Studies on the Dissociation Constants and Solubilities of Amino Acids in Ethylene Glycol+ Water Mixtures

Department of Chemistry, University of Kalyam Kalyani-741 235 Manuscript received 18 February 1993, revised 7 December 1993, accepted 9 December 1993 The dissociation constant and solubility of a number of amino adds have been determined pH-metrically and spectrophotometrlcally In ethylene glycol (EG) + water mixtures at 298 K. The free energies of transfer or amino acids from water to mixed solvents, thus obtained, have been coupled with the free energies of transfer [\(\Delta\)G\(\begin{matrix} o \\ t \end{matrix}\) (1) and \(\Delta\)G\(\begin{matrix} o \\ t \end{matrix}\)(2)] for the reactions RH2+ H20 \(\rightleftharpoons\) RH+ H30+ ...(1) and RH+ + H20 \(\rightleftharpoons\) R- + H30+ ....(2) and \(\Delta\)G\(\begin{matrix} o \\ t \end{matrix}\)(H+) values determined in our laboratory to get the free energies of transfer of RH\(\begin{matrix} + \\ 2 \\ \end{matrix}\) and R- in different mixed solvents. These give the quantitative measures or ion-solvent interactions or tlae zwltterlons, cations and anions of the amino acids. The results have been discussed in terms of structural changes of solvent mixtures resulting in the change In acid-base properties and solute-solvent Interactions. A critical assessment bas been made regarding the determination or single ion values