Na6Li4MO4(CO3)4 (M = W and Mo): An Alternative Electrolyte for High-Temperature Electrochemical Cells.

Two new acentric oxycarbonates Na6Li4MO4(CO3)4 (M = W and Mo) were synthesized via a conventional solid-state route. Their structure was determined from X-ray diffraction data on single crystals. Na6Li4MO4(CO3)4 (M = W and Mo) crystallizes in the acentric cubic P-43m space group (a ≈ 7.15 Å). It is composed of MLi4O16 units built from MO4 and LiO4 tetrahedra and linked by CO32- groups to form a three-dimensional framework in which Na+ ions are inserted. We showed from differential scanning calorimetry and powder X-ray diffraction experiments that the melting is congruent (T ∼525 °C). In the solid and molten forms, conductivity was measured for both oxycarbonates by electrochemical impedance spectroscopy with three various gas compositions (CO2 100 vol %, CO2-air 70-30 vol %, and CO2-air 20-80 vol %). Each time, the stability of the electrical behavior was checked via heating and cooling cycles. The conductivity of both solid and molten phases is purely ionic and in the same order of magnitude as for the classical molten alkali electrolyte made of Li-Na or Li-K carbonates. As activation energies are also comparable, those new oxycarbonates appear to be promising electrolytes for electrochemical devices.

On the High Sensitivity of Corrosion Resistance of NiTi Stents with Respect to Inclusions: An Experimental Evidence.

In this study, the electrochemical breakdown potentials (E b) of NiTi stents were assessed in correlation to their nonmetallic inclusion fractions in the extra low inclusion (ELI) range (inclu.% < 1% in area fraction, average size <39 µm). Quantitative investigations were performed to study the role of nonmetallic inclusions during pitting corrosion. Two stent samples with different inclusion fractions were fabricated using commercial NiTi tubes for studying the corrosion and mechanism. A survey of seven commercial stents in Europe was also conducted. Dependence was observed between the breakdown potentials and the inclusion fractions in the ELI stent (inclu.% = 0.2-0.8%), in which the breakdown potentials were found to be inversely proportional to inclusion fractions and densities (E b dropped from ∼800 to ∼400 mV). No breakdown occurred on the samples using high-purity NiTi materials (inclu.% < 0.1%). The roles of inclusions in pitting mechanisms were investigated using scanning electron microscopy (SEM) characterizations. The microstructural evidence showed that the impact of TiC and Ti2NiO x was very different in the pitting process. A maximum inclu.% ≤ 0.9% was required for obtaining E b ≥ 600 mV to meet the Food and Drug Administrations (FDA's) in vivo safety acceptance (low risk up to 6 months postimplantation). The high-purity stents (inclu.% < 0.1%) did not exhibit corrosion susceptibility until 1000 mV, suggesting superior corrosion resistance and thus long-term in vivo safety.

Pseudomonas aeruginosa manipulates redox and iron homeostasis of its microbiota partner Aspergillus fumigatus via phenazines.

The opportunistic fungal pathogen Aspergillus fumigatus is increasingly found as a coinfecting agent along with Pseudomonas aeruginosa in cystic fibrosis patients. Amongst the numerous molecules secreted by P. aeruginosa during its growth, phenazines constitute a major class. P. aeruginosa usually secreted four phenazines, pyocyanin (PYO), phenazine-1-carboxamide (PCN), 1-hydroxyphenazine (1-HP) and phenazine-1-carboxylic acid (PCA). These phenazines inhibited the growth of A. fumigatus but the underlying mechanisms and the impact of these four phenazines on A. fumigatus biology were not known. In the present study, we analyzed the functions of the four phenazines and their mode of action on A. fumigatus. All four phenazines showed A. fumigatus growth inhibitory effects by inducing production of reactive oxygen species (ROS), specifically O2(·-), and reactive nitrogen species (RNS), ONOO(-). A. fumigatus Sod2p was the major factor involved in resistance against the ROS and RNS induced by phenazines. Sub-inhibitory concentrations of PYO, PCA and PCN promote A. fumigatus growth by an independent iron-uptake acquisition. Of the four phenazines 1-HP had a redox-independent function; being able to chelate metal ions 1-HP induced A. fumigatus iron starvation. Our data show the fine-interactions existing between A. fumigatus and P. aeruginosa, which can lead to stimulatory or antagonistic effects.

