On the exciton coupling between two chlorophyll pigments in the absence of a protein environment: Intrinsic effects revealed from theory and experiment
Angewandte Chemie International Edition 128, 6356 - 6359 (2016)
On the exciton coupling between two chlorophyll pigments in the absence of a protein environment: Intrinsic effects revealed from theory and experiment
Exciton coupling between two or more chlorophyll (Chl) pigments is a key mechanism associated with colour tuning of photosynthetic proteins but it is difficult to disentangle this effect from shifts due to the protein microenvironment. Here we report the formation by electrospray ionization of the simplest coupled system, the Chl a dimer, tagged with a quaternary ammonium ion. Based on action spectroscopic studies in vacuo, the dimer complexes were found to absorb 50–70 meV to the red of monomers under the same conditions. First principles calculations predict shifts that depend somewhat on the relative orientation of the two Chls, 50 and 30 meV for structures where the Chl rings are stacked and unstacked, respectively. Our work demonstrates that Chl association alone can produce a large portion of the colour shift observed in photosynthetic macromolecular assemblies.
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- http://dx.doi.org/10.1002/ange.201601979
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- BFM acknowledges funding from the Portuguese Foundation for Science and Technology (CONT_DOUT/11/UC/405/10150/18/2008) and thanks DIPC and CFM (UPV/EHU) and the Laboratory for Advanced Computation (University of Coimbra) for support. SBN acknowledges support from the Danish Council for Independent Research (grant no. 4181- 00048B) and the Villum Foundation. AR acknowledges financial support from European Research Council (ERC-2010-AdG-267374), Spanish grant (FIS2013-46159-C3-1-P), Grupos Consolidados (IT578-13), and AFOSR Grant No. FA2386-15-1-0006 AOARD 144088, H2020-NMP-2014 project MOSTOPHOS (GA no. SEP-210187476) and COST Action MP1306 (EUSpec)