Abstract
(6-4) Photolesions between adjacent pyrimidine DNA bases are prone to secondary photochemistry. It has been shown that singlet excited (6-4) moieties form Dewar valence isomers as well as triplet excitations. We here report on the triplet state of a minimal model for the (6-4) photolesion, 1-methyl-2(1H)-pyrimidinone. Emphasis is laid on its ability to abstract hydrogen atoms from alcohols and carbohydrates. Steady-state and time-resolved experiments consistently yield bimolecular rate constants of ∼10(4) M(-1) s(-1) for the hydrogen abstraction. The process also occurs intramolecularly as experiments on zebularine (1-(β-d-ribofuranosyl)-2(1H)-pyrimidinone) show.
Highlights
2(1H)-Pyrimidinone can be regarded as the basic chemical motif from which many natural compounds such as orotic acid or pyrimidine DNA/RNA bases can be derived
For nuclear magnetic resonance (NMR) experiments, the illumination was stopped prior to complete conversion so that residual 1MP could serve as an internal standard. 1H-NMR spectra were taken with a Bruker Avance III spectrometer at 600 MHz
A characteristic positive absorption band peaking at approximately 430 nm, which is flanked by flat positive contributions for longer as well as shorter wavelengths, can be recognized
Summary
2(1H)-Pyrimidinone (see Fig. 1, P) can be regarded as the basic chemical motif from which many natural compounds such as orotic acid or pyrimidine DNA/RNA bases can be derived. ISC results in the population of a triplet state with a quantum yield φisc in the range of 0.02–0.1 (all quantum yields are reported as decimal fractions). As a result of oxygen quenching of 3(dRMP)* singlet oxygen is formed.[9] In addition, the formation of hydroxyl radicals was detected These two reactive oxygen species (ROS) are known to lead to oxidatively generated purine damages.[15,16]. We here present steady-state and flash-photolysis experiments which show that triplet excited pyrimidinones abstract hydrogen atoms from carbohydrates and related molecules. The findings are compared to results of zebularine, 2(1H)-pyrimidinone N-glycosidically bonded to β-D-ribose In this compound the abstraction occurs intramolecularly
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Schedule a callMore From: Photochemical & photobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology
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