Immobilized nitro-fluorenone derivatives as electrocatalysts for NADH oxidation

A new family of redox mediators, nitro-fluorenone derivatives, is used to modify the surface of glassy carbon electrodes. The stable, adherent thin layer can be transformed electrochemically into the corresponding hydroxylamine compound. The completely reversible two-electron oxidation of the hydroxylamine group leads to the nitroso compound, which exhibits high catalytic activity in the electrooxidation of reduced nicotinamide coenzyme (NADH). A gradual shift of the redox potential towards more positive values was observed when increasing the number of NO, substituents in the catalyst molecule. Oxidation of NADH at potentials as low as -50 mV versus Ag \ AgCl was obtained, and catalytic currents are proportional to the concentration of NADH over the range 5 mu M-2 mM. The rate constant for the catalytic process has been evaluated by cyclic voltammetry and rotating disc electrode measurements and typical values of the order of 10(4) M-1 s(-1) are obtained. (C) 1999 Elsevier Science S.A. All rights reserved.