title: Hexameric macroring of gable-porphyrins as a light-harvesting antenna mimic.
abstract: Construction of a self-assembled supramolecular macroring that has distances and orientations of porphyrin dimer units in close analogy to those of the natural light-harvesting complexes was achieved. In natural light-harvesting complexes, bacteriochlorophyll-a's are arranged in macroring structures by coordination from imidazolyl side chains. A structural determination of a light-harvesting antenna complex (LH2) elucidated the arrangement of 18 bacteriochlorophyll-a's in a slipped-cofacial way with C9 symmetry in B850 in 1995. To obtain such an elegant macroring architecture as an artificial light-harvesting complex, we connected slipped-cofacial dimers of imidazolylporphyrins in a gable-porphyrin orientation. The introduction of zinc assembled by coordination porphyrins with originally a broad molecular weight distribution (MWD). When coordination bonds were cleaved and reorganized under high dilution conditions using chloroform/methanol solution, the MWD was perfectly converged. This crop gave particle images of a uniform height by atomic force microscopy measurements. Further purification was successfully achieved by gel permeation chromatography, and the first eluting component gave a diameter corresponding to the cyclic hexamer of gable-porphyrins from a small-angle X-ray scattering measurement with synchrotron radiation. In summary, porphyrin assemblies in a macroring arrangement were constructed using the gable-porphyrin motif, and their photophysical properties are highly interesting.
authors.affiliation: Graduate School of Materials Science, Nara Institute of Science and Technology, and CREST, Japan Science and Technology Corporation (JST), 8916-5 Takayama, Ikoma, Nara 630-0101, Japan.
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Takahashi
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Kobuke
mesh_terms: D040761:Biomimetic Materials / Q000737:chemistry*; D003500:Cyclization; D008665:Metalloporphyrins / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D008958:Models, Molecular; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D012542:Scattering, Radiation; D013056:Spectrophotometry, Ultraviolet; D014965:X-Rays; D015032:Zinc / Q000737:chemistry
chemical_list: D008665:Metalloporphyrins; D045322:Photosynthetic Reaction Center Complex Proteins; D015032:Zinc