Caffeic Acid/Eu(III) Complexes: Solution Equilibrium Studies, Structure Characterization and Biological Activity.

Caffeic acid (CFA) is one of the various natural antioxidants and chemoprotective agents occurring in the human diet. In addition, its metal complexes play fundamental roles in biological systems. Nevertheless, research on the properties of CFA with lanthanide metals is very scarce, and little to no chemical or biological information is known about these particular systems. Most of their properties, including their biological activity and environmental impact, strictly depend on their structure, stability, and solution behaviour. In this work, a multi-analytical-technique approach was used to study these relationships for the Eu(III)/CFA complex. The synthesized metal complex was studied by FT-IR, FT-Raman, elemental, and thermal (TGA) analysis. In order to examine the chemical speciation of the Eu(III)/CFA system in an aqueous solution, several independent potentiometric and spectrophotometric UV-Vis titrations were performed at different M:L (metal:ligand) and pH ratios. The general molecular formula of the synthesized metal complex in the solid state was [Eu(CFA)3(H2O)3]∙2H2O (M:L ratio 1:3), while in aqueous solution the 1:1 species were observed at the optimum pH of 6 ≤ pH ≤ 10, ([Eu(CFA)] and [Eu(CFA)(OH)]-). These results were confirmed by 1H-NMR experiments and electrospray-ionization mass spectrometry (ESI-MS). To evaluate the interaction of Eu(III)/CFA and CFA alone with cell membranes, electrophoretic mobility assays were used. Various antioxidant tests have shown that Eu(III)/CFA exhibits lower antioxidant activity than the free CFA ligand. In addition, the antimicrobial properties of Eu(III)/CFA and CFA against Escherichia coli, Bacillus subtilis and Candida albicans were investigated by evaluation of the minimum inhibitory concentration (MIC). Eu(III)/CFA shows higher antibacterial activity against bacteria compared to CFA, which can be explained by the highly probable increased lipophilicity of the Eu(III) complex.

Iron Coordination Properties of Gramibactin as Model for the New Class of Diazeniumdiolate Based Siderophores.

Gramibactin (GBT) is an archetype for the new class of diazeniumdiolate siderophores, produced by Paraburkholderia graminis, a cereal-associated rhizosphere bacterium, for which a detailed solution thermodynamic study exploring the iron coordination properties is reported. The acid-base behavior of gramibactin as well as its complexing ability toward Fe3+ was studied over a wide range of pH values (2≤pH≤11). For the latter the ligand-competition method employing EDTA was used. Only two species are formed: [Fe(GBT)]- (pH 2 to 9) and [Fe(GBT)(OH)2 ]3- (pH≥9). The formation of [Fe(GBT)]- and its occurrence in real systems was confirmed by LC-HRESIMS analysis of the bacteria culture broth extract. The sequestering ability of gramibactin was also evaluated in terms of the parameters pFe and pL0.5 . Gramibactin exhibits a higher sequestering ability toward Fe3+ than EDTA and of the same order of magnitude as hydroxamate-type microbial siderophores, but smaller than most of the catecholate-type siderophores and much higher than the most known phytosiderophores.

Critical Reappraisal of Methods for Measuring Urine Saturation with Calcium Salts.

Background: Metabolic and physicochemical evaluation is recommended to manage the condition of patients with nephrolithiasis. The estimation of the saturation state (ß values) is often included in the diagnostic work-up, and it is preferably performed through calculations. The free concentrations of constituent ions are estimated by considering the main ionic soluble complexes. It is contended that this approach is liable to an overestimation of ß values because some complexes may be overlooked. A recent report found that ß values could be significantly lowered upon the addition of new and so far neglected complexes, [Ca(PO4)Cit]4- and [Ca2H2(PO4)2]. The aim of this work was to assess whether these complexes can be relevant to explaining the chemistry of urine. Methods: The Ca-phosphate-citrate aqueous system was investigated by potentiometric titrations. The stability constants of the parent binary complexes [Cacit]- and [CaPO4]-, and the coordination tendency of PO43- toward [Ca(cit)]- to form the ternary complex, were estimated. ßCaOx and ßCaHPO4 were then calculated on 5 natural urines by chemical models, including or not including the [CaPO4]- and [Ca(PO4)cit]4- species. Results: Species distribution diagrams show that the [Ca(PO4)cit]4- species was only noticeable at pH > 8.5 and below 10% of the total calcium. ß values estimated on natural urine were slightly lowered by the formation of [CaPO4]- species, whereas [Ca(PO4)cit]4- results were irrelevant. Conclusions: While [CaPO4]- species have an impact on saturation levels at higher pHs, the existence of ternary complex and of the dimer is rejected.

