Fluorescence spectral fluctuations of single LH2 complexes from Rhodopseudomonas acidophila strain 10050

We have investigated the energy landscape of the bacterial photosynthetic peripheral light-harvesting complex LH2 of purple bacterium Rhodopseudomonas acidophila by monitoring sequences of fluorescence spectra of single LH2 assemblies, at room temperature, with different excitation intensities as well as at elevated temperatures, utilizing a confocal microscope. The fluorescence peak wavelength of individual LH2 complexes was found to abruptly move between quasi-stable levels differing by up to 30 nm. These spectral shifts either to the blue or to the red were accompanied by a broadening and decrease of the intensity of the fluorescence spectrum. The frequency and size of these fluorescence peak movements were found to increase linearly with excitation intensity. Using the modified Redfield theory, changes in the realization of the static disorder accounted for the observed changes in spectral shape and intensity. Long lifetimes of the quasi-stable states suggest large free energy barriers between the different realizations

Circular Dichroism of Carotenoids in Bacterial Light-Harvesting Complexes: Experiments and Modeling

In this work we investigate the origin and characteristics of the circular dichroism (CD) spectrum of rhodopin glucoside and lycopene in the light-harvesting 2 complex of Rhodopseudomonas acidophila and Rhodospirillum molischianum, respectively. We successfully model their absorption and CD spectra based on the high-resolution structures. We assume that these spectra originate from seven interacting transition dipole moments: the first corresponds to the 0-0 transition of the carotenoid, whereas the remaining six represent higher vibronic components of the S(2) state. From the absorption spectra we get an estimate of the Franck-Condon factors of these transitions. Furthermore, we investigate the broadening mechanisms that lead to the final shape of the spectra and get an insight into the interaction energy between carotenoids. Finally, we examine the consequences of rotations of the carotenoid transition dipole moment and of deformations in the light-harvesting 2 complex rings. Comparison of the modeled carotenoid spectra with modeled spectra of the bacteriochlorophyll Q(Y) region leads to a refinement of the modeling procedure and an improvement of all calculated results. We therefore propose that the combined carotenoid and bacteriochlorophyll CD can be used as an accurate reflection of the overall structure of the light-harvesting complexes

Results from the AMANDA detector

The Antarctic Muon And Neutrino Detector Array (AMANDA) is a high-energy neutrino telescope based at the geographic South Pole. It is a lattice of photo-multiplier tubes buried deep in the polar ice, which is used as interaction and detection medium. The primary goal of this detector is the observation of astronomical sources of high-energy neutrinos. This paper shows the latest results of the search for a diffuse flux of extraterrestrial \u3bd\u3bcs with energies between 1011 eV and 10 18 eV, \u3bd\u3bcs emitted from point sources and \u3bd\u3bcs from dark matter annihilation in the Earth and the Sun