A Permanent Hole Burning Study of the FMO Antenna Complex of the Green Sulfur Bacterium Prosthecochloris aestuarii

Abstract

A permanent hole burning study on the Fenna-Matthews-Olson, or FMO, antenna complex of the green sulfur bacterium Prosthecochloris aestuarii was carried out at 6 K. Excitation resulted not only in relatively sharp features resonant with the burn wavelength but also in broad absorbance changes in the wavelength region of 800-820 nm. The shape of the latter changes was almost independent of the wavelength of excitation. Evidence is given that they are induced by a different mechanism than that which causes the resonant holes and that they may be due to a conformational change of the protein. The original spectrum was restored upon warming to 60 K. The effective dephasing times T2, as obtained from the homogeneous line widths, increased from about 0.5 ps at 803 nm to >/=20 ps at 830 nm and are in good agreement with recent measurements of accumulated photon-echo and time-resolved absorbance changes.

Exciton Simulations of Optical Spectra of the FMO Complex from the Green Sulfur Bacterium Chlorobium tepidum at 6 K

“…Taking into account the lifetime broadening of the high-energy transition does significantly improve the simulation of the absorption spectrum. This can be achieved by convoluting the homogeneous line width, as measured by hole burning, 28 with a Gaussian inhomogeneous distribution function of 80 cm -1 , keeping all other parameters the same. This resulted mainly in a strongly reduced amplitude of the band at 12 650 cm -1 in all simulated spectra.…”

Revisiting the optical properties of the FMO protein

“…In order to bridge the gap between steady-state and time-resolved spectroscopy an elaborate hole-burning experiment was performed (Franken et al. 1998). On top of broad (800–820 nm) uncorrelated signals, sharp holes were detected.…”

Exciton Structure and Energy Transfer in the Fenna–Matthews–Olson Complex

“…In the FMO species investigated here, isolated from Chlorobaculum tepidum, these are found at 12 120 cm −1 (825 nm), 12 270 cm −1 (815 nm), and at 12 420 cm −1 (805 nm), while an additional broad shoulder is found on the blue side at approximately 12 650 cm −1 (790 nm). The properties of FMO have been addressed with an array of optical techniques, ranging from steady-state absorption and fluorescence 3,17 to spectral hole-burning 18,19 and a variety of pump−probe-based techniques. 20−22 Nevertheless, the combination of closely spaced energy levels and rapid energy transfer leaves FMO as a difficult sample to probe by conventional timeresolved techniques.…”

“…The properties of FMO have been addressed with an array of optical techniques, ranging from steady-state absorption and fluorescence , to spectral hole-burning , and a variety of pump–probe-based techniques. − Nevertheless, the combination of closely spaced energy levels and rapid energy transfer leaves FMO as a difficult sample to probe by conventional time-resolved techniques. The direct relationship between spectral bandwidth and pulse length implies that either spectral or temporal resolution must be sacrificed.…”