Themed collection Supramolecular Chemistry

Showcasing a collection of cutting edge contributions by international leaders in the field of supramolecular chemistry to mark the International Year of Chemistry 2011.

From oligomers to protein-sized architectures, foldamers introduce new tools and concepts to develop bioactive substances, synthetic receptors and materials.

Supramolecular gels are fascinating soft materials with a growing list of hi-tech, niche applications. This article reviews the progress in their chemistry over the past decade.

This highlight article looks back at progress in anion receptor chemistry in the last decade and ahead to developments in sensing, catalysis and transport that are on the horizon.

By employing a click reaction, a novel method was developed for the sensitive detection of inorganic azides at as low as 21 ppb.

On desolvation, the mesoporous (3,24)-connected framework [Cu₃(L)(H₂O)₃]·(solv) (NOTT-119) shows remarkably high BET surface area (4118(200) m² g⁻¹), and pore volume (2.35 cm³ g⁻¹).

We have shown a simple, modular and efficient approach to generate a number of three-dimensional prismatic DNA nanostructures at room temperature.

Metal–organic frameworks incorporating binuclear [Sc₂(μ₂-OH)(O₂CR)₄] building blocks have been synthesised and characterised showing high BET surface areas and total H₂ uptake.

The time- and wavelength-dependent fluorescence response of a single optical sensor can distinguish between different saccharides.

Hydraphiles form ion channels in membranes that disrupt ion homeostasis, a property that is applied here for tumor ablation therapy.

As(lp)⋯π interactions have been shown to be important in providing stability to crystal structures in 20 examples.

Anion recognition of a chiral Pybox·Ca²⁺ foldamer.

An Ag(I) anilino-bis(pyrazolyl)-triazine luminophore shows multiple bright and tunable emissions influenced by a variety of supramolecular interactions.

Control over the gel/sol state of a glycoluril-organogel can be accomplished by irradiation and formation of a capsular supramolecular assembly.

Functionalized lipid domains and protein–membrane assemblies in surface bound giant vesicles were oriented via application of an electric field to introduce asymmetry in supramolecular structure and chemistry.

The interactions between Tb(III) and Eu(III) (Ln) and the chiral pyridyl based trpytophan ligands (L) 1 and 2 in CH₃CN gave rise to the formation of L₂2Tb and L₂2Eu as the main self-assembly products and not the expected L₃3Ln systems.

Three squaraine [2]catenanes are synthesized and found to have bright, deep-red fluorescence, high chemical stability, and unusual molecular dynamics.

The introduction of a disulfide functionalized tetraphosphonate cavitand on Au nanoparticles promotes the reversible assembly of a network upon addition of a suitable polymeric ditopic guest.

Chiral anti-isomer M₃L₂ metallo-cryptophanes are with tripodal cyclotriguaiacylene-derivatives, with different ligands yielding either single cages or a triply interlocking [2]catenane.

An anthracene-containing DNA probe can identify all four DNA bases at a single site in a target strand as well as the epigenetic modification C/5-MeC through different fluorescent responses upon duplex formation.

The conjugation of arginine residues at the ends of a metallo-supramolecular triple-helical cylinder enables absolute control over the helicity of the cylinder core, and significantly enhances the DNA binding and activity.

The hydrogen bond donor/acceptor reorientation in phenols is shown to happen on a single oxygen site, resulting in low barriers for reorientation.

Supramolecular synthons of the type C–H⋯π(chelate) are established in the structures of transition metal and main group element 1,1-dithiolates.

Cr₆-horseshoes act as fluoride donors towards the lanthanides, making Ln, Ln₂ and Ln₄ complexes.

We have demonstrated that an assembled viral protein cage, comprising an organic core–shell structure, can be used as a template for the size constrained synthesis of Fe₂O₃.

1,3-Alternate calix[4]arene with para-phenylene spacers connecting nitroxide monoradicals and high-spin (S = 1) diradicals provides tetraradical and octaradical scaffolds that possess conformations with slow electron spin relaxation rates (1/T₁).

Guest induced shape change of the cucurbit[8]uril cavity is likely rate limiting in the supramolecular photocatalytic cycle for CB8 mediated photodimerization of 6-methylcoumarin.

Applied potential across a carrier-containing supported liquid membrane significantly enhances both flux and selectivity.

Polyazamacrocycles belonging to the so-called “scorpiand” family display an interesting behaviour as MnSOD mimics. Crystal structures, speciation, electrochemical and in vitro SOD studies are reported.

The in vivo application in zebrafish of modular “click” fluorescent sensors with high selectivity for zinc is described.

Synthetic carbohydrate modification at sites of natural substitutions teamed up with multivalency is a route to protect cells from harmful lectins.

Structural rigidity is verified as a pre-organizational factor that acts with the macrocyclic effect such that synthesis helps in paying the cost of bringing together electropositive CH donors ready for H-bonding with chloride.

Self-assembly of oppositely charged porphyrins gives morphologically and crystallographically related structures regardless of the metals (Sn or Zn) in the porphyrins.

Both S1 and T1 energy transfer rates (porphyrin → cluster) increase from mono- to di- to tetracarboxylate[tetraphenyl-(zinc)porphyrin] adducts with [Pd₃(dppm)₃(CO)]²⁺ clusters.

A supramolecular drug delivery system has been developed via the self-assembly of a drug-based supramolecular amphiphile constructed by host–guest interaction.

The hydrogelation properties of a proline-functionalised calix[4]arene emerge as a result of extended helical structures formed via supramolecular interactions.

