A water-soluble amphiphilic poly(phenylacetylene) bearing the bulky aza-18-crown-6-ether pendants forms a one-handed helix induced by l- or d-amino acids and chiral amino alcohols through specific host-guest interactions in water. We now report that such an induced helical poly(phenylacetylene) with a controlled helix sense can selectively trap an achiral benzoxazole cyanine dye among various structurally similar cyanine dyes within its hydrophobic helical cavity inside the polymer in acidic water, resulting in the formation of supramolecular helical aggregates, which exhibit an induced circular dichroism (ICD) in the cyanine dye chromophore region. The supramolecular chirality induced in the cyanine aggregates could be further memorized when the template helical polymer lost its optical activity and further inverted into the opposite helicity. Thereafter, thermal racemization of the helical aggregates slowly took place.
A novel, optically active, cis-transoidal poly(phenylacetylene) bearing an L-proline residue as the pendant group (poly-1) was prepared by the polymerization of the corresponding monomer using a rhodium catalyst in water, and its chiroptical property was investigated using circular dichroism spectroscopy. Poly-1 showed intense Cotton effects in the UV-visible region of the polymer backbone in water, resulting from the prevailing one-handed helical conformation induced by the covalent-bonded chiral L-proline pendants and exhibited a unique helix-sense inversion in response to external, achiral, and chiral stimuli, such as the solvent and interactions with chiral small molecules. We found that poly-1 could enantioselectively trap 1,1'-2-binaphthol within its hydrophobic helical cavity inside the polymer in aqueous media and underwent an inversion of its helical sense in the presence of one of the enantiomers. The effect of the optical purity of 1,1'-2-binaphthol on the chiroptical properties of poly-1 was also investigated.
In this study, we used small-angle
neutron scattering (SANS) and
small-angle X-ray scattering (SAXS) to investigate the formation process
of silver (Ag) nanoparticles (NPs) in water-in-oil (w/o) reverse microemulsions
comprising sodium bis(2-ethylhexyl) sulfosuccinate (AOT), water, and
organic solvents (such as benzene, octane, and decane) by the photoreduction
of silver perchlorate (AgClO4). Combining SANS and SAXS,
the structural changes in the w/o microemulsions before and after
the formation of Ag NPs via photoreduction were quantitatively evaluated.
From the SANS experiments performed using the contrast-variation method,
the size of water cores containing Ag NPs and the thickness of the
AOT shells were calculated using the core–shell hard-sphere
model. The size of the Ag NPs and their aggregates was calculated
via SAXS analysis based on the polydisperse sphere model with a Schulz–Zimm
distribution. We found that aggregates of three or four primary Ag
NPs are formed by, first, the aggregation of water droplets through
the entanglement of the tails of the AOT shell, followed by the self-assembly
of Ag NPs into their aggregates because of particle–particle
attractive interactions.
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