Abstract
In the early seventies, Giuseppe Cilento (Sao Paulo University), Emil White (Johns Hopkins University) and Angelo Lamola (AT&T Bell Laboratories) postulated that typical photochemical reactions could occur in parts of living organisms if coupled to enzymatic sources of electronically excited products. Their paradoxical hypothesis of photochemistry without light was chemically anchored on the synthesis and weak chemiluminescence of several 1,2-dioxetanes, unstable cyclic peroxides whose thermal cleavage produces long-lived and reactive triplet carbonyls. Collisional reactions or energy transfer of triplet species to cellular targets could eventually result in photo products that potentially trigger normal or pathological responses. These ideas flourished in the labs of various researchers who attempted to explain the presence and biological roles of dark secondary metabolites, including plant hormones, pyrimidine dimers, alkaloid lumi-isomers, protein adducts, and mitochondrial permeators, thereby broadening the field of photobiology.
Highlights
Chemiluminescence (CL)[1] and bioluminescence (BL)[2] are cold and visible light emissions from chemical reactions in the absence and in the presence of enzymes, respectively. These phenomena are the opposite of photochemical reactions, whose chemical transformations are initiated by light
Other classical CL processes with wide analytical application potential are (i) the transition metal-catalyzed reaction of lucigenin (10,10'-dimethyl-9,9'-biacridylium salt) with hydrogen peroxide (Figure 1b) used mainly for transition metal quantification, and as a detection system for oxidative metabolism, and (ii) the base-catalyzed reaction of activated oxalate esters with hydrogen peroxide in the presence of highly fluorescent compounds called activators (ACT, Figure 1c), such as rubrene, perylene, 9,10-diphenylanthracene, chlorophyll, which have been employed for sensitive hydrogen peroxide and fluorescent compounds quantification
This review updates the advances that further corroborate Cilento-Lamola-White hypothesis of “photo(bio)chemistry without light.”. It emphasizes that photoexcited biomolecules play crucial roles in living organisms, e.g., chlorophyll in photosynthesis, rhodopsin in vision, and phytochrome in phototropism, and that chemically and enzymatically generated excited products - triplet carbonyls and singlet oxygen - may trigger important biological events in tissues never exposed to light
Summary
Chemiluminescence (CL)[1] and bioluminescence (BL)[2] are cold and visible light emissions from chemical reactions in the absence and in the presence of enzymes, respectively. Development of a wide variety of analytical assays of environmental, clinical, biological and forensic samples.[3] One of the most important and well-known CL transformations is the oxidation of luminol (5-aminophthalhydrazide) catalyzed by many transition metals (Figure 1a) and widely employed in the detection of hydrogen peroxide and a vast number of transition metal ions. It is used, for example, in the characterization of redox imbalance in cells and biological tissues, as a sensitive detection system in immunoassays or in an antioxidant capacity assay. Emil White contributed to the development of this area by describing the synthesis and properties of luminol and the firefly luciferin, two of the luminescent systems most exhaustively studied and widely used in analytical kits for pure and applied chemistry.[1,2] form of electronic excited products, which either emit light or undergo photochemical changes
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