乙二醇均相溶液中苊醌三重激发态淬灭反应的TR-ESR研究

利用时间分辨电子自旋共振(TR-ESR)方法,研究了乙二醇(EG)均相溶液中稳定自由基TEMPO和生物抗氧化剂维生素C(VC)对苊醌(ACQ)激发三重态3ACQ*的淬灭反应.光解ACQ/EG体系,观察到苊醌中性自由基ACQH*和乙二醇烷基自由基的发射/吸收+发射(E/A+E)的CIDEP信号,ACQH*和CH2(OH)CHOH由3ACQ*从EG上夺氢生成.光解ACQ/TEMPO/EG体系,3ACQ*与TEMPO相互作用将极化转移给TEMPO.光解ACQ/VC/EG体系,3ACQ*除了从EG上夺氧外,还从VC上夺氢生成VC负离子基As*-.较强的As*-的CIDEP信号表明VC对3ACQ*有明显的淬灭作用.     

杜醌自由基光化学路径的CIDEP研究

用自制的高时间分辨电子自旋共振波谱仪,测量得到了酸性、碱性和胶束环境下的光解杜醌/乙二醇(DQ/EG)溶液瞬态自由基的化学诱导动态电子自旋极化(CIDEP)谱.在光解均相DQ/EG溶液时,观察到了以增强发射的的中性杜半醌自由基(DQH.)的CIDEP信号;在碱性环境下(pH=9)和TX-100胶束环境下光解DQ/EG体系时得到杜醌负离子自由基(DQ-.)的CIDEP信号;在酸性环境下(pH=2.5)光解DQ/EG体系时,出现的又是中性杜半醌自由基(DQH.)的CIDEP信号.实验结果显示,DQH.由3DQ*与EG之间的氢原子转移反应生成,DQ.-由DQH.的去质子化反应生成,反应中伴随着极化转移.     

维生素C对菲醌三重激发态的淬灭机理及动力学研究

用时间分辨电子自旋共振技术研究了乙二醇(EG)均相溶液和反胶束溶液中抗氧化剂维生素C(VC)对菲醌(PAQ)分子激发三重态³PAQ*的淬灭反应．利用反胶束模拟生物细胞和组织的生理环境．光解PAQ/EG-H₂O均相溶液,³PAQ*与溶剂分子EG之间发生氢转移反应．当体系中加入VC后,³PAQ*不仅从EG上夺氢,还从VC上夺氢,VC对³PAQ*的淬灭速率常数为1.409×10⁸ L/(mol·s), 反应受扩散控制． 在CTAB/EG-H₂O和AOT/EG-H₂O反胶束溶液中,³PAQ*和VC之间的夺氢反应发生在反胶束的水/油界面附近,³PAQ*扩散到油/水界面的过程降低了反应的速率．对于TX-100/EG-H₂O反胶束溶液, 由于PAQ增溶于亲水的聚氧乙烯链中,VC对³PAQ*的淬灭速率常数比CTAB/EG-H₂O和AOT/EG-H₂O反胶束中的都大,甚至比EG-H₂O均相溶液中的也略大．很强的VC负离子自由基As^-的CIDEP信号来源于³PAQ*与VC之间发生抽氢反应过程中的三重态机理自旋极化转移     

光解杜醌/氢给体均相体系的CIDEP研究

以杜醌为光敏剂,用高时间分辨电子自旋共振 (TRESR)波谱仪研究了杜醌/乙二醇体系、杜醌/氮氧自由基/乙二醇体系的化学诱导动态电子自旋极化(CIDEP).实验表明,紫外激光照射下,在杜醌/乙二醇溶液中得到以三重态机理极化为主的中性杜半醌自由基DQH*和以碳为中心的乙二醇碳自由基R*(OH)2的极化信号,而加入氮氧自由基 TEMPO后,则只观测到极化的TEMPO的E+E/A极化谱,其产生机理属于以四重态为先驱的自由基-三重态对极化机理(QP-RTPM),结合极化强度的理论计算对该体系的极化形成过程进行了分析.     

