Temperature of maximum density of aqueous solutions of some <i>α</i>-amino acids

Abstract

Temperatures of maximum density (TMD) at different low concentrations of aqueous solutions of glycine, <i>α</i>-alanine, 1-serine, aspartic acid, asparagine, leucine and isoleucine have been reported. The changes in TMD with respect to that of water vary non-linearly with concentration of the amino acid. By subtracting from the observed change in TMD (∆<i>θ</i>)<i>, </i> an ideal contribution evaluated numerically, it is possible to calculate the structural part ∆<i>θ</i>_str. The quadratic dependence of ∆<i>θ</i>_str on amino acid concentration is given by ∆<i>θ</i>_str = <i>ax </i>+ <i>bx² </i> (x= mole fraction) thus enabling a graphical evaluation of the interaction parameters <i>a </i> (solute-solvent) and <i>b </i>(solute-solute). Evaluation of limiting expansibilities of the amino acids at 4°C also corroborate the findings based on <i>a </i> values.