SOLUTE-SOLVENT AND SOLUTE-SOLUTE INTERACTIONS IN THERNARY AMINO ACID SOLUTIONS AT 25 OC

This work present investigation of the density and volume behaviour of ternary amino acid solutions, comprising of two amino acids and water, at 21.98.15 K. The objective is to support building a quantitative relationship among densities, amino acid concentration and structural characteristics of the solute molecules, for predicting values of density and partial molar volumes in mixtures of amino acids, peptides and similar molecules found in living and other natural systems.\ud \ud Densities of ternary amino acid solutions, containing amino acid-1, amino acid-2 and water were measured using a vibrating tube precision densitometer at 298.15 K. Apparent and partial molar volumes were computed from density data and interpreted in terms of the accepted model for molecular salvation. Attempt has been made to correlate density of ternary solution with the densities of individual maino acids measured under similar experimental conditions. While a simple correlation seem to exit in terms of additively of densities, a precise relationship is proposed involving structural features of solute molecules and its overall hydrophobicity. Similar correlation are attempted with volume data, as well. literature data concerning densities and volumes of individual amino acids were used, in the first instance, for computing values for ternary solutions and to check additively relationships. Systematic variations among data from different sources, however, prevented a meaningful comparison and caused significant discrepancies in calculations at the desired precisions level. An extensive new data of higher precision, for densities of individual amino acids, was therefore obtained, in the temperature range, 283.15 – 3.13.15 K. Effect of temperature on amino acid densities was determined from the calculated partial molar expansibilities and interpreted in terms of structural features of solute molecules. Data pertaining at 298.15 K were used as a basis procedure were used to obtain significance of data. Least square fit procedure as applied to build correlation among density, and concentrations of each amino acid of the ternary solutions.\ud \ud It was found that density of amino acid mixtures is function of concentration of each amino acid, the solute-solute-solvent interaction parameter, Sv, and the hydrophobicity of solute molecules. Values of Sv were obtained from data of single amino acid solutions taken from the present study. Quantitative estimates of hydrophobicity in terms of Equivalent methylenes, were taken from literature and incorporated in the final algebraic equation that is believed to be the representative relationship for predicting densities and volumes of amino acid solutions of ternary and higher composition