Publications

Abstract The simultaneous torsion and mass-loss effusion technique was used to measure the vapour pressure of the crystalline complexes of iron(III) with pentane-2,4-dione (HACAC) and with 2,2,6,6-tetramethylheptane-3,5-dione (HDPM), as a function of temperature, from T = 369.3 K to T = 387.5 K and from T = 359.8 K to T = 377.8 K, respectively. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation at the mean temperature of the experimental temperature ranges, were derived for both complexes. The mean values obtained from both techniques are: for Fe(ACAC)(3), Delta(cr)(g)H(m) degrees (377.8 K)/(kJ . mol(-1)) = (124.6+/-0.9); and for Fe(DPM)(3), Delta(cr)(g)H(m) degrees(377.8 K)/ (kJ . mol(-1)) = (125.8+/-0.9). Using the estimated value of Delta(cr)(g)C(p,m)degrees = -50 J . K-1. mol(-1), for both complexes, the standard molar enthalpies of sublimation at T = 298.15 K, Delta(cr)(g)H(m) degrees (298.15 K)/(kJ . mol(-1)), were estimated as (128.6+/-0.9) and (129.3+/-1.2), respectively. From the standard molar enthalpies of formation of the gaseous complexes, the mean molar (Fe-O) bond dissociation enthalpies were derived. (C) 1996 Academic Press Limited

Abstract The interactions between UO22+ and fulvic acids (FUA) mere studied by a methodology that involves synchronous molecular fluorescence spectroscopy, to monitor the quenching of the intrinsic fluorescence of FUA by UO22+, and a self-modelling mixture analysis method (SIMPLISMA), to treat spectroscopic data, This methodology was applied to the analysis of the interaction of UO22+ with salicylic acid at pH 3.5 and with a soil FUA at pH 3.5 and 7.0, in this case in the presence of various concentrations of carbonate ion (10(-5), 10(-4) and 10(-3) mol l(-1)), From the calculated quenching fluorescence intensity profiles, using either the Stern-Volmer relationship or a non-linear least-squares method, mean conditional stability constants (log values with standard deviations in parentheses) were estimated for salicylic acid [respectively 2.72(4) and 2.77(6)], for FUA at pH 3.5 [3.93(2) and 4.4(1)] and pH 7.0 [4.06 and 4.1 (average values for the various concentrations of carbonate ion)l. The non-linear least-squares method also allowed the estimation of the number of binding sites that exist in FUA (0.11 and 0.24 mol g(-1) at pH 3.5 and 7.0, respectively).

Abstract The interaction of the beryllium ion [Be(ll)] with one of the major constituent of soil organic matter, fulvic acids (fua), was investigated. The complexation of Be(ll) by two samples of fua (amph and gran), at a concentration of 80 mg/L, was monitored by synchronous fluorescence spectroscopy at four pH values (4, 5, 6, and 7). A self-modeling curve resolution technique (evolving factor analysis) was used in the analysis of the sets of spectra collected at increasing Be(ll):fua ratio to obtain concentration profiles that ideally correspond to one type of binding site. These profiles were adjusted to a 1:1 complexation model. Quite strong complexation of Be(ll) by fua occurs at nearly neutral pH (6-7) (logarithm of the conditional stability constant between 5.6 and 6.5), indicating that fua probably affect markedly the mobility of Be(ll) in the environment.

Abstract The major binding sites for Al(III) in six samples of fulvic acids (fua) extracted form soils and leaf litters were investigated by synchronous fluorescence (SyF) spectroscopy. Two samples of fua from soil of an oak forest (two horizons, 0-5 cm, fuaol, and 5-15 cm, fuao2) and four fua like samples extracted from leaf litters (eucalyptus, fern, oak and chestnut coverture, respectively feu, fer, foa and fch) were studied. The SyF spectra of the mixtures of fua and increasing concentration of Al(III), at pH 4, were analyzed by evolving factor analysis (EFA), a self-modeling curve resolution method, to detect the number of major binding sites, their SyF spectra and SyF profiles as function of the AI(III) concentration. The overall set of calculated SyF spectra was analyzed by pattern recognition methods, such as cluster analysis and multidimensional scaling, to detect similarities and differences between them. Although there are differences in the intrinsic SyF properties of fua extracted from soils and leaf litters, the soil fua samples showing a more complex binding site composition, the most important binding site is common to all fua samples studied. The amount of this binding site was roughly estimated. It is approximately the same for all samples but for fuao2, in which the amount is twice the others.

Abstract A sample of coastal marine fulvic acids (mfua) was studied and its binding site structures that form stable complexes with metal ions were identified. A previously developed self-modeling methodology, based on the coupling of synchronous fluorescence (SyF) spectroscopy with evolving factor analysis (EFA), was used for the analysis of the interactions between mfua and two metal ions that act as probes for binding sites, namely Be(II) and A1(III). Two types of binding site structures were detected, probably of the salicylic acid and catechol types. The values of the conditional stability constants between mfua and the two metal ions were: for Be(II), at pH = 6, log K = 5.32(8); for A1(III), at pH = 3, log K = 5.1(2). The concentration of the corresponding binding sites was found to be less than one half of those found for soil fulvic acid samples.

Abstract The Cu(II) complexation properties of a dilute solution of a marine fulvic acid sample (mfua) (25 mg/L solution in 0.1 mol/L potassium nitrate at pH=6) were studied by molecular fluorescence spectroscopy. The emission and the synchronous fluorescence (SyF) modes were used to compare their advantages and limitations. In the treatment of results, spectral data were pre-processed by a self-modeling mixture analysis method (SIMPLISMA) to detect different variations (components) in the raw data and to extract the spectra and quenching profiles of these components. These profiles of the quenching provoked by the Cu(II) ion on the mfua fluorescence were analyzed by the Stern-Volmer method and by a non-linear least squares procedure to obtain the conditional stability constants (K'). The log(K') for the strongest binding sites obtained from the non-linear analysis was 4.52(8) and 5.0(1), respectively from the emission and SyF spectral data. The overall log(K') obtained from the Stern-Volmer analysis was 4.32(7) and 4.42(6), respectively.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of combustion at T = 298.15 K were measured by static bomb combustion calorimetry for liquid N,N-diethylaniline, N,N-dimethyl-m-toluidine, N,N-dimethyl-p-toluidine, and N-ethyl-m-toluidine. Vaporization enthalpies for N,N-dimethyl-m-toluidine and N-ethyl-m-toluidine were determined by correlation gas chromatography. Derived standard molar values of Delta(f)H(m) degrees(g) at 298.15 K for N,N-diethylaniline (62.1 +/- 7.6); N,N-dimethyl-m-toluidine (72.6 +/- 7.3), N,N-dimentyl-p-toluidine (68.9 +/- 7.4), N-ethyl-m-toluidine (30.5 +/- 3.8 kJ . mol(-1)) were obtained.