Studies on the protonation constants and solvation of alpha-amino acids in dioxan-water mixtures.

Koseoglu F., Kilic E., Dogan A.

Analytical biochemistry, vol.277, no.2, pp.243-6, 2000 (SCI-Expanded) identifier identifier identifier

  • Publication Type: Article / Article
  • Volume: 277 Issue: 2
  • Publication Date: 2000
  • Doi Number: 10.1006/abio.1999.4371
  • Journal Name: Analytical biochemistry
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.243-6
  • Keywords: dioxan-water mixture, alpha-amino acids, potentiometry, protonation constants, solvent effect, SUBSTITUTED SALICYLIDENEANILINES, DISSOCIATION-CONSTANTS
  • Gazi University Affiliated: Yes

Abstract

To gain more information about the effect of solvent on alpha-amino acids, the stoichiometric protonation constants of 10 alpha-amino acids (glycine, DL-alanine, DL-valine, L-leucine, L-isoleucine, DL-phenylalanine, L-serine, 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 degrees 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. (C) 2000 Academic Press.