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Addition of sugars such as sucrose to aqueous protein solutions generally stabilizes proteins against thermal denaturation by preferential exclusion of sugars from proteins (preferential hydration of proteins). In this study, we investigated the effect of sucralose, a chlorinated sucrose derivative, on protein stability and preferential solvation. Circular dichroism and small-angle X-ray scattering measurements showed that sucrose increased the denaturation temperature of myoglobin and was preferentially excluded from the protein, whereas sucralose decreased the denaturation temperature of myoglobin and was preferentially adsorbed to the protein. No clear evidence was obtained for the indirect effects of sucralose on protein destabilization via the structure and properties of solvent water from the physicochemical properties (mass density, sound velocity, viscosity, and osmolality) of aqueous sucralose solutions; therefore, we concluded that a direct protein-sucralose interaction induced protein destabilization.

The phase equilibrium property and structural and dynamical properties of pig cornea were studied by macroscopic observation of swelling behavior, dynamic light scattering (DLS), and small-angle X-ray scattering (SAXS) under various conditions. It was found that the corneal gel collapses into a compact state isotropically or anisotropically depending on the external conditions. The corneal gel collapses uniformly into a compact state at a temperature above 55 degrees C because of the denaturation of collagen, whereas it collapses along an axis parallel to the optic axis with increasing NaCl concentration. Anisotropic deswelling was also observed during desiccation. SAXS measurements revealed that the periodicity of the collagen fiber of the cornea does not change even at higher NaCl concentration, which indicates that hydration and dehydration resulting from changes in salt concentration simply cause swelling and deswelling of the glycosaminoglycan (GAG), which is located between the regular two-dimensional lattices of collagen fibers, which obliges the change in thickness. From observations of the dynamics of light scattered by the corneal gel, intensity autocorrelation functions that revealed two independent diffusion coefficients were obtained. Divergent behavior in the measured total scattered light intensities and diffusion coefficients with varying temperature was observed. That is, a slowing of the dynamic modes accompanied by increased "static" scattered intensities was observed. This is indicative of the occurrence of a phase transition as a function of temperature.

We investigated the phase behavior and the microscopic structure of the colloidal complexes constituted from neutral/polyelectrolyte diblock copolymers and oppositely charged surfactant by dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The neutral block is poly(N-isopropylacrylamide) (PNIPAM), and the polyelectrolyte block is negatively charged poly(acrylic acid) (PAA). In aqueous solution with neutral pH, PAA behaves as a weak polyelectrolyte, whereas PNIPAM is neutral and in good-solvent condition at ambient temperature, but in poor-solvent condition above approximately 32 degrees C. This block copolymer, PNIPAM-b-PAA with a narrow polydispersity, is studied in aqueous solution with an anionic surfactant, dodecyltrimethylammonium bromide (DTAB). For a low surfactant-to-polymer charge ratio Z lower than the critical value ZC, the colloidal complexes are single DTAB micelles dressed by a few PNIPAM-b-PAA. Above ZC, the colloidal complexes form a core-shell microstructure. The core of the complex consists of densely packed DTA+ micelles, most likely connected between them by PAA blocks. The intermicellar distance of the DTA+ micelles is approximately 39 A, which is independent of the charge ratio Z as well as the temperature. The corona of the complex is constituted from the thermosensitive PNIPAM. At lower temperature the macroscopic phase separation is hindered by the swollen PNIPAM chains. Above the critical temperature TC, the PNIPAM corona collapses leading to hydrophobic aggregates of the colloidal complexes.

The salt effects on phase equilibrium and dynamical properties of pig vitreous body was studied by the macroscopic observation of the swelling behavior and dynamic light scattering under various conditions. It was found that the vitreous body collapses with maintaining the shape when the concentrations of salts (NaCl, CaCl2, and MgCl2) were changed. From the observations of the dynamics of light scattered by the pig vitreous body, intensity autocorrelation functions that revealed two diffusion coefficients, Dfast and Dslow were obtained. We developed the theory for describing the density fluctuation of the entities in the vitreous gel system with sodium hyaluronate filled in the meshes of the collagen fiber network. The dynamics of collagen and sodium hyaluronate explains two relaxation modes of the fluctuation. The diffusion coefficient of collagen obtained from Dfast and Dslow is very close to that in aqueous solution, which suggests the vitreous body is in the swollen state. Divergent behavior in the measured total scattered light intensities and diffusion coefficients upon varying the concentration of salt was observed. Namely, a slowing down of the dynamic modes accompanied by increased "static" scattered intensities was observed. This is indicative of the occurrence of a phase transition upon salt concentration.

It was found that a degree of the binding of alkylphenols to N-alkylacrylamide gel increased transitionally to induce the volume phase transition of gel. Binding isotherms of nonylphenol (n-Ph), propylphenol (p-Ph), ethylphenol (e-Ph), methylphenol (m-Ph), and phenol (Ph) to N-isopropylacrylamide (NIPA), N,N-diethylacrylamide (DEA), N,N-dimethylacrylamide (DMA), and acrylamide (AM) gels were examined. Two types of binding, the site binding at beta < 1 and the multimolecular binding at beta > 1, were observed, where beta was a degree of binding to a monomeric unit of the chain. The former binding was analyzed with the Hill equation applicable to the cooperative binding and the latter binding with the Brunauer-Emmett-Teller (BET) equation applicable to the multilayer adsorption. The binding constant, K, and the Hill coefficient, N, decreased and increased, respectively, in the order of DEA, NIPA, and DMA gels in the case where the binding alkylphenol was the same. The K value increased in the order of Ph, m-Ph, e-Ph, p-Ph, and n-Ph that bound to the same type of gel. The N value was found to change little with the type of binding alkylphenol. The complexes of N-alkylamide with alkylphenol were condensed to form the ordered nanostructures that were observed as broad scattering peaks in small-angle X-ray scattering experiments. The fluorescence excimer emission was observed for the phenol-binding DMA gel, which corresponded to the condensed state of phenol.