Self-assembly of [Et,Et]-bacteriochlorophyll cF on highly oriented pyrolytic graphite revealed by scanning tunneling microscopy.
The chlorosomal light-harvesting antennae of green phototrophic bacteria consist of large supramolecular aggregates of bacteriochlorophyll c (BChl c). The supramolecular structure of (3(1)-R/S)-BChl c on highly oriented pyrolytic graphite (HOPG) and molybdenum disulfide (MoS2) has been investigated by scanning tunneling microscopy (STM). On MoS2, we observed single BChl c molecules, dimers or tetramers, depending on the polarity of the solvent. On HOPG, we observed extensive self-assembly of the dimers and tetramers. We propose C=O...H-O...Mg bonding networks for the observed dimer chains, in agreement with former ultraviolet-visible and infrared spectroscopic work. The BChl c moieties in the tetramers are probably linked by four C=O...H-O hydrogen bonds to form a circle and further stabilized by Mg...O-H bondings to underlying BChl c layers. The tetramers form highly ordered, distinct chains and extended two-dimensional networks. We investigated semisynthetic chlorins for comparison by STM but observed that only BChl c self-assembles to well-structured large aggregates on HOPG. The results on the synthetic chlorins support our structure proposition.
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Institut für Physikalische Chemie und Elektrochemie, Heinrich-Heine-Universität Düsseldorf, Germany.
Kleinermanns
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Jesorka
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Schaffner
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Holzwarth
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AR
D001426:Bacterial Proteins / Q000737:chemistry*; D001429:Bacteriochlorophylls / Q000737:chemistry*; D004220:Disulfides / Q000737:chemistry; D006108:Graphite; D006358:Hot Temperature; D016252:Microscopy, Scanning Tunneling / Q000379:methods; D008958:Models, Molecular; D008968:Molecular Conformation; D008982:Molybdenum / Q000737:chemistry
D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; D004220:Disulfides; C120931:bacteriochlorophyll f; C002084:bacteriochlorophyll c; D006108:Graphite; D008982:Molybdenum; C082964:molybdenum disulfide