Facilitated ion transfer of protonated primary organic amines studied by square wave voltammetry and chronoamperometry

The transfer of the protonated forms of heptylamine, octylamine, decylamine, procaine and procainamide facilitated by dibenzo-18-crown-6 from water to a solvent polymeric membrane has been investigated by using cyclic square wave voltammetry. The experimental voltammograms obtained are in good agreement with theoretical predictions. The values of the standard ion transfer potential, complexation constant and diffusion coefficient in water have been obtained from these experiments, and have been used to draw some conclusions about the lipophilicity of these species and the relative stability of the organic ammonium complexes with dibenzo-18-crown-6. The results have been compared with those provided by linear sweep voltammetry. Calibration graphs were obtained with both techniques. An interesting chronoamperometric method for the determination of the diffusion coefficient of the target ion in the membrane has been developed and applied to all these protonated amines.     

Multipumping Nitrite Determination in Exhaled Breath Condensate

Abstract

A flow system based on multicommutation is proposed for the rapid, clean, and inexpensive determination of nitrites in small volumes of breath condensates. The procedure exploits the colorimetric detection of nitrite with the Griess reagent [0.03% naphthylethylene diamine dihydrochloride (NED), 0.5% sulpfhanilamide, and 3.0% phosphoric acid] in acidic medium at 540 nm correcting the variations of the baseline with measurements at 424 nm. The flow system was designed with a set of solenoid micropumps to minimize sample and reagent consumption and waste generation. The detection limit was estimated as 3.8 ng mL^?1 (99.7% confidence level) with a linear response ranging up to 500 ng mL^?1. The coefficient of variation was estimated as 0.7% for a solution containing 300 ng mL^?1 nitrite (n=9). Approximately 144 determinations can be carried out per hour, consuming only 678.4 µg Griess reagent and generating 1.184 mL of effluent per determination, thus providing an environmentally friendly alternative and a nonexpensive method. The procedure was successfully applied to determine nitrite in breath condensates.     

Predictable behavior of smart materials (Cu-Zn-Al SMA)

Reliability is a critical word in industrial applications of Shape Memory Alloys. Accurate and reproducible transformation hysteresis cycles and internal loops were obtained in single crystals using a high resolution automatized equipment. From a mechanical model formulated for a single martensite plate, the shape of the hysteresis cycle is obtained by generalizing the representation toN plates. The observed time effects on the hysteresis loops related to diffusion processes were also taken into account. It allows to explain the martensite recoverable creep and the micromemory effects. Also, the room temperature effects on the parent phase (for instance, summer to winter) acting over the transformation temperature are quantified.Research carried out under the project NATO 920452. Partial support from CICYT is gratefully acknowledged. V. T. acknowledges Dir. Pol. Terr. (Generalitat of Catalonia) for useful support. Fruitful discussions with Drs. F. C. Lovey and J. L. Pelegrina of CAB-Argentina (EEC-ALA/MED contract) are acknowledged.     

The structure of β-diketones related to curcumin determined by X-ray crystallography,NMR (solution and solid state) and theoretical calculations

Structural Chemistry - Structural data are reported on sixteen ketoenols of β-diketones: solution NMR, solid-state NMR (CPMAS and MAS) and X-ray crystallography (four compounds, where three...     

Strain-enhanced sintering of iron powders

Sintering of ball-milled and un-milled Fe powders has been investigated using dilatometry, X-ray, density, and positron annihilation techniques. A considerable sintering enhancement is found in milled powders showing apparent activation energies that range between 0.44 and 0.80 eV/at. The positron annihilation results, combined with the evolution of the shrinkage rate with sintering temperature, indicate generation of lattice defects during the sintering process of milled and un-milled powders. The sintering enhancement is attributed to pipe diffusion along the core of moving dislocations in the presence of the vacancy excess produced by plastic deformation. Positron annihilation results do not reveal the presence of sintering-induced defects in un-milled powders sintered above 1200 K, the apparent activation energy being in good agreement with that for grain-boundary diffusion in -Fe. PACS 81.20.Ev; 81.20.Wk; 78.70.Bj