Effects of different buffer species on partition coefficients of drugs used in quantitative structure-activity relationships.

A study was conducted in which the same organic solvent, 1-octanol, and different buffer systems were used to obtain intercorrelations among log Pcorr values given by log P (octanol-water) = a log P (octanol-buffer) + b, where a and b are different constants for the different systems used. The range of a was 0.418-1.156 and that of b was -1.962-1.176 for the four buffer systems examined. Only with neutral drugs was the slope (a) close to 1.0 and the intercept (b) close to 0.0 for the three buffer systems studied. For acidic drugs, only 1-octanol-phosphate buffer gave a 1:1 correlation with 1-octanol-water partition coefficients. Acetate and bicarbonate buffer systems gave different correlations. For basic drugs, none of the three systems examined gave a 1:1 correlation with 1-octanol-water partition coefficients.