Electroreduction of nitrite to nitrogen oxide by a copper-containing nitrite reductase model complex incorporated into collagen film

The electrocatalytic reduction of nitrite to NO by CuMe2bpaCl2, which is a model for the active site of copper-containing nitrite reductase, incorporated into collagen film was investigated. The 77-K EPR spectrum of CuMe2bpaCl2 in the collagen matrix revealed the typical axial signals (g// = 2.26, g⊥ = 2.05, A// = 16.4 mT) of a tetragonal Cu2+ chromophore. The redox potential, which is related to the Cu+/Cu2+ couple, was − 63 mV (∆E = 72 mV) at pH 5.5. In the presence of nitrite, an increase in the cathodic current was observed in the cyclic voltammogram of CuMe2bpaCl2 in the collagen matrix. Upon reaching − 300 mV, a linear generation of NO was observed for the CuMe2bpaCl2/collagen film-coated electrode. The relationship between the rate of NO generation and the nitrite concentration in solution was analyzed using the Michaelis–Menten equation, where Vmax = 3.16 nM s− 1 and Km = 1.1 mM at pH 5.5. The current increase and the reaction rate were dependent on the pH of the solution. The mechanism of nitrite reduction by the copper complex in the collagen matrix was the same mechanism as that of the enzyme in aqueous solution.