Publications

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.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation of crystalline 1,1,1-trifluoro-4-(2-thienyl)-4-hydroxy-3-buten-2-one, HTTFA, and 1,1,1-trifluoro-4-(2-thienyl)-4-mercapto-3-buten-2-one, HTTFAS, at T = 298.15 K were measured by rotating-bomb calorimetry and the standard molar enthalpies of sublimation at T = 298.15 K were measured by microcalorimetry, with the following results: [GRAPHICS] The results demonstrate an increase in stabilization energy of approximate to (38.7 +/- 5.0) kJ.mol(-1) in HTTFA compared with thiophene and that in these molecules, the intramolecular hydrogen bond energy (O-H...O), appears approximate to 20 kJ.mol(-1) larger than for (S-H...O). (C) 1997 Academic Press Limited.

Abstract Microhole arrays created by laser photoablation of thin polymer films were used to support an organic gel phase prepared by addition of 1,3:2,4-dibenzylidene sorbitol (DBS) to a solution of o-nitrophenyloctyl ether (NPOE) and an appropriate supporting electrolyte. The preparation and properties of the organic gel phase are described and the NPOE-DBS gel is assessed. The polarized microhole supported organic gel interface is shown to be capable of use as an amperometric detector for ions. (C) 1997 Published by Elsevier Science Ltd.

Abstract The fulvic acid (fua) fractions of two samples of composted solid wastes [urban (urfua) and livestock (lsfua) wastes], commercialized to be used in agriculture as organic correctives or fertilizers, were analyzed for their affinity towards Cu(II) at pH=6. Molecular fluorescence spectroscopy (synchronous mode) was used to monitor the quenching caused by the complexation upon addition of Cu(II) to fua. Spectral data were preprocessed by a chemometric self-modeling mixture analysis method (SIMPLISMA) to detect the number of different types of fluorescent binding sites that exist in each fua, their spectra and the corresponding quenching profiles [fluorescence intensity as function of the total Cu(II) concentration]. From the analysis of the quenching profiles, the amount of binding sites (C-L) and the corresponding conditional stability constants (K') were calculated. Both fua samples have approximately C-L = 0.21 mmol/g and the logarithms of K' are 4.21(3) and 4.51(8), respectively for urfua and lsfua. The differences detected between these fua samples and those extracted from natural soils can be attributed mainly to the relatively small humification extent of the present anthropogenic fua samples.

Abstract A method for the classification of fulvic acids (FA) and similar substances Is presented, It consists of three steps: (i) for each sample, sets of synchronous molecular fluorescence spect ra as the pH is changed are acquired; (ii) the spectral set is reduced to a small number of spectra and concentration profiles of the detected components by evolving factor analysis with a gradient concentration window (EFA-GCW) are obtained; (iii) the spectra of the components of the samples are subjected to pattern recognition analysis by cluster analysis and multi-dimensional scaling. The procedure was tested with 13 samples of FA of natural and anthropogenic origin. Classification rules as a function of the origin and acid-base properties of the samples, in the form of figures with spectra and tables with spectral characteristics, were obtained. The classification according to the origin of the FA samples is useful for the evaluation of the 'extent of humification of FA, The following information on the acid-base properties of the fluorescent fractions of FA was obtained: only FA extracted from soil have fluorescent fractions with relatively strong acid character (pK(a) approximate to 3.2); all FA extracted from different origins have similar fluorescent structures with relatively weak acid character (pK(a) approximate to 6.2); in addition, FA extracted from low humified materials (leaf litter and composted wastes) have another set of similar fluorescent structures with weak acid character (pK(a) = 9.2).