基于飞秒瞬态吸收光谱的尿嘧啶激发态动力学研究
发布时间：2018-10-16 13:43
【摘要】：自然界中许多生理现象与光对核酸分子的作用密切相关,例如DNA的光损伤。理解这些现象的微观机理需要有超快时间分辨的实验方法,以探测相关分子经光激发后的超快动力学。碱基单体是核酸分子中最重要的起配对作用的部分和光反应最活跃的部分,碱基单体的激发态动力学研究是理解DNA光化学过程的基础,具有重要的科学意义和应用价值。本论文利用飞秒时间分辨瞬态吸收光谱方法,研究了尿嘧啶激发态动力学的取代效应及溶剂效应。我们采用连续紫外光探测对水溶液中尿嘧啶和其C5、C6甲基取代物胸腺嘧啶、6-甲基尿嘧啶的激发态动力学进行了研究。首次直接观察到这三种分子的热基态振动冷却,证实了从最低1ππ*态到基态(So)之间的直接IC过程。实验同时发现在水中这三种分子有相似的非辐射衰减机制：初始光激发1ππ*态同时衰减到基态和1nπ*态,其中从1ππ*态到基态的直接通道布居到基态的高振动态,振动冷却时间在2 ps左右,而1ππ*态衰减至基态的时间大于10 ps；胸腺嘧啶或6-甲基尿嘧啶中1ππ*→1nπ*→S0通道的贡献比尿嘧啶要少的多。我们的实验揭示了C5或C6甲基取代效应对尿嘧啶非辐射衰减机制的重要影响,即C5或C6甲基取代都会抑制1ππ*→1nπ*通道,而促进’1ππ*→S0直接IC通道。我们在可见、紫外光波段探测了水溶液中6-氮尿嘧啶的激发态动力学,获得了基态和激发态的布居信息。和尿嘧啶等样品不同,在6-氮尿嘧啶中没有观察到热基态振动冷却,但观察到了显著的长寿命信号。我们提出了水溶液中激发6-氮尿嘧啶无辐射衰减机制,即初始1ππ*态在0.3 ps内衰减到1nπ*态,然后1nπ*态主要通过ISC通道衰减到三重态T1,1nπ*态寿命大约在4 ps；T1衰减到基态的时间至少大于1 ns。我们的研究结果表明C6氮取代关闭了尿嘧啶中的1ππ*→So直接IC通道,使1ππ*态几乎都衰减到1nπ*态。原因可能是C6氮取代使在尿嘧啶中的C5=C6双键变为刚性更强的C5=N6双键,抑制了环平面外变形。我们分别在紫外、可见光波段探测了多种溶剂环境中尿嘧啶、6-氮尿嘧啶的激发态超快动力学,系统考察了溶剂的不同性质对这两种分子激发态弛豫过程的影响。对尿嘧啶,我们发现在除水以外的溶剂中都能观察到三重态的产生,且在非质子溶剂中的产率显著大于在质子溶剂中的产率；另外,在非质子溶剂中,振动冷却时间显著变长。我们提出尿嘧啶的激发态动力学主要受溶剂质子性影响,而不受溶剂粘度影响。对于6-氮尿嘧啶,我们发现其激发态弛豫通道在几种不同溶剂中是相同的,只是从1nπ*态到T1态的衰减时间有一定的差异,发现该衰减时间对于溶剂极性有明显的负相关依赖关系,而溶剂粘度和质子性对6-氮尿嘧啶的激发态动力学无明显影响。
[Abstract]:Many physiological phenomena in nature are closely related to the action of light on nucleic acid molecules, such as light damage of DNA. Understanding the microscopic mechanism of these phenomena requires an ultra-fast time-resolved experimental method to detect the ultrafast dynamics of the molecules after photoexcitation. Base monomer is the most important pairing part of nucleic acid molecule and the most active part of photoreaction. The kinetic study of excited state of base monomer is the basis of understanding the photochemical process of DNA and has important scientific significance and application value. In this paper, the substitution effect and solvent effect of the excited state of uracil are studied by femtosecond time-resolved transient absorption spectroscopy. The excited state kinetics of uracil and its C _ (5) C _ (6) methyl substituted thymine and 6-methyluracil in aqueous solution have been studied by continuous ultraviolet detection. The thermal ground state vibrational cooling of these three molecules is observed for the first time, and the direct IC process from the lowest 1 蟺 * state to the ground state (So) is confirmed. It is also found that these three molecules have similar non-radiative attenuation mechanisms in water: the initial photoexcited 1 蟺 * state attenuates to the ground state and 1n 蟺 * state simultaneously, in which the direct channel from 1 蟺 * state to the ground state distributes the high vibrational state to the ground state. The cooling time of vibration is about 2 ps, and the time of attenuation of 1 蟺 * state to ground state is more than 10 ps; thymidine or 6 methyl uracil. The contribution of 1 蟺 ~ (1 蟺) ~ (-1) 蟺 ~ (-1) S ~ (0) channel to uracil is much less than that of uracil. Our experiments reveal the important effect of C5 or C6-methylsubstitution on the mechanism of non-radiation attenuation of uracil. C5 or C6-methyl-substitution can both inhibit 1 蟺 * n 蟺 -channel and promote'1 蟺 * S0 direct IC channel. The excited state kinetics of 6-azouracil in aqueous solution has been detected in visible and ultraviolet band, and the population information of ground state and excited state has been obtained. Unlike the samples such as uracil, there was no vibrational cooling of the thermal ground state in 6-azouracil, but a significant long life signal was observed. We propose a radiation-free decay mechanism of 6- azouracil in aqueous solution, that is, the initial 1 蟺 * state attenuates to 1 n 蟺 * state within 0. 3 ps, and then the 1n 蟺 * state attenuates mainly through the ISC channel to the triplet T 1 1 n 蟺 * state lifetime of about 4 ps;. T1 attenuates to ground state at least 1 ns. Our results show that C6 nitrogen replaces the direct IC channel of 1 蟺 * So in uracil and almost all of the 1 蟺 * states attenuate to 1n 蟺 * state. The reason may be that the substitution of C6 nitrogen makes the C5=C6 double bond in uracil become a more rigid C5=N6 double bond, which inhibits the out-of-plane deformation of the ring. The excited state ultrafast kinetics of uracil and 6-azouracil in various solvent environments has been investigated in the ultraviolet and visible wavelengths, and the effects of different properties of solvents on the relaxation processes of these two molecular excited states have been systematically investigated. For uracil, we find that triplet can be observed in all solvents except water, and the yield in non-proton solvent is significantly higher than that in proton solvent, and in non-proton solvent, the vibration cooling time is significantly longer. We propose that the excited state kinetics of uracil is mainly affected by the proton property of the solvent, but not by the viscosity of the solvent. For 6-azouracil, we find that the excited state relaxation channel is the same in several solvents, but the decay time from 1n 蟺 * state to T1 state is different. It is found that the decay time has a negative correlation with the polarity of the solvent, while the viscosity and proton properties of the solvent have no significant effect on the excited state kinetics of 6-azouracil.
