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Studies on the Protonation Constants and Solvation of α-Amino Acids in Dioxan–Water Mixtures

✍ Scribed by Fitnat Köseoglu; Esma Kiliç; Alev Dogan

Publisher
Elsevier Science
Year
2000
Tongue
English
Weight
53 KB
Volume
277
Category
Article
ISSN
0003-2697

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✦ Synopsis

To gain more information about the effect of solvent on ␣-amino acids, the stoichiometric protonation constants of 10 ␣-amino acids (glycine, DL-alanine, DL-valine, L-leucine, L-isoleucine, DL-phenylalanine, Lserine, L-threonine, L-asparagine, and L-glutamine) in different dioxan-water mixtures have been determined potentiometrically using a combined pH electrode system calibrated in concentration units of hydrogen ion at 25°C with an ionic strength of 0.10 M. For all amino acids studied, it was observed that the log K 1 values relating to the protonation equilibria of the anionic form are almost unaltered by the change in solvent composition. However, the log K 2 values corresponding to the formation equilibria of cationic form increase with the increase in dioxan content. The variation of these constants is discussed on the basis of specific solute-solvent interactions and structural changes of amino acids from water to dioxan-water media. The zwitterionic to neutral form ratio of these acids in dioxan-water mixtures is also discussed.

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