Determination of the dissociation constants of some macrolide antibiotics in methanol-water binary mixtures by UV-spectroscopy and correlations with the kamlet and taft solvatochromic parameters

The dissociation constants of six common human and veterinary antibiotics, namely, erythromycin, roxithromycin, tilmicosin, oleandomycin, josamycin, and spiramycin in 15 %, 25 %, 40 % and 50 % (v/v) methanol-water solvent mixtures were determined by UV/pH titration and correlated with the Kamlet and Taft solvatochromic parameters, ? * , ? and ?. 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 ? * , which are solvatochromic parameters. The influence of methanol on the dissociation constants was investigated. Further, the quasi-lattice quasi-chemical (QLQC) model of preferential solvation has been applied to quantify the preferential solvation by water of electrolytes in methanol-water mixtures. © Springer Science+Business Media, LLC 2012