[26] Low-level chemiluminescence as an indicator of singlet molecular oxygen in biological systems

Abstract

Because of its high reactivity, 1 O 2 may be classed as one of the aggressive oxygen species known to arise in biological systems. Chemically, the reactions include addition to olefins (ene reactions) leading to allylic hydroperoxides, additions to diene systems leading to endoperoxides, and further types of reactions leading to dioxetanes or oxidation of certain heteroatoms. Photon counting has been applied to biological systems, and recently, evidence has accumulated that low-level chemiluminescence in the near-infrared provides useful information on oxidative processes in cells and tissues. Advantages of the technique are that it is noninvasive and provides continual monitoring. Major biological sources of 1 O 2 can be grouped into those systems involving the interaction of organic oxygen radicals, such as lipid peroxy radicals and that arise from lipid peroxidation, and those which involve reactions of reduced oxygen intermediates, such as O 2 · - , H 2 O 2 , HO·. A third group might be represented by those systems that probably involve an enzymatic activation of oxygen––that is, cyclo-oxygenase activity during prostaglandin biosynthesis. Photosensitization reactions represent a fourth category. 1 O 2 in general will arise in very low yield and must be considered as a side-product of major radical processes. This implies possible pitfalls in the interpretation of low-level chemiluminescence measurements, and extrapolation from such measurements to other reactions must be made with due caution in each case.