Publications

Abstract Bacterial cells or chitin were exposed to solutions with 100 mu M total but only 5 mu M free copper, due to the presence of a proper concentration of proline, lysine, cysteine, or ethylenediamine tetraacetate (EDTA). The influence of the nature and concentration of the particles and soluble ligands, on the sorption and on the desorption of the copper, at pH 6.50 and 25.0 degrees C, was investigated. The metal sorbed by the particles and that left in the solution were measured by atomic absorption spectrometry, after different periods of contact between particles and solution. The interpretation of the results was based on the copper(II) speciation calculated through equilibrium approaches applied to homogenous or heterogeneous systems. A significant fraction of copper bound to the organic ligands was displaced to the bacteria or chitin, and the extent of chemical reaction depended on the nature of both the soluble (or leaving) ligands and sites on the particle surface (or entering ligands), as expected by the equilibrium theory. But with chitin, the uptake of copper in the presence of cysteine or EDTA was higher than expected, which may be due to the adsorption of the soluble copper complexes on the particle surface. In consequence of a competition between soluble and particulate ligands (cells or chitin), the free copper(II) concentration decreased in the solution, even in the presence of very strong chelators. The results indicate that copper availability is not a simple function of the initial free copper concentration in the solution. Desorption of the previously fixed copper, originated by free soluble ligands indicated that the sorption of copper was ''quasireversible'' for both particles, though a larger dismissal of the equilibrium position occurred for the cells, probably due to their biological activity. Both the bacteria and chitin were able to fix metal initially bound to an organic ligand continuously for periods longer than 30 min, the kinetics of uptake varying with the nature of both the leaving and entering ligands. Therefore, long time-scale techniques, namely batch processes, warrant studies of metal availability in natural systems.

Abstract Values available in the literature for standard molar enthalpies of formation, both in the condensed and in the gaseous phases, at temperature 298.15 K, for quinolines, methylquinolines, hydroxyquinolines, methylhydroxyquinolines, aminoquinolines, cyanoquinolines, halohydroxyquinolines and nitroquinolines are reviewed, and the results are interpreted in terms of contribuitions of the different groups and of molecular structure.

Abstract The development of a FIA manifold for the determination of trace copper and lead in water by flame atomic absorption spectrometry following on-line sample preconcentration by sorbent extraction, is described. The metals were initially complexed with a diethylammonium diethyldithiocarbamate solution and retained in a column, developed specifically for this system, placed in the sample loop of an injection valve. The column was packed with bonded silica reversed phase sorbent with octadecyl functional groups. The metal complexes concentrated in the column were eluted with ethanol and directed toward the nebulization system of an atomic absorption spectrometer. The FIA based automatic system was optimised for several parameters, namely sample and eluent flow-rate and sample pH within the tubing. The enrichment factors obtained were of 15 and 23 times for the determination of copper and lead, respectively, with sampling rates of about 160 and 120 samples per hour and a RSD=1,5% (n=11). The detection limits for the same species were 0,2 and 2,7 μg/L, respectively.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation Delta(f)H(m) degrees for liquid 2- and 3-chloropyridine, and crystalline 2,3-, 2,5-, 2,6-, and 3,5-dichloropyridine were derived from the standard molar enthalpies of combustion Delta(c)H(m) degrees at T = 298.15 K in oxygen using rotating-bomb combustion calorimetry. The reaction products were: CO2(g), N-2(g), and HCl . 600H(2)O(1). The standard molar enthalpies of vaporization, or sublimation Delta (Hcr,lHm)-H-g degrees at T = 298.15 K were measured by Calvet microcalorimetry. The results are as follows: [GRAPHICS] The derived standard molar enthalpies of formation in the gaseous state are shown to fit a group additivity scheme. (C) 1997 Academic Press Limited.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of combustion, Delta(c)H(m) degrees for liquid 2- and 3-bromopyridine and for crystalline 2,5- and 2,6-dibromopyridine were determined at T = 298.15 K using a rotating-bomb combustion calorimeter. The products of the combustion in oxygen were: CO2(g), N-2(g), and HBr . 600H(2)O(I). The standard molar enthalpies of vaporization or sublimation Delta(cr,l)(g)H(m) degrees at T = 298.15 K were determined by Calvet microcalorimetry. The results were as follows: [GRAPHICS] (C) 1997 Academic Press Limited.

Abstract The standard (p(o) = 0.1 MPa) molar enthalpies of formation Delta(f)H(m)(o) at the temperature 298.15 K were determined from the standard molar enthalpies of combustion measured by static-bomb calorimetry for the liquids: di-n-propylamine, diisopropylamine, diisobutylamine, and di-sec-butylamine. The standard molar enthalpies of formation in the gaseous state were derived using both literature and estimated values for the enthalpies of vaporization. [GRAPHICS] The enthalpies of formation of aliphatic amines in the gaseous state are reviewed using group-additivity scheme. (C) 1997 Academic Press Limited.

Abstract The standard enthalpies of formation of the following fluorinated beta-diketones at T = 298.15 K were determined from their enthalpies of combustion measured using rotating bomb calorimetry. [GRAPHICS] With enthalpies of vaporization and sublimation, the enthalpies of formation of these beta-diketones were derived for the gaseous state in their enol and keto forms. Where applicable, the enthalpies of formation in the gaseous state correlated satisfactorily with values estimated by group additivity methods. (C) 1997 Academic Press Limited.

Abstract The standard molar enthalpies of formation, at 298.15 K, of crystalline copper(II) and nickel(II) complexes with 4,4'-ethylenedinitrilobis(pentan-2-one) (H(2)acacen) and with 1,1'-diphenyl-3,3'-ethylenedinitrilobis(butan-1-one) (H(2)bzacen), were determined from solution-reaction calorimetric measurements as, respectively, Delta(f)H(m)(o)[Cu(acacen), cr] = -385.1 +/- 3.2, Delta(f)H(m)(o)[Cu(bzacen), cr] = -203.4 +/- 5.1, Delta(f)H(m)(o)[Ni(acacen), cr] = -472.6 +/- 3.1 and Delta(f)H(m)(o)[Ni(bzacen), cr] = -292.2 +/- 5.1 kJ mol(-1). The standard molar enthalpies of sublimation of the same metal complexes, at 298.15 K, were obtained by effusion methods as: Delta(cr)(g)H(m)(o)[Cu(acacen) = 127.6 +/- 0.7, Delta(cr)(g)H(m)(o)[Ni(acacen)] = 129.1 +/- 0.9, Delta(cr)(g)H(m)(o)[Cu(bzacen)] = 205.6 +/- 3.0 and Delta(cr)(g)H(m)(o)[Ni(bzacen) = 201.7 +/- 2.8 kJ mol(-1). The differences between the mean metal-ligand and hydrogen-ligand bond-dissociation enthalpies were derived.