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THERMAL REQUIREMENTS OF PHOTOSENSITIZED PYRIMIDINE DIMER SPLITTING
Author(s) -
Kim SangTae,
Rose Seth D.
Publication year - 1988
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1988.tb02771.x
Subject(s) - dimer , pyrimidine dimer , indole test , photochemistry , chemistry , intramolecular force , stereochemistry , organic chemistry , biochemistry , dna , dna damage
— A cis, syn ‐pyrimidine dimer (derived from thymine and orotate) covalently linked to 5‐methoxyindole has been studied as a mechanistic model of photosensitized pyrimidine dimer splitting. In this dimer‐indole, photoinitiated electron transfer to the dimer causes splitting in a manner that parallels the mechanism by which the DNA photolyases are thought to act. Dissolved in EPA (diethyl ether‐isopentane‐ethyl alcohol, 5: 5: 1, by vol) at room temperature, the dimer‐indole exhibited indole fluorescence quenching and underwent splitting upon irradiation at 300 nm. In an EPA glass at 77 K, however, no splitting was detectable. To distinguish the effects of temperature and immobilization, photolysis experiments were performed on PMM [poly(methyl methacrylate)] films containing dimer‐indole. In PMM at room temperature, dimer‐indole underwent splitting when irradiated at 300 nm, which indicated that immobilization per se was not responsible for the failure of dimer‐indole to split at low temperature. Furthermore, no splitting was observed when dimer‐indole was irradiated in PMM at 77 K. These results imply that a step following photoinitiated, intramolecular electron transfer from indole to dimer has an insurmountable activation barrier at 77 K. The mechanistic implications for the photolyases are considered.