NDLI: UVC induced oxidation of chloropurines: excited singlet and triplet pathways for the photoreaction

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UVC induced oxidation of chloropurines: excited singlet and triplet pathways for the photoreaction

Content Provider	Royal Society of Chemistry (RSC)
Author	Kazimierczuk, Zygmunt Fontaine-Aupart, Marie-Pierre Tfibel, Francis Bojarska, Elżbieta Mouchard, Claire
Copyright Year	2008
Abstract	The phototransformation of 2-chloro, 6-chloro and 2,6-dichloropurines under UVC excitation (254 nm) has been studied and the major photoproducts have been identified using absorption spectroscopy, HPLC and mass spectrometry. It was shown that hydroxypurines were formed as the main products for all three investigated compounds both in the presence and absence of oxygen. In the case of 6-chloro- and 2,6-dichloropurine, a photodimer is also formed as a minor photoproduct in the absence of oxygen but is efficiently quenched in the presence of oxygen. Nanosecond photolysis experiments also revealed significant intersystem crossing to the triplet state of the chloropurines which has been characterized (transient absorption spectra, triplet formation quantum yields and rate constants of quenching by oxygen, Mn2+ ions and ground state). Experimental evidence allows to conclude that the triplet state is involved in photodimer formation whereas the hydroxypurine is formed from the reaction of the excited singlet state of chloropurines with the solvent (water addition) through heterolytic C–Cl bond rupture. Mass spectrometry and 1H NMR results allowed to propose a chemical pathway for dimer formation in the case of 2,6-dichloropurine in a two-step process: first a homolytic rupture of C–Cl bond in the triplet state of the molecule with the formation of purinyl radicals, which subsequently react with an excess of ground state molecules and/or hydroxypurine primarily formed.
Starting Page	1054
Ending Page	1062
Page Count	9
File Format	HTM / HTML PDF
ISSN	1474905X
Volume Number	7
Issue Number	9
Journal	Photochemical & Photobiological Sciences
DOI	10.1039/b805149f
Language	English
Publisher	Royal Society of Chemistry
Access Restriction	Open
Subject Keyword	Absorption spectroscopy Oxygen Photodissociation High-performance liquid chromatography Protein dimer Pyrimidine dimer Quantum Nanosecond Covalent bond Intersystem crossing Nuclear magnetic resonance Mass spectrometry Solvent
Content Type	Text
Resource Type	Article
Subject	Physical and Theoretical Chemistry

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