Volumetric properties of L-threonine in aqueous glucose, sucrose and L-ascorbic acid solutions

Amino acids and their derivatives are useful as models of specific aspects of more complex proteins in aqueous solution. In this paper, densities and viscosities of L-threonine in glucose-water, sucrose-water and L-ascorbic acid-water mixed solvents have been measured at 298. 15 K by an oscillating-tube densimeter and a viscositymeter. Limiting partial molar volume, transfer partial molar volume, number of hydration and viscosity B-coefficients of L-threonine have been calculated. The viscosity B-coefficients and the numbers of hydration of L-threonine mixed solvent vary with mass concentration of sugar or L-ascorbic acid. The transfer partial molar volumes from water to sugar-water or L-ascorbic acid-water mixtures have been obtained and discussed in terms of the structural hydration interaction model. The results indicate that the transfer partial molar volumes and viscosity B-coefficients of L-threonine increase with increasing of the mass concentration of sugar or L-ascorbic acid, and the hydration numbers of L-threonine decrease owing to the interaction of sugar or L-ascorbic acid with the zwitterionic groups. It is concluded that the degrees of the effect on volume and hydration number are related to the number of OH groups and the structure of mixture solvent.