【学位授予单位】：中国科学院研究生院(武汉物理与数学研究所)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O433.51
本文编号：2274544
[Abstract]:Many physiological phenomena in nature are closely related to the action of light on nucleic acid molecules, such as light damage of DNA. Understanding the microscopic mechanism of these phenomena requires an ultra-fast time-resolved experimental method to detect the ultrafast dynamics of the molecules after photoexcitation. Base monomer is the most important pairing part of nucleic acid molecule and the most active part of photoreaction. The kinetic study of excited state of base monomer is the basis of understanding the photochemical process of DNA and has important scientific significance and application value. In this paper, the substitution effect and solvent effect of the excited state of uracil are studied by femtosecond time-resolved transient absorption spectroscopy. The excited state kinetics of uracil and its C _ (5) C _ (6) methyl substituted thymine and 6-methyluracil in aqueous solution have been studied by continuous ultraviolet detection. The thermal ground state vibrational cooling of these three molecules is observed for the first time, and the direct IC process from the lowest 1 蟺 * state to the ground state (So) is confirmed. It is also found that these three molecules have similar non-radiative attenuation mechanisms in water: the initial photoexcited 1 蟺 * state attenuates to the ground state and 1n 蟺 * state simultaneously, in which the direct channel from 1 蟺 * state to the ground state distributes the high vibrational state to the ground state. The cooling time of vibration is about 2 ps, and the time of attenuation of 1 蟺 * state to ground state is more than 10 ps; thymidine or 6 methyl uracil. The contribution of 1 蟺 ~ (1 蟺) ~ (-1) 蟺 ~ (-1) S ~ (0) channel to uracil is much less than that of uracil. Our experiments reveal the important effect of C5 or C6-methylsubstitution on the mechanism of non-radiation attenuation of uracil. C5 or C6-methyl-substitution can both inhibit 1 蟺 * n 蟺 -channel and promote'1 蟺 * S0 direct IC channel. The excited state kinetics of 6-azouracil in aqueous solution has been detected in visible and ultraviolet band, and the population information of ground state and excited state has been obtained. Unlike the samples such as uracil, there was no vibrational cooling of the thermal ground state in 6-azouracil, but a significant long life signal was observed. We propose a radiation-free decay mechanism of 6- azouracil in aqueous solution, that is, the initial 1 蟺 * state attenuates to 1 n 蟺 * state within 0. 3 ps, and then the 1n 蟺 * state attenuates mainly through the ISC channel to the triplet T 1 1 n 蟺 * state lifetime of about 4 ps;. T1 attenuates to ground state at least 1 ns. Our results show that C6 nitrogen replaces the direct IC channel of 1 蟺 * So in uracil and almost all of the 1 蟺 * states attenuate to 1n 蟺 * state. The reason may be that the substitution of C6 nitrogen makes the C5=C6 double bond in uracil become a more rigid C5=N6 double bond, which inhibits the out-of-plane deformation of the ring. The excited state ultrafast kinetics of uracil and 6-azouracil in various solvent environments has been investigated in the ultraviolet and visible wavelengths, and the effects of different properties of solvents on the relaxation processes of these two molecular excited states have been systematically investigated. For uracil, we find that triplet can be observed in all solvents except water, and the yield in non-proton solvent is significantly higher than that in proton solvent, and in non-proton solvent, the vibration cooling time is significantly longer. We propose that the excited state kinetics of uracil is mainly affected by the proton property of the solvent, but not by the viscosity of the solvent. For 6-azouracil, we find that the excited state relaxation channel is the same in several solvents, but the decay time from 1n 蟺 * state to T1 state is different. It is found that the decay time has a negative correlation with the polarity of the solvent, while the viscosity and proton properties of the solvent have no significant effect on the excited state kinetics of 6-azouracil.
【学位授予单位】：中国科学院研究生院(武汉物理与数学研究所)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O433.51
【参考文献】
相关博士学位论文 前1条
1 王传亮;原子强场超快电离动力学的实验研究[D];中国科学院研究生院（武汉物理与数学研究所）;2014年
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