Characterization of a new substrate for tunneling spectroscopy

An insulating layer is produced on aluminum by glow discharge in CF₄. This substrate, used as the insulator of metal-insulator-metal diodes is characterized by Inelastic Electron Tunneling Spectroscopy as an aluminum trifluoride AlF₃. The adsorption of ammonia, benzylamine. formic and propiolic acid on this substrate is investigated. A comparison between spectra of samples obtained on this insulator and on alumina for the same dopant molecules shows significant differences which are interpreted as revealing an enhanced Lewis acidity of AlF₃ relative to Al₂O₃, determined — at least in part — by an enhanced electronegativity of surface Al⁺ cations of AlF₃.     

Multielemental speciation of trace elements in estuarine waters with automated on-site UV photolysis and resin chelation coupled to inductively coupled plasma mass spectrometry

An integrated approach for the accurate determination of total, labile and organically bound dissolved trace metal concentration in the field is presented. Two independent automated platforms consisting of an ultraviolet (UV) on-line unit and a chelation/preconcentration/matrix elimination module were specifically developed to process samples on-site to avoid sample storage prior to inductively coupled plasma mass spectrometry (ICP-MS) analysis. The speciation scheme allowed simultaneous discrimination between labile and organic stable dissolved species of seven trace elements including Cd, Cu, Mn, Ni, Pb, U and Zn, using only 5 ml of sample with detection limits ranging between 0.6 ng l⁻¹ for Cd and 33 ng l⁻¹ for Ni. The influence of UV photolysis on organic matter and its associated metal complexes was investigated by fluorescence spectroscopy and validated against natural samples spiked with humic substances standards. The chelation/preconcentration/matrix elimination procedure was validated against an artificial seawater spiked sample and two certified reference materials (SLRS-4 and CASS-4) to ensure homogenous performance across freshwater, estuarine and seawater samples. The speciation scheme was applied to two natural freshwater and seawater samples collected in the Adour Estuary (Southwestern, France) and processed in the field. The results indicated that the organic complexation levels were high and unchanged for Cu in both samples, whereas different signatures were observed for Cd, Mn, Ni, Pb, U and Zn, suggesting organic ligands of different origin and/or their transformation/alteration along estuarine water mixing.     

Fully reversible procedure for silver staining improves densitometry of complex mixtures of biopolymers resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis

Due to its high sensitivity, silver staining is a widely popular method for the revelation of biopolymers separated by both native and denaturing electrophoresis. A step-by-step method for the destaining and restaining of overdeveloped/overloaded silver-stained bands is described that is applicable to both proteins and nucleic acids. The procedure significantly improves densitometric analysis of gels that have been silver stained with either commercial kits or solutions made in-house. The method permits reproducible densitometry of silver-stained gels and allows quantification of both main and minor components in complex mixture of molecules resolved on the same gel slab. All steps may be interrupted and are readily reversible, allowing for facile densitometric analyses and photographic recording under optimized conditions. Furthermore, common artifacts such as differential staining of the two gel surfaces, localized uneven yellow-ochre background, and the presence of fold marks and fingerprints can be easily removed.     

Graphical Abstract: HCA 2/2003

The synthesis and antioxidant efficiencies of amphiphilic gallic acid derivatives are reported. To specify the impact of chemical structure on the antioxidant efficiency, several structural modifications of gallic acid were performed. The following structural features were chosen: i) introduction of hydrophobic or hydrophilic residues on the gallic acid and the type of their linkage, ii) the hydrophilic and/or lipophilic character of the whole molecule. The physico‐chemical studies of the different series prepared revealed that the antioxidant efficiency of this polyphenol depends clearly on the nature of the linkage with both hydrophilic and hydrophobic parts. A push‐pull effect is always necessary, and ester or amide bonds seem well adapted to increase the antioxidant efficiency. Second, under the oxidation conditions applied, it was observed that the hydrophilic and/or lipophilic character affects drastically the antioxidant activity of gallic acid derivatives. The results obtained are in accordance with the polar paradox, hydrophobic derivatives inhibit oxidation in an aqueous phase, whereas hydrophilic products are not efficient.