Cyclic voltammetry of aquocobalamin on clay-modified electrodes

Halogenated synthetic compounds are widespread contaminants of the environment. Although corrinoids reductively dehalogenate synthetic contaminants in solution, the redox behavior of sorbed tetrapyrroles has received limited attention. Colloidal clay suspensions were prepared as Ca2+ forms of hectorite (SHCa-1), montmorillonite (SWy-1, Syn-1, and SAz-1), and vermiculite (VTx-1) and spin coated on platinum electrodes. Cyclic voltammetry was performed with the day-modified electrodes immersed in buffered solutions containing 1.0 mM aquocobalamin. Aquocobalamin in the presence of vermiculite-coated electrodes displayed the same cathodic and anodic peak potentials as unmodified electrodes immersed in aquocobalamin solutions. All other clay-modified electrodes shifted cathodic peaks to more negative values, while anodic peak shifts varied with the clay. Hectorite caused the largest shift in formal redox potential (-104 mV) as compared to aquocobalamin in solution. The redox behavior of aquocobalamin as modified by sorption to clay minerals potentially affects dehalogenation rates.of synthetic organic compounds in the environment. Clays lowering the formal redox potential of the tetra pyrrole cre ate a potentially mo re efficient catalyst for pollutant degradation. However, thermodynamic data as obtained using cyclic 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 tetrapyrrole as well as rates of contaminant diffusion to the site of tetrapyrrole sorption.