Publications

Abstract Xanthine oxidase (XO) is a highly versatile flavoprotein enzyme, ubiquitous among species (from bacteria to human) and within the various tissues of. mammals. The enzyme catalyses the oxidative hydroxylation of purine substrates at the molybdenum centre (the reductive half-reaction) and subsequent reduction Of O-2 at the flavin centre with generation of reactive oxygen species (ROS), either superoxide anion radical or hydrogen peroxide (the oxidative half-reaction). Many diseases, or at least symptoms of diseases, arise from a deficiency or excess of a specific metabolite in the body. For an example of an excess of a particular metabolite that produces a disease state is the excess of uric acid which can led to gout. Inhibition of XO decreases the uric acid levels, and results in an antihyperuricemic effect. Allopurinol, first synthesised as a potential anticancer agent, is nowadays a clinically useful xanthine oxidase inhibitor used in the treatment of gout. There is overwhelming acceptance that xanthine oxidase serum levels are significantly increased in various pathological states like hepatitis, inflammation, ischemia-reperfusion, carcinogenesis and aging and that ROS generated in the enzymatic process are involved in oxidative damage. Thus, it may be possible that the inhibition of this enzymatic pathway would be beneficial. In this review the State of the Art will be presented, which includes a summary of the progress made over the past years in the knowledge of the structure and mechanism of the enzyme, associated pathological states, and in the efforts made towards the development of new xanthine oxidase inhibitors.

Abstract The standard (p(o) = 0,1 MPa) molar enthalpies of combustion in oxygen, at T = 298.15 K, were measured by rotative bomb calorimetry for crystalline N,N-diethyl-N'-furoylthiourea, (2-C4H3O)CONHCSN(C2H5)(2), HFET, and N,N-diisobutyl-N'-furoylthiourea, (2-C4H3O)CONHCSN(iso-C4H9)(2), HFIB. The standard molar enthalpies of sublimation of both HFET and HFIB were measured by high-temperature Calvet microcalorimetry. These values were used to derive the standard molar enthalpies of formation of the compounds, in their crystalline and gaseous phases. [GRAPHICS] (C) 2002 Published by Elsevier Science Ltd.

Abstract Complexation properties of an anthropogenic fulvic acid (FA) extracted from a composted sewage sludge (csFA) for Cu(II), Pb(II) and Cd(II) were studied at pH=6 and at a concentration of 25 mg L-1. For the case of Cu(II), a particular analysis of the complexation phenomena was done at pH values of 3, 4, 5 and 6 and at aqueous FA concentrations of 25, 50 and 100 mg L-1 by synchronous excitation molecular fluorescence spectroscopy (SyF). Potentiometric titrimetry with Cu(II). Pb(II), Cd(II) and H+ ion-selective electrodes and acid-base conductimetric titrations were used to obtain experimental information about the acid properties and complexation phenomena. A comparison of the results obtained for csFA with a natural soil FA (sFA) was made. Differences have been detected in the structural composition of the two samples and in the structure of the binding sites. In the csFA, binding site structures containing nitrogen probably play an important role in the complexation, besides oxygen containing structures. Complexation by sFA is mainly due to carboxylic and phenolic structures. Nevertheless, this work shows that csFA have macroscopic complexation properties (magnitude of the conditional stability constant and binding sites concentration) somewhat similar to the natural sFA samples.

Abstract A three-way analytical methodology experimentally based on fluorescence excitation emission matrix (EEM) and in PARAFAC and TLD chemometric analysis was assessed for the quantification of verapamil drug in a tablet formulation. A standard addition procedure generates experimental information compatible with the chemometric data analysis model allowing the estimation of verapamil with a detection limit of about 0.04 mg/l using methanol as solvent. The structure of the verapamil EEM follows a trilinear model, but background signals (first- and second-order scatter bands) did not-a trilinear three-factor model is necessary to describe experimental datasets. The comparison of a three-factor PARAFAC model with a United States Pharmacopoeia (USP) standard chromatographic method showed similar results.

