5 ± 0.2 ps for Rb. sphaeroides and 2.0 ± 0.1 ps for Rps. acidophila at liquid-helium temperature (De Caro et al. 1994). When exciting towards the blue within the B800 band (λexc < 798 nm), the fluorescence signals become broad and shift towards the red, while Γhom increases from 60–80 to ~250 GHz (between 798 nm and, at least, 788 nm). In this spectral region, inter-band B800 → B850 competes with intra-band B800 → B800 transfer, and intra-band energy-transfer times become τB800→B800 ≈ 900 fs between λexc ~ 780 and 798 nm.

At λexc < 780 nm, non-selective excitation in vibronic transitions of the B800 band takes place. The resulting fluorescence is broad with a peak at about 805 nm, independent of λexc. In this region, B800 → B800 ‘downhill’ transfer and vibrational relaxation are the dominant processes. LCZ696 nmr We conclude from these examples that FLN in combination with HB are powerful techniques for unravelling energy-transfer rates in photosynthetic GDC-0941 mw complexes at low temperature. (For discussions on energy transfer in bacterial LH complexes, see also Cheng and Silbey (2006), Novoderezhkin et al. (2003), Scholes and Fleming (2000), Sundström et al. (1999), Van Amerongen et al. (2000), Wu et al. (1996) and Zazubovich et al. (2002a).) Optical dephasing in the B850 band of purple bacteria The strong interactions between nearest-neighbour BChl molecules in the B850 band of LH2, with distances of less than 1 nm, lead to delocalization

of the excitation

to an extent Branched chain aminotransferase that is CHIR-99021 mw limited by static and dynamic disorder (Cogdell et al. 2006; Hu et al. 2002; Krueger et al. 1998; Scholes et al. 1999; Sundström et al. 1999). We will come back to this subject later. Here, we discuss the role of the protein structure in controlling the excited-state dynamics of the BChl a pigments in the B850 band. As shown above, the dynamics of a pigment within a protein is reflected by the homogeneous linewidth Γhom. In the case of B800, we saw that \( T_2^* \gg T_1 \) with Γhom determined by inter-band (B800 → B850) and intra-band (B800 → B800) energy-transfer processes. Here, we will show that in the red wing of the B850 band, Γhom is dominated by optical dephasing \( \left( T_2^* \right) \) processes characterized by a value of Γhom that is temperature dependent. Experiments were performed in our laboratory on Rb. sphaeroides (G1C, mutant): holes were burnt at a given temperature and Γhole measured as a function of burning-fluence density Pt/A. The hole widths are plotted versus Pt/A in Fig. 6a (J. Gallus and L. van den Aarssen, unpublished results). The value of Γhom is obtained from such a plot by extrapolating ½Γhole to Pt/A → 0. Similar measurements were done for temperatures between 1.2 and 4.2 K. Fig. 6 Top: a Hole width, ½ Γhole, as a function of burning-fluence density, Pt/A, of a hole burnt in the red wing of the B850 band of the LH2 complex of Rb. sphaeroides (G1C, mutant) at 1.8 K.