Publications

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.

Abstract Excitation-emission matrices (EEM) of fluorescence of aqueous solutions of humic substances (HS), and sets of EEM acquired as function of the HS concentration, were analysed by multivariate curve resolution alternating least squares (MCR-ALS). Three types of HS samples were studied: one commercial humic acid; two samples of fulvic acid (FA) extracted from a pinewood soil; two samples of FA extracted from recycled wastes. The fluorescence measurements were carried out at HS concentration between 5 and 100 mg/L and at pH 6. The application of MCR-ALS algorithm on each individual EEM, as well as on column-wise augmented matrices, allows the identification of three major fluorophores in all HS samples analysed. The emission and excitation spectra of these fluorophores were recovered and are characteristic of each sample. Moreover, the variation of the fluorescence intensities of each fluorophore with HS concentration shows deviations from linearity at HS concentration higher than 30 mg/L, depending on the fluorophore and/or sample. This behaviour reveals the existence of inner filter effects that affect the proportionally between the fluorescent signal and concentration but do not provoke measurable distortions on the fluorescence spectra of the detected fluorophores.

Abstract Radical anions of o-, m-, and p-benzoquinone were produced in a Fourier transform mass spectrometer by low energy electron attachment or collision-induced dissociation and were differentiated. Classical derivatization experiments also were carried out to authenticate the ortho and meta anions. Gas-phase techniques were used to measure the proton affinities of all three radical anions and the electron affinities of o- and m-benzoquinone. By combining these results in thermodynamic cycles, we derived heats of hydrogenation of o-, m-, and p-benzoquinone (Delta(hyd)H degrees(1o, 1m, and 1p) = 42.8 +/- 4.1, 74.8 +/- 4.1, and 38.5 +/- 3.0 kcal mol(-1), respectively) and their heats of formation (Delta(t)H degrees(1o, 1m, and 1p) = -23.1 +/- 4.1, 6.8 +/- 4.1, and -27.7 +/- 3.0 kcal mol-1, respectively). Good accord with the literature value for the para derivative was obtained. Combustion calorimetry and heats of sublimation also were measured for benzil and 3,5-di-tert-butyl-o-benzoquinone. The former heat of formation agreed with previous determinations, while the latter result (Delta(f)H degrees (g) = -73.09 +/- 0.87 kcal mol(-1)) was transformed to Delta(f)H degrees(1o) = -18.9 +/- 2.2 kcal mol(-1) by removing the effect of the tert-butyl groups via isodesmic reactions. This led to a final value of Delta(f)H degrees) = -21.0 +/- 3.1 kcal mol(-1). Additivity was found to work well for m-benzoquinone, but BDE1 and BDE2 for 1,2- and 1,4-dihydroxybenzene differed by a remarkably small 14.1 +/- 4.2 and 23.5 +/- 3.7 kcal mol(-1), respectively, indicating that o- and p-benzoquinone should be excellent radical traps.