Abstract
The cyclobutane pyrimidine dimer (CPD) formed between two adjacent thymine bases is the most abundant DNA photolesion induced by UV radiation. The quantum yield of this reaction is on the order of ~1% in DNA. This small quantum yield hampers the study of damage formation in naturally occurring DNA. Investigations with increased accuracy become possible for a locked nucleotide model compound TLpTLwhich exhibits a quantum yield of about 10% for CPD formation. Time resolved IR spectroscopy on TLpTLand two other DNA model compounds (TpT and (dT)18) reveals that: (i) The absorption changes after ~1 ps are due to CPD photodamage. (ii) The quantum efficiency of CPD formation on the few picosecond time scale equals the quantum efficiency reported in stationary experiments. CPD photodamage formation in the investigated DNA constructs is thus predominantly formed from the primarily photoexcited singletππ*state, whereas the triplet channel does not play an essential role.
Highlights
UV radiation is known to be responsible for a variety of photo lesions in DNA
The presented results show that in TLpTL and the other investigated dimerizable thymine model systems characteristic marker bands for cyclobutane pyrimidine dimer (CPD) formation are present after 1 ps
There is no signal increase on the 100 ps or ns time scale that could be related to further CPD formation
Summary
UV radiation is known to be responsible for a variety of photo lesions in DNA. It is one of the most important external hazards for the integrity of the genetic information and may lead to skin cancer [24]. Irradiation experiments on single thymine bases in diluted solutions demonstrate that CPD’s can be formed in a diffusion limited process via a long lived triplet state [11].
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