School of Chemistry - Theses

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    Synthesis and application of molecular probes for biologically important metal ions
    BUNCIC, GOJKO ( 2012)
    The synthesis and characterization of new molecular probes aimed towards studies with metal ions in biology is described. One synthetic platform involves 1,2-phenylenediamine-based ligands which are divided into two classes. The first consists of ligands with carboxylic acid functional groups. These resemble the classic hexadentate ligand H4Edta. Previous studies demonstrated that functional groups substituted at the aromatic backbone affect the binding affinities for metal ions. This proves a way of preparing a family of ligands with similar coordination properties but different binding affinities. Interesting cobalt complexes were characterised by single crystal X-ray diffraction studies. Two cobalt atoms, each complexed to one ligand in a single crystal of one of the complexes, had different coordination geometries. A fluorescent group Bodipy was successfully attached to the aromatic backbone to make a new water soluble probe which exhibited a 2-fold fluorescence enhancement in presence of Zn(II). A second class of 1,2-phenylenediamine-based ligands was established by preparation of aminopyridine ligands, which were designed to optimize selectivity for Cu(II) and Cu(I) ions. A particular focus was the length of the linker to the pyridine arms for flexible coordination around the metal centre, with a particular Cu(II) complex demonstrating the point. Interesting redox behaviours were observed in the preparation of copper complexes. One ligand H2L binds Cu(I) to form salt [CuI(H2L)]BF4 which undergoes aerial oxidation in solution. A diamagnetic salt [CuIIL•-]BF4 was isolated where π-radical anion L•- is the (1e-, 2H+) oxidation product of H2L. This analysis was confirmed by a number of techniques including monitoring of the oxidation process by electrochemistry and electronic and NMR spectroscopies. The second synthetic platform focused on bis(thiosemicarbazone) compounds. New water soluble ligands were prepared by selective transamination reactions using sulfanilic acid as the transaminating group. Studies with the new ligands revealed that good water solubility, 1:1 binding stoichiometry and the ability of ligands to form chromophoric species with Zn(II) with buffered solutions make them potential molecular probes for studies with this ion. An affinity of KD = 6.0 x 10-9 M-1 for Zn(II) was determined for one ligand Na[H2L7] via competition assays with H2Egta2-. The new ligand was applied in estimating the binding affinities of two plant proteins.