9,10-二氰基蒽光敏化香豆素加成反应的研究

光化学中的电子转移反应近年来引起了人们广泛的重视。9,10-二氰基蒽(DCA)作为贫电子敏化剂敏化的各类烯烃的光氧化反应,光重排反应,光加成反应等均有报道。我们在研究DCA光敏化香豆素反应时发现,香豆素与DCA能够发生电子转移的给体—受体加成反应,联苯(BP)可以充当二次电子转移体加速反应。     

1,4-二苯基-1,3-丁二烯的氰基蒽敏化光氧化反应

某些不能与单线态氧(~1O_2)起反应的烯烃、炔烃、硫醚和环氧化合物,在以氰基蒽为敏化剂的条件下,可发生经由光敏电子转移机理的氧化反应.近年来,Santamaria 等,Foote 等和我们都在研究这类反应.本文报道以9,10-二氰基蒽(DCA)为敏化剂、反,反-1,4-二苯基-1,3-丁二烯为反应物的电子转移光敏氧化反应,并讨论了反应机理.     

缺电子芳烃侧链基的光氧化

研究了9,10-二氰蒽(DCA)和四氯对苯二醌(TCBQ)敏化的甲苯、对氯甲苯、对氰基甲苯和对硝基甲苯的电子转移光氧化反应。DCA和TCBQ均可敏化甲苯和对氯甲苯的光氧化。产物为相应的取代苯甲酸和取代苯甲醛。DCA和TCBQ均不能有效敏化对氰基甲苯和对硝基甲苯的光氧化, 但在反应体系中加入与反应物等摩尔的联苯为共敏化剂后, 两者即可顺利氧化为相应的取代苯甲酸和取代苯甲醛。通过荧光淬灭和共敏化剂联苯、无水盐高氯酸镁、O2捕获剂对苯二醌以及电子给体对二甲氧基苯等外加试剂对光氧化的影响讨论了反应历程。     

缺电子芳烃侧链基的光氧化

研究了9,10-二氰蒽(DCA)和四氯对苯二醌(TCBQ)敏化的甲苯、对氯甲苯、对氰基甲苯和对硝基甲苯的电子转移光氧化反应。DCA和TCBQ均可敏化甲苯和对氯甲苯的光氧化。产物为相应的取代苯甲酸和取代苯甲醛。DCA和TCBQ均不能有效敏化对氰基甲苯和对硝基甲苯的光氧化, 但在反应体系中加入与反应物等摩尔的联苯为共敏化剂后, 两者即可顺利氧化为相应的取代苯甲酸和取代苯甲醛。通过荧光淬灭和共敏化剂联苯、无水盐高氯酸镁、O2捕获剂对苯二醌以及电子给体对二甲氧基苯等外加试剂对光氧化的影响讨论了反应历程。     

不同紫精在光解水释氢反应中的影响

本文研究了以非水溶性的四苯基卟啉锌为敏化剂,各种不同紫精化合物为电子中继物,胶体铂为催化剂,乙二胺四乙酸二钠盐为电子给体组成的四组分胶束体系的光分解水释氢反应。着重讨论了这些紫精化合物对该反应的影响。     

α-蒎烯,β-蒎烯的电子转移敏化光氧化反应的研究

本文从荧光淬灭、激基复合物、E_(1/2)的测定和k_a,△G的计算证明了典型的单线态氧的“探针”化合物a-蒎烯和β-蒎烯在极性溶剂中,用9,10-二氰基蒽(DCA)作敏化剂时,发生的是电子转移敏化光氧化反应。通过反应产物的分离和鉴定、溶剂效应的研究以及单线态氧和自由基淬灭剂对反应的淬灭试验,进一步讨论了该反应的机理。     

异黄樟素光异构化反应的研究

本文报道了异黄樟素光异构化反应的研究。直接光照或用二苯甲酮为敏化剂时,异黄樟素光异构化反应有利于生成其顺式异构体;以9,10-二氰基蒽(DCA)、9-氰基蒽(CNA)以及四氯苯醌为敏化剂时异构化反应有利于生成其反式异构体。我们利用色谱、色质联用、红外以及质子核磁共振等技术对异黄樟素的顺反异构体进行了分析鉴定,并初步探讨了反应机理。     

9,10-二氰基蒽光敏夺氢反应的研究

本文研究了缺电子敏化剂9,10-二氰基蒽(DCA)对苄醇类化合物(二苯甲醇、苯甲醇)及甲苯类化合物(甲苯、对-二甲苯)的光敏化夺氢反应,证明上述两类反应是经由两种不同机制进行的。     

