Theoretical studies on the influence of molecular interactions on the mechanism of electron transfer in photosynthetic reaction center ofRps. viridis

Abstract

Based on the QM/MM optimized X-ray crystal structure of the photosynthetic reaction center (PRC) of purple bacteria Rhodopseudomonas (Rps.) viridis, quantum chemistry density functional method (DFT, B3LYP/6-31G) has been performed to study the interactions between the pigment molecules and either the surrounded amino acid residues or water molecules that are either axially coordinated or hydrogen bonded with the pigment molecules, leading to an explanation of the mechanism of the primary electron-transfer (ET) reactions in the PRC. Results show that the axial coordination of amino acid residues greatly raises the E LUMO of pigment molecules and it is important for the possibility of ET to take place. Different hydrogen bonds between amino acid residues, water molecules and pigment molecules decrease the E LUMO of the pigment molecules to different extents. It is crucial for the ET taking place from excited P along L branch and sustains that the ET is a one-step reaction without through accessory bacteriochlorophyll (ABChl b). It is insufficient to treat the whole protein surrounding as a homogeneous dielectric medium.Keywords: bacteria photosynthetic reaction center, electron transfer, pigment molecule, interaction between pigment molecules and neighboring amino acid residue, DFT. SCIENCE IN CHINA (Series B)Vol. 45

Visible Light Sensitization of TiO2 Nanotubes by Bacteriochlorophyll-C Dyes for Photoelectrochemical Solar Cells

“…22 The mechanism that enables these bacteria to more efficiently use light is the self-assembly of bacteriochlorophyll molecules into structures that boost the absorption of photons, enabling the bacteria to run photosynthesis with a photon flux as low as one photon per 8 h. 23,24 Upon illumination, the bacteriochlorophyll is placed in an excited state, which is followed by transfer of charge to neighboring molecules for photosynthesis. 25,26 If the photogenerated electrons were injected into TiO 2 instead, this could potentially result in a highly efficient solar cell that would use these bacteriochlorophylls as sensitizers. The LUMO (−3.2 eV) and HOMO (−5.2 eV) levels of an aggregated mixture of BChl types including c indicate that these energy levels bracket the conduction band edge of TiO 2 (−4.2 eV), 21,27 which provides a driving force for electron injection into TiO 2 in a similar manner as the Ru-based N-719 dye used in DSSCs with a HOMO of −5.45 eV and a LUMO of −3.85 eV.…”

Study of Electronic Structures and Pigment–Protein Interactions in the Reaction Center of Thermochromatium tepidum with a Dynamic Environment

“…Tremendous experimental 100−113 and theoretical 74,97,114−127 efforts have been devoted to constructing the electronic structures of P and to explaining the directionality of CS and ET. Asymmetric charge density distributions on the two halves of P have been revealed as an intrinsic property of P, 117,119 and observed in the ground and the excited state of P 74,[100][101][102][103][104][105][106][107][108][109][110][111][115][116][117][118][119][120][121]125 as well as in the cation radical of P. 112,113,116,117 The symmetry breaking of the charge density distribution in P L and P M could result from various factors, e.g., different orientations of the side groups of two pigments 105,116,117,119 and tuning effects of the surrounding protein residues. 103,104,115,117,120 For the RCs from Rb.…”