Aqueous electrochemistry of a C-60-bearing artificial lipid bilayer membrane film immobilized on an electrode surface: Thermodynamics for the bindingof tetraalkylammonium ion to the fullerene anion

Thermodynamics for the binding of electrolyte cations, in particular, tetra alkylammonium ions, to the electrogenerated radical anion and the dianion o f the fullerene moieties in a molecular-bilayer membrane film of C-60-beari ng artificial lipid, 1, cast on an electrode surface was described. The the oretical treatment predicts a linear relationship between the half-wave pot ential (E-1/2) for the electrode reaction and electrolyte concentration in the film (c) at higher concentrations and enables us to obtain the number o f bound cation and binding constant, respectively, from the slope and inter cept of the E-1/2-ln c plot. We measured differential pulse voltammograms f or a cast film of 1 on a basal plane graphite electrode in aqueous solution containing tetraethylammonium chloride (or tetra-n-butylammonium chloride) + KCl = 0.5 M and found that E-1/2-ln c, plots for the modified electrodes are linear in a concentration range of ca. 0.002-0.14 M, where c(s) is the concentration of ammonium electrolytes in the solution phase. The analysis of the plot reveals that the fullerene radical anion forms a 1:1 complex w ith both tetraethylammonium and tetra-n-butylammonium cations and that the fullerene dianion forms a 1:2 complex with tetra-n-butylammonium cations. T he binding constants K-1 for the binding of tetraethylammonium and tetra-n- butylammonium cations to radical anions of the fullerene moieties was deter mined to be 7.93 x 10(3) and 1.71 x 10(8) M-1, respectively, provided that the partition coefficients (c/c(s),) of the tetraalkylammonium ions are uni ty.