Structure-lipophilicity relationships of neutral and protonated β-blockers Part I Intra- and intermolecular effects in isotropic solvent systems

The objectives of this study were to validate new experimental techniques used to measure the log P of protonated drugs, and to investigate the inter- and intramolecular forces influencing the partitioning behavior of beta-blockers in isotropic biphasic solvent systems. The lipophilicity parameters of a number of beta-blockers were measured by two-phase titration, centrifugal partition chromatography (CPC),and cyclic voltammetry (CV) in one or more of the following solvent systems: octanol/water, 1,2-dichloroethane/water, and dibutyl ether/water. CV proved to be a promising technique for measuring the lipophilicity of protonated beta-blockers. Derived parameters such as Delta log P (difference between log P in two different solvent systems, a parameter valid for a given solute in a given electrical form) and (difference between log P of two differnet electrical forms of a given solute, in the same system) yielded insights into inter- and intramolecular interactions characteristic of beta-blockers. The relevance of these parameters in structure-permeation relationships is explored.