Insights into the Effect of Iron and Cobalt Doping on the Structure of Nanosized ZnO

Here we report an in-depth structural characterization of transition metal-doped zinc oxide nanoparticles that have recently been used as anode materials for Li-ion batteries. Structural refinement of powder X-ray diffraction (XRD) data allowed the determination of small though reproducible changes in the unit cell dimensions of four ZnO samples (wurtzite structure) prepared with different dopants or different synthesis conditions. Moreover, large variations of the full width at half-maximum of the XRD reflections indicate that the crystallinity of the samples decreases in the order ZnO, Zn_0.9Co_0.1O, Zn_0.9Fe_0.1O/C, and Zn_0.9Fe_0.1O (the crystallite sizes as determined by Williamson–Hall plots are 42, 29, 15, and 13 nm, respectively). X-ray absorption spectroscopy data indicate that Co is divalent, whereas Fe is purely trivalent in Zn_0.9Fe_0.1O and 95% trivalent (Fe³⁺/(Fe³⁺ + Fe²⁺) ratio = 0.95) in Zn_0.9Fe_0.1O/C. The aliovalent substitution of Fe³⁺ for Zn²⁺ implies the formation of local defects around Fe³⁺ such as cationic vacancies or interstitial oxygen for charge balance. The EXAFS (extended X-ray absorption fine structure) data, besides providing local Fe–O and Co–O bond distances, are consistent with a large amount of charge-compensating defects. The Co-doped sample displays similar EXAFS features to those of pure ZnO, suggesting the absence of a large concentration of defects as found in the Fe-doped samples. These results are of substantial importance for understanding and elucidating the modified electrochemical lithiation mechanism by introducing transition metal dopants into the ZnO structure for the application as lithium-ion anode material

Straightforward Synthesis of Gold Nanoparticles Supported on Commercial Silica-Polyethyleneimine Beads

Stable silica-supported gold nanoparticles (Au_NPs) suitable for catalysis applications were conveniently obtained in a straightforward, one-step synthesis by simply adding an aqueous solution of HAuCl₄ to commercial polyethyleneimine-functionalized silica beads (SiO₂-PEI) as the only reactant without any external reducing agent and/or conventional stabilizing moieties. Six different types of Au_NPs/(SiO₂-PEI) beads termed <b>Au</b>_{<b><i>x</i>–<i>y</i></b>}<b>h</b>, where <i>x</i> is the initial HAuCl₄ concentration (1, 5, or 10 mM) and <i>y</i> is the reaction time (1 or 24 h), were prepared and characterized by UV–vis diffuse reflectance spectroscopy, X-ray fluorescence, FE-SEM microscopy, and X-ray absorption spectroscopy. The SEM micrographs of <b>Au</b>_{<b><i>x</i>–<i>y</i></b>}<b>h</b> samples showed that the particle size distribution decreases with the increase of the starting gold concentration, i.e., 70–100 nm for <b>Au</b>_<b>1–</b>_{<b><i>x</i></b>}<b>h</b>, 40–70 nm for <b>Au</b>_{<b>5</b><b>–</b>}_{<b><i>x</i></b>}<b>h</b>, and <b>Au</b>_{<b>10</b><b>–</b>}_{<b><i>x</i></b>}<b>h</b>, whereas on passing from 1 to 24 h the aggregation phenomena overcome the nucleation ones, promoting the formation of bigger aggregates at the expense of small Au_NPs. The XAS analysis as a combination of XANES and EXAFS studies provided detailed structural information regarding the coordination geometry and oxidation state of the gold atoms present on the beads. Moreover, the catalytic activity of the modified silica beads in the reduction of 4-nitrophenol to 4-aminophenol by NaBH₄ was investigated and in one case the XAS analysis was repeated after recovery of the catalyst, demonstrating further reduction of the Au site to Au(0)

Interaction of Cisplatin with Human Superoxide Dismutase

<i>cis</i>-Diamminedichloroplatinum­(II) (cisplatin) is able to interact with human superoxide dismutase (hSOD1) in the disulfide oxidized apo form with a dissociation constant of 37 ± 3 μM through binding cysteine 111 (Cys111) located at the edge of the subunit interface. It also binds to Cu₂–Zn₂ and Zn₂–Zn₂ forms of hSOD1. Cisplatin inhibits aggregation of demetalated oxidized hSOD1, and it is further able to dissolve and monomerize oxidized hSOD1 oligomers <i>in vitro</i> and <i>in cell</i>, thus indicating its potential as a leading compound for amyotrophic lateral sclerosis