Publications

Abstract Aqueous solutions of carboxylic acids and phenols at micromolar concentration levels were analysed by synchronous fluorescence (SyF) spectroscopy. A strategy, based on provoking controlled variations in SyF spectra by changing the pH and treating spectral data by evolving factor analysis with specific concentration constraints, was developed and evaluated to extract information from the SyF data to determine acid-base parameters for;simple acids and mixtures, The procedure was tested on an aqueous mixture of salicylic acid, caffeic acid and catechol as well as on pure solutions of these and other acids.

Abstract The interaction of Be(II) with two samples of fulvic acids (fua), extracted from materials present in a pinewood soil (fua2 from upper and fua3 from lower soil horizons), was followed by synchronous molecular fluorescence spectroscopy at pH = 6 and 11. The variations observed in the spectral data were analyzed by evolving factor analysis (EFA). It was found that Be(II) is a useful probe for detecting different ligand structures in complex mixtures of the fua type. The existence of common ligand structures in the two fua samples at both pH values studied was observed. These are probably of the salicylic acid type. Dihydroxylic structures of the catechol type were also detected. The logarithm of the mean conditional stability constants for coordination of the fua ligand structures of the salicylic acid type and Be(II) were obtained (at a pH of 6 and 11, respectively): fua2, 5.85(2) and 5.24(9); fua3, 6.5(1) and 5.08(4). This strong coordination indicates that fua can have an important function in the immobilization of Be(II) dispersed into the environment.

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.