Publications

Abstract Four monovarietal red wines, Tinta Roriz, Tints Barroca, Touriga Nacional, and Touriga Francesa, were studied for their complexometric properties toward copper. For the purpose, ion selective electrode potentiometric titrations were carried out, and the data were treated by two methods suitable for heterogeneous ligands: the Scatchard plot, which provided the complexation capacity (CCtotal = maximum number of moles of sites per liter), and the differential equilibrium function (DEF), which provided the conditional stability constants of the sites effectively involved in the metal complexation (K-DEF) at a given titration point. The different wines displayed similar properties: CCtotal ranged from 4.5 x 10(-3) (Tinta Barroca) to 4.9 x 10(-3) M (Touriga Francesa), and log K-DEF values were between 4.2 and 6.5. The range of log(\Cu\(bound)/CCtotal) = log theta embraced in the titration was between -0.2 and -1.9. With regard to the natural levels of copper, from 4.4 x 10(-7) (Tinta Roriz) to 1.3 x 10(-6) M (Touriga Nacional), and ligands (CCtotal) in the wines, it can be expected that copper will be strongly complexed in the studied wines (log K-DEF > 6). Studies carried out, in parallel, for solutions of isolated seed tannins and skin polyphenols (mainly anthocyans) showed that their contribution to the CCtotal of the wines was <40% for tannins and <2% for skin polyphenols. However, skin polyphenols were shown to be much stronger copper ligands (log K-DEF = 6.7, log theta = -1.5) than tannins (log K-DEF = 4.5, log theta = -1.5).

Abstract The structural elucidation of 24 xanthones with different substitution patterns was performed by spectroscopic methods, namely 2D NMR techniques, such as correlation spectroscopy (COSY), nuclear Overhauser effect (NOE), heteronuclear correlation (HETCOR) and a 1D NMR technique, selective insensitive nuclei enhanced by polarization transfer (INEPT). (C) 1997 John Wiley & Sons, Ltd.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation of eight copper(II) fluorinated beta-diketonates at the temperature 298.15 K were determined by high-precision solution and reaction calorimetry. The standard molar enthalpies of sublimation of the same copper(II) complexes at the temperature 298.15 K were determined by effusion methods. From the enthalpies of formation of the complexes in the gaseous state, the average molar dissociation enthalpies [D-m] (Cu-O) were derived and compared with identical parameters obtained for non-fluorinated copper(II) beta-diketonates. [GRAPHICS] The following abbreviations are used in the table: HTFBA, 4,4,4-trifluoro-1-phenylbutane-1,3-dione; HTFFBD, 4,4,4-trifluoro-1-(2-furanyl)-butane-1,3-dione; HTFNBD, 4,4,4-trifluoro-1-(2-naphthyl)-butane-1,3-dione; HTFHD, 1,1,1-trifluorohexane-2,4-dione; HTFMHD, 1,l,1-trifluoro5-methylhexane-2,4-dione; HTFDHD, 1,1,1-trifluoro-5,5-dimethylhexane 2,4-dione; HTFMHPD, 1,1,1-trifluoro-5-methylheptane-2,4-dione; HHPFDOD, 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyloctane-4,6-dione. (C) 1998 Academic Press.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation Delta(f)H(m)degrees(cr) at T = 298.15 K were determined using static-bomb calorimetry for crystalline 4-methylpyridine N-oxide (4MePyNO), 3-cyanopyridine N-oxide (3CNPyNO), 4-cyanopyridine N-oxide (4CNPyNO), 3-hydroxypyridine N-oxide (3OHPyNO), 2-pyridinecarboxylic acid N-oxide (2CO(2)HpyNO), 4-pyridinecarboxylic acid N-oxide (4CO(2)HPyNO), 3-methyl-4-nitropyridine N-oxide (3Me4NO(2)PyNO), 2-pyridinecarboxylic acid (2CO(2)HPy), and 4-pyridinecarboxylic acid (4CO(2)HPy). The standard molar enthalpies of sublimation Delta(c)(rg) H(m)degrees at T = 298.15 K were measured by microcalorimetry, or by a mass-loss effusion technique, and from the enthalpies of formation of the gaseous compounds the dissociation enthalpies D(m)degrees of the (N+-O-) dative covalent bonds were derived. [GRAPHICS] Comparison has been made with D(m)degrees(N-O) values in pyridine N-oxide derivatives. (C) 1998 Academic Press.

