The ability of a family of M4, M8 and M12 coordination cages to effect catalytic oxidative degradation of a family of xanthene-based dyes using peroxymonosulfate (PMS) has been investigated in water. The M12 cages bind one dye molecule inside the central cavity; the M8 cages bind multiple anionic dye molecules around the external cage surface; the smallest M4 cages do not interact strongly with the dyes. Three separate sets of experiments showed that octanuclear Co8 was the most effective catalyst due to a combination of (i) its ability to bind multiple dye molecules around its surface in solution, and (ii) the Co(II)/Co(III) redox couple which activates the PMS anion by reducing it to the reactive species SO4˙- close to the cage-bound substrates. Control experiments showed that replacing Co(II) by Fe(II), Ni(II) or Zn(II) in isostructural M8 cages removed catalytic activity, which specifically requires the Co(II)/Co(III) couple; and the effectiveness of the catalysis is guest-dependent according to parameters such as charge, hydrophobicity and inductive effect of substituents on the xanthene core. Overall the Co8 cage fulfils three functions of (i) binding the guest, (ii) activating the PMS using the Co(II)/Co(III) couple, and (iii) accumulating the SO4˙- anions around the cationic cage surface close to bound guests.

The crystalline sponge method has proven invaluable in the preparation and analysis of supramolecular host/guest complexes if the host can be obtained in a suitable crystalline form, allowing the analysis of guest binding modes inside host cavities which can inform other studies into processes such as catalysis. Here, we report the structures of a set of ten host/guest complexes using an octanuclear coordination cage host with a range of small-molecule neutral organic guests including four aromatic aldehydes and ketones, three cyclic lactams, and three epoxides. In all cases, the cavity-bound guests are anchored by a collection of CH•••O hydrogen-bonding interactions between an O atom on the guest and a convergent set of CH protons at a pocket on the cage interior surface. Depending on guest size and the presence of solvent molecules as additional guests, there may be one or two cavity-bound guests, with small aromatic guests forming π-stacked pairs. Some guests (the lactams) participate in additional NH•••F H-bonding interactions with surface-bound fluoroborate anions, which indicate the type of anion/guest interactions thought to be responsible for solution-phase catalytic reactions of bound guests.

This review article summarises work from the author's group on catalysis using coordination cages over the (approximate) period 2018-2024. Recent insights discussed include (i) the general mechanism of catalysis, which involves co-location of reaction partners using orthogonal interactions involving the cage cavity (neutral hydrophobic substrates) and the surface anion-based reaction partners; (ii) the role of the cage exterior surface in facilitating catalysis in some cases; (iii) quantitative analysis of anion-binding to the cage surface, as a complement to measurement of binding constants of neutral guests inside the cavity; (iv) a new type of redox-based catalysis using reactive oxygen species, which are generated by reaction of oxidants such as H2O2 and HSO5- with Co(ii)/Co(iii) redox couples in the cage superstructure. Collectively the results discussed provide signficant new possibilities for further exploration of catalysis using supramolecular assemblies. Recent work on catalysed reactions using coordination cage hosts, including new mechanistic insights and reactions types, is reviewed.

The ability of an octanuclear cubic coordination cage to catalyse a nucleophilic aromatic substitution reaction on a cavity-bound guest was studied with 2,4-dinitrofluorobenzene (DNFB) as the guest/substrate. It was found that DNFB undergoes a catalysed reaction with hydroxide ions within the cavity of the cubic cage (in aqueous buffer solution, pH 8.6). The rate enhancement of kcat/kuncat was determined to be 22, with cavity binding of the guest being required for catalysis to occur. The product, 2,4-dinitrophenolate (DNP), remained bound within the cavity due to electrostatic stabilisation and exerts two apparently contradictory effects: it initially auto-catalyses the reaction when present at low concentrations, but at higher concentrations inhibits catalysis when a pair of DNP guests block the cavity. When encapsulated, the UV/Vis absorption spectrum of DNP is red-shifted when compared to the spectrum of free DNP in aqueous solution. Further investigations using other aromatic guests determined that a similar red-shift on cavity binding also occurred for 4-nitrophenolate (4NP) at pH 8.6. The red-shift was used to determine the stoichiometry of guest binding of DNP and 4NP within the cage cavity, which was confirmed by structural analysis with X-ray crystallography; and was also used to perform catalytic kinetic studies in the solution-state. An octanuclear cubic coordination cage catalyses the nucleophilic aromatic substitution reaction of a cavity-bound guest, 2,4-dinitrofluorobenzene (DNFB). The product 2,4-dinitrophenolate (DNP) remained bound within the cavity, providing both autocatalysis in the early stages and inhibition in the late stages of the reaction. A red-shift in the UV/Vis spectrum revealed 1 : 2 host to guest binding, this was confirmed by X-ray crystallography analysis. image

