Absorption shifts of diastereotopically ligated chlorophyll dimers of photosystem I

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Suomivuori , C-M , Fliegl , H , Starikov , E B , Balaban , T S , Kaila , V R I & Sundholm , D 2019 , ' Absorption shifts of diastereotopically ligated chlorophyll dimers of photosystem I ' , Physical Chemistry Chemical Physics , vol. 21 , no. 13 , pp. 6851-6858 . https://doi.org/10.1039/C9CP00616H

Title: Absorption shifts of diastereotopically ligated chlorophyll dimers of photosystem I
Author: Suomivuori, Carl-Mikael; Fliegl, Heike; Starikov, Evgeni B.; Balaban, T. Silviu; Kaila, Ville R. I.; Sundholm, Dage
Contributor: University of Helsinki, Stanford University
University of Helsinki, University of Oslo
University of Helsinki, Technical University of Munich
University of Helsinki, Department of Chemistry
Date: 2019-04-07
Language: eng
Number of pages: 8
Belongs to series: Physical Chemistry Chemical Physics
ISSN: 1463-9076
URI: http://hdl.handle.net/10138/301468
Abstract: The light-harvesting chlorophyll (Chl) molecules of photosynthetic systems form the basis for light-driven energy conversion. In biological environments, the Chl chromophores occur in two distinct diastereotopic configurations, where the alpha and beta configurations have a magnesium-ligating histidine residue and a 17-propionic acid moiety on the opposite side or on the same side of the Chl ring, respectively. Although beta-ligated Chl dimers occupy conserved positions around the reaction center of photosystem I (PSI), the functional relevance of the alpha/beta configuration of the ligation is poorly understood. We employ here correlated ab initio calculations using the algebraic-diagrammatic construction through second order (ADC(2)) and the approximate second-order coupled cluster (CC2) methods in combination with the reduced virtual space (RVS) approach in studies of the intrinsic excited-state properties of alpha-ligated and beta-ligated Chl dimers of PSI. Our ab initio calculations suggest that the absorption of the alpha-ligated reaction-center Chl dimer of PSI is redshifted by 0.13-0.14 eV in comparison to the beta-ligated dimers due to combined excitonic coupling and strain effects. We also show that time-dependent density functional theory (TDDFT) calculations using range-separated density functionals underestimate the absorption shift between the alpha- and beta-ligated dimers. Our findings may provide a molecular starting point for understanding the energy flow in natural photosynthetic systems, as well as a blueprint for developing new molecules that convert sunlight into other forms of energy.
Subject: 116 Chemical sciences

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