Macroscopic and Microscopic Protonation Equilibria of Some α-Amino Acids in Dimethyl Sulfoxide-Water Mixtures

Doʇan A., ASLAN N., Erden P. E., CANEL E., Klllç E.

Journal of Solution Chemistry, vol.44, no.8, pp.1705-1722, 2015 (SCI-Expanded) identifier

  • Publication Type: Article / Article
  • Volume: 44 Issue: 8
  • Publication Date: 2015
  • Doi Number: 10.1007/s10953-015-0363-8
  • Journal Name: Journal of Solution Chemistry
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.1705-1722
  • Keywords: Dimethyl sulfoxide-water mixture, Macroscopic/microscopic protonation constant, Solvent effect, α-Amino acid, α-Amino acid ester
  • Ankara Haci Bayram Veli University Affiliated: Yes

Abstract

© 2015 Springer Science+Business Media New York.The acid-base chemistry of multidentate (bio)ligands are usually characterized in terms of macroscopic protonation constants, log10 K (or pK), which are composites of the microscopic constants (log10 k or pk) for the individual groups. In this study, macroscopic protonation constants of some α-amino acid (glycine, l-alanine, l-valine, l-leucine, l-phenylalanine, l-serine) and protonation constants of their methyl- and ethyl- esters in dimethyl sulfoxide-water mixtures (10-40 % dimethylsulfoxide by volume) were studied by potentiometric technique at 25.0 ± 0.1 °C under a nitrogen atmosphere, and at ionic strength of 0.10 mol·L-1 sodium chloride. The protonation constants were calculated by using the Best computer program and the constants were evaluated for microscopic protonation constants of these α-amino acids. The protonation constants are discussed on the basis of solute-solvent interactions. The constants were influenced by changes in solvent composition. The dipolar ionic form, however, still greatly predominates, even in 40 % dimethyl sulfoxide.