Demetrio Milea

Sequestering Ability of Phytate toward Biologically and Environmentally Relevant Trivalent Metal Cations

Quantitative parameters for the interactions between phytate (Phy) and Al(3+), Fe(3+), and Cr(3+) were determined potentiometrically in NaNO(3) aqueous solutions at I = 0.10 mol L(-1) and T = 298.15 K. Different complex species were found in a wide pH range. The various species are partially protonated, depending on the pH in which they are formed, and are indicated with the general formula MH(q)Phy (with 0 ≤ q ≤ 6). In all cases, the stability of the FeH(q)Phy species is several log K units higher than that of the analogous AlH(q)Phy and CrH(q)Phy species. For example, for the MH(2)Phy species, the stability trend is log K(2) = 15.81, 20.61, and 16.70 for Al(3+), Fe(3+), and Cr(3+), respectively. The sequestering ability of phytate toward the considered metal cations was evaluated by calculating the pL(0.5) values (i.e., the total ligand concentration necessary to bind 50% of the cation present in trace in solution) at different pH values. In general, phytate results in a quite good sequestering agent toward all three cations in the whole investigated pH range, but the order of pL(0.5) depends on it. For example, at pH 5.0 it is pL(0.5) = 5.33, 5.44, and 5.75 for Fe(3+), Cr(3+), and Al(3+), respectively (Fe(3+) < Cr(3+) < Al(3+)); at pH 7.4 it is pL(0.5) = 9.94, 9.23, and 8.71 (Al(3+) < Cr(3+) < Fe(3+)), whereas at pH 9.0 it is pL(0.5) = 10.42, 10.87, and 8.34 (Al(3+) < Fe(3+) < Cr(3+)). All of the pL(0.5) values, and therefore the sequestering ability, regularly increase with increasing pH, and the dependence of pL(0.5) on pH was modeled using some empirical equations.

SALMO and S3M: A saliva model and a single saliva salt model for equilibrium studies

A model of synthetic saliva (SALMO, SALiva MOdel) is proposed for its use as standard medium in in vitro equilibrium and speciation studies of real saliva. The concentrations come out from the literature analysis of the composition of both real saliva and synthetic saliva. The chief interactions of main inorganic components of saliva, as well as urea and amino acids, are taken into account on the basis of a complex formation model, which also considers the dependence of the stability constants of these species on ionic strength and temperature. These last features allow the modelling of the speciation of saliva in different physiological conditions deriving from processes like dilution, pH, and temperature changes. To simplify equilibrium calculations, a plain approach is also proposed, in order to take into account all the interactions among the major components of saliva, by considering the inorganic components of saliva as a single 1 : 1 salt (MX), whose concentration is c MX = (1/2)∑c i (c i = analytical concentration of all the ions) and z ion charge calculated as z=±(I/c MX)1/2 = ±1.163. The use of the Single Saliva Salt Model (S3M) considerably reduces the complexity of the systems to be investigated. In fact, only four species deriving from internal ionic medium interactions must be considered.

Chelating Agents for the Sequestration of Mercury(II) and Monomethyl Mercury(II)

Both mercury(II) and monomethyl mercury(II) poisonings are of great concern for several reasons. As it happens for other metals, chelation therapy is the most indicated treatment for poisoned patients. The efficacy of the therapy and the reduction of side-effects can be sensibly enhanced by an accurate knowledge of all the physiological mechanisms involved in metal uptake, transport within and between various tissues, and (possibly) clearance. All these aspects, however, are strictly dependent on the chemical speciation (i.e., the distribution of the chemical species of a component in a given system) of both the metal and the chelating agent in the systems where they are present. In this light, this review analyzes the state of the art of research performed in this field for mercury(II) and methylmercury(II). After a brief summary of their main sources, the physiological patterns for the treatment of mercury poisoning have also been considered. The binding ability of various chelating agents toward mercury has been then analyzed by modeling the behavior of the main classes of ligands present in biological fluids and/or frequently used in chelation therapy. Their sequestering ability has been successively evaluated by means of a semiempirical parameter already proposed for its objective quantification, and the main characteristics of an efficient chelating agent have been evaluated on this basis.

