Chem. J. Chinese Universities ›› 2021, Vol. 42 ›› Issue (7): 2136.doi: 10.7503/cjcu20210117

• Article • Previous Articles     Next Articles

Theoretical Study on the Excited State Properties and Photophysical Mechanism of Selenothymine and Adenine Base Pairs in DNA Environment

PENG Qin, FANG Yeguang, ZHANG Tengshuo, CUI Ganglong(), FANG Weihai()   

  1. Key Laboratory of Theoretical and Computational Photochemistry,Ministry of Education,College of Chemistry,Beijing Normal University,Beijing 100875,China
  • Received:2021-02-26 Online:2021-07-10 Published:2021-06-03
  • Contact: CUI Ganglong E-mail:ganglong.cui@bnu.edu.cn;fangwh@bnu.edu.cn
  • Supported by:
    the National Natural Science Foundation of China(21688102)

Abstract:

Multi-state second-order perturbation approach was applied, the combination of quantum mecha-nics/molecular mechanics methods, under the theoretical framework of the QM(MS-CASPT2//CASSCF)/MM, to study the relevant minima, conical intersections, crossing points, and excited-state relaxation paths in the lowest five electronic states(i.e., S0, S1, S2, T2, and T1) of 2- and 4-selenothymine and adenine bases(2SeT-A and 4SeT-A) in DNA. Although 2SeT-A and 4SeT-A share similar electron excitation states, their electron structural characteristics are different due to the different n and π orbitals involved, resulting in a higher vertical and adiabatic excitation energy for 2SeT-A than for 4SeT-A. In addition, both 2SeT-A and 4SeT-A have different minimum energy structures and inactivation pathways in the DNA environment. For 2SeT-A, after excitation, the system first reaches the S2(ππ*) state in the Franck-Condon region, then relaxes to the S2 state minimal energy structure, and finally to the S1nπ*) state. Next, the S1→T1 process with a large S1/T1 spin-orbit coupling reaches the T1(ππ*) state, which can be arrived to the S0 state again through the T1/S0 intersection. But the minimum energy structure of T1 and the barrier of 22.6 kJ/mol between T1/S0 intersection make the system stay in the lowest T1 triplet state for a period of time. 4SeT-A has similar photophysical process of S2→S1→T1, but its S2→S1 internal transformation process needs to overcome the energy barrier of 60.7 kJ/mol. The results reveals the different sources of the excitation state properties and photophysical mechanisms of 2SeT-A and 4SeT-A base pairs in DNA environment, and provides insight into the mechanism, which will help to understand the excitation state properties and photophysical mechanisms of bases substi- tuted by selenium atoms in complex environment.

Key words: Selenothymine, QM/MM, Excitation state property, Photophysics, MS-CASPT2

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