Determination of acid–base dissociation constants of azahelicenes by capillary zone electrophoresis

Abstract

CZE was employed to determine acid-base dissociation constants (pK(a)) of ionogenic groups of azahelicenes in methanol (MeOH). Azahelicenes are unique 3-D aromatic systems, which consist of ortho-fused benzene/pyridine units and exhibit helical chirality. The pK(a) values of pyridinium groups of the studied azahelicenes were determined from the dependence of their effective electrophoretic mobility on pH by a nonlinear regression analysis. The effective mobilities of azahelicenes were determined by CZE at pH range between 2.1 and 10.5. Thermodynamic pK(a) values of monobasic 1-aza[6]helicene and 2-aza[6]helicene in MeOH were determined to be 4.94 +/- 0.05 and 5.68 +/- 0.05, respectively, and pK(a) values of dibasic 1,14-diaza[5]helicene were found to be equal to 7.56 +/- 0.38 and 8.85 +/- 0.26. From these values, the aqueous pK(a) of these compounds was estimated.

Determination of acid dissociation constants of triazole fungicides by pressure assisted capillary electrophoresis

“…In general, potentiometric [14,21] and UV/Vis spectrophotometric titrations [21], NMR [22] or capillary electrophoresis (CE) [23][24][25] are the commonly used methods for pK a determinations. These techniques are sufficiently precise and accurate, nevertheless in the case of spectrophotometric and potentiometric titrations and NMR, the studied compounds have to be available in relatively large amount and in the analytical grade purity.…”

The dependence of the electrophoretic mobility of small organic ions on ionic strength and complex formation

“…Significant applications include separation of short peptides [6][7][8][9][10][11][12], organic anions [13,14], proteins, and protein ''charge ladders'' [15][16][17], stereoisomers [18], and also the study of complex formation [12,[19][20][21]. There are a number of factors that influence the effectiveness of separating species in a particular system and these include the solvent, composition of BGE, temperature, pH, sample concentration, nature of the capillary (its diameter, whether it is ''coated'', etc.…”

Analysis of Binding Equilibrium of Phenylalkylamines to Brij 58 Micelle through the Measurement of Electrophoretic Mobility by CZE

“…Capillary zone electrophoresis is widely used for the determination of acid dissociation constants [3][4][5][6][7][8][9][10][11]. The CZE determination is based on the deprotonation or protonation of an acid or a base as an analyte with varying pH of the separation buffer, which results in the changes in effective electrophoretic mobility of the analyte.…”

“…Acid dissociation equilibrium is a typical example to be analyzed through the electrophoretic mobility [1,[3][4][5][6][7][8][9][10][11]. The analysis is based on the measurement of effective electrophoretic mobility of an acid or a base.…”

“…It is noticed in the CZE analysis that the analytes need not be of high purity, measurements are made at low concentration of analytes with even low solubility to water and suitable chromophores, small amount of analytes are used in the measurements, and exact knowledge of concentration is not needed for the mobility measurements [1]. Utilizing the prominent characteristics of the CZE analysis, acid dissociation constants of azahelicenes [3], synthesized drug of hetetoarylaminoethanols [4], and cephalosporin antibiotics [5] have been determined in an aqueous solution. Temperature dependence of acid dissociation constant has also been evaluated by CZE, utilizing the heat release characteristic of a capillary [6].…”