Gareth W. V. Cave

Artificial exosomes as tools for basic and clinical immunology.

Dendritic cell derived exosomes are able to mediate and modulate immune responses in vivo by semi-direct T cell activation. T cells can eradicate primary, metastatic, relapsed tumours and ameliorate otherwise fatal viral infections. Not surprisingly activation and expansion of T cells has become one of the main focuses for immunotherapy. Using nanotechnology, we have developed targeted and traceable in vivo artificial exosomes by coating liposomes (FDA approved) with an optimized number of MHC Class I/peptide complexes and a selected specific range of ligands for adhesion, early activation, late activation and survival T cell receptors. These targeted artificial exosomes are traceable both in vitro and in vivo via fluorescent and Magnetic Resonance Imaging and facilitate imaging of specific areas by applying localised nuclear magnetic interactions of hydrogens via super paramagnetic labels. Here we show that artificial exosomes activate and expand functional antigen specific T cells at sufficient levels. This novel system has potential basic and clinical applications in immunology where the study of membrane interactions is desired.

Supramolecular blueprint approach to metal-coordinated capsules

An important problem in designing any large network is the assembly of systems that are resilient to change. From a chemical point of view, an analogy can be used where one requires supramolecular assemblies to maintain their dimensionality combined with limited structural perturbation in response to variation in its intermolecular framework. The identification of hydrogen-bonded framework patterns within experimentally known supramolecular assemblies that are structurally robust to disruption and selective hydrogen substitution are envisioned to act as a supramolecular blueprint or template for metal-ion retroinsertion. Here, we report the formation of a large neutral discrete pseudo-spherical coordination capsule assembled from 6 pyrogallol[4]arene ligands and 24 Cu(II) metal ions. Amazingly, this coordination capsule is structurally analogous to its hydrogen-bonded counterpart. This result shows a robust ability of pyrogallol[4]arene molecules to self-assemble into large hexameric cage structures from either the hydrogen-bonding or metal-ligand coordination process. The identification of robust supramolecular assemblies that conserve their structure in response to interchangeability between hydrogen-bonded networks for metal coordination, or inversely, represents an important advancement in supramolecular design.

The Dynamic Chemistry of Molecular Borromean Rings and Solomon Knots

The dynamic solution equilibria between molecular Borromean rings (BRs) and Solomon knots (SKs), assembled from transition metal-templated macrocycles, consisting of exo-bidentate bipyridyl and endo-tridentate diiminopyridyl ligands, have been examined with respect to the choice of the metal template and reaction conditions employed in the synthesis of the metalated BRs, otherwise known as Borromeates. Three new Borromeates, their syntheses templated by Cu(II), Co(II), and Mn(II), have been characterized extensively (two by X-ray crystallography) to the extent that the metal centers in the assemblies have been shown to be distanced sufficiently from each other not to communicate. The solid-state structure of the Co(II)-Borromeate reveals that six MeOH molecules, arranged in a [O--H...O] hydrogen bonded, chair-like conformation, are located within its oxophilic central cavity. When a mixture of Cu(II) and Zn(II) is used as the source of templation, there exists a dynamic equilibrium, in MeOH at room temperature, between a mixed-metal BR and a SK, from which the latter has been fractionally crystallized. By employing appropriate synthetic protocols with Zn(II) or Cd(II) as the template, significant amounts of SKs are formed alongside BRs. Modified crystallization conditions resulted in the isolation of both an all-zinc BR and an all-zinc SK, crystals of which can be separated manually, leading to the full characterization of the all-zinc SK by (1)H NMR spectroscopy and X-ray crystallography. This doubly interlocked [2]catenate has been identified retrospectively in recorded spectra, where it was attributed previously to a Borromeate with a Zn(II) cation coordinated to the oxophilic interior walls of the ensemble. Interestingly, these Zn(II)-templated assemblies do not interconvert in MeOH at room temperature, indicating the significant influence of both the metal template and solvent on the solution equilibria. It would also appear that d(10) metal ions favor SK formation-no evidence of Cu(II)-, Co(II)-, or Mn(II)-templated SKs has been found, yet a 1:0.9 ratio of BR:SK has been identified by (1)H NMR spectroscopy when Cd(II) is used as the template.

Recent advances in solventless organic reactions: towards benign synthesis with remarkable versatility

A paradigm shift away from using solvents in organic synthesis as solventless reactions can lead to improved outcomes, and more benign synthetic procedures, in for example aldol condensation reactions, sequential aldol and Michael addition reactions en route to Kröhnke type pyridines, reactions leading to 3-carboxycoumarins, benzylidenes, 4-aryl-1,4-dihydropyridines and 2-aryl-1,2,3,4-tetrahydroquinazolines, and oligomerisation reactions for the synthesis of cavitands; kinetic considerations for the reaction of two solids can only be explained if a eutectic melt is formed during the reaction.

Solvent-free synthesis of calix[4]resorcinarenes

Calix[4]resorcinarenes may be prepared in high yield and purity by direct reaction of resorcinol and benzaldehyde derivatives in the presence of a catalytic amount of solid acid and at ambient temperature under solvent-free conditions. This represents a viable alternative to traditional solution phase methodology. The solvent-free method measures up well with respect to energy usage, solvent wastes and associated hazards, reaction time and yield. In addition, the relevant benzaldehyde derivatives are prepared in polypropylene glycol, which is readily recycled.

Toward benign syntheses of pyridines involvingsequential solvent free aldol and Michael addition reactions

Krohnke type pyridines are readily accessible via a sequential solventless aldol condensation and Michael addition involving solid NaOH, followed by treatment with ammonium acetate in acetic acid, as a one pot reaction, which enables both symmetrical and unsymmetrical 2,6-bisaryl substituted pyridines to be isolated in high yield, typically >75%.

Benign approaches for the synthesis of bis-imine Schiff bases

Pure bis-imine Schiff bases are readily accessible in high yield, typically >95%, when aliphatic diamine/aldehyde condensation reactions are carried out under solvent-free conditions or in poly(propyleneglycol) (PPG) as a recyclable reaction medium, with negligible waste.

Investigations into Chain Length Control over Solid-State Pyrogallol[4]arene Nanocapsule Packing

Upon crystallising a series of pyrogallol[4]arenes from ethyl acetate as hydrogen bonded nanocapsules, structural study allows for the determination of the dependence of inter-capsule spacing on the chain length present at the lower rims of these ‘bowl-shaped’ molecules. Surprisingly, these nanocapsules pack closest together when a hexyl chain length is employed, and reasons for this phenomenon are suggested.

Solvent-free, direct synthesis of supramolecular nano-capsules

The single step direct synthesis of pyrogallol[4]arene via a solvent free protocol yields the pure product as a self-assembled nano-capsule, comprised of six macrocyclic building blocks.

Efficient synthesis of pyridines via a sequential solventless aldol condensation and Michael addition

The aldol condensation of an enolisable ketone and a benzaldehyde followed by Michael addition of the enone with a second enolisable ketone under solvent free conditions leads to the quantitative formation of a diketone, which can be readily converted to a pyridine (typically >80% overall yield) via a double condensation in the presence of ammonium acetate in acetic acid, allowing access to a diverse range of oligopyridyls including bipyridyls and terpyridyls.