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: 0091210
• 负责人: Warren Beck
• 金额: $ 33万
• 依托单位: Michigan State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-06-01 至 2004-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0091210&HistoricalAwards=false
• 关键词: Excited; State; Reaction; Dynamics; Bacteriochlorophyll

Beck, Warren F.MCB-0091210Photosynthesis is responsible for most of the biological energy and oxygen on this planet. The first event in photosynthesis is primary charge separation at the reaction center chlorophyll pair. This research program will employ femtosecond coherent Raman spectroscopy to study the excited-state vibrational motions of bacteriochlorophyll dimers. The experimental focus is on the pair of bacteriochlorophylls in the B820 subunit of the purple bacterial light-harvesting protein LH1. B820 shares many of the structural features of the primary electron donor P of the purple bacterial reaction center. The research plan is designed to test the hypothesis that bacteriochlorophyll dimers undergo a nearly barrierless adiabatic surface crossing to a charge-transfer state following excitation of the lower exciton state. The main idea is that certain normal modes of vibration of the bacteriochlorophyll monomer and possibly collective modes of the bacteriochlorophyll dimer serve to mix electronic charge-transfer states with the neutral dimer exciton states. Femtosecond coherent Raman spectroscopy will be conducted with impulsive pump-probe and transient grating methods to detect the vibrational modes that mix the neutral and charge-transfer excited states of the bacteriochlorophyll dimer. The Raman spectra that are obtained with the B820 system will be compared with those that are observed in B777, the monomeric species that is prepared by splitting B820 into single bacteriochlorophyll-polypeptide complexes. In addition, synthetic alpha and beta polypeptides will be used to prepare pure systems containing alpha, beta and beta2 hosts for bacteriochlorophyll dimers. The research program will address how photosynthesis involves paired chlorophyll structures. In broader terms the work will address the role of vibrational coherence in fast chemical reactions in proteins.

Beck，Warren F.MCB-0091210光合作用负责地球上大部分的生物能量和氧气。光合作用中的第一个事件是在反应中心叶绿素对的初级电荷分离。本研究计画将利用飞秒相干拉曼光谱来研究细菌叶绿素二聚体的激发态振动运动。实验的重点是对细菌叶绿素的B820亚基的紫色细菌捕光蛋白LH 1。B820与紫色细菌反应中心的初级电子供体P有许多共同的结构特征。该研究计划的目的是测试的假设，细菌叶绿素二聚体经历了一个几乎无势垒的绝热表面穿越到一个电荷转移状态激发较低的激子状态。其主要思想是，某些正常模式的振动的细菌叶绿素单体和可能的集体模式的细菌叶绿素二聚体混合电子电荷转移状态与中性二聚体激子状态。飞秒相干拉曼光谱将与脉冲泵浦探测和瞬态光栅的方法进行检测的振动模式，混合的中性和电荷转移激发态的细菌叶绿素二聚体。将用B820系统获得的拉曼光谱与在B777中观察到的光谱进行比较，B777是通过将B820分裂成单个细菌叶绿素-多肽复合物而制备的单体物质。此外，合成的α和β多肽将用于制备含有细菌叶绿素二聚体的α、β和β 2宿主的纯系统。该研究计划将解决光合作用如何涉及成对的叶绿素结构。从更广泛的角度来看，这项工作将解决蛋白质快速化学反应中振动相干性的作用。