The examination of the dissociation constants of sulfonamides is essential in drug-design studies and in explaining the biopharmaceutical properties of substances. The dissociation constants of ten common human and veterinary antibiotics, namely, sulfadiazine, sulfamerazine, sulfamethoxazole, sulfathiazole, sulfamonomethoxine, sulfamethoxypyridazine, sulfadimethoxine, sulfafurazole, sulfadoxine, and sulfaquinoxaline, in water and in 15 %, 23 %, and 30 % (v/v) acetonitrile−water mixtures were determined by a UV/pH titration method and correlated with the Kamlet and Taft solvatochromic parameters, π*, α, and β. Kamlet and Taft’s general equation was reduced to two terms by combined factor analysis and target factor analysis in these mixtures: the independent term and polarity/polarizability π*, which is a solvatochromic parameter. Further, the quasi-lattice quasi-chemical (QLQC) theory of preferential solvation has been applied to quantify the preferential solvation by water of electrolytes in acetonitrile−water mixtures.

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The solute−solvent interactions of four anticancer drugs, daunorubicin, doxorubicin, vincristine sulfate, and 6-thioguanine, have been studied in acetonitrile− water mixtures up to 50 % acetonitrile by volume fraction using a UV/pH titration method. The acidity constants have been calculated with the STAR (stability constants by absorbance readings) program. The interactions between the four anticancer drugs and the solvent studied, acetonitrile−water mixtures, was identified using the microscopic parameters (Kamlet and Taft's solvatochromic parameters: α, β, and π*). The Kamlet and Taft general equation for pK a1 and pK a2 values of 6-thioguanine, doxorubicin, daunorubicin, and vincristine sulfate was reduced to two terms (the independent term and the hydrogen-bond-donating ability, α) or three terms (the independent term, polarity/polarizability, π*, and the hydrogen-bond-donating ability, α) using linear regression analysis in acetonitrile−water mixtures. The Kamlet and Taft equations can be used to predict the acidity constants of daunorubicin, doxorubicin, vincristine sulfate, and 6-thioguanine at any acetonitrile composition, which would be helpful in practical work during chromatographic method development.