Tautomeric and microscopic protonation equilibria of some α-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 constant...

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Bibliographic Details
Published in:Analytical biochemistry 2007-06, Vol.365 (1), p.7-13
Main Authors: Doğan, Alev, Kılıç, Esma
Format: Article
Language:English
Subjects:
Amino acid
Amino Acids - chemistry
Dipolar ion
Ethanol - chemistry
Hydrogen-Ion Concentration
Kinetics
Microscopic/Tautomeric protonation constants
Models, Chemical
Potentiometry
Protons
Solvent effect
Solvents - chemistry
Stereoisomerism
Temperature
Water - chemistry
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Summary: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.
ISSN:0003-2697
1096-0309
DOI:10.1016/j.ab.2007.02.019