分子氧对光合作用原初反应模拟体系中能量转移的影响

叶绿素吸收光能后,在光合作用能量传递的途径中,质醌被认为是原初光反应中叶绿素光能转换的原初受体。因此研究能量转移的模拟光合作用原初反应体系,用醌类化合物做光激发叶绿素的电子受体,为研究电子传递途径、方式和可能的机理,受到了相当的重视。在这类相当广泛的研究中,虽然提出了各说不一的机理,但其结果都得到了叶绿素阳离子((chl⁺)和半醒阴离子(Q^-)自由基,肯定了光激发的叶绿素能量首先传递给醒的结论。     

质体醌类化合物的合成研究

醌环的取代基对醌类化合物进行光合作用的电子传递过程有很大影响. 我们设想若能在保持与醌环上的甲基相近体积的条件下, 将其中一个甲基换成氯原子, 这样, 这类化合物醌环上的电子密度显然会低于质体醌, 从而进一步研究它们在光合作用中的作用, 有助于进一步阐明光合作用机制, 以3-氯-2-甲基苯胺为原料, 经氧化, 自由烷基化反应, 合成了十六个具有不同长侧链结构的质体醌类似物.     

带有长侧链醌类化合物的Langmuir膜及其表面电势

泛醌(Ubiquinone)和质体醌(Plastoquinone)作为非蛋白电子载体存在于动物线粒体呼吸链和植物光合作用链中.这两类物质在生物膜上有活性.     

叶绿素的提取纯化方法

自然界中,太阳能转化成化学能的最主要途径是光合作用过程。光合作用过程中担任把光能吸收转化成化学能的主要角色是含镁的卟啉类化合物——叶绿素。由于叶绿素起着如此重要作用,因此引起了很多科学工作者的兴趣。他们把叶绿素提取分离出来,测定了它的分子结构、化学物理性质。在1962年全合成了其中最重要的一种——叶绿素a。叶绿素在光合器官中有不同的存在状态,起着不同的作用。有的叶绿素起捕获光能的功能,它们吸收光能并将光能传递到作用中心去;有的处在作用中心,推动把光能转化成化学能的原初过程。要说明叶绿素是怎样和蛋白质、磷脂、质醌等复合在一起的,这种复合体是怎样发挥固定光能的功能的,这是近年来受到广泛重视的研究课题之一。很多人都想通过研究纯粹的叶绿素和它的衍生物的光化学物理性质,体外重组和模拟光合作用过程     

2,6-二甲氧基-3-烷基-1,4-苯醌的合成

取代的1,4-苯醌类化合物广泛存在于自然界的植物和动物体内。其中有一部分已证明具有明显生理活性。最重要的取代1,4苯-醌类化合物是泛醌(ubiquinone)和质体醌(plastoquinone)。它们是动物线粒体呼吸链和植物光合作用链中重要的非蛋白电子载体。2,6-二甲氧基-1,4-苯醌(4)存在于许多植物的树皮和木心中。它的生理作用目前还知道得     

光合反应中心原初电子转移机理的理论研究

用量子化学密度泛函B3LYP方法在3-21G水平上计算细菌光合反应中心原初电子给体P960和绿色植物PSⅡ光合反应中心原初电子给体P680的电子结构,然后研究轴向配位的组氨酸残基和周围蛋白质环境的影响,最后探讨其原初电子转移机理。计算结果表明：(1)细菌光合作用反应中心原初电子给体P960-h的HOMO主要是由与M分支相连的组成单元上原子的原子轨道组成,而它的LUMO则两个组成单元上原子的原子轨道都有贡献;PSⅡ反应中心中原初电子给体P680的HOMO和LUMO均主要由与D1蛋白相连的组成单元上原子的原子轨道组成。这些计算结果能够从反应中心最核心的部分-原初电子给体的电子结构方面解释Rps.uiridis反应中心和PSⅡ反应中心原初电子转移只沿一个分支进行的的途径选择性。(2)虽然与细菌反应中心原初电子给体超分子P960的两个细菌叶绿素分子形成轴向配位的组氨酸残基His并未参与超分子P960-h的HOMO和LUMO的组成,但是由于其轴向配位,使得P960-h的ELUMO显著地升高到高于辅助细菌叶绿素和去镁细菌叶绿素的相应值,使得原初电子转移反应能够顺利进行。否则原初电子转移反应很难进行。PSⅡ反应中心的情况,与细菌反应中心十分相似。(3)细菌反应中心辅助细菌叶绿素(ABChlb)中的Mg离子与最近的组氨酸残基His中的N原子的距离和原初电子给体P960中的相应的Mg-N的距离相似,因此同样应该考虑此轴向配位的组氨酸残基,此时原初电子转移反应是沿L分支从P960-h经ABChlb到去镁细菌叶绿素(BPheob)的两步电子转移过程。而PSⅡ反应中心的辅助叶绿素不存在His的轴向配位,这应是与细菌反应中心的重要区别之一,此时原初电子转移应是沿Dl分支从P680-h到Pheoa的一步电子转移过程,但同时也不能完全排除从P680-h到AChla到Pheoa的二步电子转移过程。     

