Potentiometric studies on the protonation constants and solvation of some α-amino acid methyl- and ethyl esters in ethanol-water mixtures

Abstract

The stoichiometric protonati on constants of 15 esters (methyl and ethyl esters of glycine, _L-alanine, _L -valine, _L - leucine, _L -phenylalanine, _L -serine, _L -methionine and methyl ester of _L -isoleucine) in 20-80% (v/v)<i> </i>ethanol-water mixtures have been determined. The effect of solvent on α -amino acid methyl- and ethyl esters have also been determined at ionic strength of 0. 1 <i>M </i>NaCl and at 25°C<i> </i>under nitrogen atmosphere. A potentiometric<i> </i>method is used and the calculation of the constants has been carried<i> </i>out using PKAS computer programme. The logarithm of the<i> </i>protonation constants of α-amino acid esters is found to decrease<i> </i>linearly with increase in ethanol contents. The variation of these<i> </i>constants is discussed on the basis of specific solute-solvent interactions.