Enhancement of hydrolysis through the formation of mixed hetero-metal species

In order to analyze the formation of hetero-metal polynuclear hydrolytic species, in this paper, we reported some results of an investigation (at I = 0.16molL(-1) in NaNO(3), at t = 25 degrees C by potentiometry, ISE-H(+), glass electrode) on the hydrolysis of several mixtures (in different ratios) of two couples of cations: dioxouranium(VI)/copper(II) and dioxouranium(VI)/diethyltin(IV). The elevated total concentrations of cations 0.005 </= SigmaC(M) molL(-1) </= 0.05) adopted in these measurements induced us to study again the hydrolysis of uranyl, for which no suitable literature data are available in these particular experimental conditions. All measurements were performed by two different operators, using completely independent instruments and reagents. Many different speciation models were considered in the calculations, including the simultaneous refinement of homo- and hetero-metal species, and a statistical analysis of obtained results was proposed too. Main results can be summarized as follows: [Formula: see text] and Cu(2+) form three hetero-metal polynuclear hydrolytic species [(UO(2))Cu(OH)(3+), (UO(2))Cu [Formula: see text] and (UO(2))(2)Cu [Formula: see text] , with log beta(pqr) = -2.93 +/- 0.01, -7.34 +/- 0.03 and -13.78 +/- 0.03, respectively], all those common to their simple speciation without the other cation; [Formula: see text] and (C(2)H(5))(2)Sn(2+) form seven mixed hydrolytic species [(UO(2))(DET)(OH)(3+), (UO(2))(DET) [Formula: see text] , (UO(2))(2)(DET) [Formula: see text] , (UO(2))(DET)(2) [Formula: see text] , (UO(2))(2)(DET) [Formula: see text] , (UO(2))(DET)(2) [Formula: see text] and (UO(2))(2)(DET) [Formula: see text] , with log beta(pqr) = -2.5 +/- 0.2, -4.74 +/- 0.02, -10.70 +/- 0.06, -10.34 +/- 0.03, -15.70 +/- 0.06, -15.58 +/- 0.06 and -27.9 +/- 0.1, respectively] that are of the same kind of those formed by uranyl; formation of mixed hydrolytic species causes a significant enhancement of the percentage of hydrolyzed metal cations, modifying the solubility and, therefore, the bioavailability of these cations. We also determined, for dioxouranium(VI)/copper(II) system, the corresponding complex formation enthalpies and entropies by direct calorimetric measurements. We obtained DeltaH(112) = 47.9 +/- 0.6 and DeltaH(214) = 92.9 +/- 0.5kJmol(-1), TDeltaS(112) = 6 +/- 1 and TDeltaS(214) = 14 +/- 1kJmol(-1) (+/-S.D.), respectively, for the formation of (UO(2))(Cu) [Formula: see text] and (UO(2))(2)(Cu) [Formula: see text] species (according to reaction 2). We also calculated the single enthalpic and entropic contributes to the extra-stability that these species show with respect to the corresponding homo polynuclear ones.

Speciation of phytate ion in aqueous solution. Non covalent interactions with biogenic polyamines

Abstract The noncovalent interactions of phytate (Phy6-) with biogenic amines were studied potentiometrically in aqueous solution, at t= 25°C. Several species are formed in the different H+-Phy6--amine (A) systems, which have the general formula Ap(Phy)Hq(12-q)-, with p ≤ 3 and 6 ≤ q ≤ 10. The stability of these species is strictly dependent on the charges involved in the formation equilibria. For the equilibrium pHiAi+ + Hj(Phy)(12-j)- = Ap(Phy)Hq(12q)-, (q = pi + j)we found the relationship logK= aζ (ζ is the charge product of reactants), where a= 0.35(0.03, valid for all the amines; this roughly indicates an average free energy contribution per bond -ΔG0 = 4.0 ± 0.2 kJ mol-1. A slightly more sophisticated equation is also proposed for predicting the stability of these species. Owing to the quite high (partially protonated) phytate charge, the stability of Ap(Phy)Hq(12-q)- species is quite high, making phytate a strong amine sequestering agent in a wide pH range.

Pb(II) adsorption by a novel activated carbon alginate composite material. A kinetic and equilibrium study

The adsorption capacity of an activated carbon - calcium alginate composite material (ACAA-Ca) has been tested with the aim of developing a new and more efficient adsorbent material to remove Pb(II) ion from aqueous solution. The study was carried out at pH=5, in NaCl medium and in the ionic strength range 0.1-0.75molL-1. Differential Pulse Anodic Stripping Voltammetry (DP-ASV) technique was used to check the amount of Pb(II) ion removed during kinetic and equilibrium experiments. Different kinetic (pseudo first order, pseudo second order and Vermuelen) and equilibrium (Langmuir and Freundlich) models were used to fit experimental data, and were statistically compared. Calcium alginate (AA-Ca) improves the adsorption capacity (qm) of active carbon (AC) in the ACAA-Ca adsorbent material (e.g., qm=15.7 and 10.5mgg-1 at I=0.25molL-1, for ACAA-Ca and AC, respectively). SEM-EDX and thermogravimetric (TGA) measurements were carried out in order to characterize the composite material. The results of the speciation study on the Pb(II) solution and of the characterization of the ACAA-Ca and of the pristine AA-Ca and AC were evaluated in order to explain the specific contribution of AC and AA-Ca to the adsorption of the metal ion.

