Anion-Dependent Hydrogen-Bond Polarity Switching in Ethylene-bridged Urea Oligomers

The reversible coordination of anions to an N,N'-disubstituted 3,5-bis(trifluoromethyl)phenylurea located at a terminus of a linear chain of ethylene-bridged hydrogen-bonded ureas triggers a cascade of conformational changes. A series of hydrogen-bond polarity reversals propagates along the oligomer, leading to a global switch of its hydrogen-bond directionality. The induced polarity switch, transmitted through four reversible urea groups, results in a change in emission and excitation wavelengths of a fluorophore located at the opposite terminus of the oligomer. The molecule thus behaves as a chemical sensor with a relayed remote spectroscopic response to variations in anion concentration. The polarity switch induced by anion concentration constitutes an artificial communication mechanism for conveying information through oligomeric structures.

Cooperative interaction between organic and inorganic moieties in hybrid silica nanohelices for enantioselective interaction

Hybrid nanometric helical structures formed by the molecular assemblies of dicationic gemini surfactants with tartrate counterions covered with helical silica walls interact differently with matching or mismatching enantiomers of the tartrate. The difference of the interaction is based on the cooperativity between the chiral crystalline gemini surfactant molecular organization/conformation and the rigid chiral nanospace formed by the helical silica wall.

Chirality in polythiophenes: A review

Chiroptical polythiophene (PTh), as one of the most important chiral conductive polymers, is an emerging and hot topic in chiral materials, which shows great application potentials in fields as diverse as chiral sensing and separation, asymmetry catalysis, chiroptoelectronics, and even chiro-spintronics. This review summarizes progress in chiral polythiophenes (PThs) in the past 10 years, including the synthesis, properties and applications. Main focus is placed on the manner in which chirality is implemented and the optical activity of the chiral PThs. We showcase examples in which the chirality of PThs is induced by side chain substituents with point, planar, and axial chirality or arises from external chiral media. Application of chiral PThs is also included. Finally, perspectives for further development are offered.

Inverse Evolution of Helicity from the Molecular to the Macroscopic Level Based on N-Terminal Aromatic Amino Acids

Precise control of the emergence of macroscopic helicity with specific handedness is promising in rationally designing chiral nanomaterials, but it is rather challenging. Herein, we present a protocol to address the transmission of helicity at a molecularly resolved level to a macroscopically resolved level, in which process supramolecular chirality undergoes an inversion. A series of N-terminal aromatic amino acids could self-assemble in water, enabling the occurrence of helicity at the molecularly resolved scale, evidenced by the single crystal structure and chiroptical responses. While it failed to transmit the helicity to the macroscopic scale for individual self-assembly, the coassembly with small organic binder through hydrogen bonding interactions allows for the emergence of helical structures at the nano/micrometer scale. Experimental and theoretical results demonstrate that the introduction of extra hydrogen bonds enables a moderate crystallinity of coassemblies with remaining one-dimensional orientation to enhance the helical growth. The transmission of helicity to higher levels by coassembly is accompanied by the helicity inversion, resulting from the exchange of hydrogen bonds. This study presents a rational protocol to precisely control the emergence of macroscopic helicity from molecularly resolved helicity with finely tailored handedness, providing a deeper understanding of the chirality origin in the assembled systems in order to facilitate the design and construction of functional chiral nanomaterials.

The Cooperative Effect of Both Molecular and Supramolecular Chirality on Cell Adhesion

Although helical nanofibrous structures have great influence on cell adhesion, the role played by chiral molecules in these structures on cells behavior has usually been ignored. The chirality of helical nanofibers is inverted by the odd-even effect of methylene units from homochiral l-phenylalanine derivative during assembly. An increase in cell adhesion on left-handed nanofibers and weak influence of cell behaviors on right-handed nanofibers are observed, even though both were derived from l-phenylalanine derivatives. Weak and negative influences on cell behavior was also observed for left- and right-handed nanofibers derived from d-phenylalanine, respectively. The effect on cell adhesion of single chiral molecules and helical nanofibers may be mutually offset.

Helical Mesoporous Tantalum Oxide Nanotubes: Formation, Optical Activity, and Applications

Nanomaterials with helical morphologies have attracted much attention owing to their potential applications as nanosprings, chirality sensors and in chiral optics. Single-handed helical Ta₂ O₅ nanotubes prepared through a supramolecular templating approach are described. The handedness is controlled by that of the organic self-assemblies of chiral low-molecular-weight gelators (LMWGs). The chiral LMWGs self-assemble into single-handed twisted nanoribbons through H-bonding, hydrophobic association, and π-π stacking. The Ta₂ O₅ nanotubes are formed by the adsorption and polycondensation of Ta₂ O₅ oligomers on the surfaces and edges of the twisted organic nanoribbons followed by removal of the template. The optical activity of the nanotubes is proposed to originate from the chiral defects on the inner surfaces of the tubular structures. Single-handed twisted LiTaO₃ nanotubes can also be prepared using Ta₂ O₅ nanotubes.

