含甲硫氨酸二肽的单电子氧化反应：激光闪光光解研究

运用248nm激光光解瞬态吸收光谱研究了中性水溶液中丙氨酰甲硫氨酸(Ala-Met)和N-甲酰甲硫氨酰色氨酸(N-Formyl-Met-Trp)的单电子氧化反应过程,分别观察到+和含硫三电子键的生成,但在N-甲酰甲硫氨酰色氨酸体系中没有观察到\+的生成。提出了+和含硫三电子键的生成机理,认为N-甲酰甲硫氨酰色氨酸体系不能生成+三电子键是源于其本身的分子结构。     

丙酮三重态与含芳香氨基酸肽的物理化学过程

用激光闪光光解瞬态吸收光谱研究了水溶液中含芳香氨基酸残基肽的光敏化反应过程.结果表明,在丙酮存在的含色氨酸残基肽(Trp-Gly,n-f-Met-Trp,Trp-Phe)体系的光解,丙酮三重态与Trp分别通过三重态-三重态(T-T)激发能转移和电子转移生成Trp激发三重态和N中心自由基(Trp/N^·);丙酮三重态仅与含酪氨酸残基肽(Phe-Tyr)通过电子转移生成Tyr酚氧自由基(Tyr/O^·).在色氨酰酪氨酸(Trp-Tyr)与丙酮的光解体系中,观察到分子内的电子转移,即由Trp/N^·-Tyr→Trp-Tyr/O^·自由基的生成过程     

维生素K3的激发三重态与色氨酸、酪氨酸电子转移氧化反应的激光闪光光解研究

利用时间分辨的激光闪光光解技术研究了乙腈-水混合溶液(1:1,V/V)中2-甲基萘醌(通常称为维生素K3)的激发三重态对色氨酸、酪氨酸的光敏氧化机理.通过瞬态吸收光谱的变化可以推断维生素K3的激发三重态可以与色氨酸、酪氨酸发生电子转移反应,反应形成的维生素K3阴离子自由基的吸收峰可以直接从瞬态吸收谱图中观察到.维生素K3与色氨酸、酪氨酸的电子转移反应的速率分别为1.1×109和0.6×109L·mol-1·s-1.吉布斯自由能(ΔG)的计算结果表明维生素K3的激发三重态与色氨酸、酪氨酸电子转移反应在热力学上是可行的.     

Hamilton受体与萘之间光诱导电子转移和三重态能量传递研究

将两个2,6-二氨基吡啶衍生物与异酞酸相连, 得到一个袋状巴比妥酸衍生物受体(Hamilton受体, H-receptor), 同时合成了带有萘基团的巴比妥酸衍生物(G-Np), 两者在非极性溶剂中形成氢键体系, 二氯甲烷溶剂中表观结合常数KAPP＝(4.9±0.5)×104 mol－1•L. 稳态荧光发射光谱和磷光发射光谱研究表明, 室温下H-receptor和G-Np之间主要发生单重态电子转移过程, 77 K下, H-receptor与G-Np之间发生三重态能量传递过程. 本研究为Hamilton氢键体系的理论研究提供了一个新的模型, 对理解氢键在生命体系中的作用有重要的意义.     

7-硝基-8-羟基喹啉的合成

以8-羟基喹啉为原料,经硝化和脱磺酸基保护两步反应合成了7-硝基-8-羟基喹啉,总收率69％,纯度高于99％.其结构经1H NMR,13C NMR和HR-MS确证.     

N-羟乙基-1,8-萘二酰亚胺探针与核苷间电子转移的激光闪光光解研究

核酸与核酸前体参与的电子转移(ET)作用能够直接或间接导致核酸主链和碱基侧链的断裂,因此对核酸碱基光动态损害机理的深入研究具有重要的理论和实际意义．其中,核酸荧光探针逐渐成为研究生物分子的主要技术之一,借助于时间分辨的瞬态吸收光谱技术,检测荧光探针激发态物种及其与核酸之间发生电子转移作用而产生的活性中间体,能够深入了解光断裂反应的最初步骤,揭示核酸断裂电子转移反应的微观机理．     

2,6-二氨基-3,5-二硝基吡嗪-1-氧化物的合成

研究了2,6-二氨基-3,5-二硝基吡嗪-1-氧化物(LLM-105)的合成新方法. 该方法是以2,6-二氯吡嗪和甲醇钠作为起始原料, 经烷氧基化、硝化、胺化、N-氧化四步反应得到LLM-105, 总收率为50%. 用¹H NMR, ¹³C NMR, IR, MS和元素分析对LLM-105及其中间体结构进行了表征.     

