Abstract
We have found that coherent excitation, with approximate 30 fs pulses, of the optically-allowed 1Bu+(0) and the overlapped, optically-forbidden 1Bu-(2) or 3Ag-(1) levels of carotenoids (spheroidene or lycopene) generates stimulated emission from the 1Bu-(0) and 3Ag-(0) level [T. Miki, Y. Kakitani, Y. Koyama and H. Nagae, Chem. Phys. Lett. 457 (2008) 222 ]. Also, we have shown that the axial coordination to the Mg atom of bacteriochlorophyll, i.e., the penta-coordinated state, in the presence or absence of additional axial interaction, can be probed by the width of the 25Mg-NMR signal [Y. Kakitani, Y. Koyama, Y. Shimoikada, T. Nakai, H. Utsumi, T. Shimizu and H. Nagae, accepted by Biochemistry].
We are applying these techniques to determine the 1Bu-(0) and 3Ag-(0) levels of the above carotenoids, and the axial coordination / interaction of B800 and B850 bacteriochlorophyll a, when bound to the LH2 complexes from Rba. sphaeroides 2.4.1 and Rsp. molischianum.