Highly efficient photoswitching tetranuclear rhenium(I) tricarbonyl diimine complexes with a stilbene-like bridging ligand are reported. Directly populating excited states localized on the bridging ligand results in effective photoisomerization.

Expanding a bis-β-diketone ligand by extending the bridge between the coordination domains from phenylene to biphenylene leads to a near 5-fold increase in the central cavity, one THF molecule occupies the small cavity while the expanded analogue holds four.

Chirality can be transferred to preformed fractal aggregates of a Cu(II) metalloporphyrin, whose CD spectrum is initially silent, through the interaction with polyglutamic acid molecules acting as the source of chiral information.

A novel approach for improving a supramolecular solar cell by redox tuning through fluoride anion binding to the redox active host is demonstrated.

A [2]rotaxane flip-switch can exist in either of two distinct co-conformers. Fine-tuning the charge transfer chromophores in a series of flip-switches yielded a unique optical signal (purple colour) for one of the interactions allowing for facile determination of the position of the flip-switch equilibrium and the distribution of co-conformers.

Mild Lewis acids enhance thermal conversion of vinylheptafulvene (VHF) to dihydroazulene (DHA), while stronger Lewis acids promote ring-opening of DHA.

Chain end complexation of a functional PNIPAM by a cucurbit[8]uril-viologen complex causes a shift in its lower critical solution temperature (LCST) by over 5 °C.

Combined use of supramolecular and coordination chemistry results in a new family of uranyl-bearing hybrid materials.

Sodium and barium metal cation templation has been used to construct a pyridine N-oxide containing [2]rotaxane which undergoes a pirouetting molecular motion upon addition and removal of these cations

Gas phase calculations and experiments agree that binding strengths depend strongly on the proximity of the binding sites for two ions.

A gemini guest induces the self-assembly of a homodimeric capsule when interacting with a calixarene-based host in neutral aqueous solution.

Chiral diporphyrin receptor 1 enabled the naked-eye detection of an aromatic explosive as well as chiral discrimination in NMR.

The use of “double-headed” phenolic oximes produces a trigonal antiprismatic [Fe^III₃]₂ cluster with an “internal cavity” filled with an additional Fe³⁺ ion.

A dicopper(I) complex is incorporated into extended architectures through reversible carboxylate templation under pH control forming [2+2] and [3+3] metallomacrocycles.

Two enantiotropic polymorphs of a dumbbell shaped molecule possess similar packing arrangements but one of the polymorphs shows anomalously anisotropic thermal expansion while the other does not.

Cyclo[2]benzimidazole is a new host for anions that turns on its luminescence up to 150 fold upon binding.

A new one-pot self-assembly process is used to create a three-dimensional extended, metal–organic rotaxane framework (MORF) that incorporates encircled “struts”.

Scrambling experiments suggest that oligomers cross-linked by four imine bonds are kinetically trapped, limiting the synthesis of covalent ladders with five or more rungs.

Two new crystalline polymorphs and an amorphous phase of curcumin, the most active chemical ingredient of turmeric, are reported. The new Form 2 has higher solubility and dissolution rate compared to the known commercial form.

The morphology of the aggregates formed from the self-assembly of aryl triazole amphiphiles is disrupted upon the binding of a bromide anion due to the conformational changes experienced by these receptors.

The relaxivity of the gadolinium compound is regulated by the presence of adenosine.

Symmetric oligothiophene derivatives containing hydrogenbonding groups form self-supporting organogels with conductive supramolecular networks of 1D nanostructures.

A functionalised fullerene incorporating a double-chelating group binds transition metal cations and acts as an effective vehicle for delivering metals into carbon nanotubes.

We have shown that the addition of imine substituents to a tripodal pyrrole results in a versatile platform for both metallation and supramolecular interactions.

The extent of methylation of a guest's ammonium nitrogen controls the predominant binding site with the cucurbit[8]uril host.

Adding methyl groups to hexaphenylbenzene weakens key C–H⋯π interactions, thereby decreasing enthalpies of sublimation and showing that materials with weak cohesion can be made by identifying and obstructing key interactions.

Recrystallisation of Ag[L¹] (HL¹ = 3{5}-[pyrid-2-yl]-5{3}-tert-butylpyrazole) in the presence of exogenous anions leads to two polymorphs of [Ag₃(μ-Br)(μ-L¹)₂], and to [Ag₁₀(μ-L¹)₈]Cl₂ (shown). In contrast, Ag[L²] (HL² = 3{5}-[isoquinol-1-yl]-5{3}-tert-butyl-pyrazole) crystallises as a cyclic tetrameric molecule.

A reactive supramolecular hydrogel reacts with hydrophobic aldehydes causing disassembly of the fibrillar network and release of molecules entrapped within.

The pH-responsive cryptophane spontaneously assembles in water from two cyclotribenzylenes and three linker units in the presence of a suitable guest.

The porous polyhedral complex [Cu₄L(H₂O)₄]solv (NOTT-140), incorporating an octacarboxylate isophthalate linker, shows scu topology comprising octahedral and cuboctahedral cages; desolvated NOTT-140a shows impressive storage capacities for CH₄, CO₂ and H₂.

Detection of anions with cation sensors: the combination of a fluorescent indicator and a calcium salt can be used to sense low millimolar concentrations of fluoride ions in water and in complex samples such as dental health products.

A new class of phosphonate monoester ligands is used to make a porous MOF with a structure that is supported by weak van der Waals interactions between alkyl chains.

The structural landscape for the 4,4′-bipyridine–4-hydroxybenzoic acid system consists of two polymorphs and two pseudopolymorphs.

The ratio of helical diastereomers for Ni–salen based metallofoldamers varies significantly depending upon the nature of the chiral diamine subunit.