The nature of the 825-nm band was confirmed to have a double origin seven years later by means of Stark hole-burning studies (Rätsep et al. 1998). However, in this case, the nature of these states was assumed to be much more localized, with the excitons mainly spread over

one BChl a molecule. Structural heterogeneity in the complex leads to a variation in the excitation energy of the lowest energy state in the subunits of the trimer. This view was tested by temperature-dependent hole-burning experiments on the FMO protein from Chlorobium tepidum (Rätsep et al. 1999). The 825-nm absorption band was fitted with three Gaussian bands of ∼55cm−1 at 823.0, 825.0, and 827.0 nm, respectively. The dependence of hole width and hole growing kinetics on the burning frequency confirms that there are three bands contributing see more to the 825-nm band. Triplet minus singlet (T − S) spectra measured by Louwe et al. (1997a) shows that the triplet state is localized on a single BChl a since it demonstrates the same properties as monomeric BChl a a in organic solvents. The orientations of excitonic transitions in the Q y band were determined relative to the triplet-carrying molecule. In contrast to earlier measurements, fluorescence line narrowing experiments showed that the 825-nm absorption band can be accounted for by a single transition in the range of temperature from 4 K to room

temperature (Wendling et al. 2000). This transition is coupled to protein phonons Selleck Tubastatin A and vibrations in the chromophore. The effect of Selleckchem H 89 disorder on the lowest energy band in the trimer was further studied by Monte Carlo simulations (Hayes et al. 2002). The lowest energy band could be fitted with three nearly Gaussian bands of almost identical intensity. One of those band was

centered at the absorption maximum of the 825 nm band, while the maxima of the other two bands where shifted by ∼−17 and ∼+26cm−1, respectively. Summarizing, the outcome of different experimental techniques do not agree on the nature of the 825 nm band. While some state that this band is due to a single transition, others Ponatinib in vitro include a distribution of the lowest exciton energy in the different subunits of the trimer to account for the observations. Nonlinear spectra and exciton dynamics in the FMO protein This section will discuss both the experimental and theoretical aspects of the time-resolved spectra of the FMO protein. Previously, in “Exciton nature of the BChl a excitations in the FMO protein” and “Coupling strengths, linewidth, and exciton energies”, the excitonic structure and simulations of the linear optical spectra were reviewed. Starting from this knowledge, it is a small, yet complex step to simulate the time-dependent behavior of the exciton states. After optical excitation, the population in the exciton states eventually decays back to the ground state.