Publications

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation for 2-, 3-, and 4-phenylpyridine in the, gas phase were derived from the standard molar enthalpies of combustion, in oxygen, at 298.15 K, measured by static bomb combustion calorimetry. The standard molar enthalpies of vaporization for 2-, 3-, and 4-phenylpyridine at T = 298.15 K were measured by correlation-gas chromatography. The enthalpy of sublimation of 4-phenylpyridine was obtained as a weighted mean of the value derived from the vaporization and fusion enthalpy values and the value measured directly by Calvet microcalorimetry. The following enthalpies of formation were then derived: 2-phenylpyridine, g = 228.3 +/- 5.8 kJ.mol(-1); 3-phenylpyridine, g = 240.9 +/- 5.5 kJ.mol(-1); 4-phenylpyridine, g = 240.0 +/- 33 kJ.mol(-1). The most stable geometries of all phenylpyridine isomers were obtained using both restricted Hartree-Fock (RHF) and density functional theory (DFT/B3LYP) methods. The resulting geometries were then used to obtain estimates of enthalpies of formation of the three isomers of phenylpyridine, which are in good agreement with the experimental values. A theoretical interpretation of the effect of the phenyl ring has on the relative stabilities of the three molecules is presented.

Abstract The speciation of Pb and Cu in white and red table wines was investigated, in order to estimate their respective bioavailability to man. For this purpose, wines were subjected to in vitro gastrointestinal digestion, and the following properties were studied in the wines and in their gastric and intestinal digests: (1) the average conditional stability constant (K-av) of the strongest complexes (those inert to cathodic voltammetry) and of the respective ligand concentration (CCinert); (2) the distribution of the metal among the different bands of reverse phase high performance liquid chromatography (RP-HPLC) (groups of compounds of different molecular weight and/or polarity); (3) the total metal concentration and metal present in the soluble and in the dialyzable fractions of the digest. The CCinert of the red wines and the respective, digests were much greater than those of the white wines and their digests. The conditional stability constants of the strongest soluble complexes after the digestion ranged between 5.9 and 6.1 for Pb, These parameters could not be determined for Cu, After the digestion the dialyzable metal fraction (a relative index of the metal potentially available for interaction with the inner biologic ligands) was only 16% of the total Pb in red wine, 62% in white Verde and 75% in white wine, For Cu the dialyzable metal fraction was 45% of the total metal in red wine, 64% in white Verde and 98% in white wine.

Abstract In the present work, the influence of Cu concentration on alcoholic fermentation by Saccharomyces cerevisiae was studied in white grape musts and in YNB medium containing glucose. In the YNB medium, the yield of ethanol, relative to the control, doubled in the presence of 0.50 and 1.0 mM Cu. As for production of ethanol from musts, only minor effects were observed at different Cu concentrations, which indicates that Cu levels do not effect changes in fermentation, and, therefore, are below any toxic level regarding the yeast performance.

Abstract Information about the speciation of Pb and Cu in different types of Port wines (white, single-year and blended aged red, and young red wines) was gathered to estimate their respective bioavailabilities to man. For this purpose, wines were subjected to in vitro simulated gastrointestinal digestion, and the following properties were studied in the wines and its gastric and intestinal digests: (1) average conditional stability constant (K-av) of the Cu complexes (by potentiometry), of the strongest Pb complexes (those inert to cathodic voltammetry, K'(av)), and of the respective ligand concentrations (CC or CCinert); (2) the distribution of the metal among the different groups of compounds of different molecular weights and/or polarities in the different bands separated by reverse phase high-performance liquid chromatography; (3) the total metal concentration present in the wines and the respective fractions present in the soluble and in the dialyzable fractions of the digest (an estimation of the assimilable fraction). The study showed that the complexing affinity for Pb (expressed by either CCinert or K'(av)) of white and very aged red Port wines was lower than for the remainder of the wines. For Cu, the strength of the ligands in the white wines was lower (<log K-av values) than in the other wines, but their concentrations (CC) were higher. For Pb, CCinert was much higher after the digestion than for the untreated wines, whereas the log K'(av) values were <similar to>1 order of magnitude lower. These parameters could not be determined for Cu in the gastrointestinal digests. For all of the studied wines the dialyzable fraction of Pb during the intestinal digestion was low (10-22% of the total Ph) and the dialyzable fractions of Cu were close to 50% of the total Cu.

Abstract Ion-selective electrode potentiometry and cathodic voltammetric techniques were used to study the Pb complexometric properties of four monovarietal wines, 'Touriga Nacional' (TN), 'Touriga Francesa' (TF), 'Tinta Roriz' (TR) and 'Tinta Barroca' (TB). The data from titrations of the samples with a Pb solution were treated by two methods suitable for systems involving polymeric heterogeneous ligands: (1) the Scatchard plot, which provided the total complexation capacity of the sample (CCtotal) and average conditional stability constants (K-av), and (2) the differential equilibrium function (DEF), which provided values for differential conditional stability constants (K-DEF) as a function of the titration point. The CCtotal of the wines ranged between 4.5 x 10(-3) M (TF) and 1.0 x 10(-2) M (TN). Potentiometric titrations provided values of log(\Pb\bound/CCtotal) = log theta between 0.015 and 0.45, and the respective log K-av between 5.6 (TF) (log K-DEF between 4.7 and 5.5) and 3.0 (TR) (log K-DEF between 2.8 and 3.7). Cathodic voltammetry, carried out only for TR and TN, provided the concentrations of only the strongest ligands of the wines. (i.e. those that are operationally inert), which were 27 mu M (TR) and 43 mu M (TN), and two different log K-av for TN, 7.6 and 6.6, and only one, 7.2, for TR, for log theta 0.0025-0.015 (TN) and 0.0014-0.0075 (TR). Since the values of log theta in wines are lower than those embraced in the experiments, this study indicates that Pb is strongly complexed in wines. Therefore, a low bioavailability of Pb can be expected.

