【作者】 隋小娴；

【导师】 郑旭明；

【作者基本信息】 浙江理工大学 ， 应用化学， 2012， 硕士

【摘要】 核酸碱基是核苷酸的重要组成部分，其光化学反应动力学行为在核酸UV光损伤中扮演着不可忽视的角色，这些光化学行为使碱基中的电子由基态跃迁为激发态，电子激发态有时会衰变成有害的光化学产物，进而对生物体造成基因突变等伤害。近几十年来，众多科研小组主要运用荧光弛豫等方法，研究核酸碱基激发态弛豫动力学过程，发现其第一电子激发态（S1）的寿命大约在1ps左右，并且迅速经内转换衰变到基态。基于这一内转换衰变过程的复杂性，近年来已提出许多可能的衰变过程，在其激发态势能面的锥形交叉等机理方面取得了重大突破。但荧光弛豫等方法本身分辨率过低（大于等于100fs），导致了其无法检测到Franck-Condon(F-C)区（50fs以内）的激发态结构动力学行为，从而使得在这一过程中的电子激发态寿命值本身以及势能面锥形交叉点位置等方面都存在疑问。共振拉曼光谱学通过获取反应坐标信息来研究激发态结构动力学,特别是在F-C区域势能面交叉和电子态耦合等方面发挥重要作用，为电子激发态衰变机理的研究做出其他方法都无法替代的贡献。本文采用共振拉曼光谱技术研究了5-氨基尿嘧啶(5Au)，6-氨基尿嘧啶(6Au)，3-氨基-2-环己烯酮(ACyO)以及对苯醌及其衍生物(PBQ/BQ/HQ)在不同溶剂中的激发态结构动力学。并结合密度泛函理论计算方法讨论了其光化学反应在微观反应动力学上的调控因素。取得了一些有意义的研究成果:（1）测量固体5-氨基尿嘧啶和6-氨基尿嘧啶的傅立叶变换红外和拉曼光谱，并利用密度泛函理论进行计算，为振动模的指认提供依据。根据水溶液中的吸收光谱，确定共振拉曼实验的激发波长，分别对5Au，6Au在273.9nm，266nm，252.4nm和228.4nm激发波长下的共振拉曼光谱进行测量取谱，分析讨论由取代基位置调控的激发态结构动力学。对比共振拉曼光谱指认结果，分析异同，发现两者有相似的振动模，即取代基HN9H剪式振动和环上N3H/C5H/N1H弯曲振动模，以及NCN反对称伸缩振动模。而在涉及到整个环的变形振动方面则存在较大差异，这说明氨基取代基的位置不同,致使调控F-C区结构动力行为的反应坐标存在巨大差异，这影响了整个环的光化学反应动力学行为，最终导致其电子激发态衰变寿命的不同。（2）为了找出调控氨基尿嘧啶环激发态动力学的子结构，对氨基尿嘧啶的简单模型化合物3-氨基-2-环己烯酮进行相关研究。考察其固态，水溶液和乙腈溶液中的傅立叶变换红外和拉曼光谱，并利用密度泛函理论进行计算，为振动模的指认提供依据。根据电子光谱，确定共振拉曼实验的激发波长，进行3-氨基-2-环己烯酮在水溶液和乙腈溶液中299.1nm，282.4nm，273.9nm和266nm激发波长下的共振拉曼光谱的测量，分析讨论从而了解其由溶剂调控的激发态结构动力学过程（如态的耦合）。并运用含时波包理论分析乙腈溶液中的共振拉曼振动模强度。研究结果表明3-氨基-2-环己烯酮Franck-Condon区结构动力学很大程度上是由C1C2=C3的反对称伸缩+C1=O7伸缩振动模调控的，而H11C4H10/H14C6H15剪式振动模，环的呼吸振动模和H16N8H17摇摆振动模的参与，体现了其反应坐标的多维性。与尿嘧啶的氨基衍生物比较，发现氨基尿嘧啶环中主导其激发态结构动力学的主要结构是：O=C-C=C-。这一研究发现，为探索核酸碱基激发态寿命及其衰变机理提供了一个全新的视角。（3）选取同样含有O=C-C=C-子结构的对苯醌及其衍生物进行研究。考察对苯醌及其衍生物的傅立叶变换红外和拉曼光谱，并利用密度泛函理论进行计算，为振动模的指认提供依据。根据各自的吸收光谱，分别确定共振拉曼实验的激发波长，测量相应激发波长下的共振拉曼光谱，将三种醌类物质从紫外光谱与共振拉曼光谱两个方面入手进行对比，找出主导对苯醌这一模型化合物激发态结构动力学的反应坐标，再将母体化合物与研究体系的主化合物6-氨基尿嘧啶及其相关物质比较，从而为氨基尿嘧啶的相关研究提供帮助。更多还原

