Publications

Abstract The following standard molar enthalpies of formation in the gaseous state at 298.15 K were determined from the enthalpies of combustion of the crystalline solids and the respective enthalpies of sublimation: 2,2'-bipyridine, 267.9 +/- 3.0 kJ mol(-1); 2,4'-bipyridine, 284.2 +/- 2.7 kJ mol(-1); 4,4'-bipyridine, 293.1 +/- 3.6 kJ mol(-1). Ab initio geometry optimizations of these molecules at the 3-21G level suggest that those with at least one ortho nitrogen atom assume near planar conformations preferentially, while the others have nonplanar most stable forms.

Abstract The standard (p(o) = 0.1 MPa) molar enthalpies of combustion, at the temperature 298.15 K for crystalline N,N'-ethylenebis(4-aminopent-3-en-2-one), {CH3COCH:C(CH3)NHCH2 .}(2), H(2)ACACEN, and N,N'-ethylenebis(3-amino-1-phenylbut-2-en-1-one), H(2)BZACEN, {C6H5COCH:C(CH3)NHCH2 .}(2), were measured by static bomb-combustion calorimetry in oxygen. The standard molar enthalpies of sublimation of both compounds were measured by effusion techniques. These values were used to derive the standard molar enthalpies of formation of the compounds, in both the crystalline and the gaseous phases.

Abstract The standard (p(o) = 0.1 MPa) enthalpies of combustion at the temperature T = 298.15 K were measured by static-bomb calorimetry for crystalline 4-nitropyridine N-oxide and for pyridine-3-carboxylic acid N-oxide. The standard enthalpies of sublimation at T = 298.15 K were measured for 4-nitropyridine N-oxide by microcalorimetry and for pyridine-3-carboxylic acid N-oxide by a mass-loss effusion technique. -Delta(c)H(m)(o)(cr)/(kJ.mol(-1)) Delta(cr)(g)H(m)(o)(kJ.mol(-1)) 4-O2N-c-C-5 H4NO 2556.3 +/- 0.5 108.9 +/- 0.3 3-HO2C-c-C5H4NO 2698.2 +/- 0.7 152.3 +/- 1.9 From the standard 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)) in 4-O2N-c-C5H4NO, 258.5 +/- 5.3; in 3-HO2C-c-C5H4NO, 252.8 +/- 2.7. The standard molar enthalpies of sublimation of 2-H3C-c-C5H4NO and 3-H3C-c-C5H4NO were measured by microcalorimetry: (78.2 +/- 2.2) kJ.mol(-1) and (82.2 +/- 2.4) kJ.mol(-1), respectively, permitting the comparison of D(N-O) values in several pyridine N-oxide derivatives.

Abstract The effect of electrolyte type and concentration on the differential capacitance of the 1,2-dichloroethane/water interface has been measured. The results show that the differential capacitance is controlled by the pair ion (1)-counter-ion (2), where 1 and 2 denote the different phases. At constant organic electrolyte composition the capacity increases in the order, F-<SO42-<HO-<ClO4-,Li+<H+<K+<Mg2+<Ba2+<Sr(2+)approximate to Ca2+. By contrast, at positive potentials and constant aqueous electrolyte composition, the capacitance decreases in the order, TPA(+)>MTMA(+)>TBA(+)>TOA(+),TPB->TCPB-. In very dilute solutions, the effects are not noticeable.

Abstract The effect of suspended solid particles on the anodic stripping voltammetric signals of CU2+, Pb2+, Cd2+ and Zn2+ was studied. In the size range between 2 and 30 mu m, inorganic suspended particles do not affect the differential capacity of the electrode. The agitation rate usually used for anodic stripping voltammetry (52.4-261.8 rad s(-1)) does not promote mass transfer. Therefore, the decrease in the anodic stripping voltammetric peak current intensity can be used to study adsorption on surfaces.

