Search

This paper describes the gelation of symmetric dendrimers based on building blocks constructed from L-lysine. These dendrimers form gel-phase materials in nonpolar organic solvents. The thermal properties and concentration dependence of the gelation were investigated, and it was found that there was a clear dendritic effect on the behavior of the soft materials formed, with higher generation dendrimers giving rise to more thermally stable gels. Variable temperature 1H NMR studies indicated that this behavior was probably a consequence of more extensive interdendrimer hydrogen bonding occurring between the peptidic groups in the higher generation dendrimers. The supramolecular aggregates were found to have a fibrillar structure, with the dimensions and alignment of the fibers being dependent on dendritic generation. Circular dichroism measurements confirmed that these fibers possessed chiral organization of the peptidic groups on the supramolecular (nano) scale, assigned as helicity. This paper indicates that dendritic functionalization provides a useful way of tuning gel-phase materials properties, with clear dendritic effects on gel formation being quantified for the first time, hence illustrating the way dendritic functionalization can play a positive role in the formation of highly functional organic materials with desirable properties.

A concise, convergent asymmetric synthesis of the 4-substituted-1,4-dihydropyridine 1 [Ohnmacht, C. J., Jr.; Trainor, D. A.; Forst, J. M.; Stein, M. M.; Harris, R. J. Patent No. 5,622, 964] has been achieved via a novel asymmetric Michael addition of an optically pure vinylogous amide to an α,β-unsaturated ketone. The overall process is three steps from readily available starting materials and provides an economical manufacturing route to the title compound, which was required as a candidate drug for the treatment of urinary incontinence.

This paper describes the synthesis of gold nanoparticles stabilized by two series of new dendritic disulfide ligands with alkene groups at their peripheries. Intraparticle cross-linking of the alkene groups around the periphery of each nanoparticle was achieved by Grubbs' metathesis. It was demonstrated that cross-linking of the organic ligand has no effect on the size or morphology of the inorganic gold core as determined by TEM and UV-vis measurements. However, the introduction of cross-linking at the surface of the ligand enhances the stability of the gold nanocore toward chemical etchant agents (NaCN) and thermal treatment. The impact of cross-linking on nanoparticle stability is greater when the cross-linking is closer to the nanoparticle surface (i.e., using lower generation dendritic ligands). Attempts to perform further synthetic transformation on the hybrid materials in order to remove the gold core led to insoluble products composed predominantly of the dendritic ligand.

A series of gold nanoparticles stabilised by ‘Newkome-type’ dendritic branching has been synthesised and fully characterised. In particular, the properties and behaviour of these hybrid materials are compared with those of a previously reported set of nanoparticles stabilised by dendrons constructed using l -lysine building blocks. The rates of cyanide-induced nanoparticle decomposition were determined, and it was found that the rate of decomposition increased on the introduction of dendritic branching. Furthermore, ‘Newkome-type’ dendrons were significantly more effective at protecting the encapsulated gold nanoparticle than the l -lysine based dendrons. It is proposed that this observation can be explained on the basis of more effective packing and surface coverage by the ‘Newkome-type’ dendrons. Importantly, this study therefore demonstrates that the organic chemical structure of dendritic ligands plays a crucial role in controlling the reactivity of self-assembled hybrid nanostructures.

Gold nanoparticles with diameters of ca. 13 nm were synthesised by UV irradiation of a supramolecular organogel into which HAuCl4 and tetraoctylammonium bromide had been diffused—the gel network plays an essential role in nanoparticle stabilisation.

This paper reports the synthesis of dendrons containing a spermine unit at their focal point. The dendritic branching is based on L-lysine building blocks, and has terminal oligo(ethyleneglycol) units on the surface. As a consequence of the solubilising surface groups, these dendrons have high solubility in solvents with widely different polarities (e.g., dichloromethane and water). The protonated spermine unit at the focal point is an effective anion binding fragment and, as such, these dendrons are able to bind to polyanions. This paper demonstrates that polyanions can be bound in both dichloromethane (using a dye solubilisation assay) and in water (competitive ATP binding assay). In organic media the dendritic branching appears to have a pro-active effect on the solubilisation of the dye, with more dye being solubilised by higher generations of dendron. On the other hand, in water the degree of branching has no impact on the anion binding process. We propose that in this case, the spermine unit is effectively solvated by the bulk solvent and the dendritic branching does not need to play an active role in assisting solubility. Dendritic effects on anion binding have therefore been elucidated in different solvents. The dendritic branching plays a pro-active role in providing the anion binding unit with good solubility in apolar solvent media.

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.

The shift of the DP role as a traditional administrative function to an integral element of the company's strategy calls for top‐level computer people with all‐round business acumen. Executive searches (head‐hunting) proves more effective than word or mouth, advertising or agencies. British Telecom employed such a search, which is described, immediately after privatisation.