1,721,004 research outputs found
Metal-catalysed carbon—carbon bond formation in the reaction of β-dicarbonyls with nitriles
No full textElectroanalytical and spectrophotometric investigations on the metal(II)?1,2-bis(diphenylphosphino)ethane?acetylacetonate system (M = Ni, Pd, or Cu) in acetonitrile
No full textRole of the nature of the metal centre in the catalysed addition of ?-dicarbonyls to electrophilically activated nitriles
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Catalytic activity of bovine lactoperoxidase supported on macroporous poly(2-hydroxyethyl methacrylate-co-glycidyl methacrylate)
No full text2-Hydroxyethyl methacrylate (HEMA) and glycidyl methacrylate (GMA) (molar ratio 85/15) are copolymerised
upon c-ray exposure at 78 C in the presence of water to give a hydrophilic resin with a porosity that favours the
anchoring of bovine-lactoperoxidase (LPO). The resin, after mincing and sieving, is obtained as irregular microparticles
with size ranging from 80 to 1000 lm. The morphology of the resin in the swollen state is investigated with Inverse
Steric Exclusion Chromatography and ESR. The catalytic activity of immobilised and soluble LPO is monitored
and compared for 14 days at 4 C as well as enzyme stability toward thermal inactivation and resistance to denaturing
agents (acidity, urea, organic solvents). The results reveal a higher stability of supported LPO both in aqueous and
organic media as compared with the free enzyme. Evaluation of kinetic parameters of immobilised LPO suggests that
the enzyme turns out to be mainly linked to the external surface of the supporting particles
The Issue of Morphology and Molecular Accessibility of Swollen Gel-Type Resin: An Integrated Inverse Steric Exclusion Chromatograpy -Electron Spin Resonance (ISEC - ESR) - NMR Approach
No full textStructural characterization of two solid state forms of the complex bis(1,1'-bis(diphenylphosphino)ferrocene) rhodium(I) tetraphenylborate.
No full textThis paper describes a work aimed at determining the molecular structure of a rhodium(I) complex along an experimental track in which a conventional X-ray single crystal structural analysis was accidentally preceded by a powder X-ray diffractometric investigation. The complex [Rh(dppf)(2)]BPh(4) (dppf=1,1'-bis(diphenylphosphino)ferrocene) was obtained from dichloroethane in two crystalline forms, hereafter referred to as alpha and beta, which are different in colour and in the content of lattice-entrapped solvent. Conventional and synchrotron powder wide angle X-ray diffractometry (WAXS), FT-IR, P-31 and H-1 NMR spectroscopy demonstrate that alpha and beta are dimorphic forms of the same molecular entity. The observed WAXS spectrum of the alpha form was computationally fitted (R=11.3%) with that calculated for [Rh(dppf)(2)]BPh(4), upon assuming that the molecular geometry of the title complex was identical to that of the already determined iridium analogue, i.e. square-planar with a pronounced tetrahedral distortion. X-ray single crystal structural analysis confirmed this conclusion. FT-IR, DSC and TG analyses have also been employed for a solid state characterization of the two species
Characterisation of Solute Mobility in Hypercross-Linked Resins in Solvents of Different Polarity: Two Promising Supports for Catalysis
No full textTwo hypercross-linked resins stemming from a gel-type poly-chloromethylated styrene-divinylbenzene resin (GT) in beaded form are investigated with a combination of spectroscopic techniques (EPR and time-domain (TD)-NMR spectroscopy) to evaluate their use as supports for the development of operationally flexible heterogeneous metal catalysts, suitable to be employed in liquid and gas phase. The first resin (HGT) is the direct product of the hypercross-linking reaction, whereas the second one (HGS) is the sulphonated analogue of HGT obtained by exchanging approximately 3 wt % of the chloromethyl groups with sulphonic groups. HGT and HGS absorb both polar and apolar solvents in the permanent nanoporosity created by the hypercross-linking, and NMR data highlight that the pore size is not affected by the different properties of the investigated liquid media. The EPR analysis of the dry resins reveals that during the hypercross-linking process paramagnetic species are formed in the HGT beads, which persist in the sulphonated resin. The mobility of solutes inside the polymers framework was investigated with EPR spectroscopy upon soaking the resins with solutions of two spin probes (2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL)) in THF, toluene, n-heptane and water. The EPR spectra show that, depending on the solvent, the two resins can act as sorbents, able to trap the solutes in the polymer framework, or as simple supports that allow free diffusion of the solutes. Our results suggest that HGT and HGS are promising supporting materials for metal catalysts, provided one chooses carefully the solvent to be employed for the catalysed reaction as this choice strongly affects the mobility of the substrates and, thus their effective reactivity
Nanostructure and molecular accessibility of gel-type resins for supported bio-catalysis. Part I. Poly-hydroxyethylmethacrylatehydroxypropylmethacrylate-trimethylolpropanetrimethacrylate
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