Biomedical subjects

Alexandra L Pickering

Publications and source records attributed to Alexandra L Pickering.

5 recordsLinked to original sources

PubMed2005

Controllable growth of chains and grids from polyoxomolybdate building blocks linked by silver(I) dimers.

Molecular growth processes utilizing a beta-octamolybdate synthon and {Ag2} dimers are described and the directing influence of "encapsulating" cations and coordinating solvent is also demonstrated. The growth of two 1D chains, (nBu4N)2n[Ag2Mo8O26]n (1) and (nBu4N)2n[Ag2Mo8O26(CH3CN)2]n (2), is achieved when nBu4N+ ions are used, and the diameter of the chains can be expanded by the coordination of CH3CN solvent (2). The formation of a type of gridlike structure in which 1D chains are crossed-over each other in alternatively packed layers is achieved in DMSO as the solvent; DMSO acts as a linking group to give (nBu4N)2n[Ag2Mo8O26(dmso)2]n (3), which, similar to 1 and 2, still incorporates the Bu4N+ ions that exert an "encapsulating" influence. However, in (HDMF)n[Ag3(Mo8O26)(dmf)4]n (4) the relatively bulky Bu4N+ ions are exchanged for protonated DMF cations, thereby allowing the chains to condense to a 2D array. The building block concept is further enforced by the isolation of a "monomeric" unit (Ph4P)2[Ag2Mo8O26(dmso)4] (5), which is isolated when the Ph4P+ ions are so "encapsulating" as to prevent aggregation of the {Ag-Mo8-Ag} building blocks. The nature of the AgAg dimers in each of the compounds 1-4 is examined by DFT calculations and the interplay between these Ag-Ag interactions and the structure types is described.

Acetonitriles↗

PubMed2004

General one-pot, three-step methodology leading to an extended class of N-heterocyclic cations: spontaneous nucleophilic addition, cyclization, and hydride loss.

A new class of phenanthridinium derivative has been isolated from the reaction of 2-bromoethyl-phenanthridinium bromide with a range of primary amines in excellent yields. The reaction pathway is unprecedented and proceeds via three cascade steps: nucleophilic attack of a primary amine on the iminium moiety of a heteroaromatic ring system and cyclization to form a five-membered ring, followed by hydride loss to yield a rearomatized dihydro-1H-imidazo[1,2-f]phenanthridinium derivative. A range of NMR phase transfer experiments were carried out to elucidate the mechanistic pathway, and the methodology has been further developed by means of a biphasic system using N-bromosuccinimide as a co-oxidizing agent. The method has also been extended to other N-heterocyclic cation derivatives such as quinolinium and quinazolinium.

Journal Article↗

PubMed2004

Coordination networks through the dimensions: from discrete clusters to 1D, 2D, and 3D silver(I) coordination polymers with rigid aliphatic amino ligands.

The use of a ligand directed strategy in the assembly of discrete clusters, 1D chains, 2D layers, and 3D networks using aliphatic N-donor ligands has been investigated. The ligands are a family of amines with rigid backbones [cis,cis-1,3,5-triaminocyclohexane (cis-tach), cis,trans-1,3,5-triaminocyclohexane (trans-tach), cis-1,3-diaminocyclohexane (cis-dach), and cis-3,5-diaminopiperidine (cis-dapi)], and their complexation with Ag(I) salts results in a diverse set of architectures with the following compositions: [Ag3(cis-tach)2]F3.4CH(3)OH.0.5H2O (1), [Ag3(cis-tach)2]F3.6H2O (2), ([Ag(cis-dach)]ClO4)n (3), ([Ag(cis-tach)]NO3)n (4), ([Ag(trans-tach)]PF6)n(5), and ([Ag(cis-dapi)]CF3SO3)n (6). Structural analysis shows that compounds 1 and 2 are discrete M(3)L(2) cage-type clusters with varying solvent molecule content. Short Ag...Ag contacts (3.021(8) A) are observed to dimerize discrete units in compound 2. Compound 3 is a 1D zigzag chain formed by coordination to the two primary amines of cis-dach, whereas the tridentate ligands in compounds 4 and 5 (cis-tach and trans-tach, respectively) are able to form tubular architectures by virtue of their ability to "wrap" round the channel walls. An infinite 2D coordination network is demonstrated by compound 6, in which the three coplanar amino donors of cis-dapi coordinate to the trigonal planar Ag(I) ions to form a layered structure of 6(3) topology. These are compared with a previously reported 3D structure, ([Ag(trans-tach)]NO3)n (7), that belongs to this family of architectures.

Journal Article↗

PubMed2003

Polymeric silver(I) coordination tubes.

Isolated polymeric Ag(I) coordination tubes are self-assembled from the rigid triamino ligands cis,cis-1,3,5-triaminocyclohexane (cis-tach) and cis,trans-1,3,5-triaminocyclohexane (trans-tach), forming two topologically equivalent framework motifs.

Journal Article↗

PubMed2003

Controlling dimensionality of silver(I) coordination networks with rigid aliphatic amino ligands: from a 2D to a 3D network of unprecedented topology comprising helical channels.

Ligand-directed 2D and 3D Ag(I) coordination networks are self-assembled from the rigid, topologically related tri-amino ligands cis-3,5-diaminopiperidine (cis-dapi) and cis,trans-1,3,5-triaminocyclohexane (trans-tach), yielding two networks of differing dimensionality including a 3D network of unprecedented topology comprising helical channels.

Journal Article↗