核苷酸和芳香酮的电子转移和质子转移反应研究

利用时间分辨的激光闪光光解方法在1∶1乙腈/水溶液中得到了4种核苷酸和芳香酮的瞬态吸收光谱,通过瞬态吸收光谱的变化研究了鸟苷酸、腺苷酸、胞苷酸、胸腺苷酸猝灭二苯甲酮、呫吨酮激发三重态的反应。由于实验中生成了抽氢自由基和负离子自由基,以及核苷酸正离子在水中的快速抽氢反应,推断出芳香酮和鸟苷酸、腺苷酸的反应机理是先发生电子转移后发生质子转移。而在芳香酮和胞苷酸、胸腺苷酸的反应中没有观察到相应的抽氢自由基和负离子自由基的瞬态吸收峰,由此推断出它们和胞苷酸、胸腺苷酸没有发生电子转移和质子转移反应。对瞬态吸收峰处的时间衰减曲线进行拟合得到了核苷酸猝灭芳香酮的速率常数,可以看到随着反应自由能变ΔG的增大,反应速率常数逐渐减小。     

C60激发三重态被哌嗪猝灭特性研究

本文使用激光诱导瞬态吸收光谱装置，研究了C60激发三重态在乙腈／甲苯混合溶剂中的光物理性质，得到了^3C60^#的激发态寿命、自猝灭速率常数和时间分辩的瞬态吸收光谱。此外，实验中引入了哌嗪作为激发三重态猝灭剂，我们发现哌嗪能有效的猝灭^3C60^#，猝灭速率常数kq接近扩散控制极限，改变混合溶剂的比例，相应的猝灭速率常数值也发生变化，即知随混合溶剂极性的增加而增加，随溶剂粘度的增加而减小，稳态光解实验反映了反应物向产物转化过程中在紫外-可见波段吸收强度的变化。     

C60激发三重态被哌嗪猝灭特性研究

本文使用激光诱导瞬态吸收光谱装置,研究了C60激发三重态在乙腈/甲苯混合溶剂中的光物理性质,得到了3C60的激发态寿命、自猝灭速率常数和时间分辩的瞬态吸收光谱.此外,实验中引入了哌嗪作为激发三重态猝灭剂.我们发现哌嗪能有效的猝灭3C60,猝灭速率常数kq接近扩散控制极限.改变混合溶剂的比例,相应的猝灭速率常数值也发生变化,即kq随混合溶剂极性的增加而增加,随溶剂粘度的增加而减小.稳态光解实验反映了反应物向产物转化过程中在紫外-可见波段吸收强度的变化.     

虚时间分裂算符方法研究溶剂电子转移动力学

在Sumi-Marcus理论中，采用虚时间分裂算符方法研究电子转移动力学．此方法具体应用于计算嗪-1和N,N-二甲基苯胺分子之间的电子转移速率常数．通过计算得到的两种反应物态的平均速率常数和一个长时间的速率常数，揭示了不同的sink函数时的电子转移动力学．在数值模拟过程中还发现了一些新的电子转移特性．     

β-胡萝卜素在乙腈体系中的激光光解研究

利用纳秒级激光光解瞬态吸收光谱装置,研究了以乙腈作为溶剂,以2-萘乙酮作为敏化剂的体系在355nm激光作用下敏化产生β-胡萝卜素激发三重态的机制,并进一步研究了β-胡萝卜素激发三重态的性质。研究显示2-萘乙酮和β-胡萝卜素的二元体系在355nm激光作用下,2-萘乙酮首先被激发为其激发三重态(420nm),2-萘乙酮激发三重态与β-胡萝卜素发生激发能转移,产生β-胡萝卜素激发三重态(510nm)。通过激发能转移的方法测得了β-胡萝卜素激发三重态在最大吸收波长510nm处的摩尔消光系数为23000L·mol-1·cm-1。改变β-胡萝卜素的浓度测得了其激发三重态在乙腈体系中的衰变反应速率常数6·5×104s-1,其在乙腈体系中的三重态寿命为15·6μs。同时获得了激发态2-萘乙酮与β-胡萝卜素之间激发能转移反应的速率常数1·5×1010L·mol-1·s-1。     

激光闪光光解研究二羟基蒽醌和腺嘌呤/胞嘧啶的电子转移反应

采用纳秒时间分辨的激光闪光光解技术研究了乙腈/水混合溶液中二羟基蒽醌和腺嘌呤或胞嘧啶之间的电子转移反应. 在355 nm紫外光作用下,经由系间窜跃产生的三重态二羟基蒽醌与两碱基分别发生电子转移反应,其中碱基作为典型的电子给体. 基于测量到的反应瞬态中间体的动力学淬灭速率,两个反应过程被认为分步进行,先电子转移之后发生质子转移反应. 通过研究表观淬灭速率与两个碱基浓度的依赖关系,分别得到了两个双分子间电子转移反应的速率常数,分别是9.0×10⁸ L/(mol·s) (胞嘧啶)、3.3×10⁸ L/(mol·s) (腺嘌呤).     

