紫色光合细菌中类胡萝卜素三重态的起源
The origin of carotenoid triplets in purple photosynthetic bacteria
中文总结 AI 辅助
该研究采用飞秒受激共振拉曼光谱结合四维全局分析，明确紫色光合细菌LH2的类胡萝卜素三重态源于细菌叶绿素a的三重态-三重态转移，而非单线态裂变。
中文摘要 AI 辅助
光合天线蛋白在捕获光能的同时保护生物体免受光损伤。类胡萝卜素分子在后者过程中至关重要，可有效淬灭光子吸收后产生的有害（细菌）叶绿素激发态。通过系间窜越形成的（细菌）叶绿素三重态尤为重要，因为在缺乏类胡萝卜素淬灭的情况下，它们会敏化高氧化性的单线态氧。在嗜酸红微菌（Rhodoblastus acidophilus）的捕光复合物2（LH2）中，填充类胡萝卜素暗态和三重态的途径仍存在争议，涉及细菌叶绿素向类胡萝卜素的三重态-三重态转移，和/或类胡萝卜素分子自身通过单线态裂变产生三重态。瞬态吸收一直是理解这些生物光保护的核心，但光谱拥挤限制了区分这些途径所需的重叠物种分离。通过对该蛋白在不同共振条件下应用飞秒受激共振拉曼光谱（FSRRS），结合全局分析向四维（波数、时间、强度和共振条件）的扩展，我们分离了类胡萝卜素暗态流形的每个组分及其动力学。观察到寿命约60 ps的纠缠三重态对S*/1(TT)，比在溶液中的寿命长约8倍。然而，这种稳定并未开辟出分离三重态或类胡萝卜素-细菌叶绿素a异裂的途径。在细菌叶绿素a激发下，还解析出从细菌叶绿素a到类胡萝卜素的三重态-三重态转移，其符合单一2100 ps的组分。因此，LH2中的类胡萝卜素三重态是由细菌叶绿素a的光保护性三重态-三重态转移产生的，而非通过单线态裂变。
英文摘要
Photosynthetic antenna proteins harvest light energy while at the same time protecting the organism against photodamage. Carotenoid molecules are essential in the latter process, efficiently quenching unwanted (bacterio)chlorophyll excited states created after photon absorption. (Bacterio)chlorophyll triplets, formed by inter-system crossing, are particularly significant, since in the absence of carotenoid quenching, they sensitise the highly oxidative singlet oxygen. In light-harvesting complex 2 (LH2) from Rhodoblastus acidophilus, the pathways that populate carotenoid dark and triplet states remain controversial, involving bacteriochlorophyll-to-carotenoid triplet-triplet transfer and/or generation of triplets by the carotenoid molecules themselves through singlet fission. Transient absorption has been central to understanding photoprotection in these organisms, but spectral congestion limits the separation of the overlapping species needed to discriminate between these pathways. By applying femtosecond stimulated resonance Raman spectroscopy (FSRRS) in different resonance conditions to this protein, in combination with an extension of global analysis to four dimensions (wavenumber, time, intensity and resonance condition), we separate each component of the carotenoid dark-state manifold together with its kinetics. An entangled triplet pair S*/1(TT) is observed, which lives about 60 ps, some eight times longer than in solution. However, this stabilisation does not open a pathway to separated triplets or to carotenoid-BChl a heterofission. Triplet-triplet transfer from bacteriochlorophyll a to carotenoid is also resolved under BChl a excitation, and fits cleanly as a single 2100 ps component. The carotenoid triplet in LH2 is thus produced by photoprotective triplet-triplet transfer from BChl a, and not by singlet fission.
