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Under illumination with 450 nm light, porous BiVO4 photoelectrodes support photoeletrochemical Kolbe coupling with up to near quantitative faradaic efficiency and apparent quantum yield of 12% at applied voltages

A PEG-Tyr block copolymer forms a kinetically stable colloidal solution in water at room temperature which undergoes an irreversible conversion to a gel phase upon heating. A micellar solution and a gel can therefore be studied under identical experimental conditions. This made it possible to compare physical properties and chemical reactivity of micelles and gels in identical chemical environments and under identical conditions. EPR spectra of the spin-labelled copolymer showed that tyrosine mobility in gels was slightly reduced compared to micelles. Chemical reactivity was studied using photochemical degradation of tyrosine and tyrosine dimerization, in the absence and in the presence of an Fe(iii) salt. The reactivity trends were explained by reduced tyrosine mobility in the gel environment. The largest reactivity difference in gels and micelles was observed for bimolecular dityrosine formation which was also attributed to the reduction in molecular mobility.

The formation of alginate gel from low molecular weight alginate and very low molecular weight alginate in the presence of divalent cations was investigated using Electron Paramagnetic Resonance (EPR) spectroscopy. The transition from sol to gel in the presence of divalent cations was monitored by the changes in the dynamics of spin labelled alginate. The immobilisation of the spin labelled alginate in the gel reflects the strength of interaction between the cation and alginate chain. Diffusion experiments showed that both the cation and alginate polyanion in the gel fibres can exchange with molecules in solution. In particular, we showed that dissolved alginate polyanions can replace alginates in the gel fibres, which can hence diffuse through the bulk of the gel. This illustrates the surprisingly highly dynamic nature of these gels and opens up the possibility of preparing multicomponent alginate gels via polyanion exchange process.

The polymerisation inhibitor, 2-nitrophenol reacts with radicals generated in self-initiated thermal styrene polymerisation to form the unexpected benzoxazine 1. We propose the mechanism for the formation of 1 and show that it is produced by a radical mediated C–H activation.

EPR spectroscopy and spin-trapping experiments showed that polymer-encapsulated Au nanoparticles promote aldehyde oxidation via a radical pathway by initiating formation of acyl radicals.

Disproportionation of TEMPO in acids leads to the formation of an N-oxoammonium salt, which can further decompose under thermal conditions, yielding the corresponding hydroxylamine, N(2)O, CO(2) and a series of dimerisation products. Overall, acid-catalysed thermal decay of TEMPO leads to ca. 80% yield of hydroxylamine.

Oxidation of gold nanoparticles protected by thiolated β-cyclodextrin molecules, leads to formation of water-soluble polycyclodextrin nanocapsules held together by S–S bonds.

Formation of organogels from covalently linked polyethylene glycols and cyclodextrins and their encapsulation/release properties were monitored with EPR spectroscopy using spin labels and spin probes; changes in molecular tumbling rates provided information on spin probe/label location inside the gel network, and molecular properties of the gel.

TEMPO-based spin probes and beta-cyclodextrin form 1 ratio 2 guest-host complexes in viscous aqueous glycerol solutions at low temperatures. The spin probe mobility in these complexes is much higher than in the bulk glassy solution. The similar tumbling rates of the spin probe in viscous host-guest complexes and in solvent-free complexes suggest that the complexation effectively shields the nitroxide unit from the solvent molecules. This is consistent with the low activation barrier for molecular tumbling of immobilised label.

The formation of radicals in the gas phase oxidation of cyclohexane over metal oxides was studied using spin trapping and EPR spectroscopy; the results confirmed that during the catalytic initiation, the oxygen responsible for the radicals formation originates from the lattice of the metal oxide.

Reactions of chloroform over triphenylphosphine-protected Au nanoparticles have been studied using electron paramagnetic resonance (EPR) spectroscopy and a spin trapping technique. Two competing reactions, abstraction of hydrogen and halogen atoms, were identified. The hydrogen abstraction reaction showed an inverse kinetic isotope effect. Treatment of nanoparticles with oxidizing or reducing reagents made it possible to tune the selectivity of radical formation from halogen to hydrogen (deuterium) abstraction. Treatment with PbO(2) promoted the deuterium abstraction reaction followed by the loss of nanoparticle activity, whereas treatment with NaBH(4) regenerated the nanoparticle activity towards Cl atom abstraction. X-ray photoelectron spectroscopy showed an increased Au:P ratio upon treatment with oxidizing reagents. This is likely due to the oxidation of some phosphine ligands to phosphine oxides which then desorb from the nanoparticle surface.

N-Heterocyclic carbene coated Au and Pd nanoparticles have been prepared by a ligand exchange reaction; although carbenes quantitatively displaced the thioether and phosphine ligands from the nanoparticle surface, the resultant nanoparticles spontaneously leached metal complexes and aggregated in solution.

Convolution-based fitting of EPR spectra makes it possible to simultaneously determine concentrations of TEMPO and oxygen in TEMPO-inhibited polymerisations and autoxidations; this method is useful for understanding the chemistry of inhibitor mixtures.

We report on the use of EPR spectroscopy and spin trapping technique to detect free radical intermediates formed in the presence of gold nanoparticles. Phosphine- and amine-protected gold nanoparticles were found to initiate air oxidation of organic substrates containing active hydrogen atoms, such as amines and phosphine oxides. Nanoparticles protected by stronger bound ligands (e.g., thiols) were inactive in these reactions. We also found that gold nanoparticles are able to abstract a halogen atom from the halogenated compounds, presumably due to the high affinity of gold metal for halogens. Reaction of Au nanoparticles with chloroform showed an unusual inverse isotope effect. The trichloromethyl spin adduct was observed when Au nanoparticles were mixed with CDCl(3) but not with CHCl(3). This unexpected behaviour suggests that C-H bond breaking is not the rate-determining step in Au-initiated hydrogen abstraction.

This article discusses recent publications on chemical reactivity in large organic structures, including supramolecular systems (e.g., host–guest complexes), dendrimers, colloids (e.g., micelles, vesicles, microemulsions), nanoparticles and thin films. Although these systems are very different structurally, the main factors affecting organic reactivity in these assemblies are similar. These effects are: (i) proximity of functional groups in organised assemblies that may facilitate reactions between them (“proximity effect”); (ii) partitioning of the reagents between the bulk solvent and the organised assembly, which determines the local concentration of reagents in the vicinity of the functional group (“solvent effect”); (iii) unique properties of the interface between the organic assembly and the bulk solution (“interface effect”); (iv) restricted and/or anisotropic mobility of organic molecules in the organised assembly (“steric effect”). This article aims to describe each effect using examples from different types of organic assemblies. The review covers literature published in 2006 and early 2007.

The self-assembly of dendritic building blocks containing multiple terminal alkenes on their surfaces yields soft gel-phase materials--subsequent Grubbs' metathesis leads to covalent cross-linking between the alkenes and the formation of robust swellable gels.

L-Lysine based dendrimers containing a disulfide moiety at the core were synthesized. These novel ligands were used to stabilize Au nanoparticles via a one-phase chemical reduction method. The size of the resultant nanoparticles was found to decrease with increasing dendritic generation. Furthermore, the thermal stability of the nanoparticles in solution was shown to be controlled by the extent of branching in the protecting dendritic shell.