Publications

Abstract This review presents some recent developments in the field of electroanalytical sensors. We first explain the working principle of electrochemistry at the interface between two immiscible electrolyte solutions (ITIES), illustrated by the example of copper transferring through a water/1,2-dichloroethane interface when the ionophore 1,4,7,10-tetrathiacyclododecane is present in the organic phase. The obtained results show that assisted ion-transfer reactions take place with both Cu-I and Cu-II, but that the interfacial process is complicated by the fact that Cut disproportionates in water and that Cu-II can be reduced in the organic phase. Based on the same experimental methodology, a new type of amperometric detector for non-redox ions has been developed using a composite polymer membrane supporting a gelified organic phase that can incorporate an ionophore such as valinomycin. We report here the use of a (o-nitrophenyl octyl ether)-(poy(vinyl chloride) (NPOE-PVC) gel micro-interface as a detector for cations and anions in ion-exchange chromatography. The main advantage of this approach is that selectivity and sensitivity can be tailored by the choice of the ionophore and by the polarisation potential. This ion detector has also been incorporated in a miniaturised total-analysis system (mu-TAS) fabricated in a polymer sheet by UV-laser photoablation. This microfabrication technique is used for the prototyping of a disposable capillary-electrophoresis microsystem comprising on-chip injector, separation column and electrochemical detector. This system is further used with built-in carbon-ink electrodes for the detection of electroactive species. These microsystems are now under development for immune-sensor applications.

Abstract The adsorption behaviour of n-hexanol on a Au (111) single-crystal electrode from aqueous 0.2 mol dm(-3) NaClO4 was studied on the basis of dynamic capacity measurements and of capacitive charge measurements by chronocoulometry. The charge density, sigma(M), as a function of the applied potential, E, and of the n-hexanol concentration was analysed thermodynamically, yielding the Gibbs surface excess, Gamma, and the Gibbs energy of adsorption, Delta(ads)G degrees, of n-hexanol as a function of potential and concentration. The results of the thermodynamic analysis of the adsorption data at the potential of maximum adsorption are discussed in comparison with the literature data for the adsorption of this compound on Hg [1,2] and on silver single-crystals [3,4]. The results obtained show that the adsorption process could be described by a Frumkin isotherm, the parameters of which were determined and discussed. The values of the standard Gibbs energy of adsorption suggest physical adsorption of the alcohol, without the existence of specific interactions of the adsorbed molecules with gold. Differences and inconsistencies for the results obtained from the analysis of charge and capacity data are discussed in terms of the experimental technique.

Abstract Cyclic voltammetry and capacitance measurements were performed using gold single crystal electrodes with 13 different crystallographic orientations. The experiments were performed in solutions of four different oxoanions: perchlorate, nitrate, sulphate and phosphate. Evidence of surface structure sensitivity was deduced for both the anion adsorption and surface oxidation phenomena. The current density and differential capacity profiles exhibit features that seem characteristic of the orientation of the terraces but are also sensitive to the density and orientation of the steps. For all of the gold faces under study, the anion adsorbability increases in the following order: ClO4- < NO3- < SO42 < H2PO4. A parallel between this order of adsorbability and the degree of stereochemical 'matching' between the anions and the surface atomic arrangement is suggested.

Abstract A set of parameters consistent with the CHARMM force field has been determined for molecular dynamics simulations of several DOTA- and DOTP-Ln(III) chelates. Bonding and van der Waals parameters were derived from the available experimental data and analogy to similar ones in the existing force field. Net atomic charges were derived from ab initio calculations at the Hartree-Fock level to reproduce molecular electrostatic potentials (ESPs), with an effective core potential (ECP) basis set for the metal ion and the 6-31G* basis set for the ligand atoms. The charges are consistent with the TIP3P water model. Preliminary molecular dynamics simulations of the lanthanide chelates in aqueous solution were performed using the Nose-Hoover thermostat at 300 K. The new parameters correctly predicted the molecular structures and stability of the chelates major and minor isomers. (C) 1999 John Wiley & Sons, Inc. Int J Quant Chem 73: 237-248, 1999.

Abstract The standard (p(O) = 0.1 MPa) molar enthalpy of combustion at T = 298.15 K of crystalline benzanthrone was determined as Delta(c)H(m)(O) = -(8114.7 +/- 2.0) kJ.mol(-1) by static-bomb calorimetry, and the standard molar enthalpy of formation of the crystal at T = 298.15 K was derived as Delta(f)H(m)(O)(cr) = -(4.1 +/- 3.0) kJ.mol(-1). Vapour pressure as a function of temperature was measured using the mass-loss Knudsen effusion technique, from which the standard molar enthalpy of sublimation at T = 298.15 K was derived as Delta(cr)(g)H(m)(O)= (126.6 +/- 0.6) kJ.mol(-1). The standard molar enthalpy of sublimation at T = 298.15 K was also measured by the quartz oscillator method, Delta(cr)(g)H(m)(O) (129.7 +/- 2.1) kJ.mol(-1) (C) 1999 Academic Press.

