Liquid Chromatographic Determination of pKa Value of 1- (2-methylbenzonitrile)-3-benzylbenzimidazolium bromide as a Drug Candidate in Acetonitrile-Water Binary Mixtures

The ionization/protonation (pKa) constant, which is a physicochemical parameter that directly affects the pharmacokinetic properties of a drug such as absorption, distribution, metabolism, and excretion (ADME), is currently determined by analytical methods. The effect of pH of the mobile phase on the chromatographic behavior of 1-(2- methylbenzonitrile)-3-benzylbenzimidazolium bromide (2) which its synthesis, fully characterization, and antiproliferative activity properties were studied previously, and the protonation constant (pKa) value were determined in this study. The pKa value of compound 2, benzimidazolium salt, was determined by the reverse-phase liquid chromatographic (RPLC) method at 25 ºC. sspKa values were evaluated using retention time (tR) in acetonitrile-water binary mixtures with acetonitrile (ACN) percentages of 40%, 45%, 50% and 55% (v/v). The aqueous pKa wwpKa value of the synthesized compound was calculated from the sspKa value using the macroscopic parameters (dielectric constant and mole fraction) which play an important role in the solvent properties. Obtained wwpKa values were found to be 11.290 and 11.241, respectively. In addition, the degree of ionization of the related compound was calculated using the wwpKa values.