Mechanism of the Decay of Thymine Triplets in DNA Single Strands

Abstract

The decay of triplet states and the formation of cyclobutane pyrimidine dimers (CPDs) after UV excitation of the all-thymine oligomer (dT)18 and the locked dinucleotide TLpTL were studied by nanosecond IR spectroscopy. IR marker bands characteristic for the CPD lesion and the triplet state were observed from ∼1 ns (time resolution of the setup) onward. The amplitudes of the CPD marker bands remain constant throughout the time range covered (up to 10 μs). The triplet decays with a time constant of ∼10 ns presumably via a biradical intermediate (lifetime ∼60 ns). This biradical has often been invoked as an intermediate for CPD formation via the triplet channel. The present results lend strong support to the existence of this intermediate, yet there is no indication that its decay contributes significantly to CPD formation.

Triplet‐Induced Lesion Formation at CpT and TpC Sites in DNA

“…In particular it was found that under UVC irradiation direct excitation of thymine bases in TT sequences is the major pathway forming CPD lesions within 1 ps via a singlet excited state . Population of the triplet state via intersystem crossing can also yield CPD lesions but is limited by the overall triplet yield on the order of 0.01 and a comparatively small quantum yield for dimerization to occur from this state …”

Identification of charge separated states in thymine single strands

“…This matches our recent findings that the triplet excited thymine in (dT) 18 exhibits a lifetime of 10 ns and decays via the formation of a biradical and not via a CT state. 25 In a recent quantum chemical study, CT states between thymine bases have been discussed to be the starting point for the formation of the (6-4) lesion. 17 The decay of such a charge transfer state was predicted to yield oxetane intermediates, as precursors of the (6-4) adduct.…”

Aerobic oxidation of alcohols on Au/TiO2 catalyst: new insights on the role of active sites in the oxidation of primary and secondary alcohols

“…In Fig. 7a, b, the values of the C 6 -C 6 0 and C 5 -C 5 0 distances and average angle formed by the velocity vectors of the atoms C 5 and C 5 0 with the C 5 -C 5 0 vector (h 5 and h 5 0 ), and by the velocity vectors of the atoms C 6 and C 6 0 with the C 6 -C 6 0 vector (h 6 and h 6 0 ), are plotted at the moment of the 3 BR/S 0 transition. Those trajectories that underwent dimerization are represented by green pentagons.…”

“…This photolesion, which can take place in both the singlet and triplet manifolds, has been extensively investigated spectroscopically [2][3][4][5][6][7] and computationally [8][9][10][11][12][13][14][15]. The triplet pathway is a much slower process [7] and exhibits a smaller yield [6,16] than the singlet mechanism due to inefficient intersystem crossing. As a consequence, this pathway yields very weak spectroscopic signals that preclude unambiguous statements regarding the mechanism [5][6][7].…”

“…The triplet pathway is a much slower process [7] and exhibits a smaller yield [6,16] than the singlet mechanism due to inefficient intersystem crossing. As a consequence, this pathway yields very weak spectroscopic signals that preclude unambiguous statements regarding the mechanism [5][6][7]. In order to enhance the triplet signals, photosensitization is commonly used, increasing the ThiT dimerization yield [5,[17][18][19].…”