Thermodynamic Radius Research Articles

Effect of sucrose on the dimerization of α-chymotrypsin allowance for thermodynamic nonideality arising from the presence of a small inert solute

The space-filling effects of sucrose on the dimerization of α-chymotrypsin have been investigated by sedimentation equilibrium studies on the enzyme in acetate-chloride buffer, pH 3.9, I 0.2. From the extent of enhancement of the apparent dimerization constant in the presence of 0.05–0.16 M sucrose, it is concluded that this effect of thermodynamic nonideality finds quantitative explanation in terms of excluded volume. However, the suggested approximation that the radius of an inert small solute would be sufficiently small to be neglected in the calculation of covolumes (D.J. Winzor and P.R. Wills, Biophys. Chem. 25 (1986) 243) has not withstood the more stringent test afforded by the present study of α-chymotrypsin dimerization. A value of 0.34 nm for the effective thermodynamic radius of sucrose was inferred from the covolume for self-interaction obtained by frontal gel chromatography on Sephadex G-10 under the conditions of the ultracentrifugal studies. Finally, results of sedimentation equilibrium experiments on α-chymotrypsin in the presence of 0.1 M glycerol were also shown to be consistent with interpretation in terms of the model of space-filling effects entailing complete exclusion of small solute from the hydrated protein domain.

Crystal lattice energy of aluminum hydrides and borohydrides of metals of groups Ia and IIa

1. The values of the thermodynamic radii (rt) of borohydride and aluminum hydride ions were calculated. 2. The crystal lattice energy of borohydrides and aluminum hydrides of IA and IIA were calculated on the basis of rt[ElH4−] according to the Kapustinskii equation, from the Born-Haber cycle; and by the method of comparative calculation. 3. The energy of formation of RbAlH4, addition of (H−) to [AlH3], and other conversions was calculated on the basis of the energy of formation of the gaseous aluminum hydride ion. 4. A correspondence was detected between the nature of the changes in the crystal lattice energy and certain properties of aluminum hydrides and borohydrides: the thermal stability, solubility, and ability for formation from the elementary substances.