Recently, single-handed helical metal oxide nanotubes with optical activity have attracted much attention.They can be used as asymmetric catalysts. Herein, single-handed helical tantalum oxide (Ta 2 O 5 ) nanotubes were prepared using a supramolecular templating approach. Field-emission scanning electron microscopy images showed that the handedness of the Ta 2 O 5 nanotubes was controlled by that of the template organic self-assembly. Circular dichroism (CD) spectra revealed that the nanotubes exhibited optical activity.Because straight Ta 2 O 5 nanotubes also exhibit optical activity, there is no relationship between the optical activity and handedness of the Ta 2 O 5 nanotubes. The CD spectrum simulated using timedependent density functional theory indicated that chiral point defects were responsible for the optical activity. It was also found that the chirality of Ta 2 O 5 could be transferred to stacked poly(n-nonyl-2methylpropylsilane).
In mixtures of water and dimethyl sulfoxide, 4'-(n-dodecyloxy)-1,1'-biphenyl-4-carbonyl Ala-Ala dipeptides can self-assemble into tubular structures that are formed by coiled nanoribbons. The twist and stacking handedness of biphenylene groups were studied using circular dichroism and confirmed by theoretical chemical calculations. The handedness of the coiled nanoribbons and the stacking handedness of biphenylene groups are controlled by the chirality of alanine at the C-terminus, whereas the twist handedness of biphenylene groups is determined by the chirality of alanine at the N-terminus. H NMR spectra indicated that the hydrogen bond formed by the N-H group of alanine at the N-terminus plays an important role in the formation of organic self-assemblies. On the basis of small-angle X-ray scattering characterization, a dimer structure was proposed to form through the terminal COOH groups.
Four Phe-Ala lipodipeptides with different stereochemical structures are observed to self-assemble into twisted nanoribbons in water. The handedness of the twisted nanoribbons is controlled by the chirality of the phenylalanine near the alkyl chain, while the stacking handedness of the phenyl and carbonyl groups is determined by the alanine at the C-terminal. The homochiral and heterochiral lipodipeptides self-assemble into parallel and antiparallel β-sheet structures, respectively. The H NMR, FTIR, X-ray diffraction, and circular dichroism characterizations indicate that these phenomena are mainly driven by the interaction between neighboring phenyl groups and H-bonding among the amide groups.
Polybissilsesquioxanes with single-handed helical morphologies attracted much attention during the last decade, which could be applied as asymmetric catalysts and chiral stationary phases. Herein, a pair of chiral biphenylene-bridged bissilsesquioxanes were synthesized. They self-assembled into helical bundles in ethanol, behavior that was confirmed in field emission scanning electron microscopy images. Circular dichroism analysis indicated that the biphenylene groups twisted in a single-handed fashion. Single-handed helical polybissilsesquioxane bundles were prepared via polycondensation of the bissilsesquioxanes, using a self-templating approach. Because of the shrinkage that occurred during polycondensation, the helical pitches of the bundles were shorter than those of their corresponding organic self-assemblies. The wide-angle X-ray diffraction pattern indicated that there were no π-π interactions among the diphenylene groups. The circular dichroism spectra indicated that the chirality was successfully transferred from the bissilsesquioxane self-assemblies to the polybissilsesquioxane. The polybissilsesquioxanes displayed a capacity for the adsorption of nitrobenzene and had potential application for enantioseparation.
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