由8-硝基喹啉羧酸钾衍生的有机胶

一类由8-硝基喹啉羧酸盐衍生的新的有机凝胶可在1：1四氢呋喃/甲醇中选择性地形成，其超结构通过原子力显微镜、扫描电镜以及透射电镜技术得到表征。     

含能材料2,6-二胺-3,5-二硝基吡嗪-1-氧化物的B3LYP 研究

在B3LYP/6-31G^**水平下,研究了LLM-105的稳定几何构型,并进行了集居数分析,自然键轨道(NBO)分析,成键轨道分析,以及振动光谱分析。根据计算可知,LLM-105分子中所有原子均处于同一平面,分子是由一个除了H以久所有原子均参与的大的Ⅱ共轭体系构成;分子内存在着较强的氢键,使分子的稳定性增强;以C-NO2的C-N键键强度最小,可能是分解引发键,在爆炸时最先断裂。     

Electron Transfer Reaction Between Desoxyadenosine and Triplet 2-Methyl-l, 4-naphthaquinone： A Laser Photolysis Study

Introduction Electron transfer oxidation of DNA by triplet artificial photonuclease reveals a bright prospect of its application in biology and medicine. Both molecular orbital calculation and laser experiments have indicated that the homo guanine sequence should be the final localization site of photoexcited hole via long range migration within DNA. However, the direct observation of the produced ion pairs of biomolecules especially the stabilized radical cation DNA or its components is hampered by the overwhelming transient absorption of protonated radical anion of photosensitizers, such as 2-methyl-1,4-naphthaguinonel （MQ）.     

Electron Transfer Reaction Between Desoxyadenosine and Triplet 2-Methyl-1,4-naphthaquinone:A Laser Photolysis Study

Introduction ElectrontransferoxidationofDNAbytripletartifi cialphotonucleaserevealsabrightprospectofitsappli cationinbiologyandmedicine.Bothmolecularorbital calculationandlaserexperimentshaveindicatedthat thehomoguaninesequenceshouldbethefinallocaliza tio…     

Solvent Effect on the Photoinduced Electron Transfer Reaction Between Thioxanthen-9-one and Diphenylamine

Photoinduced chemical reaction between thioxanthen-9-one (TX) and diphenylamine (DPA) were investigated by the nanosecond laser flash photolysis. With photolysis at 355 nm, the triplet TX (³TX^*) is produced via a Franck-Condon excitation and intersystem crossing. In the transient absorption spectra of the reduction of ³TX^* by DPA in pure and aqueous CH₃CN, four bands are clearly observed and assigned to absorption of ³TX^*, TXH^·, TX^·- and DPA^·+, respectively. With the increase of solvent polarity, the blue-shift was observed for all absorption bands of the intermediates. With the aid of dynamic decay curves, an electron transfer followed by a protonation process is confirmed for the reduction of ³TX^* by DPA. The quenching rate constants of ³TX^* by DPA very slightly decrease from 9.7×10⁹ L/(mol·s) in pure CH₃CN, to 8.7×10⁹ L/(mol·s) in CH₃CN:H₂O (9:1), 8.0×10⁹ L/(mol·s) in CH₃CN:H₂O (4:1) and 7.5×10⁹ L/(mol·s) in CH₃CN:H₂O (1:1). Therefore water plays a minor role in the title reaction, and moreover no obvious medium effect of solvent polarity is observed for the electron transfer between ³TX^* and DPA, indicating that the ³nπ^* and ³ππ^* states of TX have the approximate ability to attract an electron from DPA.     

Electron transfer from triplet thymine and thymidine to lipoic acid

Electron transfer from the triplet excited state of thymine or thymidine to the disulphide compound lipoic acid (RSSR) was studied using KrF laser flash photolysis (248 nm, 20 ns). The electron transfer reaction rate constants, measured at 310 nm, were determined to be 1.3×10¹⁰ M⁻¹ s⁻¹ and 6.9×10⁹ M⁻¹ s⁻¹ for thymine and thymidine respectively. The transient absorbance at 400 nm in the presence of the quencher is attributed to the anion radical of lipoic acid.     

