Publications

Abstract Cyclic, differential pulse and square wave voltammetry were applied to develop an electroanalytical procedure for the determination of a group of herbicides used to treat rice crops: molinate, bensulfuron-methyl, mefenacet and thiobencarb. The oxidation mechanism causes adsorption problems and consequent poisoning of the electrode surface by the products of the electrochemical reaction. Parameters such as pH, frequency and electrochemical electrode surface treatment were optimized. The analytical methodology developed using square wave voltammetry was applied to the determination of molinate and bensulfuron-methyl in simple or mixed commercial products.

Abstract In this work several methods for evaluation of the degree of lipid oxidation and antioxidant activity are reviewed. Some aspects related to the recent advances mentioned in the literature are also reported.

Abstract Binary and ternary mixtures of some of the following heavy metal ions Zn(II), NI(II), Pb(II), Co(II) and Cd(II) were analyzed by a ligand substitution kinetic method. Three-way data matrices were generated by acquisition of W-Vis spectra (332-580 nm) as a function of the time of a substitution reaction observed between the complex of the heavy metal ions with the non selective metallochromic indicator 4-(2-pyridylazo) resorcinol (PAR) and EDTA, and of different relative concentration of the metal ions (1-6 mM). The PARAFAC trilinear model, without restrictions, was used in the data analysis. A full decomposition of the data matrices was obtained (spectra, concentration and time profiles). It was shown that ligand substitution kinetic methods coupled to three-way chemometric analytical methods can be used for the development of robust sensors for the analysis of binary [Zn(II) + Ni(II), Pb(II) + Cd(II), Zn(II) + Pb(II)] or ternary [Zn(II) + Pb(II) + Co(II)] mixtures of metal ions in the micromolar concentration range.

Abstract The concentrations of heavy metals (Cd, Cr, Cu, Ni, Pb, Zn) were determined in river sediments collected at the Ave river basin (Portugal) to obtain a general classification scenery of the pollution in this highly polluted region. Multivariate data analysis techniques of clustering, principal components and eigenvector projections were used in this classification. Five general areas with different polluting characteristics were detected and several individual heavy metal concentration abnormalities were detected in restricted areas. A good correlation between the overall metal contamination determined by multivariate analysis and metal pollution indexes for all sampling stations was obtained. Some preliminary experiments showed that the metal concentrations normalised to the volatile matter content in the sediment fraction with grain size < 63 mu m seems to be an adequate method for assessing metal pollution.

Abstract We describe an ongoing project in Portugal aimed at developing and distributing software for teaching and learning basic sciences (Physics, Chemistry and Mathematics). The project, which is a joint effort of the Portuguese Societies for Physics, Chemistry and Mathematics with partial government support, has produced and distributed 20 programs (mainly simulations, educational games and databases). These programs and respective manuals were recently brought together in a CD-ROM, called `Omniscience' (http://www.fis.uc.pt/Omni/omni.html) which has been sent to all Portuguese middle and high schools. The project is doing multimedia development both off-line (`Periodic Table Multimedia', included in the same CD) and on-line (Internet pages with educational resources). Links in the CD-ROM allow for the on-line information.

Abstract This review presents some recent developments in the field of electroanalytical sensors. We first explain the working principle of electrochemistry at the interface between two immiscible electrolyte solutions (ITIES), illustrated by the example of copper transferring through a water/1,2-dichloroethane interface when the ionophore 1,4,7,10-tetrathiacyclododecane is present in the organic phase. The obtained results show that assisted ion-transfer reactions take place with both Cu-I and Cu-II, but that the interfacial process is complicated by the fact that Cut disproportionates in water and that Cu-II can be reduced in the organic phase. Based on the same experimental methodology, a new type of amperometric detector for non-redox ions has been developed using a composite polymer membrane supporting a gelified organic phase that can incorporate an ionophore such as valinomycin. We report here the use of a (o-nitrophenyl octyl ether)-(poy(vinyl chloride) (NPOE-PVC) gel micro-interface as a detector for cations and anions in ion-exchange chromatography. The main advantage of this approach is that selectivity and sensitivity can be tailored by the choice of the ionophore and by the polarisation potential. This ion detector has also been incorporated in a miniaturised total-analysis system (mu-TAS) fabricated in a polymer sheet by UV-laser photoablation. This microfabrication technique is used for the prototyping of a disposable capillary-electrophoresis microsystem comprising on-chip injector, separation column and electrochemical detector. This system is further used with built-in carbon-ink electrodes for the detection of electroactive species. These microsystems are now under development for immune-sensor applications.

Abstract The adsorption behaviour of n-hexanol on a Au (111) single-crystal electrode from aqueous 0.2 mol dm(-3) NaClO4 was studied on the basis of dynamic capacity measurements and of capacitive charge measurements by chronocoulometry. The charge density, sigma(M), as a function of the applied potential, E, and of the n-hexanol concentration was analysed thermodynamically, yielding the Gibbs surface excess, Gamma, and the Gibbs energy of adsorption, Delta(ads)G degrees, of n-hexanol as a function of potential and concentration. The results of the thermodynamic analysis of the adsorption data at the potential of maximum adsorption are discussed in comparison with the literature data for the adsorption of this compound on Hg [1,2] and on silver single-crystals [3,4]. The results obtained show that the adsorption process could be described by a Frumkin isotherm, the parameters of which were determined and discussed. The values of the standard Gibbs energy of adsorption suggest physical adsorption of the alcohol, without the existence of specific interactions of the adsorbed molecules with gold. Differences and inconsistencies for the results obtained from the analysis of charge and capacity data are discussed in terms of the experimental technique.

Abstract Cyclic voltammetry and capacitance measurements were performed using gold single crystal electrodes with 13 different crystallographic orientations. The experiments were performed in solutions of four different oxoanions: perchlorate, nitrate, sulphate and phosphate. Evidence of surface structure sensitivity was deduced for both the anion adsorption and surface oxidation phenomena. The current density and differential capacity profiles exhibit features that seem characteristic of the orientation of the terraces but are also sensitive to the density and orientation of the steps. For all of the gold faces under study, the anion adsorbability increases in the following order: ClO4- < NO3- < SO42 < H2PO4. A parallel between this order of adsorbability and the degree of stereochemical 'matching' between the anions and the surface atomic arrangement is suggested.

Abstract A set of parameters consistent with the CHARMM force field has been determined for molecular dynamics simulations of several DOTA- and DOTP-Ln(III) chelates. Bonding and van der Waals parameters were derived from the available experimental data and analogy to similar ones in the existing force field. Net atomic charges were derived from ab initio calculations at the Hartree-Fock level to reproduce molecular electrostatic potentials (ESPs), with an effective core potential (ECP) basis set for the metal ion and the 6-31G* basis set for the ligand atoms. The charges are consistent with the TIP3P water model. Preliminary molecular dynamics simulations of the lanthanide chelates in aqueous solution were performed using the Nose-Hoover thermostat at 300 K. The new parameters correctly predicted the molecular structures and stability of the chelates major and minor isomers. (C) 1999 John Wiley & Sons, Inc. Int J Quant Chem 73: 237-248, 1999.