Abstract Resulting from a collaboration among three departments, the standard enthalpies of formation of some crystalline bis(8-hydroxyquinolate) metal complexes were determined by reaction-solution calorimetry. Enthalpies of hydrolysis were measured for several samples of each complex using various acidic solvents. 8-hydroxyquinoline is written as Hox. At 298.15 K, DELTA(f)H(m)- (M(ox)2,cr)/(kJ mol-1) values are: Mg(ox)2, -516.0 +/- 4.0; Ca(ox)2, -607.7 +/- 4.4; Sr(ox)2, - 585.9 +/- 4.1; Ba(ox)2, -573.4 +/- 4.5; Cu(ox)2, - 103.3 +/- 3.3; Zn(ox)2, - 271.5 +/- 3.6; Cd(ox)2, - 179.6 +/- 4.3; Pb(ox)2, - 145.3 +/- 3.8; Mn(ox)2, -307.1 +/- 3.7; Fe(ox)2, -219.7 +/- 4.5; Co(ox)2, -160.4 +/- 4.2; Ni(ox)2, - 165.5 +/- 5.6. Where feasible, standard enthalpies of sublimation at 298.15 K were determined by measuring vapour pressures as functions of temperature. DELTA(cr)gH(m)(-)(M(ox)2)/(kJ mol-1) values are: Mg(ox)2, 230.2 +/- 4.0; Cu(ox)2, 168.7 +/- 7.3; Zn(ox)2, 183.2 +/- 6.3; Cd(ox)2, 201.7 +/- 7.5; Pb(ox)2, 187.1 +/- 6.2; Mn(ox)2, 194.6 +/- 10.4; Co(ox)2, 205.3 +/- 4.0; Ni(ox)2, 175.4 +/- 6.7. From the standard enthalpies of formation in the gaseous state, the mean metal-ligand dissociation enthalpies were derived and compared with corresponding values for other complexes of these metals.

Abstract Square wave voltametry (SWV) has been successfully applied to arrays of liquid/liquid (L/L) microinterfaces formed across microholes perforated on a polyester film. The study ClO4- ion transfer from water to 1,2-dichloroethane (DCE) showed that the experimental parameters E(SW), E(S), and f are identical to those found for the reversible electron transfer on solid microelectrodes.

Abstract The separation of the diastereoisomers of cinnamoyl derivatives have been studied by thin-layer (TLC) and high performance liquid chromatography (HPLC). TLC separations on two different layers and with two different solvent systems are described. HPLC separation was carried out on a reversed-phase column (Lichrosorb RP-8, 5 mu m) using an isocratic elution [acetonitrile : water-acetic acid (95 : 5)]. The series of compounds includes the cis/trans isomers of ethyl esters of caffeic, ferulic and isoferulic acids.

Abstract The variations observed in synchronous fluorescence spectra of aqucous solutions (pH = 4) of three fuivic acids (fua) upon variation of the concentration of Ai” were anaiyzed by evoiving factor anaiysis (EFA). The three fua samples were extracted from materiais present in a pine wood sou: dry pine needies and the upper and iower sou horizons. The presence of AI” induces quenching and eahancement of bands in the synchronous fluorescence spectra, and concentration constraints are pro posed for lhe EFA anaiysis that allow lhe caicuiation, on a seif-modeiing curve resolution basis, of the number of components that show iineariy independent variations, their spectra, and corresponding concentration profiles. Simuiated and experimentai data seta of simpie known com pounds (catechoi, catfeic acid, sahcyiic acid, and morin) were aiso studied as the first vaiidation of the experimental and data treatment procedures. © 1994 SocieLy for Applicd Spectroscopy.

Abstract Concentrations of Cd, Cr, Cu, Ni, Pb and Zn in surface sediments and aquatic mosses from the Cavado river basin were determined in order to evaluate the overall metal contamination and trace the main pollution sources. The natural background levels were calculated for both plants and sediments (fraction < 63 mum) collected at uncontaminated sites and concentrations were normalized to the natural levels. The maximum resulting contamination factors in the aquatic mosses ranged from 6 (Zn) to 101 (Cr). In the sediments the accumulation rates are lower, between 3 (Zn) and 18 (Pb). The degree of contamination was also evaluated by calculating a metal pollution index and the more polluted reaches were identified. Metal concentration variations in plants and sediments in two different surveys ( 1988 and 1989) were studied by factor analysis. Three factors are sufficient to characterize data variance. Factors corresponding to plants and sediments show different metal composition and provide evidence that industrial effluents and drainage waters from a mining area are the main causes of variations of element concentrations. The seasonal variations of metal concentrations both in plants and sediments are also discussed.