On the Chiral Homogeneity of Nature: From Atoms to Small Molecules

The genesis of enantiopurity in nature, as exemplified by terrestrial amino acids and sugars, has fascinated scientists for more than 150 years. This is a field where we know what we do not know. Starting from theoretical treatments postulated more than 50 years ago, numerous hypotheses, theories, and experiments have been formulated to claim niches of logic and truth. Such arguments vary from purely speculative, often bizarre, to sound enough in terms of reproducibility and feasible generation of mirror symmetry breaking. Although we cannot exclude a biotic origin (i.e,. homochirality was an a posteriori event where one enantiomer tripped and the other survived and evolved, in close resemblance to a Darwinian-like process), most data and models available are consistent with an abiotic origin that amplified small and stochastic imbalances to produce enantiopure homogeneity prior to life. This analysis revisits recent theoretical background and experiments, which appear to be prebiotically credible, and focuses on primordial molecules such as amino acids. This by no means implies a recreation of the origin of life on Earth, as this task will likely be a surmise forever. These strategies reveal a high degree of robustness and prove how home-made enantiopurity can be accomplished. Such routes should, in addition, be of enormous practical interest for the production of chiral materials and drugs.     

Supramolecular Assemblies Constructed by Cucurbituril-Catalyzed Click Reaction

Cucurbituril homologues are multi-functional macrocycles that can find applications in many areas and have numerous interesting features setting them apart from the other macrocycles. Among them, the ability of one of the cucurbituril homologues, cucurbit[6]uril (CB6), to catalyze 1,3-dipolar cycloaddition in a regiospecific fashion is truly exceptional. Using this feature, small molecules can be clicked together to form complex structures in a very efficient way. Accordingly, in this article we review recent research involving the use of CB6-catalyzed 1,3-dipolar cycloaddition or the click reaction of CB6 in the construction of supramolecular assemblies including rotaxanes, pseudorotaxanes, polyrotaxanes, polypseudorotaxanes, molecular switches, machines, and nanovalves.     

Why Are Biological Systems Homochiral?

Self-assembling and self-organizable dendrons, dendrimers, and dendronized polymers produce chiral supramolecular architectures that have been developed as biological mimics. Here we review our work on the self-assembly of homochiral, heterochiral, and racemic dendritic dipeptides, and address one of the most fundamental questions of biological systems: Why are biological systems homochiral and not heterochiral or racemic and, if they were heterochiral or racemic, how would they look and function by comparison with contemporary homochiral biological systems?     

Encapsulation of Drug Molecules by Cucurbiturils: Effects on their Chemical Properties in Aqueous Solution

The effects of the encapsulation of drugs and other molecules of biomedical interest by cucurbit[n]uril (n=5–8, 10) host molecules on the chemical properties of the drugs in aqueous solution are reviewed. The cucurbituril complexation of drug molecules has been shown to generally increase the guests’ pK_a values through preferential inclusion of the protonated species, modulate other equilibria involving the guest, improve the solubility in aqueous solution, reduce the toxicity and other side effects, as well as enhance the stability and targeted delivery of the drug molecule. These benefits have led to an increasing interest in the applications of cucurbit[n]urils in novel drug formulations.     

Dynamic Combinatorial Chemistry in Chemical Catalysis

Despite the progress in the field of dynamic combinatorial chemistry (DCC), dynamic combinatorial catalysis has received considerably less attention. Some first studies, however, have provided proof of principle and demonstrated that DCC-based approaches are also applicable in catalyst development. This provides interesting new tools that are complementary to rational catalyst design and traditional combinatorial strategies. As such, DCC may become highly valuable in the field of dynamic combinatorial catalysis, due also to the practical importance of catalysis. In this review we focus on the principles of dynamic combinatorial catalysis and provide an overview by the introduction of different concepts related to the development of libraries and selection procedures in catalysis.     

Discovery and Mechanism of Type III Secretion System Inhibitors

The Type III Secretion System (TTSS) is indispensable for virulence of many Gram-negative pathogenic bacteria, including Escherichia coli, Salmonella spp., Yersinia spp., Vibrio spp., Chlamydia spp., Shigella spp., Pseudomonas spp., Xanthomonas spp., and Auromonas spp. Such pathogenic bacteria are responsible for diseases such as plague, shigellosis, chlamydia, cholera, pneumonia, and gastroenteritis. This review offers insights into the known inhibitors of the TTSS, their discovery, and their mode of action.     

Advanced Functional Materials Constructed from Pillar[n]arenes

Pillar[n]arenes are new generation of supramolecular macrocyclic host, which exhibit excellent host−guest recognition properties. In the last decade, functional materials constructed from pillar[n]arenes have been attracted more and more attention and displayed outstanding characteristics, such as stimuli-responsiveness, self-healing and adaptability. In this mini-review, we provide a survey of the pillar[n]arene-based literatures covering light-harvesting systems, functional hydrogels, and solid materials. It is anticipated that more and more pillar[n]arenes-based advanced materials with multi-functional properties will appear in the near future.     

Nitroxide Radicals with Cucurbit[n]urils and Other Cavitands

The interface of nitroxide radicals with cucurbit[n]urils (CB[n]) is covered in this review. Either used as spin probes, spin labels, or stoppers for paramagnetic rotaxanes, nitroxides offer new opportunities to investigate CB[n] and their inclusion complexes, especially thanks to EPR spectroscopy. On the other hand, CB[n] also offer interesting opportunities to modulate nitroxide properties such as protection or structuring. The multiple back and forth between the two well-established areas where nitroxides bring information about CB[n], and CB[n] modulate nitroxide properties, have enabled to shed some light at this new interesting interface.     

Chromatographic partitioning of cesium by a macroporous silica‐calix[4]arene‐crown supramolecular recognition composite

A macroporous silica‐based 1,3‐[(2,4‐diethyl‐heptylethoxy)oxy]‐2,4‐crown‐6‐calix[4]arene (Calix[4]arene‐R14) supramolecular recognition polymeric composite, (Calix[4]+Oct)/SiO₂‐P, was synthesized. It was performed by impregnating and immobilizing Calix[4]arene‐R14 and n‐octanol into the pores of the macroporous SiO₂‐P particles support. n‐Octanol was used to modify Calix[4]arene‐R14 through hydrogen bonding. The effect of eight typical fission products contained in highly active liquid waste (HLW) on the adsorption of Cs(I), one of the heat generators, was investigated at 298 K by examining the effect of contact time and the HNO₃ concentration in a range of 0.3–7.0 M. (Calix[4]+Oct)/SiO₂‐P showed excellent adsorption ability and high selectivity for Cs(I) at 4.0 M HNO₃ over the tested elements. The partitioning of Cs(I) from a simulated HLW was operated by (Calix[4]+Oct)/SiO₂‐P packed column. Cs(I) was able to be effectively eluted by water and separated from the tested metals. It is demonstrated that (Calix[4]+Oct)/SiO₂‐P is promising to apply in chromatographic separation of Cs(I) from HLW. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Photosensitized hydrogen evolution from water using a single-walled carbon nanotube/fullerodendron/SiO2 coaxial nanohybrid

A coaxial nanohybrid consisting of a single-walled carbon nanotube (SWCNT), fullerodendron, and SiO(2) shows high-efficiency light-driven hydrogen evolution from water. Upon visible light irradiation, SWCNT/fullerodendron/SiO(2) coaxial nanohybrid shows hydrogen evolution activity in the presence of methyl viologen (MV(2+)), benzyldihydronicotinamide (BNAH), and a colloidal polyvinyl alcohol(PVA)-Pt.