title: Excitons in intact cells of photosynthetic bacteria.
abstract: Live cells and regular crystals seem fundamentally incompatible. Still, effects characteristic to ideal crystals, such as coherent sharing of excitation, have been recently used in many studies to explain the behavior of several photosynthetic complexes, especially the inner workings of the light-harvesting apparatus of the oldest known photosynthetic organisms, the purple bacteria. To this date, there has been no concrete evidence that the same effects are instrumental in real living cells, leaving a possibility that this is an artifact of unnatural study conditions, not a real effect relevant to the biological operation of bacteria. Hereby, we demonstrate survival of collective coherent excitations (excitons) in intact cells of photosynthetic purple bacteria. This is done by using excitation anisotropy spectroscopy for tracking the temperature-dependent evolution of exciton bands in light-harvesting systems of increasing structural complexity. The temperature was gradually raised from 4.5 K to ambient temperature, and the complexity of the systems ranged from detergent-isolated complexes to complete bacterial cells. The results provide conclusive evidence that excitons are indeed one of the key elements contributing to the energetic and dynamic properties of photosynthetic organisms.
authors: Institute of Physics, University of Tartu , Riia 142, Tartu 51014, Estonia.
authors: Arvi
authors: A
authors: Freiberg
authors: Mihkel
authors: M
authors: Pajusalu
authors: Margus
authors: M
authors: Rätsep
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D003902:Detergents / Q000737:chemistry; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000378:metabolism*; D009930:Organic Chemicals / Q000737:chemistry; D010788:Photosynthesis; D020560:Proteobacteria / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; D003902:Detergents; D045342:Light-Harvesting Protein Complexes; D009930:Organic Chemicals; C057718:6-(Dimethylamino)-2-((1E,3E)-4-(4-(dimethylamino)phenyl)-1,3-butadien-1-yl)-1-ethylquinolinium perchlorate