Optically active polymer film tuned by a chirally self-assembled molecular organogel

A Molecular Shape Recognitive HPLC Stationary Phase Based on a Highly Ordered Amphiphilic Glutamide Molecular Gel

Chiral glutamide-derived lipids form self-assembled fibrous molecular gels that can be used as HPLC organic phases. In this study, HPLC separation efficiency was improved through the addition of branched amphiphilic glutamide lipids to the side chains of a terminally immobilized flexible polymer backbone. Poly(4-vinylpyridine) with a trimethoxysilyl group at one end was grafted onto the surface of porous silica particles (Sil-VP15, polymerization degree = 15), and the pyridyl side chains were quaternized with a glutamide lipid having a bromide group (BrG). Elemental analysis indicated that the total amount of the organic phase of the prepared stationary phase (Sil-VPG15) was 38.0 wt%, and the quaternization degree of the pyridyl groups was determined to be 32.5%. Differential scanning calorimetric analysis of a methanol suspension of Sil-VPG15 indicated that the G moieties formed a highly ordered structure below the phase transition temperature even on the silica surface, and the ordered G moieties exhibited a gel-to-liquid crystalline phase transition. Compared with a commercially available octadecylated silica column, the Sil-VPG15 stationary phase showed high selectivity toward polycyclic aromatic hydrocarbons, and particularly excellent separations were obtained for geometrical and positional isomers. Sil-VPG15 also showed highly selective separation for phenol derivatives, and bio-related molecules containing phenolic groups such as steroids were successfully separated. These separation abilities are probably due to multiple interactions between the elutes and the highly ordered functional groups, such as the pyridinium and amide groups, on the highly ordered molecular gel having self-assembling G moieties.

Supramolecular gelatons: towards the design of molecular gels

The concept of supramolecular gelatons for the design of gels was proposed and described.

Anomalous photovoltaic effect based on molecular chirality: influence of enantiomeric purity on the photocurrent response in π-conjugated ferroelectric liquid crystals

Photovoltaic effect based on molecular chirality was observed in π-conjugated ferroelectric liquid crystals.

Memorized chiral arrangement of gemini surfactant assemblies in nanometric hybrid organic–silica helices

The chiral arrangement of non-chiral gemini surfactant molecules induced by enantiomeric tartrate counterions was maintained by hybridization with silica matrices even after the removal of the counterions as chiral sources.

Gelation induced supramolecular chirality: chirality transfer, amplification and application

Supramolecular chirality defines chirality at the supramolecular level, and is generated from the spatial arrangement of component molecules assembling through non-covalent interactions such as hydrogen bonding, van der Waals interactions, π-π stacking, hydrophobic interactions and so on. During the formation of low molecular weight gels (LMWGs), one kind of fascinating soft material, one frequently encounters the phenomenon of chirality as well as chiral nanostructures, either from chiral gelators or even achiral gelators. A view of gelation-induced supramolecular chirality will be very helpful to understand the self-assembly process of the gelator molecules as well as the chiral structures, the regulation of the chirality in the gels and the development of the "smart" chiral materials such as chiroptical devices, catalysts and chiral sensors. It necessitates fundamental understanding of chirality transfer and amplification in these supramolecular systems. In this review, recent progress in gelation-induced supramolecular chirality is discussed.

Metathesis within self-assembled gels: transcribing nanostructured soft materials into a more robust form

This article reports the covalent capture of self-assembled gel-phase materials using alkene metathesis. Gels assembled from a gelator functionalized with peripheral alkene groups were reacted with Grubbs' second generation catalyst, added as a solution to the top of the gel and allowed to diffuse into the material for 24 h. Using this approach, the fibrillar self-assembled network was covalently captured, yielding a large amount of insoluble material that was robust, thermally stable, and highly swellable in solvents compatible with the gelator. Scanning electron microscopy demonstrated that the insoluble metathesized material contained nanoscale fibers, which were aligned into rigid fiber bundles on drying. When the gelator was assembled in the presence of a second non-cross-linkable gelator, self-sorting took place, giving rise to two independent gelator networks. Metathesis then generated an insoluble material in which the individual gel fibers of the cross-linkable gelator were captured, whereas the nonreactive gelator could be washed away. Intriguingly, using this approach appeared to hinder the alignment of gel fibers into rigid fiber bundles. Instead, individual, well-defined, robust gelator nanofibers were visualized in the dried materials. In addition, the material synthesized this way appeared to be even more highly porous and swellable on the addition of solvent. In summary, this article demonstrates that metathesis is an effective way to capture nanostructured gel-phase materials covalently, with the judicious choice of additives helping to control the morphology and behavior of the materials generated. This approach to nanofabrication could ultimately give rise to nanostructured polymeric materials with a wide range of applications.

