PHOTOCHEMISTRY and PHOTOBIOLOGY WITHOUT LIGHT

Abstract

Abstract-This review covers the literature since 1980 on chemically and enzymatically generated electronically excited species. The emphasis lies on triplet states of carbonyl products that are derived from dioxetanes and dioxetanones as precursors or from suitable enzymatic oxygenations. Singlet oxygen. an important excited state species in biological processes, is not explicitly treated. The utilization of triplet excited carbonyl products to promote photochemical and photobiological transformations by energy transfer are of primordial interest and not the photomechanistic behavior, photophysical properties and inherent photochemical reactions of such excited state species. Thus, the coverage concentrates on photodamage of DNA and RNA., the photochemistry of favins, vitamin D, tryptophan, arachidonic acid, chlorophyll, lipid peroxidation, urocanase activation, excitation of chlorophlasts, and the aerobic oxidation of Schiff bases derived from amino acids and proteins. The potential perspectives of employing authentic dioxetanes and enzymatically generated dioxetane intermediates as effective photon equivalents in photochemotherapy, phototoxicity, photoaffinity labeling and photogenotoxicity are pointed out, in the hope of stimulating more intensive activity in this emerging and novel bioorganic and photobiological field.

Theoretical study of the dark photochemistry of 1,3-butadiene via the chemiexcitation of Dewar dioxetane

“…2,[6][7][8] Since then, chemical reactivity and transformation of excited triplet and singlet species chemically produced in the thermolysis of dioxetanes, dioxetanones, or oxalates have been used for the determination of chemiexcitation yields. 4,5,9 In addition, the chemienergetic species have been used to induce excited-state chemistry of target molecules by energy transfer. [9][10][11] Similar phenomena have been postulated to occur in biological systems catalyzed by enzymes such as peroxidases since the excited species were of the type expected from cleavage of a dioxetane/dioxetanone intermediate.…”

Genotoxicity studies of benzofuran dioxetanes and epoxides with isolated DNA, bacteria and mammalian cells

“…structure 2a in Table I) are most mutagenic [18]. Since dioxetanes serve as efficient chemical source of triplet-excited carbonyl compounds [1] and the S. typhimurium strain TA100 is sensitive to photochemical damage, it was expected that the lesions induced by benzofuran dioxetanes would be ofphotochemica1 origin. However, the DNA lesions inS.…”

“…There is convincing evidence that 1 ,2-dioxetanes are involved in enzymatic oxidation processes [1). For example, they were postulatedas labile intermediates in the dioxygenase-activated aerobic metabolism of arenes.…”

“…Nonetheless, recently we have observed that heteroaromatic dioxetanes such as those from benzofurans 2 [18] and furocoumarins 3 [19] are strongly mutagenic in the S. typhimurium strain TA I 00. In spite of the fact that dioxetanes are effective agents to perform photobiology in the dark [1], the mutagenic darnage in- 2 Sa duced by benzofuran dioxetanes in the S. typhimurium strain TAIOO could not be photoreactivated [11 ], which implies that the DNA Iesions are not pyrimidine dimers.…”

“…( 1) configurated vicinal diol product excludes the popular [6] arene oxide mechanism as possible alternative. Moreover, the fact that chemiluminescence was observed in the reaction of 7 ,8-dihydroxy-7 ,8-dihydrobenzo[a]pyrene with microsomal cytochrome P-450 suggests that a dioxetane intermediate is also involved in this enzymatic oxidation [7].…”