Abstract Four monovarietal red wines, Tinta Roriz, Tints Barroca, Touriga Nacional, and Touriga Francesa, were studied for their complexometric properties toward copper. For the purpose, ion selective electrode potentiometric titrations were carried out, and the data were treated by two methods suitable for heterogeneous ligands: the Scatchard plot, which provided the complexation capacity (CCtotal = maximum number of moles of sites per liter), and the differential equilibrium function (DEF), which provided the conditional stability constants of the sites effectively involved in the metal complexation (K-DEF) at a given titration point. The different wines displayed similar properties: CCtotal ranged from 4.5 x 10(-3) (Tinta Barroca) to 4.9 x 10(-3) M (Touriga Francesa), and log K-DEF values were between 4.2 and 6.5. The range of log(\Cu\(bound)/CCtotal) = log theta embraced in the titration was between -0.2 and -1.9. With regard to the natural levels of copper, from 4.4 x 10(-7) (Tinta Roriz) to 1.3 x 10(-6) M (Touriga Nacional), and ligands (CCtotal) in the wines, it can be expected that copper will be strongly complexed in the studied wines (log K-DEF > 6). Studies carried out, in parallel, for solutions of isolated seed tannins and skin polyphenols (mainly anthocyans) showed that their contribution to the CCtotal of the wines was <40% for tannins and <2% for skin polyphenols. However, skin polyphenols were shown to be much stronger copper ligands (log K-DEF = 6.7, log theta = -1.5) than tannins (log K-DEF = 4.5, log theta = -1.5).

Abstract The structural elucidation of 24 xanthones with different substitution patterns was performed by spectroscopic methods, namely 2D NMR techniques, such as correlation spectroscopy (COSY), nuclear Overhauser effect (NOE), heteronuclear correlation (HETCOR) and a 1D NMR technique, selective insensitive nuclei enhanced by polarization transfer (INEPT). (C) 1997 John Wiley & Sons, Ltd.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation of eight copper(II) fluorinated beta-diketonates at the temperature 298.15 K were determined by high-precision solution and reaction calorimetry. The standard molar enthalpies of sublimation of the same copper(II) complexes at the temperature 298.15 K were determined by effusion methods. From the enthalpies of formation of the complexes in the gaseous state, the average molar dissociation enthalpies [D-m] (Cu-O) were derived and compared with identical parameters obtained for non-fluorinated copper(II) beta-diketonates. [GRAPHICS] The following abbreviations are used in the table: HTFBA, 4,4,4-trifluoro-1-phenylbutane-1,3-dione; HTFFBD, 4,4,4-trifluoro-1-(2-furanyl)-butane-1,3-dione; HTFNBD, 4,4,4-trifluoro-1-(2-naphthyl)-butane-1,3-dione; HTFHD, 1,1,1-trifluorohexane-2,4-dione; HTFMHD, 1,l,1-trifluoro5-methylhexane-2,4-dione; HTFDHD, 1,1,1-trifluoro-5,5-dimethylhexane 2,4-dione; HTFMHPD, 1,1,1-trifluoro-5-methylheptane-2,4-dione; HHPFDOD, 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyloctane-4,6-dione. (C) 1998 Academic Press.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation Delta(f)H(m)degrees(cr) at T = 298.15 K were determined using static-bomb calorimetry for crystalline 4-methylpyridine N-oxide (4MePyNO), 3-cyanopyridine N-oxide (3CNPyNO), 4-cyanopyridine N-oxide (4CNPyNO), 3-hydroxypyridine N-oxide (3OHPyNO), 2-pyridinecarboxylic acid N-oxide (2CO(2)HpyNO), 4-pyridinecarboxylic acid N-oxide (4CO(2)HPyNO), 3-methyl-4-nitropyridine N-oxide (3Me4NO(2)PyNO), 2-pyridinecarboxylic acid (2CO(2)HPy), and 4-pyridinecarboxylic acid (4CO(2)HPy). The standard molar enthalpies of sublimation Delta(c)(rg) H(m)degrees at T = 298.15 K were measured by microcalorimetry, or by a mass-loss effusion technique, and from the enthalpies of formation of the gaseous compounds the dissociation enthalpies D(m)degrees of the (N+-O-) dative covalent bonds were derived. [GRAPHICS] Comparison has been made with D(m)degrees(N-O) values in pyridine N-oxide derivatives. (C) 1998 Academic Press.