Publications

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.

Abstract An evolving factor analysis procedure with concentration constraints (gradient concentration window) was applied to the analysis of data sets of aqueous Fourier transform infrared (FT-IR) spectra of carboxylic acids (acetic, malonic and succinic acids) collected in experiments with varying pH. Besides the calculation of the number of acid-base systems, this procedure allowed the calculation of the FT-IR spectra of the acid-base species present in equilibrium as well as the corresponding pK(a) values.

Abstract The interaction of AI(III) with two samples of fulvic acids (fua), extracted from materials present in a pinewood soil (fua2 from the upper soil horizon, or leaf litter, and fua3 from lower soil horizons), was followed by synchro nous fluorescence (SyF) spectroscopy at pH 4. The variations observed in the inverted second-derivative spectral data were analyzed by SIMPLISMA, a self-modeling curve resolution technique. Three: binding sites were detected for each fua sample, and their spectra and SyF intensity profiles were obtained. Conditional stability constants for coordination of one binding site of each fua and AI(III) were obtained (log values): fua2, 5.65(15); fua3, 4.64(2). The experimental and data analysis methodologies were validated by analysis of data obtained for salicylic acid under the same conditions. The log value found for its conditional stability constant for AI(III) coordination at pH 4 was 4.34(15).

Abstract Three fulvic acids (fua) extracted from a Portuguese pinewood soil (dry pine needles, fua1, leaf litter, fua2, and lower soil horizon, fua3) have been studied by synchronous molecular fluorescence spectroscopy (SyF) at variable pH and by potentiometric pH titrations. The number of macroscopic acid-base systems and their pK(a)s were calculated by analysis of the SyF-pH hyphenated data with a self-modeling curve resolution technique (evolving factor analysis, EFA). Four macroscopic acid-base systems were detected in the fulvic acid samples (with pK(a)s around 3.0, 4.5, 7.0 and 9.0). The concentrations of the groups responsible for the acid-base systems were calculated by a standard non-linear least squares adjustment of pH potentiometric titration curves using the pK(a) values obtained by EFA. The procedure detected differences between the three fua: the concentration of carboxylic groups increased from fua1 to fua3 but, in contrast, the concentration of the phenolic groups decreased. These results correlate well with the expected extent of humification of the samples.