Absorption shifts of diastereotopically ligated chlorophyll dimers of photosystem I. Issue 13 (15th March 2019)

• Record Type: Journal Article
• Authors: Suomivuori, Carl-Mikael; Fliegl, Heike; Starikov, Evgeni B.; Balaban, T. Silviu; Kaila, Ville R. I.; Sundholm, Dage
• Is Part Of: Physical chemistry chemical physics. Volume 21:Issue 13(2019)
• Page Start: 6851
• Page End: 6858
• Publication Date: 2019-03-15
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c9cp00616h
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : Excited-state properties of α- and β-ligated chlorophyll dimers of photosystem I were studied at ab initio correlated levels of theory. 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 α and β 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 β-ligated Chl dimers occupy conserved positions around the reaction center of photosystem I (PSI), the functional relevance of the α/β 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 α-ligated and β-ligated Chl dimers of PSI. Our ab initio calculations suggest that the absorption of the α-ligated reaction-center Chl dimer of PSI is redshifted by 0.13–0.14 eV in comparison to the β-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 α- and β-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.