Polycondensation and stabilization of chirally ordered molecular organogels derived from alkoxysilyl group- containing L-glutamide lipid

A lipophilic L-glutamide-derived lipid with a triethoxysilyl headgroup (Si-lipid) was newly synthesized as a self-assembling organogelator to stabilize the chirally ordered state of the aggregates. The Si-lipid formed nanofibrous network structures in various organic solvents such as benzene, cyclohexane, and dimethylformamide and entrapped them to form gels. The gels were transformed to sols by heat, and this gel-to-sol transition was thermally reversible. Polycondensation of the triethoxysilyl groups was carried out by acid-catalyzed hydrolysis and condensation in a benzene gel and confirmed by 29Si CP/MAS NMR and FT-IR measurements. After polycondensation, a gel state was maintained, and the thermal and mechanical stabilities of the aggregates increased markedly. Interestingly, polycondensation in chloroform and acetonitrile induced gelation, whereas no gelation was observed before polycondensation. Xerogel, which was prepared by freeze drying organogels, had fibrous network structures similar to those of the original gels. A strong CD signal was observed around the amide bonds in a cyclohexane gel at 20 degrees C, indicating that the gel contained chirally oriented structures based on intermolecular hydrogen bonds. An enhanced CD signal was observed even after polycondensation of the ethoxysilyl group of Si-lipid (poly(Si-lipid)) and was maintained at 70 degrees C, which is above the temperature of the gel-to-sol phase transition of the original gel. These results indicate that the formation of siloxane network structure among the fibrous aggregates stabilizes the chiral orientation of lipid aggregates.

Lost in translation? Chirality effects in the self-assembly of nanostructured gel-phase materials

Gel-phase materials are generated when molecular building blocks assemble into nanoscale architectures, usually 'one-dimensional' fibrils, which hierarchically assemble into bundles and subsequently form an entangled sample spanning network, capable of preventing the flow of bulk solvent. This tutorial review explores the vital role of chirality in gel formation. In particular, we focus on how fundamental self-assembly processes can translate molecular scale chiral information into nanoscale architectures, and then into the macroscopic behaviour of the gel. Chiral molecular gels have potential applications in nanofabrication and as addressable functional nanomaterials.

Use of fluorescence spectroscopy to study polymeric materials with porous structure based on imprinting by self-assembled fibrillar networks

Different polymeric materials have been prepared from the organogels formed by a polymerizable methacrylic mixture (methyl methacrylate/ethylene glycol dimethacrylate, 1:1, w/w) and the macrocyclic pseudopeptide 1. The use of (2,4,6-trimethylbenzoyl)diphenylphosphine oxide as a very efficient radical initiator allows polymeric materials in which the structure of the fibrils formed by self-assembly of the organogelator 1 is truly preserved to be obtained. Removal of the pseudopeptidic molecule provides materials with a porous structure reflecting that of the original self-assembled fibrils. The use of fluorescent probes such as rhodamine B and pyrene greatly facilitate the study of the porous structures formed and, accordingly, that of the morphology of the original fibrils. Those studies reveal the presence of a permanent porosity and the organization of the substructures as a porous network. This confirms the existence of a nucleation and growth mechanism for the generation of the fibrils, giving rise to the formation of spherulitic structures. Those spherulites are additionally linked by connections of variable size. A series of diffusion experiments allowed establishment of a direct dependence of the inner porosity of the materials on the amount of self-organizing template used for their preparation.

Gelating-induced supramolecular chirality of achiral porphyrins: chiroptical switch between achiral molecules and chiral assemblies

Chiral low molecular weight organogelators which can gel nearly all kinds of common organic solvents were designed. The gelators could also form organogels with other functional compounds, which could not form the organogel themselves. Achiral porphyrins were employed as functional compounds to form the co-gel with the gelator in DMSO and interesting properties were found. Although no chirality was observed when the achiral porphyrin derivative containing a long alkyl chain was mixed with the gelator in hot DMSO solution, supramolecular chirality of the achiral porphyrin was induced when cooling to form an organogel. Based on the thermo-reversible property of the organogel, a thermo-driven supramolecular chiroptical switch was proposed through the switch between achiral molecule and chiral molecular assemblies.