title: The supramolecular organization of self-assembling chlorosomal bacteriochlorophyll c, d, or e mimics.
abstract: Bacteriochlorophylls (BChls) c, d, and e are the main light-harvesting pigments of green photosynthetic bacteria that self-assemble into nanostructures within the chlorosomes forming the most efficient antennas of photosynthetic organisms. All previous models of the chlorosomal antennae, which are quite controversially discussed because no single crystals could be grown so far from these organelles, involve a strong hydrogen-bonding interaction between the 3(1) hydroxyl group and the 13(1) carbonyl group. We have synthesized different self-assemblies of BChl c mimics having the same functional groups as the natural counterparts, that is, a hydroxyethyl substituent, a carbonyl group and a divalent metal atom ligated by a tetrapyrrole. These artificial BChl mimics have been shown by single crystal x-ray diffraction to form extended stacks that are packed by hydrophobic interactions and in the absence of hydrogen bonding. Time-resolved photoluminescence proves the ordered nature of the self-assembled stacks. FT-IR spectra show that on self-assembly the carbonyl frequency is shifted by approximately 30 cm(-1) to lower wavenumbers. From the FT-IR data we can infer the proximal interactions between the BChls in the chlorosomes consistent with a single crystal x-ray structure that shows a weak electrostatic interaction between carbonyl groups and the central zinc atom.
authors.affiliation: Institute for Synchrotron Radiation, Karlsruhe Institute of Technology, Forschungszentrum Karlsruhe, Postfach 3640, D-76021 Karlsruhe, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Jochum
authors.forename: Chilla Malla
authors.initials: CM
authors.lastname: Reddy
authors.forename: Andreas
authors.initials: A
authors.lastname: Eichhöfer
authors.forename: Gernot
authors.initials: G
authors.lastname: Buth
authors.forename: Jedrzej
authors.initials: J
authors.lastname: Szmytkowski
authors.forename: Heinz
authors.initials: H
authors.lastname: Kalt
authors.forename: David
authors.initials: D
authors.lastname: Moss
authors.forename: Teodor Silviu
authors.initials: TS
authors.lastname: Balaban