N1-甲基鸟嘌呤阳离子脱质子动力学的研究

doi:10.6023/A14090666

化学学报 ›› 2014, Vol. 72 ›› Issue (11): 1182-1186.DOI: 10.6023/A14090666 上一篇

研究论文

N¹-甲基鸟嘌呤阳离子脱质子动力学的研究

吴丽丹, 节家龙, 刘坤辉, 苏红梅

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 E-mail:khliu@iccas.ac.cn;hongmei@iccas.ac.cn
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

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).

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摘要/Abstract

在所有DNA碱基中, 鸟嘌呤碱基G具有最低的氧化电位, 导致其最容易被氧化. G碱基被单电子氧化成为G正离子自由基(G^+·), G^+·存在两个脱质子位点, 其中脱嘧啶环上亚氨基质子N¹-H比脱环外氨基质子N²-H更有利, 因而在普通G碱基中研究脱N²-H的过程无法排除脱N¹-H过程的干扰, 使得其脱N²-H的动力学迄今尚不明确. 在本文中, 通过将G碱基上的N¹-H用CH₃取代(即mG), 采用纳秒时间分辨瞬态紫外可见吸收光谱方法研究了mG碱基单电子氧化后脱质子N²-H的动力学. 根据瞬态紫外可见吸收光谱, 确定了mG^+·脱质子的产物是mG(N²-H)^·, 即脱质子的位点是N²-H. 进一步通过测量mG(N²-H)^·的生成速率常数与mG的浓度依赖关系, 得到室温下SO₄^-·单电子氧化mG生成 mG^+·的速率常数为(3.7±0.1)×10⁹ L·mol^-1·s^-1以及 mG^+·脱N²-H的速率常数为(7.1±0.2)×10⁶ s^-1. 并通过检测不同温度下mG^+·脱N²-H的速率常数, 利用阿仑尼乌斯方程得出脱质子N²-H的活化能为19.9±1.0 kJ·mol^-1. 这些结果可为DNA碱基的氧化损伤过程提供更为丰富的动力学信息.

关键词: N₁-甲基鸟嘌呤, 脱质子, 单电子氧化, 速率常数, 活化能

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

引用此文

吴丽丹, 节家龙, 刘坤辉, 苏红梅. N¹-甲基鸟嘌呤阳离子脱质子动力学的研究[J]. 化学学报, 2014, 72(11): 1182-1186.

Wu Lidan, Jie Jialong, Liu Kunhui, Su Hongmei. Deprotonation Kinetics of 1-Methylguanine After One-Electron Oxidation[J]. Acta Chimica Sinica, 2014, 72(11): 1182-1186.

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N¹-甲基鸟嘌呤阳离子脱质子动力学的研究

Deprotonation Kinetics of 1-Methylguanine After One-Electron Oxidation

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