Static and Dynamic Protein Impact on Electronic Properties of Light-Harvesting Complex LH2

Abstract

A comparative analysis of the temperature dependence of the absorption spectra of the LH2 complexes from different species of photosynthetic bacteria, i.e., Rhodobacter sphaeroides, Rhodoblastus acidophilus, and Phaeospirillum molischianum, was performed in the temperature range from 4 to 300 K. Qualitatively, the temperature dependence is similar for all of the species studied. The spectral bandwidths of both B800 and B850 bands increases with temperature while the band positions shift in opposite directions: the B800 band shifts slightly to the red while the B850 band to the blue. These results were analyzed using the modified Redfield theory based on the exciton model. The main conclusion drawn from the analysis was that the spectral density function (SDF) is the main factor underlying the strength of the temperature dependence of the bandwidths for the B800 and B850 electronic transitions, while the bandwidths themselves are defined by the corresponding inhomogeneous distribution function (IDF). Slight variation of the slope of the temperature dependence of the bandwidths between species can be attributed to the changes of the values of the reorganization energies and characteristic frequencies determining the SDF. To explain the shift of the B850 band position with temperature, which is unusual for the conventional exciton model, a temperature dependence of the IDF must be postulated. This dependence can be achieved within the framework of the modified (dichotomous) exciton model. The slope of the temperature dependence of the B850 bandwidth is then defined by the value of the reorganization energy and by the difference between the transition energies of the dichotomous states of the pigment molecules. The equilibration factor between these dichotomous states mainly determines the temperature dependence of the peak shift.

Davydov Splitting of Excitons in Cyclic Bacteriochlorophyll a Nanoaggregates of Bacterial Light‐Harvesting Complexes between 4.5 and 263 K

“…acidophila were studied over similar broad temperature range. The outcome of these measurements, parallel to that obtained by former researches, [33][34][35][36][37] is presented in Figures 5 a,b for absorption and fluorescence, respectively. There is substantial blue-shift and broadening of both spectra with temperature.…”

Light harvesting complex II B850 excitation dynamics

“…In general, these are site dependent but due to the symmetry and relative homogeneity within the ring we set 1 / ␥ j =1/ ␥ = 100 fs and j = = 200 cm −1 to match parameters determined from fits to spectroscopic data. 48,49 Fourth order Runga-Kutta numerical integration with a 1 fs time step was used to integrate the hierarchical equations of motion. For one B850 ring ͑18 BChls͒ using an eighth order system bath coupling ͑L trunc =4͒ and two temperature correction terms, 424 270 matrices are required.…”

The effect of correlated bath fluctuations on exciton transfer

“…6-8, 41, 54-56 In the case of the B850 ring of LH2 this includes only the Q y excited state of the B850 Bchls. 20,[56][57][58][59][60][61][62] The Hamiltonian is 6,53,63,64 …”