Enrico Prenesti

Spectrum–structure correlation for visible absorption spectra of copper(II) complexes in aqueous solution

Abstract In this study an analysis of visible spectrophotometric data was carried out using more than 100 copper(II) complexes formed by ligands with different coordination environments, and whose aim is the λmax value estimation for equatorially-coordinated copper(II) complexes in solution. Calculations were performed with a least-squares procedure and a bootstrap-based method for accuracy assessment. The results obtained are in good agreement to previous reports describing the coordination of amino, peptide (negatively-charged), pyridine-imidazole nitrogen and carboxylate oxygen, while it was possible to calculate an individual contribution for hydroxide, alcoholate and water oxygen donors. The spectrum–structure correlation for copper(II) complexes in solution is widely discussed in this paper, and an estimation of the uncertainty in relation to the prediction of λmax of copper(II) complexes has also been made.

Ultraviolet–circular dichroism spectra for structural analysis of copper(II) complexes with aliphatic and aromatic ligands in aqueous solution

An attempt has been made to identify the characteristic positions, and their eventual displacements with changing co-ordination, of the charge-transfer bands involving donor groups located on molecules of biological interest [L-malic acid, N-acetyl-L-aspartic acid, (1R,2R)-cyclohexane-1,2-diamine, L-alanyl-L-alanine, L-γ-glutamyl-L-Iµ-lysine, N-acetyl-L-histidine, β-alanyl-L-histidine and N-benzoylglycyl-L-histidyl-L-leucine] such as carboxylate, alcoholate, amine, deprotonated peptide and imidazole. Information about the species formed in solution was obtained by means of pH-metric readings while ultraviolet–circular dichroism spectra were recorded, at fixed pH values, 298 K and I= 0.1 mol dm–3, for the proton–ligand and proton–copper(II)–ligand systems, in order to evaluate a spectrum for each complex formed in solution. Intraligand and charge-transfer bands were assigned for each spectrum with the aim of relating spectral features to the structure of the species formed in solution.

Copper(II) complexes of N-(phosphonomethyl)glycine in aqueous solution: a thermodynamic and spectrophotometric study

Copper(II) complexes with the herbicide N-(phosphonomethyl)glycine (glyphosate) have been investigated in aqueous solution by means of pH-metric measurements at different temperatures, 5 </= T </= 45 degrees C, calorimetry and visible spectrophotometry. Potentiometric data, at all the considered temperatures in the range 2.5 </= pH </= 10.5, can be explained assuming the formation of the species CuLH(0), CuL(-), CuLH(2 -)(- 1), CuL(4 -)(2) and Cu(2)L(+). By using thermodynamic data and calculated electronic spectra for each complex a structural definition is proposed for the different species. Copper(II)-glyphosate complexes are quite stable and must be taken into account in the speciation of natural fluids.

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.

Chemical relevance of the copper(II)-L-carnosine system in aqueous solution : a thermodynamic and spectrophotometric study

Abstract The copper(II)— l -carnosine (L − ) system has been re-investigated in aqueous solution, at I = 0.1 mol dm −1 , different temperatures (5⩽ t ⩽45°C) and with metal to ligand ratios ranging from 3:1 to 1:3. Both potentiometry and visible spectrophotometry were employed. From an overall consideration of all experiments, [CuLH] 2+ , [CuL] + , [CuLH −1 ]°, [Cu 2 L 2 H −2 ]° and [Cu 2 LH −1 ] 2+ were recognized as the species which provide the best interpretation of experimental data. The complex formation constants, determined at different temperatures, allowed us to obtain reliable values of Δ H ° and good estimates of Δ C ° p . From visible spectrophotometric measurements, carried out at different pH and metal to ligand ratios, it was possible to calculate the electronic spectrum of each complex formed in solution. A structure is also proposed for each species, on the basis of thermodynamic and spectral results.

Acid-base properties of a river sediment: Applicability of potentiometric titrations

Abstract The application of potentiometric titrations to the study of the acid-base properties of a river sediment was investigated. A set of alkalimetric titrations were performed on suspensions containing different sediment-solution ratios and EMF measurements were elaborated by a suitable computer program. After the optimisation of the titration procedure, it was possible to refine conditional acid constants. For the considered sediment it was possible to calculate three protonation constants. Comparing calculated pKa with those reported in literature for the characterisation of humic and fulvic material of various origins and for inorganic hydrous oxides, it appears that calculated values are in the range indicated for the assignment of the constants to organic and inorganic titratable groups that can be present on the surface of a natural sediment.

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.

L-γ-glutamyl-L-ϵ-lysine and L-glutamyl-L-ϵ-lysine coordination properties towards copper(II) and nickel(II) in aqueous solution

Abstract The complex formation between copper(II) or nickel(II) and the alifatic dipeptides L-γ-glutamyl-L-ϵ-lysine and L-glutamyl-L-ϵ-lysine has been studied in aqueous solution at 25°C and ionic strength 0.1 mol·dm−3 by means of pH-metric and spectroscopic measurements. In L-γ-glutamyl-L-ϵ-lysine, two α-aminoacidic residues are located at a long distance from each other, and are so far from peptide nitrogen atom that the involvement of dissociated peptide group in coordination is not favored. As a consequence, a small number of complexes is formed, either with copper(II) or nickel(II), and the ML° species predominates over the others. In L-glutamyl-L-ϵ-lysine, the amino group of glutamyl residues is adjacent to the peptide group whose dissociation occurs in the presence of both copper(II) and nickel(II). Either potentiometric or spectroscopic data suggest the formation of a high number of complexes with the absence of a dominant species both for copper(II) and nickel(II): MLH22+, MLH+, M2L2H+, M2L2°, M2L2H−1−, M2L2H−22−, ML2H2°, ML2H−, ML22+, M2L2+, and M2LH−1+ (M=copper(II) or nickel(II)). Since both of the ligands can form homobinuclear complexes with each of the metal ions investigated, mixtures containing both metal ions and one of the peptide ligands have been studied too, but the relevance of heterobinuclear species is not remarkable. The spectroscopic data obtained for single species in solution allowed us to propose the probable structure in solution for several copper(II) complexes.

Formation and stability of proton-amine-inorganic anion complexes in aqueous solution

Interaction of some amines with inorganic ligands was studied potentiometrically in aqueous solutions at 25°C at different ionic strengths. The systems taken into account were: meta-PP, meta-TPP, en-PP, en-TPP, en-HPO42−, dap-SO42−, tetren-HPO42−, 6da-PP and 8da-TPP (meta=methylamine, en=ethylenediamine, tetren=tetraethylenepentamine, dap=1,2-diaminopropane, 6da=1,6-hexanediamine, 8da=1,8-octanediamine, PP=pyrophosphate, TPP=tripolyphosphate). Several ALHr species are formed for all the studied mixed systems (A=amine, L =inorganic ligand), and in some cases ApLqHr species were also found. The stability of mixed proton-ligand-ligand species is proportional to the charges involved in the complexation reaction and, to some extent, it depends on steric characteristic of the ligands. A simple relationship has been found between formation constants of mixed ligand species and charges involved in the complexation reaction. The ionic strength dependence of formation constants has been taken into account, and it was found that, also for these types of mixed complexes, a general equation independent of the nature of the reactants can be used.