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Hydroxypyrone derivatives have a good bioavailability in rats and mice and have been used in drug development. Moreover, they show chelating properties towards vanadyl cation that could be used in insulin-mimetic compound development. In this work, the formation of coordination compounds of oxovanadium(IV) with four kojic acid (5-hydroxy-2-(hydroxymethyl)-4-pyrone) derivatives was studied. The synthetized studied ligands (S2, S3, S4, and SC) have two or three kojic acid units linked through diamines or tris(2-aminoethyl)amine chains, respectively. The chemical systems were studied by potentiometry (25 &deg, C, ionic strength 0.1 mol L&minus, 1 with KCl), and UV-visible and EPR spectroscopy. The experimental data were analyzed by a thermodynamic and a chemometric (Multivariate Curve Resolution&ndash, Alternating Least Squares) approach. Chemical coordination models were proposed, together with the species formation constants and the pure estimated UV-vis and EPR spectra. In all systems, the coordination of the oxovanadium(IV) starts already under acidic conditions (the cation is totally bound at pH higher than 3&ndash, 4) and the metal species remain stable even at pH 8. Ligands S3, S4, and SC form three coordination species. Two of them are probably due to the successive insertion of the kojate units in the coordination shell, whereas the third is most likely a hydrolytic species.

International audience; 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.

This work reports a study of the proton-binding capacity of biopolymers obtained from different materials supplied by a municipal biowaste treatment plant located in Northern Italy. One material was the anaerobic fermentation digestate of the urban wastes organic humid fraction. The others were the compost of home and public gardening residues and the compost of the mix of the above residues, digestate and sewage sludge. These materials were hydrolyzed under alkaline conditions to yield the biopolymers by saponification. The biopolymers were characterized by 13C NMR spectroscopy, elemental analysis and potentiometric titration. The titration data were elaborated to attain chemical models for interpretation of the proton-binding capacity of the biopolymers obtaining the acidic sites concentrations and their protonation constants. The results obtained with the models and by NMR spectroscopy were elaborated together in order to better characterize the nature of the macromolecules. The chemical nature of the biopolymers was found dependent upon the nature of the sourcing materials.

The charge-transfer complexes have scientific relevance because this type of molecular interaction is at the basis of the activity of pharmacological compounds and because the absorption bands of the complexes can be used for the quantification of electron donor molecules. This work aims to assess the stability of the charge-transfer complexes between the electron acceptor 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and two drugs, procaine and atenolol, in acetonitrile and ethanol. The stability of DDQ in solution and the time required to obtain the maximum complex formation were evaluated. The stoichiometry and the stability of the complexes were determined, respectively, by Job’s plot method and by the elaboration of UV–vis titrations data. The latter task was carried out by using the non-linear global analysis approach to determine the equilibrium constants. This approach to data elaboration allowed us to overcome the disadvantages of the classical linear-regression method, to obtain reliable values of the association constants and to calculate the entire spectra of the complexes. NMR spectra were recorded to identify the portion of the donor molecule that was involved in the interaction. The data support the participation of the aliphatic amino groups in complex formation and exclude the involvement of the aromatic amine present in the procaine molecule.

The synthesis, physico-chemical, and biological characterisation of a short series of carnosine amides bearing NO-donor nitrooxy functionalities are described. The NO-donor carnosine analogues and their des-NO derivatives display carnosine-like properties, differing from the lead for their high serum stability. The newly-synthesised compounds are able to complex Cu(2+) ions at physiological pH, displaying significant copper ion sequestering ability, and protect LDL from oxidation catalysed by Cu(2+) ions. All products show moderately-potent HNE quenching activity. The NO-donor compounds 7c-f relaxed rat aorta strips via an NO-dependent mechanism. In vivo evaluation of organ protection in a model of cerebral ischaemia/reperfusion injury, using the selected NO-donor 7e and its des-NO analogue 7a, showed that both derivatives protect from hypoxia-induced brain damage, at lower concentrations than carnosine; 7e also decreased serum TNF-α levels. This class of NO-donor carnosine amides is worthy of further study as potential tools for treating a wide range of chronic vascular and neurodegenerative diseases in which NO-bioavailability is reduced.

