Yoshihiro Taniguchi

Fourier transform infrared spectroscopy in high-pressure studies on proteins

Several aspects of the application of Fourier transform infrared spectroscopy (FTIR) in high-pressure studies on proteins are reviewed. Basic methodological considerations regarding spectral band assignments, quantitative analysis, and choice of pressure calibrants are also placed within the scope of this paper. This work attempts to evaluate recent developments in the field of high-pressure FTIR of proteins and its prospects for future. Particular attention is paid to the phenomenon of protein aggregation.

NMR studies on dynamic behavior of water molecule in aqueous denaturant solutions at 25 °C: Effects of guanidine hydrochloride, urea and alkylated ureas

Abstract The spin-lattice relaxation times (T1) of the 17O nucleus of a water molecule in guanidine hydrochloride, urea, and alkylated ureas at 25 °C were measured by NMR spectroscopy. Urea has no significant effect on the water structure. Also, guanidine hydrochloride as a stronger denaturant than urea does not perturb the water structure similar to urea. The change in the dynamic structure (BR) of water was proportional to the carbon number of the alkyl chain of the alkylated urea. Compared to the results of alcohols and tetraalkylammonium solution, it is clear that the contribution of one carbon of the alkyl chain to the water structure is independent of the type of solute. The BR of urea and its alkylated substances show a good correlation with the concentration of denaturation midpoints obtained on sperm whale myoglobin and cytochrome c. Because the water structure is not perturbed by urea and guanidine hydrochloride, these results indicate that the effect of hydrophobic hydration of denaturants becomes important for the denaturation of a protein with increasing hydrophobicity of the denaturants.

The solubility of volatile anaesthetics in water at 25.0°C using 19F NMR spectroscopy

Abstract Anaesthetic concentration is very important for the quantitative treatment of anaesthesia theory. Traditionally concentration values have been derived from the water/gas partition coefficient. However, the values from many investigators show discrepancies. This study reports the accurate solubility of methoxyflurane (9.1 mM), halothane (18.0 mM), enflurane (11.9 mM) and isoflurane (13.5 mM) in water at 25.0°C using 19 F NMR spectroscopy. The method has advantages in that the dissolved molecule in solution can be separately quantified from undissolved anaesthetic. Saturated solutions of the anaesthetic agents were prepared in situ in a NMR tube to avoid pressure and temperature changes in the solution.

High pressure study on molecular conformational equilibria of n‐pentane

The n‐pentane molecule has the basic conformations, TT, TG, and GG. It is important for understanding the conformational behavior of chain molecules. We have studied the effect of pressure on the conformations of n‐pentane in the condensed phase by using high pressure infrared spectroscopy with a diamond anvil cell up to 28.9 kbar. Compression of liquid n‐pentane increases the concentration of the more globular conformers, while the TT conformer only exists as a high pressure solid. The volume changes for TT to TG, TG to GG, and TT to GG forms are −1.0±0.2, −1.1±0.3, and −2.1±0.3 cm3/mol, at 20 °C, respectively. The conformational volume changes in liquid n‐alkanes are discussed in terms of the solvent‐excluded volume.

Near-infrared spectra of water and aqueous electrolyte solutions at high pressures

The near-infrared spectra (9500 to 11000 cm−1) of pure water and aqueous solutions of alkali halides, MgCl2, NaClO4, and R4NBr were measured at temperatures between 10 and 55°C and pressures up to 500 MPa. From the analysis of the absorption spectra the following conclusions are drawn. (1) The ice I-like open structure is destroyed and the packed structure is formed as the pressure is increased. (2) The open structure of water is destroyed by the addition of alkali halides and MgCl2 and water molecules are restricted around the ions by ion-dipole interactions. This results in a loosening of the O−H bond. (3) The perchlorate ion destroys the open structure of water and the ion-dipole interaction with water is insignificant. (4) The Bu4N+ ion forms water structure around the ion similar to that of the clathrate open structure.

