Browsing by Author "Skelton, BW"

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    Ionophoric properties of a tetra-tetrazole functionalised calix[4]arene
    (Taylor and Francis Group, 2015-10-23) D'Alessio, D; Skelton, BW; Lengkeek, NA; Fraser, BH; Krause-Heuer, AM; Muzzioli, S; Stagni, S; Massi, M; Ogden, MI
    The synthesis and characterisation of p-t-butylcalix[4]arene functionalised at the lower rim with four tetrazole moieties is reported. The macrocycle is found to be a poorer ionophore for lanthanoid cations than the bis-tetrazole–substituted analogue. Solution-phase photophysical studies strongly suggested that the cations interacted only weakly with the calixarene ligand. A mixed sodium/triethylammonium salt of the calixarene ligand was crystallised in the presence of lanthanoid cations and structurally characterised. Strong intramolecular interactions are hypothesised to be the cause of the observed behaviour. © 2015 Taylor & Francis
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    Lanthanoid complexation by a tris-tetrazole-functionalised calix[4]arene
    (John Wiley & Sons, Inc, 2016-12-19) D'Alessio, D; Skelton, BW; Sobolev, AN; Krause-Heuer, AM; Fraser, BH; Massi, M; Ogden, MI
    The synthesis and characterization of 5,11,17,23-tetra-tert-butyl-25-hydroxy-26,27,28-tris(tetrazol-5-ylmethoxy)calix[4]arene is reported. Purification of the macrocycle required the use of preparative HPLC techniques. The macrocycle was found to be a poorer ligand for complexation of lanthanoid cations than the bis(tetrazole) analogue, but somewhat more effective than the tetrakis(tetrazole)-substituted derivative. Two metal complexes of the tris(tetrazole)–calixarene were structurally characterised. A polymeric sodium salt of the tris(tetrazole)–calixarene was isolated from a solution containing yttrium and a sodium acetate buffer. A praseodymium complex was isolated in the presence of an ammonium acetate buffer, where the calixarene acts as a unidentate ligand, bound to the metal atom through one tetrazole N-atom. Increasing the amount of buffer resulted in the crystallisation of a metal-free ammonium salt of the calixarene. © 2016 John Wiley & Sons, Inc.
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    Lanthanoid “bottlebrush” clusters: remarkably elongated metal–oxo core structures with controllable lengths
    (Journal of the American Chemical Society, 2014-10-04) D'Alessio, D; Sobolev, AN; Skelton, BW; Fuller, RO; Woodward, RC; Lengkeek, NA; Fraser, BH; Massi, M; Ogden, MI
    Large metal–oxo clusters consistently assume spherical or regular polyhedral morphologies rather than high-aspect-ratio structures. Access to elongated core structures has now been achieved by the reaction of lanthanoid salts with a tetrazole-functionalized calixarene in the presence of a simple carboxylate co-ligand. The resulting Ln19 and Ln12 clusters are constructed from apex-fused Ln5O6 trigonal bipyramids and are formed consistently under a range of reaction conditions and reagent ratios. Altering the carboxylate co-ligand structure reliably controls the cluster length, giving access to a new class of rod-like clusters of variable length. © 2014 American Chemical Society
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    The synthesis and fluorescence profile of novel thalidomide analogues
    (Elsevier B.V., 2015-10-21) Kampmann, SS; Skelton, BW; Yeoh, GC; Abraham, LJ; Lengkeek, NA; Stubbs, KA; Heath, CH; Stewart, SG
    Herein we describe the synthesis of various simple N-alkyl thalidomide derivatives in order to determine their fluorescence excitation and emission profile. Following this, a series of more complex fragments were attached through a Huisgen 1,3-dipolar cycloaddition providing a more diverse fluorescence profile. A thalidomide azide derivative was also found to be particularly reactive in a copper-free click reaction with two known cyclooctynes. © 2015 Elsevier Ltd.
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    Synthesis, structure and conformational mobility of tetra-substituted cyanomethoxy p-tert-butylcalix[4]arenes
    (Royal Society of Chemistry, 2016-04-04) D'Alessio, D; Krause-Heuer, AM; Skelton, BW; Fraser, BH; Massi, M; Ogden, MI
    The syntheses and single crystal X-ray structure determinations of 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(cyanomethoxy)calix[4]arene (partial-cone conformer), 5,11,17,23-tetra-tert-butyl-25,27-bis(diethylcarbamoylmethoxy)-26,28-bis(cyanomethoxy)calix[4]arene (cone and partial-cone conformers), 5,11,17,23-tetra-tert-butyl-25,26,27-tris(cyanomethoxy)-28-hydroxycalix[4]arene, and 5,11,17,23-tetra-tert-butyl-25-diethylcarbamoylmethoxy-26,27,28-tris(cyanomethoxy)calix[4]arene (cone conformer) are reported. The calixarenes are found to be conformationally mobile when heated in DMSO, favouring the partial-cone conformer at equilibrium. The tris-substituted cyanomethoxy derivative was found to assume the partial-cone conformation in the solid state. Attempts to convert nitrile groups to tetrazole moieties in derivatives containing both amide and nitrile groups were unsuccessful. © The Authors - CC-BY licence
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    Triamidetriamine bearing macrobicyclic and macrotricyclic ligands: potential applications in the development of copper-64 radiopharmaceuticals
    (American Chemical Society, 2013-12-16) Tan, KV; Pellegrini, PA; Skelton, BW; Hogan, CF; Greguric, I; Barnard, PJ
    A versatile and straightforward synthetic approach is described for the preparation of triamide bearing analogues of sarcophagine hexaazamacrobicyclic cage ligands without the need for a templating metal ion. Reaction of 1,1,1-tris(aminoethyl)ethane (tame) with 3 equiv of 2-chloroacetyl chloride, yields the tris(α-chloroamide) synthetic intermediate 6, which when treated with either 1,1,1-tris(aminoethyl)ethane or 1,4,7-triazacyclononane furnished two novel triamidetriamine cryptand ligands (7 and 8 respectively). The Co(III) and Cu(II) complexes of cryptand 7 were prepared; however, cryptand 8 could not be metalated. The cryptands and the Co(III) complex 9 have been characterized by elemental analysis, 1H and 13C NMR spectroscopy, and X-ray crystallography. These studies confirm that the Co(III) complex 9 adopts an octahedral geometry with three facial deprotonated amido-donors and three facial amine donor groups. The Cu(II) complex 10 was characterized by elemental analysis, single crystal X-ray crystallography, cyclic voltammetry, and UV–visible absorption spectroscopy. In contrast to the Co(III) complex (9), the Cu(II) center adopts a square planar coordination geometry, with two amine and two deprotonated amido donor groups. Compound 10 exhibited a quasi-reversible, one-electron oxidation, which is assigned to the Cu2+/3+ redox couple. These cryptands represent interesting ligands for radiopharmaceutical applications, and 7 has been labeled with 64Cu to give 64Cu-10. This complex showed good stability when subjected to l-cysteine challenge whereas low levels of decomplexation were evident in the presence of l-histidine. © 2013 American Chemical Society