Potentiometric studies on the protonation constants and solvation of some alpha-amino acid benzyl- and t-butyl- esters in ethanol-water mixtures


Dogan A., Kilic E.

TURKISH JOURNAL OF CHEMISTRY, vol.29, no.1, pp.41-47, 2005 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 29 Issue: 1
  • Publication Date: 2005
  • Journal Name: TURKISH JOURNAL OF CHEMISTRY
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus, TR DİZİN (ULAKBİM)
  • Page Numbers: pp.41-47
  • Keywords: potentiometry, protonation constants, solvent effect, amino acid esters, DISSOCIATION-CONSTANTS, SOLVENTS, EQUILIBRIUM
  • Gazi University Affiliated: Yes

Abstract

To gain more information about the effect of solvent on a-amino acid benzyl- and t-butyl- esters, the stoichiometric protonation constants of 10 esters (glycine benzyl ester, L-alanine benzyl ester, L-valine benzyl ester, L-serine benzyl ester, glycine t-butyl ester, L-alanine t-butyl ester, L-valine t-butyl ester, L-leucine t-butyl ester, L-phenylalanine t-butyl ester and L-isoleucine t-butyl ester) in 20%-80% (v/v) ethanol-water mixtures were determined at an ionic strength of 0.10 M NaCl and at 25.0 +/- 0.1 degrees C under nitrogen atmosphere. A potentiometric method was used and the calculation of constants was carried out using the PKAS computer program. The logarithm of the protonation constants of the above-mentioned a-amino acid esters linearly decreased with increases in ethanol contents but the values that determined 80% ethanol did not follow this linear trend. The variation of these constants is discussed on the basis of specific solute-solvent interactions.