Immobilized nitro-fluorenone derivatives as electrocatalysts for NADH oxidation

A new family of redox mediators, nitro-fluorenone derivatives, is used to m odify the surface of glassy carbon electrodes. The stable, adherent thin la yer can be transformed electrochemically into the corresponding hydroxylami ne compound. The completely reversible two-electron oxidation of the hydrox ylamine 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 obse rved when increasing the number of NO, substituents in the catalyst molecul e. Oxidation of NADH at potentials as low as -50 mV versus Ag \ AgCl was ob tained, and catalytic currents are proportional to the concentration of NAD H over the range 5 mu M-2 mM. The rate constant for the catalytic process h as been evaluated by cyclic voltammetry and rotating disc electrode measure ments and typical values of the order of 10(4) M-1 s(-1) are obtained. (C) 1999 Elsevier Science S.A. All rights reserved.