INCLUSION COMPLEXATION OF TETRATHIAFULVALENE IN CYCLODEXTRINS AND BIOELECTROANALYSIS OF THE GLUCOSE-GLUCOSE OXIDASE REACTION

Tetrathiafulvalene (TTF) forms water-soluble inclusion complexes with alpha-, hp-beta- and gamma-cyclodextrin (CD). Cyclic voltammetry (CV) has been performed at a stationary electrode to characterize these TTF:CD inclusion complexes. The CV analysis yielded average peak separations of 63 mV and diffusion limited currents, indicating completely reversible electron transfer. The half-wave potential (E(1/2)) of the complex shifted to more positive values with increasing CD concentration, permitting use of a modified Nernst equation to estimate the complexation ratio and the equilibrium formation constant (K-form) of the complexes. The complexation ratio was determined as 1:2, 1:1 and 1:1 for TTF with alpha-CD, hp-beta-CD and gamma-CD, respectively. The K-form for these complexes was then estimated to be 5.44 x 10(3) m(6)/kmol(2), 5.40 x 10(3) m(3)/kmol and 0.141 x 10(3) m(3)/kmol. The diffusion coefficients (Do) for 1 mol/m(3) TTF in alpha-CD varied from 4.44 x 10(-11) to 0.76 x 10(-11) m(2)/s as the alpha-CD concentration increased from 3 to 50 mol/m(3). The D-0 values for hp-beta-CD varied from 12.9 x 10(-11) to 4.03 x 10(-11) m(2)/s over the same cyclodextrin range whereas those of gamma-CD ranged from 2.20 x 10(-12) to 1.75 x 10(-12) m(2)/s. CV curves for TTF:hp-beta-CD in the presence of glucose and GOx showed a large anodic current with no discernible peaks, indicating bioelectrocatalysis. The ratio of this current to the diffusion limited current was used to determine the second-order homogeneous rate constant k(s) for the reaction with GOx, which demonstrated the efficiency of the inclusion complex as a mediator. The k(s) value for 1 mol/m(3) TTF decreased from 3.84 x 10(5) to 1.04 x 10(5) m(3)/kmols with an increase in hp-beta-CD concentration from 3 to 15 mol/m(3). Extremely high diffusion and kinetic parameters in 3 mol/m(3) CD solutions were due to insolubility of TTF at low CD concentrations, and indicated that the CD concentration must be maintained above this level.