National Research Council of Canada. NRC Biotechnology Research Institute
Tetrathiafulvalene (TTF) forms water-soluble inclusion complexes with α-, hp-β- and γ-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 () 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 (Kform) of the complexes. The complexation ratio was determined as 1:2, 1:1 and 1:1 for TTF with α-CD, hp-β-CD and γ-CD, respectively. The Kform for these complexes was then estimated to be 5.44 × 10³ m⁶/kmol², 5.40 × 10³ m³/kmol and 0.141 × 10³ m³/kmol. The diffusion coefficients (Do) for 1 mol/m³ TTF in α-CD varied from 4.44 × 10⁻¹¹ to 0.76 × 10−11 m²/s as the α-CD concentration increased from 3 to 50 mol/m³. The Do values for hp-β-CD varied from 12.9 × 10⁻¹¹ to 4.03 × 10⁻¹¹ m²/s over the same cyclodextrin range whereas those of γ-CD ranged from 2.20 × 10−12 to 1.75 × 10−12 m2/s. CV curves for TTF: hp-β-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 ks for the reaction with GOx, which demonstrated the efficiency of the inclusion complex as a mediator. The ks value for 1 mol/m3 TTF decreased from 3.84 × 10⁵ to 1.04 × 10⁵ m³/kmol s with an increase in hp-β-CD concentration from 3 to 15 mol/m³. Extremely high diffusion and kinetic parameters in 3 mol/m³ CD solutions were due to insolubility of TTF at low CD concentrations, and indicated that the CD concentration must be maintained above this level.
Chemical Engineering Science50, no. 12 (June 1995): 1867–1876.