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Determination of the Dissociation Constants of Urocanic Acid Isomers in Aqueous Solutions

Determination of the Dissociation Constants of Urocanic Acid Isomers in Aqueous Solutions (E)- and (Z)-Urocanic acids are endogenous chemicals in the normal mammalian skin. The first and the second thermodynamic dissociation constants (pK a1 and pK a2) of urocanic acid isomers were determined using UV spectrophotometry in aqueous solutions. The values with standard deviation (pK a1 = 3.43 ± 0.12 and pK a2 = 5.80 ± 0.04) and (pK a1 = 2.7 ± 0.3 and pK a2 = 6.65 ± 0.04) were obtained to (E)- and (Z)-urocanic acids, respectively. The second dissociations were studied also by potentiometric titration in aqueous sodium chloride solutions up to the isotonic salt concentration (0.154 mol dm−3), and the second thermodynamic dissociation constants as well as activity parameters for both isomers were determined at temperature 25°C and for (E)-urocanic acid also at 37°C. The obtained pK a2 values were close to those found by UV spectrophotometry. The equations for the calculation of the second stoichiometric dissociation constants of urocanic acid isomers on molality and molarity scale in aqueous sodium chloride solutions were derived. The obtained pK a1 and pK a2 values for (Z)-urocanic acid appear to be essentially lower than some previously reported values in literature. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Monatshefte für Chemie - Chemical Monthly Springer Journals

Determination of the Dissociation Constants of Urocanic Acid Isomers in Aqueous Solutions

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References (35)

Publisher
Springer Journals
Copyright
Copyright © 2007 by Springer-Verlag
Subject
Chemistry; Chemistry/Food Science, general; Analytical Chemistry; Inorganic Chemistry; Organic Chemistry; Physical Chemistry; Theoretical and Computational Chemistry
ISSN
0026-9247
eISSN
1434-4475
DOI
10.1007/s00706-007-0687-1
Publisher site
See Article on Publisher Site

Abstract

(E)- and (Z)-Urocanic acids are endogenous chemicals in the normal mammalian skin. The first and the second thermodynamic dissociation constants (pK a1 and pK a2) of urocanic acid isomers were determined using UV spectrophotometry in aqueous solutions. The values with standard deviation (pK a1 = 3.43 ± 0.12 and pK a2 = 5.80 ± 0.04) and (pK a1 = 2.7 ± 0.3 and pK a2 = 6.65 ± 0.04) were obtained to (E)- and (Z)-urocanic acids, respectively. The second dissociations were studied also by potentiometric titration in aqueous sodium chloride solutions up to the isotonic salt concentration (0.154 mol dm−3), and the second thermodynamic dissociation constants as well as activity parameters for both isomers were determined at temperature 25°C and for (E)-urocanic acid also at 37°C. The obtained pK a2 values were close to those found by UV spectrophotometry. The equations for the calculation of the second stoichiometric dissociation constants of urocanic acid isomers on molality and molarity scale in aqueous sodium chloride solutions were derived. The obtained pK a1 and pK a2 values for (Z)-urocanic acid appear to be essentially lower than some previously reported values in literature.

Journal

Monatshefte für Chemie - Chemical Monthly – Springer Journals

Published: Aug 13, 2007

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