一种新型含有噁二唑单元的有机太阳能电池染料敏化剂的合成

通过Sonogashira偶联反应合成了一种三苯胺作为电子给体、噁二唑单元作为电子传输体、羧酸部分作为电子受体的新型染料敏化剂。通过核磁、高分辨质谱、紫外光谱对此化合物的结构和性能进行了表征和测试。氧化还原电位计算表明,此化合物可以作为二氧化钛电极的敏化剂。     

以9,10-二氰基蒽为敏化剂对几种硫醚光氧化初级反应机理的研究

本文研究了多种硫醚化合物对9,10-二氰基蒽(DCA)的荧光猝灭过程,并观察到DCA与硫醚间形成的激基复合物的荧光发射峰。这些证据表明,受光激发后DCA与硫醚之间发生了电子转移。以DCA作敏化剂可氧化异丁基硫醚、羟乙基硫醚以及难以被单线态氧氧化的苯基硫醚。其反应机理可能经历了电子转移,生成氧负离子(superoxide),然后再氧化硫醚生成亚砜这样的过程。     

Cofactor Recycling Mechanism in Asymmetric Biocatalytic Reduction of Carbonyl Compounds Mediated by Yeast: Which is the Efficient Electron Donor?

In asymmetric reduction of carbonyl compounds mediated by microorganisms, the cofactors that transfer hydride should be regenerated by using a recycling system. In most cases, this recycling system consists of carbohydrate molecules, especially glucose or sucrose. Other molecules such as ethanol and acetate have been used as electron donors too. The reduction can even be conducted without added electron donors. To improve biocatalytic synthesis, it is important to understand the cofactor recycling mechanism. In this work, the hydride‐transfer mechanism in cofactor regeneration, which takes place in bioreduction mediated by yeast, was studied by means of an isotope tracing technique. The results show that, when glucose was used, the NADH involved in the glycolysis was consumed directly in the formation of ethanol and was not used in the bioreduction. Hence, the regeneration of cofactors in the reduction is not coupled with glycolysis. Nevertheless, glucose is an efficient electron donor that transfers hydride through the hexose monophosphate (HMP) pathway in which the main hydrogen source is C‐1 and C‐3 hydrogen of glucose. Ethanol is not a good electron donor, since, when it was used, only a small quantity of hydrogen was transferred from this molecule, and the main hydrogen source was water. Therefore, the ethanol oxidation pathway may not be efficient. In the absence of added auxiliary substrates, the yeast cells may use electron donors stored in its cellules. However, in this case we observed that the main hydrogen source for cofactor recycling was water, while only very few hydrogen atoms were from unexchangeable sites. This is similar to the case in which ethanol is used, and is in contradiction with the HMP pathway if stored glucose was the electron donor. The question that remains to be investigated is “what is the efficient electron donor recycling mechanism in the yeast cellules?”     

[2.2]- and [3.3]Paracyclophane as Bridging Units in Organic Dyads for Visible-Light-Driven Dye-Sensitized Hydrogen Production

Novel donor–acceptor dyads containing [2.2]- and [3.3]paracyclophane (PCP) as the bridging moiety were synthesized and used to effectively fabricate dye-sensitized hydrogen production systems. All the prepared compounds had a phenothiazine and a cyanoacrylic acid/pyridinyl acrylonitrile moiety acting as an electron donor and acceptor, respectively. Although cyclic voltammetry measurements showed similar electron-donating properties among all the synthesized dyads, the lowest absorption energy of the [2.2]PCP moiety was lower than that of the [3.3]PCP one; this was due to its shorter distance between benzene rings, which could effectively drive the charge transfer between the donor and acceptor chromophores. Under visible light (>395 nm), a dyad-loaded photocatalyst in a 0.5 M aqueous glycerol solution generated detectable hydrogen gases. The optimal turnover number and photocurrent order exhibited the same trend as the hydrogen production rate since the suggested number of excited photons played a critical role in hydrogen production.     

PROFLAVIN CATALYZED PHOTOPRODUCTION OF HYDROGEN FROM ORGANIC COMPOUNDS

Abstract— Methyl viologen was reduced by EDTA and other organic compounds when aqueous solutions of these compounds were irradiated near 440 nm in the presence of catalytic quantities of proflavin. The photoreduced methyl viologen was readily oxidized in the dark by the enzyme hydrogenase or platinum asbestos. When the entire reaction was run in the light with hydrogenase or platinum, continuous production of hydrogen was observed. The yield of hydrogen was approximately stoichiometric to the EDTA present establishing that methyl viologen and proflavin were acting catalytically. To establish the structural requirements of the electron donor, eighty compounds were tested at seven pH values between 4 and 10. Of these, twenty served as electron donors for the photoproduction of hydrogen. The effective donors contained either a secondary or tertiary nitrogen atom with one or more carboxymethyl or β-hydroxyethyl groups, or a sulfhydryl group. The system could also reduce benzyl viologen but not methylene blue. Riboflavin did not replace proflavin for the photoproduction of hydrogen, This system may have potential for producing hydrogen with solar energy.     