乙二醇均相及其TX-100胶束溶液中光敏分子菲醌的激光光解研究

用时间分辨电子自旋共振（TR-ESR）和瞬态吸收光谱技术,研究了菲醌在乙二醇均相及其TX-100含水胶束溶液中的光化学反应机理。化学诱导动态电子极化（CIDEP）谱和瞬态吸收光谱都表明,在乙二醇均相溶液中,菲醌光激发三重态3PAQ* 夺取氢原子形成中性自由基PAQH.,三重态机理是CIDEP形成的主要机理。在TX-100含水胶束溶液中,光解主要得到菲醌负离子基PAQ-．,PAQ-．由PAQH.解离形成,解离过程中伴随着极化转移。     

丙酮/1,2-丙二醇体系的化学诱导动态电子自旋极化研究

285 nm紫外激光照射下,用时间分辨电子自旋共振(TRESR)波谱仪研究了光解丙酮/1,2-丙二醇(ACETONE/PG)体系,得到了丙酮羰自由基(CH3)2.COH和1,2-丙二醇羰自由基CH3.COHCHOH的发射/吸收(E/A)型极化信号,这是一个自由基对(RPM)极化过程。在酸性环境中,溶剂分子的CIDEP谱明显减弱,(CH3)2.COH的CIDEP谱无明显变化,由此可判断光解ACETONE/PG体系是一个夺氢反应;在碱性环境中,(CH3)2.COH反应生成负离子基(CH3)2.CO-.     

光解对苯醌/甲酰胺体系的CIDEP实验研究

以对苯醌为光敏剂,用高时间分辨电子自旋共振(TRESR)波谱仪研究了对苯醌/甲酰胺体系在酸性、碱性、胶束环境下的化学诱导动态电子自旋极化(CIDEP).光解对苯醌/甲酰胺体系,得到了以苯醌负离子基PBQ·-为主的,同时伴随稍弱的苯半醌自由基PBQH·-的发射CIDEP谱;光解碱性环境和胶束环境下的对苯醌/甲酰胺体系,只得到PBQ·-的CIDEP信号;光解酸性环境下的对苯醌/甲酰胺体系,只得到PBQH·的CIDEP信号.实验结果表明对苯醌负离子基PBQ·-由苯半醌自由基PBQ·解离得到.     

光解丙酮/乙二醇体系的CIDEP实验研究

紫外激光照射下,用时间分辨电子自旋共振(TRESR)波谱仪研究了光解ACETONE/EG体系的化学诱导动态电子极化(CIDEP),得到了丙酮羰自由基(CH3)2C.OH和乙二醇羰自由基CH2OH C.HOH的发射/吸收(E/A)型极化信号,这是一个RPM极化过程.在胶束环境中,不同表面活性剂以及不同的浓度对体系极化的影响是不同的.阳离子表面活性剂CTAB对体系中生成的自由基的极化机理没有产生显著影响,而加入体系中TX-100的浓度对体系的极化机理却产生了很大的影响.在ACETONE/EG体系中,随着TX-100浓度的增加,TM机理对极化强度的贡献明显增大.     

285 nm激光光解对苯醌-乙二醇体系的CIDEP波谱解析

在285 nm紫外激光辐照下,用时间分辨电子自旋共振(TRESR)波谱仪研究了对苯醌/乙二醇(PBQ/EG)体系,得到了发射的苯半醌中性自由基PBQH.和乙二醇碳自由基R.(OH)2的CIDEP谱.在化学诱导动态电子极化(CIDEP)基本原理的基础上,建立合理的计算模型,编写相应的程序,对PBQH.和R.(OH)2的CIDEP形成机理进行了定量的解析.通过对不同延时下该体系各种自由基及不同机理成分的对比,明显看出由RPM形成的PBQH.比由TM形成的PBQH.衰减快.这种分析方法可以推广应用于其它体系的CIDEP实验谱的解析.     

吩噻嗪-1,4萘醌-乙二醇体系光化学过程的时间分辨ESR研究

用时间分辨ESR方法研究了吩噻嗪(PTH)-1,4-萘醌(NQ)-乙二醇(RH)体系中的光化学过程.只观察到萘醌的中性半醌自由基NQH^*的全发射极化的CIDEP(化学诱导动态极化)信号,并未观察到极化的萘醌负离子NQ·^-*的CIDEP信号,表明RH与三重态NQ间的质子转移反应远比PTH与NQ间的电子转移反应为快.NQH·^*的CIDEP信号随pH值的变化表明体系中同时有极化自由基NQH·^*与NQH·₂^+*存在,并且其间有质子交换.     

Viscosity Effect Study on Quenching of Photoinduced Excited Triplet Duroquinone by TEMPO

ABSTRACT

Quenching dynamics of excited quinone molecules are given much attention in photochemistry and biochemistry. In order to study the viscosity effect on the quenching of triplet excited state of duroquinone (³DQ?) by stable radical, 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO), this study measured chemically induced dynamic electron polarization (CIDEP) spectra and transient absorptive spectra in various solvents. The solvents used were ethylene glycol, 1,2-propanol and their mixtures with different ratio in volume. The Stern-Volmer plot was obtained form CIDEP spectra of photolysis of DQ with different TEMPO concentrations. Combining the slope of the Stern-Volmer plot with lifetime of ³DQ?, determined from the ³DQ? transient absorbance decay curve, the quenching rate constants of ³DQ? by TEMPO were calculated in each solvent. The results indicate that the quenching rate constant is viscosity-dependent, and that it decreases linearly with the increase in solvent viscosity in the range used in our experiment.     

