Liquid water behaves differently from other substances at low temperatures. Recent studies of supercooled liquid water suggest the existence of two liquid waters with different densities, low-density liquid (LDL) and high-density liquid (HDL), at low temperatures, the so-called "water polyamorphism", and the fluctuations between the two waters may be responsible for the anomalous behavior of low-temperature water. Here, in order to understand the effect of solute on the polymorphic behavior of water, I experimentally investigated the polyamorphic transitions of low concentration polyol aqueous solutions under high pressure, which is related to the polyamorphic transition of pure water. From the temperature, solute concentration, and solute nature dependences of polyamorphic transition, it is found that the state of solvent water in polyol aqueous solutions can be consistently classified by two waters, LDL and HDL. In addition, the OH groups in a polyol molecule seem to stabilize HDL-like solvent water, and conversely the hydrophobic groups may stabilize LDL-like solvent water.

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To control the solidification process during industrial polymer melt processing, it is crucial to understand the effect of adding additive agents, such as a filler, a plasticizer, a nucleating agent, and so on, to a polymer on its crystallization behavior under the rapid cooling condition. The crystallization behavior of polypropylene (PP) / hydrophobic-modified cellulose nanofiber (CNF) composite was investigated using fast scanning calorimetry (FSC). FSC was very useful to reveal the crystal nucleating effect of hydrophobic modified CNFs because it allowed us to investigate the change of crystallization temperature range in the wide range of cooling rate, and the crystallization kinetics in the wide temperature range.

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The folding and unfolding of nucleic acids (DNA and RNA) are essential for these functions in cells. These behaviours are also widely used for various technical applications using nucleic acids. To understand the biological mechanism of nucleic acids function and design materials of nucleic acids, the biophysical approach using thermodynamics is highly useful and important. The stability prediction of duplexes of nucleic acids have been developed and widely used. However, it has been also noted that such predictions cannot be always adopted to prediction in various solution conditions, especially the cellular conditions, because the concentrations of cations and cosolutes in the intracellular condition termed molecular crowding are different from those in the standard experimental condition. Moreover, the crowding condition in cells is spatiotemporally variable. Therefore, it is highly demanded to establish the prediction method available in cellular conditions for the stability of various structures of nuclei acids. This article reviews the biophysicochemical background predicting nucleic acids stability and our recent studies for the prediction of these stability in the cellular conditions.

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Quasi-elastic neutron scattering (QENS) is a method to investigate dynamic behavior of molecules and molecular assemblies both in the temporal scale from picosecond to nanosecond and in the spatial scale from 0.1 to 10 nm. By using a selective deuteration, dynamic behavior of each component could be estimated. In order to investigate the relation between biocompatible materials and hydration water, we have done several QENS experiments on hydrated lipid membranes and hydrated polymers. From the results of deuterated DMPC and water, we have shown that the hydration water could be categorized into three types; tightly bound water, loosely bound water, and free water. The diffusion coefficient of the tightly bound water was almost the same as that of lipid molecules, and that of the loosely bound water is one order of magnitude less than that of bulk water and the free water. The deceleration of hydration water was also observed in the experiments on PMMA and water. These results indicated that the dynamic behavior of hydration water is affected by the interaction with materials, which suggests that the intermediate water exists near biocompatible materials.

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The Hansen solubility parameters (HSPs) of some ionic liquids with different combinations of cations and anions were measured and calculated. The Hansen solubility sphere method was used to calculate the HSPs of ionic liquids from experimental data on the solubility evaluation of the ionic liquids in some organic solvents. It was found that the double-sphere method rather than the general single-sphere method was suitable for this evaluation. For double-sphere analysis, the high polarity side sphere represents an ionic domain and the nonpolar side sphere represents a neutral domain. The value as the center of each sphere was assumed to be the HSP for each domain. The calculation results confirmed that the positions of the double-sphere in Hansen’s 3D-diagram for the ionic liquid depended on the types of cation and anion.

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