Rationally Developed Organic Salts of Tolfenamic Acid and Its β-Alanine Derivatives for Dual Purposes as an Anti-Inflammatory Topical Gel and Anticancer Agent

A new series of primary ammonium monocarboxylate (PAM) salts of a nonsteroidal anti-inflammatory drug (NSAID), namely, tolfenamic acid (TA), and its β-alanine derivatives were generated. Nearly 67 % of the salts in the series showed gelling abilities with various solvents, including water (biogenic solvent) and methyl salicylate (typically used for topical gel formulations). Gels were characterized by rheology, electron microscopy, and so forth. Structure-property correlations based on single-crystal and powder XRD data of several gelator and nongelator salts revealed intriguing insights. Studies (in vitro) on an aggressive human breast cancer cell line (MDA-MB-231) with the l-tyrosine methyl ester salt of TA (S7) revealed that the hydrogelator salt was more effective at killing cancer cells than the mother drug TA (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay); displayed better anti-inflammatory activity compared with that of TA (prostaglandin E₂ assay); could be internalized within the cancer cells, as revealed by fluorescence microscopy; and inhibited effectively migration of the cancer cells. Thus, the easily accessible ambidextrous gelator salt S7 can be used for two purposes: as an anti-inflammatory topical gel and as an anticancer agent.

Supramolecular Helical Systems: Helical Assemblies of Small Molecules, Foldamers, and Polymers with Chiral Amplification and Their Functions

In this review, we describe the recent advances in supramolecular helical assemblies formed from chiral and achiral small molecules, oligomers (foldamers), and helical and nonhelical polymers from the viewpoints of their formations with unique chiral phenomena, such as amplification of chirality during the dynamic helically assembled processes, properties, and specific functionalities, some of which have not been observed in or achieved by biological systems. In addition, a brief historical overview of the helical assemblies of small molecules and remarkable progress in the synthesis of single-stranded and multistranded helical foldamers and polymers, their properties, structures, and functions, mainly since 2009, will also be described.

Twisted and tubular silica structures by anionic surfactant fibers encapsulation

Organic molecules imprinting can be used for introducing specific properties and functionalities such as chirality to mesoporous materials. Particularly organic self-assemblies can work as a scaffold for templating inorganic materials such as silica. During recent years chiral imprinting of anionic surfactant for fabrication of twisted rod-like silica structures assisted by co-structuring directing agent were thoroughly investigated. The organic self-assemblies of anionic surfactants can also be used for introducing other shapes in rod-like silica structures. Here we report the formation of amphiphilic N-miristoyl-l-alanine self-assemblies in aqueous solution upon stirring and at presence of l-arginine. These anionic surfactant self-assemblies form fibers that grow by increasing the stirring duration. The fibers were studied using transmission electron microscopy, infra-red spectroscopy and vibrational circular dichroism. Addition of silica precursor 1,2-bis(triethoxysilyl)ethylene and co-structuring directing agent N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride at different stages of fibers' growth leads to formation of different silica structures. By controlling stirring duration, we obtained twisted tubular silica structures as a result of fibers encapsulation. We decorated these structures with gold nanoparticles by different methods and measured their optical activity.

Supramolecular Gels by Design: Towards the Development of Topical Gels for Self-Delivery Application

Following a supramolecular synthon approach, simple salt formation has been employed to gain access to a series of supramolecular gelators derived from the well-known non-steroidal anti-inflammatory drug (NSAID) ibuprofen. A well-studied gel-inducing supramolecular synthon, namely primary ammonium monocarboxylate (PAM), has been exploited to generate a series of PAM salts by reacting ibuprofen with various primary amines. Remarkably, all of the salts (S1-S7) thus synthesized proved to be good to moderate gelators of various polar and nonpolar solvents. Single-crystal and powder X-ray diffraction studies established the existence of the PAM synthons in the gel network, confirming the efficacy of the supramolecular synthon approach employed. Most importantly, the majority of the salts (S2, S3, S6, and S7) were capable of gelling methyl salicylate (MS), an important ingredient found in many commercial topical gels. In vitro experiments (MTT and PGE2 assays) revealed that all of the salts (except S3 and S7) were biocompatible (up to 0.5 mm concentration), and the most suited one, S6, displayed anti-inflammatory ability as good as that of the parent drug ibuprofen. A topical gel of S6 with methyl salicylate and menthol was found to be suitable for delivering the gelator drug in a self-delivery fashion in treating skin inflammation in mice. Histological studies, including immunohistology, were performed to further probe the role of the gelator drug S6 in treating inflammation. Cell imaging studies supported cellular uptake of the gelator drug in such biomedical application.

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.

Aggregation-induced scaffolding: photoscissable helical polysilane generates circularly polarized luminescent polyfluorene

An enantiopair of rigid rod-like helical polysilanes as a photoscissible scaffold allowed the production of CPL- and CD-active dioctylpolyfluorene aggregates associated with complete removal by a polysilane-selective photoscissoring reaction at 313 nm.

Conformational Switching of a Foldamer in a Multicomponent System by pH-Filtered Selection between Competing Noncovalent Interactions

Biomolecular systems are able to respond to their chemical environment through reversible, selective, noncovalent intermolecular interactions. Typically, these interactions induce conformational changes that initiate a signaling cascade, allowing the regulation of biochemical pathways. In this work, we describe an artificial molecular system that mimics this ability to translate selective noncovalent interactions into reversible conformational changes. An achiral but helical foldamer carrying a basic binding site interacts selectively with the most acidic member of a suite of chiral ligands. As a consequence of this noncovalent interaction, a global absolute screw sense preference, detectable by (13)C NMR, is induced in the foldamer. Addition of base, or acid, to the mixture of ligands competitively modulates their interaction with the binding site, and reversibly switches the foldamer chain between its left and right-handed conformations. As a result, the foldamer-ligand mixture behaves as a biomimetic chemical system with emergent properties, functioning as a "proton-counting" molecular device capable of providing a tunable, pH-dependent conformational response to its environment.