ELECTRONIC-STRUCTURE OF MODEL CHLOROPHYLL SYSTEMS
ELECTRONIC-STRUCTURE OF MODEL CHLOROPHYLL SYSTEMS
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DOI：
10.1002/qua.560230424
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发表时间：
1983-01-01
影响因子：
2.2
通讯作者：
ZERNER, MC
中科院分区：
文献类型：
--
作者：
EDWARDS, WD;ZERNER, MC
本文报道了用中间忽略微分重叠/光谱法对镁卟啉和吗啡及其正离子和负离子的基态和激发态的检测。我们发现，在很小的能量代价下，可以获得相当大的面外坐标的变化。这些几何变化可以单独用来解释在叶绿素可见波段观察到的大范围光谱位移，这是依赖于位置的。这些计算还表明，在大约20,000 cm−1时，卟啉到Mg的电荷转移激发，如果填充并允许弛豫，则成为最低激发的单重态。这表明光合作用的初始光化学事件可能是激发到可见qband，然后内部转换到电荷转移状态，并伴随着Mg原子向环平面外的移动。这种运动可能导致分子间电荷转移，并使Mg原子弛豫回环平面。本文讨论了这些模式叶绿素的正离子和负离子的性质，以及它们在光合作用中作为电子供体和初始电子受体的潜在作用。
An examination of the ground and excited states of magnesium porphine and pheoporphine and their positive and negative ions using the intermediate neglect of differential overlap/spectroscopic method is reported. It is found that rather large changes in the Mg out‐of‐plane coordinate can be attained at very little cost in energy. These geometric changes alone can be used to explain the large range of spectroscopic shifts observed in the visible band of chlorophyll that are site dependent. These calculations also show a porphyrin to Mg charge transfer excitation at about 20,000 cm−1, which, if populated and allowed to relax, becomes the lowest excited singlet. This suggests that the initial photochemical event in photosynthesis may be excitation to the visibleQband followed by internal conversion to the charge transfer state accompanied by movement of the Mg atom out of the plane of the ring. This movement could result in intermolecular charge transfer, and relaxation of the Mg atom back to the plane of the ring. The nature of the positive and negative ions of these model chlorophylls is discussed in light of their role as the electron donor and their potential role as initial electron acceptor in photosynthesis.