Publications

Abstract Square wave voltametry (SWV) has been successfully applied to arrays of liquid/liquid (L/L) microinterfaces formed across microholes perforated on a polyester film. The study ClO4- ion transfer from water to 1,2-dichloroethane (DCE) showed that the experimental parameters E(SW), E(S), and f are identical to those found for the reversible electron transfer on solid microelectrodes.

Abstract The separation of the diastereoisomers of cinnamoyl derivatives have been studied by thin-layer (TLC) and high performance liquid chromatography (HPLC). TLC separations on two different layers and with two different solvent systems are described. HPLC separation was carried out on a reversed-phase column (Lichrosorb RP-8, 5 mu m) using an isocratic elution [acetonitrile : water-acetic acid (95 : 5)]. The series of compounds includes the cis/trans isomers of ethyl esters of caffeic, ferulic and isoferulic acids.

Abstract The variations observed in synchronous fluorescence spectra of aqucous solutions (pH = 4) of three fuivic acids (fua) upon variation of the concentration of Ai” were anaiyzed by evoiving factor anaiysis (EFA). The three fua samples were extracted from materiais present in a pine wood sou: dry pine needies and the upper and iower sou horizons. The presence of AI” induces quenching and eahancement of bands in the synchronous fluorescence spectra, and concentration constraints are pro posed for lhe EFA anaiysis that allow lhe caicuiation, on a seif-modeiing curve resolution basis, of the number of components that show iineariy independent variations, their spectra, and corresponding concentration profiles. Simuiated and experimentai data seta of simpie known com pounds (catechoi, catfeic acid, sahcyiic acid, and morin) were aiso studied as the first vaiidation of the experimental and data treatment procedures. © 1994 SocieLy for Applicd Spectroscopy.

Abstract Concentrations of Cd, Cr, Cu, Ni, Pb and Zn in surface sediments and aquatic mosses from the Cavado river basin were determined in order to evaluate the overall metal contamination and trace the main pollution sources. The natural background levels were calculated for both plants and sediments (fraction < 63 mum) collected at uncontaminated sites and concentrations were normalized to the natural levels. The maximum resulting contamination factors in the aquatic mosses ranged from 6 (Zn) to 101 (Cr). In the sediments the accumulation rates are lower, between 3 (Zn) and 18 (Pb). The degree of contamination was also evaluated by calculating a metal pollution index and the more polluted reaches were identified. Metal concentration variations in plants and sediments in two different surveys ( 1988 and 1989) were studied by factor analysis. Three factors are sufficient to characterize data variance. Factors corresponding to plants and sediments show different metal composition and provide evidence that industrial effluents and drainage waters from a mining area are the main causes of variations of element concentrations. The seasonal variations of metal concentrations both in plants and sediments are also discussed.

Abstract The radical chain addition of tosyl iodide to some alkenes has been studied. The reaction was carried out at room temperature under visible light, giving the usual high yields of beta-iodo sulfones. These adducts were transformed into the corresponding unsaturated sulfones. Relative reactivities of the addition of the tosyl radical to alkenes were measured in acetonitrile, dichloromethane and carbon tetrachloride, the effect of the solvent being important only with polarized alkenes. such as vinyl and allyl cyanides, which are stabilized in solvents with greater pi* and AN parameters. The delocalization of the unpaired electron in the adduct radicals over the carbonyl and cyano groups is not important; the phenyl group is the only group that is able to affect the reactivity. increasing it notably. Polar and steric effects are dominant in all the other cases.

Abstract For more than ten years our laboratory has been engaged in extending a modular microcalorimetric system designed for accurate work in several areas of basic and applied chemistry and biology. The system includes a very stable thermostatted water bath that can house up to four twin heat-conduction microcalorimeters. The calorimeters are used with various flow vessels or insertion vessels ranging from simple closed ampoules to stirred vessels fitted with injection tubes, devices facilitating dissolution processes (1, g, s), electrodes (pH, p(O2)), optical cables or equipment for electrochemical processes.

Abstract The variations observed in the synchronous fluorescence spectra of a soil fulvic acid, collected in the north of Portugal, with pH (between 2 and 7) and with Cu(II) concentration (at pH 3, 4, 5 and 6 and total copper concentrations between 0.005 and 4 mM depending on the pH) were studied by SIMPLISMA, a self-modelling mixture analysis technique. Three components were deeected when varying the pH, corresponding to three acid-base equilibria with pK(a) values around 3.0, 5.0 and 6.0, and their individual spectra were obtained. Two components were detected when varying the Cu(II) concentration, corresponding to two different ligand sites, and their spectra and concentration profiles (based on the two detected pure variables) were obtained. The spectrum of one binding site is similar to the component associated with the acid-base equilibrium with pK(a) = 3.0 and that of the other binding site is similar to the sum of the spectra of the components associated with the other two acid-base equilibria. Using a 1:1 stoichiometry for complex formation, complexation capacities (C-L) and stability constants (K) were calculated for the two binding sites at the four pH values. The calculated stability constants were log K-1 = 3.42(4), log K-2 = 3.05(5) at pH 3, log K-1 = 4.17(3), log K-2 = 3.71(1) at pH 4, log K-1 = 4.51(3), log K-2 = 3.95(2) at pH 5 and log K-1 = 4.57(3), log K-2 = 4.03(1) at pH 6.

Abstract Seven heat conduction calorimeters have been evaluated in terms of sensitivity and thermal response time. The use of a dynamic method to correct for the thermal inertia of the calorimeter is shown to reduce by one order of magnitude the time required to conduct a stepwise titration experiment involving a fast reaction. The ability to determine association constants of strong 1:1 complexes has been evaluated in terms of the precision of determining thermal energy.