Chemiexcitation: Mammalian Photochemistry in the Dark †

A 1,2-dioxetane, which thermally decomposes between the two oxygens and two carbons to yield two carbonyls, one of which is excited to a high-energy triplet state in a process termed “chemiexcitation”. Chemiexcited molecules underlie invertebrate bioluminescence but recently have been found to occur in mammalian cells, sometimes causing pathogenic effects. AbstractLight is one way to excite an electron in biology. Another is chemiexcitation, birthing a reaction product in an electronically excited state rather than exciting from the ground state. Chemiexcited molecules, as in bioluminescence, can release more energy than ATP. Excited states also allow bond rearrangements forbidden in ground states. Molecules with low-lying unoccupied orbitals, abundant in biology, are particularly susceptible. In mammals, chemiexcitation was discovered to transfer energy from excited melanin, neurotransmitters, or hormones to DNA, creating the lethal and carcinogenic cyclobutane pyrimidine dimer. That process was initiated by nitric oxide and superoxide, radicals triggered by ultraviolet light or inflammation. Several poorly understood chronic diseases share two properties: inflammation generates those radicals across the tissue, and cells that die are those containing melanin or neuromelanin. Chemiexcitation may therefore be a pathogenic event in noise- and drug-induced deafness, Parkinson's disease, and Alzheimer's; it may prevent macular degeneration early in life but turn pathogenic l...
Source: Photochemistry and Photobiology - Category: Science Authors: Tags: Special Issue Invited Review Source Type: research