Júlio D. Pedrosa de Jesus

Preparation of zinc oxide and zinc sulfide powders by controlled precipitation from aqueous solution

ZnO and ZnS powders were prepared from aqueous solutions of zinc salts in the presence of ethylenediamine or triethanolamine. The morphology of the powders was analysed by scanning electron microscopy and infrared spectroscopy. The effect of the experimental conditions upon the size and shape of the particles is described with a special emphasis on the role of the organic ligand.

Synthetic hollow zinc oxide microparticles

The preparation of hollow particles of ZnO by calcination of hydrozincite coated poly(styrene) beads is reported. Synthetic studies have been performed on such polymer/inorganic composite precursors in order to establish the optimum conditions for the preparation of the ZnO particles. The morphological properties of the powders were characterised by optical microscopy and scanning electron microscopy. The micrometric ZnO particles show morphological characteristics related to the template used in their preparation.

Synthesis and structural characterisation of new RuII[12]aneS4 complexes with polypyridylic and related ligands

The reaction between cis-[Ru(dmso)Cl2] (dmso=dimethylsulfoxide) and the macrocycle 1,4,7,10-tetrathiacyclododecane ([12]aneS4) gives the complex cation [Ru([12]aneS4)(dmso)Cl]+. A new series of RuII([12]aneS4) complexes were obtained by replacing the dmso and the chlorine ligands with polypyridylic or related monodentate ligands. Complexes with the general formula [Ru([12]aneS4)(L)]2+, where L=bidentate ligand: dipyridylamine (dipa); 5-phenyl-1,10-phenanthroline (5-phen); 1,10-phenanthroline-5,6-dione (5,6-dione); o-phenylenediamine (pda) or 4,4′-diphenyl-2,2′-dipyridyl (dbp) have been synthesised. Related complexes containing monodentate ligands, [Ru([12]aneS4)(CH3CN)Cl]+, [Ru([12]aneS4)(CH3CN)2]2+ and [Ru([12]aneS4)(ind)Cl)]+ (ind=indazole) were also prepared. The complexes were characterised by NMR, UV/Vis and IR spectroscopy and their electrochemical behaviour was studied by cyclic voltammetry. The X-ray single crystal diffraction structures of the complexes [Ru([12]aneS4)(dmso)Cl]Cl, [Ru([12]aneS4)(CH3CN)2][PF6]2, [Ru([12]aneS4)(CH3CN)Cl]PF6, [Ru([12]aneS4)(5,6-dione)][PF6]2·2CH3CN, [Ru([12]aneS4)(5-phen)][PF6]2 and [Ru([12]aneS4)(ind)Cl]PF6·CH3CN were determined. All complexes exhibit a distorted cis-octahedral environment with the macrocycle adopting a folded conformation.

Structural characterisation of RuII [9]aneS3 polypyridyl complexes by NMR spectroscopy and single crystal X-ray diffraction

Abstract The synthesis of a series of Ru II complexes with the thioether ligand [9]aneS 3 and various polypyridyl ligands was carried out using [Ru(dmso) 4 Cl 2 ] as a starting material. The first synthetic step involved the introduction of the thioether ligand and the isolation of the compound [Ru([9]aneS 3 ) (dmso)Cl 2 ]. The polypyridyl ligands were then exchanged to give a series of complexes [Ru([9]aneS 3 )(X)(Cl] + (X = 1, 10-phenanthroline (phen), 2,2′-bipyridyl (bpy), 4,4′-diphenyl-2,2′,-bipyridyl (dbp) and 4,7′-diphenyl-1, 10-phenanthroline (dip)). These complexes were characterised by NMR and UV spectra. The complxes with X= phen and bpy were crystallised and single crystal X-ray diffraction studies carried out. Distorted octahedral coordination geometry was observed for both complexes. The equatorial planes are formed by two macrocyclic sulfur donor atoms and two nitrogen atoms from polypyridyl (bpy or phen). The hexa-co-ordination is achieved via a chlorine and the remaining sulfur, macrocyclic atom. The [9]aneS 3 macrocyclic ligand adopts a [333] facial arrangement. The results from NMR studies for [Ru([9]aneS 3 )(phen)Cl] + and [Ru([9]aneS 3 )(bpy)Cl] + indicate that both complexes exist as two forms in solution with C s symmetry consistent with a [333] facial arrangement.

N.m.r. studies of complexes of molybdenum(VI) with tartaric acid in aqueous solution

SummaryComplex formation between molybdate ions and R,R-(+)-tartaric acid has been studied in aqueous solution, and to a limited extent in DMSO, over a range of concentrations and pH at 298K, using1H and13C n.m.r. techniques. Only four main species are evident; two, which have Mo: L ratios of 1∶1 and 1∶2, are bondedvia a carboxylic oxygen atom and an adjacent hydroxyl oxygen atom. The 1∶2 species forms stereospecifically. The other two main species contain bridging tartaric acid molecules, and a 2∶2 species, also formed stereo-specifically in solution, have been isolated and characterised in the solid state. A limited number of experiments with racemic acid and meso-tartaric acid indicate that only a few species are formed in these systems and with a good deal of stereospecificity also.

