Tautomeric and microscopic protonation equilibria of some alpha-amino acids.
The acid-base equilibria of several amino acids, namely glycine, l-alanine, l-valine, l-leucine, l-phenylalanine, l-serine, l-methionine, and l-isoleucine, have been characterized in terms of microscopic protonation constants and tautomeric ratios. In this study, the microscopic protonation constants and tautomeric ratios of eight amino acids in different ethanol-water mixtures have been determined. The variation of microscopic constants of amino acids is discussed on the basis of solute-solvent interactions, and the ratio of dipolar ionic form to neutral form is determined in ethanol-water mixtures (20/80% ethanol by volume). The dipolar ionic form still greatly predominates, even in 80% ethanol, as estimated from potentiometric titration data.
Doğan
Alev
A
Department of Science, Faculty of Gazi Education, Gazi University, Ankara 6100, Turkey. alevd@gazi.edu.tr
Kiliç
Esma
E
D000596:Amino Acids / Q000737:chemistry*; D000431:Ethanol / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008956:Models, Chemical; D011199:Potentiometry; D011522:Protons; D012997:Solvents / Q000737:chemistry; D013237:Stereoisomerism; D013696:Temperature; D014867:Water / Q000737:chemistry*
D000596:Amino Acids; D011522:Protons; D012997:Solvents; D014867:Water; D000431:Ethanol