Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

The density and ultrasound velocity of glycine, dl-alanine, dl-2-aminobutyric acid, and dl-norvaline were measured in pure water as a function of amino acid molality and temperature. On the basis of the correlation between apparent molar volume and hydration number, the excess volume of water in the hydrate complexes of selected amino acids was analyzed. The excess volume of water in the hydrate complexes was computed to be negative indicating that the formation of hydrate complexes is accompanied with the compression of water volume. The excess volume of water also exhibited linear behavior with molar mass of hydrocarbon side chains. This finding leads us to compute the contributions of zwitterion and hydrocarbon side chain to the excess volume of water. The negative magnitude of excess volume of water in the hydrate complex of zwitterion increases with increasing temperature which is explained in the light of Frank Wen model of water in an aqueous electrolyte solution, whereas the positive magnitude of excess volume of water in the hydrate complexes of hydrocarbon side chain decreases with an increase in temperature which is attributed to the melt of rigid hydration structures around a hydrophobic group at elevated temperatures.