Physicochemical characterization of phosphinic pseudopeptides by capillary zone electrophoresis in highly acidic background electrolytes

Abstract

Phosphinic pseudopeptides (i.e., peptide isosteres with one peptide bond replaced by a phosphinic acid moiety) were analyzed and physicochemically characterized by capillary zone electrophoresis in the pH range of 1.1-3.2, employing phosphoric, phosphinic, oxalic and dichloroacetic acids as background electrolyte (BGE) constituents. The acid dissociation constant (pK(a)) of phosphinate group in phosphinic pseudopeptides and ionic mobilities of these analytes were determined from the pH dependence of their effective electrophoretic mobilities corrected to standard temperature and constant ionic strength of the BGEs. It was shown that these corrections are necessary whenever precise mobility data at very low pH are to be determined. Additionally, it was found that the ionic mobilities of the phosphinic pseudopeptides and pK(a) of their phosphinate group are affected by the BGE constituent used. The variability of migration behavior of the pseudopeptides can be attributed to their ion-pairing formation with the BGE components.

Determination of acid–base dissociation constants of amino‐ and guanidinopurine nucleotide analogs and related compounds by capillary zone electrophoresis

“…It was achieved by thermostating the outer polyimide capillary surface to constant temperature of 247C and by setting the input power to the value of 0.66 W per meter of capillary length, which causes 17C temperature increase inside the capillary, resulting in the constant temperature 257C of the BGE inside the capillary. The value of 0.66 W/m for 17C temperature increase was determined from the electric conductivity measurements of an aqueous standard solution of potassium chloride in the same capillary and from the known temperature dependence of its conductivity, as described in our previous paper [32].…”

“…The most frequently applied detection for CZE estimation of pK a is the direct UV-absorption detection [6,7,9,10,13,[30][31][32]; however, conductometric [12], amperometric [23], and indirect UVabsorption [33] detection schemes have been also used. The pK a values of the ionogenic groups in both aqueous and nonaqueous media were determined using the different linear or nonlinear regression analysis of the pH dependence of effective electrophoretic mobility of analyzed compounds [1].…”

Determination of pKa values of diastereomers of phosphinic pseudopeptides by CZE

“…(11)- (15). Regression analysis was performed independently for each diastereomer of the pseudopeptides whereas an equal value of the effective mobility was used for unresolved diastereomers.…”

“…The experimental effective mobilities were corrected to temperature increase inside the capillary due to Joule heating according to a published procedure [15]. Briefly, the heat dissipation capability of the separation capillary in the CE apparatus was calibrated with KCl solution of a tabulated temperature course of specific conductivity.…”

Analysis of Ion-Association Reaction in Aqueous Solution and Its Utilization by Capillary Zone Electrophoresis

“…Acid dissociation constants (pKa) obtained agreed well with the reported values. Acid dissociation constants of phosphinate group in phosphinic pseudopeptides were determined in highly acidic media, 39 and pKa values of water-insoluble organic acids were determined in water-methanol mixed solvent and then extrapolating to water. 40 Continuous two-steps of acid dissociation constants were also analyzed with anthraquinone compounds through affinity capillary electrophoresis by using a nonlinear regression method.…”