The hydrolysis of VO 2+ and the complex with sulfate were studied potentiometrically, spectrophotometrically and calorimetrically, in NaCl aqueous solution (0 I ≤ 1 mol L − 1 ) and at t = 25 °C. The formation of two hydrolytic species VO(OH) + and VO 2 (OH) 2 2+ and one complex with sulfate was found, with log β = − 5.65 for the reaction VO 2+ + H 2 O = VO(OH) + + H + , log β = − 7.02 for the reaction 2VO 2+ + 2H 2 O = (VO) 2 (OH) 2 2+ + 2H + and log K = 1.73 for VOSO 4 0 species (at I = 0.1 mol L − 1 and t = 25 °C). For these species, using calorimetric data, Δ H and T Δ S values were also obtained. By using the above values, interactions of VO 2+ with acetate ( ac ), malonate ( mal ), succinate ( suc ), 1,2,3-propanetricarboxylate ( tca ) and 1,2,3,4-butanetetracarboxylate ( btc ) ligands were studied potentiometrically and spectrophotometrically. The formation of ML + , ML 2 0 and MLOH 0 for ac ; ML 0 , MLH + , ML 2 2− and ML 2 H − for mal ; ML 0 , MLH + and MLOH − for suc ; ML − and MLH 0 for tca and ML 2− , MLH − and MLH 2 0 for btc were found. Formation constants are reported at I = 0.1 mol L − 1 , together with SIT parameters for the dependence on ionic strength. By visible spectrophotometric measurements, λ max and e max values for the relevant species in solution were determined.

In this study, the structure–absorptivity relationship problem is dealt with, on the basis of a considerable mass of data (117 complexes) concerning equatorial complexes of copper(II) in aqueous solution. Some spectrophotometric measurements have been carried out and as well as some molar absorptivity calculations on copper(II)–ammonia (e640=77 M−1 cm−1 for the Cu(NH3)42+ species) and copper(II)–biuret (e505=46 M−1 cm−1 for the Cu(C2H3N3O2)22− species) systems have been made, in order to complete the quantitative information necessary for the discussion. It was found that the qualitative relationship between emax and λmax, for the complexes in question is traceable back to a hyperbolic type of path; the dispersion of the data in the cartesian plane (emax, λmax) is analyzed and discussed. It has been found that the dissociated peptide nitrogen is, amongst those under study (namely: amino nitrogen; peptide nitrogen; imidazole nitrogen; carboxylate oxygen; alcoholate oxygen; hydroxide oxygen; water oxygen), that which corresponds to the major increase of emax for copper(II). On the contrary, the one which corresponds to the minor increase is the imidazole donor (that is pyridine nitrogen of imidazole residue), which manifests the ability to lower the emax values of the equatorial complexes of copper(II). Moreover, contrary to what has been previously demonstrated for λmax, for emax it does not appear to be correct to schematize the ligand with its donor groups in order to assess spectrum–structure correlations. Consequently, this study contains a type of methodological proposal, even beyond the metal ion specifically in question, for the analyses of the selection criteria of the molecular characteristics that a ligand must possess in order to form a co-ordination compound of analytical interest with a determined metal ion.

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.

The complex formation between copper(II) and the tetrapeptide glycyl-glycyl- l -histidyl- l -alanine ([H 3 L] 2+ ) has been studied in aqueous solution at t = 25°C and I = 0.1 mol dm −3 by potentiometric, visible spectrophotometric and circular dichroism measurements. All the experimental techniques show that the complex [CuLH −2 ] − is predominant over a wide pH range, while the monodentate [CuLH] 2+ is formed in the acidic region and a further deprotonated [CuLH −3 ] 2− species exists at pH higher than 10. The formation constants of the three above complexes are reported and a structure is proposed on the basis of spectroscopic results. The structure of [CuLH −2 ] − species very probably involves four nitrogen donors in the plane, excluding coordination by the l -alanine residue, while it seems likely that [CuLH −3 ] 2− is formed by simple dissociation of the N-1 pyrrole hydrogen.

