Photosensitized Thymine Dimerization via Delocalized Triplet Excited States

• Published in: Chemistry : a European journal Vol. 21; no. 47; pp. 17051 - 17056
• Main Authors: Miro, Paula, Lhiaubet-Vallet, Virginie, Marin, M. Luisa, Miranda, Miguel A.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 16.11.2015; WILEY‐VCH Verlag; Wiley; Wiley Subscription Services, Inc
• Subjects: Chemical reactions; Chemistry; Chemistry, Multidisciplinary; Cycloaddition Reaction; Degrees of freedom; Dimerization; Dimers; DNA damage; Energy Transfer; Excitation; Formations; Mathematical analysis; nucleobases; Photochemistry; Photosensitizing Agents - chemistry; Physical Sciences; Pyrimidine Dimers - chemistry; reaction mechanisms; Science & Technology; Stereoisomerism; Thymine; Thymine - chemistry; Thymine - metabolism; ROOM-TEMPERATURE; DNA damage; DNA-DAMAGE; dimerization; reaction mechanisms; 6-4 PHOTOPRODUCT; CYCLOADDITION; CYCLOBUTANE PYRIMIDINE DIMERS; ELECTRON-TRANSFER; nucleobases; photochemistry; DIELS-ALDER REACTION; BENZOPHENONE; ENERGY-TRANSFER; PATERNO-BUCHI
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201502719

A new mechanism of photosensitized formation of thymine (Thy) dimers is proposed, which involves generation of a delocalized triplet excited state as the key step. This is supported by chemical evidence obtained by combining one benzophenone and two Thy units with different degrees of freedom, whereby the photoreactivity is switched from a clean Paternò–Büchi reaction to a fully chemo‐, regio‐, and stereoselective [2+2] cycloaddition. Nucleobase dimerization: A new mechanism of photosensitized formation of thymine dimers is proposed. When the sensitizer (Sens) and the two thymine units (Thy) can adopt a free relative arrangement, a 3[Sens⋅⋅⋅Thy]* exciplex can be formed with the appropriate geometry to assemble a triplet triplex 3[Sens⋅⋅⋅Thy⋅⋅⋅Thy]*, which ultimately affords a thymine cyclobutane dimer ThyThy (see scheme).