Abstract The effect of the pH (in the range between 3 to 6) on the stability of the complexes formed between the stronger fluorescent binding sites of a soil fulvic acid (FA) and Cu(II), Ni(II) and Fe(III) ions, at a concentration of 25 mg L-1 in KNO3 0.1 M, was studied The analytical methodology consisted on monitoring the synchronous fluorescence spectra of FA as function of the metal ion concentration. Spectral data were preprocessed by SIMPLISMA, a self-modeling mixture analysis method, to obtain improved quenching profiles to be used in the estimation of equilibrium parameters. Two methods were used in the interpretation of the quenching profiles: (i) graphical procedures based in Stern-Volmer analysis; and (ii) a non-linear least-squares procedure. Both two methods allowed estimation of the conditional stability constants (Kc). However, the Stern-Volmer analysis originated useful results only when the logarithm of Kc is relatively small (Log Kc < 5). Besides the calculation of Kc, the two methods allowed the estimation of the percentage of fluorescent structures not accessible for the complexation of the three metal ions. The Log Kc were: Cu(II) ion, 3.42 +/- 0.04, 4.12 +/- 0.07, 4.63 +/- 0.07 and 5.1 +/- 0.3 respectively for pH = 3, 4, 5 and 6; Ni(II) ion, 3.1 +/- 0.1, 3.48 +/- 0.06, and 4.03 +/- 0.07 respectively for pH = 4, 5 and 6; Fe(III) ion, 5.7 +/- 0.2 and 5.86 +/- 0.09 respectively for pH = 3 and 4.

Abstract Butyltin compounds are widespread contaminants which have also been found in some wines, determined by Liquid-liquid extraction followed by alkylation with a Grignard reagent and gas chromatography-mass spectrometric (GC-MS) analysis. A promising alternative to this extraction/derivatization method is the one-step tetraethylborate in situ ethylation/solid-phase micro-extraction (SPME) method. In this work, a SPME-GC-MS method for the determination of butyltin compounds in wine was optimised. The optimised parameters concerned the pre-treatment with tetramethylammonium. hydroxide, matrix modification with sodium chloride, tetraethylborate concentration, extraction time and temperature, and the GC separation program. The analytical figures of merit of the optimised method (range, limit of detection (LOD) and reproducibility) were evaluated. The sensitivity (range 20-1421 kcounts mug(-1) 1(-1) as Sn) and LOD (range, 0.01-0.2 mug 1(-1) as Sn) depended greatly on the butyltin species to be measured and on the type of wine. For the tested species (monobutyltin, dibutyltin and tributyltin) the highest sensitivities were achieved for Port wine samples, followed by red wine > white wine > white Verde wine. The method allowed acceptable repeatability (relative standard deviation (R.S.D.), 6-8%; n = 4) and reproducibility (R.S.D., 8-9%; n = 3).

Abstract Butyltin compounds are widespread contaminants that have also been found in some wines. The purpose of the present work was to make a survey of butyltin compounds in Portuguese wines. Forty-three table wines and 14 Port wines were analyzed for butyltin contents by using solid-phase microextraction gas chromatography mass spectrometry (SPME-GC-MS). In 14% of the analyzed wine samples, measurable dibutyltin (DBT) was found at concentrations ranging between 0.05 and 0.15,mug/L as Sn. Monobutyltin (MBT) was also observed (0.05 mug/L as Sn) in just a single wine. A search for the possible sources of DBT residues found in the wines was carried out. Therefore, some plastics and oak wood used in the process of wine-making, which have been directly in contact with the musts or the wines, were studied to check their possible release of butyltins. The eventual presence of DBT was also tested directly along the vinification process, from the must to the finished product. The results suggest that high-density polyethylene containers used in the transfer of wine in an early stage of the vinification process may be the main sources of these contaminants. Therefore, it is recommendable that plastic materials to be used in wineries be previously tested for the release of butyltin compounds.

Abstract A chemiluminescent flow system for bromate detection, based on the reaction of bromate with sulphite in acid medium and using the steroid hydrocortisone as sensitiser, was studied. A factorial analysis strategy for the study of the effect on the system response of the experimental factors, flow rates of two pumps (Q(1) - acid sulphite plus hydrocortisone aqueous solution; Q(2) carrier, water), sample injection volume (V-L), reactor volume (V-R), sulphite concentration (C-S), hydrocortisone concentration (C-H) and acid concentration (C-A), was used. Screening analysis of the system performance was made using Plackett Burman designs. The system optimisation procedure was achieved by three levels three factors full factorial designs. V-L and C-H are the most significant factors - a quadratic C-H term was also observed to be significant. The optimised system responded linearly (logarithm of the detector signal as function of the logarithm of the bromate concentration) in the concentration range between 3.6 x 10(-7) and 5.0 x 10(-4) M with a limit of detection of about 8.0 x 10(-8) M (about 10 microg/l). An analysis of some interfering ions was made and it was suggested that bromide and chloride begin to quench chemiluminescence when they are in a 10-fold excess relatively to bromate concentration.