Determination of acid dissociation constants of flavin analogues by capillary zone electrophoresis

Abstract

Acid dissociation constants (pKa) of nine kinds of flavin analogues as molecular catalyst candidates were determined by CZE. Although some of the analogues are instable and degradable under the light exposure or in alkaline aqueous solutions, the effective electrophoretic mobility of the flavin analogue of interest has been measured with the residual substance. The pKa values of the flavin analogues were analyzed through the changes in the effective electrophoretic mobility with varying pH of the separation buffer. One or two steps pKa values were determined by the analysis. One of the degraded species from the flavin analogues, lumichrome, was also detected in the CZE analysis, and its pKa values were also determined. While coexisting impurities generated over the storage conditions were found in some analogues, the pKa values of the target analogues were successfully determined with the help of the CZE separations. A pressure‐assisted CZE was utilized for the determination or the estimation of the pKa values of such analogues as possessing carboxylic acid moiety.

Development of Novel Analysis and Characterization Methods Utilizing Reaction Dynamics in a Separation Capillary

“…pK a values of acid-degradable pravastatin [18] and hexamethylenetetramine [19] were determined under degraded conditions without any interference from the degraded species. Determination of acid dissociation constants by CE was also successful with alkaline-degradable catecholamines [20], ascorbic acid [21], and flavin derivatives [22]. Heat-degradable bupropion [23] and hydrochlorothiazide [24] were also examined.…”

p<i>K</i>_a Determination of Strongly Acidic C-H Acids Bearing a (Perfluoroalkyl)sulfonyl Group in Acetonitrile by Means of Voltammetric Reduction of Quinone

“…12 The experimental values are usually determined by means of potentiometry, UV spectrometry, and capillary electrophoresis. [13][14][15] High-performance liquid chromatography (HPLC), isothermal titration calorimetry, and voltammetry have been also utilized. 12,[16][17][18][19] These methods are performed mainly in aqueous media, thus their application is limited to weak acids.…”