Acta Chimica Sinica ›› 2014, Vol. 72 ›› Issue (11): 1182-1186.DOI: 10.6023/A14090666 Previous Articles    



吴丽丹, 节家龙, 刘坤辉, 苏红梅   

  1. 中国科学院化学研究所 分子反应动力学国家重点实验室 北京 100190
  • 投稿日期:2014-09-28 发布日期:2014-10-22
  • 通讯作者: 刘坤辉, 苏红梅;
  • 基金资助:

    项目受国家自然科学基金(No. 21333012)、"973"基金(No. 2013CB834602)及中国科学院先导专项(No. XDB12020200)资助

Deprotonation Kinetics of 1-Methylguanine After One-Electron Oxidation

Wu Lidan, Jie Jialong, Liu Kunhui, Su Hongmei   

  1. State Key Laboratory of Molecular Reaction Dynamics, Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
  • Received:2014-09-28 Published:2014-10-22
  • Supported by:

    Project supported by the National Natural Science Foundation of China (No. 21333012), the National Basic Research Program of China (No. 2013CB834602), and the Chinese Academy of Sciences (No. XDB12020200).

Among the four natural DNA bases, guanine (G) is the most sensitive to oxidation due to its lowest oxidation potential. When G base is oxidized to guanine cation radical (G), it will deprotonate from both the imino proton N1-H and the amino proton N2-H. According to the pKa values for N1-H and N2-H deprotonation, the main deprotonation site in G base is N1-H which would interfere with the N2-H deprotonation, making the kinetics of N2-H deprotonation difficult to be measured. Herein, the N2-H deprotonation kinetics is investigated using 1-methylguanosine (mG), where N1-H is substituted by methyl group to avoid the N1-H deprotonation and N9-H is substituted by ribose to ensure enough solubility of methylguanine in water, by nanosecond transient absorption (ns-TA) spectroscopy. By 355 nm photolysis of Na2S2O8, the highly oxidizing radical SO4 is generated, which will oxidize mG to mG instantaneously. The time-resolved absorption spectra obtained for reaction of mG with SO4 exhibits transient absorptions for mG(N2-H)· featured by absorption band at 600 nm, indicating that the mG deprotonation product is mG(N2-H)· and the deprotonation site is therefore validated to be N2-H. The mG concentration dependence of mG(N2-H)· formation rate constant is assessed through changing the mG concentration from 0.25 mmol·L-1 to 5 mmol·L-1. The concentration dependence experiment reveals that the rate-limiting step to form mG(N2-H)· is the bimolecular reaction of mG with SO4 when mG concentration is lower than 2 mmol·L-1 and the bimolecular reaction rate constant to form mG is (3.7±0.1)×109 L·mol-1·s-1; when mG concentration is above 2 mmol·L-1, the rate-limiting step to form mG(N2-H)· is the first-order mG deprotonation and the N2-H deprotonation rate constant is (7.1±0.2)×106 s-1. Furthermore, the N2-H deprotonation rate constant is measured at different temperatures varying from 278 K to 298 K. According to Arrhenius equation, the activation energy barrier for the N2-H deprotonation is determined to be 19.9±1.0 kJ· mol-1. These results can provide valuable kinetic information on the oxidative damage of DNA.

Key words: 1-methylguanine, deprotonation, one-electron oxidation, rate constant, activation energy barrier