Electrochemical detection of nitromethane vapors combined with a solubilization device.

During the past decade, the number of terrorism acts has increased and the need for efficient explosive detectors has become an urgent worldwide necessity. A prototype, Nebulex™, was recently developed in our laboratory. Basically, it couples the solubilization of an analyte from the atmosphere by a nebulization process and in-situ detection. This article presents the development and integration of an electrochemical sensor for the detection of nitromethane, a common chemical product that can be used to make an improvised explosive device. A gold screen-printed electrode was used in a flow-cell and a detection limit of 4.5 µM was achieved by square wave voltammetry. The detection method was also determined to be selective toward nitromethane over a large panel of interfering compounds. Detection tests with the Nebulex™ were thus carried out using a custom-made calibrated nitromethane vapor generator. Detection times of less than one minute were obtained for nitromethane contents of 8 and 90 ppmv. Further measurements were performed in a room-measurement configuration leading to detection times in the range of 1-2 min, clearly demonstrating the system's efficiency under quasi-real conditions.

Detergent binding as a sensor of hydrophobicity and polar interactions in the binding cavities of proteins.

To evaluate the role of hydrophobic and electrostatic or other polar interactions for protein-ligand binding, we studied the interaction of human serum albumin (HSA) and beta-lactoglobulin with various aliphatic (C10-C14) cationic and zwitterionic detergents. We find that cationic detergents, at levels that do not cause unfolding, interact with a single site on beta-lactoglobulin and with two primary and five to six secondary sites on HSA with an affinity that is approximately the same as that with which zwitterionic (dimethylamineoxide) detergents interact, suggesting the absence of significant electrostatic interactions in the high-affinity binding of these compounds. The binding affinity for all of the groups of compounds was dependent upon hydrocarbon chain length, suggesting the predominant role of hydrophobic forces, supported by polar interactions at the protein surface. A distinct correlation between the binding energy and the propensity for micelle formation within the group of cationic or noncharged (nonionic and zwitterionic) detergents indicated that the critical micellar concentration (CMC) for each of these detergent groups, rather than the absolute length of the hydrocarbon chain, can be used to compare their hydrophobicities during their interaction with protein. Intrinsic fluorescence data suggest that the two primary binding sites on serum albumin for the zwitterionic and cationic compounds are located in the C-terminal part of the albumin molecule, possibly in the Sudlow II binding region. Comparisons with previous binding data on anionic amphiphiles emphasize the important contribution of ion bond formation and other polar interactions in the binding of fatty acids and dodecyl sulfate (SDS) by HSA but not by beta-lactoglobulin. Electrostatic interactions by cationic detergents played a significant role in destabilizing the protein structure at high binding levels, with beta-lactoglobulin being more susceptible to unfolding than HSA. Zwitterionic detergents, in contrast to the cationic detergents, had no tendency to unfold the proteins at high concentrations.

Thermodynamic study of the protonation of dimethyldodecylamine N-oxide micelles in aqueous solution at 298 K. Establishment of a theoretical relationship linking critical micelle concentrations and pH.

Dodecyldimethylamine N-oxide (DDAO) is a zwitterionic surfactant with acid-base properties. The proton dissociation constant of this surfactant was determined by a novel potentiometric method at "controlled chemical potential" of the proton using a classical pH-glass electrode. When the DDAO was in its monomeric form, the pKa was about 5, consistent with the value commonly reported in the literature. However, a unique proton dissociation constant specific to the micellar form of this surfactant could not be obtained. We found that the acid-base behavior of the DDAO micelles depended on their environment. Indeed, we were able to establish thermodynamic relations linking the critical micellar concentration to the degree of protonation of the micelles. The experimental values were in good accordance with this model.