Towards an understanding of solvent extraction--electroanalytical characterization of chloride-leaching solutions.

Solvent extraction has been employed to purify media simulating chloride-leaching solutions resulting from complex sulfide concentrate processing, and cyclic voltammetry (CV) has been chosen to characterize those hydrometallurgical aqueous phases. The possibilities of the CV technique were investigated by the evaluation of the adequacy of a specific organic extractant, triisobutylphosphine sulfide, aimed to efficiently and selectively extract silver from a complex chloride medium, additionally containing tenfold to 40-fold molar concentrations of iron, copper and lead. The influence of the oxidation state of the metallic ions present in the feed solution, namely Cu(II) and Cu(I), is considered. The possibilities of CV analysis for the characterization of stripping solutions are also illustrated.

Study of DNA hybridization on polypyrrole grafted with oligonucleotides by photocurrent spectroscopy.

Recognition of DNA sequences by biochemical sensor is generally performed by analysis after completion of hybridization. Using a technique able to directly translate the biological event into an electrical signal allows the in situ monitoring of the hybridization kinetics. In this aim, the photoelectrochemical behavior of one electroactive polymeric sensor based on a copolymer of polypyrrole and polypyrrole-oligonucleotide has been investigated in aqueous solution. This sensor has been studied as such (i) and in two other situations: (ii) when the copolymer is in presence of non-complementary oligonucleotides; and (iii) when the copolymer is in presence of complementary oligonucleotides. From the photocurrent spectra obtained at -0.6 V/SCE versus incident energy the allowed direct and indirect transitions for each polymer have been evidenced. The photocurrent evolution during hybridization and adsorption processes has been recorded in real time and the hybridization kinetics has revealed to be comparable with mass variations obtained by quartz crystal microbalance under the same experimental conditions.

The use of rat, rabbit or human bone marrow derived cells for cytocompatibility evaluation of metallic elements.

Rat, rabbit and human bone marrow cells were cultured according to the method previously reported for cells of rat origin [1] and were exposed, or not (control), to corrosion products of a Co-Cr orthopaedic alloy as well as to metal salts containing Co2+, Cr3+ and Cr6+. Cells were cultured for 21 days and analysed for the following biochemical parameters: intracellular MTT reduction (i.e. cell viability/proliferation), alkaline phosphatase (ALP) activity and protein production. Morphological observations included both histochemistry (detection of ALP-positive cells, calcium and phosphate deposits) and scanning electron microscopy (SEM). Control cultures of rat and rabbit cells showed higher proliferation rates than human cells at the start of culture, but they all reached similar values on day 21. Protein production was parallel to cell proliferation. In contrast, ALP activity of rat cultures was much stronger than rabbit or human cultures. All cell types were able to develop the osteogenic phenotype in vitro.Co-Cr extract caused inhibitory effects on cell viability, on ALP activity and, to a lower extent, on protein production of all rat, rabbit and human cell cultures. Compared to rat and rabbit cultures, human cultures were the most sensitive to metal ions exposure.