Factor analysis applied to the correlation between dissociation constants and solvatochromic parameters in water-acetonitrile mixtures: II. Study of solvent effects on the dissociation of functional groups of diuretics, quinolones, buffers and peptides

Abstract

The acid dissociation constants of series of substances with differing structural features in several acetonitrile-water mixtures were subjected to factor analysis (FA). A further target factor analysis (TFA) indicated that the Kamlet and Taft general equation was reduced in these mixtures to two or three terms: the independent term and that related to the polarity/polarizability π ∗ solvatochromic parameter, and additionally, to the hydrogen bond acceptor basicity β solvatochromic parameter. Thus, relationships between p K values and π ∗ or π ∗ and β values showing excellent correlations were established, which allowed us to calculate the p K values of substances in any acetonitrile-water mixture up to 70% (w/w). Also, the variation in the p K value with the percentage of acetonitrile in the hydro-organic mixtures could be explained in terms of the preferential solvation by water of electrolytes in the mixture studied.