Publications

Abstract The synthetic power of the recently developed cascade annulations of beta-(hetero)aryl-alpha-nitro-alpha,beta-enals with the pyrrolidine-derived enamine of 2,2-dimethyl-1,3-dioxan-5-one is demonstrated by the first convergent route to (+/-)-tetrodotoxin.

Abstract Reported in the present work are the values of the gaseous standard (p degrees = 0.1 MPa) molar enthalpies of formation of 3-hydroxybenzaldehyde (3HBA), 4-hydroxybenzaldehyde (4HBA), and 3,5-di-tert-butyl-2-hydroxybenzaldehyde (3,5DTBHBA), at T = 298.15 K. For the three compounds, the values were derived from measurements of the standard molar energies of combustion of the crystalline compounds, using a static bomb calorimeter {Delta(c)H degrees m(3HBA) = -(3298.3 +/- 1.3) kJ . mol(-1) . Delta(c)H degrees(m)(4HBA) = -(3291.8 +/- 0.9) kJ . mol(-1) . Delta(c)H degrees(m)(3, 5DTBHBA) = -(8502.6 +/- 2.9) kJ . mol(-1)}, together with the standard molar enthalpies of sublimation, at T = 298.15 K, derived from the vapour pressures measured at different temperatures using the Knudsen effusion technique {Delta(g)(cr)H degrees m(3HBA) = (100.1 +/- 0.6) kJ . mol(-1) . Delta (g)(cr)H degrees(m)(4HBA) = (102.5 +/- 0.5) kJ . mol(-1), Delta(g)(cr)H degrees(m)(3, 5DTBHBA) = (96.0 +/- 0.5) kJ . mol(-1)}

Abstract Bread is consumed worldwide by man, thus contributing to the regular ingestion of certain inorganic species such as chloride. It controls the blood pressure if associated to a sodium intake and may increase the incidence of stomach ulcer. Its routine control should thus be established by means of quick and low cost procedures. This work reports a double-channel flow injection analysis (FIA) system with a new chloride sensor for the analysis of bread. All solutions are prepared in water and necessary ionic strength adjustments are made on-line. The body of the indicating electrode is made from a silver needle of 0.8 mm i.d. with an external layer of silver chloride. These devices were constructed with different lengths. Electrodes of 1.0 to 3.0 cm presented better analytical performance. The calibration curves under optimum conditions displayed Nernstian behaviour, with average slopes of 56 mV decade(-1), with sampling rates of 60 samples h(-1). The method was applied to analyze several kinds of bread, namely pao de trigo, pao integral, pao de centeio, pao de mistura, broa de milho, pao sem sal, pao meio sal, pao-de-leite, and pao de agua. The accuracy and precision of the potentiometric method were ascertained by comparison to a spectrophotometric method of continuous segmented flow. These methods were validated against ion-chromatography procedures.

Abstract The concentration of some anions (Cl, F, NO(3). and SO(4)). cations (Na, K, Ca, and Mg), pH and conductivity was determined in seven sampling points in the Serra da Estrela Mountains (Portugal) to verify if the application of road deicing with salt provokes impact in the water quality. Multivariate chemometric data analysis techniques of clustering and factor analysis were used. Preliminary analysis shows an overall conductivity increase in late spring and a decrease in late summer. A strong association between sodium chloride and the conductivity was observed by cluster analysis. Factor analysis supports the previous results and shows that the variation of the concentration of sodium chloride is the main source of the variance of the data along the year. In conclusion, the spreading of salt during the winter creates a local and seasonal impact on the water quality.

Abstract The mixed system between p-sulfonatocalix[4]arene and tetradecyltrimethylammonium bromide forms unilamellar vesicles after sonication of the aqueous dispersion. Furthermore these vesicles can be stored, without use of lyoprotectants, by lyophilization and then rehydration without change in size or shape.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation of 2-chloro-4,6-dinitroaniline and 4-chloro2,6-dinitroaniline, in the gaseous phase, at T = 298.15 K, were derived from the combination of the values of the standard molar enthalpies of formation, in the crystalline phase, and of the standard molar enthalpies of sublimation, at the same temperature. The standard molar enthalpies of formation, in the crystalline phase, were derived from the standard massic energies of combustion, in oxygen, measured by rotating-bomb combustion calorimetry. The standard molar enthalpies of sublimation were calculated, by the application of the Clausius-Clapeyron equation, to the vapour pressures at several temperatures, measured by Knudsen effusion technique. [GRAPHICS] The values of the standard molar enthalpies of formation of 2-chloro-4,6-dinitroaniline and 4-chloro2,6-dinitroaniline, in the gaseous phase, at T = 298.15 K, are discussed in terms of enthalpic increments, and the enthalpy of isomerization between the two compounds is compared with the same parameter for two isomers of chloronitroaniline, Studied in previous works.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpy of formation of 4-methyldibenzothiophene, in the gaseous phase, at T = 298.15 K, was derived from the combination of the values of the standard molar enthalpy of formation, in the crystalline phase, at T = 298.15 K, and the standard molar enthalpy of sublimation, at the same temperature. The standard molar enthalpy of formation in the crystalline phase, determined from the standard massic energy of combustion, in oxygen, is (70.9 +/- 4.8) kJ . mol(-1) and was measured by rotating-bomb combustion calorimetry. From Calvet microcalorimetry measurements, the standard molar enthalpy of sublimation obtained is (90.3 +/- 0.7) kJ . mol(-1).

Abstract The rheological behaviour of chitosan solutions in 250 mM acetate buffer was studied at different pHs (25 degrees C). The intrinsic viscosity decreased from similar to 17 dL/g to similar to 14 dL/g when the pH increased from 4.7 to 6.0. Concentrated solutions (0.5-3.0% w/w) exhibited a shear-thinning behaviour which increased with increasing chitosan concentration and decreasing pH. A good fitting of the experimental data to the Cross and Carreau flow models was obtained. The elasticity of the solutions decreased with increasing pH and decreasing chitosan concentration, as a consequence of increased chain flexibility. The interaction of chitosan with whey proteins (WPI) was studied by isothermal titration calorimetry (ITC) and turbidity measurements, at different pHs (3.0-6.0) and ionic strengths (100 and 250 mM). ITC results showed that electrostatics is the main driving force for chitosan: WPI interaction, as an increase in ionic strength lead to a smaller interaction. A pH and chitosan: WPI ratio dependence of aggregate formation was clearly observed by turbidimetry. At pH 3.0, there was no change in turbidity upon addition of chitosan, whereas at pH 4.0 and 6.0, the turbidity values varied with chitosan: WPI ratio and were smaller at 250 mM than those at 100 mM. The rheology of chitosan:WPI coacervates was studied in acetate buffer (100 and 250 mM), at pH 5.5, mixing ratios of 0.25:1 and 0.10:1. Time dependent flow behaviour, higher G' and G '' values and higher elasticity were observed for the coacervates, originating mainly from the electrostatic interactions between the protein and the polysaccharide chains.

Abstract In the crystal of the title compound, C(12)H(16)N(2)OS, inversion dimers linked by pairs of N-H center dot center dot center dot S hydrogen bonds occur, generating R(2)(2)(8) loops. The molecules are also linked by weak C-H center dot center dot center dot O hydrogen bonds. The structure is isostructural with that of N'-benzoyl-N,N-diethylselenourea [Bruce et al. (2007). New J. Chem. 31, 1647-1653].