Understanding the Solution Behavior of Epinephrine in the Presence of Toxic Cations: A Thermodynamic Investigation in Different Experimental Conditions.

The interactions of epinephrine ((R)-(-)-3,4-dihydroxy-α-(methylaminomethyl)benzyl alcohol; Eph-) with different toxic cations (methylmercury(II): CH3Hg+; dimethyltin(IV): (CH3)2Sn2+; dioxouranium(VI): UO22+) were studied in NaClaq at different ionic strengths and at T = 298.15 K (T = 310.15 K for (CH3)2Sn2+). The enthalpy changes for the protonation of epinephrine and its complex formation with UO22+ were also determined using isoperibolic titration calorimetry: HHL = -39 ± 1 kJ mol-1, HH2L = -67 ± 1 kJ mol-1 (overall reaction), HML = -26 ± 4 kJ mol-1, and HM2L2(OH)2 = 39 ± 2 kJ mol-1. The results were that UO22+ complexation by Eph- was an entropy-driven process. The dependence on the ionic strength of protonation and the complex formation constants was modeled using the extended Debye-Hückel, specific ion interaction theory (SIT), and Pitzer approaches. The sequestering ability of adrenaline toward the investigated cations was evaluated using the calculation of pL0.5 parameters. The sequestering ability trend resulted in the following: UO22+ >> (CH3)2Sn2+ > CH3Hg+. For example, at I = 0.15 mol dm-3 and pH = 7.4 (pH = 9.5 for CH3Hg+), pL0.5 = 7.68, 5.64, and 2.40 for UO22+, (CH3)2Sn2+, and CH3Hg+, respectively. Here, the pH is with respect to ionic strength in terms of sequestration.

Interaction of N-acetyl-l-cysteine with Na+, Ca2+, Mg2+ and Zn2+. Thermodynamic aspects, chemical speciation and sequestering ability in natural fluids.

The estimation of thermodynamic parameters of N-Acetyl-L-cysteine (NAC) protonation were determined in NaCl(aq), (CH3)4NCl(aq), (C2H5)4NI(aq), employing various temperature and ionic strengths conditions, by potentiometric measurements. The interaction of NAC with some essential metal cations (e.g., Ca2+, Mg2+ and Zn2+) was investigated as well at 298.15 K in NaCl(aq) in the ionic strength range 0.1 ≤ I/mol dm-3 ≤ 1.0. The values of protonation constants at infinite dilution and at T = 298.15 K are: log K 1 H = 9.962 ± 0.005 (S-H) and log K 2 H = 3.347 ± 0.008 (COO-H). In the presence of a background electrolyte, both log K 1 H and log K 2 H values followed the trend (C2H5)4NI ≥ (CH3)4NCl ≥ NaCl. The differences in the values of protonation constants among the three ionic media were interpreted in terms of variation of activity coefficients and formation of weak complexes. Accordingly, the determination of the stability of 4 species, namely: NaL-, NaHL0 (aq), (CH3)4NL-, (CH3)4NHL0 (aq) was assessed. In addition, as regards the interactions of Mg2+, Ca2+ and Zn2+ with NAC, the main species where the ML0 (aq), ML(OH)-, and ML2 2-, that were found to be important in the chemical speciation of NAC in real multicomponent solutions. The whole set of the data collected may be crucial for the development of NAC-based materials for natural fluids selective decontamination from heavy metals.

Ga complexes of 8-hydroxyquinoline-2-carboxylic acid: Chemical speciation and biological activity.

