Energy Transfer in Photosystem I of Cyanobacteria Synechococcus elongatus: Model Study with Structure-Based Semi-Empirical Hamiltonian and Experimental Spectral Density

Abstract

We model the energy transfer and trapping kinetics in PSI. Rather than simply applying Förster theory, we develop a new approach to self-consistently describe energy transfer in a complex with heterogeneous couplings. Experimentally determined spectral densities are employed to calculate the energy transfer rates. The absorption spectrum and fluorescence decay time components of the complex at room temperature were reasonably reproduced. The roles of the special chlorophylls (red, linker, and reaction center, respectively) molecules are discussed. A formally exact expression for the trapping time is derived in terms of the intrinsic trapping time, mean first passage time to trap, and detrapping time. The energy transfer mechanism is discussed and the slowest steps of the arrival at the primary electron donor are found to contain two dominant steps: transfer-to-reaction-center, and transfer-to-trap-from-reaction-center. The intrinsic charge transfer time is estimated to be 0.8 approximately 1.7 ps. The optimality with respect to the trapping time of the calculated transition energies and the orientation of Chls is discussed.

Lateral Segregation of Photosystem I in Cyanobacterial Thylakoids

“…The intermonomer couplings, V MN;mn ; MÞN; were computed using the transitiondipole approximation according to Sener et al (2004). Excitation transfer kinetics in the PSI arrays can be described using Förster theory as an approximation (Sener et al, 2002(Sener et al, , 2004Croce and van Amerongen, 2013;Yang et al, 2003;van Stokkum et al, 2013). where J MN;mn are the spectral overlap integrals defined by Sener et al (2004).…”

Scalable High-Performance Algorithm for the Simulation of Exciton Dynamics. Application to the Light-Harvesting Complex II in the Presence of Resonant Vibrational Modes

“…Mainly two approximate methods for calculating the exciton dynamics have been applied to LHC II, modified Redfield theory 32 and the combined Förster-Redfield approach, 34,37 which interpolates between the two approximations. 57 The time-scale for the Chlb/Chla transfer obtained by both methods differs by one order of magnitude. 27,32,[34][35][36][37] The combined Förster-Redfield theory requires an empirical parameter M cr for separating the exciton Hamiltonian between a strongly coupled part H strong ex with all off-diagonal elements set to zero except those |J mn | > M cr and the remaining weakly coupled sites.…”

Characterization of Low-Energy Chlorophylls in the PSI-LHCI Supercomplex from Chlamydomonas reinhardtii. A Site-Selective Fluorescence Study

“…The processes of energy equilibration between these low-energy Chls and bulk Chls were extensively studied (see reviews 1,2 ), but the nature, location, and function of these red Chls are still not fully understood. [3][4][5][6][7][8][9][10][11][12] The red forms of Chls were characterized in detail for PSI core complexes from several species of cyanobacteria. At 6 K, two spectral pools of these Chls were identified with steadystate absorption/fluorescence line narrowing techniques: one with absorption maximum at 703 nm (C703, Synechococcus PCC 7942) or 708 nm (C708; Synechocystis PCC 6803, Thermosynechococcus elongatus (T. elongatus), Spirulina platensis (S. platensis)) and the other one with absorption maximum at 719 nm (T. elongatus) or at 740 nm (S. platensis).…”