Silvia Berto

Interaction of copper(II) with imidazole pyridine nitrogen-containing ligands in aqueous medium: a spectroscopic study

UV (300-400 nm) and FT/IR (4000-850 cm(-1)) spectra were considered for a structural discussion of the copper(II) complexes formed with a series of imidazole-containing ligands (namely L-histidine, N-acetyl-L-histidine, histamine, L-histidine methyl ester and carnosine) in aqueous solution (T=25 degrees C, I=0.1 M). A shoulder at 330 nm was recorded for the main copper(II) complexes with all the ligands considered with the exception of carnosine: this singularity is discussed and a spectrum-structure correlation is proposed. epsilon(330) values were evaluated for CuL (59 M(-1) cm(-1)) and Cu(2)L(2)H(-2) (577 M(-1) cm(-1)) complexes with histamine and for CuL(2) (49 M(-1) cm(-1)) and CuL(3) (163 M(-1) cm(-1)) with N-acetyl-L-histidine, thus indicating the usefulness of UV spectra in the explored region for the purpose of structural definition. FT/IR spectra (recorded both in aqueous solution and on the residue of evaporated solutions of carnosine and N-acetyl-L-histidine only) help to reveal a significant conformational rearrangement of the ligand, corresponding to complex formation in solution: in fact, modifications in the fingerprint region of the FT/IR spectrum for the dimer of carnosine are observed. Indications of a copper(II)-imidazole nitrogen interaction are also obtained from FT/IR data in the 1000-1100 cm(-1) range.

Effect of viticulture practices on concentration of polyphenolic compounds and total antioxidant capacity of Southern Italy red wines

This study aims to assess the effect of three wine grape varieties, three training systems and two bud loads on the Total Antioxidant Capacity (TAC) and polyphenolic composition of Southern Italy red wines produced, during two vintages. Overall, Primitivo, Malvasia nera of Brindisi-Lecce and Montepulciano as grape varieties, single Guyot (SG), single spur pruned low cordon (SLC) and single spur pruned high wire cordon (HSLC) as training systems, 8 and 12 buds/plant as bud loads were compared. Significant differences in the polyphenolic families were shown by the grape varieties and by modifying the vine growing practices. Moreover, the results demonstrated that varieties influenced the TAC (indicating the Malvasia as the more effective one), that SLC led to the lowest level of TAC and that 8 buds/plant increased it. The relationship between antioxidant indexes and the concentration of single polyphenolic families was evaluated and the highest correlation was found between the total polyphenols and the proanthocyanidins family.

Potentiometric and spectrophotometric characterization of the UO22+-citrate complexes in aqueous solution, at different concentrations, ionic strengths and supporting electrolytes

Abstract In this paper we report an investigation on the interactions between dioxouranium(VI) and citrate using potentiometry (H+-glass electrode) and UV-spectrophotometry. Potentiometric measurements were carried out in NaCl and KNO3 aqueous solutions at t = 25 ºC in a wide range of experimental conditions (concentrations, ligand/metal molar ratio, pH, titrants). Measurements in NaCl were carried out at different ionic strength values (0.1 ≤ I/mol L−1 ≤ 1.0); different procedures were employed for the acquisition of experimental data and careful analysis of these data performed. In all cases the speciation model that best fits experimental data takes into account the formation of the following species: UO2(Cit)−, (UO2)2(Cit)22−, (UO2)2(Cit)2(OH)24− , (UO2)2(Cit)2(OH)3−, (UO2)2(Cit)(OH)2−, (UO2)2(Cit)(OH)0, (UO2)3(Cit)2(OH)55−. The dependence on ionic strength of formation constants was taken into account by using both a simple Debye–Hückel type equation and the SIT (specific ion interaction theory) approach. Moreover, a visible absorption spectrum for each complex reaching a significant percentage of formation in solution (KNO3 medium) has been calculated to characterise the compounds found by pH-metric refinement. Recommended values for the uranyl-citrate species were proposed for each ionic strength values in NaCl aqueous solution. Comparison with literature stability constants is reported too.