The binding ability of 8-hydroxyquinoline-2-carboxylic acid (8-HQA) towards Ga3+ has been investigated by ISEH+ (Ion Selective Electrode, glass electrode) potentiometric and UV/Vis spectrophotometric titrations in KCl(aq) at I = 0.2 mol dm-3 and at T = 298.15 K. Further experiments were also performed adopting both the metal (with Fe3+ as competing cation) and ligand-competition approaches (with EDTA as competing ligand). Results gave evidence of the formation of the [Ga(8-HQA)]+, [Ga(8-HQA)(OH)], [Ga(8-HQA)(OH)2]- and [Ga(8-HQA)2]- species, the latter being so far the most stable, as also confirmed by ESI-MS analysis. Experiments were also designed to determine the stability constants of the [Ga(EDTA)]- and [Ga(EDTA)(OH)]2- in the above conditions. Due to the relevance of Ga3+ hydrolysis in aqueous systems, literature data on this topic were collected and critically analyzed, providing equations for the calculation of mononuclear Ga3+ hydrolysis constants at T = 298.15 K, in different ionic media, in the ionic strength range 0 < I / mol dm-3 ≤ 1.0. The synthesis and characterization (by ElectroSpray Ionization - Mass Spectrometry (ESI-MS), Attenuated Total Reflectance - Fourier-Transform Infrared Spectroscopy (ATR-FTIR) and ThermoGravimetric Analysis (TGA)) of Ga3+/8-HQA complexes were also performed, identifying [Ga(8-HQA)2]- as the main isolated species, even in the solid state. Finally, the potential effects of 8-HQA and Ga3+/8-HQA complex towards human microbiota exposed to ionizing radiation were evaluated (namely Actinomyces viscosus, Streptococcus mutans, Streptococcus sobrinus, Pseudomonas putida, Pseudomonas fluorescens and Escherichia coli), as well as their anti-proliferative and anti-inflammatory properties. A radioprotective effect of Ga3+/8-HQA complex was observed on Actinomyces viscosus, while showing a potential radiosensitizing effect against Streptococcus mutans and Streptococcus sobrinus. No cytotoxicity on RAW264.7 murine macrophage cells was observed, neither for the free ligand or Ga3+/8-HQA complex. Nevertheless, Ga3+/8-HQA complex highlighted potential anti-inflammatory properties.

A tutorial on potentiometric data processing. Analysis of software for optimization of protonation constants.

Defining the distribution of the chemical species in a multicomponent system is a task of great importance with applications in many fields. To clarify the identity and the abundance of the species that can be formed by the interaction of the components of a solution, it is fundamental to know the formation constants of those species. The determination of equilibrium constants is mainly performed through the analysis of experimental data obtained by different instrumental techniques. Among them, potentiometry is the elective technique for this purpose. As such, a survey was run within the NECTAR COST Action - Network for Equilibria and Chemical Thermodynamics Advanced Research, to identify the most used software for the analysis of potentiometric data and to highlight their strengths and weaknesses. The features and the calculation processes of each software were analyzed and rationalized, and a simulated titration dataset of a hypothetic hexaprotic acid was processed by each software to compare and discuss the optimized protonation constants. Moreover, further data analysis was also carried out on the original dataset including some systematic errors from different sources, as some calibration parameters, the total analytical concentration of reagents and ionic strength variations during titrations, to evaluate their impact on the refined parameters. Results showed that differences on the protonation constants estimated by the tested software are not significant, while some of the considered systematic errors affect results. Overall, it emerged that software commonly used suffer from many limitations, highlighting the urgency of new dedicated and modern tools. In this context, some guidelines for data generation and treatment are also given.

Silver(I) pyrrole- and furan-2-carboxylate complexes - From their design and characterization to antimicrobial, anticancer activity, lipophilicity and SAR.

