Electrocatalytic properties of a modified electrode with an asymmetric nickel(II)-tetraaza[14]annulene complex

Modified electrodes are made by incorporting proper modifiers on electrode surfaces. They are promising for minimizing overpotential, enhancement of selectivity, improvement of sensitivity, and prevention of electrode fouling,(1,2) A large number of tetraaza macrocyclic ligands containing various metals have received much attention due to the usefulness as models for porphyrins and corrin rings in biological systems.(3-5) Many of these complexes have been found to be effective catalysts in the solid state for various substrates such as CO2, O-2, olefin, alcohol, NO, N2O, NO3-, and dithiodipropionic acid.(6-10) Most of tetraaza macrocyclic complexes reported have symmetric structure. The macrocyclic complex such as Ni(II)-5,7,12,14-tetramethyldibenzo[b,i] [1,4,8,11]tetraaza-[14]annulene complex can be deposited on the electrode surface by oxidative electropolymerization and the film of which catalyzes the reduction of CO2.(11) We have synthesized new Ni(II)-tetraaza tetraaza[14]annulene complexes which have asymmetric structures.(12) The asymmetric complexes are expected that the electrochemical characteristics are similar to those of the symmetric ones. Hence we intended to apply the electrochemical characteristics of the newly synthesized complexes to the electrocatalytic analysis of substrates. In this paper we describe electrochemical catalytic properties of the asymmetric Ni(II)-macrocyclic complex containing dianionic benzotetraaza[14]annulene ligand. The glassy carbon electrodes modified with the asymmetric Ni(II)-tetraaza[14]annulene complex (polymer modified GC electrode) is applied to the electrocatalytic detection for the reduction of oxygen and the oxidations of oxalate and L-ascorbic acid. The stability and the effect of the polymer thickness on the responses of the electrodes are also described.