ELECTROCHEMICAL STUDIES OF METAL-COMPLEXES IN SODIUM DODECYL-SULFATE MICELLAR SOLUTION

An electrochemical investigation of the effect of sodium dodecyl sulfa te (SDS) surfactant micelles on the redox behavior of the cobalt compl exes [Co(terpy)2](ClO4)2.H2O and [Co(phen)3](ClO4)3.2H2O has been carr ied out in 0.20 M LiCF3SO3 solutions using cyclic voltammetry, chronoa mperometry, and chronocoulometry. The dependence of measured diffusion coefficients on the SDS concentration has been used to estimate micel lar binding constants and partition coefficients for oxidized and redu ced species by fitting D(O) and D(R) values to a two-state model invol ving bound and free complexes. Changes in half-wave potentials with ad ded surfactant are discussed in terms of net stabilization of oxidized and reduced species in micellar subphases and related to values of pa rtition coefficients and diffusion coefficients measured for the redox probes. Estimates of the electrostatic and hydrophobic contributions to micellar binding for different ions have been obtained. Heterogeneo us electron transfer rate constants and exit rates for SDS solubilized Co(terpy)2(3+) have also been measured. The half-life of the first-or der exit rate process for the bound species was found to increase with increased surfactant concentrations.