Two silver(I) complexes with biologically relevant heterocyclic ligands, pyrrole and furan-2- carboxylic acid, were synthesized and their composition was confirmed using elemental, spectral, thermal and structural analyses. The {[Ag(Py2c)]}n (AgPy2c, Py2c = pyrrole-2-carboxylate) and {[Ag(Fu2c)]}n (AgFu2c, Fu2c = furan-2-carboxylate) solubility and stability in biological test stock solution were confirmed by 1H NMR spectroscopy. The X-ray analysis has enabled us to determine typical argentophilic interactions and bridging carboxylate coordination mode of both ligands. Potentiometric data analysis by BSTAC program resulted in the determination of the stability constant of only one species, i.e., the ML (M = Ag+, L = Fu2c-), log ßML = 0.59 ± 0.04. Antimicrobial and anticancer tests were performed against selected microorganisms and cell lines with new silver(I) complexes and compared with AgSD (silver(I) sulfadiazine) and cisplatin. From their microbial toxicity point of view, selectivity was determined against lactobacilli (AgPy2c is 8× more effective against S. aureus and E. coli and AgFu2c is 8× more effective against E. coli and 4× against S. aureus). AgFu2c significant anticancer activity was determined against Jurkat cell lines (IC50 = 8.00 µM) and was similar to cisPt (IC50 = 6.3 µM) similarly to its selectivity (SI (AgFu2c) = 7.3, SI (cisPt) = 6.4, SI = selectivity index). In addition, cell cycle arrest was observed already in the Sub-G0 phase during a flow cytometry experiment. To evaluate the AgPy2c and AgFu2c bioavailability we also discuss their Lipinski's Rule of Five.

Modeling the acid-base properties of glutathione in different ionic media, with particular reference to natural waters and biological fluids.

The acid-base properties of γ-L-glutamyl-L-cysteinyl-glycine (glutathione, GSH) were determined by potentiometry (ISE-H(+), glass electrode) in pure NaI((aq)) and in NaCl((aq))/MgCl(2(aq)), and NaCl((aq))/CaCl(2(aq)) mixtures, at T = 298.15 K and different ionic strengths (up to I(c) ~ 5.0 mol L(-1)). In addition, the activity coefficients of glutathione were also determined by the distribution method at the same temperature in various ionic media (LiCl((aq)), NaCl((aq)), KCl((aq)), CsCl((aq)), MgCl(2(aq)), CaCl(2(aq)), NaI((aq))). The results obtained were also used to calculate the Specific ion Interaction Theory (SIT) and Pitzer coefficients for the dependence on medium and ionic strength of glutathione species, as well as the formation constants of weak Mg(j)H( i )(GSH)((i+2j-3)) and Ca(j)H(i)(GSH)((i+2j-3)) complexes. Direct calorimetric titrations were also carried out in pure NaCl((aq)) and in NaCl((aq))/CaCl(2(aq)) mixtures at different ionic strengths (0.25 ≤ I (c )/mol L(-1) ≤ 5.0) in order to determine the enthalpy changes for the protonation and complex formation equilibria in these media at T = 298.15 K. Results obtained are useful for the definition of glutathione speciation in any aqueous media containing the main cations of natural waters and biological fluids, such as Na(+), K(+), Mg(2+), and Ca(2+). Finally, this kind of systematic studies, where a series of ionic media (e.g., all alkali metal chlorides) is taken into account in the determination of various thermodynamic parameters, is useful for the definition of some trends in the thermodynamic behavior of glutathione in aqueous solution.

Evaluation of adsorption ability of cyclodextrin-calixarene nanosponges towards Pb2+ ion in aqueous solution.

Different cyclodextrin-calixarene nanosponges (CyCaNSs) have been characterized by means of FFC-NMR relaxometry, and used as sorbents to remove Pb2+ ions from aqueous solutions. Considering that the removal treatments may involve polluted waters with different characteristics, the adsorption experiments were performed on solutions without and with the addition of background salts, under different operational conditions. The adsorption abilities and affinities of the nanosponges towards Pb2+ ions were investigated by measuring the metal ion concentration by means of Inductively Coupled Plasma Emission Spectroscopy (ICP-OES) and Differential Pulse Anodic Stripping Voltammetry (DP-ASV). The acid-base properties of nanosponges and of metal ion as well as their interactions with the other interacting components of the systems have been considered in the evaluation of adsorption mechanism. Recycling and reuse experiments on the most efficient adsorbents were also performed. On the grounds of the results obtained, post-modified CyCaNSs appear promising materials for designing environmental remediation devices.