噻吨酮光物理和光化学行为对溶剂的依赖性（英文）

本文利用纳秒瞬态吸收光谱技术,在不同溶剂中,研究了噻吨酮的光物理和光化学行为.TX的激发三重态(~3TX~*)涉及2种电子态,~3nπ~*和~3ππ~*态.随着溶剂极性的增强,~3ππ~*态的贡献加大.在CH_3CN,CH_3CN/CH_3OH(1:1)和CH_3CN/H_2O(1:1)溶剂中,~3TX~*的自猝灭速率常数k_(sq)逐渐减小.这可能由于通过氢键形成的激基复合物阻碍了~3TX~*的碰撞猝灭.二苯胺通过电子转移还原~3TX~*,生成TX~(·-)阴离子和DPA~(·+)阳离子自由基.溶剂对该转移过程的影响不明显,表明TX的~3nπ~*和~3ππ~*态夺取电子的能力相近.然而,溶剂的依赖性在TX~(·-)的猝灭过程中表现明显.在强酸性条件下(pH=3.0),质子化的TX和非质子化的TX之间存在着动态平衡.在激发光作用下,生成~3TXH~(+*),光谱上呈现出520 nm处的吸收峰.     

光致分子间电子转移-受体分子结构对转移速率的影响

本文利用超快时间分辨瞬态光栅光谱技术研究了受体分子结构对光致分子间电子转移速率的影响,以罗丹明101和罗丹明6G在苯胺中的溶液作为研究样品. 苯胺到两种染料分子之间的前向电子转移时间常数以及后续的从染料分子到苯胺的反向电子转移时间常数可以被测得. 结果表明无论是前向电子转移还是反向电子转移,罗丹明6G都较罗丹明101进行得更快. 通过量子化学计算以及后续分析,发现更具柔性的罗丹明6G分子和苯胺之间具有更强的分子间电子耦合从而导致更大的分子间电子转移速率.     

光诱导噻吨酮与二苯胺间电子转移反应的溶剂化效应

利用纳秒激光闪光光解技术研究了噻吨酮(TX)和二苯胺(DPA)的光化学反应．在355 nm光激发下,TX的基电子态跃迁至第一激发态进而通过系间窜越生成三重态³TX^*. 在乙腈/水混合溶剂中,³TX^*与DPA反应体系的瞬态吸收光谱呈现出四个谱峰,分别对应³TX^*、TXH^·、TX^·-和DPA^·+的吸收. 随着溶剂极性的增大,这些吸收峰均发生红移. 结合动力学测量,³TX^*与DPA的反应机理被证实为电子转移伴随质子转移过程. ³TX^*与DPA反应的猝灭速率常数随溶剂极性的增大而缓慢减小,9.7×10⁹ L/(mol·s)(纯乙腈)、8.7×10⁹ L/(mol·s)(乙腈:水=9:1)、8.0×10⁹ L/(mol·s)(乙腈:水=4:1)和7.5×10⁹ L/(mol·s)(乙腈:水=1:1). 质子溶剂-水在此反应中的作用不明显,溶剂的极性对³TX^*与DPA电子转移速率的影响不大,表明³TX^*的³nπ^*和³ππ^*三重态吸引DPA中电子的能力相仿.     

黄素体系电子转移过程光谱研究

黄素类物质在生物体内广泛存在,是许多电子转移反应的活性中心,也是电子传递链的重要组成部分。其受到光照激发后引起的电子转移,是许多生命过程的基础与起始步骤。特别地,一种名为隐花色素的黄素蛋白在光激发后经一系列电子转移形成自旋相关自由基对,被认为是最有可能的生物磁敏物质,更使黄素体系电子转移过程的动力学,特别是自旋动力学过程倍受关注。对黄素电子转移过程及相关机理进行研究,有助于厘清多种生命过程的化学机理与影响因素。为此,科学界综合运用了多种仪器与测试手段,其中主要包括紫外-可见光谱,荧光光谱,瞬态吸收光谱,光化学诱导动态核极化（Photo-CIDNP）技术等。通过多年的研究,对黄素在生物体内的作用机理与电子转移过程的认识经历了由浅入深,不断深入的过程。紫外-可见光谱（UV-Vis）主要用于研究黄素系统中的电子激发,自旋动力学和电子转移。结合理论计算,UV-Vis还可以识别电子转移中涉及的基团并进行定量分析。荧光光谱可以识别电子受激发的物质,在反应过程中观察黄素和半醌中间体的产生和消耗,并确定其氧化还原和质子化状态。瞬态吸收光谱适于观测反应过程中出现的短寿命物种,其中飞秒泵浦探测技术的引入大大提高了观测的时间分辨率,并且可以通过光谱特征区分单重态和三重态的自由基对。光化学诱导动态核极化核磁共振（NMR）可以直接观察电子-核自旋动力学过程。磁场依赖性photo-CIDNP NMR揭示了控制单重态与三重态互变的因素,并提出了生物地磁导航可能依赖的化学机制。腔吸收与单分子光谱的运用,从技术上提高了实验装置的灵敏度并降低检测限。主要介绍黄素体系电子转移过程研究所运用的各种光谱手段与取得的成果,并展望其未来。     

