High affinity crown ether complexes in water: thermodynamic analysis, evidence of crystallography and binding of NAD+

Enhanced molecular binding affinity toward aromatic dications by anthracene-derived crown ethers in water

The pursuit of high molecular binding affinity using conventional crown ethers in water remains a challenging task in the field of supramolecular chemistry and may hold great promise in the creation of advanced biocompatible nanoconstructs. In this work, the molecular binding strength toward a series of structurally relevant cationic guests has been greatly enhanced by tetrasulfonated 1,5-dianthracenyl-42-crown-10 and as investigated by means of ¹H NMR, UV-vis, and fluorescence spectroscopy, the host-guest association constants can reach up to 10⁸ M^-1 order of magnitude in aqueous solution. X-ray crystal diffraction analysis further demonstrates that the aromatic dication can be tightly encapsulated in the ring of anthracene-derived crown ether via multiple π-stacking and electrostatic interactions. Meanwhile, the obtained association constants are remarkably higher than the ones in the cases of the known benzene- and naphthalene-derived sulfonated crown ethers, substantiating that the appropriate extension of π-conjugation in the molecular skeleton of crown ether is a feasible method in attaining a highly affiliative host-guest complex. Taken together, our results indicate that the anthracene-based sulfonated crown ether can be developed as a new family of water-soluble macrocyclic receptors in the fabrication of functional nanoarchitectures.

Temperature-responsive supramolecular hydrogels

Hydrogels comprise a class of soft materials which are extremely useful in a number of contexts, for example as matrix-mimetic biomaterials for applications in regenerative medicine and drug delivery. One particular subclass of hydrogels consists of materials prepared through non-covalent physical crosslinking afforded by supramolecular recognition motifs. The dynamic, reversible, and equilibrium-governed features of these molecular-scale motifs often transcend length-scales to endow the resulting hydrogels with these same properties on the bulk scale. In efforts to engineer hydrogels of all types with more precise or application-specific uses, inclusion of stimuli-responsive sol-gel transformations has been broadly explored. In the context of biomedical uses, temperature is an interesting stimulus which has been the focus of numerous hydrogel designs, supramolecular or otherwise. Most supramolecular motifs are inherently temperature-sensitive, with elevated temperatures commonly disfavoring motif formation and/or accelerating its dissociation. In addition, supramolecular motifs have also been incorporated for physical crosslinking in conjunction with polymeric or macromeric building blocks which themselves exhibit temperature-responsive changes to their properties. Through molecular-scale engineering of supramolecular recognition, and selection of a particular motif or polymeric/macromeric backbone, it is thus possible to devise a number of supramolecular hydrogel materials to empower a variety of future biomedical applications.

The recent progress of synergistic supramolecular polymers: preparation, properties and applications

Interactions for forming supramolecular polymers were reviewed together with their unique properties and applications with detailed examples.

Programming permanent and transient molecular protection via mechanical stoppering

Chemical protection is an essential tool in synthetic chemistry, which involves blocking reactive sites on a molecule through covalent bonds. Physical approaches, such as encapsulation and host-mediated protection, have emerged as interesting alternatives that use steric bulk to inhibit reactivity. Here, we report the protection of a redox-active viologen through its incorporation into mechanically interlocked molecules (MIMs), namely hetero[4]rotaxanes. The viologen was confined inside a host cavity and flanked by two mechanical stoppers, which allowed for permanent and transient protection. Deprotection occurred on-demand via an unstoppering process, triggered by a proton transfer, polarity effect, or a thermal stimulus. We anticipate that permanent and transient mechanical stoppering could be incorporated into devices to function as molecular probes, transport/delivery systems, or stimuli-controlled degradable materials.

Molecular Receptors for Recognition and Sensing of Nucleotides

Nucleotides are constituents of nucleic acids and they have a variety of functions in cellular metabolism. Synthetic receptors and sensors are required to reveal the role of nucleotides in living organisms and mechanisms of signal transduction events. In recent years, a large number of nucleotide-selective synthetic receptors have been devised, which utilize different molecular designs and sensing mechanisms. This Minireview presents recent progress in the design of synthetic molecular receptors for selective recognition of nucleotides in aqueous solution. The binding properties of receptors and the origins of their selectivity for a particular nucleotide are discussed.

Self-assembly of two-dimensional structures in water from rigid and curved amphiphiles with a low molecular weight

Rigid and curved amphiphiles with very low molecular weight (MW < 500 Da) self-assemble into two-dimensional structures in water.

Energetics and the molecular structure of an ion-paired supramolecular system in water

The forces that bind the components of a host-guest complex to generate a stable supramolecular system are noncovalent interactions. The enthalpy of this association, Δ_asH°, usually measured using calorimetry, quantifies the magnitude of such interactions and is directly related to the stability of the supramolecular complex formed. Using Calvet calorimetry to determine the enthalpies of solution and reaction in water, the enthalpy of association was derived for a supramolecular system formed by the anionic macrocycle anti-disulfodibenzo[24]crown-8 ([DSDB24C8]^2-) and the dicationic guest paraquat [PQT]²⁺. The calorimetric results show an exothermic association process, which indicates the generation of strong interactions between the components of the ion pair. This is consistent with the formation of a stable supramolecular complex [PQT][DSDB24C8], whose spatial arrangement in aqueous solution is proposed based on spectroscopic analysis.

Light-controlled reversible formation and dissociation of nanorods via interconversion of pseudorotaxanes

Nanorod-like supramolecular aggregates are fabricated by the self-assembly of the amphiphilic [2]pseudorotaxane, which can be dissociated and rebuilt by the alternating UV/vis irradiation.

Exocyclic self-assembly behavior of carboxylic acid and lariat ether macrocyclic hosts: regulation by pendent arm

An exocyclic supramolecular building block through O–H⋯N hydrogen bonding interaction for the assembly of di-sidearm dibenzo-diazacrown ethers bearing a flexibility sidearm with PTA acid.

A pH-responsive amphiphilic supramolecular graft copolymer constructed by crown ether based molecular recognition

Based on the bis(m-phenylene)-32-crown-10/paraquat molecular recognition motif in water, we have successfully prepared an amphiphilic supramolecular graft copolymer by the combination of modified hydrophilic poly(ethylene oxide) and hydrophobic polystyrene. It could self-assemble into pH-responsive bilayer vesicles in water.

A Cu2+ specific metallohydrogel: preparation, multi-responsiveness and pillar[5]arene-induced morphology transformation

A Cu²⁺ specific metallohydrogel was constructed from a terpyridine-based low molecular weight ligand. The metallohydrogel showed multi-responsiveness and its morphology could be transformed by pillararene-based host–guest interaction.

Reversible formation of supramolecular polymer networks via orthogonal pillar[10]arene-based host–guest interactions and metal ion coordinations

Reversible supramolecular polymer networks were constructed by orthogonal pillar[10]arene-based host–guest molecular recognition, terpyridine–Zn²⁺, and carbene–Ag⁺ coordinations.

Synthesis of a novel water-soluble cylindrical macrotricyclic host and its complexation with N-methylquinolinium and N-methylisoquinolinium salts: formation of 1 : 2 complexes in water

A water-soluble cylindrical macrotricyclic host could form 1 : 2 complexes with N-methylquinolinium or N-methylisoquinolinium salts in water solution and in the solid state.