title: A combined quantum mechanics/molecular mechanics study of the one- and two-photon absorption in the green fluorescent protein.
abstract: We present for the first time a QM/MM study of the one- and two-photon absorption spectra of the GFP chromophore embedded in the full protein environment described by an advanced quantum mechanically derived polarizable force field. The calculations are performed on a crystal structure of the green fluorescent protein (GFP) using the polarizable embedding density functional theory (PE-DFT) scheme. The importance of treating the protein environment explicitly with a polarizable force field and higher-order multipoles is demonstrated, as well as the importance of including water molecules close to the chromophore in the protein barrel. For the most advanced description we achieve good agreement with experimental findings, with a peak at 405 nm for the neutral and a peak at 475 nm for the anionic form of the GFP chromophore. The presence of a dark OPA state, as suggested by other studies to explain the discrepancies between OPA and TPA spectra, is not supported by our calculations.
authors.affiliation: Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø, N-9037 Tromsø, Norway.
authors.forename: Arnfinn Hykkerud
authors.initials: AH
authors.lastname: Steindal
authors.forename: Jógvan Magnus Haugaard
authors.initials: JM
authors.lastname: Olsen
authors.forename: Kenneth
authors.initials: K
authors.lastname: Ruud
authors.forename: Luca
authors.initials: L
authors.lastname: Frediani
authors.forename: Jacob
authors.initials: J
authors.lastname: Kongsted
mesh_terms: D049452:Green Fluorescent Proteins / Q000737:chemistry*; D017785:Photons; D011789:Quantum Theory; D013050:Spectrometry, Fluorescence
chemical_list: D049452:Green Fluorescent Proteins