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Abstract  

To reveal the denaturation mechanism of lysozyme by dimethyl sulfoxide (DMSO), thermal stability of lysozyme and its preferential solvation by DMSO in binary solutions of water and DMSO was studied by differential scanning calorimetry (DSC) and using densities of ternary solutions of water (1), DMSO (2) and lysozyme (3) at 298.15 K. A significant endothermic peak was observed in binary solutions of water and DMSO except for a solution with a mole fraction of DMSO (x 2) of 0.4. As x 2 was increased, the thermal denaturation temperature T m decreased, but significant increases in changes in enthalpy and heat capacity for denaturation, ΔH cal and ΔC p, were observed at low x 2 before decreasing. The obtained amount of preferential solvation of lysozyme by DMSO (∂g 2/∂g 3) was about 0.09 g g−1 at low x 2, indicating that DMSO molecules preferentially solvate lysozyme at low x 2. In solutions with high x 2, the amount of preferential solvation (∂g 2/∂g 3) decreased to negative values when lysozyme was denatured. These results indicated that DMSO molecules do not interact directly with lysozyme as denaturants such as guanidine hydrochloride and urea do. The DMSO molecules interact indirectly with lysozyme leading to denaturation, probably due to a strong interaction between water and DMSO molecules.

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Abstract  

Enthalpies of mixing of R- and S-enantiomers of dicarboxylic acids such as 2-methylbutanedioic acid (MBA), 2-hydroxylbutanedioic acid (HBA), 2-methylpentanedioic acid (MPA) and 2-hydroxyl-2-methylbutanedioic acid (HMBA) in ethanol solution have been measured for a large range of mole fraction of heterochiral dicarboxylic acid at 298.15 K. Also densities of ethanol solution of the dicarboxylic acids were determined. Enthalpies of mixing were exothermic for all the concentrations. Enthalpic stabilization on mixing was increased with decreasing concentration of all dicarboxylic acids measured. Sequence of enthalpic stabilization on mixing was MBA mixing was MBA<DHBA<MPA<HMBA<HBS at 0.5 mass%.

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Abstract  

Enthalpies of mixing of R- and S-enantiomers of liquid chiral compounds such as 2-aminohexane, 2-aminoheptane, 2-aminooctane, 2-aminononane, 1-(4-chlorophenyl)-ethylamine, 1-(4-fluorophenyl)ethylamine, 2-amino-butane-1-ol have been measured over the whole range of mole fractions at 298.15 K. Mixing of heterochiral liquids observed, realized enthalpic destabilization over entire compositions. The extreme values of enthalpies of mixing and the intermolecular interaction obtained by the molecular mechanics calculations showed a linear correlation, except the few compounds measured.

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Summary  

The time dependences of the thermal power of aqueous myoglobin solutions were measured by microcalorimeter at 298.15 K. Exothermic reactions occurred in aqueous myoglobin solutions due to the metabolism of aerobic microbes, and these roughly consisted of four phases. The generation times obtained were about (555) min for the logarithmic exothermal reaction phase. The total energies were considerably dependent on the amount of oxygen present, suggesting strongly that the exothermic reaction was caused by aerobic microbes. The apparent thermal metabolic rates were positively dependent on the concentration of myoglobin, probably because of the effects of myoglobin as a food source and/or as a donor of oxygen.

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Abstract  

Excess enthalpies (H E) of 17 binary mixtures of o- and m-isomers of dichlorobenzene, difluorobenzene, methoxymethylbenzene, dimethylbenzene, dimethoxybenzene, aminofluorobenzene, fluoronitrobenzene, diethylbenzene, chlorofluorobenzene, fluoroiodobenzene, bromofluorobenzene, chloromethylbenzene, fluoromethylbenzene, bromomethylbenzene, iodomethylbenzene, fluoromethoxybenzene, dibromobenzene at 298.15 K were measured. All excess enthalpies measured were very small, and those of o-+m-isomers of aminofluorobenzene, dibromobenzene and iodomethylbenzene were negative but 14 other binary mixtures of isomers were positive over the whole range of mole fractions. H E of o-+m-isomers of dimethoxybenzene showed the largest enthalpic instability and those of aminofluorobenzene showed the largest enthalpic stability. There was a correlation between dipole–dipole interaction, dipole–induced dipole interaction or entropies of vaporization and excess partial molar enthalpies at infinite dilution.

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Calorimetric study on inclusion of some alcohols into α-cyclodextrin cavities

Molecular mechanical calculation of hydration Gibbs energies

Journal of Thermal Analysis and Calorimetry
Authors:
T. Kimura
,
M. Fujisawa
,
Y. Nakano
,
T. Kamiyama
,
T. Otsu
,
M. Maeda
, and
S. Takagi

Abstract  

The enthalpies of transfer 2-propanol, 1,2-butanediol (BD) and 1-hexanol from aqueous to aqueous α-cyclodextrin (CD) solutions have been determined by microcalorimetry at various mole fractions at 298.15 K. To clarify stabilities of inclusion complexes in aqueous solutions, hydration Gibbs energies calculation of inclusion complex of CD-alcohol were performed by using the molecular mechanics with the MMFF94s force field in the generalized born/surface area (GB/SA) model. The largest stabilization in Gibbs energy is obtained by the hydration (Δhyd H) of α-CD-1,2-butanediol complex among α-CD-butanediol isomers complexes.

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Abstract  

A single crystal calorimetry of a heptacopper(II) complex of [Cu73-Cl)23-OH)6-(d-pen-disulfide)3] which has a double-cubane structure supported by d-penicillaminedisulfides has been performed at low-temperature region below 8 K. This compound is a metal complex which contains seven Cu(II)s in a cluster unit. These Cu(II)s are magnetically coupled each other by strong intra-complex interactions. The heat capacities under magnetic fields exhibit Schottky type anomalies explained by the Zeeman splitting of the doublet ground state of the complex. The g-value of the ground state is evaluated as 1.86 from the systematic analysis of the Schottky peak under magnetic fields. The first excited state of the cluster seems to be separated at least by several Kelvins, which is consistent with the theoretical calculations and magnetic susceptibility results.

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