| Abstract: | The chemiluminescence reaction of lucigenin (Luc2+?2NO3?, N,N′‐dimethyl‐9,9′‐biacridinium dinitrate) at gold electrodes in dioxygen‐saturated alkaline aqueous solutions (pH 10) was investigated in detail by the use of electrochemical emission spectroscopy. We noted that both O2 and Luc2+ are reduced on a gold electrode in aqueous solution of pH 10 in almost the same potential region. From this fact, we expected chemiluminescence based on a radical–radical coupling reaction of superoxide ion (O2·?) and one‐electron reduced form of Luc2+ (Luc·+, a radical cation). Chemiluminescence was actually observed in the potential range where O2 and Luc2+ were simultaneously reduced at the electrodes. The effects were examined upon addition of enzymes, i.e. superoxide dismutase (SOD) and catalase, into the solution and the substitution of heavy water (D2O) for light water (H2O) as a solvent on the chemiluminescence. In the presence of native and active SOD, chemiluminescence was completely absent. On the other hand, chemiluminescence was observed, unchanged in the presence of either denatured and inert SOD or catalase. In addition, the amount of chemiluminescence in D2O solution was about three times greater than that in H2O solution. These results, together with cyclic voltammetric results, suggest that O2·? participates directly in the chemiluminescence but H2O2 does not, and the chemiluminescence results from the coupling reaction between O2·? and Luc·+ under the present experimental conditions. These chemically unstable species, O2·? and Luc·+, are produced during the simultaneous electroreduction of O2 and Luc2+. The coupling reaction between those radical species would lead to the formation of a dioxetane‐type intermediate and, finally, to chemiluminescence. The chemiluminescence reaction mechanism is discussed. Copyright © 2002 John Wiley & Sons, Ltd. |