Abstract The even chain length cerium(III) carboxylates from the octanoate to the octadecanoate have been synthesised by metathesis. Thermogravimetry shows the presence of coordinated water for the short chain homologues, whereas the longer chain ones only contain adsorbed water. X-Ray diffraction and IR spectral measurements show that the solid phase has a lamellar, bilayer structure with planes of the cerium(III) ions coordinated to the carboxylate groups. The phase behaviour of the carboxylates has been studied by DSC and polarized-light microscopy. One or more mesophases are observed over the temperature range 70-120 degrees C and melting occurs between 130 and 150 degrees C. The textures observed on the polarizing microscope clearly show the anisotropic nature of the mesophases. Although the overall enthalpy and entropy of melting of these compounds increase with increasing chain length, the values are considerably lower than expected for complete fusion of the alkyl chains. Competition between melting of the chains and changes in the metal-carboxylate coordination region is the major factor responsible for the differences observed in the phase behaviour between the short and long chain derivatives.

Abstract Catanionic mixtures are aqueous mixtures of oppositely charged surfactants which display novel phase behavior and interfacial properties in comparison with those of the individual surfactants. One phase behavior property is the ability of these systems;to spontaneously form stable vesicles at high dilution. The phase behavior of the mixture sodium dodecyl sulfate (SDS) - didodecyldimethylammonium bromide (DDAB) in water has been studied in detail, and two regions of isotropic vesicular phases (anionic-rich and cationic-rich) were identified. Cryo-transmission electron microscopy allowed direct visualization of relatively small and polydisperse unilamellar vesicles on the SDS-rich side. Monitoring of the microstructure evolution from mixed micelles to vesicles as the surfactant mixing ratio is varied toward equimolarity was also obtained. Further information was provided by water self-diffusion measurements by pulsed field gradient spin-echo NMR. Water molecules can be in fast or slow exchange between the inside and outside of the vesicle with respect to the experimental time scale, depending on membrane permeability and vesicle size. For the SDS-rich vesicles, a slow-diffusing component of very low molar fraction observed for the echo decays was traced down to very large vesicles in solution, Light microscopy confirmed the presence of vesicles of several microns in diameter. Thus, polydispersity seems to be an inherent feature of the system.

Abstract Mixtures of the three major metabolites of acetylsalicylic acid (salicylic, gentisic and salicyluric acid) were analyzed by synchronous molecular fluorescence spectroscopy. Three-way data matrices were generated by acquisition of spectra as a function bf the pH (between 2 and 11) and of different relative concentrations of the three components. The PARAFAC trilinear model, without restrictions and using one factor per metabolite, was used in the data analysis. A full decomposition of the data matrices into the spectra, concentration and pH profiles was obtained. This result shows that molecular fluorescence spectroscopy can be used for the development of robust analytical methods for th simultaneous determination of the three major metabolites of acetylsalicylic acid in complex background samples.

Abstract The standard (p degrees = 0.1 MPa) massic energies of combustion Delta(c)u degrees at T = 298.15 K were measured by static bomb combustion calorimetry for 5-amino-6-nitroquinoline and 4-aminoquinaldine, from which the standard molar enthalpies of formation of both compounds, in the crystalline state, were derived. The standard molar enthalpies of sublimation Delta(cr)(g)H(m)degrees of the same compounds were derived from the Knudsen effusion measurements of the vapour pressures as a function of the temperature. [GRAPHICS] The derived standard molar enthalpies of formation in the gaseous state are shown to fit a group addictivity scheme. (C) 1998 Academic Press.

Abstract Six leaf litter extracts (LLE) (eucalyptus (Eucaliptus globulus), fern (Pteridium aquilinium), oak (Quercus robur), chestnut (Castanea sativa), laurel (Laurus nobilis), and ulex (Ulex europoeus) canopies) were isolated following an extraction procedure similar to that used for fulvic acids (FA) and were characterized by elemental analysis and UV-Vis, FT-IR, and synchronous molecular fluorescence (SyF) spectroscopies. Moreover, information about their interaction with the Cu(II) ion in aqueous solution (100 mg/L of LLE in 0.1 M KNO(3) at pH = 6) was obtained from the measurement of SyF spectra at increasing concentrations of Cu(II). These spectral sets were treated by a self-modeling mixture analysis method (SIMPLISMA) to obtain improved quenching profiles to be used in the estimation by the method of Ryan and Weber of the conditional stability constants (K(c)), concentration of binding sites, and percentage of fluorescent binding sites accessible for complexation. For comparison purposes, two samples of FA extracted from two horizons of an oak forest soil (0-5 cm and 5-15 cm) were also studied. The spectroscopic data obtained for LLE and FA were different. The results suggest that LLE are characterized by relatively high concentrations of individualized simple molecules and include reactive structures (alkene and protein residues). The ratio of aliphatic/aromatic structures was higher in LLE than for FA. Both LLE and soil FA form stable complexes with Cu(II), but the logarithm of the conditional stability constant of the 1:1 complexes is larger for LLE (about 5) than for the soil FA (about 4.5).