Dielectric relaxation and ac conduction of AgTlTe2 amorphous semiconductor

Measurements of the dielectric properties of AgTlTe₂ in the solid and liquid states were carried out in a wide range of frequencies and temperatures. The material shows dielectric dispersion. Cole-Cole diagrams have been used to determine the distribution parameter and the molecular relaxation time. The ac conduction mechanism and dielectric loss are attributed to correlated barrier hopping in the amorphous solid.     

Rapid determination of salbutamol in pharmaceutical preparations by chiral capillary electrophoresis

A fast and simple method of chiral capillary electrophoresis (CE) has been applied to the analysis of salbutamol in different pharmaceutical preparations. Using of a 25 mM acetate buffer (pH 5.0), containing 13.1 mg/mL carboxymethyl-beta-cyclodextrin (CM-beta-CD), an applied voltage of 20 kV and a temperature of 25 degrees C, the enantiomers of salbutamol could be separated in about 2 min. Three different pharmaceutical preparations (two syrups, one oral solution, and two kind of tablets) containing a racemate of salbutamol were injected directly in the CE system, following dilution in dimethyl sulfoxide (DMSO). Appreciable differences in the retention times were observed for salbutamol enantiomers in the different formulations studied, which were attributed to the effect of the matrix components on the electrophoretic mobility. The standard addition method was used for the calibration due to the existence of matrix interferences. Finally, the stability of the enantiomers of salbutamol in the oral solution was studied calculating the enantiomeric ratio values when the solution was injected immediately after being opened in the first case and after being opened and stored in the fridge for two months in the second case.     

Cation assisted binding and cleavage of dinitrogen by uranium complexes

The role of alkali promoters in N₂ cleavage by metal complexes remains poorly understood despite its relevance to the industrial production of ammonia from N₂. Here we report a series of alkali bound-oxo-bridged diuranium(iii) complexes that provide a unique example of decreasing N₂ binding affinity with increasing cation size (from K to Cs). N₂ binding was found to be irreversible in the presence of K. A N₂ complex could be isolated in the solid state in the presence of the Rb cation and crystallographically characterized, but N₂ binding was found to be reversible under vacuum. In the presence of the Cs cation N₂ binding could not be detected at 1 atm. Electrochemical and Computational studies suggest that the decrease in N₂ binding affinity is due to steric rather than electronic effects. We also find that weak N₂ binding in ambient conditions does not prevent alkali assisted N₂ cleavage to nitride from occurring. More importantly, we present the first example of cesium assisted N₂ cleavage leading to the isolation of a N₂ derived multimetallic U/Cs bis-nitride. The nitrides readily react with protons and CO to yield ammonia, cyanate and cyanide.

N₂ binding affinity decreases markedly in a series of isostructural U(iii)–alkali ions complexes with increasing cation size. N₂ binding is undetectable in the Cs analogue, but the first example of cesium-assisted N₂ cleavage to bis-nitride was observed at ambient condition.     

Preparation and characterization of carboxylic-containing poly(methyl methacrylate) nanolatexes

Poly(methyl methacrylate) (PMMA)-based latex particles bearing carboxylic groups at the surface were prepared via emulsion polymerization. The polymerization recipe and process were optimized in order to target monodisperse particles with diameters around 100 nm. The polymerizations were performed using 4,4-azobis(4-cyanopentanoic) acid (ACPA) as initiator and sodium dodecyl sulphate (SDS) as surfactant. The polymerization conversion was determined by both gas chromatography and gravimetry. The final latexes were characterized with respect to particle size, size distribution, surface charge density, electrokinetic properties (i.e. electrophoretic mobility vs pH and ionic strength) and colloidal stability (i.e. coagulation rate constants vs pH and stability factor vs ionic strength).     

Short,Enantiospecific Syntheses of Indolizidines 209B and 209D,and Piclavine A from Diethyl-L-Glutamate

The 1H-pyrrole derivative obtained from diethyl L -glutamate hydrochloride and tetrahydro-2,5-dimethoxyfuran was cyclized with BBr₃ to ethyl (5S)-5,6,7,8-tetrahydro-8-oxoindolizine-5-carboxylate ( 18 ). Catalytic hydrogenation of 18 over Pd/C in AcOH gave ethyl (5S,8aR)-octahydroindolizine-5-carboxylate ( 21 ), whereas hydrogenation over Rh/Al₂O₃ in EtOH/AcOH 99:1 afforded mainly ethyl (5S,8S,8aS)-octahydro-8-hydroxyindolizine-5-carboxylate ( 22 ). By functional-group interconversions, 21 was transformed into piclavine A ( 1 ) and indolizidine 209D ( 2 ). Similarly, (5R,8R,8aS)-octahydro-5-pentylindolizine-8-methanol ( 37 ), the final relay for indolizidine 209B ( 3 ), was obtained from 22 .     