Complexation of Hg2+, CH3Hg+, Sn2+ and (CH3)2Sn2+ with phosphonic NTA derivatives

The complex formation between Hg2+, CH3Hg+, Sn2+ and (CH3)2Sn2+ with some phosphonic derivatives of nitrilotriacetic acid (NTA), namely N-(phosphonomethyl)iminodiacetic acid (PMIDA, NTAP), N,N-bis(phosphonomethyl)glycine (NTA2P) and [bis(phosphonomethyl)amino]methylphosphonic acid (NTA3P), has been studied using potentiometry in NaCl aqueous solution at I = 0.1 mol L−1 and T = 298.15 K. In order to evaluate the possible use of these ligands as sequestering agents towards the above-cited cations, some selected systems have been investigated at different ionic strengths, for a better modelling of their speciation and their binding ability in real conditions. For the same reason, the protonation enthalpy changes of the three chelants have been determined by direct calorimetric titrations, in order to define their acid–base behaviour at different temperatures. The results obtained have been compared with the literature data on NTA complexes in order to evaluate and model the effect of the number of carboxylic and/or phosphonic groups of the ligands towards their efficacy in the chelation of the investigated cations. To this aim, the stability constants of NTA with Sn2+ have also been determined here for the first time, since, to our knowledge, this system has never been investigated before.

Alkali Metal Ion Complexes with Phosphates, Nucleotides, Amino Acids, and Related Ligands of Biological Relevance. Their Properties in Solution

Alkali metal ions play very important roles in all biological systems, some of them are essential for life. Their concentration depends on several physiological factors and is very variable. For example, sodium concentrations in human fluids vary from quite low (e.g., 8.2 mmol dm(-3) in mature maternal milk) to high values (0.14 mol dm(-3) in blood plasma). While many data on the concentration of Na(+) and K(+) in various fluids are available, the information on other alkali metal cations is scarce. Since many vital functions depend on the network of interactions occurring in various biofluids, this chapter reviews their complex formation with phosphates, nucleotides, amino acids, and related ligands of biological relevance. Literature data on this topic are quite rare if compared to other cations. Generally, the stability of alkali metal ion complexes of organic and inorganic ligands is rather low (usually log K < 2) and depends on the charge of the ligand, owing to the ionic nature of the interactions. At the same time, the size of the cation is an important factor that influences the stability: very often, but not always (e.g., for sulfate), it follows the trend Li(+) > Na(+) > K(+) > Rb(+) > Cs(+). For example, for citrate it is: log K ML = 0.88, 0.80, 0.48, 0.38, and 0.13 at 25 °C and infinite dilution. Some considerations are made on the main aspects related to the difficulties in the determination of weak complexes. The importance of the alkali metal ion complexes was also studied in the light of modelling natural fluids and in the use of these cations as probes for different processes. Some empirical relationships are proposed for the dependence of the stability constants of Na(+) complexes on the ligand charge, as well as for correlations among log K values of NaL, KL or LiL species (L = generic ligand).

Sequestration of Alkyltin(IV) Compounds in Aqueous Solution: Formation, Stability, and Empirical Relationships for the Binding of Dimethyltin(IV) Cation by N- and O-Donor Ligands

The sequestering ability of polyamines and aminoacids of biological and environmental relevance (namely, ethylenediamine, putrescine, spermine, a polyallylamine, a branched polyethyleneimine, aspartate, glycinate, lysinate) toward dimethyltin(IV) cation was evaluated. The stability of various dimethyltin(IV) / ligand species was determined in NaClaq at t = 25°C and at different ionic strengths (0.1 ≤ I/mol L−1 ≤ 1.0), and the dependence of stability constants on this parameter was modeled by an Extended Debye-Hückel equation and by Specific ion Interaction Theory (SIT) approach. At I = 0.1 mol L−1, for the ML species we have log K = 10.8, 14.2, 12.0, 14.7, 11.9, 7.7, 13.7, and 8.0 for ethylenediamine, putrescine, polyallylamine, spermine, polyethyleneimine, glycinate, lysinate, and aspartate, respectively. The sequestering ability toward dimethyltin(IV) cation was defined by calculating the parameter pL50 (the total ligand concentration, as −log CL, able to bind 50% of metal cation), able to give an objective representation of this ability. Equations were formulated to model the dependence of pL50 on different variables, such as ionic strength and pH, and other empirical predictive relationships were also found.

On the complexation of metal cations with “pure” diethylenetriamine-N,N,N′,N′′,N′′-pentakis(methylenephosphonic) acid

The complex formation between a series of biologically, environmentally, and technologically relevant cations (namely Sn2+, Zn2+, Cu2+, Fe2+, Fe3+ and Al3+) and diethylenetriamine-N,N,N′,N′′,N′′-pentakis(methylenephosphonic) acid (DTPMPA) has been investigated in NaCl aqueous solutions at I = 0.1 and 0.3 mol dm−3 and T = 298.15 K. The ligand used has been obtained in sufficient purity by a new efficient synthetic procedure for the determination of accurate and reliable data on its acid–base properties and metal complex formation. The stability constants determined in this work under different experimental conditions have been then used to assess the speciation of many systems containing the above-cited cations, and to quantify the sequestering ability of DTPMPA toward them, by means of the calculation of several pL0.5 values under various conditions simulating those of many real systems where this chelant is employed as a cationic sequestrant. Finally, some 1H- and 31P-NMR studies have also been performed to gain a further insight into the binding mode of DTPMPA toward metal cations.