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- Title
Multiple Electronic and Structural Factors Control Cyclobutane Pyrimidine Dimer and 6-4 Thymine-Thymine Photodimerization in a DNA Duplex.
- Authors
Conti, Irene; Martínez‐Fernández, Lara; Esposito, Luciana; Hofinger, Siegfried; Nenov, Artur; Garavelli, Marco; Improta, Roberto
- Abstract
The T-T photodimerization paths leading to the formation of cyclobutane pyrimidine dimer (CPD) and 6-4 pyrimidine pyrimidone (64-PP), the two main DNA photolesions, have been resolved for a T-T step in a DNA duplex by two complementary state-of-the-art quantum mechanical approaches: QM(CASPT2//CASSCF)/MM and TD-DFT/PCM. Based on the analysis of several different representative structures, we define a new-ensemble of cooperating geometrical and electronic factors (besides the distance between the reacting bonds) ruling T-T photodimerization in DNA. CPD is formed by a barrierless path on an exciton state delocalized over the two bases. Large interbase stacking and shift values, together with a small pseudorotation phase angle for T at the 3′-end, favor this reaction. The oxetane intermediate, leading to a 64-PP adduct, is formed on a singlet T→T charge-transfer state and is favored by a large interbase angle and slide values. A small energy barrier (<0.3 eV) is associated to this path, likely contributing to the smaller quantum yield observed for this process. Eventually, a clear directionality is always shown by the electronic excitation characterizing the singlet photoactive state driving the photodimerization process: an exciton that is more localized on T3 and a 5′-T→3′-T charge transfer for CPD and oxetane formation, respectively, thus calling for specific electronic constraints.
- Subjects
CYCLOBUTANE derivatives; PHOTODIMERIZATION; PYRIMIDINES; THYMINE; ELECTRONIC structure
- Publication
Chemistry - A European Journal, 2017, Vol 23, Issue 60, p15177
- ISSN
0947-6539
- Publication type
Article
- DOI
10.1002/chem.201703237