Time-Resolved ESR and ENDOR on Triplet States in Photosynthetic Antenna Complexes

类胡萝卜素在光合生物中用于防止叶绿素三重态对单线态氧的有害光致敏。利用时间分辨ESR、ENDOR和瞬态吸收技术研究类胡萝卜素在细菌、藻类和高等植物光合天线复合物中的光保护机制。三态电子自旋与类胡萝卜素多烯链质子之间的各向同性和各向异性超精细相互作用将通过时间分辨ENDOR进行分析。这将导致三联体携带色素的分配和它们的电子结构的确定。这项研究的结果将导致改进现有的x射线结构数据和/或确定激发态中可能发生的结构变化。通过时间分辨ESR将获得三重态自旋动力学的温度依赖性的详细理解，并将使我们能够区分发生在各种天线和反应中心配合物中的三重态能量转移的不同机制。类胡萝卜素对光合生物（植物、藻类和一些细菌）的生存至关重要。它们起着重要的保护作用，使生物体在不刺激产生剧毒的单线态氧的情况下，摆脱多余的能量。这个过程涉及到所谓的三重态从叶绿素到类胡萝卜素的转移。到目前为止，人们对这种能量转移的理解只是笼统的，而且在许多情况下，对负责这种转移的实际色素的识别是缺乏的。此外，三联激发的类胡萝卜素或叶绿素与环境之间的动态相互作用的细节还不清楚。这项工作将填补这一空白。该项目由生物科学理事会分子和细胞生物科学部的分子生物物理学计划和数学与物理科学理事会化学部门的物理化学计划提供支持。

Angerhofer, AlexanderMCB-9983034Carotenoids are used in photosynthetic organisms to protect against the harmful photoinitiated sensitization of singlet oxygen by chlorophyll triplet states. The photoprotection mechanism of the carotenoids will be studied in bacterial, algal and higher plant photosynthetic antenna complexes using time-resolved ESR, ENDOR, and transient absorption techniques. The isotropic and anisotropic hyperfine interaction between the triplet electron spin and the carotenoid polyene chain protons will be analyzed by the time-resolved ENDOR. This will lead to the assignment of the triplet-carrying pigments and the determination of their electronic structures. The results of this research will lead to refinements of currently available X-ray structural data and/or the determination of structural changes that may occur in the excited triplet states. A detailed understanding of the temperature dependence of the triplet spin dynamics will be obtained by time-resolved ESR and will allow us to distinguish the different mechanisms of triplet energy transfer that take place in various antenna and reaction center complexes.Carotenoids are essential for the survival of photosynthetic organisms (plants, algae, and some bacteria). They serve an important protective role that allows the organism to get rid of excess energy without stimulating the production of singlet oxygen which is highly toxic. The process involves a transfer of a so-called triplet state from the chlorophylls to the carotenoids. This transfer of energy has so far been understood only in general terms and in many cases the identification of the actual pigments responsible for it is lacking. Furthermore, the details of the dynamic interaction between the triplet excited carotenoids or chlorophylls and their environment are not well understood. This work will fill this gap. This project is supported by the Molecular Biophysics Program in the Division of Molecular and Cellular Biosciences in the Directorate for Biological Sciences and the Physical Chemistry Program in the Division of Chemistry in the Mathematical and Physical Sciences Directorate.