The use of organophosphorus chemical warfare agents still remains an ongoing global threat. Here we investigate the binding of small-molecule organic guests including phosphate esters, sulfonate esters, carbonate esters and a sulfite ester - some of which act as simulants for organophosphorus chemical warfare agents - in the cavity of a water-soluble coordination cage. For several of these guest species, binding constants in the range 102 to 103 M-1 were determined in water/DMSO (98 : 2 v/v) solution, through a combination of fluorescence and 1H NMR spectroscopy, and subsequent fitting of titration data to a 1 : 1 binding isotherm model. For three cage/guest complexes crystallographic structure determinations were possible: in two cases (with guests phenyl methanesulfonate and phenyl propyl carbonate) the guest lies inside the cavity, forming a range of CH & ctdot;O hydrogen-bonding interactions with the cage interior surface involving CH groups on the cationic cage surface that act as H-bond donors and O atoms on the guests that act as H-bond acceptors. In a third case, with the guest 4-nitrophenyl-methanesulfonate, the guest lies in the spaces outside a cage cavity between cages and forms weak CH & ctdot;O interactions with the cage exterior surface: the cavity is occupied by a network of H-bonded water molecules, though this guest does show cavity binding in solution. For the isomeric guests 4-nitrophenyl-methanesulfonate and 4-nitrophenyl methyl sulfite, hydrolysis in water/DMSO (98 : 2 v/v) could be monitored colorimetrically via appearance of the 4-nitrophenolate anion; both showed accelerated hydrolysis rates in the presence of the host cage with second-order rate constants for the catalysed reactions in the range 10-3 to 10-2 M-1 s-1 at pH 9. The typical rate dependence on external pH and the increased reaction rates when chloride ions are present (which can bind inside the cavity and displace other cavity-bound guests) imply that the catalysed reaction actually occurs at the external surface of the cage rather than inside the cavity. Simulants of organophosphate chemical warfare agents can bind in the cavity of an octanuclear coordination cage (the figure shows a carbonate-based guest), resulting in some cases in catalysed hydrolytic decomposition.

Correction for ‘Cu(i) diimine complexes as immobilised antibacterial photosensitisers operating in water under visible light’ by Martin V. Appleby et al., Mater. Adv., 2020, 1, 3417–3427, https://doi.org/10.1039/D0MA00642D.

Inclusion of photoswitchable azobenzene units as spacers into ditopic bridging ligands L-m and L-p, containing two chelating pyrazolyl-pyridine termini, allows formation of metal complex assemblies with Co(II) that undergo a range of light-induced structural transformations. One notable result is the light-induced conversion of a Co-2(L-p)(3) dinuclear triple helicate (based on the E ligand isomer) to a C-3-symmetric Co-4(L-p)(6) assembly, assumed to be an edge-bridged tetrahedral cage, based on the Z ligand isomer. Another is the preparation of a series of Co-4(L-m)(6) complexes, of which Co-4(E-L-m)(6) was crystallographically characterised and consists of a pair of Co-2(L-m)(2) double helicates connected by an additional two bridging ligands which span the pair of helicate units, giving a cyclic Co-4 array in which one and then two bridging ligands alternate around the periphery. A set of Co-4(L-m)(6) complexes could be prepared containing different ratios of Z : E ligand isomers (0 : 6, 2 : 4, 4 : 2 and 6 : 0) of which Co-4(Z-L-m)(2)(E-L-m)(4) was particularly stable and dominated the speciation behaviour, either during light-induced switching of the ligand geometry in pre-formed complexes, or when ligand isomers were combined in different proportions during the preparation. These examples of (i) interconversion between Co2L3 (helicate) and (ii) Co4L6 (cage) assemblies with L-p, and the interconversion between a series of Co4L6 assemblies Co-4(Z-L-m)(n)(E-L-m)(6-n) with L-m, constitute significant advances in the field of photoswitchable supramolecular assemblies.

