TRANSFER OF PROTONATED ANESTHETICS ACROSS THE WATER O-NITROPHENYL OCTYL ETHER INTERFACE - EFFECT OF THE ION STRUCTURE ON THE TRANSFER KINETICS AND PHARMACOLOGICAL ACTIVITY

Voltammetric and impedance measurements were used to study the transfe r of protonated forms of local anesthetics (procaine, tetracaine, coca ine, prilocaine, bupivacaine, lidocaine, dibucaine) between water (W) and o-nitrophenyl octyl ether (o-NPOE). The ion structure was shown to have little effect on the ion transport properties in the bulk aqueou s phase, as characterized by the diffusion coefficient, D-w=(7-10) x 1 0(-6) cm(2) s(-1), as well as in the bulk o-NPOE phase. as characteriz ed by the diffusion coefficient D-0=(5-6) x 10(-7) cm(2) s(-1): and at the Wl o-NPOE interface, as characterized by the apparent standard ra te constant, k(0)(s)=0.013 cm s(-1). While ion transport in the bulk o f a phase is influenced mainly by the ion size and medium viscosity (S tokes law), the rate of interfacial ion transfer comprises the contrib utions of the ion distribution in the electrical double layer and of t he activated transfer step, which compensate largely for each other. T he pharmacological activity of local anesthetics correlates with the s tandard potential differences of their protonated forms at the Wlo-NPO E interface. This activity can be related to the ion partition between the body fluid and the membrane, or to the rate of membrane ion trans fer at a constant potential difference.