FT-EPR and HPLC study of the mechanism of 4-chlorophenol photolysis

The mechanism of 4-chlorophenol (4CP) photolysis was investigated with the aid of Fourier Transform Electron Paramagnetic Resonance (FT-EPR) and pulsed-laser photolysis combined with High Performance Liquid Chromatography (HPLC) detection-of stable (diamagnetic) products. With FT-EPR transient free radicals produced by pulsed-laser excitation of solutions of 4CP in alcohols could be identified. Time profiles of the FT-EPR spectra provided information on reaction kinetics and Chemically Induced Dynamic, Electron Polarization (CIDEP) effects. It was found that 4CP photolysis in alcohols leads to the simultaneous formation of the phenoxyl radical and radicals produced by hydrogen abstraction from the solvent. CIDEP patterns establish that these radicals are formed in a reaction sequence involving a triplet state precursor and radical pair intermediate. Results of earlier transient optical absorption measurements indicate that the triplet precursor must be the carbene 4-oxocyclohexa-2,5-dienylidene. This assignment is supported by the finding that photolysis of quinone diazide in a hydrogen-donating solvent gives the same free radical products as those obtained from 4CP. The formation of the phenoxyl radical intermediate accounts for the finding that photolysis of deoxygenated solutions of 4CP in alcohols gives phenol as stable diamagnetic product. By contrast, photolysis of aerated and deoxygenated aqueous solutions of 4CP produces benzoquinone and hydroquinone as primary products, respectively.     

Photo-Induced Electron Transfer in P3DDT, P3OT, M3EH-PPV Conjugated Polymers Blended with Maleic Anhydride in THF Solution Under UV Flash Photolysis Studied by Means of CW TR ESR

Free-radical signals of positive polarons in conjugated polymer chains and maleic anhydride (MA) anion radicals were registered in poly(3-octylthiophene) P3OT:MA and (poly[2,5-dimethoxy-1,4-phenylene-1,2-ethenylene-2-methoxy-5-(2-ethylhexyloxy)?C(1,4-phenylene-1,2-ethenylene)]) M3EH-PPV:MA blends in tetrahydrofuran (THF) solutions under ultraviolet flash photolysis (308?nm) by continuous-wave time-resolved electron spin resonance. Their emissive chemically induced dynamic electron polarization (CIDEP) originated mainly from excited triplet states (triplet mechanism of CIDEP) and partly by from the radical pair mechanism due to the singlet?Ctriplet mixing states. The observed M3EH-PPV polaron spectrum (g ₀?=?2.0029) supports the supposition that the previously registered CIDEP spectra in P3DDT:MA blends (g ₀?=?2.0021) can be attributed to the polaron signals instead of the possible solvate electron signal one.     

CIDEP Created by the Quenching of Photo-Excited Tryptophan at Protein Surface: A Challenge to CIDEP Probing of Protein Structural Changes

Quenching of the triplet excited state of molecular tryptophan by nitroxide radical in 1,4-dioxane and water solutions was investigated by means of time-resolved electron paramagnetic resonance (EPR) and Fourier-transform (FT)-EPR. The chemically induced dynamic electron polarization (CIDEP) signals with net emissive phase were recorded at these quenching events and were analyzed through radical-triplet pair mechanism. The CIDEP time profiles were well reproduced by Bloch and kinetic equations, assuming radical-triplet pair mechanism with the appropriate quenching rate constants. From a comparison of the simulation and the experiment, CIDEP enhancement factor in 1,4-dioxane was determined to be −30 × P _eq, where P _eq is the spin polarization of nitroxide at thermal equilibrium. Net emissive CIDEP was also observed by FT-EPR measurements on the nitroxide quenching of the triplet excited state of tryptophan residue in α-lactalbumin. Magnitude of CIDEP created in α-lactalbumin/nitroxide system depends on the pH condition of α-lactalbumin solution, which is related to protein folding dynamics. We argue the CIDEP mechanism at the α-lactalbumin surface and propose a possibility of a novel CIDEP method to probe a protein surface and structural changes.     

化学诱导动态电子极化自由基-三重态对理论中选择三重态淬灭的证明

用时间分辨ESR测出的吩噻嗪/2,2,6,6-四甲基哌啶氮氧自由基(TEMPO)光诱导产生的三重态发射CIDEP信号可用Blätter提出的自由基-三重态对机理来解释,由荧光光谱及脉冲激光光声微量量热实验结果直接证明了Bläter理论关于自由基只选择淬灭双重自旋态的自由基/三重态对中的三重态的假设.