A theoretical study of the light-induced cross-linking reaction of 5-fluoro-4-thiouridine with thymine. Issue 21 (12th May 2017)

• Record Type: Journal Article
• Authors: Chang, Xue-Ping; Xiao, Pin; Han, Juan; Fang, Wei-Hai; Cui, Ganglong
• Is Part Of: Physical chemistry chemical physics. Volume 19:Issue 21(2017)
• Page Start: 13524
• Page End: 13533
• Publication Date: 2017-05-12
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c7cp01511a
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : In contrast to photophysics of thio-substituted nucleobases, their photoinduced cross-linking reactions with canonical nucleobases remain scarcely investigated computationally. Abstract : In contrast to photophysics of thio-substituted nucleobases, their photoinduced cross-linking reactions with canonical nucleobases remain scarcely investigated computationally. In this work, we have adopted combined CASPT2/PCM//CASSCF and B3LYP-D3/PCM electronic structure methods to study this kind of photochemical reaction of 5-fluoro-4-thiouridine (truncated 5-fluoro-1-methyl-4-thiouracil used in calculations) and 1-methylthymine (referred to as thymine for clarity hereinafter). On the basis of CASPT2/PCM computed results, we have proposed two efficient excited-state relaxation pathways to populate the lowest T1 state of the complex of 5-fluoro-1-methyl-4-thiouracil and thymine from its initially populated S2 ( 1 ππ*) state. In the first one, the S2 system first hops to the S1 state via an S2 /S1 conical intersection, followed by a direct S1 → T1 intersystem crossing process enhanced by large S1 /T1 spin–orbit coupling. In the second path, the resultant S1 system first jumps to the T2 state, from which an efficient T2 → T1 internal conversion occurs. The T1 cross-linking reaction is overall divided into two phases. The first phase is a stepwise and nonadiabatic photocyclization reaction, which starts from the T1 complex and ends up with an S0 thietane intermediate. The second phase is a thermal reaction. The system first rearranges its four- and six-membered rings to form three new rings; then, an S0 fluorine atom transfer occurs, followed by the formation of photoproducts. Finally, the present work paves the way for studying light-induced cross-linking reactions of thionucleobases with canonical bases in DNA and RNA.