Netsu Sokutei

Complexation of some bivalent transition metal with halide and pseudohalide ions has been studied by calorimetry and spectrophotometry in some nonaquenus solvents and their mixtures. Formation costants, enthalpies and entropies of formation of complexes vary strongly depending on the solvent. Solvent effects on the thermodynamic parameters are discussed in terms of solvation of ions and solvent-solvent interactions in the bulk. The coordination structure change upon complexation, which occurs in a different manner depending on the metal ion and ligand, will be also discussed.

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The conformational stability of a protein in an aqueous solution is described by the Gibbs free energy of unfolding between the native and random conformation.
The free energy of unfolding consists of two contributions: the hydration around the molecule, and the intramolecular interactions. A method to calculate the free energy of hydration from the accessible surface area (ASA) of the constituent atomic groups in a protein has been developed assuming a proportionality of the free energy to ASA. Similarly, the free energy of unfolding for the chain in vacuo can also be calculated from the ASA, using the unfolding thermodynamics derived from the experimental data of 10 proteins. Thus, our method can predict the unfolding thermodynamics of a protein with a known tertiary structure. The predicted values of 4 other proteins agreed well with the experimentally derived values. This method also accounted for the temperature dependences of the free energy of unfolding and the enthalpy changes of T4 lysozyme, and the occurrence of cold denaturation at a low temperature. This method was applied to the unfolding thermodynamics of the poly (L-alanine) helix. The calculated enthalpy change is close to the value determined in a recent calorimetric study of a 50-residue alanine-rich helix, and the results suggest that helix formation is enthalpy-driven.

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Molecular-based ferro/antiferromagnets designed on the basis of the through-space interaction approach are reviewed with emphasis on the magnetic heat capacity. The thermodynamical analyses of two exemplary cases, decamethylferrocenium tetracyanoethenide and organic free radical MOTMP, are presented, in which main aspects of interest are the magnetic entropy, symmetry of magnetic interaction, magneto-structural correlation, lattice-dimensionality crossover, temperature dependence of heat capacity in the ordered phase, estimation of short range ordering effect, and mean-field treatment. Works on TANOL, TPV, and p-NPNN radicals are also reviewed. It is shown that the magneto-structural correlation is a very delicate subject in molecular-based magnets. They often exhibit remarkable short range order effects characteristic to low-dimensional magnets even when any low-dimensionality cannot be identified in the crystal structures. More careful analysis, including reexamination of usefulness of interaction-path concept, is required for systematic and consistent description of magnetic lattice structures.

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