MECHANISM OF A JUMPING OFF FERRICENIUM IN GLUCOSE OXIDASE-D-GLUCOSE-FERROCENE MICELLAR ELECTROCHEMICAL SYSTEMS

Incorporation of ferrocene (Fc), decamethylferrocene (DMFc), and n-dod ecylferrocene (DDFc) into inner cavities of anionic, cationic, and non ionic micelles in aqueous solution tunes their observed redox potentia ls E(1/2). The cyclic voltammetry study showed that anionic micelles o f sodium dodecylsulfate (SDS) decrease while cationic and nonionic mic elles of cetyltrimethylammonium bromide (CTAB) and Triton X-100, in co ntrast, increase E(1/2) of Fc The effect of positively and negatively charged micelles on E(1/2) in the case of DMFc was basically the same. Thus, solubilized ferrocene, but not its decamethyl and dodecyl analo gs, couples electrochemically with glucose oxidase and provides a sign ificant catalytic current in the presence of D-glucose. The rate const ants for the oxidation of the reduced enzyme by the ferricenium ion ar e independent of the nature of the surfactant and, in the presence of 5% EtOH, fall in the range (4.3-5.7) x 10(5) M(-1) s(-1) Based on this observation, a mechanism of the ''jumping off'' ferricenium is presen ted and discussed. It is believed that Fc(+) is captured by the enzyme in the rate-limiting step after its fast reversible dissociation from the micelle. The absence of such a coupling for n-dodecylferrocene in the Triton X-100 and CTAB micelles suggests that the ''jump off'' is likely hampered by the hydrophobic side chain of this ferrocene deriva tive.