1. The serum oxalate concentration rises in chronic renal failure and it is only partially eliminated by regular dialysis treatment. However, the recent literature is not conclusive on whether progressive oxalate retention and secondary oxalosis should be expected in patients on regular dialysis treatment. 2. To further investigate this, we have estimated the state of saturation with respect to calcium oxalate mono-hydrate in plasma ultrafiltrates from 28 patients on maintenance haemodialysis and eight healthy control subjects, matched for sex and age. Five patients had type I primary hyperoxaluria and histologically proven oxalosis, whereas 23 had oxalosis-unrelated renal diseases. Dialysis efficiency was quantified as the KdTd/V of urea. Samples were obtained from each patient before, immediately after and 48 h after a dialysis session. Fasting samples were obtained from the control subjects. Oxalate was determined in both plasma ultrafiltrates and the whole dialysate by ion-exchange chromatography, after a non-delayed and [14C]oxalate-recovery-controlled procedure. The state of saturation with calcium oxalate monohydrate was estimated by means of a computer system which solved the interactions among 45 complex species. 3. The fasting plasma oxalate concentration (means ± sd) in ultrafiltrates from healthy subjects was 3.8 ± 1.5 (range 1.4–5.8) μmol/l, and the state of saturation with calcium oxalate monohydrate was 0.096 ± 0.04. The 23 patients with oxalosis-unrelated chronic renal failure had a pre-dialysis plasma oxalate concentration of 49.8 ± 14.0 μmol/l, which yielded a state of saturation with calcium oxalate monohydrate of 1.0 ± 0.3; dialysis produced a steep decrease in the state of saturation with calcium oxalate monohydrate and the samples remained undersaturated at 48 h from the end of the session. The pre-dialysis oxalate concentration in plasma ultrafiltrates from patients with primary oxalosis was 170 ± 21 μmol/l, so as to exceed saturation by more than threefold. The samples remained above saturation even at the end of dialysis. 4. In 116 ultrafiltrates the state of saturation with calcium oxalate monohydrate was closely dependent on the plasma oxalate concentration but not on the plasma calcium concentration. The pre-dialysis state of saturation with calcium oxalate monohydrate was poorly influenced by the residual renal function and was independent of the sex, age, body weight or time on dialysis. 5. The results of the present study suggest that, unless chronic renal failure is due to primary hyperoxaluria, the extracellular body fluid of patients on current dialysis is often undersaturated with calcium oxalate and this is inconsistent with progressive oxalate accumulation and secondary systemic oxalosis. However, since some tissues may generate or selectively accumulate oxalate, local formation of crystalline deposits may still occur on regular haemodialysis.

Constantes de protonation d'EDTA, NTA, diphosphate et tripolyphosphate et de stabilite des complexes

Formation constants of calcium complexes with malonate (mal2−), in the ranges 10 ⩽ t ⩽ 50°C and 0.05 ⩽ I ⩽ 0.9 mol dm−3, were determined by means of alkalimetric titrations in aqueous solution. The species found in this system were [Ca(mal)]0 and [Ca(Hmal)]+; also, the hydrolysis of Ca2+ was taken into account. The effect of ionic medium on the formation constants was studied by using different background salts (KNO3, NaNO3, Et4NI and Et4NBr); the parameters defining ionic strength dependence were calculated from the values of stability constants obtained at different ionic strengths. ΔH and ΔS values were obtained from temperature coefficients of stability constants. A general equation, useful for correlating the formation constants in the studied temperature and ionic strength ranges, has been found. It has also been found that, by considering all the significant interactions in the solution, the formation constants are dependent on temperature and ionic strength only. Literature data are discussed and compared with those obtained in this work.

The protonation constants of 2,2′-bipyridyl, 1,10-phenanthroline, 1,3-diaminopropane, l -histidine and histamine have been determined potentiometrically, in the temperature range 10–40° and at ionic strengths ranging from 0.04 to 1 (potassium chloride). The dependence of the protonation constants on ionic strength is described by a simple general equation. The enthalpy changes for the protonation of the ligands have been calculated from the temperature dependence of the protonation constants.

The ternary copper(II)-malonate-glycinate system has been investigated by potentiometric measurements using a glass electrode, at 37° and at different ionic strengths (0.01≤I≤1.0 mol dm−3), with KNO3 as background salt. Complex formation between K+ and malonate has also been taken into account, and the parameters for the dependence on ionic strength have been obtained for each formation constant. A general equation, valid for all the complexes formed in this system, for the dependence, log K=f(I), is also proposed. The stabilization parameters of the ternary complex are also analyzed as a function of the ionic strength.

Alkali-metal and calcium(II) complexes of monocarboxylate A–(acetate and salicylate), dicarboxylate A2–(malonate, maleate, succinate, malate, tartrate, phthalate, and oxydiacetate), or amino acid HA (glycine or L-histidine) ligands have been studied potentiometrically, using a glasssaturated calomel electrode, at different temperatures and ionic strengths. The monocarboxylate ligands form [MA] and the dicarboxylates [MA] and [M(HA)] species (charges omitted) with both alkali metals and calcium. Glycine and L-histidine form [MA]+ and [M(HA)]2+{and [M(H2A)]3+ for L-histidine} complexes with Ca2+, whilst alkali metals form only [M(HA)]+ with glycine. Some interesting regularities in the formation constants are pointed out. From the dependence on temperature of formation constants, values of ΔH⊖ and ΔS⊖ have been determined. The function log β=f(I) has been carefully studied in the range 0.02 ⩽I⩽ 1 mol dm–3. The reliability of a new model for the dependence on ionic strength of formation constants (when dealing with weak complexes it is in practice impossible to use the constant ionic medium method) is widely discussed. Two methods of calculation are described and the more general method has been checked by simulated curves.

