprotective effect of trehalose in lysozyme aqueous solutions has been investigated by Brillouin scattering and modulated-temperature differential scanning calorimetry (MDSC). MDSC experiments show that the isothermal kinetics of thermally irreversible denaturation can be described by the Arrhenius equation. By the addition of trehalose, the irreversible denaturation of lysozyme is suppressed, and its activation energy is half that of the denaturation without trehalose. The sound velocity of lysozyme–trehalose–water ternary solutions obviously depends on the trehalose concentration. With increasing trehalose concentration, the sound velocity becomes higher because the hydration of trehalose reduces the hydrogen bonds between water molecules. Moreover, hydration around lysozyme molecules increases the sound velocity further. Trehalose molecules tend to aggregate with lysozyme molecules at high trehalose concentrations. The bioprotective effect of trehalose probably originates from the mechanical suppression of conformational fluctuations of lysozyme molecules.

Brillouin Scattering Study of Cluster Structure in Lower Alcohol Water Mixtures

The concentration dependences of sound velocity in lower alcohols [ethanol, 1-propanol, ethylene glycol (EG)] water mixtures were determined by Brillouin scattering. The cluster structures of the alcohol water mixtures were analyzed using the nonlinear coupling equation. The number of nearest neighboring water molecules for an alcohol molecule and the coupling constant between sound velocity and clusters were determined accurately. These parameters show the correlation between the size of an alkyl group and the number of hydroxyl groups of an alcohol molecule.

Brillouin and Raman Scattering Study of Ethylene Glycol Aqueous Solutions

We studied the cluster structure of ethylene glycol aqueous solutions by Brillouin and Raman scattering. We measured the ultrasonic sound velocity of the sample by Brillouin scattering. From the concentration dependence of the sound velocity, we studied the cluster structure in the solution. We showed that the number of H2O molecule neighboring a EG molecule becomes a little higher with increasing temperature and the intermolecular interaction between EG and H2O molecules weakened with increasing temperature. In Raman scattering study, We studied the hydrogen bond in the solution using the OD stretching band. We revealed that the strength of the hydrogen bond is independent of the EG concentration.

Dynamical Properties on the Thermal Denaturation of Lysozyme‐Trehalose Solution

We studied the dynamics of lysozyme solution and the bioprotective effect of trehalose. Thermodynamics and elastic properties related to the thermal denaturation were investigated by Modulated‐temperature DSC (MDSC) and Brillouin scattering. By MDSC measurements, it is found that the thermal stability of lysozyme depends on the trehalose concentration, and trehalose suppresses the denaturation induced by pH change. The sound velocity of lysozyme‐trehalose solution is studied as a function of trehalose concentration. With increasing trehalose concentration, the number density of tetrahedral structure of water molecules decreases. Furthermore, we reveal the interaction between lysozyme and trehalose increases, especially around room temperature. We suggerst that trehalose molecules tend to associate lysozyme by preferential hydration, and the trehalose‐induced bioprotection phenomenon may result from the mechanical suppression of lysozyme unfolding.

Terahertz Time Domain Spectroscopy of Glass‐Forming Materials

The terahertz dynamics of glass‐forming liquids has been studied by terahertz time domain spectroscopy. The real and imaginary parts of dielectric constants have been determined accurately by the transmission measurements using the dual‐thickness geometry. The complex dielectric spectra of aqueous solutions of ethylene glycol clearly show the existence of relaxation processes at room temperature. As the concentration of ethylene glycol increases, the relaxation time of the main relaxation process becomes longer. It is attributed to the destruction of the hydrogen‐bonded tetrahedral structure of water and the formation of clusters consists of water and ethylene glycole molecules.