CYCLIC VOLTAMMETRY OF AQUOCOBALAMIN ON CLAY-MODIFIED ELECTRODES

Halogenated synthetic compounds are widespread contaminants of the env ironment. Although corrinoids reductively dehalogenate synthetic conta minants in solution, the redox behavior of sorbed tetrapyrroles has re ceived limited attention. Colloidal clay suspensions were prepared as Ca2+ forms of hectorite (SHCa-1), montmorillonite (SWy-1, Syn-1, and S Az-1), and vermiculite (VTx-1) and spin coated on platinum electrodes. Cyclic voltammetry was performed with the day-modified electrodes imm ersed in buffered solutions containing 1.0 mM aquocobalamin. Aquocobal amin in the presence of vermiculite-coated electrodes displayed the sa me cathodic and anodic peak potentials as unmodified electrodes immers ed in aquocobalamin solutions. All other clay-modified electrodes shif ted cathodic peaks to more negative values, while anodic peak shifts v aried with the clay. Hectorite caused the largest shift in formal redo x potential (-104 mV) as compared to aquocobalamin in solution. The re dox behavior of aquocobalamin as modified by sorption to clay minerals potentially affects dehalogenation rates.of synthetic organic compoun ds in the environment. Clays lowering the formal redox potential of th e tetra pyrrole cre ate a potentially mo re efficient catalyst for pol lutant degradation. However, thermodynamic data as obtained using cycl ic voltammetry cannot be used to make definitive predictions about the kinetics of contaminant dehalogenation. Reductive dehalogenation will be a function of altered eletrochemical properties of the tetrapyrrol e as well as rates of contaminant diffusion to the site of tetrapyrrol e sorption.