Publications

Abstract The standard (po = 0.1 MPa) molar enthalpies of combustion at the temperature 298.15 K were measured by static-bomb calorimetry for p -azoxyanisole and p-azoxyphenetole, and the standard molar enthalpies of sublimation of the temperature 298.15 K were measured by microcalorimetry. [[formula]] From the standard the molar enthalpies of formation of the gaseous compounds, the molar dissociation enthalpies of the N-O bonds were derived: D (N-O)/(kJ·mol-1): p-azoxyanisole, 317.2±5.7; p-azoxyphenetole, 320.4±4.9. Microcalorimetric measurements were made to derive the molar enthalpies of the transitions: crystal-to-liquid: for p-azoxyanisole, (29.3±0.8) kJ·mol-1, (1.0±0.5) kJ·mol-1; and for p-azoxyphenetole, (27.0±0.8) kJ·mol-1, (1.7±0.6) kJ·mol-1, respectively.

Abstract The variations observed in synchronous fluorescence spectra of fulvic acids have been characterised by principal component analysis and evolving factor analysis. Fulvic acids from coastal marine waters (mfua) were examined as a function of pH (between 2 and 7) and Cu(II) concentration. Fulvic acids from soil (sfua) were examined as a function of pH (between 2 and 7) and Cu(II), Co(II) and Ni(II) concentration. Fluorescence properties of sfua are characterised by a constant plus three varying components (defined by three individual spectra), corresponding to three acid-base equilibria with pK(a) values of 3.0, 4.6 and 6.4. For mfua, a constant plus two varying components (defined by three individual spectra) were detected, corresponding to two acid-base equilibria with pK(a) values of 3.1 and 5.3. The influence of the ions on the acid-base equilibrium diagrams is also quantified.

Abstract The standard (p-degrees = 0.1 M Pa) molar enthalpies of formation at 298.15 K in the gaseous state of some beta-ketoimines, RCOCH=C(CH3)NHR1, were determined from their enthalpies of combustion and of sublimation, DELTA(f)H(m)degrees(g)/kJ mol-1: R=CH3, {R1 = C6H5, -66.0 +/- 4.2; R1 = p-C6H4NO2, -98.9 +/- 5.0}: R = C6H5, {R1 = H, -48.7 +/- 3.5; R1 = CH3, -53.7 +/- 4.7; R1 = C6H5, 69.1 +/- 4.2). From these results it is shown that the increase in delocalization energy from R = CH3 to R = C6H5 matches the corresponding increase between acetylacetone and benzoylacetone. Crystal structures are reported for R = CH3, R1 = p-C6H4NO2, and R = C6H5 {R1 = H, R1 = CH3}, and show that those beta-ketoimines with R = C6H5 have a more delocalized structure in the -COCH=C(CH3)NH-moiety than those with R = CH3 in accord with the thermochemical results.

Abstract Partial molar heat capacities at infinite dilution, C(p,2)infinity, have been determined calorimetrically for D-mannitol and D-sorbitol in water, dimethyl sulfoxide and formamide, at 298.15 K. The C(p,2)infinity values obtained, which are similar for the three solvents, are much higher than the heat capacities for the pure compounds. The large DELTAC(p)infinity values for the dissolution process are believed to be partly due to the existence of several rotamers in solution. Sorbitol seems to be more sensitive than mannitol to specific solvent effects.

Abstract 1,3-Dihydroxy-2-methylxanthone (X1), its 4-chloro and 4-bromo derivatives (X1-Cl and X1-Br), and 1,3-dihydroxy-4-methylxanthone were investigated for their inhibition activities toward MAO. A hyperbolic function was derived to fit the data and to calculate IC50 values. The compounds proved to be reversible and selective inhibitors of MAO-A, with X1 displaying the highest activity (IC50 = 3.7 muM).

Abstract A general procedure for the simultaneous analysis of phenolic compounds by a reversed-phase high performance liquid chromatography (RP-HPLC) is described. The series of compounds embraces the cis/trans isomers of caffeic, ferulic and isoferulic acids and the coumarins - esculetin, scopoletin and isoscopoletin. In order to establish the experimental conditions, leading to an optimal resolution, several test mixtures were analysed. HPLC separation was carried out on a reversed-phase column ( Lichrosorb RP-8, 5 mum), using aqueous tetrahydrofuran as a mobile phase.

Abstract Potentials of zero charge, E(sigma=0), and the temperature coefficients of E(sigma=0) for stepped surfaces of sold single crystals (511), (533), (331) and (311) were obtained from the minimum of the differential capacity curve in dilute HClO4 solutions. The results are compared with those obtained for the low index faces and dilute in terms of the effect of the surface density of steps and the step orientation. The possible relevance of the effect of steps on the interaction of water with gold surfaces is discussed.