In this study, we report the synthesis and characterization of some heteroleptic Cr(III) complexes of the form [Cr(Phen)2L](OTf)3, where Phen = 1,10-phenanthroline and L is either 2,2'-bipyridine (bpy) or its derivatives, such as 4,4'-dimethyl-2,2'-bipyridine (4,4'-DMB), 4,4'-dimethoxy-2,2'-bipyridine (4,4'-DMOB), 4,4'-ditert-butyl-2,2'-bipyridine (4,4'-dtbpy), 5,5'-dimethyl-2,2'-bipyridine (5,5'-DMB), 4,4'-dimethoxycarbonyl-2,2'-bipyridine (4,4'-dmcbpy) or 1,10-phenanthroline derivatives, such as 5-methyl-1,10-phenanthroline (5-Me-Phen) and 4,7-dimethyl-1,10-phenanthroline (4,7-DMP). Heteroleptic complexes were prepared in two stages via the intermediate [Cr(Phen)2(CF3SO3)2](CF3SO3) and five examples have been crystallographically characterized. Steady-state absorption and luminescence emission characteristics of these complexes were measured in 1 M HCl solutions. The luminescence quantum yield of these complexes was found to be the lowest for [Cr(Phen)2(4,4'-dmcbpy)](OTf)3 and the highest for [Cr(Phen)2(4,4'-DMB)](OTf)3 with values of 0.31 × 10-2 and 1.48 × 10-2, respectively. The calculated excited state energy, E0-0, was found to vary within the narrow range of 163.1-165.0 kJ mol-1 across the series. Transient absorption spectra in degassed, air-equilibrated, and oxygen-saturated 1 M HCl aqueous solutions were also measured at different time decays and demonstrated no significant differences, indicating the absence of any ion-separated species in the excited state. Excited-state decay traces at the wavelength of maximum absorption were used to calculate oxygen quenching rate constants, kq, which were found to be in the range 3.26-5.27 × 107 M-1 s-1. Singlet oxygen luminescence photosensitized by these complexes was observed in D2O, and its luminescence intensity at 1270 nm was used for the determination of singlet oxygen quantum yields for these complexes, which were in the range of 0.20-0.44, while the fraction of the excited 2E state quenched by oxygen was in the range of 0.22-0.68, and the efficiency of singlet oxygen production was in the range of 0.44-0.90. The mechanism by which the excited 2E state is quenched by oxygen is explained by a spin statistical model that predicts the balance between charge transfer and noncharge transfer deactivation pathways, which was represented by the parameter pCT that was found to vary from 0.35 to 0.68 for this series of Cr(III) complexes.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The multivalent presentation of glycans leads to enhanced binding avidity to lectins due to the cluster glycoside effect. Most materials used as scaffolds for multivalent glycan arrays, such as polymers or nanoparticles, have intrinsic dispersity: meaning that in any sample, a range of valencies are presented and it is not possible to determine which fraction(s) are responsible for binding. The intrinsic dispersity of many multivalent glycan scaffolds also limits their reproducibility and predictability. Here we make use of the structurally programmable nature of self-assembled metal coordination cages, with polyhedral metal-ion cores supporting ligand arrays of predictable sizes, to assemble a 16-membered library of perfectly monodisperse glycoclusters displaying valencies from 2 to 24 through a careful choice of ligand/metal combinations. Mono- and trisaccharides are introduced into these clusters, showing that the synthetic route is tolerant of biologically relevant glycans, including sialic acids. The cluster series demonstrates increased binding to a range of lectins as the number of glycans increases. This strategy offers an alternative to current glycomaterials for control of the valency of three-dimensional (3-D) glycan arrays, and may find application across sensing, imaging, and basic biology.

The host-guest chemistry of O,O '-diisopropyl fluorophosphate (DFP), a phosphonofluoridate G-series chemical warfare agent simulant, was investigated in the presence of a number of octanuclear cubic coordination cage hosts. The aim was to demonstrate cage-catalysed hydrolysis of DFP at near neutral pH: however, two octanuclear coordination cages, H-PEG (containing water-solubilising PEG groups) and H-W (containing water-solubilising hydroxymethyl groups), were actually found to increase the lifetime of DFP in aqueous buffer solution (pH 8.7). Crystallographic analysis of DFP with a structurally related host cage revealed that DFP binds to windows in the cage surface, not in the internal cavity. The phosphorus-fluorine bond is directed into the cavity rather than towards the external environment, with the cage/DFP association protecting DFP from hydrolysis. Initial studies with the chemical warfare agent (CWA) sarin (GB) with H-PEG cage in a buffered solution also showed a drastically reduced rate of hydrolysis for sarin when bound in the host cage. The ability of these cages to inhibit hydrolysis of these P-F bond containing organophosphorus guests, by encapsulation, may have applications in forensic sample preservation and analysis.