Study of polyoxotungstates with the Keggin structure by cyclic voltammetry

Abstract Cyclic voltammetry was used to study, in aqueous solution (pH 2–6), polyoxotungstates with the Keggin structure with the general formula α-[XW11M(H2O)O39]n−, X=P, Si, B and M=Cr(III), Fe(III), Co(II,III), Ni(II). The results provide valuable information on the comparative ease of reduction of the several species studied and on the stability of the reduced species. The transition metal substituted heteropolytungstates proved to be, in general, more difficult to reduce than the corresponding lacunary species, under the same conditions. For all species, the peak potentials shift to more negative values as the pH increases. In the range of potentials studied (−1100 mV to 1100 mV), only the boron compounds could be reduced irreversibly. The dependence of the reduction potentials on the pH was studied for the Ni(II) complexes. For some of the complexes, in acidic solutions (pH 2.2), namely [PW11Ni(H2O)O39]5−, a new species, resulting from the two-electron reduction, was observed. This was attributed to an isomerization α → β of the reduced anions.

Nephrotoxicity of CCA-treated wood: A comparative study with As2O5 and CrO3 on mice

The purpose of this work was to assess the acute toxicity on male mice to a chromated copper arsenate (CCA) solution, a widespread wood preservative used in building industry until 2002. Animals were subcutaneously injected with CCA (7.2mg/kg arsenic and 10.2mg/kg chromium per body weight), CrO(3) (10.2mg/kg), As(2)O(5) (7.2mg/kg) and NaCl (0.9%) per se, during 48h and 96h, for histopathology, histochemistry, chromium and arsenic analysis. The results showed some histopathological changes within renal tubules lumen of CCA exposed animals (during 48h, and 96h), and CrO(3) (for the period of 96h). Furthermore, the renal levels of arsenic and chromium in treated animals were statistically more evident than controls. Although, the same contents of pentavalent arsenic and hexavalent chromium were injected into treated animals with CCA and with the prepared solutions of As(2)O(5) and CrO(3), a different distribution of the pattern of these compounds was observed in kidneys.

The chemistry of uranium dispersion in groundwaters at the Pinhal do Souto Mine, Portugal

Solution studies of H-autunite, H2(UO2)2(PO4)2, and its K+, Na+, Li+, Ca2+, Mg2+, Cu2+ and Ni2+ analogues, have been carried out and solution stability constants determined. These values are in excellent agreement with those recently reported by other workers at 298.2 K and ionic strength equal to zero. separate field study involving groundwaters collected from the oxidized zone of the Pinhal do Souto mine, Portugal, has been undertaken. Here the principal uranium minerals are autunite, Ca(UO2)2(PO4)2·nH2O and torbernite Cu(UO2)2(PO4)2·nH2O. Detailed analyses of and calculations of species distributions in these samples indicate that currently circulating groundwaters are undersaturated with respect to these two minerals by two to four orders of magnitude. The mineralogical and geochemical significance of these results is discussed.

Effect of Cr(V) on reproductive organ morphology and sperm parameters: An experimental study in mice

BackgroundCr(V) species are formed during the intracellular reduction of Cr(VI), a ubiquitous environmental pollutant. In this study, the acute toxicity of a physiologically stable Cr(V) compound, [CrV-BT]2- (BT = bis(hydroxyethyl)aminotris(hydroxymethyl)methane) was investigated in the male reproductive system of sexually mature 60-day-old male ICR-CD1 mice.MethodsEight-week-old animals were subcutaneously injected daily with a dose of ca 8 μmol of Cr/mouse, during 5 days. The control group was injected with 0.5 mL of BT buffer. Testis and epididymis morphology was evaluated using light and transmission electron microscopy. Epididymal sperm counts, motility and acrosome integrity were also assayed using standard methods.ResultsSeminiferous epithelium abnormalities were detected in the CrV-BT experimental group, including intraepithelial vacuolation, and remarkable degeneration of Sertoli cells, spermatocytes and spermatids. The premature release of germ cells into the tubular lumen was also evident. Histological evaluation of epididymal compartments revealed apparently normal features. However, the epididymal epithelium presented vacuolation. [CrV-BT]2- induced a reduction in sperm acrosome integrity. However, sperm motility and density were not significantly affected.ConclusionThis in vivo study using a Cr(V) compound, provides evidence for the potential reproductive hazards caused on male reproductive system by species containing chromium in intermediate oxidation states.

Photochemical studies of the MoVI citric acid complex Mo2O5OH(H2O)(C6H5O7)2

SummaryThe bridged dimeric MoVI complexes of citric acid M2[Mo2O5OH(H2O)(C6H5O7)] · 0.5 H2O, M=K+, NH4+, have been synthesized. In the solid state they undergo an irreversible photochemical reaction to yield CO2, MoV species and acetone dicarboxylic acid. In aqueous solution the ligand decomposition proceeds further to yield acetone as the main product. The results are compared with other related studies.