对光合作用机制研究的一些展望与两点建议

今后我国光合作用研究既要全面开展又要重点突出。现拟就光合作用机制的研究作一些展望,并对重点工作作两点建议。光合作用原初反应的研究原初反应,即光能通过叶绿素转变为化学能的最初步骤,是光合作用的核心问题。自本世纪20年代Warburg将光化学的两个原则运用到光合作用研究开始,物理学家们即着手研究光量子对叶绿素分子激发的状态。和从固体物理学方面研究光对叶绿素的激发。     

泛醌类化合物研究进展

泛醌在线粒体和光合作用的电子迁移系统中起着十分重要的作用。本文对天然泛醌的分离方法,各类合成泛醌类似物的合成方法,结构特点和化学性质作一简要介绍。     

取代四苯基卟啉蒽醌化合物的合成、结构和光物理性质

在光合作用模拟研究中,人们常选用与叶绿素具有相同π体系的卟啉类化合物作为电子给体,与另一电子受体组成合成反应中心。由于自然界光台作片用中,多数电子受体都是由醌类承担,因此,对卟啉醌共价相连化合物的研究     

玻碳电极上多巴胺的氧化还原机理

用电化学方法和光谱电化学方法详细研究了多巴胺(DA)在玻碳(GC)电极表面的反应机理.结果表明DA的电氧化是一个单电子转移过程而不是一个双电子转移过程,在此过程中有半醌自由基中间体存在.用多种电化学手段测定了电极反应动力学参数,提出了新的电极反应机理.     

The Role of Interface on the Properties of Cluster Assemblies

Atomic clusters characterized by finite size, low dimensionality, and reduced coordination number exhibit many novel properties that are very different from their bulk. As these clusters are assembled, their properties can be significantly altered due to the interaction of these clusters with each other as well as with their support. This paper provides a brief review of the cluster properties that are affected when clusters are deposited on metallic or organic substrates, isolated in matrices or in zeolite cages, coated with acetate ligands, or simply allowed to self-assemble without the presence of any reactive species. It is shown that the interface between the clusters and their support can play an important role on the properties of clusters as their unique characteristics do.     

功能性两亲嵌段共聚物的研究进展

功能性两亲嵌段共聚物因自身独特的性质而在靶向输送、控制释放、分子识别等领域得到广泛的应用.本文对这类嵌段共聚物的合成方法、其胶束的形成机理、制备形式、表征手段以及一些常见的具有光学活性的两亲嵌段共聚物及其应用进行了综述.     

Occurrence, biological activities and synthesis of kaurane diterpenes and their glycosides

This paper presents a review on kaurane diterpenes and their glycoside derivatives, covering aspects of their occurrence, biological activities and the synthesis of these natural products and their analogues. First, it shows and classifies diterpenes, in accordance with the already established structural criteria in the literature. Then, kaurane diterpenes are presented, focusing on their chemical structures, occurrence in the plant kingdom and their main, recently described, biological activities. Moreover, the most significant works, published between 1964 and November 2006, which describe the total synthesis or structural transformations of some kaurane diterpenes, including either semisynthetic and/or microbiological methodologies, are consisely reviewed. At this point, some general considerations on glycosides are introduced, and kaurane glycosides are presented and discussed on the basis of their toxic importance and occurrence in the plant kingdom, having focused on related aspects of their biological activities and the relationships between these activities and the structural factors of their molecules. Finally, the principal methods of glycosidation by enzymatic and chemical processes are both presented, and a few papers on the synthesis of kaurane glycosides are succinctly discussed.     