Electronic energy exchange in high-temperature air

Kinetic processes with the participation of electronic states of atoms and molecules in air behind the shock wave front were analyzed. All metastable levels of molecular and atomic oxygen and nitrogen and nitrogen oxide molecules situated below the dissociation energy were analyzed. In high-temperature air, atom and molecule electronic states are formed in dissociation and recombination, electronic energy exchange in collisions of particles, and chemical exchange reactions. The formation of excited electronic states in the recombination of atoms and isoenergy vibrational energy transfer from highly excited vibrational levels into electronic energy is the fastest process. The quenching of metastable particles occurs in collisions between particles, dissociation and recombination, and chemical exchange reactions. A database on electronic energy exchange rate constants in high-temperature air is presented.     

Electron Spin Resonance of Alkali Metal Contact Ion Pairs of 2,6-di-tert-Butylbenzoquinone in Non Polar Solvent

The question whether excited triplet states of quinones react with a number of substrates such as alcohols, phenols, and amines, via electron transfer mechanism has attracted much attention in recent years. The existence of some triplet exciplex was postulated by Kobashi et al¹ in their study of hydrogen atom abstraction by p-chloranil using laser flash spectrocopic detection. In some recent e.s.r. and CIDEP studies^2,3, however, there is no compelling evidence that the photoreduction of quinones and benzophenones undergoes an initial electron transfer mechanism. It should be noted that most of the e.s.r. studies of quinone radical anions had been carried out in polar solvents. In flash photolysis studies some evidence has indeed been obtained^1,4 in which the efficiency of hydrogen abstraction by excited triplet quinones increases with solvent polarity and therefore it is possible that the initial primary process involves electron transfer followed immediately by proton transfer. On the other hand, we     

牛血清白蛋白与荧光增白剂相互作用的荧光光谱法研究

应用荧光光谱法研究了牛血清蛋白与荧光增白剂CBS-X、BBU、VBL的相互作用.通过Stern-Volmer方程、Lineweaver-BurK方程和双对数曲线进行计算,研究了FWA对BSA内源荧光的猝灭机制.FWA对BSA内源荧光的猝灭主要为静态猝灭和荧光共振能量转移猝灭.测定了荧光增白剂CBS-X、BBU、VBL对BSA的猝灭常量和扩散常量(283 K),确定了荧光增白剂与BSA结合位点数均为1.根据Frster非辐射能量转移理论,计算了BSA与荧光增白剂分子间的结合距离和能量转移效率.通过测定283 K和298 K时供体与受体分子间结合常量,计算了BSA与荧光增白剂作用的热力学参量.BSA与FWA作用的ΔH<0,ΔS>0,并以此确定了BSA 与荧光增白剂分子主要通过静电力进行作用.     

Photoinduced Gas-Phase Electron Transfer Reactions

The electron transfer quenching process, when a reactive excited state is singlet or triplet, for gas-phase systems (benzophenone and anthraquinone with amines and pyridine as well as carbazole with halomethanes) was systematically investigated using time-resolved fluorescence. Bimolecular rate constants were obtained. Variable-temperature measurements were performed for eight donor-acceptor pairs. It was found that under solvent-free conditions various quenchers differing in photochemical reactivity led to change in quenching rates by almost three orders of magnitude. Positive and negative temperature dependences for the electron transfer rate constants were observed. The data were analyzed in terms of the Marcus-Jortner theory.     

