Excited-State Reaction Dynamics of Bacteriochlorophyll Dimers

细菌叶绿素二聚体的激发态反应动力学

• 批准号: 9728134
• 负责人: Warren Beck
• 金额: $ 10万
• 依托单位: Vanderbilt University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-02-01 至 1999-01-21
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9728134&HistoricalAwards=false
• 关键词: Excited; State; Reaction; Dynamics; Bacteriochlorophyll

9728134 Beck This research project is designed to test the hypothesis that bacteriochlorophyll dimers in asymmetric protein environments populate intradimer charge-transfer states after optical preparation of the lower exciton state. In order to test this hypothesis, the investigator will characterize the excited-state coherent wavepacket motions that arise during light-induced charge transfer in two asymmetric systems: the bacteriochlorophyll a dimer in the B820 subunit of the LH1 light-harvesting complex, as isolated from Rhodospirillum rubrum G9, and the carbocyanine dye 3,3'-diethylthiatri-carbocyanine iodide (DTTCI). Dynamic absorption spectroscopy will be used to characterize the modulations of the photobleaching and stimulated-emission signals that arise from coherent wavepacket motion on the ground and excited states, respectively. Stimulated-photon-echo and transient-grating spectroscopy will be used to examine the electronic dephasing of the initially prepared state. The wavepacket motions exhibited by B820 will be compared to those exhibited by monomeric bacteriochlorophyll a and by the intact LH1 ring system, where dimer-dimer interactions are thought to be important, to see if the surface-crossing dynamics observed in B820 are specific to bacteriochlorophyll dimers. The long-term goal of the proposed work is to obtain a detailed understanding of the dynamics of charge transfer in both target systems in terms of the potential-energy surfaces that are involved and in terms of the vibrational modes that promote the reaction. This research project will use laser spectroscopy with femtosecond pulses of light to study how electrons are transferred in pairs of bacteriochlorophyll molecules. Bacteriochlorophyll molecules are used by photosynthetic plants and bacteria in light-harvesting structures and in reaction centers, where some of the energy of the absorbed light is converted to chemical energy. The structure of the reaction center from purple bacteria contains a pair of ba cteriochlorophyll molecules that act as the trigger point for the fast events that lead to storage of energy. The work in this research project will study reactions in a simple bacteriochlorophyll-containing protein and in an important type of organic dye; both systems exhibit very fast electron-transfer reactions that occur just after absorption of light. In addition to contributing to the understanding of the mechanism of the light reactions of photosynthesis, this research project will contribute to the general understanding of how solar energy can be converted by chemical systems into stored forms of energy. In the long term, the project will help determine how light-absorbing molecules can be physically organized in materials to obtain energy-storing devices or novel catalysts.

9728134贝克这项研究项目旨在测试不对称蛋白质环境中的细菌叶绿素二聚体在光学准备低激子态后填充在传统分子内的电荷转移态的假设。为了验证这一假说，研究人员将表征在两个不对称系统中光诱导电荷转移过程中出现的激发态相干波包运动：从红色红螺菌G9中分离出来的LH1光捕获复合体B820亚基中的细菌叶绿素a二聚体，以及碳菁染料3，3‘-二乙硫基三碳菁碘(DTTCI)。动态吸收光谱将被用来表征光漂白和受激发射信号的调制，这些信号分别由地面和激发态上的相干波包运动引起。受激光量子回波和暂态光栅谱将被用来检测初始制备状态的电子退相。B820所表现出的波包运动将与单体细菌叶绿素a和完整的LH1环系统所表现出的运动相比较，在这些环系中，二聚体-二聚体相互作用被认为是重要的，以确定B820中观察到的表面跨越动力学是否是细菌叶绿素二聚体所特有的。拟议工作的长期目标是根据所涉及的势能面和促进反应的振动模式，详细了解两个目标系统中的电荷转移动力学。这项研究项目将使用飞秒脉冲激光光谱学来研究电子如何在细菌-叶绿素分子对中转移。细菌-叶绿素分子被光合作用的植物和细菌用在捕光结构和反应中心，在那里吸收的光的部分能量被转化为化学能。来自紫色细菌的反应中心的结构包含一对准叶绿素分子，它们充当导致能量储存的快速事件的触发点。这项研究项目中的工作将研究一种简单的含细菌叶绿素的蛋白质和一种重要的有机染料中的反应；这两个系统都表现出非常快的电子转移反应，这些反应在光吸收后立即发生。除了有助于理解光合作用的光反应机制外，这项研究项目还将有助于对太阳能如何通过化学系统转化为储存形式的能量的总体理解。从长远来看，该项目将有助于确定光吸收分子如何在材料中进行物理组织，以获得储能设备或新型催化剂。