Ryan S. Walmsley

Imidazole-functionalized polymer microspheres and fibers – useful materials for immobilization of oxovanadium(IV) catalysts

Both polymer microspheres and microfibers containing the imidazole functionality have been prepared and used to immobilize oxovanadium(IV). The average diameters and BET surface areas of the microspheres were 322 μm and 155 m2 g−1 while the fibers were 1.85 μm and 52 m2 g−1, respectively. XPS and microanalysis confirmed the incorporation of imidazole and vanadium in the polymeric materials. The catalytic activity of both materials was evaluated using the hydrogen peroxide facilitated oxidation of thioanisole. The microspheres were applied in a typical laboratory batch reactor set-up and quantitative conversions (>99%) were obtained in under 240 min with turn-over frequencies ranging from 21.89 to 265.53 h−1, depending on the quantity of catalyst and temperature. The microspherical catalysts also proved to be recyclable with no drop in activity being observed after three successive reactions. The vanadium functionalized fibers were applied in a pseudo continuous flow set-up. Factors influencing the overall conversion and product selectivity, including flow rate and catalyst quantity, were investigated. At flow rates of 1–4 mL h−1 near quantitative conversion was maintained over an extended period. Keeping the mass of catalyst constant (0.025 g) and varying the flow rate from 1–6 mL h−1 resulted in a shift in the formation of the oxidation product methyl phenyl sulfone from 60.1 to 18.6%.

pH-metric chemical speciation modeling and studies of in vitro antidiabetic effects of bis[(imidazolyl)carboxylato]oxidovanadium(IV) complexes.

A range of bidentate N,O-donor ligands of the imidazolyl-carboxylate moiety, which partially mimic naturally occurring bioligands, were prepared and reacted with the oxidovanadium(IV) ion to form the corresponding bis-coordinated oxidovanadium(IV) complexes. The aqueous pH-metric chemical speciation was investigated using glass electrode potentiometry, which allowed for the determination of protonation and stability constants of the ligands and complexes, respectively. The species distribution diagrams generated from this information gave evidence that the bis[(imidazolyl)carboxylato]oxovanadium(IV) complexes possess a broad pH-metric stability. The complexes improved glucose uptake in cell cultures using 3T3-L1 adipocytes, C2C12 muscle cells and Chang liver cells. The PTP inhibition studies indicated that the mechanism underlying insulin-stimulated glucose uptake was possibly via the protein tyrosine phosphorylation through the inhibition of the protein tyrosine phosphatase 1B (PTP 1B). The vanadium compounds also demonstrated the inhibition of D-dimer formation, suggesting that these compounds could potentially relieve a hypercoagulative state in diabetic patients.

Nanofiber-supported metal-based catalysts

Catalysis utilizing heterogeneous catalysts remains favoured in the chemical industry due to their ease of separation and recyclability compared to homogeneous catalysts. Electrospun nanofibers as catalyst support materials can enhance catalyst performance due to increased surface area-to-volume ratio. Recently, metal oxides and metallic nanoparticles immobilized onto electrospun nanofibers have displayed enhanced catalytic activities towards various reactions. Metal ion complexes supported on electrospun nanofibers, via coordination to the desired functional groups of polymer chains, have also been applied as heterogeneous catalysts in some organic syntheses. The nanofiber-based catalytic materials exhibited good catalytic activities for various reactions, as well as good recyclability and reusability. Concerns over the mechanical and chemical stability of electrospun nanofibers as well as the metal ion leaching sometimes occurring when employed under extreme conditions are also emphasized. This review covers progress in the fabrication and catalytic applications of various metal-based catalysts immobilized onto nanofibers. It will also highlight the challenges associated with the use of electrospun nanofibers in catalysis.

Separation of Copper(II) from Base Metals in an Acidic Synthetic Sulfate Leach Solution Using a Novel 1-Octylimidazole-2-Aldoxime Extractant

The design and application of a novel bidentate imidazole-oxime extractant, 1-octylimidazole-2-aldoxime, for the separation of copper from base metals in a solvent extraction system is presented in this report. This extractant was used alongside dinonylnaphthalene sulfonic acid (DNNSA) as a bulky counterion, and an optimized molar ratio of 1:60 for the metal ions to the extractant was used while the DNNSA concentration was 0.020 M. The effective separation of copper from the other base metals was achieved under these conditions with good extraction efficiency in Shellsol 2325 as diluent. The ΔpH 0.5 ≈ 1.05 was obtained for the separation of copper from nickel in the extraction order of Cu2+ > Ni2+ > Zn2+ > Cd2+> Co2+ as a function of pH. At pH 1.65 the extracted copper from a synthetic mixture of the base metals reached 90.1%, and this method required a two-step extraction process to recover 98.2% copper with negligible nickel and cobalt impurities. The stripping of the copper from the loaded organic phase using TraceSelect sulfuric acid at pH 0.35 yielded 96.6% of the loaded quantity after the second stage of stripping. An investigation of the chemistry involved in this separation system showed that the species formed between the metal ions and the ligand, 1-methylimidazole-2-aldoxime, are isostructural with an octahedral geometry from the evidence of solid-state studies. The second stability constants (log β2) for the complex formation reactions were of the order; Cu2+ (14.9) > Ni2+ (14.4) > Zn2+ (8.8) > Co2+ (8.7), which is the same pH-metric order of the extraction curves. Thus the separation of copper from the other base metals was thermodynamically driven. Therefore, 1-octylimidazole-2-aldoxime, with its bidentate character in coordination, proved useful for application as an extractant of copper from other base metals in a sulfate medium.