Measurement of total antioxidant capacity of human plasma: Setting and validation of the CUPRAC–BCS method on routine apparatus ADVIA 2400

BACKGROUND Quantification of Total Antioxidant Capacity (TAC) of human plasma is an important clinical target, since many diseases are suspected to be related with oxidative stress. The CUPRAC-BCS (BCS=Bathocuproinedisulfonic acid) method was chosen since it works using the photometric principle, with stable and inexpensive reagents and at physiological pH. METHODS The method is based on the complex equilibria between Cu(II)-BCS (reagent) and Cu(I)-BCS. Cu(I)-BCS complex is formed by reducing ability of the plasma redox active substances. The photometric signal is achieved at 478 nm and calibration is performed using urate as a reference substance. RESULTS Linearity, linear working range, sensitivity, precision, LoD, LoQ, selectivity and robustness have been considered to validate the method. Absorbance at 478 nm was found linear from 0.0025 up to 2.0 mmol L(-1) of urate reference solution. Precision was evaluated as within-day repeatability, Sr=4 µmol L(-1), and intermediate-precision, SI(T)=15 µmol L(-1). LoD and LoQ, resulted equal to 7.0 µmol L(-1) and 21 µmol L(-1) respectively while robustness was tested having care for pH variation during PBS buffer preparation. Tests on plasma (80 samples) and on human cerebrospinal fluid (30 samples) were conducted and discussed. CONCLUSIONS By the analytical point of view, the photometric method was found to be simple, rapid, widely linear and reliable for the routine analysis of a clinical laboratory. By the clinical point of view, the method response is suitable for the study of chemical plasma quantities related to redox reactivity.

Temporal trends of elements in Turin (Italy) atmospheric particulate matter from 1976 to 2001

The temporal trends of major, minor and trace elements in the total atmospheric particulate sampled in the urban area of Turin (Italy) were determined for the following years: 1976, 1986, 1996 and 2001. The wavelength dispersive X-ray fluorescence (WD-XRF) technique was adopted to determine the concentrations of Ba, Br, Ca, Cl, Cr, Cu, Fe, K, Mg, Mn, Ni, Pb, S, Ti and Zn. A smaller number of samples was also analysed by ICP atomic emission spectroscopy (ICP-AES) and the results were compared with those obtained by WD-XRF to confirm their validity. A clear seasonal pattern with higher concentrations of the aforementioned elements in the cold periods was observed. Moreover, a change in the chemical composition of atmospheric particulate matter was evidenced, particularly between the first (1976 and 1986) and the last (1996 and 2001) years. This change can be attributed both to the greater contribution of Pb and Br to atmospheric pollution in the past and, in recent years, to the higher level of pollutants associated with increased vehicular traffic and industrial activities. The application of chemometric techniques (Principal Component Analysis and Cluster Analysis) allowed us to speculate about the main emitting sources influencing the total atmospheric particulate in these years.

Phototransformation of the Herbicide Propanil in Paddy Field Water

When irradiated in paddy-field water, propanil (PRP) undergoes photodegradation by direct photolysis, by reactions with •OH and CO3•-, and possibly also with the triplet states of chromophoric dissolved organic matter. Irradiation also inhibits the nonphotochemical (probably biological) degradation of PRP. The dark- and light-induced pathways can be easily distinguished because 3,4-dichloroaniline (34DCA, a transformation intermediate of considerable environmental concern) is produced with almost 100% yield in the dark but not at all through photochemical pathways. This issue allows an easy assessment of the dark process(es) under irradiation. In the natural environment, we expect PRP photodegradation to be important only in the presence of elevated nitrate and/or nitrite levels, e.g., [NO3-] approaching 1 mmol L-1 (corresponding to approximately 60 mg L-1). Under these circumstances, •OH and CO3•- would play a major role in PRP phototransformation. Because flooded paddy fields are efficient denitrification bioreactors that can achieve decontamination of nitrate-rich water used for irrigation, irrigation with such water would both enhance PRP photodegradation and divert PRP dissipation processes away from the production of 34DCA, at least in the daylight hours.

Properties of the humic-like material arising from the photo-transformation of L-tyrosine.

