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, φ
R-, is represented as follows:
φR+=1/m-x{m(Φ
1-φCl-)-x(φ
R±+φ
H+)}, K
1=x
2/m-x,
in which
m is total concentration of amino acid,
x is concentration of zwitterion, K
1, is ioni-zation constant of carboxyl-groups, Φ
1, 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(Φ
2-φNa
+)-x(φ
R±+φ
OH-)}, K
2=x
2/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 (-NH
3+);
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.
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