Publications

Abstract Some recent illustrations of the phase behavior of polymer-amphiphile systems in solution are presented. Surfactant-polymer association is demonstrated for various amphiphilic synthetic and biological polymers both on a macroscopic and on a single molecular level.

Abstract The Knudsen mass-loss effusion technique was used to measure the vapour pressures of five crystalline dicarboxylic acids as a function of temperature. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation were derived by using the Clausius-Clapeyron equation and the standard molar entropies of sublimation were calculated. The standard molar enthalpies and entropies of sublimation at T = 298.15 K were also calculated by using the estimated value of the standard molar heat capacity of sublimation Delta(cr)(g)C(p,m)(O), = -50 J K-1 mol(-1): [GRAPHICS] The sublimation enthalpy increments for a CH2 group in straight-chain dicarboxylic acids with less than nine methylene groups were calculated as (7.9 +/- 0.4) kJ.mol(-1). The available values for the enthalpies of sublimation of straight-chain dicarboxylic acids with more than eight methylene groups are discussed in terms of partial cyclization. The standard molar enthalpies of formation of dicarboxylic acids in the gaseous phase have been derived. (C) 1999 Academic Press.

Abstract The standard (p(o) = 0.1 MPa) molar enthalpies of formation for crystalline 3-methoxy-2-nitro-, 4-methoxy 3-nitro-, and 3-methoxy-4-nitrobenzoic acid were derived from the standard molar enthalpies of combustion, in oxygen, at the temperature 298.15 K, measured by static bomb combustion calorimetry, the Knudsen mass-loss effusion technique was used to measure the vapour pressures of these crystals as functions of temperature, and the standard molar enthalpies of sublimation, at T = 298.15 K, were derived by the Clausius-Clapeyron equation. The standard molar enthalpies of sublimation, at T = 298.15 K, for the three nitrobenzoic acids were also determined using the Knudsen mass-loss effusion technique. [GRAPHICS] The standard molar enthalpies of formation in the gaseous state are shown to fit a group additivity scheme. (C) 1999 Academic Press.

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.