Ca2+ enhanced electrocatalytic oxidation of NADH by immobilized nitro-fluorenones

Glassy carbon electrodes are modified with nitro-fluorenone derivatives, a new family of catalyst precursors for electrocatalytic nicotinamide adenine dinucleotide (NADH) oxidation. One of the nitro substituents is electrochemically converted into a reversible NO/NHOH redox couple producing a very efficient mediator for the electrooxidation of the coenzyme. The catalytic efficiency can be enhanced by adding Ca2+ ions to the electrolyte, leading most likely to a specific complexation with the phosphate groups of the coenzyme. This makes NADH less hydrophilic and therefore favors its contact with the organic catalyst monolayer. A further increase in catalytic activity is obtained by introducing a carboxy group into the catalyst molecule. In this case Ca2+ seems to act as a bridging ion between NADH and the catalyst, coordinating their interaction and thus enhancing the electron transfer efficiency. (C) 1999 Elsevier Science S.A. All rights reserved.