Generation of ion-radical chlorophyll states in the light-harvesting antenna and the reaction center of cyanobacterial p
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ORIGINAL ARTICLE
Generation of ion‑radical chlorophyll states in the light‑harvesting antenna and the reaction center of cyanobacterial photosystem I Dmitry A. Cherepanov1 · Ivan V. Shelaev1 · Fedor E. Gostev1 · Arseniy V. Aybush1 · Mahir D. Mamedov2 · Vladimir A. Shuvalov1,2,3 · Alexey Yu. Semenov1,2 · Victor A. Nadtochenko1 Received: 15 November 2019 / Accepted: 24 February 2020 © Springer Nature B.V. 2020
Abstract The energy and charge-transfer processes in photosystem I (PS I) complexes isolated from cyanobacteria Thermosynechococcus elongatus and Synechocystis sp. PCC 6803 were investigated by pump-to-probe femtosecond spectroscopy. The formation of charge-transfer (CT) states in excitonically coupled chlorophyll a complexes (exciplexes) was monitored by measuring the electrochromic shift of β-carotene in the spectral range 500–510 nm. The excitation of high-energy chlorophyll in lightharvesting antenna of both species was not accompanied by immediate appearance of an electrochromic shift. In PS I from T. elongatus, the excitation of long-wavelength chlorophyll (LWC) caused a pronounced electrochromic effect at 502 nm assigned to the appearance of CT states of chlorophyll exciplexes. The formation of ion-radical pair P700+A1− at 40 ps was limited by energy transfer from LWC to the primary donor P700 and accompanied by carotenoid bleach at 498 nm. In PS I from Synechocystis 6803, the excitation at 720 nm produced an immediate bidentate bleach at 690/704 nm and synchronous carotenoid response at 508 nm. The bidentate bleach was assigned to the formation of primary ion-radical state PB+Chl2B−, where negative charge is localized predominantly at the accessory chlorophyll molecule in the branch B, Chl2B. The following decrease of carotenoid signal at ~ 5 ps was ascribed to electron transfer to the more distant molecule C hl3B. The reduction of phylloquinone in the sites A1A and A1B was accompanied by a synchronous blue-shift of the carotenoid response to 498 nm, pointing to fast redistribution of unpaired electron between two branches in favor of the state PB+A1A−. Keywords Electron transfer · Electrochromism · Carotenoid bandshift · Exciplex · Femtosecond absorption spectroscopy · Photosynthesis · Cyanobacteria
Introduction
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11120-020-00731-0) contains supplementary material, which is available to authorized users. * Dmitry A. Cherepanov [email protected] 1
N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Moscow, Russia
2
A.N. Belozersky Institute of Physical‑Chemical Biology, Moscow State University, Kosygina st., 4, Moscow, Russia 117991
3
Institute of Basic Biological Problems, Pushchino Scientific Center for Biological Research, Russian Academy of Sciences, Pushchino, Moscow Region, Russia
Photoinduced charge-transfer (CT) within a system of excitonically coupled pigments is a fundamental process responsible for the solar energy transductio
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