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Two‐Component Fibers/Gels and Vesicles Formed from Hetero‐Double‐Helices of Pseudoenantiomeric Ethynylhelicene Oligomers with Branched Side Chains
Author(s) -
Saito Nozomi,
Shigeno Masanori,
Yamaguchi Masahiko
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201200280
Subject(s) - vesicle , dynamic light scattering , chemistry , pentamer , tetramer , crystallography , oligomer , solvent , fiber , side chain , polymer chemistry , stereochemistry , materials science , polymer , nanoparticle , nanotechnology , organic chemistry , biochemistry , membrane , enzyme
A methodology for the formation of fibers/gels and vesicles by molecular assembly and for controlling their properties is presented. Two‐component systems of pentamer ( P )‐ 5 and tetramer ( M )‐ 4 pseudoenantiomeric ethynylhelicenes with decyloxycarbonyl (D) and 4‐methyl‐2‐(2‐methylpropyl)‐1‐pentyloxycarbonyl (bD) side‐chains have been examined. Distinct aggregates were formed by changing the solvent for the three combinations of ( P )‐bD‐ 5 /( M )‐bD‐ 4 , ( P )‐D‐ 5 /( M )‐bD‐ 4 , and ( P )‐D‐ 5 /( M )‐D‐ 4 . In toluene, ( P )‐bD‐ 5 /( M )‐bD‐ 4 , ( P )‐D‐ 5 /( M )‐bD‐ 4 , and ( P )‐D‐ 5 /( M )‐D‐ 4 all formed gels and fibrous assemblies were observed by AFM. The minimum gel‐forming concentration (MGC) decreased in the order ( P )‐bD‐ 5 /( M )‐bD‐ 4 >( P )‐D‐ 5 /( M )‐bD‐ 4 >( P )‐D‐ 5 /( M )‐D‐ 4 . In diethyl ether, vesicular formation was observed by dynamic light scattering (DLS), AFM, and TEM, and the size of the vesicles decreased in the order ( P )‐bD‐ 5 /( M )‐bD‐ 4 >( P )‐ D ‐ 5 /( M )‐bD‐ 4 >( P )‐ D ‐ 5 /( M )‐ D ‐ 4 . Both fiber/gel and vesicle formation were accompanied by enhanced CDs and redshifted UV/Vis absorption bands with a change in color to deep yellow. These are novel two‐component oligomeric systems that form assemblies of fibers/gels or vesicles depending on the solvent, and the structures and properties of the assemblies can be fine‐tuned by changing the combination of oligomers. In m ‐difluorobenzene, a homogeneous solution was obtained with ( P )‐D‐ 5 /( M )‐bD‐ 4 , which again exhibits enhanced CDs and redshifted UV/Vis absorptions. Vapor pressure osmometry analysis showed the formation of a bimolecular heteroaggregate. The study has indicated that pseudoenantiomeric oligomers form hetero‐double‐helices that hierarchically assemble to form fibers/gels and vesicles.