Electron spin polarisation in the photoreduction of xanthone in alcohol: effect of concentration and temperature

Time-resolved EPR studies of the hydrogen abstraction reaction of photoexcited xanthone in 2-propanol were carried out as a function of the concentration of xanthone and the sample temperature. The temperature was varied from 22°C to about ?30°C, and the concentration from about 0.2 to 4.0?mM. At low temperature or concentration, the observed spectra of the xanthone ketyl radical and the propan-2-olyl radical could be simulated as a superposition of a hyperfine-independent component due to the emissive triplet mechanism and a hyperfine-dependent component due to the S–T₀ radical pair mechanism. However, with an increase in the concentration of xanthone, the relative contribution of TM decreases, and, concomitantly, the net absorptive component of only the xanthone ketyl radical increases. As the spin polarisation mechanisms do not predict any concentration dependence, this unusual behaviour is explained by invoking the enhancement of the spin–lattice relaxation rates due to Heisenberg spin exchange occurring at high local concentrations of the radicals. The net absorptive signal is attributed to thermally equilibrated radicals. The observed temperature dependence of the spin polarisation behaviour is similarly explained. The origin of the net absorptive signal in the TREPR spectra of the acetone?2-propanol system is also attributed to thermally equilibrated radicals. The self-quenching mechanism of xanthone is proposed to be an electron-transfer reaction from an excited xanthone molecule to another xanthone in the ground state.     

Cs(6P)+(Ne,N2)碰撞能量转移

在气体样品池条件下,研究了Cs(6P3/2) (Ne,N2)碰撞能量转移过程.用调频半导体激光器激发Cs原子至Cs(6P3/2)态,在不同的Ne或N2气压下,测量了直接6P3/2→6S1/2荧光和转移6P1/2→6S1/2荧光,对于6P3/2与Ne的碰撞,电子态能量仅能转移为Ne原子的平动能.在与N2的碰撞中,向分子振转态的转移是重要的.利用速率方程分析,可以得到碰撞转移速率系数,对于Ne,6PJ精细结构碰撞转移速率系数为1.45×10-12cm3·s-1.对于N2,测量6P Ne和6P N2二种情况下荧光的相对强度比,确定精细结构速率系数为1.64×10-12cm3·s-1,6P态猝灭速率系数为4.88×10-12cm3·s-1.     

The decisive role of pericyclic reactions in the thermal decomposition of organophosphorus compounds

The understanding of the thermal decomposition chemistry of chemical warfare nerve agents is largely limited by the scarcity of kinetic data. Because of the high toxicity of these molecules, experimental determination of their chemical properties is very difficult. In the present work, a comprehensive detailed kinetic model for the decomposition of sarin and some simulants, i.e. di-isopropyl methyl phosphonate (DIMP), diethyl methylphosphonate (DEMP), and triethyl phosphate (TEP) were developed, containing possible molecular and radical pathways. The importance of unimolecular pericyclic decomposition led to evaluate precisely the rate constants of these reactions with high level theoretical calculations. The QCISD(T)/cc-PV∞QZ//B2PLYPD3/6–311+G(2d,d,p) level of theory was selected after a benchmark. The contribution of hindered rotors was included with the 1D-HR-U approach. Tunneling was taken into account for H-atom transfer. Transition state theory was used to calculate high-pressure limit rate constants and pressure dependent rate constants were calculated using Master Equation modeling. The model was validated against experimental pyrolysis and oxidation experimental data available in literature. Flux analyses showed that whatever the conditions are, the first step of decomposition of the studied phosphorus compounds are pericyclic eliminations leading to successive decompositions, whereas bond-breaking or H-atom abstraction remain negligible, even at high temperature.     

Fluorescence quenching as a method of identification of the character of photoreactions in excited states of molecules

We consider the steady-state monochromatic excitation of a luminophore that has fluorescent products. We consider how the fluorescence of singlet states is affected by different means of quenching highlying excited states such as quenching with impurities, temperature quenching, and shortening the lifetime with induced transitions in the light field. We show that the use of different methods of fluorescence quenching opens new possibilities for studying photoreactions that proceed via excited singlet states. Our consideration concerns a wide range of primary photoprocesses, such as electron density redistribution (internal electron transfer) in the excited state, protolytic reactions, intramolecular proton transfer (phototautomerization), hydrogen bond formation, intermolecular relaxation of molecules in solutions, and formation of excimers and exciplexes. The obtained relations have been used to analyze experimental fluorescence spectra of solutions of some organic compounds, including derivatives of 3-hydroxyflavone and 3-aminophthalimide, subjected to quenching by different methods.     

N_2(B~3Ⅱ_g)高振动态在Xe原子中的碰撞激发和弛豫

在用双光子激发产生的Xe(5p~56p)原子与N_2分子碰撞过程中,有效地生成了N_2(B~3П_g,v=9～14)振动激发态.观察到相应的Δv=4的N_2(B~3П_g-A~3∑_u~+)辐射跃迁萤光,测量了Xe(6p)原子在N_2中的淬灭速率常数,对碰撞弛豫过程进行了讨论.