			Home About us Contact

Exhaustive Study (exhaustive + study)

Distribution by Scientific Domains

Chemistry	50%
Polymers and Materials Science	33%

Selected Abstracts

Cloud point preconcentration prior to capillary zone electrophoresis: Simultaneous determination of platinum and palladium at trace levels

ELECTROPHORESIS, Issue 18 2005
Soledad Cerutti Professor
Abstract The incorporation of a cloud point extraction (CPE) step prior to capillary electrophoresis (CE) for simultaneously determining platinum and palladium at sub-,g/L levels is presented and evaluated. The analytes were extracted as 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol complexes, at pH,2.0, mediated by micelles of the nonionic surfactant polyethyleneglycolmono- p -nonylphenyl ether (PONPE 7.5). The separation,determination step was developed from 150,,L of the extracted surfactant-rich phase diluted with 50,,L of acetonitrile (ACN). An exhaustive study of the variables affecting the cloud point extraction with PONPE 7.5 and the CZE step was done. The type and composition of the background electrolytes (BGEs) were investigated with respect to separation selectivity, reproducibility, and stability. A BGE of 50,mM monobasic sodium phosphate containing 30% ACN, pH 4.53 was found to be optimal for the separation of metal chelates. Detection was performed at 576,nm. An enrichment factor of 250 was obtained for the preconcentration of 50,mL of sample solution. The detection limits for the preconcentration of 50,mL of sample were 0.04,,g/L for Pt and 0.08,,g/L for Pd. As an analytical demonstration, ultratrace concentrations of platinum and palladium were conveniently quantitated in spiked water and urine samples. [source]

Biomimetic Self-Assembly of Tetrapeptides into Fibrillar Networks and Organogels

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 27 2008
Sajid Iqbal
Abstract The self-assembly features of a family of tetrapeptides with a silk-inspired structure are presented. An exhaustive study of the influence of the terminal alkyl chain length in this process is undertaken. Scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD), FTIR spectroscopy, and circular dichroism were used for structural analysis. These compounds, as in the natural model, self-assemble into antiparallel ,-sheet structures that further organize to form fibrillar aggregates. Furthermore, some of them arecapable of forming a crowded network that entraps thesolvent leading to physical gels with different microscopic morphologies. A model for the assembly process is proposed.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

Conformationally Biased Selective Alkylation of trans -Cyclohexane-1,2-bis(sulfonamide) Assisted by Solvent-Tuned Protecting Groups: Applications to the Synthesis of a Large Optically Active Polyazamacrocycle,

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 17 2006
Carmen Peña
Abstract The selective alkylation of (R,R)-cyclohexane-1,2-bis(sulfonamide) with trityl bromoalkyl ethers has been studied in detail. The major formation of either mono- or dialkylated compounds clearly depends on the right combination of protecting groups and the reaction solvent. An exhaustive study suggests that this effect can be reasonably explained by the conformational preferences of the monoalkylated compounds, which also depend on the reaction medium, solvophobic effects and weak intramolecular interactions. Structural analysis by NOE measurements showed the presence of folded conformations in solution for all the tested examples. Monte Carlo conformational searches supported this proposal, showing a very good correlation between the fraction of folded species and the selectivity towards monoalkylation. Finally, tuning of the reaction conditions, leading to either extended or folded conformations of the monoalkylated synthetic intermediates, was exploited for the efficient synthesis of a large optically active polyazamacrocycle. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

Influence of Activation Temperature on Reaction Kinetics in Recycled Clay Waste,Calcium Hydroxide Systems

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2008
Moisés Frías
Obtaining pozzolanic materials from recycling of industrial waste and byproducts is a priority action of environmental policy all over the world. This paper describes the effect of activation conditions on the reaction kinetics in calcined clay waste (CCW)/calcium hydroxide systems. The CCW used in this work shows excellent qualities for use as supplementary cementing material in the manufacture of commercial blended cements. This research work presents an exhaustive study about the kinetics of a pozzolanic reaction in this cementing system. The results obtained by different techniques (DTA/TG, X-ray diffraction, and SEM/EDAX) confirm that the activation conditions (in the range 700°,800°C and 2,5 h of retention) have a direct effect on the formation and evolution of hydrated phases. Low activation temperatures favor the CSH gels' formation, while at higher temperatures aluminates (C4AH13) and aluminum silicate hydrates (C4ASH8, hydrotalcites) are predominant. [source]

On the Use of the Nanoindentation Unloading Curve to Measure the Young's Modulus of Polymers on a Nanometer Scale

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 22 2005
Davide Tranchida
Abstract Summary: The nanoindentation test is a fundamental tool to assess the link between morphology and mechanical properties. The preliminary results of a more exhaustive study about the applicability to polymers of the most used procedure to determine elastic modulus by indentation are reported in this short communication. A departure of the experimental conditions from the theoretical assumptions and results that give rise to the Oliver and Pharr analysis is shown to occur under a wide range of experimental conditions, with applied loads and penetration depths covering several orders of magnitude and using different indenter geometries. Unloading curves with exponents significantly larger than 2 are observed in disagreement with the contact mechanics approach used by Oliver and Pharr. An AFM image obtained in non contact mode of an indentation induced by a sharp AFM tip with a maximum applied load of ca 1.2 µN on amorphous PET. [source]

Structural study of the low-temperature phase of TlH2PO4 at 180,K

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2002
E. Álvarez-Otero
The low-temperature phase of TlH2PO4 has been studied by X-ray diffraction. A structural model is proposed with space group P. This model is compared with the structure of the antiferroelectric phase of TlD2PO4 at room temperature to analyze the expected isomorphism at low temperature. Given the structural distortion of TlH2PO4, such isomorphism present in the common high-temperature phase is not recovered in this phase. Through the analysis of the displacements of the PO4 groups there is some evidence that the ordering of the H atoms responsible for the appearance of antiferroelectricity seems to be incomplete. An exhaustive study of the detected ferroelastic domains is also performed. [source]