Photochemical Hydrogen Abstraction and Electron Transfer Reactions of Tetrachlorobenzoquinone with Pyrimidine Nucleobases

Pentachlorophenol, a widespread environmental pollutant that is possibly carcinogenic to humans, is metabolically oxidized to tetrachloroquinone (TCBQ) which can result in DNA damage. We have investigated the photochemical reaction dynamics of TCBQ with two pyrimidine type nucleobases (thymine and uracil) upon UVA (355 nm) excitation using the technique of nanosecond time-resolved laser flash photolysis. It has been found that 355 nm excitation populates TCBQ molecules to their triplet state ³TCBQ^*, which are highly reactive towards thymine or uracil and undergo two parallel reactions, the hydrogen abstraction and electron transfer, leading to the observed photoproducts of TCBQH· and TCBQ·^- in transient absorption spectra. The concomitantly produced nucleobase radicals and radical cations are expected to induce a series of oxidative or strand cleavage damage to DNA afterwards. By characterizing the photochemical hydrogen abstraction and electron transfer reactions, our results provide potentially important molecular reaction mechanisms for understanding the carcinogenic effects of pentachlorophenol and its metabolites TCBQ.     

H-Atom Transfer Reaction of Photoinduced Excited Triplet Duroquinone with Tryptophan and Tyrosine in Acetonitrile-Water and Ethylene Glycol-Water Homogeneous Solutions

Laser flash photolysis was used to investigate the photoinduced reactions of excited triplet bioquinone molecule duroquinone (DQ) with tryptophan (Trp) and tyrosine (Tyr) in acetonitrile-water (MeCN-H\begin{document}$_2$\end{document}O) and ethylene glycol-water (EG-H\begin{document}$_2$\end{document}O) solutions. The reaction mechanisms were analyzed and the reaction rate constants were measured based on Stern-Volmer equation. The H-atom transfer reaction from Trp (Tyr) to \begin{document}$^3$\end{document}DQ\begin{document}$^*$\end{document} is dominant after the formation of \begin{document}$^3$\end{document}DQ\begin{document}$^*$\end{document} during the laser photolysis. For DQ and Trp in MeCN-H\begin{document}$_2$\end{document}O and EG-H\begin{document}$_2$\end{document}O solutions, \begin{document}$^3$\end{document}DQ\begin{document}$^*$\end{document} captures H-atom from Trp to generate duroquinone neutral radical DQH\begin{document}$^\bullet$\end{document}, carbon-centered tryptophan neutral radical Trp\begin{document}$^\bullet$\end{document}/NH and nitrogen-centered tryptophan neutral radical Trp/N\begin{document}$^\bullet$\end{document}. For DQ and Tyr in MeCN-H\begin{document}$_2$\end{document}O and EG-H\begin{document}$_2$\end{document}O solutions, \begin{document}$^3$\end{document}DQ\begin{document}$^*$\end{document} captures H-atom from Tyr to generate duroquinone neutral radical DQH\begin{document}$^\bullet$\end{document} and tyrosine neutral radical Tyr/O\begin{document}$^\bullet$\end{document}. The H-atom transfer reaction rate constant of \begin{document}$^3$\end{document}DQ\begin{document}$^*$\end{document} with Trp (Tyr) is on the level of 10\begin{document}$^9$\end{document} L\begin{document}$\cdot$\end{document}mol\begin{document}$^{-1}$\end{document}\begin{document}$\cdot$\end{document}s\begin{document}$^{-1}$\end{document}, nearly controlled by diffusion. The reaction rate constant of \begin{document}$^3$\end{document}DQ\begin{document}$^*$\end{document} with Trp (Tyr) in MeCN/H\begin{document}$_2$\end{document}O solution is larger than that in EG/H\begin{document}$_2$\end{document}O solution, which agrees with Stokes-Einstein relationship qualitatively.     

Photoinduced Electron and H-atom Transfer Reactions of Xanthone by Laser Flash Photolysis

The property of the lowest excited triplet states of xanthone in acetonitrile was investigated using time-resolved laser °ash photolysis at 355 nm. The transient absorption spectra and the quenching rate constants(kq) of the excited xanthone with several amines were determined. Good correlation between lgkq and the driving force of the reactions suggests the electron transfer mechanism, except aniline and 3-nitroaniline (3-NO2-A) which showed energy transfer mechanism. With the appearance of ketyl radical, hydrogen atom transfer also happened between xanthone and dimethyl-p-toluidine, 3,5,N,N-tetramethylaniline, N,N-dimethylaniline, and triethylamine. Therefore, both electron transfer and H-atom transfer occured in these systems. Great discrepancies of kq values were discovered in H-atom abstraction reactions for alcohols and phenols, which can be explained by di?erent abstraction mechanisms. The quenching rate constants between xanthone and alcohols correlate well with the ?-C?H bonding energy of alcohols.