94 research outputs found
Role of quantum coherence in chromophoric energy transport
The role of quantum coherence and the environment in the dynamics of
excitation energy transfer is not fully understood. In this work, we introduce
the concept of dynamical contributions of various physical processes to the
energy transfer efficiency. We develop two complementary approaches, based on a
Green's function method and energy transfer susceptibilities, and quantify the
importance of the Hamiltonian evolution, phonon-induced decoherence, and
spatial relaxation pathways. We investigate the Fenna-Matthews-Olson protein
complex, where we find a contribution of coherent dynamics of about 10% and of
relaxation of 80%.Comment: 5 pages, 3 figures, included static disorder, correlated environmen
Suppression of quantum oscillations and the dependence on site energies in electronic excitation transfer in the Fenna-Matthews-Olson trimer
Energy transfer in the photosynthetic complex of the Green Sulfur Bacteria
known as the Fenna-Matthews-Olson (FMO) complex is studied theoretically taking
all three subunits (monomers) of the FMO trimer and the recently found eighth
bacteriochlorophyll (BChl) molecule into account. We find that in all
considered cases there is very little transfer between the monomers. Since it
is believed that the eighth BChl is located near the main light harvesting
antenna we look at the differences in transfer between the situation when BChl
8 is initially excited and the usually considered case when BChl 1 or 6 is
initially excited. We find strong differences in the transfer dynamics, both
qualitatively and quantitatively. When the excited state dynamics is
initialized at site eight of the FMO complex, we see a slow exponential-like
decay of the excitation. This is in contrast to the oscillations and a
relatively fast transfer that occurs when only seven sites or initialization at
sites 1 and 6 is considered. Additionally we show that differences in the
values of the electronic transition energies found in the literature lead to a
large difference in the transfer dynamics
The CCG-domain-containing subunit SdhE of succinate:quinone oxidoreductase from Sulfolobus solfataricus P2 binds a [4Fe–4S] cluster
In type E succinate:quinone reductase (SQR), subunit SdhE (formerly SdhC) is thought to function as monotopic membrane anchor of the enzyme. SdhE contains two copies of a cysteine-rich sequence motif (CXnCCGXmCXXC), designated as the CCG domain in the Pfam database and conserved in many proteins. On the basis of the spectroscopic characterization of heterologously produced SdhE from Sulfolobus tokodaii, the protein was proposed in a previous study to contain a labile [2Fe–2S] cluster ligated by cysteine residues of the CCG domains. Using UV/vis, electron paramagnetic resonance (EPR), 57Fe electron–nuclear double resonance (ENDOR) and Mössbauer spectroscopies, we show that after an in vitro cluster reconstitution, SdhE from S. solfataricus P2 contains a [4Fe–4S] cluster in reduced (2+) and oxidized (3+) states. The reduced form of the [4Fe–4S]2+ cluster is diamagnetic. The individual iron sites of the reduced cluster are noticeably heterogeneous and show partial valence localization, which is particularly strong for one unique ferrous site. In contrast, the paramagnetic form of the cluster exhibits a characteristic rhombic EPR signal with gzyx = 2.015, 2.008, and 1.947. This EPR signal is reminiscent of a signal observed previously in intact SQR from S. tokodaii with gzyx = 2.016, 2.00, and 1.957. In addition, zinc K-edge X-ray absorption spectroscopy indicated the presence of an isolated zinc site with an S3(O/N)1 coordination in reconstituted SdhE. Since cysteine residues in SdhE are restricted to the two CCG domains, we conclude that these domains provide the ligands to both the iron–sulfur cluster and the zinc site
Mössbauer Spectroscopy on Respiratory Complex I: The Iron–Sulfur Cluster Ensemble in the NADH-Reduced Enzyme Is Partially Oxidized
EPR, ENDOR, and Special TRIPLE measurements of P•+ in wild type and modified reaction centers from Rb. sphaeroides
Scalable High-Performance Algorithm for the Simulation of Exciton Dynamics. Application to the Light-Harvesting Complex II in the Presence of Resonant Vibrational Modes
Multiscale model of light harvesting by photosystem II in plants
The first step of photosynthesis in plants is the absorption of sunlight by pigments in the antenna complexes of photosystem II (PSII), followed by transfer of the nascent excitation energy to the reaction centers, where long-term storage as chemical energy is initiated. Quantum mechanical mechanisms must be invoked to explain the transport of excitation within individual antenna. However, it is unclear how these mechanisms influence transfer across assemblies of antenna and thus the photochemical yield at reaction centers in the functional thylakoid membrane. Here, we model light harvesting at the several-hundred-nanometer scale of the PSII membrane, while preserving the dominant quantum effects previously observed in individual complexes. We show that excitation moves diffusively through the antenna with a diffusion length of 50 nm until it reaches a reaction center, where charge separation serves as an energetic trap. The diffusion length is a single parameter that incorporates the enhancing effect of excited state delocalization on individual rates of energy transfer as well as the complex kinetics that arise due to energy transfer and loss by decay to the ground state. The diffusion length determines PSII’s high quantum efficiency in ideal conditions, as well as how it is altered by the membrane morphology and the closure of reaction centers. We anticipate that the model will be useful in resolving the nonphotochemical quenching mechanisms that PSII employs in conditions of high light stress
Structure-based simulation of linear optical spectra of the CP43 core antenna of photosystem II
The linear optical spectra (absorbance, linear dichroism, circular dichroism, fluorescence) of the CP43 (PsbC) antenna of the photosystem II core complex (PSIIcc) pertaining to the S(0) → S(1) (Q(Y)) transitions of the chlorophyll (Chl) a pigments are simulated by applying a combined quantum chemical/electrostatic method to obtain excitonic couplings and local transition energies (site energies) on the basis of the 2.9 Å resolution crystal structure (Guskov et al., Nat Struct Mol Biol 16:334-342, 2009). The electrostatic calculations identify three Chls with low site energies (Chls 35, 37, and 45 in the nomenclature of Loll et al. (Nature 438:1040-1044, 2005). A refined simulation of experimental spectra of isolated CP43 suggests a modified set of site energies within 143 cm(-1) of the directly calculated values (root mean square deviation: 80 cm(-1)). In the refined set, energy sinks are at Chls 37, 43, and 45 in agreement with earlier fitting results (Raszewski and Renger, J Am Chem Soc 130:4431-4446, 2008). The present structure-based simulations reveal that a large part of the redshift of Chl 37 is due to a digalactosyldiacylglycerol lipid. This finding suggests a new role for lipids in PSIIcc, namely the tuning of optical spectra and the creation of an excitation energy funnel towards the reaction center. The analysis of electrostatic pigment-protein interactions is used to identify amino acid residues that are of potential interest for an experimental approach to an assignment of site energies and energy sinks by site-directed mutagenesis
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