Electrochemistry of methanofullerenes embedded in hydrophobic ammonium cation films

The electrochemical behavior of several methanofullerenes, including methyl-C₆₁-propionic acid esters (Ph-C₆₁-(CH₂)₂COOC _n H_{2n + 1}, n = 1–4, 8), in tetraoctyl- and didodecyldimethylammonium bromide films on conducting glass was studied. A cyclic voltammetry study showed that the introduction of methanofullerene derivatives in a cation matrix led to redox transformations of these compounds at potentials accessible for aqueous solutions. The shift of their formal potentials toward positive values is mainly caused by the electrostatic interactions of the reduction products (methanofullerene anions) with the matrix cations. The chemical stability of the reduction products is provided by their hydrophobic microenvironment in the matrix in all cases. This makes it possible to perform quasireversible redox transformations in neutral aqueous media. The duration of the adjustment of the structure of the coating depends on the solvent used for its preparation, the length of the alkyl radical in the ester group of methanofullerene, and the length of the alkyl chain between the cyclopropane fragment and the COOC _n H_{2n + 1} group. The redox potentials of methanofullerene Ph-C₆₁-(CH₂)₂COOC₂H₅ incorporated in the didodecyldimethylammonium bromide film lie in the range of higher negative values relative to the potentials of the compound in the tetraoctylammonium bromide film.