In‐depth diffusion of oxygen into LDPE exposed to an Ar–O2 atmospheric post‐discharge: a complementary approach between AR‐XPS and Tof‐SIMS techniques

The in‐depth oxygen diffusion into a low density polyethylene film is performed in the post‐discharge of an atmospheric plasma torch, supplied in argon as carrier gas and with or without oxygen as reactive gas. The chemical and structural properties of the polymer surface and bulk are studied in terms of plasma parameters (treatment time, power, and reactive gas flow rate). A good correlation between XPS and Fourier transform infrared spectroscopy analyses is demonstrated. The penetration depth of oxygen into the bulk of the polymer is investigated by angle resolved‐XPS and time‐of‐flight SIMS. It is shown that, depending on the plasma conditions, oxygen could penetrate up to 20–40 nm into the low density polyethylene during the atmospheric plasma treatment. Copyright © 2014 John Wiley & Sons, Ltd.     

Physico-chemical control over the single- or double-wall structure of aluminogermanate imogolite-like nanotubes

It is known that silicon can be successfully replaced by germanium atoms in the synthesis of imogolite nanotubes, leading to shorter and larger AlGe nanotubes. Beside the change in morphology, two characteristics of the AlGe nanotube synthesis were recently discovered. AlGe imogolite nanotubes can be synthesized at much higher concentrations than AlSi imogolite. AlGe imogolite exists in the form of both single-walled (SW) and double-walled (DW) nanotubes, whereas DW AlSi imogolites have never been observed. In this article, we give details on the physicochemical control over the SW or DW AlGe imogolite structure. For some conditions, an almost 100% yield of SW or DW nanotubes is demonstrated. We propose a model for the formation of SW or DW AlGe imogolite, which also explains why DW AlSi imogolites or higher wall numbers for AlGe imogolite are not likely to be formed.     

Enhanced adsorption of arsenic onto maghemites nanoparticles: As(III) as a probe of the surface structure and heterogeneity

When normalized per unit of surface area, the quantity of arsenic adsorbed at the maghemite surface remains constant for particles between 300 and 20 nm. However, nanoparticles smaller than 20 nm exhibit enhanced adsorption capacity. The origin of this observed size-dependence for adsorption or "nano effect" is unclear. Arsenic was chosen as a probe of the surface structure to explore adsorption mechanisms occurring at the surface of maghemite nanoparticles (6 nm). Two factors contributing to the enhanced reactivity of nanoscale maghemites were determined. The first is related to a size-dependent structural modification of the surface of particles and the decrease of the occupancy of the tetrahedral site that leaves vacant, highly reactive adsorption sites. In particular, there is a site localized in a six-membered iron octahedral ring. This site is the only one for which an oxidation of As(III) occurs. The second factor relates to the thermodynamics of a decrease of the surface free energy. The high density of As adsorbed at the saturation of the surface can be related to crystal growth.     

Gating of single molecule transistors: combining field-effect and chemical control

Previously we have demonstrated that several structural features are crucial for the functionality of molecular field-effect transistors. The effect of additional structural aspects of molecular wires is explored. These include the type of, the thiol binding location on, and the chemical substitutions of a conjugated system. Pentacene, porphyrin, and the Tour-Reed devices are utilized as model systems. The thiol binding location is shown to have a varied effect on the transmission of a system depending on the molecular orbitals involved. Substitution by electron withdrawing and donating groups is illustrated to have a substantial effect on the transmission of single molecule devices. The substitution effect is either a simple energy shifting effect or a more complicated resonance effect, and can be used to effectively tune the electronic behavior of a single molecule field effect transistor.     

Traumatic Stress,Chronic Ethanol Exposure,or the Combination,Alter Cannabinoid System Components in Reward and Limbic Regions of the Mouse Brain

The cannabinoid system is independently affected by stress and chronic ethanol exposure. However, the extent to which co-occurrence of traumatic stress and chronic ethanol exposure modulates the cannabinoid system remains unclear. We examined levels of cannabinoid system components, anandamide, 2-arachidonoylglycerol, fatty acid amide hydrolase, and monoacylglycerol lipase after mouse single-prolonged stress (mSPS) or non-mSPS (Control) exposure, with chronic intermittent ethanol (CIE) vapor or without CIE vapor (Air) across several brain regions using ultra-high-performance liquid chromatography tandem mass spectrometry or immunoblotting. Compared to mSPS-Air mice, anandamide and 2-arachidonoylglycerol levels in the anterior striatum were increased in mSPS-CIE mice. In the dorsal hippocampus, anandamide content was increased in Control-CIE mice compared to Control-Air, mSPS-Air, or mSPS-CIE mice. Finally, amygdalar anandamide content was increased in Control-CIE mice compared to Control-Air, or mSPS-CIE mice, but the anandamide content was decreased in mSPS-CIE compared to mSPS-Air mice. Based on these data we conclude that the effects of combined traumatic stress and chronic ethanol exposure on the cannabinoid system in reward pathway regions are driven by CIE exposure and that traumatic stress affects the cannabinoid components in limbic regions, warranting future investigation of neurotherapeutic treatment to attenuate these effects.     

