Quenching of triplet acetone by derivatives of sorbic acid, a conjugated diene able to halt melanocyte DNA pyrimidine dimerization in the dark. Triplet carbonyls generated in vivo are endowed with the potentiality to trigger typically photochemical reactions in the dark leading to loss or gain of cellular functions. This isthe case of DNA cyclobutane pyrimidine dimerization reported to occur in melanocytes several hours after UV light exposure (Brash, Douki, Bechara, and coworkers, Science2015). Electronic excitation of DNA bases was reached by triplet species produced by the endogenous peroxynitrite-mediated oxidation of melanin. This system will be mimicked using tetraethyl dioxetane as a clean source of triplet acetone, which canbe monitored by energy transfer to fluorescent sodium 9,10-dibromoanthracene-2-sulfonate (DBAS) and quenching by sorbic acid derivatives (trans,trans-2,4-hexadienoates, conjugated dienes). In comparison, triplet acetone will eventually also be generated by the aerobic oxidation of isobutene catalyzed by HRP (horseradish peroxidase). Cis, trans isomerization of the exciplex diene-triplet acetone is expected to occur and allow us to choose the prevalent isomer as a triplet carbonyl marker invivo experiments. In addition, sorbic acid will be modified by esterification with a long chain alcohol or a cell penetrating peptide (CPP) aiming to increase sorbate cellular incorporation and quenching of triplet carbonyl into melanocyte cultures to prevent "dark" pyrimidine dimerization. The experiments will require the preparation of TMDand CPPs, Stern-Volmer plots in a illuminometer, and the separation of cis, transsorbate isomers by HPLC. The results of this project may corroborate a connection between generation of CPDs in the absence of light and melanocyte carcinogenesis.
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