Cyclic voltammetry of ferrocene carboxylic acid cyclodextrin inclusion complexes

The cyclic voltammetry of ferrocene carboxylic acid (FcA^-) was studied in the presence of α, β and γ cyclodextrin (CD). CD affects the magnitude of the peak currents and the position of the peak potentials of the ferrocene carboxylic acid system. A model was set up to simulate the effect of CDs on the electrochemistry of the above species, and also to characterise the formation of the inclusion complexes. Formation constants for the complexes were evaluated in aqueous solution by comparing simulated voltammograms and practical results. It is found that the use of peak potentials (E_f, E_b) rather than formal potentials of FcA^- (E⁰₁′), and the FcA^-CD complex (E⁰₂′), in the simulation is more valid in the evaluation of the formation constants. The ability of the CD isomers to form complexes was found to follow the order β > γ > α. A brief study of the interactions of ferrocene dicarboxylic acid with CDs showed no evidence of second sphere complex formation. It was found also that cyclodextrins enhanced the solubility of unsubstituted ferrocene in water.