Achiral polysilane aggregates can recognize the chirality of low-molecular-weight compounds. It was found that they can also record the stirring direction. Poly(n-decyl-2-methylpropylsilane), poly(n-nonyl-2-methylpropylsilane), poly(n-decyl-2-ethylbutylsilane), and poly(n-decyl-(S)-2-methylbutylsilane) aggregates were prepared in a mixture of tetrahydrofuran/isopropanol. Although the optical activity of the aggregates of the polysilane with chiral side chains was not tunable by changing the direction of the vortex flow, that of the aggregates of the optically inactive polysilane had a strong relationship to the direction, time, and rate of the vortex flow. The chiral stacked polysilanes were proposed to exist at the surfaces of the aggregates. The optically inactive polysilanes also exhibited optical activity under shear force with a distinct signal in the linear dichroism (LD) spectra of the achiral aggregates in vortex flows. However, the LD signals did not have a significant influence on the circular dichroism signals.

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. Chirality 28:44–48, 2016. © 2015 Wiley Periodicals, Inc.

Single-handed twisted titania tubular nanoribbons were prepared through sol-gel transcription using a pair of enantiomers. Handedness was controlled by that of the template. The obtained samples were characterized using field-emission electron microscopy, transmission electron microscopy, diffuse reflectance circular dichroism (DRCD), and X-ray diffraction. The DRCD spectra indicated that the titania nanotubes exhibit optical activity. Although the tubular structure was destroyed after being calcined at 700 °C for 2.0 h, DRCD signals were still identified. However, the DRCD signals disappeared after being calcined at 1000 °C for 2.0 h. The optical activity of titania was proposed to be due to chiral defects. Previous results showed that straight titania tubes could be used as asymmetric autocatalysts, indicating that titania exhibit chirality at the angstrom level. Herein, it was found that they also exhibit DRCD signals, indicating that there are no obvious relationships between morphology at the nano level and chirality at the angstrom level. The nanotube chirality should originate from the chiral defects on the nanotube inner surface. The Fourier transform infrared spectra indicated that the chirality of the titania was transferred from the gelators through the hydrogen bonding between N-H and Ti-OH. Chirality 27:543–550, 2015. © 2015 Wiley Periodicals, Inc.

Single-handed helical silica nanotubes containing chiral organic self-assemblies were prepared by using a supramolecular templating approach. After carbonization and the removal of the silica, single-handed helical carbonaceous nanotubes that contained twisted carbonaceous nanoribbons were obtained. It is believed that the nanotubes formed as a result of the adsorption of low-molecular-weight gelators. The twisted nanoribbons were formed because of the carbonization of the organic self-assemblies. The samples were characterized by using field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and circular dichroism. For the samples carbonized at 900 °C for 3.0 h, a partially graphitized structure was identified. The circular dichroism (CD) spectra indicated that the twisted nanoribbons exhibited optical activity. The CD spectrum was simulated by using time-dependent density functional theory. The results suggested that the CD signals originated from the chiral stacking of aromatic rings.

Single-handed, helical, 4,4′-biphenylene-bridged polybissilsesquioxane nanotubes were prepared by using the self-assemblies of a pair of chiral low-molecular-weight gelators as templates. Single-handed, helical, carbon/silica nanotubes were obtained after carbonization of the self-assemblies, and single-handed helical carbonaceous nanotubes were then obtained by removal of silica with aqueous HF. Samples were characterized by using field-emission SEM, TEM, X-ray diffraction, thermogravimetric analysis, Raman spectroscopy, and circular dichroism. The polysilsesquioxane and carbonaceous structures exhibited optical activity. The walls of the carbon/silica and carbonaceous nanotubes were predominantly amorphous carbon. The surface area of the left-handed, helical, carbonaceous nanotubes was 1439 m² g⁻¹, and such materials have potential applications as catalyst supports, chirality sensors, supercapacitor electrodes, and adsorbents.

Mesoporous 1,4-phenylene-silica nanorings were prepared using cetyltrimethylammonium bromide (CTAB) and (S)-2-methyl-1-butanol as a chiral dopant in concentrated aqueous NH₃ solutions. Transmission electron microscopy images of the samples indicated that the nanorings were formed by bending nanorods 360°. With increasing the stirring speed or the (S)-2-methyl-1-butanol/CTAB molar ratio, the morphologies of mesoporous 1,4-phenylene-silicas changed from helical nanofibers to nanorings, and then to nano-saddles. Circular dichroism spectra of these hybrid silicas indicated that they were chiral.

The morphology, pore architecture and crystallinity of the mesoporous 1,4-phenylene-silicas were controlled using the mixtures of cetyltrimethylammonium bromide (CTAB) and sodium dodecylsulfate (SDS). When the SDS/CTAB molar ratio increased from 0 to 1.0, the morphology of the mesoporous 1,4-phenylene-silicas changed in a sequence of sphere, hexagonal short rod, worm-like, bent flake and flower-like structure; the pore architecture of them changed from a hexagonal arranged tubular structure to a lamellar one; and the organization of the smallest repeat units within the wall changed from a random structure to a crystalline structure. At the SDS/CTAB molar ratios of 0.3 and 0.5, 1,4-phenylene-silica nanofibers with lamellar mesopores outside and tubular pore channels inside were obtained. The lamellar mesopores should be formed by merging the rod-like micelles during the reaction process.

Left-handed double twisted silica nanoribbons were prepared through a sol-gel transcription approach in the mixtures of ethanol and water. The self-assemblies of a chiral low-molecular-weight amphiphile served as the templates. The samples were characterized using X-ray diffraction, transmission electron microscope and scanning electron microscope. These double twisted silica nanoribbons were several micrometers in length, 50 to 70 nm in wideness, about 15 nm in thickness. The silica nanoribbons can be prepared in a large scale.

A sol-gel transcription process was carried out using an anionic gelator 12K and TMAPS as the co-structure-directing agent, as well as 4,4′-bis(triethoxysilyl)biphenyl as a hybrid silica source. It is interesting to find that the chirality of the organic self-assemblies of 12K was successfully transferred to the 4,4′-biphenylene-silica nanoribbons which are potentially applied in chiral catalysis.

Single-handed helical silica nanotubes that can trap water and organic solvents were prepared by sol-gel transcription under dilute gelator concentrations.