The UVB photolysis of L-tyrosine yields species with fluorescence and absorption spectra that are very similar to those of humic substances. By potentiometric measurements, chemical modeling and the application of NMR, mass spectrometry and laser flash photolysis, it was possible to get insights into the structural and chemical properties of the compounds derived by the L-tyrosine phototransformation. The photolytic process follows aromatic-ring hydroxylation and dimerization. The latter is presumably linked with the photoinduced generation of tyrosyl (phenoxy-type) radicals, which have a marked tendency to dimerize and possibly oligomerize. Interestingly, photoinduced transformation gives compounds with protogenic and complexation capabilities similar to those of the humic substances that occur naturally in surface waters. This finding substantiates a new and potentially important abiotic (photolytic) pathway for the formation of humic compounds in surface-water environments.

Modeling the photochemical transformation of nitrobenzene under conditions relevant to sunlit surface waters: Reaction pathways and formation of intermediates.

Nitrobenzene (NB) would undergo photodegradation in sunlit surface waters, mainly by direct photolysis and triplet-sensitized oxidation, with a secondary role of the *OH reaction. Its photochemical half-life time would range from a few days to a couple of months under fair-weather summertime irradiation, depending on water chemistry and depth. NB phototransformation gives phenol and the three nitrophenol isomers, in different yields depending on the considered pathway. The minor *OH role in degradation would make NB unsuitable as *OH probe in irradiated natural water samples, but the selectivity towards *OH could be increased by monitoring the formation of phenol from NB+*OH. The relevant reaction would proceed through ipso-addition of *OH on the carbon atom bearing the nitro-group, forming a pre-reactive complex that would evolve into a transition state (and then into a radical addition intermediate) with very low activation energy barrier.

Development of a speciation model for the interpretation of the acid-base properties of grape red wines

Abstract Starting with known analytical concentrations related to the considered Italian red grape table wines, we now expound the methodology which allows us to establish a relationship among (a) the molar concentration of a series of substances of routine measurement, (b) the total acidity and (c) the pH value of each fluid at a thermodynamic level. The experimental pH value of each wine is compared with the calculated one, obtained as a result of a thermodynamic simulation based on the contemporary treatment of a series of chemical equilibria (17 reactants, 77 equilibria). Accurate equilibrium constant values are previously refined on test substances components of red wines (namely: acetic, tartaric, succinic and citric acid) starting by pH-metric readings (at 25°C) recorded in appropriate experimental conditions. In fact, the chemical conditions take care of both the solvent composition, as regards the amount of ethanol, and the ionic strength value, to take into account the effect due to the background electrolytes. In order to achieve information on ion pair formation in the wine, we have now carried out a series of titration using tetraethylammonium iodide as background salt. Using protonation constant values in both KCl or tetraethylammonium iodide, and a series of measurements with calcium(II) ion, the stability of Ca2+- and K+- complexes (or ion pairs) with some reference ligands has been evaluated. A new hemical model has then been built to interpret in terms of chemical equilibria the pH of each wine, which allows as well to obtain a reliable estimation of the free concentration of both Ca2+ and K+, useful to solve technological problems related to many steps of the wine production and evolution. Operative advantages, with respect to typical oenological problems, are shown passing from the analytical to the equilibrium composition of each wine.

Assessing the formation of weak sodium complexes with negatively charged ligands

The stability of sodium complexes with poly-carboxylic and polyamino-carboxylic acids is investigated with ion-selective electrode-Na(+) potentiometry, working at strictly constant ionic strength. It is observed that the formation constants of the Na(+) complexes with monoligand stoichiometry (ML) increase with the number of charges on the ligand. For example, in poly-carboxylic acids this dependency is linear and is well captured by an experimental equation. A different behaviour is observed for the poly-amino carboxylic acids, which show higher complexation capabilities reaching a plateau of the binding energy past a specific ligand size. The experimental results are discussed qualitatively using ab initio calculations based on DFT B3LYP, and the principal electronic characteristics of the ligands under investigation are identified. As a result of the flexibility imparted by the long chains of polyamino-carboxylic ligands, both experimental and theoretical models demonstrate that nitrogen atoms in proximity of Na(+) ions can participate in the metal coordination, thus providing further stabilization for the complexes. Moreover, by increasing the ligand size the stabilization gained in terms of ΔG reached a plateau for EDTA, in agreement with experimental observations.