Charge-Transfer Character of the Low-Energy Chl a Qy Absorption Band in Aggregated Light Harvesting Complexes II

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• 作者：Adam Kell ; Ximao Feng ; Chen Lin ; Yiqun Yang ; Jun Li ; Michael Reus ; Alfred R. Holzwarth ; Ryszard Jankowiak
• 刊名：Journal of Physical Chemistry B
• 出版年：2014
• 出版时间：June 12, 2014
• 年：2014
• 卷：118
• 期：23
• 页码：6086-6091
• 全文大小：294K
• 年卷期：v.118,no.23(June 12, 2014)
• ISSN：1520-5207

文摘

One of the key functions of the major light harvesting complex II (LHCII) of higher plants is to protect Photosystem II from photodamage at excessive light conditions in a process called 鈥渘on-photochemical quenching鈥?(NPQ). Using hole-burning (HB) spectroscopy, we investigated the nature of the low-energy absorption band in aggregated LHCII complexes - which are highly quenched and have been established as a good in vitro model for NPQ. Nonresonant holes reveal that the lowest energy state (located near 683.3 nm) is red-shifted by 4 nm and significantly broader (by a factor of 4) as compared to nonaggregated trimeric LHCII. Resonant holes burned in the low-energy wing of the absorption spectrum (685鈥?10 nm) showed a high electron鈥損honon (el-ph) coupling strength with a Huang鈥揜hys factor S of 3鈥?. This finding combined with the very low HB efficiency in the long-wavelength absorption tail is consistent with a dominant charge-transfer (CT) character of the lowest energy transition(s) in aggregated LHCII. The value of S decreases at shorter wavelengths (<685 nm), in agreement with previous studies (J. Pieper et al., J. Phys. Chem. B 1999, 103, 2422鈥?428), proving that the low-energy excitonic state is strongly mixed with the CT states. Our findings support the mechanistic model in which Chl鈥揅hl CT states formed in aggregated LHCII are intermediates in the efficient excited state quenching process (M. G. M眉ller et al., Chem. Phys. Chem. 2010, 11, 1289鈥?296; Y. Miloslavina et al., FEBS Lett. 2008, 582, 3625鈥?631).