A molecule of luminol bound as guest inside a Co8 coordination cage host undergoes oxidation by H2O2 to generate chemiluminescence by a process in which the Co(II) ions in the cage superstructure activate the H2O2: accordingly the cage not only co-locates the reactants but also acts as a redox partner in the catalysis. The luminescence from oxidation of the cavity-bound luminol can transfer its excitation energy to surface-bound fluorescein molecules in an unusual example of Chemiluminescence Resonance Energy Transfer (CRET).

A Co 12 coordination cage performs catalytic oxidation of bound fluorescein by a mechanism involving redox activation of HSO 5 − using metal ions in the superstructure.

We demonstrate how different modes of guest binding with a Co8L12 cubic cage can be determined using ESI-MS. High stoichiometry guest binding was observed, with the guests preferentially binding externally, but internal guest inclusion was also seen at higher guest loading.

The value of postgraduates teaching in undergraduate chemistry laboratories has been a subject of interest at universities in the UK, Europe, USA, Australia, and New Zealand. The role of the teaching assistant (TA) is already well-established in many laboratories in the USA, and such roles have been increasing in popularity in the UK. Postgraduate (PG) demonstrators are however commonplace in UK higher education institutions (HEIs). Despite this, reports of formalized postgraduate programs involving a significant teaching component in the UK are rare. Here, we report on the first example of a Chemistry UK Graduate Teaching Assistant (GTA) program that started at The University of Sheffield in 2010. To the best of our knowledge, this is the first program reported of its type in the UK. For over 10 years, this program has resulted in a cohort of 24 GTAs who work alongside PG demonstrators in the laboratory and graduate with not only a chemistry Ph.D. but also enhanced teaching experience and professional development. Students in the GTA program have taken on a number of valuable roles, which are described herein. Positive outcomes include development of employability skills, contribution to the consistency of teaching, and knowledge transfer through involvement in training other PG demonstrators. The standard and consistency of the efforts of the GTA cohort have been demonstrated by a significant number receiving recognition for their teaching by gaining Fellowship of the Higher Education Academy (FHEA) accreditation, which is often associated with academic staff who are involved in teaching.

In this work we compare and contrast the hydrolysis of two different aromatic esters using an octanuclear cubic Co8 coordination cage host as the catalyst. Diacetyl fluorescein (DAF) is too large to bind inside the cage cavity, but in aqueous solution it interacts with the exterior surface of the cage via a hydrophobic interaction with K = 1.5(2) × 104 M-1. This is sufficient to bring it into close proximity to the layer of hydroxide ions which also surrounds the 16+ cage surface even at modest pH values, accelerating the hydrolysis of DAF to fluorescein with kcat/kuncat (the rate acceleration for that fraction of DAF in contact with the cage surface in the equilibrium) ≈50. This is far smaller than many known examples of catalysis inside a cage cavity, but at the exterior surface it is potentially general with no cavity-imposed size/shape limitations for guest binding. In contrast 4-nitrophenyl acetate (4NPA) binds inside the cage cavity with K = 3.5(3) × 103 M-1 and as such is surrounded in solution by the hydroxide ions which accumulate around the cage surface. However its hydrolysis is actually inhibited: either because of a geometrically unfavourable geometry of the bound substrate which makes it inaccessible to surface-bound hydroxide, or because the necessary volume expansion/geometry change associated with formation of a tetrahedral intermediate cannot be accommodated inside the cavity. Any 4NPA that is free in solution as part of the equilibrium undergoes catalysed hydrolysis at the cage exterior surface in the same way as DAF, but the effect is limited by the low affinity of 4NPA for the exterior surface. We conclude that exterior-surface catalysis can be effective and potentially general; and that cavity-binding of guests can result in negative, rather than positive, catalysis.

Correction for 'Disentangling contributions to guest binding inside a coordination cage host: analysis of a set of isomeric guests with differing polarities' by Cristina Mozaceanu et al., Dalton Trans., 2022, 51, 15263-15272, https://doi.org/10.1039/D2DT02623F.

