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EnglishThe TâT photodimerization paths leading to the formation of cyclobutane pyrimidine dimer (CPD) and 6â4 pyrimidine pyrimidone (64-PP), the two main DNA photolesions, have been resolved for a TâT 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 TâT 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 3â²-end, favor this reaction. The oxetane intermediate, leading to a 64-PP adduct, is formed on a singlet TâT 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 T3and a 5â²-Tâ3â²-T charge transfer for CPD and oxetane formation, respectively, thus calling for specific electronic constraints.
| Titolo: | Multiple Electronic and Structural Factors Control Cyclobutane Pyrimidine Dimer and 6â4 ThymineâThymine Photodimerization in a DNA Duplex |
| Autore/i: | Conti, Irene; Martãnez-fernã¡ndez, Lara; Esposito, Luciana; Hofinger, Siegfried; Nenov, Artur; Garavelli, Marco; Improta, Roberto |
| Autore/i Unibo: | |
| Anno: | 2017 |
| Rivista: | |
| Digital Object Identifier (DOI): | http://dx.doi.org/10.1002/chem.201703237 |
| Abstract: | The TâT photodimerization paths leading to the formation of cyclobutane pyrimidine dimer (CPD) and 6â4 pyrimidine pyrimidone (64-PP), the two main DNA photolesions, have been resolved for a TâT 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 TâT 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 3â²-end, favor this reaction. The oxetane intermediate, leading to a 64-PP adduct, is formed on a singlet TâT 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 T3and a 5â²-Tâ3â²-T charge transfer for CPD and oxetane formation, respectively, thus calling for specific electronic constraints. |
| Data stato definitivo: | 2017-11-15T17:07:55Z |
| Appare nelle tipologie: | 1.01 Articolo in rivista |
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