title: Nanotubes of Biomimetic Supramolecules Constructed by Synthetic Metal Chlorophyll Derivatives.
abstract: Various supramolecular nanotubes have recently been built up by lipids, peptides, and other organic molecules. Major light-harvesting (LH) antenna systems in a filamentous anoxygenic phototroph, Chloroflexus (Cfl.) aurantiacus, are called chlorosomes and contain photofunctional single-wall supramolecular nanotubes with approximately 5 nm in their diameter. Chlorosomal supramolecular nanotubes of Cfl. aurantiacus are constructed by a large amount of bacteriochlorophyll(BChl)-c molecules. Such a pigment self-assembles in a chlorosome without any assistance from the peptides, which is in sharp contrast to the other natural photosynthetic LH antennas. To mimic chlorosomal supramolecular nanotubes, synthetic models were prepared by the modification of naturally occurring chlorophyll(Chl)-a molecule. Metal complexes (magnesium, zinc, and cadmium) of the Chl derivative were synthesized as models of natural chlorosomal BChls. These metal Chl derivatives self-assembled in hydrophobic environments, and their supramolecules were analyzed by spectroscopic and microscopic techniques. Cryo-transmission electron microscopic images showed that the zinc and cadmium Chl derivatives could form single-wall supramolecular nanotubes and their outer and inner diameters were approximately 5 and 3 nm, respectively. Atomic force microscopic images suggested that the magnesium Chl derivative formed similar nanotubes to those of the corresponding zinc and cadmium complexes. Three chlorosomal single-wall supramolecular nanotubes of the metal Chl derivatives were prepared in the solid state and would be useful as photofunctional materials.
authors.affiliation: Graduate School of Life Sciences, Ritsumeikan University , Kusatsu, Shiga 525-8577, Japan.
authors.forename: Sunao
authors.initials: S
authors.lastname: Shoji
authors.affiliation: Institute for Chemical Research, Kyoto University , Uji, Kyoto 611-0011, Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Ogawa
authors.affiliation: Faculty of Engineering, Kumamoto University , Kumamoto, Kumamoto 860-8555, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Hashishin
authors.affiliation: Graduate School of Life Sciences, Ritsumeikan University , Kusatsu, Shiga 525-8577, Japan.
authors.forename: Shin
authors.initials: S
authors.lastname: Ogasawara
authors.affiliation: Graduate School of Life Sciences, Ritsumeikan University , Kusatsu, Shiga 525-8577, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Watanabe
authors.affiliation: Faculty of Textile Science and Technology, Shinshu University , Ueda, Nagano 386-8567, Japan.
authors.forename: Hisanao
authors.initials: H
authors.lastname: Usami
authors.affiliation: Graduate School of Life Sciences, Ritsumeikan University , Kusatsu, Shiga 525-8577, Japan.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Tamiaki
keywords: AFM; chlorophyll; chlorosome; cryo-TEM; self-assembly; single-wall nanotube; supramolecule