STUDIES IN THE PHYSICAL CHEMISTRY OF AMINO ACIDS AND PROTEINS

Abstract

Electrostrictions of the solvent due to ionized groups of α-amino acids were estimated. Apparent molal volume of amino acid zwitterion is calculated from the density of neutral solutions. The app. mol. vol. of amino acid cation, φR-, is represented as follows: φR+=1/m-x{m(Φ1-φCl-)-x(φR±+φH+)}, K1=x2/m-x, in which m is total concentration of amino acid, x is concentration of zwitterion, K1, is ioni-zation constant of carboxyl-groups, Φ1, φ+ and φCl are the app. mol. vol. of solute, H+ and Cl-. By the same principle the app. mol. vol. of amino acid anion, φR-, is φR-=1/m-x{m(Φ2-φNa+)-x(φR±+φOH-)}, K2=x2/m-x, in which K2 is ionization constant of amino-group. Comparing the app. mol. vol. of cation, anion, and zwitterion of amino acid and using atomic volume of hydrogen, 3.1 cc, the electro-striction of solvent due to charged groups were obtained as follows: glycine, 2.1 cc/mol (electrostriction due to -COO-), 8.2 (-NH3+); dl-alanine, 3.8, 6.8; dl-α-amino-n-butyric acid, 3.9, 7.0; dl-α=amino-n-valeric acid, 3.7, 7.1; α-amino-isobutyric acid, 3.7, 5.5; dl-valine, _??_. O, 5.2; l-leucine, 3.1, 6.9.