Publications

Abstract The phase behavior of several binary sodium bile salt-water systems is investigated over the entire concentration range, with emphasis on concentrated regions beyond the isotropic solution phase. The studied bile acid salts comprise the free salt sodium deoxycholate (SDC), the taurine conjugates sodium taurocholate (STC), sodium taurodeoxycholate (STDC), and sodium taurochenodeoxycholate (STCDC) and the glycine conjugate sodium glycodeoxycholate (SGDC). A combination of classical techniques is used, including phase diagram determination, polarizing microscopy, H-2 NMR, and small-angle X-ray scattering (SAXS). The aggregation behavior in the isotropic micellar solutions of STC and STDC is also investigated by pulsed-field gradient NMR self-diffusion. The optical textures and the data from SAXS and H-2 NMR clearly point to the formation of hexagonal liquid crystals, possibly of the reverse type, beyond the micellar solution for all the bile salts. Several unusual kinetic effects, such as very slow equilibration times and the formation of transient spherulitic crystals in biphasic regions, are observed. The phase diagrams and structural data are qualitatively discussed in terms of the molecular structure and solubility of the different salts. The formation of lyotropic liquid crystals by bile salts, which has remained unknown for decades, is clearly demonstrated in this work.

Abstract The standard (p(o) = 0.1 MPa) molar enthalpies of combustion in oxygen of crystalline N-benzoyl-N',N'-diethylurea, PhCONHCON(Et)(2) (HBETU) and N-benzoyl-N',N'- diisobutylurea, PhCONHCON(iBu)(2) (HBIBU), were measured at T = 298.15 K by static bomb combustion calorimetry. The standard molar enthalpies of sublimation of both compounds were measured using microcalorimetry. These values were used to derive the standard molar enthalpies of formation of the compounds in their crystalline and gaseous phases, respectively. -Delta (c)u(o)(cr)/(J . g(-1)) Delta H-g(cr)m(o)(kJ . mol(-1)) N-benzoyl-N',N'-diethylurea 29756.9 +/- 9.6 132.2 +/- 1.4 N-benzoyl-N',N'-diisobutylurea 33047.0 +/- 9.3 137.5 +/- 2.9 (C) 2000 Academic Press.

Abstract The association between alpha -cyclodextrin and three monoalcohols (1-pentanol, 1-hexanol, and 1-heptanol) in (glycerol + water) was studied by titration microcalorimetry at T = (288.15, 298.15, and 308.15) K. The apparent thermodynamic parameters for the binding reactions, the equilibrium constant K(obs) and enthalpy of reaction Delta H-r(m)o(obs), were calculated from the calorimetric results. Knowing from a prior study that glycerol associates with alpha -cyclodextrin in aqueous solution, the Observed values were corrected for this equilibrium, assuming as a model that there is identical linkage. The intrinsic values of the thermodynamic parameters for the binding reaction, K(int) and Delta H-r(m)o(int). were then calculated for the three studied temperatures. From these values, the change in Gibbs free energy and entropy upon binding, Delta (r)G(m)(o)(int) and Delta S-r(m)o(int), respectively, were also calculated. From the temperature dependence of the enthalpy changes, the change in heat capacity for the binding reactions Delta C-r(p,m)o was obtained. The values of the intrinsic thermodynamic parameters are compared with the corresponding ones in water. For all compounds and temperatures, there is an increase in binding strength, as reflected by higher K values. The fact that the intrinsic parameters have different values from the ones observed in water shows that the glycerol linkage to the monoalcohols binding to alpha -cyclodextrin explains just part of the change in the observed parameters, indicating that glycerol is also acting as a co-solvent, thus affecting the solution interactions. (C) 2000 Academic Press.

Abstract The antiradical activity of caffeic acid (1), dihydrocaffeic acid (5), and their corresponding n-alkyl esters was evaluated by using the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH.) method. Dihydrocaffeic acid (5) was the most potent compound, having an antiradical effect higher than that of (+/-)-alpha-tocopherol, whereas caffeic acid (1) was less efficient. Esterification of the carboxyl group of dihydrocaffeic acid (5) had a dramatic effect on its antiradical potency, but similar effects were not observed for caffeic acid (1) derivatives. The n-alkyl esters of both phenolic series had similar potencies, and their antiradical activities were independent of the alkyl chain length, Dose-dependent scavenger effects were found in both series. Acid-base properties of the compounds, evaluated by using potentiometry and spectrophotometry, showed that the catechol moiety had pK(a2) and pK(a3) values of 9.24-9.02 and 11.38-10.99 in the dihydrocaffeic series and 8.48-8.24 and 11.38-11.07 in the caffeic series, respectively. Antiradical activity and pK(a) values of the compounds were not related.

Abstract The standard (p(O) = 0.1 MPa) molar enthalpies of combustion in oxygen, at T = 298.15 K, for crystalline D-, L- and DL-valine were measured by static-bomb calorimetry, in the presence of an auxiliary of combustion to improve the complete oxidation reaction. These values were used to derive the standard molar enthalpies of formation of the crystalline compounds, at T = 298.15 K, as -(612.9 +/- 1.5) kJ . mol(-1), -(614.7 +/- 1.3) kJ . mol(-1) and -(617.1 +/- 1.0) kJ . mol(-1), respectively, for the D-, L- and DL-valine. The reliability of the results obtained is commented upon and compared with literature results for other alpha-amino acid isomers. (C) 2000 Academic Press.

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.