Remarkable influence of surface composition and structure of oxidized iron layer on orange I decomposition mechanisms

Although the decomposition of water pollutants in the presence of metallic iron is known, the reaction pathways and mechanisms of the decomposition of azo-dyes have been meagerly investigated. The interface phenomena taking place during orange I decomposition have been investigated with the use of infrared external reflection spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. The studies presented in this paper establish that there are close relationships between the composition and structure of the iron surface oxidized layers and the kinetics and reaction pathway of orange decomposition. The influence of the molecular structure of azo-dye on the produced intermediates was also studied. There are remarkable differences in orange I decomposition between pH 3 and pH 5 at 30 degrees C. Decomposition at pH 3 is very fast with pseudo-first-order kinetics, whereas at pH 5 the reaction is slower with pseudo-zero-order kinetics. At pH 3, only one amine, namely 1-amino-4-naphthol, was identified as an intermediate that undergoes future decomposition. Sulfanilic acid, the second harmful reduction product, was not found in our studies. At pH 3, the iron surface is covered only by a very thin layer of polymeric Fe(OH)(2) mixed with FeO that ensures orange reduction by a combination of an electron transfer reaction and a catalytic hydrogenation reaction. At pH 5, the iron surface is covered up to a few micrometers thick, with a very spongy and porous layer of lepidocrocite enriched in Fe(2+) ions, which slows the electron transfer process. The fastest decomposition reaction was found at a potential near -300 mV (standard hydrogen electrode). An addition of Fe(2+) ions to solution, iron preoxidation in water, or an increase of temperature all result in an increasing decomposition rate. There is no single surface product that would inhibit the decomposition of orange. This information is crucial to perform efficient, clean and low cost waste water treatment. The findings presented here make the treatment of wastewater in the presence of metallic iron a very promising solution.     

MAOS of Sugar Phenylosazones and their Derived Pyrazoles and Triazoles

Microwave‐assisted organic synthesis (MAOS) has proven to be practical to provide heterocycles from sugar osazones; an efficient method was developed for the characterization of sugars via their osazones 1–4 using microwave irradiation. The microwave‐assisted organic synthesis irradiation technique has been applied to convert d‐arabino‐hexose phenylosazone to 2‐phenyl‐4‐(d‐arabinotetrahydroxybutyl‐1,2,3‐triazole (5), which was then oxidized to the corresponding aldehyde whose oxime 9 was transformed to 4‐cyano‐2‐phenyltriazole 10. The condensation of 7 with thiosemicarbozide gave 10. Degradation of 1 afforded mesoxaldehyde 1,2‐bisphenylhydrazone 11, which cyclized to 1‐phenyl‐4‐phenylazo‐pyrazole (12) under acidic conditions. Irradiation of 6 in HBr/AcOH afforded 4‐(d‐arabino‐2′,3′‐di‐O‐acetyl‐1′,4′‐dibromobutyl)‐2‐phenyl‐2H‐1,2,3‐triazole. The acetylated phenylosazone was converted to furopyridazine 14. The irradiation of phenylosazone with acetic anhydride in pyridine gave the respective O‐acetyl derivative, whereas with boiling acetic anhydride gave the pyrazole 14, which afforded 15 and 16.      

EVALUATION OF A FIBER-OPTIC SENSOR FOR STRAIN MEASUREMENT AND AN APPLICATION TO CONTACT MECHANICS

A surface attached fiber-optic sensor has been evaluated for maximum strain measurement capability in simple tension experiments to better understand the basic mechanisms of fiber-optic sensor failure. A fiber-optic sensor was then evaluated for its applicability to measure strains under more complex loading conditions, for example, contact strains. Experimental work has shown that while the surface attached fiber sensor fails at much lower strain levels than that achievable by conventional strain gages, unlike conventional strain gages, the fiber-optic sensor shows linearity up until the failure point. This failure point is well within the parameters for typical experiments in our laboratory. Fiber-optic sensors also showed their applicability to contact mechanics.     

Swelling effects in cross-linked polymers by thermogravimetry

A Brazilian coal power plant generates a waste composed by the fly and bottom ashes produced from coal combustion and by a spent sulfated lime generated after SO₂ capture from combustion gases. This work presents a study of the early stages of the hydration of composites formed by this waste and a type II Portland cement, which will be used for CO₂ capture. The cement substitution degrees in the evaluated composites were 10, 20, 30 and 40%, and the effect of the coal power unit waste on the hydration reaction was analyzed on real time by NCDTA, during the first 40 h of hydration. The results show that the higher is the substitution degree, the higher is the retarding effect on the cement hydration process. Actually, by respective thermogravimetric (TG) and derivative thermogravimetric (DTG) analysis on initial cement mass basis, this effect is caused by double exchange reactions among Ca and Mg components of the waste, during the first 4 h of hydration, which promote a much higher exothermic effect in the NCDTA curve, simultaneously to respective induction periods. The pozzolanic reactions, due to the presence of the waste silica and alumina containing amorphous phases, consume part of the original Ca(OH)₂ content existent in the waste in the case of 30 and 40% substituted pastes, and also from part of the Ca(OH)₂ produced in cement hydration reactions, in the case of the 10 and 20% substituted pastes.     

Hopping transport in organic semiconductor system

The electrical conductivity of cupferron and some of its divalent transition metal complexes has been studied in the temperature range 0–150°C, in the amorphous state. An important result was found; namely that the temperature dependence of the conductivity is characteristic of the Mott hopping mechanism and identical with that of layers made by evaporating Ge, Si and carbon. It seems that only the physical structure determines the mechanism of conduction in amorphous materials, while the chemical composition is of minor importance.