Electrochemically triggered reaction of a surface-confined reagent:: Mechanistic and EQCM characterization of redox-active self-assembling monolayers derived from 5,5′-dithiobis(2-nitrobenzoic acid) and related materials

The adsorption processes and electrochemical behavior of DTNB (5, 5'-dithiobis(2-nitrobenzoic acid) adsorbed onto gold electrodes have been investigated in aqueous phosphate buffer/0.1 M NaNO3 electrolyte solutions using cyclic voltammetry in conjunction with the electrochemical quartz crystal microbalance. DTNB adsorbs onto gold electrode surfaces, and upon potential cycling past -0.55V, is transformed into the hydroxylamine which exhibits a well-behaved pH-dependent redox couple centered at -0.04 V at pH 7.0. To elucidate the mechanism of this electrochemically triggered surface-confined transformation, nine different compounds with structures similar to that of DTNB have also been studied. From these studies, it appears that the nitrogroup is responsible for the redox behavior and a mechanism for the overall reaction is proposed. The pH dependence of the redox response has been investigated and the kinetics of electron transfer evaluated. In addition, the EQCM technique has been employed to follow the deposition process in real time as well as the characteristics of the charge transfer associated with the surface-confined redox-active couple. The electrocatalytic activity of such modified electrodes toward the oxidation of NADH has also been explored.