Effect of pressure on the internal rotation angle of biphenyl in carbon disulfide

The effect of pressure on the conformation of biphenyl in carbon disulfide was measured by using high pressure infrared spectroscopy with a diamond anvil up to 13 kbar. Pressure effects on the nonplanar vibrational modes indicate that the dihedral angle decreases at the rate of 2° kbar−1. Under high pressure the frequency of the C–H stretching vibrational modes shifts to blue so that the repulsive force becomes more predominant in the solute–solvent interactions between CH and CS2 molecule. The decrease in the dihedral angle of biphenyl induced by compression is related to the change of the intrinsic volume of the biphenyl molecule.

Raman and nuclear magnetic resonance studies on the concentration dependence of orientational relaxation times of the nitrate ion in dilute aqueous solution

The perpendicular orientational relaxation time (τ⊥) of the nitrate ion was determined as a function of concentration by the Raman line shape analysis (ν1 stretch) in aqueous LiNO3 and KNO3 solutions in the range of 0.2–1 M and by the nuclear magnetic resonance (NMR) T1 measurement (14N) in MNO3 (M=Li, Na, K, and Cs) solutions in the range of 0.02–1 M; the parallel orientational relaxation time (τ∥) was also determined by the NMR measurement for the solutions enriched in 17O. Both τ⊥ and τ∥ increase linearly with increasing concentration up to 1 M; the limiting values of τ⊥ and τ∥ were 1.25 and 1.9 ps, respectively. The slope increases with the surface charge density of the countercation except for Li+. These trends are predicted in very dilute solutions by the continuum theory developed in the previous paper. The anomalous behavior of Li+ was explained in terms of its strong hydration.

High pressure rolling‐ball viscometer of a corrosion‐resistant type

A high pressure rolling‐ball viscometer was designed for use with corrosive solutions such as electrolytes, using a glass inner cell with a glass cylinder and its piston. The viscosities of water and 2.55‐m sodium chloride aqueous solution were measured up to 375 MPa at 25 °C with an error of less than ±1%.

NMR studies on dynamic behavior of water molecules in tetraalkylammonium bromide-D2O solutions at 5–25°C+☆

Abstract The spin-lattice relaxation times (T 1 ) of D and 17 O nuclei of D 2 O molecules in tetraalkylammonium bromides (R 4 NBr; R=Me, Et, Pr, Bu), dilute aqueous solutions were measured at the concentration of 0.2 to 1.0 mol/kg and at the temperature of 5 to 25 °C. The relative spin-lattice relaxation rate, R 1 /R 1 0 (R 1 =1/T 1 ) at 25 °C increased linearly with increasing concentration of tetraalkylammonium bromide solutions. But, it varied nonlinearly against the concentration below 20 °C and the deviation increased with decreasing temperature. The dynamic hydration number (n DHN ) of D and 17 O nuclei of a D 2 O molecule in the hydration sphere of tetraalkylammonium ions had good correlation with the molecular size, except for the Bu 4 N + ion. The deviation of n DHN of Bu 4 N + ion at low temperature reflected the caging effect due to the association through hydrogen bonding among water molecules as the association increases at lower temperature. It was suggested that the rotational anisotropy ( τ + D / τ + 170 ) of water molecules can be used as a new indicator to classify three types of hydration; negative, positive, and hydrophobic hydrations.

Raman study of the trans–gauche conformational equilibrium of 1,2-dichloroethane in water: Experimental evidence for the hydrophobic effect

The effect of water on the trans–gauche conformational equilibrium of 1,2-dichloroethane has been studied by Raman spectroscopy. From the intensities of C–Cl stretching bands and their temperature dependencies, we determined the free energy and enthalpy difference between the conformers in water and organic solvents. Although the solvent effect on the free energy apparently agrees with a dielectric continuum model, the enthalpy in aqueous solutions deviates largely from the values expected from that model. The positive deviations (∼3.5 kJ/mol) in the enthalpy are compensated by an increase in the entropy term. This behavior is consistent with the picture of a hydrophobic interaction.