Metal/ligand coordination cages provide versatile opportunities for exploitation of useful photophysical properties in self-assembled systems. The metal ions or ligands can themselves be chromophoric and display useful photophysical properties, as in many simpler coordination complexes: but the hollow capsule-like nature of coordination cages means that the binding of guests inside the central cavities adds substantially to the possibilities for functional behaviour, as the guests may themselves be chromophoric or may interact with the array of excited-state chromophores in the cage that surrounds a bound guest. This chapter summarises the rapidly developing field of photoactive coordination cages and their applications in areas from size-/shape-specific sensing of substrates to photoinduced chemical transformations that occur inside the cage cavities.

Luminescent cyanometallate [Ir(ppy)2(CN)2]– (ppy = C6H5C5H4N) has recently gained attention due to its desired photophysical properties. Our research group reported that the [Ir(ppy)2(CN)2]– has shown a negative solvatochromism like [Ru(bipy)(CN)4]2–, resulting in a blue-shift of the UV-Vis absorption bands in the water. Therefore, to gain insight into the specific solvent-solute interaction governed by the hydrogen bond in the solvation hydration shell, density functional theory (DFT) calculations were performed on the singlet ground state of the [Ir(ppy)2(CN)2]– and its solvent environment in the water at B3LYP level theory. It was demonstrated, seven water molecules provided a good description of the relevant spectra: IR and UV-Vis. The calculation reproduced the positions and intensities of the observed n(CºN) bands at 2069 and 2089 cm–1. The calculated MLCT transition wavelength was 366 nm vs. a measured value of 358 nm, differing by 8 nm. The study revealed the water molecules interacted with cyanide ligands through CN⋯H-OH type hydrogen bonds and water-water interactions (HO-H⋯OH2 type hydrogen bonds) were involved in the solvation hydration shell around the [Ir(ppy)2(CN)2]–.

Chapter 17 Supramolecular Catalysis with a Cubic Coordination Cage: Contributions from Cavity and External-Surface Binding Christopher G. P. Taylor, Christopher G. P. Taylor University of Warwick, Department of Chemistry, Coventry, CV4 7AL UKSearch for more papers by this authorMichael D. Ward, Michael D. Ward University of Warwick, Department of Chemistry, Coventry, CV4 7AL UKSearch for more papers by this author Christopher G. P. Taylor, Christopher G. P. Taylor University of Warwick, Department of Chemistry, Coventry, CV4 7AL UKSearch for more papers by this authorMichael D. Ward, Michael D. Ward University of Warwick, Department of Chemistry, Coventry, CV4 7AL UKSearch for more papers by this author Book Editor(s):Piet W.N.M. van Leeuwen, Piet W.N.M. van Leeuwen INSA Toulouse, 135 Avenue de Rangueil, Toulouse Cedex 4, 31077 FranceSearch for more papers by this authorMatthieu Raynal, Matthieu Raynal Sorbonne Université, CNRS, 4, place Jussieu, Paris Cedex 5, 75252 FranceSearch for more papers by this author First published: 31 December 2021 https://doi.org/10.1002/9783527832033.ch17 AboutPDFPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShareShare a linkShare onFacebookTwitterLinked InRedditWechat Summary An octanuclear cubic M 8 L 12 coordination cage has a central cavity with volume c. 400 Å 3 , which is optimal for accommodating small organic guests. In water, appropriately sized neutral organic guests bind strongly (up to 10 6 M −1 ) driven by the hydrophobic effect; in addition, the cationic (16+) surface of the cage accumulates anions in the portals at the center of each of the six faces, resulting in a structure whereby a high local concentration of anions is held close to, and surrounding, the cavity-bound substrate. This leads to highly effective cage-based catalysis of the Kemp elimination (reaction of cavity-bound benzisoxazole with surface-bound hydroxide ions to give 2-cyanophenolate), which is accelerated by a factor of up to 2 × 10 5 with multiple turnovers. More generally, catalyzed reactions between a neutral organic species and an anion, such as phosphate ester hydrolysis and an aldol condensation, can occur at the cage exterior surface, as the same two orthogonal interactions result in colocation of reaction partners, viz . hydrophobic association between organic substrate and the cage exterior surface, as well as local accumulation of anions because of the cage charge. Supramolecular Catalysis: New Directions and Developments RelatedInformation