title: Theoretical Characterization of the Spectral Density of the Water-Soluble Chlorophyll-Binding Protein from Combined Quantum Mechanics/Molecular Mechanics Molecular Dynamics Simulations.
abstract: Over the past decade, both experimentalists and theorists have worked to develop methods to describe pigment-protein coupling in photosynthetic light-harvesting complexes in order to understand the molecular basis of quantum coherence effects observed in photosynthesis. Here we present an improved strategy based on the combination of quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) simulations and excited-state calculations to predict the spectral density of electronic-vibrational coupling. We study the water-soluble chlorophyll-binding protein (WSCP) reconstituted with Chl a or Chl b pigments as the system of interest and compare our work with data obtained by Pieper and co-workers from differential fluorescence line-narrowing spectra (Pieper et al. J. Phys. Chem. B 2011, 115 (14), 4042-4052). Our results demonstrate that the use of QM/MM MD simulations where the nuclear positions are still propagated at the classical level leads to a striking improvement of the predicted spectral densities in the middle- and high-frequency regions, where they nearly reach quantitative accuracy. This demonstrates that the so-called "geometry mismatch" problem related to the use of low-quality structures in QM calculations, not the quantum features of pigments high-frequency motions, causes the failure of previous studies relying on similar protocols. Thus, this work paves the way toward quantitative predictions of pigment-protein coupling and the comprehension of quantum coherence effects in photosynthesis.
authors.affiliation: Department de Fisicoquímica, Facultat de Farmàcia, Universitat de Barcelona , Av. Joan XXIII s/n, Barcelona, Barcelona 08028, Spain.|Department of Chemistry, University of California , Berkeley, California 94720, United States.
authors.forename: Andreana M
authors.initials: AM
authors.lastname: Rosnik
authors.affiliation: Department de Fisicoquímica, Facultat de Farmàcia, Universitat de Barcelona , Av. Joan XXIII s/n, Barcelona, Barcelona 08028, Spain.
authors.forename: Carles
authors.initials: C
authors.lastname: Curutchet
mesh_terms: D001937:Brassica / Q000378:metabolism; D002734:Chlorophyll / Q000737:chemistry* / Q000378:metabolism; D000077194:Chlorophyll A; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry* / Q000378:metabolism; D056004:Molecular Dynamics Simulation; D010940:Plant Proteins / Q000737:chemistry* / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011789:Quantum Theory; D014867:Water / Q000737:chemistry*
chemical_list: D045342:Light-Harvesting Protein Complexes; D010940:Plant Proteins; C115715:WSCP protein, Brassica oleracea; D014867:Water; D002734:Chlorophyll; C037184:chlorophyll b; D000077194:Chlorophyll A