Interactions Of Chromium Research Articles

Cell viability after simultaneous interactions of chromium(III) and iron(III)

Cell viability after simultaneous interactions of chromium(III) and iron(III)

English

Chromium(III), copper(II) and lead(II) are among the heavy metals produced and released in large amounts by anthropogenic sources worldwide, including Burkina Faso. Previous studies have demonstrated the successful application of domestic natural mixed clays for the removal of these metal ions as a cheap and environmentally friendly method. Qualitative mineralogical characterization of the clays revealed that they consist of kaolinite, illite, orthrose and quartz, and minor quantities of albite and montmorillonite. pHPZC for the clays, as determined by potentiometric titrations, are in the range 6.8 to 7.3. In this study, the interactions of chromium(III), copper(II) and lead(II) ions with these clay minerals were examined by the use of extended X-ray absorption fine structure (EXAFS) spectroscopy. Cr3+ forms tetrameric hydrolysis complexes on the mineral surface with a Cr–O bond distance of 1.98 A, and two Cr···Cr distances at 3.02 and 3.62 A. This is indicative of a tetrameric [Cr4(OH)6(H2O)12]6+ entity bound to the clay mineral surface. A distance of 3.17 A, regarded as a Cr···Fe distance, indicates that one Cr3+ ion in the hydrolyzed tetramer binds to two oxygens in the mineral surface which are bound to either one or two iron(III) ions in the surface. Pb2+ binds two oxygen atoms at an average bond distance of 2.31 A, with a significant contribution of linear multiple scattering from the PbO2 entity. The EXAFS results of Cr3+ sorption are consistent with the presence of a hydrolysis product of polymeric Cu2+ species with a surface complex or precipitate. Key words: Sorption, extended X-ray absorption fine structure (EXAFS) spectroscopy, clay, precipitation, Burkina Faso.

Interactions of Chromium (III) and Chromium (VI) with Bovine Serum Albumin Studied by UV Spectroscopy, Circular Dichroism, and Fluorimetry

In the present work, the interactions of bovine serum albumin (BSA) with chromium (III) chloride, potassium dichromate, and chromate were studied by fluorescence, circular dichroism, and UV-vis absorbance spectroscopy. Fluorescence quenching of BSA by chromium (III) was found to be a dynamic process in the beginning, turning static at later stages. Spectroscopic data show that both dichromate and chromate bind in similar electrostatic fashion to BSA and does not follow the fluorescence quenching observation for chromium (III).

Mechanisms of heavy metal sorption on alkaline clays from Tundulu in Malawi as determined by EXAFS

Chromium(III), copper(II), zinc(II), cadmium(II), mercury(II) and lead(II) cations are among the most common heavy metal pollutants in industrial waste waters. In our continued work on cost effective wastewater heavy metal removal agents and methods using local material, this study examines the interactions of chromium(III), copper(II), zinc(II), cadmium(II), mercury(II) and lead(II) cations with natural mixed clay minerals from Tundulu in Malawi using extended X-ray absorption fine structure (EXAFS) spectroscopy. The mixed clays were previously characterised and found to contain illite, low ordered kaolinite, mixed layer minerals and the non-clay mineral carbonate fluoroapatite with a mean pH PZC of 9.63. The EXAFS analyses provided qualitative evidence that oxygen atoms occupy the first coordination shells in all the studied central atoms. The metal species on the clay mineral surfaces seem to be adsorbates and/or precipitates of hydrolysis products. Chromium(III) forms a polynuclear hydrolysis complex on the mineral surface with Cr–O bond and Cr⋯Cr distances of 2.00 and 3.03 Å, respectively, which is indicative of a chain structure with edge sharing CrO 6 octahedra. Copper(II) is bound to phosphate groups on the surface at low pH and has a first shell of coordinated oxygen atoms with Jahn–Teller distortion as revealed by different Cu–O bonds of 1.96 Å for the equatorial ones, at 2.30 and 2.65 Å for the axial oxygens, and a Cu–P distance at 3.29 Å is distinguished as well. Upon treatment at neutral pH copper(I) oxide seems to be the main precipitation product on the clay surface. At neutral pH zinc(II) forms also polynuclear hydrolysis complexes with Zn–O bond and Zn⋯Zn distances of 2.01 and 3.11 Å, respectively, which shows the presence of edge sharing ZnO 4 tetrahedra. Cadmium(II) is adsorbed to the clay surfaces as a six-coordinated CdO 6 complex in octahedral fashion, but it is not possible to distinguish if cadmium is hydrated or partly hydrolysed. Mercury(II) is present as linear O–Hg–O units but without any observable Hg⋯Hg distance at high pH showing that mercury(II) is hydrolysed but not present as mercury(II) oxide. At low pH, linear O–Hg–Hg–O units are present showing that mercury(II) is reduced to mercury(I). No precise chemical environment around the lead(II) could be obtained for the lead(II) treated clays due to formation of different hydrolysis structures with multiple coordination numbers by lead(II) salts on the mixed clays.

Interactions of chromium(III) complexes with hydrous .delta.-alumina: rearrangements in the coordination sphere studied by electron spin resonanace and electron spin-echo spectroscopies

Chromium(III) complex binding mechanisms to hydrous δ-Al 2 O 3 are investigated by applying ESR and ESEEM spectroscopies. Adsorption isotherms of the Cr(H 2 O) 6 3+ and the Cr(oxalate) 3 3− complexes can ben monitored adequately either by conventional analysis (AAS) or by measuring the spin concentration of the adsorbed species. Because of the inertness of chromium(III) species, time-resolved changes of ligand exchange reactions can be identified. Optical reflectance and ESR spectra indicate the gradual transition from outer-sphere to inner-sphere binding mechanisms