RESUMO
The electrochemical behaviour of several cationic dextran polyelectrolytes, aminodextran (AD), cationic dextran (CD) and diethylaminoethyl dextran (DEAE-D), at the polarized water/1,2-dichloroethane interface was studied. An investigation into the influence of the scan rate, concentration, pH, the nature and the concentration of the anion present in the organic electrolyte and the effect of the polymer molecular weight is presented. Different responses were obtained and explained considering the structural difference between these species, mainly the position of the positive charge in the macromolecule. The AD polymer is not transferred to the organic phase, regardless of molecular weight, while CD and DEAE-D are transferred from the aqueous to the organic phase at E = 0.650 V, independent of the polymer concentration and of the molecular weight. The shape of the voltammograms corresponding to DEAE-D transfer as well as the magnitude of the peak currents and the peak potential values were all dependent on the pH of the aqueous phase solution and on the nature and concentration of the anion present in the organic electrolyte. Based on this dependence, we postulated a mixed mechanism, which involves the transfer of dissolved and adsorbed DEAE-D molecules.
Assuntos
Dextranos/química , Eletrólitos/química , Dicloretos de Etileno/química , Água/química , Cátions , Eletroquímica , Concentração de Íons de Hidrogênio , Estrutura Molecular , Peso MolecularRESUMO
The interaction of Co hexagonal magnetic nanoparticles (MNPs) with distearoyl phosphatidyl glycerol (DSPG) and distearoyl phosphatidic acid (DSPA) films adsorbed at a water/1,2-dichloroethane interface is studied employing cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), capacity curves and interfacial pressure-area isotherms. DSPA and DSPG adsorb at the interface forming homogenous films and producing a blocking effect on the transfer process of tetraethyl ammonium (TEA(+)), used as a probe cation. In the presence of Co NPs this effect is reversed and the reversible transfer process for TEA(+) is reestablished, to a greater or lesser extent depending on the structuration of the film. Co-DSPA hybrid films have a homogeneous structure while Co-DSPG films present different domains. Moreover, the presence of Co on DSPA film modifies the partition coefficient of the organic electrolyte into the hydrocarbon layer.
Assuntos
Nanopartículas de Magnetita/química , Fosfolipídeos/química , Adsorção , Dicloretos de Etileno/química , Ácidos Fosfatídicos/química , Fosfatidilgliceróis/química , Propriedades de Superfície , Água/químicaRESUMO
The transfer of six dendritric molecules, DMs, across the water/1,2-dichloroethane interface was investigated using cyclic voltammetry. From the variation of peak potential with pH, two different mechanisms of transfer were postulated depending on the nature of the molecules. Voltammetric parameters were employed to evaluate the hydrophilic/hydrophobic character and calculate the acid dissociation constant of these molecules. The results were explained taking into account the nature and multiplicity of functional surface groups.
Assuntos
Dendritos/metabolismo , Eletroquímica/métodos , Dicloretos de Etileno/química , Água/química , Físico-Química/métodos , Concentração de Íons de Hidrogênio , Espectroscopia de Ressonância Magnética , Modelos Biológicos , Modelos Químicos , Nanopartículas , Nanotecnologia/métodos , Solventes/química , Espectroscopia de Infravermelho com Transformada de Fourier , Propriedades de SuperfícieRESUMO
This work presents the second phase of a groundwater remediation program for the migration control of a 1,2-dichloroethane (1,2-DCA) contaminated plume which includes natural attenuation at a distance downgradient from the source area. The conceived system for the plume migration control, implemented just after a major accidental release of 1,2-DCA in the soil, included a 300 m long physical barrier (cement-bentonite diaphragm wall) and 12 extraction wells. Results of field investigations have provided evidence that 1,2-DCA was naturally biodegrading into vinyl chloride as well as ethene under the natural anaerobic-reducing conditions at the site. In that case, source control measures were implemented to accelerate the overall remediation process. Although the results are favorable, the natural degradation of the 1,2-DCA does not guarantee acceptable levels of concentrations. Therefore, a pilot test to evaluate the enhancement of these processes is being carried out through the use of a biosparging system. This test is being implemented near the source to achieve sequential aerobic-anaerobic treatment zones.
Assuntos
Água Doce/química , Hidrocarbonetos Clorados/química , Dióxido de Silício/química , Poluentes Químicos da Água/análise , Poluição Química da Água/análise , Biodegradação Ambiental , Dicloretos de Etileno/química , Movimentos da Água , Poluição Química da Água/prevenção & controleRESUMO
Mercuric bromide-promoted glycosylation of Fmoc-Ser-OBn and Fmoc-Thr-OBn with 2-acetamido-2-deoxy-3,4,6-tri-O-acetyl-alpha-D-glucopyranosyl chloride in refluxing 1,2-dichloroethane gave the corresponding beta-glycosides in good yields (64 and 62%, respectively). Direct coupling of the commercially available Fmoc-Ser-OH and Fmoc-Thr-OH carboxylic acids under similar conditions gave the corresponding beta-glycosides, possessing free carboxyl groups, in moderate yields (50 and 40%, respectively).