Low Temperature Excitation Transfer in the Fmo Complex. Simulations

Abstract

Electronic excited state (EES) models for the Fenna-Matthews-Olson (FMO) antenna complex of the green bacterium P. aestuarii have generally been based on obtaining an optimal match between the information contents of the optical steady-state spectra and the molecular organization [1-4]. Recent spectral and kinetic information gathered from probing the excited state processes through ultrafast measurements [5-7] have not yet been used effectively for further refinement of the EES and for quantification of the relation between the EES and the excited state kinetics. Recently, absorption difference spectrum (ADS) simulations have been reported for two of the models [1] by Buck et al. [6]. Important messages communicated in this study were: simulation of the ADS is another effective source of information; different models that can be rated equally acceptable in interpretation of steady-state spectra can yield broadly dissimilar ADS simulations; therefore, ADS simulations should be useful in distinguishing between different models and should be integrated as an important element of refinement in the further modeling. We have carried out simulations of absorption (ABS), linear dichroism (LD), singlet-triplet absorption difference (STAD) and ADS data in this strategy. We summarize our preliminary results on the EES structure and on the connection between the EES structure and the excited state kinetics.