Hydrothermal synthesis, characterization and Raman studies of Eu3+ activated Gd2O3 nanorods

Eu3+ (8 mol%) activated gadolinium oxide nanorods have been prepared by hydrothermal method without and with surfactant, cityl trimethyl ammonium bromide (CTAB). Powder X-ray diffraction (PXRD) studies reveal that the as-formed product is in hexagonal Gd(OH)(3):Eu phase and subsequent heat treatment at 350 and 600 degrees C transforms the sample to monoclinic GdOOH:Eu and cubic Gd2O3:Eu phases, respectively. The structural data and refinement parameters for cubic Gd2O3:Eu nanorods were calculated by the Rietveld refinement. SEM and TEM micrographs show that as-obtained Gd(OH)(3):Eu consists of uniform nanorods in high yield with uniform diameters of about 15 nm and lengths of about 50-150 nm. The temperature dependent morphological evolution of Gd2O3:Eu without and with CTAB surfactant was studied. FTIR studies reveal that CTAB surfactant plays an important role in converting cubic Gd2O3:Eu to hexagonal Gd(OH)(3):Eu. The strong and intense Raman peak at 489 cm(-1) has been assigned to A(g) mode, which is attributed to the hexagonal phase of Gd2O3. The peak at similar to 360 cm(-1) has been assigned to the combination of F-g and E-g modes, which is mainly attributed to the cubic Gd2O3 phase. The shift in frequency and broadening of the Raman modes have been attributed to the decrease in crystallite dimension to the nanometer scale as a result of phonon confinement. (C) 2010 Elsevier B.V. All rights reserved.

Synthesis and Antioxidant Activity of Peptide-Based Ebselen Analogues

A series of di- and tripeptide-based ebselen analogues has been synthesized. The compounds were characterized by H-1, C-13, and Se-77 NMR spectroscopy and mass spectral techniques. The glutathione peroxidase (GPx)-like antioxidant activity has been studied by using H2O2, tert-butyl hydroperoxide (tBuOOH), and cumene hydroperoxide (Cum-OOH) as substrates, and glutathione (GSH) as a co-substrate. Although all the peptide-based compounds have a selenazole ring similar to that of ebselen, the GPx activity of these compounds highly depends on the nature of the peptide moiety attached to the nitrogen atom of the selenazole ring. It was observed that the introduction of a phenylalanine (Phe) amino acid residue in the N-terminal reduces the activity in all three peroxide systems. On the other hand, the introduction of aliphatic amino acid residues such as valine (Val) significantly enhances the GPx activity of the ebselen analogues. The difference in the catalytic activity of dipeptide-based ebselen derivatives can be ascribed mainly to the change in the reactivity of these compounds toward GSH and peroxide. Although the presence of the Val-Ala-CO2Me moiety facilitates the formation of a catalytically active selenol species, the reaction of ebselen analogues that has a Phe-Ile-CO2Me residue with GSH does not generate the corresponding selenol. To understand the antioxidant activity of the peptide-based ebselen analogues in the absence of GSH, these compounds were studied for their ability to inhibit peroxynitrite (PN)-mediated nitration of bovine serum albumin (BSA) and oxidation of dihydrorhodamine 123. In contrast to the GPx activity, the PN-scavenging activity of the Phe-based peptide analogues was found to be comparable to that of the Val-based compounds. However, the introduction of an additional Phe residue to the ebselen analogue that had a Val-Ala dipeptide significantly reduced the potency of the parent compound in PN-mediated nitration.