Mechanisms and energetics of benzophenone photosensitized thymine damage and repair from Paternò-Büchi cycloaddition

• Published in: Physical chemistry chemical physics : PCCP Vol. 25; no. 24; pp. 1652 - 16526
• Main Authors: Su, Yingli, Shen, Yan, Li, Xiangyuan, Ren, Haisheng
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 21.06.2023
• Subjects: Benzophenones - chemistry; Bonding; Covalent bonds; Cycloaddition; Cycloaddition Reaction; Damage; Photosensitivity; Ring opening; Thymine; Thymine - chemistry
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d3cp00482a

Here, we report the detailed mechanisms of benzophenone (BZP) photosensitized thymine damage and repair by Paternò-Büchi (PB) cycloaddition. It was found that the head-to-head and head-to-tail PB cycloadditions lead to the formation of the C-O bonds in the 3 (nπ*) state and the 3 (ππ*) state, respectively. The conical intersection occurs before the head-to-tail C-O bonding. Then, the C-C bonds are formed via intersystem crossing (ISC). The C-O bonding is the rate-determining step of PB cycloaddition. For the cycloreversion reactions, the ring-opening processes completely occur in the singlet excited states of oxetanes. The head-to-head oxetane goes through a conical intersection before cycloreversion with a little energy barrier of 1.8 kcal mol −1 . The head-to-tail oxetane splits without a barrier. Then, the ISC processes take place to restore thymine. Throughout the ring-closing and ring-opening processes, ISC plays an important role. These findings are in good agreement with the available experimental findings. We hope that this comprehensive work can provide a deeper understanding of photosensitive DNA damage and repair. Here, we report the detailed mechanisms of benzophenone (BZP) photosensitized thymine damage and repair by Paternò-Büchi (PB) cycloaddition.