【Abstract】 Photochemical reaction dynamics of nucleic acid base which is an importantcomponent of nucleotide plays a significant role in the UV photodamage of nucleicacids. The electrons in base transit from ground state to excited state byphotochemical reaction, while excited electronic state sometimes is apt to decay intoharmful photochemical products, which can cause mutations and interfere with thenormal cellular processing of DNA.In recent decades, efforts have been made in the study of the relaxation dynamicsof excited-state nucleic acid bases using fluorescence relaxation techniques. Thelifetimes of the first electric dipole-allowed state (S1) have been observed to bearound1ps, and fast decay to the ground state via internal conversion (IC) has alsobeen proposed. Based on this transformation of the complexity of the process in thedecay, in recent years the decay many different mechanisms have been put forward,and the major breakthrough has been obtained. Fluorescence relaxation techniquescan not detect to excited state structure dynamics in the Franck-Condon (F-C) region(in50fs), because of their low resolution (100fs). So that the lifetime in the processof electronic excited and the position of potential surfaces intersection are not clear.Resonance Raman spectral technique has a unique advantage on the research ofthe conical intersection and vibronic coupling in the F-C region, on other aspects, itprovides irreplaceable contributions for electronic excited states decay mechanism.In this paper, the excited state structural dynamics of5-aminouracil (5Au),6-aminouracil (6Au),3-amino-2-cyclohexen-1-one (ACyO) and relatedanthraquinones (PBQ/BQ/HQ) in different solvents systems have been studied by theResonance Raman spectra in combination with DFT calculation and discussed theinfluential factors to tune the photochemical reactions. Main conclusions of thepresent work are summarized as follows,(1) The FT-IR and FT-Raman spectra of5-aminouracil and6-aminouracil in solid state. Density functional theory calcualtions were done to help elucidate thevibrational band assignments. Resonance Raman spectra were respectively obtainedfor5-aminouracil and6-aminouracil in water solution with252.4,228.4,273.9, and266nm excitation wavelength in resonance with the CT-band absorption spectrum toexamine the excited state structural dynamics and the state-mixing or curve-crossingtuned by substituent groups. There are many of the same vibration modes such asHN9H scissor, N3H/C5N/N1H bend asysm NCN stretch in Resonance Raman spectra.While there are also some differences in ring deformation. It suggusts that the excitedstate structural dynamics and reaction coordination of the ring are inflution indifference of substituent positions, and then lead to different life of the electronicexcited states decay.(2) To find out the substructure which is the factor to tune the photochemicalreactions of aminouracil ring, the study of3-amino-2-cyclohexen-1-one that is modelcompound of aminouraci has been completed. The FT-IR and FT-Raman spectra of3-amino-2-cyclohexen-1-one in solid state and/or in solvents of water and acetonitrilehave been researched. Density functional theory calcualtions were done to helpelucidate the vibrational band assignments. Resonance Raman spectra were obtainedfor ACyO in different solutions with299.1,282.4,273.9, and266nm excitationwavelength in resonance with the CT-band absorption spectrum to examine theexcited state structural dynamics and the state-mixing or curve-crossing tuned bysolvents. A preliminary resonance Raman intensity analysis using the time-dependentwave-packet theory and simple model was done for ACyO in acetonitrile solvent.Resonance Raman spectroscopic probing of the excited state curve-crossing orstate-mixing was proposed. The largest changes in the displacements take place withthe anti-symmetric C1C2=C3stretch+C1=O7stretch11(1588cm-1,=0.92, λ=672cm-1). The vibrational reorganizational energy of this mode accounts for56.6%of thetotal vibrational reorganizational energy. Moderate changes in the displacements takeplace for H11C4H10/H14C6H15scissor15, the ring breath34+37, and the H16N8H17rock25vibrational degree of freedom. In acetonitrile solvent the Franck-Condonregion structural dynamics of ACyO have multidimensional character. Compared with 6Au, it is clear that O=C-C=C-plays a significant role in excited state structuraldynamics of uracil ring. This discovery provides a new perspective to the study ofexcited states relaxation dynamic mechanism.(3) As the compound which also contains O=C-C=C-, anthraquinones have beenstudied. The FT-IR and FT-Raman spectra of related anthraquinones which are alsothe model compounds of uracil in solid state. Density functional theory calcualtionswere done to help elucidate the vibrational band assignments. Resonance Ramanspectra were respectively obtained for related anthraquinones with the CT-bandabsorption spectrum to examine the excited state structural dynamics and thestate-mixing or curve-crossing, and subsequently offer some useful help to the studyof aminouracil by the comparison between parent compound and6-aminouracil that isthe lord compounds research system.更多还原