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The unified equation for the evaluation of first order reactions in dynamic electrophoresis
Author(s) -
Trapp Oliver
Publication year - 2006
Publication title -
electrophoresis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.666
H-Index - 158
eISSN - 1522-2683
pISSN - 0173-0835
DOI - 10.1002/elps.200500708
Subject(s) - isomerization , chemistry , capillary electrophoresis , reaction rate constant , captopril , elution , aqueous solution , kinetics , tris , kinetic energy , analytical chemistry (journal) , chromatography , catalysis , organic chemistry , medicine , biochemistry , physics , quantum mechanics , blood pressure , radiology
The unified equation was validated for first order reactions in dynamic CE with a data set of 31 250 elution profiles. Comparison with the results from conventional iterative computer simulation revealed that the unified equation is superior in terms of success rate and precision. The unified equation was applied to determine the cis‐trans isomerization rate constants of the angiotensin converting enzyme inhibitor captopril. The separation of the rotational cis‐trans isomeric drug has been performed in an aqueous 66 mM citric acid/Tris buffer at pH 3.0 in a 50 cm polyacrylamide‐coated fused‐silica capillary. Interconversion profiles featuring pronounced plateau formation and peak broadening were observed. Activation parameters Δ H ≠ and Δ S ≠ were obtained from temperature‐dependent measurements between 10 and 25°C in 2.5 K steps. From the activation parameters the isomerization barriers of captopril at 37°C under acidic conditions were calculated to be Δ G ≠ trans→cis = 90.6 kJ/mol and Δ G ≠ cis→trans = 84.6 kJ/mol. By comparison of the kinetic data with the results obtained under basic conditions (pH 9.3) a mechanism of isomerization could be proposed.