The synthesis and characterization of aliphatic sulfonic acid cation exchangers for HPLC

Summary Two oxidation procedures for the synthesis of silicabased aliphatic sulfonic acid cation-exchangers for HPLC are described. Several reaction conditions for oxidizing a terminal-bonded thiol with organic peroxides are provided along with their yields, capacities, reproducibility, and chromatographic behavior. Also, three methods for determining exchange capacity are discussed, and their relationship to the capacity factors of charged solutes is compared. The maximum capacity determined by the titration of the bonded silica was 0.34 meq/gram. The general problems of synthesizing cation-exchangers, measuring their efficiencies and exchange capacities, and evaluating their overall performances are outlined.     

Nontargeted UHPLC–MS for the Study of the Diversity of Flavonoid Glycosides in Different Fermented Teas

Chromatographia - Although black tea and dark tea are both fermented teas, their fermentation processes are varied a lot and strongly affect their chemical components. The flavonoids which are the...     

Direct observation of the protonation state of an imino sugar glycosidase inhibitor upon binding

Glycosidases are some of the most ubiquitous enzyme in nature. Their biological significance, coupled to their enormous catalytic prowess derived from tight binding of the transition state, is reflected in their importance as therapeutic targets. Many glycosidase inhibitors are known. Imino sugars are often potent inhibitors, yet many facets of their mode of action, such as their degree, if any, of transition-state "mimicry" and their protonation state when bound to the target glycosidase remain unclear. Atomic resolution analysis of the endoglucanase, Cel5A, in complex with a cellobio-derived isofagomine in conjunction with the pH dependence of Ki and kcat/KM reveals that this compound binds as a protonated sugar. Surprisingly, both the enzymatic nucleophile and the acid/base are unprotonated in the complex.     

Laboratory measurement of human cytokines.

Cytokines mediate and modulate different physiological systems. Accurate and sensitive methods for their measurement are being developed using bioassays, immunoassays, measurement of their mRNA, receptor binding assays, and immunochemical procedures. The most clinically significant cytokines and their assay methods are briefly reviewed. The need for standardization of assays is stressed.     

Liquid-phase oxidation of hydrocarbons in the presence of different types of phase-transfer reagents

The autoxidation of cyclohexene, tetralin and cumene was investigated in the presence of non-ionic, anionic and cationic surfactants and it was found that all three types of phase-transfer reagents are able to influence the rate of oxidation. If their HLB values are not too low (> 3) or not too high (< 15) all the non-ionic surfactants increase the rate of oxidation, otherwise they exert a slight inhibitory effect. If present in acid form, anionic surfactants all increase the rate of oxidation, while their Na-salts slightly inhibit the oxidation. Cationic surfactants all increase the autoxidation rate, but their catalytic efficiencies depend strongly on the experimental conditions. It was shown that the phosphonium ion-type surfactants are quickly oxidized by hydroperoxide present, but their catalytic and phase-transfer capabilities are not detectably reduced. In biphasic systems, the catalytic activities of cationic surfactants are strongly reduced by the presence of water as a separate phase. Light scattering measurements demonstrated that all three types of surfactants are prone to self-association when their concentrations are increased, and this limits their influence on the rate of oxidation. The oxidation rate is strongly reduced when non-ionizing but strongly solvating solvents are simultaneously applied in the reaction mixture. The rate-diminishing effect seems to correlate with the sequence of solvating ability of the solvents. It was pointed out that the presence of hydroperoxide is essential for the PTC-catalyzed oxidation of hydrocarbons. It is thought that the cationic and the anionic surfactants interact with the more nucleophilic (the inner one) and the more electrophilic (the outer one) O-atom of hydroperoxide, respectively, whereby homolysis of the O---O bond is facilitated. The non-ionic surfactants exert their rate-influencing effects through H-bond formation. In the PTC-catalyzed oxidation of hydrocarbons, the rate changes linearly only in a narrow range of PTC, hydroperoxide and substrate concentrations, and consequently the turnover number is not suitable to characterize the oxidation.     

Thermodynamics of Alkali Metal Uranovanadates

Thermodynamic data on the alkali metal uranovanadates are summarized, thermodynamic functions of their formation and reactions of their synthesis are examined.     

A Convenient Synthesis of Novel Phosphoramide Mustard Analogues of 2-Arylquinolone

A series of novel phosphoramide mustard analogues of 2-arylquinolones are synthesized through a convenient and facile phosphorylated reaction, and their structures are elucidated by NMR, IR, and HR MS. The amino acid esters and phosphoryl nitrogen mustard are linked to 2-arylquinolone to improve their undesirable physicochemical and biological properties.