Acta Chim. Sinica ›› 2018, Vol. 76 ›› Issue (6): 475-482.DOI: 10.6023/A17120557 Previous Articles     Next Articles

Article

实验与理论研究G-四链体中鸟嘌呤自由基阳离子脱质子反应

王英辉a,b, 节家龙a,b, 赵红梅a,b, 白羽a, 秦佩萱c, 宋迪a,b   

  1. a 中国科学院化学研究所 北京分子科学国家实验室 北京 100190;
    b 中国科学院大学 北京 100049;
    c 北京市三帆中学 北京 100088
  • 收稿日期:2017-12-27 出版日期:2018-06-15 发布日期:2018-04-20
  • 通讯作者: 宋迪,E-mail:songdi@iccas.ac.cn E-mail:songdi@iccas.ac.cn
  • 基金资助:

    项目受国家自然科学基金(Nos.21773257,21373233和91441108)资助.

Deprotonation of Guanine Radical Cation in G-Quadruplex: A Combined Experimental and Theoretical Study

Wang Yinghuia,b, Jie Jialonga,b, Zhao Hongmeia,b, Bai Yua, Qin Peixuanc, Song Dia,b   

  1. a Beijing National Laboratory for Molecular Science(BNLMS), Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190;
    b University of Chinese Academy of Sciences, Beijing 100049;
    c Beijing Sanfan Middle School, Beijing 100088
  • Received:2017-12-27 Online:2018-06-15 Published:2018-04-20
  • Contact: 10.6023/A17120557 E-mail:songdi@iccas.ac.cn
  • Supported by:

    Project supported by the National Natural Science Foundation of China (Nos. 21773257, 21373233 and 91441108).

G-Quadruplex can be a promising candidate as molecular electronic device due to the ability of transferring hole. Extensive studies have reported that fast deprotonation of guanine radical cation (G·+) to form a neutral radical G(-H)· is the most important reaction in competition with hole transfer in DNA, hindering potential applications of DNA in molecular electronics. We thus carry out joint experimental and theoretical studies on deprotonation of G·+ in human telomere G-quadruplex AG3(T2AG3)3by using nanosecond laser flash photolysis and quantum chemical calculations. Upon 355 nm laser photolysis of Na2S2O8, instantaneously generated SO4·- radical oxidizes G base in the G-quadruplex to G·+. In the time-resolved absorption spectra that record the reaction of G-quadruplex with SO4·- at different temperatures, the transient absorptions of G(N(2)-H)· featured by absorption band at 640 nm are observed. It turns out that the G-quadruplex deprotonation product is G(N(2)-H)· and the deprotonation site is thereby validated to be amino proton. To obtain the activation energy of the G·+ deprotonation in G-quadruplex, the N(2)-H deprotonation rate constants at different temperatures varying from 280 to 300 K in steps 5 K are measured at a high G-quadruplex concentration, where the deprotonation has been proved to be the rate-limiting step in our previous work. Based upon Arrhenius equation, the deprotonation activation energy of G·+ in G-quadruplex is determined to be 20.0±1.0 kJ/mol. Further, the potential energy profile for the G·+ deprotonation in G-quadruplex is calculated at M062X/6-31G(d) level by carefully taking into account hydration environment of G·+ in G-quadruplex. The calculated energy barrier of 26.4 kJ/mol matches with the measured activation energy value, indicating the calculated potential energy profile can describe the deprotonation process of G·+ in the G-quadruplex. These theoretical and experimental results provide valuable dynamics information and mechanistic insights for potential applications of DNA structures in electronic device.

Key words: G-quadruplex, guanine radical cation, deprotonation reaction, activation energy, potential energy profile