Publications

Abstract A novel separation method, i.e. electro-assisted solvent extraction, based on the principles of two-phase electrochemistry, has been demonstrated for the successful separation of Ni2+, Cu2+ and Cd2+ ions. 2-Heptanone has been used as the organic solvent for the transfer of Ni2+, Cu2+ and Cd2+ facilitated by 2,2';6',2 "-terpyridine. It is shown that extraction efficiency depends on the concentration ratio of ligand to metal ion and importantly, on the applied interfacial potential difference. Tt was Found that Ni2+ (not Cd2+ or Cu2+) extraction is suppressed in the presence of Mg2+ ion due to competitive complexation.

Abstract Electrochemical evidence of the surface reconstruction, induced thermally or potentially, was sought for ten gold single crystals with high Miller index faces, in order to assess the influence of the nature and density of steps. Occurrence of thermally and electrochemically induced surface reconstruction was deduced for the following stepped faces: Au(755), Au(332), Au(533), Au(410), Au(771) and Au(331). The structure of the reconstructed surfaces seems to be-dictated by the geometry of the terraces, while the extension of the phenomena is constrained by the density and orientation of steps. This study was conducted in the presence of the following oxoanions: perchlorate, nitrate, sulphate and phosphate, in order to rationalize the influence of adsorption on the surface structure transitions. Results were interpreted in the light of the known reconstruction mechanisms for the gold low index faces.

Abstract The assisted transfer of Cu(II) by interfacial complexation with 6,7-dimethyl-2,3-di(2-pyridyl)quinoxaline (DMDPQ) is studied at the polarised water\1,2-dichloroethane junction. Thermodynamic and kinetic aspects were addressed by cyclic voltammetry and in situ spectrophotometric measurements. The dependence of the half wave transfer potential on the ligand concentration suggests that the equilibrium is effectively displaced towards a 1:3 (metal:ligand) stoichiometry, with an association constant of log beta(3)degrees = 26.0. Visible spectra recorded by reflection from the aqueous phase showed the presence of two absorption bands at 400 and 500 nm associated with the Cu(II) complex. Chronoabsorptometric studies in the presence of a ligand excess suggest that the assisted transfer kinetics are effectively controlled by the diffusion of the metal ion to the interface.

Abstract Disadvantages of the some zwitterionic pH buffers are (i) that they can interact with metal ions as well as protons, and (ii) that they may have a surfactant effect in chemical or in vitro biological or biochemical studies. This has to be taken into account when a buffer is selected. Here, the copper-complexing capacity and the surfactant activity of three compounds, 3-[N,N-bis (2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid (DIPSO), N-(2-hydroxyethyl)piperazine-N'-(2-hydroxypropanesulfonic acid) (HEPPSO), and piperazine-Ni,N'-bis(2-ethanesulfonic acid) (Pipes), were investigated. Global stability constants (log beta(abc)) of copper(II)-buffer complexes were determined, at 25 degrees C, 0.5 M ionic strength, and at 0.8 mM buffer concentration, by pH and pCu ion-selective electrode measurements. Here, beta(abc) corresponds to the equilibrium: aCu(2+) + bL(-) + cH(+) <-> (CUaLbHc)((2a-b+c)); HL = DIPSO or HEPPSO; c: +1 = proton; -1 = hydroxide. Using SUPERQUAD constants were calculated, giving: DIPSO: log beta(110) = 5.02, log beta(120) 8.99, log beta(130) = 13.0, log beta(140) = 16.3, log beta(14-1) = 9.26, log beta(14-2) = 0.645, log beta(150) = 20.5, log beta(160) = 24.3, log beta(16-1) 16.1, log beta(16-2) = 8.98; HEPPSO: log beta(110) = 4.29, log beta(120) = 8.35, log beta(130) = 12.1, log beta(140) = 15.9, log beta(150) = 19.6, log beta(160) = 23.4, log beta(16-1) = 14.9. The pK(a) values were determined at higher buffer concentrations, giving a value 7.33 for DIPSO and 7.84 for HEPPSO at 2.0 mM buffer concentration. Effects of buffer concentration on stability and acidity constants were investigated and compared with measurements using voltammetric and potentiometric stripping analysis, confirming no copper(II) complexation by Pipes. Surfactant activities were determined using alternating current polarography, confirming marked surface activity of 10 mM of DIPSO or HEPPSO. (C) 1998 Academic Press.

Abstract Ion association at the interface between two immiscible electrolyte solutions may manifest itself as a marked increase in the interfacial capacity, This effect is illustrated by experimental investigations in which the ions in the organic phase are varied, while the composition of the aqueous phase is kept constant. The increase in the capacity is explained by a simple lattice-gas model. The magnitude of this effect depends both on the association constant and the width of the interface. (C) 1997 Elsevier Science S.A.

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.