NMR Study of the Reductive Decomposition of [BMIm][NTf2 ] at Gold Electrodes and Indirect Electrochemical Conversion of CO2.

Potential controlled electrolyses of [BMIm][NTf2 ] ionic liquid were performed at a gold cathode under nitrogen atmosphere. The structures of the major conversion products of the BMIm+ cation were elucidated on the basis of 1D and 2D nuclear magnetic resonance (NMR) analyses and gas chromatography (GC) analysis of the volatile compounds. Recombination of the imidazol-2-yl radicals, generated at the electrode by single electron transfer, leads to neutral diastereomeric dimers in equal proportions, with a faradaic efficiency of 80 %, while disproportionation of these radicals and/or reaction with hydrogen atoms adsorbed at the electrode generates a neutral monomer with 20 % faradaic efficiency. Both pathways also yield the N-heterocyclic carbene imidazolin-2-ylidene, which is involved in fast proton exchange with the parent BMIm+ cation. The reductive decomposition products of the BMIm+ cation are no longer detected if the pre-electrolysed sample is reacted with CO2 , which undergoes an indirect reduction and generates the carboxylate adduct.

Electrochemical discrimination between G-quadruplex and duplex DNA.

Analytical tools enabling the discrimination between duplex DNA and G-quadruplex DNA are necessary to unravel the biological function(s) of G-quadruplexes. A methodology relying on the electrochemical response of the electroactive hexaammineruthenium(III) cation at DNA-modified surfaces is presented. A characteristic voltammetric peak is evidenced for all the investigated G-quadruplex sequences, encompassing various types of folding and numbers of quartets. In contrast, no such peak is detected for dsDNA sequences. The occurrence of the voltammetric peak is the consequence of a strong association between the hexaammineruthenium ligand and the surface-immobilized G-quadruplexes. The peak potential points to a significant contribution of nonelectrostatic interactions between the electroactive ligand and G-quadruplexes. The very good efficiency of the discrimination methodology is demonstrated by comparing a G-quadruplex and its corresponding duplex.

Elongated thrombin binding aptamer: a G-quadruplex cation-sensitive conformational switch.

Aptamer-based biosensors offer promising perspectives for high performance, specific detection of proteins. The thrombin binding aptamer (TBA) is a G-quadruplex-forming DNA sequence, which is frequently elongated at one end to increase its analytical performances in a biosensor configuration. Herein, we investigate how the elongation of TBA at its 5' end affects its structure and stability. Circular dichroism spectroscopy shows that TBA folds in an antiparallel G-quadruplex conformation with all studied cations (Ba(2+), Ca(2+), K(+), Mg(2+), Na(+), NH(4)(+), Sr(2+) and the [Ru(NH(3))(6)](2+/3+) redox marker) whereas other structures are adopted by the elongated aptamers in the presence of some of these cations. The stability of each structure is evaluated on the basis of UV spectroscopy melting curves. Thermal difference spectra confirm the quadruplex character of all conformations. The elongated sequences can adopt a parallel or an antiparallel structure, depending on the nature of the cation; this can potentially confer an ion-sensitive switch behavior. This switch property is demonstrated with the frequently employed redox complex [Ru(NH(3))(6)](3+), which induces the parallel conformation at very low concentrations (10 equiv per strand). The addition of large amounts of K(+) reverts the conformation to the antiparallel form, and opens interesting perspectives for electrochemical biosensing or redox-active responsive devices.

Waste electrical and electronic equipments as urban mines in Burkina Faso: Characterization and release of metal particles.

Like other developing countries, Burkina Faso is one of the preferential destinations for second-hand electrical and electronic equipments (EEE). At the end of their life, these EEEs are classified as waste electrical and electronic equipment (WEEE) including Printed Circuit Boards (PCB). A particle size reduction is realized for the release of metals by shredding and grinding to obtain particles smaller 1.5 mm. A granulometric sorting was realized and nine granulometric portions were obtained. Particles were characterized by optical microscopy and Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (EDS). The experiments confirmed that the fractions contained polymers, glass fibers and metals under the form of single metals or alloys. The release of metal was efficient for particles with a size smaller than 0.71 mm. Three digestion procedures were experimented on four components to assess the impact on metals leaching. Microwave-assisted digestion method was the best procedure, compared to the analysis methods ISO 11466: 1995, and method 3050B, adapted. The characterization by Inductively coupled plasma atomic emission spectroscopy (ICP-AES) of these PCBs exhibited important amounts of precious metals (Ag, Au, Pd) and other metals in greater quantities (Cu, Pb, Ni, Co, etc.), leading to their qualification as "Urban Mines" calling for their recovery. The characterization of metals in each granulometric portion is realized. Precious and others metals were distributed in all granulometric size portions. So granulometric size reduction was not efficient for metal separation and recovery from PCBs and alternative methods should be investigated for selective precious metal recovery.

On the interaction between [Ru(NH3)6]3+ and the G-quadruplex forming thrombin binding aptamer sequence.

The interaction between the thrombin binding aptamer (TBA), a G-quadruplex forming DNA sequence, and the electroactive hexaammineruthenium(III) cation has been studied by electrochemical methods and circular dichroism spectroscopy. When TBA is immobilised on a gold surface in a typical aptasensor configuration, the [Ru(NH3)6](3+) cation can be bound to the electrode surface through its interaction with the TBA sequence. This interaction is strong enough to enable the ruthenium complex to remain at the surface when the electrode is immersed in an electrolyte free of [Ru(NH3)6](3+), meaning that the complex does not diffuse back into the solution. A stoichiometry of 2 [Ru(NH3)6](3+) per TBA strand has been determined, indicating that the interaction differs from the conventional, non-specific electrostatic charge compensation, for which a 5 to 1 ratio would be expected between the triply charged cation and the 15 bases sequence. It is shown that this interaction takes place not only at the surface, but also when both TBA and hexaammineruthenium(III) are dissolved in solution. Under such conditions, a similar stoichiometry of 2 [Ru(NH3)6](3+) per TBA strand has been evidenced by two independent methods, namely circular dichroism spectroscopy and differential pulse voltammetry.

High charge-carrier mobility in pi-deficient discotic mesogens: design and structure-property relationship.

Hexaazatrinaphthylene (HATNA) derivatives with six alkylsulfanyl chains of different length (hexyl, octyl, decyl and dodecyl) have been designed to obtain new potential electron-carrier materials. The electron-deficient nature of these compounds has been demonstrated by cyclic voltammetry. Their thermotropic behaviour has been studied by means of differential scanning calorimetry and polarised optical microscopy. The supramolecular organisation of these discotic molecules has been explored by temperature-dependent X-ray diffraction on powders and oriented samples. In addition to various liquid crystalline columnar phases (Col(hd), Col(rd)), an anisotropic plastic crystal phase is demonstrated to exist. The charge-carrier mobilities have been measured with the pulse-radiolysis time-resolved microwave-conductivity technique. They are found to be higher in the crystalline than in the liquid crystalline phases, with maximum values of approximately 0.9 and 0.3 cm(2) V(-1) s(-1), respectively, for the decylsulfanyl derivative. Mobilities strongly depend on the nature of the side chains.