TEMPERATURE OF MAXIMUM DENSITY OF AQUEOUS-SOLUTIONS OF SOME ALPHA-AMINO-ACIDS

Temperatures of maximum density (TMD) at different low concentrations of aqueous solutions of glycine, alpha-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 (DELTA-theta), an ideal contribution evaluated numerically, it is possible to calculate the structural part DELTA-theta-str. The quadratic dependence of DELTA-theta-str on amino acid concentration is given by DELTA-theta-str = ax + bx2 (x = mole fraction) thus enabling a graphical evaluation of the interaction parameters a(solute-solvent) and b(solute-solute). Evaluation of limiting expansibilities of the amino acids at 4-degrees-C also corroborate the findings based on a values.