Publications

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).

Abstract The interaction of Fe(III) with two samples of fulvic acids (FAs) extracted from a pinewood soil (FA2: horizon 0-10 cm; FA3: horizon 10-25 cm) was monitored by synchronous fluorescence (SyF) spectroscopy at four pH values (3, 4, 5, and 6). Spectral data were preprocessed by SIMPLISMA, a self-modeling curve-resolution method, and from the calculated quenching profiles, equilibrium parameters for the interaction of Fe(III) and FAs were obtained (conditional stability constants [K(c)s] and ligand site concentrations). The calculated log K(c)s were (I = 0.1 M KNO3; standard deviation in parentheses) FA2, pH = 3, 4.9 (2) pH = 4, 4.7 (2), pH = 5, 5.1 (4), and pH = 6, 5.1 (1); FA3, pH = 3, 5.48 (1); pH = 4, 4.96 (7), pH = 5, 4.89 (1), and pH = 6, 5.1 (2), where I is the ionic strength. These results show that FA forms quite stable soluble complexes with Fe(III) in the acid pll range.

Abstract The acid-base properties of two samples of anthropogenic fulvic acids (FA) extracted from the untreated sewage sludge (rsFA) of a municipal wastewater treatment plant and from the compost (csFA) obtained in the aerobical digestion of this sludge were studied. Potentiometric titrimetry, infrared spectroscopy and synchronous molecular fluorescence (SyF) spectroscopy were used to obtain experimental information about the acid-base properties of the samples. Moreover, the SyF spectral data which were collected as function of the pH were analysed by a self-modelling curve resolution technique, evolving factor analysis with a gradient concentration window (EFA-GCW), to calculate the number of acid-base systems, their SyF spectra and the corresponding distribution diagrams, from which the pK(a) values were estimated. Two acid-base systems with pK(a) values about 6.2 and 8.9 were detected for rsFA and three systems with pK(a) values about 3.8, 6.6 and 9.4 for csFA. The amounts of acid groups directly titrated in water were (standard deviations in brackets) about 6.8(1) for rsFA and 6.73(3) for csFA. This information for rsFA and csFA was compared with similar information for natural soil FA samples extracted from a pinewood soil. Beyond different structural composition, this comparison showed that the anthropogenic samples have a higher amount of acid structures, but the structures of natural samples have stronger acid properties.

Abstract Os sistemas coloidais mistos são objecto de intensa investigação no domínio da química-física actual. A nível molecular apresentam grande diversidade de estruturas auto-agregadas e de forças de interacção; exibem também propriedades macroscópicas versáteis, de vasta aplicabilidade práctica. Nesta tese, o comportamento e a micro-estrutura de fase de sistemas aquosos mistos surfactante-surfactante e polímero-surfactante são investigados, contendo ambos cosolutos de cargas opostas. Abordam-se tópicos centrais tais como separação de fase associativa em sistemas mistos, formação de vesículos termodinamicamente estáveis e interacções polímero-vesículo. É conhecido o forte sinergismo nas propriedades de solução e interfaciais de misturas de surfactantes de carga oposta em água (misturas cat-an-iónicas). Por outro lado, o comportamento e a estrutura de fase destes sistemas, em regime diluído e concentrado, tem sido alvo de estudos menos sistemáticos. A formação espontânea de vesículos estáveis para baixa concentração de surfactante - vesículos termodinamicamente estáveis - em misturas cataniónicas tem suscitado enorme interesse em anos recentes, dadas as suas implicações teóricas e potencialidades técnicas. O sistema anfifílico estudado neste trabalho é composto por um surfactante catiónico de dupla cadeia e um surfactante aniónico de cadeia única, assumindo como tal características de sistema-modelo. Interacções electrostáticas e efeitos de empacotamento geométrico contribuem em graus de complexidade variável para as estruturas micro-heterogéneas observadas. O diagrama de fases pseudo-ternário do sistema é inicialmente investigado para a gama total de concentração de surfactante, incluindo a identificação de regiões multifásicas, por técnicas de microscopia de luz polarizada e de desdobramento quadrupolar do deutério. Na zona diluída, duas regiões monofásicas de vesículos estáveis, contendo excesso de um ou de outro surfactante, são delineadas e caracterizadas. O uso complementar de microscopia de transmissão electrónica associada a criogenia (cryo-TEM) e microscopia de luz associada a técnicas de vídeo (VEM) fornece a visualização de uma vasta gama de tamanhos e de estruturas agregadas. Métodos de RMN de auto-difusão molecular para caracterização quantitativa são usados em paralelo, obtendo-se resultados não-clássicos para a auto-difusão da água em soluções polidispersas de vesículos. Posteriormente, os efeitos micro-estruturais e de comportamento de fase resultantes da adição de macromoléculas a uma solução de vesículos cataniónicos de carga oposta são investigados. Dois polielectrólitos catiónicos derivados da hidroxi-etil-celulose, um homopolímero e um heteropolímero com cadeias alquílicas laterais são usados. As macromoléculas interagem fortemente com a bicamada vesicular, dando origem à formação de estruturas vesiculares facetadas e estruturas discoidais; para concentracções elevadas de polímero, observa-se a formação de um novo tipo de gel vesículo-polímero.