Publications

Abstract The build up and electrochemical characterization of interfacial composite nanostructures containing a cationic polyelectrolyte and negatively charged mercaptosuccinic acid stabilized gold nanoparticles (AuNps) is reported. The nanostructures were formed at the interface between two immiscible electrolyte solutions in which the organic phase is an immobilized 2-nitrophenyl octyl ether/PVC gel. The growth of the multilayer was verified with UV-vis spectra, and approximately a linear increase in UV-vis absorbance with increasing number of layers was observed. The interfacial capacitance of the multilayers was measured as a function of the potential and a theoretical model was developed to explain the results. The excellent agreement between theoretical and experimental capacitance curves allows us to conclude that nanocomposites behave similarly to polyelectrolyte multilayers, with the outmost layer determining the alternating sign of the outer surface charge density. Cyclic voltammograms were used to evaluate the transfer rate constant across the multilayers of a model drug, metoprolol, and the standard probe tetraethylammonium cation. The apparent rate constants were slightly larger than in other studies in the literature and decrease with the increasing number of layers.

Abstract Polyelectrolyte/gold nanoparticle multilayers composed Of poly(L-lysine) (pLys) and mercaptosuccinic acid (MSA) stabilized gold nanoparticles (Au NPs) were built up using the electrostatic layer-by-layer self-assembly technique upon a gold electrode modified with a first layer of MSA. The assemblies were characterized using UV-vis absorption spectroscopy, cyclic and square-wave voltammetry, electrochemical impedance spectroscopy, and atomic force microscopy. Charge transport through the multilayer was studied experimentally as well as theoretically by using two different redox pairs [Fe(CN)(6)](3-/4-) and [Ru(NH3)(6)](3+/2+). This paper reports a large sensitivity to the charge of the outermost layer for the permeability of these assemblies to the probe ions. With the former redox pair, dramatic changes in the impedance response were obtained for thin multilayers each time a new layer was deposited. In the latter case, the multilayer behaves as a conductor exhibiting a strikingly lower impedance response, the electric current being enhanced as more layers are added for Au NP terminated multilayers. These results are interpreted quite satisfactorily by means of a capillary membrane model that encompasses the wide variety of behaviors observed. It is concluded that nonlinear slow diffusion through defects (pinholes) in the multilayer is the governing mechanism for the [Fe(CN)(6)](3-/4-) species, whereas electron transfer through the Au NPs is the dominant mechanism in the case of the [Ru(NH3)(6)](3+/2+) pair.

Abstract (Chemical Equation Presented) Shedding light on luciferase: Luciferyl coenzyme A (1) was synthesized and it was found that luciferase catalyzes light production from luciferyl coenzyme A and AMP. The results of this study open perspectives for new bioanalytical methods and are strong evidence for the evolutionary relationship between firefly luciferase and acyl-CoA synthetases. © 2005 Wiley-VCH Verlag GmbH & Co. KGaA.

Abstract Electrochemical impedance spectroscopy and cyclic voltammetry are employed to characterize poly(styrenesulfonate)/poly(allylamine hydrochloride) multilayers assembled onto cysteamine-modified gold surfaces. The influence of the supporting electrolyte and temperature on the impedance response is studied because of both its practical interest and the need to test further the capillary membrane model recently developed by Barreira et al. [J. Phys. Chem. B 2004, 108, 17973]. The results obtained are interpreted quite satisfactorily in terms of this model, thus providing additional support to its usefulness for the description of ionic transport through polyelectrolyte multilayers. It is observed that the nature of the supporting electrolyte affects the film resistance and the electrode coverage. The temperature dependence of the diffusion coefficient is shown to follow the Arrhenius law, and the activation energy is estimated as 61 kJ/mol. Experiments with a large number of layers are also included to show that the impedance response of the multilayer then resembles that of a homogeneous membrane.

Abstract The standard enthalpy of formation and the enthalpy of sublimation of crystalline 2-hydroxyphenazine-diN-oxide, at T = 298.15 K, were determined from isoperibol static bomb combustion calorimetry and from Knudsen effusion experiments, as -76.7 +/- 4.2 kJ center dot mol(-1) and 197 5 kJ center dot mol(-1), respectively. The sum of these two quantities gives the standard enthalpy of formation in the gas-phase for this compound, Delta(f)H(m)degrees(g) = 120 6 KJ center dot mol(-1). This value was combined with the gas-phase standard enthalpy of formation for 2-hydroxyphenazine retrieved from a group estimative method yielding the mean (N-O) bond dissociation enthalpy, in the gas-phase, for 2-hydroxyphenazine-di-N-oxide. The result obtained with this strategy is < DHmdegrees (N - O)> = 263 +/- 4 KJ center dot mol(-1), which is in excellent agreement with the B3LYP/6-311+G(2d,2p)// B3LYP/6-31G(d) computed value, 265 KJ center dot mol(-1).

Abstract The standard (p degrees = 0. 1 MPa) molar enthalpies of formation, Delta(f)H degrees(m), for crystalline 1 -hydroxyisoquinoline, 5-hydroxyisoquinoline and 1,5-diidroxyisoquinoline, were derived from the standard molar enthalpies of combustion, in oxygen, at the temperature 298.15 K, measured by static bomb-combustion calorimetry. The standard molar enthalpies of sublimation, Delta(cr)(g)H degrees(m), at T = 298.15 K, were determined by Calvet microcalorimetry. The results were as follows: [GRAPHICS] The derived standard molar enthalpies of formation, in the gaseous state, are analysed in terms of enthalpic increments and interpreted in terms of molecular structure.

Abstract A method involving solid-phase micro extraction ( SPME) and gas chromatography with electron capture detection (SPME-GC-ECD) has been optimised for identification and quantification of 2,4,6-trichloroanisole (TCA) at ng L-1 concentrations in disinfected ( chlorinated) water samples. A central composite design was used for factorial analysis of four factors, three factors related to the SPME (PDMS fibre) procedure ( adsorption time, temperature of the sample during headspace sampling, and desorption time) and one related to the GC operation ( the rate of increase of the temperature of the GC oven). Good linearity ( linear correlation coefficient greater than 0.999) was observed for TCA concentrations up to 50 ng L-1, limits of detection and quanti. cation of 0.7 and 2.3 ng L-1, respectively, and good precision ( relative standard deviation 2.8% and 3.4% for 5 and 30 ng L-1 of TCA, respectively). Besides TCA, this system also enables the detection and quanti. cation of the four trihalomethanes in the mu g L-1 concentration range with limits of detection and quanti. cation of approximately 0.3 mu g L-1 and 1 mu g L-1, respectively.

Abstract Olives from three cultivars (Olea europaea Cv. Cobrancosa, Madural and Verdeal Transmontana) were subject to a biometric characterization of the fruit and endocarp. Olives were harvested in a selected olive grove, where the three cultivars are present, guaranteeing the homogeneity of the pedologic and climate conditions. Five trees from each cultivar, to a total of 15 trees, and 40 olives for each tree were picked up, to a total of 200 olives per cultivar. Each olive was characterized by 26 fruit and endocarp parameters as recommended by Conseil Oleicole Internationale (COI). A linear discriminant analysis was performed in order to assess the discrimination capacity of the measurement parameters between the three cultivars. An almost full discrimination of the olives from different cultivars was only achieved when fruit and endocarp, data was analyzed together.