Studies on the macroscopic protonation constants of some α-amino acids in ethanol–water mixtures

Both to demonstrate whether the predominant species are dipolar ion or the neutral form and to predict the change of dipolar form to neutral form ratio in ethanol–water mixtures, the macroscopic protonation constants of eight α-amino acid (glycine, l-alanine, l-valine, l-leucine, l-phenylalanine, l-...

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Bibliographic Details
Published in:Analytical biochemistry 2002-10, Vol.309 (1), p.75-78
Main Authors: Dogan, Alev, Köseoglu, Fitnat, Kiliç, Esma
Format: Article
Language:English
Subjects:
Amino Acids - chemistry
Ethanol - chemistry
Ethanol–water mixture
Kinetics
Macroscopic protonation constants
Potentiometry
Protons
Solvent effect
Solvents - chemistry
Temperature
Water - chemistry
α-Amino acid
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Summary:Both to demonstrate whether the predominant species are dipolar ion or the neutral form and to predict the change of dipolar form to neutral form ratio in ethanol–water mixtures, the macroscopic protonation constants of eight α-amino acid (glycine, l-alanine, l-valine, l-leucine, l-phenylalanine, l-serine, l-methionine, and l-isoleucine) were determined potentiometrically in 20–80% (v/v) ethanol–water mixtures at 25 °C with an ionic strength of 0.10 M. The calculation of the constants was carried out using a PKAS computer program. The effect of solvent composition on the protonation constants and the dipolar ionic to neutral form ratio of these acids in the mixed solvents are discussed. One can conclude that the dipolar form of amino acids, HA ±, dominates in ethanol–water mixtures.
ISSN:0003-2697
1096-0309
DOI:10.1016/S0003-2697(02)00254-3