Electrocatalytic NADH oxidation using an electrode based on Meldola blue immobilized on silica coated with niobium oxide

The immobilization of meldola blue (MB) on silica gel coated with niobium oxide (SN) and electrochemical investigation of its behavior as well as the electrocatalytical oxidation of nicotinamide adenine dinucleotide in reduced form (NADH) by this modified electrode are described. The modified silica containing 1.4 mmol g(-1) of niobium oxide dispersed on its surface adsorbed 55 mumol g(-1) of MB. SN containing MB adsorbed on its surface (SNMB) was mixed with carbon paste to prepare modified electrodes. Cyclic voltammetry of this modified electrode showed a quite reversible redox couple with a formal potential of -60 mV (vs. SCE) at pH 7.0. assigned to the immobilized MB. This formal potential is 60 mV more positive than that observed for MB in solution and this shift was attributed to the acidity of SN. The formal potential was independent of the solution pH in the range between 4 and S. A linear response range between 1.0 x 10(-5) and 7.50 x 10(-4) mol L-1 NADH concentration at pH 7.0 was observed. The electrocatalytical properties of the electrode to oxidize NADH was investigated and showed an interesting behavior. The heterogeneous electron transfer rate. k(cbp) was 1852 M(-1)s(-1) and the Michaelis-Menten constant, was 0.27 mM at pH 7,0 with the electrode coverage of about 4.4 x 10(-9) mol cm(-2), evaluated from the rotating disk electrode (RDE) experiments. The slight increase in the reaction rate with the solution pH was assigned to the thermodynamic driving force. This behavior can confirm a possible formation of a charge transfer complex between meldola blue and coenzyme.