Use of chemical modification and spectroscopic techniques to determine the binding and coordination of gadolinium(III) and neodymium(III) ions by alfalfa biomass

Metal pollution in the aqueous environment has become an important issue in the past few decades leading to extensive research in the area of pollution remediation. Most of the recent research in this area has been in bioremediation including phytofiltration and phytoextraction. Although there has been a lot of research done in the field of metal interactions with plants, the actual mechanism(s) and ligands involved are not well understood. Through a series of batch experiments, including pH profiles, time dependency studies, and capacity experiments, we have investigated the binding of Gd(III) and Nd(III) to alfalfa biomass. Batch pH studies showed that the optimum binding was at pH 5.0 for both elements. The time dependency experiments showed that the binding occurs within the first 5 min of contact and remains constant for up to 60 min. In addition, chemical modifications to the alfalfa biomass were performed to indirectly determine the ligands on the biomass responsible for metal binding. For Gd(III) binding, it was shown that the carboxyl groups on the biomass play the most important role in metal ion binding. However, for Nd(III), not only was it found that the carboxyl groups play an important role in the binding, but in addition, the amino groups on the biomass also play an important role in the binding of the metal ions. Further studies using X-ray absorption spectroscopy (XAS) showed that the Gd(III) and Nd(III) ions were bound to the alfalfa biomass through oxygen (or nitrogen ligands), which were coordinated to carbon atoms. The lanthanide complexes within the biomass included some coordinated water molecules.     

Sims analysis of the distribution of hydrogen absorbed by gold electrodes during the evolution of hydrogen

Gold electrodes were charged with hydrogen by strong cathodic treatment in 0.5 M H₂SO₄. The concentration of hydrogen was then studied by SIMS both along the surface and in depth by etching in the ion beam. With electrodes consisting of a small number of crystals, the absence of abnormal hydrogen concentration at the grain boundaries seems to rule out diffusion along this route. The profiles observed seem to be consistent with a simple model of uniform bulk diffusion.     

Photoluminescent detection of the impurity band in Si(P)

A new photoluminescent band in the spectra of phosphorus-doped silicon at concentrations near the Mott transition is reported. It is attributed to the recombination of an electron in the impurity band with a free hole.     

Complexation of dimethylmagnesium with alpha-diimines; structural and EPR characterisation of single electron and alkyl transfer products

Treatment of dimethylmagnesium with the alpha-diimine ligands Ar'N=C(R)C(R)=NAr' [R = naphth-1,8-diyl (1), H (2), CH3 (3); Ar' = 2,6-diisopropylphenyl] in diethyl ether provides the neutral methyl-bridged dimeric complexes [(alpha-diimine-.)Mg+(mu-CH3)]2 via single electron transfer (SET) to the coordinated diimine and elimination of a methyl radical. These biradical species have been characterised by EPR spectroscopy and, for the ligand , X-ray crystallography. In the presence of THF the reaction of ligand proceeds to the diamagnetic [(ene-1,2-diamide)Mg(THF)3] complex in which the diimine ligand has been doubly reduced to an ene-diamide by two successive SET processes. Comparison of the structural data for the free ligand with that obtained for the alpha-diimine radical anion and ene-diamide complexes shows the expected increases in C-N, and decreases in C-C, bond lengths within the N-C-C-N unit consistent with the progressive reduction of the ligand. In the case of ligand , reaction at low temperature provides the complex [Mg(mu2-Me){Ar'NC(Me)2C(Me)NAr'}]2 in which methyl transfer to a ligand imine carbon atom has occurred. This species has also been structurally characterised. This contrasts with the formation of the radical species at room temperature, and indicates the involvement of an intermediate in which the radical products of the SET process are held in close proximity by the solvent cage. Two competing processes of methyl radical escape and methyl transfer to the ligand account for the formation of the observed products at different temperatures.     

A new technique to examine individual pollutant particle and fibre deposition and transit behaviour in live mouse trachea

During respiration, particles suspended in the air are inhaled and unless cleared by airway defences they can remain and affect lung health. Their size precludes the use of standard imaging modalities so we have developed synchrotron phase-contrast X-ray imaging (PCXI) methods to non-invasively monitor the behaviour of individual particles in live mouse airways. In this study we used these techniques to examine post-deposition particle behaviour in the trachea. PCXI was used to monitor the deposition and subsequent behaviour of particles of quarry dust and lead ore; fibres of asbestos and fibreglass; and hollow glass micro-spheres. Visibility was examined in vitro and ex vivo to avoid the complicating effects of surrounding tissue and respiratory or cardiac motion. Particle behaviour was then examined after deposition onto the tracheal airway surfaces of live mice. Each particle and fibre looked and behaved differently on the airway surface. Particles lodged on the airway shortly after deposition, and the rate at which this occurred was dependent on the particle type and size. After the live-imaging experiments, excised airway samples were examined using light and electron microscopy. Evidence of particle capture into the airway surface fluids and the epithelial cell layer was found. PCXI is a valuable tool for examining post-deposition particulate behaviour in the tracheal airway. These first indications that the interaction between airways and individual particles may depend on the particle type and size should provide a novel approach to studying the early effects of respired particles on airway health.     

A statistical theory of orientational ordering at the free surface of a liquid of ellipsoidal molecules

The surface tension γ of a system of ellipsoidal molecules is evaluated approximately using a generalized Fowler-Kirkwood-Buff model. The pair potential is modelled as u(r/σ) where r is the centre of mass distance and σ is an angle dependent range parameter determined by the shape anisotropy of the molecule. It is shown that if the pair correlation function g scales as g(r/σ) γ can be mapped onto the value for a system of spheres, multiplied by an angular integral which takes into account approximately both the anisotropic molecular shape as well as possible orientational order. It is shown that γ is lowered when the orientational order parameter Q ≠ 0, implying that isotropic molecular liquids may be partially ordered near the free surface. The surface favours parallel ordering of rod-like particles in a direction in the plane of the surface. For plate-like particles, ordering with the plates in the plane of the surface is favoured. In both cases the anchoring energies increase sharply with the shape anisotropy of the molecule. These results are qualitatively consistent with the surface properties of non-polar nematic liquid crystals.