Publications

Abstract The enantioselectivity of the gold chiral surfaces towards the electrocatalvtic oxidation of D- and L-glucose in neutral phosphate-buffered media is reported. Two enantiomorphic surfaces were used, Au{32}(R) and Au{321}(S), and results obtained by cyclic voltammetry were compared with two non-chiral surfaces having the same terrace and step orientations, Au(111) and Au(211). All enantioselective effect is observed, Au {321}(R) exhibits a higher activity for D-glucose while Au{3 2 1}(S) exhibits a higher activity for L-glucose. The corresponding en anti oselectivity factor was estimated to 10% for the process occurring at lower potential values and to 50% for the process at higher potential values. These results represent the first evidence that gold chiral surfaces are capable of enantiomeric discrimination.

Abstract The first unequivocal thermochemical/calorimetric determination of the enthalpies of combustion, phase change, and formation of a pair of (E)- and (Z)-disubstituted olefins of the type XCH=CHX, where X is an electron withdrawing group, is reported in this paper for the isomeric species dimethyl fumarate and dimethyl maleate (X = COOCH3). The corresponding density functional calculations, corrected for vibrational and thermal effects, confirm that the former isomer is more stable by some 30 kJ mol(-1).

Abstract This paper reports the results of our thermochemical/calorimetric determination of the enthalpies of combustion, phase change, and formation of isatin, isatoic anhydride, and N-methylisatin. The density functional calculations accompanied by vibrational and thermal corrections were also performed for these compounds and N-methylisatoic anhydride. Through a combination of theoretical calculations and associated isodesmic reactions, we have deduced that isatin has some antiaromatic character and isatoic anhydride enjoys some aromatic stabilization.

Abstract The standard (pdegrees = 0.1 MPa) molar energies of combustion in oxygen, at T = 298.15 K, of four liquids: 2-ethylpyridine, 4-ethylpyridine, ethylpyrazine and 2,3-diethylpyrazine were measured by static bomb calorimetry in an oxygen atmosphere. The values of the standard molar enthalpies of vaporization, at T = 298.15 K, were obtained by Calvet microcalorimetry, allowing the calculation of the standard molar enthalpies of formation of the compounds, in the gas phase, at T = 298.15 K: 2-ethylpyridine (79.4 +/- 2.6) kJ mol(-1); 4-ethylpyridine (81.0 +/- 3.4) U mol(-1); ethylpyrazine (146.9 +/- 2.8) kJ mol(-1); and 2,3-diethylpyrazine (80.2 +/- 2.9) kJ mol(-1). The most stable geometries of all ethylpyridine and ethylpyrazine isomers were obtained using the density functional theory with the B3LYP functional and two basis sets: 6-31G* and 6-31IG**. These calculations were then used to obtain estimates of the enthalpies of formation of all isomers, including those not experimentally studied, through the use of isodesmic reactions. A discussion of the relationship between structure and energetics of the isomers is also presented.

Abstract The quantification of metal-chelating activity of caffeic and ferulic acids (1 and 2. resp.) was successfully performed by using a potentiometric system with data-analysis computer programs. The method was applied to two phenolic models, which have been systematically reported as antioxidants. Although a chain-breaking mechanism was proposed, several studies pointed out the possibility of complexation of transition metals that can participate in single-electron reactions and mediate the formation of oxygen-derived free radicals. In this work, the complexation properties towards Cu-11 were investigated by potentiometry with a glass electrode. Acidity constants of the ligands (phenolic acids) and the formation constants of the ligand-metal complexes were evaluated by potentiometry. The modeling of the titration curves and the data treatment were performed with the computer programs Superquad and Best. A detailed quantitative examination of the complexation species formed in the Cu-11/caffeic acid (1) and Cu-11/ferulic acid (2) systems is presented together with the formation constants (log P). Results have shown that the complexation properties of the two phenolic acids towards the transition metal are quite different: the activity of caffeic acid (1) was found higher than that of ferulic acid (2). ne data are important to get insight into the mechanism of action of antioxidants. and. in this case, could partially explain the efficacy of caffeic acid in the protection of LDL oxidative damage. In addition. the analytical method developed could be applied to quantify the chelating activity of important biological compounds, such as allopurinol, uric acid, cinnamic acids, flavonoids, and anthocianins, and, in that way, could be a valuable tool to understand the mechanisms underlying their protective effects.

Abstract Two analytical methods for the quality control of dihydrocodeine in commercial pharmaceutical formulations have been developed and compared with reference methods: a square wave voltammetric (SWV) method and a flow injection analysis system with electrochemical detection (FIA-EC). The electrochemical methods proposed were successfully applied to the determination of dihydrocodeine in pharmaceutical tablets and in oral solutions. These methods do not require any pretreatment of the samples, the formulation only being dissolved in a suitable electrolyte. Validation of the methods showed it to be precise, accurate and linear over the concentration range of analysis. The automatic procedure based on a flow injection analysis manifold allows a sampling rate of 115 determinations per hour.