title: Synthesis and optical properties of chlorin monomer, dimer and trimer on an amino nitrogen atom.
abstract: Naturally occurring chlorophyll-a was chemically modified to methyl 3-aminomethyl-pyropheophorbides-a including primary, secondary, and tertiary amines. Reductive amination of methyl pyropheophorbide-d possessing the 3-formyl group with ammonia efficiently gave a chlorin dimer covalently linked with CH2NHCH2 at the 3-position, which was transformed into a trimer through the substitution at the amino group. Conformational analyses by (1)H NMR spectroscopic observation and molecular modeling estimation indicated that the dimer and trimer were apt to form closely packed structures. Chlorin chromophores in the dimer and trimer were weakly interacted in dichloromethane to shift their Qy absorption bands to longer wavelengths by 4-6nm than the maxima of the corresponding monomer. In the red-shifted Qy region, the trimer gave an S-shaped circular dichroism band by exciton coupling of composite chlorin units. All the semi-synthetic chlorophyll derivatives were highly fluorescent and no intramolecular quenching was observed even in the trimer. The behaviors would be ascribable to the formation of compact conformers and suppression of intramolecular motion, which are important to construct light-harvesting antenna complexes in phototrophs and their model systems.
authors.affiliation: Graduate School of Life Sciences, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan. Electronic address: tamiaki@fc.ritsumei.ac.jp.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Tamiaki
authors.affiliation: Graduate School of Life Sciences, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan.
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Nagai
authors.affiliation: Graduate School of Life Sciences, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Tanaka
authors.affiliation: Graduate School of Life Sciences, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Tatebe
mesh_terms: D008958:Models, Molecular; D008968:Molecular Conformation; D009584:Nitrogen / Q000737:chemistry*; D011166:Porphyrins / Q000737:chemistry*
chemical_list: D011166:Porphyrins; C006969:chlorin; D009584:Nitrogen
keywords: Chlorophyll; Fluorescence emission data; Light-harvesting antenna; Photosynthesis; Visible absorption spectra