Are analytical standards and reagents really reliable?

Quality assurance is one of the major challenges in analytical chemistry, whatever the scope of application. The quality of analytical standards is very seldom questioned; however, sometimes odd results are obtained, and all the other potential sources of discrepancies are eliminated. So, we investigated the reliability of three analytical standards and reagents implemented for radiochemical and chemical characterizations of nuclear waste. In particular, this work examined the purity of a source of tritiated dodecane, the trueness of a certified concentration value and the purity for a diethylenetriaminepentaacetic acid (DTPA) reagent and the trueness of a certified concentration value for a multi-anion standard used in an interlaboratory comparison exercise. It was shown that the source of tritiated dodecane contains 60 % of tritiated impurities. The trueness of the DTPA concentration certified by the supplier was questioned due to the presence of impurities in the solution. It was proven that the long-term stability of the multi-anion standard was not guaranteed for nitrite. The results clearly demonstrated that, despite the certificates delivered by the suppliers, caution has to be taken toward the reliability of the analytical standards and reagents.     

Abiotic C?C bond formation under environmental conditions: Kinetics of the aldol condensation of acetaldehyde in water catalyzed by carbonate ions (CO32−)

The role of C? C bond‐forming reactions such as aldol condensation in the degradation of organic matter in natural environments is receiving a renewed interest because naturally occurring ions, ammonium ions, NH⁺₄, and carbonate ions, CO₃^2?, have recently been reported to catalyze these reactions. While the catalysis of aldol condensation by OH^? has been widely studied, the catalytic properties of carbonate ions, CO₃^2?, have been little studied, especially under environmental conditions. This work presents a study of the catalysis of the aldol condensation of acetaldehyde in aqueous solutions of sodium carbonate (0.1–50 mM) at T = 295 ± 2 K. By monitoring the absorbance of the main product, crotonaldehyde, instead of that of acetaldehyde, interferences from other reaction products and from side reactions, in particular a known Cannizzaro reaction, were avoided. The rate constant was found to be first order in acetaldehyde in the presence of both CO₃^2? and OH^?, suggesting that previous studies reporting a second order for this base‐catalyzed reaction were flawed. Comparisons between the rate constants in carbonate solutions and in sodium hydroxide solutions ([NaOH] = 0.3–50 mM) showed that, among the three bases present in carbonate solutions, CO₃^2?, HCO₃^?, and OH^?, OH^? was the main catalyst for pH ≤ 11. CO₃^2? became the main catalyst at higher pH, whereas the catalytic contribution of HCO₃^? was negligible over the range of conditions studied (pH 10.3–11.3). Carbonate‐catalyzed condensation reactions could contribute significantly to the degradation of organic matter in hyperalkaline natural environments (pH ≥ 11) and be at the origin of the macromolecular matter found in these environments. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 676–686, 2010     

Bioactive molecules in Kalanchoe pinnata leaves: extraction, purification, and identification

Kalanchoe pinnata (Lam.) Pers. (syn. Bryophyllum pinnatum; family Crassulaceae) is a popular plant used in traditional medicine in many temperate regions of the world and particularly in South America. In Guyana, the leaves are traditionally used as an anti-inflammatory and antiseptic to treat coughs, ulcers, and sores. The purpose of this study was to implement a method for targeting and identifying molecules with antimicrobial activity, which could replace chemical preservatives in cosmetic applications. The leaves were extracted by a method based on pressurized liquid extraction (PLE), using different solvents. A study of antimicrobial activity and cytotoxicity tests were performed to select the most interesting extract. To isolate one or more active molecules, the selected crude extract was fractionated by centrifugal partition chromatography (CPC) and then antimicrobial activity and cytotoxicity of each fraction were tested under the same procedure. The last step consisted of identifying the main compounds in the most active fraction by LC-MS/MS.