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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Direct Determination of the S_1 Excited-State Energies of Xanthophylls by Low-Temperature Fluorescence Spectroscopy
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Direct Determination of the S_1 Excited-State Energies of Xanthophylls by Low-Temperature Fluorescence Spectroscopy

机译：低温荧光光谱法直接测定叶黄素的S_1激发态能

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摘要

The xanthophylls, violaxanthin, lutein, and zeaxanthin, associated with the antenna protein assembly of Photosystem II (PS II) play roles as light-harvesting pigments and protective agents in the photosynthetic apparatus of higher plants. The dissipation of excitation energy exceeding that needed for photosynthesis is thought to be regulated by an enzymatic process known as the xanthophyll cycle where violaxanthin and zeaxanthin are reversibly interconverted, but the role of the cycle in controlling the process in vivo is not clear. The two hypotheses are (i) direct quenching of chlorophyll excited states by the xanthophylls and (ii) indirect quenching via carotenoid-mediated changes in the structure of the light-harvesting complexes. These mechanisms depend on the structures and/or energetics of the xanthophyll pigments, which have not yet been fully elucidated. In this work, fluorescence spectroscopy at 77 K has been used to determine the energies of the S_1 excited states of violaxanthin, zeaxanthin, and the major xanthophyll component of green plants, lutein. High performance liquid chromatography (HPLC) was carried out just prior to the spectroscopic experiments to obtain isomerically pure samples devoid of fluorescent contaminants. The experiments at cryogenic temperatures provide enhanced resolution compared to room-temperature studies, reveal clearly the vibronic features of the fluorescence line shapes, and allow precise, direct assignments of the spectral origins and electronic-state energies of the molecules. The results are important for broadening our understanding of the mechanisms of light-harvesting and nonphotochemical dissipation of excess energy in plants.
机译：叶绿素，紫黄质，叶黄素和玉米黄质与Photosystem II（PS II）的天线蛋白组件相关，在高等植物的光合作用设备中起着集光色素和保护剂的作用。人们认为激发光能的耗散超过了光合作用所需的能量，这被称为叶黄素循环的酶促过程调节，其中紫黄质和玉米黄质可逆地相互转化，但是该循环在体内控制过程中的作用尚不清楚。这两个假设是（i）叶黄素直接猝灭叶绿素的激发态，以及（ii）通过类胡萝卜素介导的光收集复合物结构的改变而间接猝灭。这些机制取决于尚未充分阐明的叶黄素色素的结构和/或能量。在这项工作中，已使用77 K的荧光光谱法测定了紫草黄质，玉米黄质和绿色植物叶黄素的主要叶黄素成分的S_1激发态的能量。刚好在光谱实验之前进行了高效液相色谱（HPLC），以获得不含荧光污染物的异构纯样品。与室温研究相比，在低温温度下进行的实验提供了更高的分辨率，清楚地揭示了荧光线形状的振动特征，并允许分子的光谱起源和电子态能量的精确，直接分配。这些结果对于拓宽我们对植物中多余能量的光捕获和非光化学耗散机制的理解非常重要。

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