Chronoamperometric study of Tl(I) reduction at gramicidin-modified phospholipid-coated mercury electrodes

An investigation into the effect of gramicidin on the kinetics of the Tl(I) /Tl(Hg) process at dioleoyl phosphatidylcholine (DOPC)- and modified-DOPC-c oated electrodes has been performed using chronoamperometry and cyclic volt ammetry. In this system, the Tl+ reduction mechanism resembles a CrEr type mechanism. The thermodynamic (K) and kinetic (k) parameters were measured a nd conform to a process whereby the Tl+ ion is complexed by the gramicidin in the monolayer K = k(1)/k(-1) is a partition coefficient representing the concentration of Tl+ in the monolayer relative to the concentration of Tl in solution. k = k(1) + k(-1) relates to the rate at which partition prece ding the charge transfer is attained. The values of the rate constants are consistent with the published values of the ion entry and exit rate constan ts of the bimolecular gramicidin channel. Approximate coverage values of gr amicidin available for Tl+ binding and transport can be calculated which ar e low. K decreases with increase in negative potential. K increases by a fa ctor of 5 in layers of DOPC with PS and by a factor of between 2 and 3 in l ayers of DOPC with retinol. k(1) increases in layers of DOPC with PS by a f actor of 10.