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光合作用提供了这个星球上的大部分生物能量和氧气。光合作用的第一个事件是反应中心叶绿素对处的初级电荷分离。该研究计划将采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。实验重点是紫色细菌光捕获蛋白 LH1 的 B820 亚基中的一对细菌叶绿素。 B820 与紫色细菌反应中心的主要电子供体 P 具有许多相同的结构特征。该研究计划旨在测试以下假设：细菌叶绿素二聚体在较低激子态激发后经历几乎无障碍的绝热表面跨越到电荷转移态。主要思想是细菌叶绿素单体的某些正常振动模式和细菌叶绿素二聚体可能的集体模式用于将电子电荷转移态与中性二聚体激子态混合。飞秒相干拉曼光谱将采用脉冲泵浦探针和瞬态光栅方法进行，以检测混合细菌叶绿素二聚体的中性和电荷转移激发态的振动模式。使用 B820 系统获得的拉曼光谱将与 B777 中观察到的拉曼光谱进行比较，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种。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β2宿主的纯系统。该研究计划将解决光合作用如何涉及配对叶绿素结构。从更广泛的角度来看，这项工作将解决振动相干性在蛋白质快速化学反应中的作用。