Abstract Accurate experimental enthalpies of formation measured using static bomb combustion calorimetry, the "vacuum sublimation" drop calorimetry method, and the Knudsen-effusion method are reported for the first time for four azoles: 1-methylimidazole (1MeIMI), 1-methylpyrazole (1MePYR), 1-benzylimidazole (1BnIMI), and 1-benzylpyrazole (1BnPYR). These values and those corresponding to imidazole (1HIMI), pyrazole (1HPYR), 1-ethylimidazole (1EtIMI), 1-ethylpyrazole (1EtPYR), 1-phenylimidazole (1PhIMI), and 1-phenylpyrazole (1PhPYR) are compared with theoretical values using the G2(MP2) and the B3LYP/ 6-311*G(3df,2p)//6-31G(d) approaches. In general, there is a very good agreement between calculated and experimental values for the series of N-substituted imidazoles, while the agreement is less good for the series of the N-substituted pyrazoles. Experimentally, the gap between the enthalpies of formation of imidazoles and pyrazoles decreases significantly upon N-substitution, while the theoretical estimates indicate that this decrease is smaller.

Abstract Mixed surfactant systems have been, for a long time, one of the favorite areas for experimental studies on interfacial and bulk properties of surfactants. Beyond the well-known synergistic properties, with relevance to technical applications, recent studies increasingly focus on the bulk aggregation behavior. As moro systematic and detailed experimental data is collected (for example, by use of scattering and direct imaging techniques), increasingly refined theoretical models are developed. Most references reviewed here clearly show both the trends. Topics such as micellar growth, micelle-to-vesicle transition and equilibrium vesicle formation in dilute systems tin particular in catanionic systems) continue to expand and sometimes pose challenges to conventional notions of surfactant self-organization. As the rich polymorphism of mixed aggregates is unraveled, the possibilities of using them for broader goals also increase (e.g. mesoporous materials and polymer-aggregate gels).

Abstract The standard (p(o) = 0.1 MPa) molar enthalpies of combustion in oxygen, at T = 298.15 K, for crystalline 2-iodosobenzoic acid, (OI)C6H4COOH, and 4-nitrosophenol, (ON)C6H4OH, were measured by rotating-bomb calorimetry and static-bomb calorimetry, respectively. These values were used to derive the standard molar enthalpies of formation of the crystalline compounds. [GRAPHICS] An indirect method was used for assessing the dissociation enthalpy of the (I-O) bond in the iodoso derivative, D-m(o)(I-O)/(kJ . mol(-1)) = (264.5 +/- 8.1), which is the first value reported for an iodine-oxygen bond in an organic molecule. (C) 1999 Academic Press.

Abstract The standard (p(o) = 0.1MPa) molar enthalpies of formation for 2-, 3-, and 4-tert-butylphenol and 2,4- and 2,6-di-tert-butylphenol in the gaseous phase were derived from the standard molar enthalpies of combustion, in oxygen, at 298.15 K, measured by static bomb combustion calorimetry and the standard molar enthalpies of evaporation at 298.15 K, measured by Calvet microcalorimetry: 2-tert-butylphenol, -184.7 +/- 2.6 kJ mol(-1); 3-tert-butylphenol, -198.0 +/- 2.1 kJ mol(-1); 4-tert-butylphenol, -187.3 +/- 3.3 kJ mol(-1); 2,4-di-tert-butylphenol -283.3 +/- 3.8 kJ mol(-1), 2,6-di-tert-butylphenol -272.0 +/- 4.0 kJ mol(-1). The most stable geometries of all mono- and disubstituted phenols as well as those of the corresponding radicals were obtained, respectively, by ab initio restricted Hartree-Fock (RHF) and restricted Hartree-Fock open shell (ROHF) methods with the 6-31G* basis set. The resulting geometries were then used to obtain estimates of the effect of the tert-butyl substituent on the O-H bond dissociation energy and on the formation enthalpies of all substituted phenols.

Abstract Structural and phase behavior effects resulting from the addition of a polyelectrolyte to a solution of oppositely charged vesicles are investigated in this work. Two cationic polyelectrolytes derived from hydroxyethylcellulose were used: JR400, a homopolymer, and Quatrisoft LM200, a polymer modified with alkyl side chains. The vesicles are composed of mixed anionic surfactant (sodium dodecyl sulfate) and cationic surfactant (didodecyldimethylammonium bromide), bearing 29 mol % of the caf;ionic amphiphile. The phase behavior for the two mixed polymer-surfactant systems was investigated for polymer concentrations between 0.001 and 3 wt%. Three main regions were found in the two-phase maps, upon polymer addition: (i) a bluish solution phase; (ii) a wide region of phase separation, containing a precipitate and a solution; and (iii) a polymer-rich gel region, forming upon charge reversal of the system. Cryo-TEM imaging of the solution phase shows the formation of faceted vesicles and disklike aggregates, upon addition of JR400. Fbr the LM200 system, besides the formation of faceted vesicles, clusters of vesicles and other bilayer structures are imaged. In the polymer-rich phase of JR400, membrane fragments, disklike aggregates, and vesicles are also found. These bilayer aggregates are likely to be involved with the polymer in highly connected networks, giving rise to the observed bluish gels. Electrostatic interactions, reinforced by hydrophobic interactions in the case of LM200, are the main driving force for the structural transitions observed.