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E-Journal of Chemistry
Volume 9 (2012), Issue 2, Pages 517-524

Effect of Solvent on Protonation Equilibria of L-Proline and L-Valine in 1, 2-Propanediol-Water Mixtures

School of Chemistry, Andhra University, Visakhapatnam-530003, India

Received 27 June 2011; Accepted 27 August 2011

Copyright © 2012 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Protonation equilibria of L-proline and L-valine in varying compositions (0.0-60.0% v/v) of 1, 2-Propanediol-water mixtures were investigated pH-metrically. Titrations were performed at 303.0 K and the ionic strength of the medium was maintained at 0.16 mol L-1 using sodium chloride. The best fit chemical models of the protonation equilibria were based on crystallographic R-factor, Χ2, skewness, and kurtosis. All the protonation constants of proline and valine increased with increasing propanediol content. This is attributed to the dielectric constant of the medium.