Folding-Promoted TBACl-Mediated Chemo- and Regioselective Demethylations of Methoxybenzene-Based Macrocyclic Pentamers

Macrocyclic host molecules with aromatic building blocks: the state of the art and progress

Macrocyclic host molecules play the central role in host-guest chemistry and supramolecular chemistry. The highly structural symmetry of macrocyclic host molecules can meet people's pursuit of aesthetics in molecular design, and generally means a balance of design, synthesis, properties and applications. For macrocyclic host molecules with highly symmetrical structures, building blocks, which could be described as repeat units as well, are the most fundamental elements for molecular design. The structural features and recognition ability of macrocyclic host molecules are determined by the building blocks and their connection patterns. Using different building blocks, different macrocyclic host molecules could be designed and synthesized. With decades of developments of host-guest chemistry and supramolecular chemistry, diverse macrocyclic host molecules with different building blocks have been designed and synthesized. Aromatic building blocks are a big family among the various building blocks used in constructing macrocyclic host molecules. In this feature article, the recent developments of macrocyclic host molecules with aromatic building blocks were summarized and discussed.

Macrocyclic pentamers functionalised around their periphery as potential building blocks

The elaboration of a five-fold symmetric macrocyclic aromatic pentamer bearing peripheral benzyloxy and hydroxyl groups is described. These could be used to explore further functionalisation for use as pentagonal building blocks. The internal fluorine-substituted macrocycle has been prepared via a one-pot procedure which is an improvement on the stepwise chain growth approach reported in the literature.

The elaboration of a five-fold symmetric macrocyclic aromatic pentamer bearing peripheral benzyloxy and hydroxyl groups is described. The macrocycle bearing internal fluorine substituents has been prepared via a one-pot procedure.

Campestarenes: new building blocks with 5-fold symmetry

New campestarene derivatives bear functional groups designed to facilitate the formation of supramolecular assemblies of these 5-fold symmetric building blocks.

Surprisingly High Selectivity and High Affinity in Mercury Recognition by H-Bonded Cavity-Containing Aromatic Foldarands

In the absence of macrocyclic ring constraints, few synthetic systems, possessing a mostly solvent-independent well-folded conformation that is predisposed for highly selective and high affinity recognition of metal ions, have been demonstrated. We report here such a unique class of conformationally robust modularly tunable folding molecules termed foldarands that can recognize Hg²⁺ ions surprisingly well over 22 other metal ions. Despite the lack of sulfur atoms and having only oxygen-donor atoms in its structure, the best foldarand molecule, i.e., tetramer 4, exhibits a selectivity factor of at least 19 in differentiating the most tightly bound Hg²⁺ ion from all other metal ions, and a binding capacity that is ≥18 times that of thio-crown ethers. These two noteworthy binding characters make possible low level removal of Hg²⁺ ions. With a [4]:[Hg²⁺] molar ratio of 5:1 and a single biphasic solvent extraction, the concentration of Hg²⁺ ions could be reduced drastically by 98% (from 200 to 4 ppb) in pure water. 4 could also effect a highly efficient reduction in mercury content by 98% (from 500 to 10 ppb) in artificial groundwater via multiple successive extractions with an overall consumption of 4 being 9:1 in terms of [4]:[Hg²⁺] molar ratio.

Computation-guided improved one-pot synthesis of macrocyclic cation-binding aromatic pyridone pentamers

By using polar DMF to relax the H-bonded rigid backbone and to lower the energetic penalty associated with the sterically-crowded environment, the yields for BOP-mediated one-pot synthesis of pentameric macrocycles can be improved from 10-25% as obtained in CH₂Cl₂ to 13-47% when 15% DMF in CH₂Cl₂ was used as the reaction medium.

Tuning cation-binding selectivity and capacity via side chain-dependent molecular packing in the solid state

Cavity-containing macrocycles assemble, via side chain-dependent molecular packing, into various nanostructures able to bind cations in varying selectivities and capacities.

The Dynamics, energetics and selectivity of water chain-containing aquapores created by the self-assembly of aquafoldamer molecules

Self-assembled hollow tubular aquapores were found to be stable, very dynamic yet highly selective toward recognition of water molecules.

Size-dependent patterned recognition and extraction of metal ions by a macrocyclic aromatic pyridone pentamer

A macrocyclic aromatic pyridine pentamer was found to exhibit patterned recognition of metal ions and efficiently extract larger ions, such as Cs⁺, Ba²⁺, Tl⁺, Au⁺, K⁺ and Rb⁺ preferentially over the other 18 smaller metal ions from the aqueous phase into the chloroform layer.

A conformationally switchable fluorescent oligophenol foldamer for selective sensing of copper(ii) ions

A stimuli-responsive hexameric oligophenol host undergoes amine-induced co-operative folding and fluorescence quenching, enabling easy classification of the bound metal ion guests as well as selective sensing of Cu²⁺ ions.