Publications

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.

Abstract The standard (p degrees = 0.1MPa) molar enthalpies of formation for liquid 1-ethylimidazole and 1-ethylpyrazole were derived from the standard molar enthalpies of combustion Delta cHm degrees in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry. The molar heat capacities of both liquids were measured in the temperature range (280 to 365)K by differential scanning calorimetry. The standard molar enthalpies of vaporization Delta lgHm degrees, at the temperature T = 298.15K were measured by Calvet microcalorimetry. The derived standard molar enthalpies of formation in the gaseous state are compared. [GRAPHICS] (C) 1999 Academic Press.

Abstract The Knudsen mass-loss effusion technique was used to measure the vapour pressure as a function of temperature for trans-cinnamic acid and nine substituted methoxy and dimethoxy cinnamic acids. From the temperature dependence of the vapour pressure the standard molar enthalpies and entropies of sublimation, at 298.15 K, were calculated for all the studied compounds using the estimated value Delta(cr)(g)c(p,m)(o) = -50 J.K-1.mol(-1). The results obtained for trans-cinnamic acid and for the trans-methoxy and trans-dimethoxy cinnamic acids together with literature results for benzoic acid and substituted methoxy and dimethoxy benzoic acids allowed us to derive the correlation: Delta(cr)(g)H(m)(o){T(p = 0.5 Pa)}/(kJ.mol(-1)) = (0.623 +/- 0.026).{T(p = 0.5 Pa)/K} + (-106.3 +/- 9.4) where T(p = 0.5 Pa) is the temperature at which the equilibrium vapour pressure of each crystalline compound is 0.5 Pa. (C) 1999 Academic Press.