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Determination of dissociation constants of compounds with potential cognition enhancing activity by capillary zone electrophoresis
Author(s) -
Lišková Anna,
Křivánková Ludmila
Publication year - 2005
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.200500433
Subject(s) - chemistry , capillary electrophoresis , sodium formate , formate , absorbance , electrolyte , analytical chemistry (journal) , dissociation constant , counterion , chloride , molecule , sodium , chromatography , ion , inorganic chemistry , organic chemistry , biochemistry , receptor , electrode , catalysis
Accurate determination of p K a values is important for proper characterization of newly synthesized molecules. In this work we have used CZE for determination of p K a values of new compounds prepared from intermediates, 2, 3 and 4‐(2‐chloro‐acetylamino)‐phenoxyacetic acids, by substituting chloride for 2‐oxo‐pyrrolidine, 2‐oxo‐piperidine or 2‐oxo‐azepane. These substances are expected to have a cognition enhancing activity and free radicals scavenging effect. Measurements were performed in a polyacrylamide‐coated fused‐silica capillary of 0.075 mm ID using direct UV detection at 254 nm. Three electrolyte systems were used for measurements to eliminate effects of potential interactions between tested compounds and components of the BGE. In the pH range 2.7–5.4, chloride, formate, acetate and phosphate were used as BGE co‐ions, and sodium, β‐alanine and ϵ‐aminocaproate as counterions. Mobility standards were measured simultaneously with the tested compounds for calculations of correct electrophoretic mobilities. Several approaches for the calculation of the p K a values were used. The values of p K a were determined by standard point‐to‐point calculation using Henderson–Hasselbach equation. Mobility and pH data were also evaluated by using nonlinear regression. Three parameter sigmoidal function fitted the experimental data with correlation coefficients higher than 0.99. Results from CZE measurements were compared with spectrophotometric measurements performed in sodium formate buffer solutions and evaluated at wavelength where the highest absorbance difference for varying pH was recorded. The experimental p K a values were compared with corresponding values calculated by the SPARC online calculator. Results of all three used methods were in good correlation.