Publications

Abstract The standard (p degrees = 0.1 MPa) molar enthalpy of formation for liquid 2,4,6-trimethylpyridine was derived from the standard molar enthalpy of combustion, measured by static bomb combustion calorimetry in oxygen, at the temperature T=298.15 K: Delta(f)H(m) degrees = -(31.0 +/- 2.3) kJ.mol(-1). (C) 1997 Academic Press Limited.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation Delta(f)H(m) degrees for crystalline 5-, 6-, 8-nitroquinoline and 8-nitroquinaldine were derived from the standard molar enthalpies of combustion in oxygen at T = 298.15 K Delta(c)H(m) degrees, measured by static bomb combustion calorimetry; the Knudsen mass-loss effusion technique was used to measure the vapour pressures of the crystals as functions of temperature, and the standard molar enthalpies of sublimation, at T = 298.15 K, Delta(cr)(g)H(m) degrees were derived by the Clausius-Clapeyron equation. Direct measurements of the standard molar enthalpies of sublimation, using microcalorimetry, for 5-, 6-, 8-nitroquinoline, and 8-nitroquinaldine confirmed the values from the Knudsen technique. [GRAPHICS] (C) 1997 Academic Press Limited.

Abstract The standard (p° = 0.1 M Pa) molar enthalpies of formation for 4-methylbiphenyl, 4,4'-dimethylbiphenyl and 4,4'-dimethyl-2,2'bipyridine were derived from the standard molar enthalpies of combustion, in oxygen, at T= 298.15 K, measured by static-bomb combustion calorimetry. The standard molar enthalpies of sublimation, at T= 298.15 K, were measured by Calvet microcalorimetry. Theoretical calculations at the ab initia restricted Hartree-Fock (RHF) level with second-order Moller-Plesset (MP2) perturbation theory correlation corrections and density functional theory (DFT) have been carried out for all these molecules in order to access their stabilitites relative to the non-substituted ones. The theoretical results are in general good agreement with the experimental results.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation for 4-methylbiphenyl, 4,4'-dimethylbiphenyl and 4,4'-dimethyl-2,2-'bipyridine were derived from the standard molar enthalpies of combustion, in oxygen, at T = 298.15 K, measured by static-bomb combustion calorimetry. The standard molar enthalpies of sublimation, at T = 298.15 K, were measured by Calvet microcalorimetry. Theoretical calculations at the ab initio restricted Hartree-Fock (RHF) level with second-order Moller-Plesset (MP2) perturbation theory correlation corrections and density functional theory (DFT) have been carried out for all these molecules in order to access their stabilitites relative to the non-substituted ones. The theoretical results are in general good agreement with the experimental results.

Abstract The differential capacity of a large number of liquid-liquid interfaces has been determined by impedance spectroscopy. Even in the absence of ion pairing, the interfacial capacity was always larger than predicted by Gouy-Chapman theory. These findings are explained within a simple model, in which an extended mixed-boundary layer exists at the interface, whose thickness extends over several solvent diameters.

Abstract A fixed analytical window of observation, 5 mu mol l(-1) free copper and 100 mu mol l(-1) total copper, but methods different in nature, operation mode and time scale were applied, in parallel, at pH 6.50 and 16 degrees C, to solutions with copper complexes of very different thermodynamic stabilities. Ethylenediaminetetraacetic acid (EDTA), L-cysteine, L-lysine, L-proline and succinate were used as metal buffers. Chitin (batch and column modes), chelex-100 (column mode) and normal pulse anodic stripping voltammetry (NPASV, -0.3 V deposition potential) were used as techniques. A strategy, based on using the mass of polymer that provided uptake of free copper similar to that taken up by Pseudomonas syringae bacterial cells in absence of ligands, was used for all but NPASV methods. Flame atomic absorption spectrophotometry was used for metal detection. The lability of copper complexes with simple organic ligands showed a strongly operational character. The time scale of the physicochemical method used for the determination of lability was not the only parameter inherent to the method that influenced the extent of copper complex dissociation. The nature of both initial and competing ligands and the operation mode may also condition the speciation results.

Abstract The standard (p(o) = 0.1 MPa) enthalpies of formation Delta(f)H(m)(o)(cr) at the temperature T = 298.15 K were determined using static-bomb calorimetry for crystalline 5-methoxybenzofurazan (5MeOBFN), 5-methoxybenzofurazan-1-oxide (4MeOBFNO), 5-methylbenzofurazan-1-oxide (5MeBFNO), and 4-nitrobenzofurazan-1-oxide (4NO(2)BFNO); using rotating-bomb calorimetry for 5-chlorobenzofurazan-1-oxide (5CIBFNO). The standard enthalpies of sublimation Delta(cr)(g)H(m)(o) at T = 298.15 K were measured by microcalorimetry and, from the enthalpies of formation of the gaseous compounds, the dissociation enthalpies D-m(o) of the (N+-O-) dative covalent bonds were derived.

Abstract A fully automated flow injection analysis (FIA) dilution system bared on the Zone sampling technique is described. The system relies on the use of a PC-compatible microcomputer for instrumental control and data acquisition and processing. The computer controls two rotatory valves which select different portions of the injected sample plug and then are re-sampled toward the detector. The system automatically chooses a suitable dilution factor for each sample. The dilution system was coupled to an atomic absorption spectrometer and to a flame photometer for the determination of Ca, Mg, Na, K, Cu, Sn and Fe in highly concentrated water samples. The methodology affords up to 10 000-fold dilution factors with good precision (RSD < 3%) and high sampling rates (never lower than 90 determinations per hour).