A dehydrogenation mechanism of metal hydrides based on interactions between Hdelta+ and H-

This paper describes a reaction mechanism that explains the dehydrogenation reactions of alkali and alkaline-earth metal hydrides. These light metal hydrides, e.g., lithium-based compounds such as LiH, LiAlH4, and LiNH2, are the focus of intense research recently as the most promising candidate materials for on-board hydrogen storage applications. Although several interesting and promising reactions and materials have been reported, most of these reported reactions and materials have been discovered by empirical means because of a general lack of understanding of any underlying principles. This paper describes an understanding of the dehydrogenation reactions on the basis of the interaction between negatively charged hydrogen (H-, electron donor) and positively charged hydrogen (Hdelta+, electron acceptor) and experimental evidence that captures and explains many observations that have been reported to date. This reaction mechanism can be used as a guidance for screening new material systems for hydrogen storage.     

Modifying effects of cysteine and aromatic sulfhydryl and disulfide agents on the radiation-induced decomposition of thymidine

Steady-state γ radiolysis of oxygen-free aqueous solution of thymidine has been carried out in the presence of cysteine and five aromatic sulfydryl and disulfide agents. The common major mode of action of these compounds is their ability to scavenge water radiolysis species including OH^• radicals and solvated electrons. In addition, cysteine and the two compounds with a free SH group were found to act as hydrogen donor leading to an increase in the formation of the 5R and 5S diastereoisomers of 5,6-dihydrothymidine and 5-hydroxy-5,6-dihydrothymidine. Two sulfhydryl agents including cysteine were also found to chemically repair the radiation-induced osidic radicals through efficient hydrogen donation mechanisms. It should be noticed that hydrogen atom transfer to hydroxyl and electron thymidine adducts leads to the decomposition of the thymine moiety.     

稳定同位素方法研究模型化合物之间的氢转移反应

二十烷,菲作为模型化合物,以四氢萘为供氢剂,在临氮及临氢体系中应用氘代四氢萘考察供氢剂的氢转移反应,发现供氢剂抑制烷烃的裂化,其作用是通过脱氢湮灭自由基来抑制裂化反应。临氮及临氢条件下,与正二十烷与菲的二元体系相比,正二十烷,菲和四氢萘三元体系中四氢萘不仅能生成较多的菲的氢化芳烃产物,而且稳定同位素方法表明氘代四氢萘可以向菲和菲的氢化芳烃产物转移更多的氘,同时发现H12－四氢萘和D12－四氢萘的供氢（氘）率上存在着动力学同位素效应。     

稳定同位素方法研究正构烷烃与四氢萘二元体系的反应

以正构烷烃作为模型化合物的热反应、临氢反应、临氢催化反应中,添加供氢剂抑制正构烷烃所裂化;气相氢和供氢剂的供氢参与饱和烯烃,两者是性质不同的氢源,前者加速裂化,后者抑制裂化。供氢剂供氢行为依赖于反应体系自由基的多少和温度以及反应过程,反应体系较多的自由基和较高的反应温度有利于供氢行为。稳定同位素方法研究模型化合物的裂化反应表明,供氢剂的作用是通过脱氢湮灭自由基来抑制裂化反应,同时发现H12－四氢萘和D12－四氢萘的供氢（氘）率上存在着动力学同位素效应,在临氢及临氢催化体系中尤其是临氢催化体系中,动力学同位素效应变得不再明显。     

Reactivity of tert-butoxyl radicals towards substituted indole derivatives

Tert-butoxyl radicals react with indole and methyl substituted derivatives by hydrogen abstraction. For those compounds which are unsubstituted at the N-atom, hydrogen abstraction takes place almost exclusively at the N? H bond. The reactivity of these compounds correlates with their donor electron capacity, pointing to significant contribution of charge transfer to the transition state stability. Substitution at the N atom considerably decreases the reactivity.     

Self－assembly of Novel Hetero[3]rotaxane, [2]Rotaxanes and [2]Catenane

One linear template 13 and one cyclophane template 15, both incorporating two electron rich 1,4‐dialkoxybenzene units and one diamide unit, have been synthesized. By utilizing donor‐acceptor interaction and/or intermolecular hydrogen bonding assembling principles, one novel hetero[3]rotazane 22·4Cl, possessing one neutral and one tetracationic ring components, has been synthesized from 13, through neutral [2]rotaxane 21 as intermediate. With 15 as template, tetracationic [2]catenane 23·4PF₆ was assembled by using donor‐acceptor interaction, but no neutral [2]rotaxane could be obtained under the typical conditions of hydrogen bonding assembling principle. The interlocked supramolecular compounds have been characterized and their spectral properties are investigated.