The dissociation constant (pKa) is one of the most significant properties of a substance
chemical moiety which has to be estimated with accuracy. Liquid chromatographic, spectrophotometric
and potentiometric methods are often employed for determination of pKa values of compounds. This
study describes the practice of these three methods to the determination of dissociation constant
values of famotidine and ranitidine in acetonitrile-water binary mixtures. From these constants,
aqueous dissociation constants of investigated substances were calculated by different approaches.
Moreover, estimation of aqueous pKa values ( wwpKa ) can also be predicted by computational
method (Marvin Sketch) on the basis of molecular structure. Results obtained from wwpKa values are compared with
Marvin Sketch program and literature values.
Keywords: Acetonitrile-water mixtures, aqueous pKa value, dissociation constant, H2 receptor antagonists, molecular structure,
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