Bioelectrocatalysis of a water-soluble tetrathiafulvalene2-hydroxypropyl-β-cyclodextrin complex

Water-soluble 2-hydroxypropyl-β-cyclodextrin (hp-β-CyD), a cyclic and non-reducing oligosaccharide, was used to enclose tetrathiafulvalene (TTF) to from a water-soluble complex. The molar ratio of hy-β-CyD to TTF in TTF-saturated solutions was about 2.8 and the complex was much more stable than free TTF in aqueous solutions. The cyclic voltammogram of the TTF-hp-β-CyD complex exhibited two oxidation waves with E_p values of 210 mV (TTF → TTF⁺) and 415 mV (TTF⁺ → TTF²⁺) at a glassy carbon electrode vs. Ag/AgCl. The former was relatively reversible and had a pH-independent E_p, while the latter was not reversible due to the decomposition of TTF²⁺ and had a strongly pH-dependent E_p. Application of this novel complex as a homogeneous mediator for the enzyme-catalyzed electrooxidation of glucose, hypoxanthine and lactate, respectively at a glassy carbon electrode was successfully demonstrated. A well-defined catalytic wave was also obtained from NADH,illustrating the feasibility of the TTF-hp-β-CyD complex for bioreactions involving NADH dehydrogenases. The complex for bioelectrocatalysis was then investigated as membrane electrodes of glucose oxidase and xanthine oxidase. Fast response, high sensitivity and a large range of linearity were observed.