【摘要】：自然界中許多生理現(xiàn)象與光對核酸分子的作用密切相關(guān),例如DNA的光損傷。理解這些現(xiàn)象的微觀機理需要有超快時間分辨的實驗方法,以探測相關(guān)分子經(jīng)光激發(fā)后的超快動力學(xué)。堿基單體是核酸分子中最重要的起配對作用的部分和光反應(yīng)最活躍的部分,堿基單體的激發(fā)態(tài)動力學(xué)研究是理解DNA光化學(xué)過程的基礎(chǔ),具有重要的科學(xué)意義和應(yīng)用價值。本論文利用飛秒時間分辨瞬態(tài)吸收光譜方法,研究了尿嘧啶激發(fā)態(tài)動力學(xué)的取代效應(yīng)及溶劑效應(yīng)。我們采用連續(xù)紫外光探測對水溶液中尿嘧啶和其C5、C6甲基取代物胸腺嘧啶、6-甲基尿嘧啶的激發(fā)態(tài)動力學(xué)進行了研究。首次直接觀察到這三種分子的熱基態(tài)振動冷卻,證實了從最低1ππ*態(tài)到基態(tài)(So)之間的直接IC過程。實驗同時發(fā)現(xiàn)在水中這三種分子有相似的非輻射衰減機制：初始光激發(fā)1ππ*態(tài)同時衰減到基態(tài)和1nπ*態(tài),其中從1ππ*態(tài)到基態(tài)的直接通道布居到基態(tài)的高振動態(tài),振動冷卻時間在2 ps左右,而1ππ*態(tài)衰減至基態(tài)的時間大于10 ps；胸腺嘧啶或6-甲基尿嘧啶中1ππ*→1nπ*→S0通道的貢獻(xiàn)比尿嘧啶要少的多。我們的實驗揭示了C5或C6甲基取代效應(yīng)對尿嘧啶非輻射衰減機制的重要影響,即C5或C6甲基取代都會抑制1ππ*→1nπ*通道,而促進’1ππ*→S0直接IC通道。我們在可見、紫外光波段探測了水溶液中6-氮尿嘧啶的激發(fā)態(tài)動力學(xué),獲得了基態(tài)和激發(fā)態(tài)的布居信息。和尿嘧啶等樣品不同,在6-氮尿嘧啶中沒有觀察到熱基態(tài)振動冷卻,但觀察到了顯著的長壽命信號。我們提出了水溶液中激發(fā)6-氮尿嘧啶無輻射衰減機制,即初始1ππ*態(tài)在0.3 ps內(nèi)衰減到1nπ*態(tài),然后1nπ*態(tài)主要通過ISC通道衰減到三重態(tài)T1,1nπ*態(tài)壽命大約在4 ps；T1衰減到基態(tài)的時間至少大于1 ns。我們的研究結(jié)果表明C6氮取代關(guān)閉了尿嘧啶中的1ππ*→So直接IC通道,使1ππ*態(tài)幾乎都衰減到1nπ*態(tài)。原因可能是C6氮取代使在尿嘧啶中的C5=C6雙鍵變?yōu)閯傂愿鼜姷腃5=N6雙鍵,抑制了環(huán)平面外變形。我們分別在紫外、可見光波段探測了多種溶劑環(huán)境中尿嘧啶、6-氮尿嘧啶的激發(fā)態(tài)超快動力學(xué),系統(tǒng)考察了溶劑的不同性質(zhì)對這兩種分子激發(fā)態(tài)弛豫過程的影響。對尿嘧啶,我們發(fā)現(xiàn)在除水以外的溶劑中都能觀察到三重態(tài)的產(chǎn)生,且在非質(zhì)子溶劑中的產(chǎn)率顯著大于在質(zhì)子溶劑中的產(chǎn)率；另外,在非質(zhì)子溶劑中,振動冷卻時間顯著變長。我們提出尿嘧啶的激發(fā)態(tài)動力學(xué)主要受溶劑質(zhì)子性影響,而不受溶劑粘度影響。對于6-氮尿嘧啶,我們發(fā)現(xiàn)其激發(fā)態(tài)弛豫通道在幾種不同溶劑中是相同的,只是從1nπ*態(tài)到T1態(tài)的衰減時間有一定的差異,發(fā)現(xiàn)該衰減時間對于溶劑極性有明顯的負(fù)相關(guān)依賴關(guān)系,而溶劑粘度和質(zhì)子性對6-氮尿嘧啶的激發(fā)態(tài)動力學(xué)無明顯影響。
[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.
【學(xué)位授予單位】：中國科學(xué)院研究生院(武漢物理與數(shù)學(xué)研究所)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：O433.51

【參考文獻(xiàn)】

相關(guān)博士學(xué)位論文 前1條

1 王傳亮;原子強場超快電離動力學(xué)的實驗研究[D];中國科學(xué)院研究生院（武漢物理與數(shù)學(xué)研究所）;2014年

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本文編號：2274544