Arthur L. Thayer

MECHANISMS OF 1,2-DIOXETANE DECOMPOSITION: THE ROLE OF ELECTRON TRANSFER

Abstract— The chemiluminescence from the cleavage of a number of 1,6‐diaryl‐2,5,7,8‐tetraoxabicyclo[4.2.0]octanes 1 has been examined. The ease of oxidation of (object) the aryl moiety strongly influences both the stability and chemiluminescence efficiency of these 1,2‐dioxetanes. When Ar is difficult to oxidize, 1 is comparable in stability to simple. alkyl‐substituted 1,2‐dioxe‐tanes and affords triplet excited states in moderate yield. Both biradical and concerted cleavage mechanisms have been suggested to explain this behavior. However, when Ar is a readily oxidized group, 1 is substantially destahilized and gives excited singlet states in high yield. In this instance 1 is analogous to a number of bioluminescent systems. Cleavage mechanisms involving intramolecular electron transfer are proposed to account for this observation. In certain cases thermolysis of 1 occurs by both types of mechanism in competition, and the electron transfer mechanism may be selectively catalyzed by polar, protic media.

Singlet molecular oxygen in biological systems: Non-quenching of singlet oxygen-mediated chemiluminescence by superoxide dismutase

Summary Chemiluminescence measurements indicate that superoxide dismutase does not significantly quench singlet molecular oxygen. 1-Phospha-2,8,9-trioxaadamantane ozonide is used as a singlet oxygen source. However, superoxide dismutase effectively inhibits the chemiluminescence produced by xanthine-xanthine oxidase or potassium superoxide. It is, therefore, likely that superoxide dismutase produces triplet molecular oxygen from its copper-containing active site during the dismutation of superoxide anion radicals, unlike the non-enzymatic dismutation reaction which yields singlet oxygen.