Binary and ternary complexes (homo- and hetero-polynuclear) formed in the system copper(II)–nickel(II)–δ-DL- hydroxylysine have been studied by potentiometry at different temperatures and by visible spectrophotometry. In the presence of both copper(II) and nickel(II) a quite complicated complexation scheme has been observed, with the participation of the acid and aminoethanol moieties of the ligand molecule and the consequent formation of mono- and poly-nuclear species: [ML]+, [M(HL)]2+, [M(HL)2]2+, [ML2H]+, [NiLH2]3+, [NiL2], [NiL3]–, and [M2L2H–2], [M2L2H–2]2+,[Cu2L2H–1]+, [Ni2L2]2+(with M = Cu2+ or Ni2+ and L–= anion of δ-hydroxylysine). In addition to the above binary complexes, the mixed-metal species [CuNiL2H–2] and [Cu2NiL2H–2]2+ have been found in solution. Structures in solution of relevant species have been proposed, both on the basis of visible spectra calculated for each copper(II) complex and upon thermodynamic parameters obtained by potentiometric measurements at different temperatures.

The formation of complexes between sulphate ion and the alkali metal ions (M+ = Li+, Na+, K+, Rb+ or Cs+) was investigated. The experiments were carried out measuring potentiometrically the hydrogen ion concentration, at t = 37°C and variable ionic strengths (0.03 ⩽ I ⩽ 0.5 mol dm−3). For each alkali metal ion, in addition to the value of the stability constant, we obtained the parameters which define the dependence of the stability constant on ionic strength. The order of stability for [M(SO4)]− complexes is Li+ > Na+ < K+ < Rb+ < Cs+. The results seem to confirm that the differences in the protonation constants obtained using different ionic media may be explained in terms of complex formation between the ligand and the alkali metal ions.

The ternary Cu2+-Ni2+-citrate (cit3−) system was investigated potentiometrically in aqueous solution, at different temperatures, 10≤t≤45°C, and ionic strengths, 0.03≤I≤0.8 mol dm−3, using potassium nitrate or tetraethylammonium bromide as background salt. Since the citrate anion forms weak complexes with potassium, the stability constants here reported differ according to whether the potassium association is considered or not. In the presence of both Cu2+ and Ni2+, the mixed metal species, [CuNi(cit)2H−2]4− is formed with citrate in solution, in addition to the various binary complexes. We have obtained the dependence for all the formation constants on ionic strength and temperature. The previous suggestions concerning a general equation for describing the dependence, log β=f(I), are confirmed; from the study of log β=f(T) we have obtained the values of thermodynamic parameters. The dependence of ΔH on ionic strength is discussed.

The state of saturation of urine with calcium salts has been estimated by means of a computer model system whose accuracy has been improved by the use of stability constants of 31 complexes which were re-determined at 37 degrees C and at the actual ionic strength of urine. The experimental determination of the concentration solubility products of calcium oxalate monohydrate (CaOx) and of calcium hydrogen phosphate dihydrate (bsh) allows an expression of the saturation degree as free concentration product ratio beta CaOx and beta bsh. Morning urine samples from 50 healthy controls and 50 idiopathic calcium stone-formers and 24 h urines from 40 normal subjects and 192 stone-formers, taking normal diet were investigated by this technique. From our results urine supersaturation with calcium oxalate salts seems to play an important role in calcium stone disease. Hypercalciuria and hyperoxaluria seem to be the main pathological features in this regard. The data concerning beta bsh values have not confirmed previous reports in which this parameter was found to be increased in stone-formers.

The protonation constants of oxalic acid were determined potentiometrically at 37°C in different media—NaNo 3 , KNO 3 and Et 4 NI, 0.03⩽ I ⩽ 0.3. From these data it was possible to determine the formation of the complexes [Na(ox)] − and [K(ox)] − and [K(ox)] − , and to calculate their stability constants. Simultaneous analysis of potentionmetric and calorimetric data (this work and literature) enabled the temperature and ionic strength dependendence of the equilibrium parameters to be obtained for the protonation of oxalate. Recalculation of some literature data gave the Δ H value for the formation of the [Na(ox)] − complex. The thermodynamic parameters obtained allowed us to confirm the hypothesis that dicarboxylate anions chelate with alkali-metal ions and that these complexes are mainly entropically stabilized.

Equilibrium study of iron(II) and manganese(II) complexes with citrate ion in aqueous solution at 37 °C and I = 0.15 mol dm −3 (KNO 3 ) is reported. New species, relevant to coordination of citrate to the active site of aconitase, are evidenced. On the basis of stability constants values of dimeric species Fe 2 cit 2 H −2 and Mn 2 cit 2 H −2 , an hypothersis is proposed on the inhibition of enzymatic activity by manganous ion. Considerations on the possible effects of the existence of the new species found on the gastrointestinal absorption of some metal ions are also reported.