The Solution Behavior of Dopamine in the Presence of Mono and Divalent Cations: A Thermodynamic Investigation in Different Experimental Conditions.

The interactions of dopamine [2-(3,4-Dihydroxyphenyl)ethylamine, (Dop-)] with methylmercury(II) (CH3Hg+), magnesium(II), calcium(II), and tin(II) were studied in NaCl(aq) at different ionic strengths and temperatures. Different speciation models were obtained, mainly characterized by mononuclear species. Only for Sn2+ we observed the formation of binuclear complexes (M2L2 and M2LOH (charge omitted for simplicity); M = Sn2+, L = Dop-). For CH3Hg+, the speciation model reported the ternary MLCl (M = CH3Hg+) complex. The dependence on the ionic strength of complex formation constants was modeled by using both an extended Debye-Hückel equation that included the Van't Hoff term for the calculation of enthalpy change values of the formation and the Specific Ion Interaction Theory (SIT). The results highlighted that, in general, the entropy is the driving force of the process. The sequestering ability of dopamine towards the investigated cations was evaluated using the calculation of pL0.5 parameter. The sequestering ability trend resulted to be: Sn2+ > CH3Hg+ > Ca2+ > Mg2+. For example, at I = 0.15 mol dm-3, T = 298.15 K and pH = 7.4, pL0.5 = 3.46, 2.63, 1.15, and 2.27 for Sn2+, CH3Hg+, Ca2+ and Mg2+ (pH = 9.5 for Mg2+), respectively. For the Ca2+/Dop- system, the precipitates collected at the end of the potentiometric titrations were analyzed by thermogravimetry (TGA). The thermogravimetric calculations highlighted the formation of solid with stoichiometry dependent on the different metal:ligand ratios and concentrations of the starting solutions.

8-Hydroxyquinoline-2-Carboxylic Acid as Possible Molybdophore: A Multi-Technique Approach to Define Its Chemical Speciation, Coordination and Sequestering Ability in Aqueous Solution.

8-hydroxyquinoline-2-carboxylic acid (8-HQA) has been found in high concentrations (0.5-5.0 mmol·dm-3) in the gut of Noctuid larvae (and in a few other lepidopterans), in which it is proposed to act as a siderophore. Since it is known that many natural siderophores are also involved in the uptake and metabolism of other essential elements than iron, this study reports some results on the investigation of 8-HQA interactions with molybdate (MoO42-, i.e., the main molybdenum form in aqueous environments), in order to understand the possible role of this ligand as molybdophore. A multi-technique approach has been adopted, in order to derive a comprehensive set of information necessary to assess the chemical speciation of the 8-HQA/MoO42- system, as well as the coordination behavior and the sequestering ability of 8-HQA towards molybdate. Chemical speciation studies have been performed in KCl(aq) at I = 0.2 mol·dm-3 and T = 298.15 K by ISE-H+ (glass electrode) potentiometric and UV/Vis spectrophotometric titrations. CV (Cyclic Voltammetry), DP-ASV (Differential Pulse-Anodic Stripping Voltammetry), ESI-MS experiments and quantum mechanical calculations have been also performed to derive information about the nature and possible structure of species formed. These results are also compared with those reported for the 8-HQA/Fe3+ system in terms of chemical speciation and sequestering ability of 8-HQA.

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 NaCl(aq) at t = 25 degrees C and at different ionic strengths (0.1

A critical approach to the toxic metal ion removal by hazelnut and almond shells.

The adsorption capacity of ground hazelnut (HS) and almond (AS) shells towards Pb(II) and Cd(II) has been studied at pH = 5, in NaNO3 and NaCl ionic media, in the ionic strength range 0.05-0.5 mol L-1. Kinetic and equilibrium experiments were carried out by using the Differential Pulse Anodic Stripping Voltammetry technique to check the amount of the metal ion removed by HS and AS materials. Different kinetic and equilibrium equations were used to fit experimental data and a statistical study was done to establish the suitable model for the data fitting. A speciation study of the metal ions in solution was also done in order to evaluate the influence of the ionic medium on the adsorption process. TGA-DSC, FT-IR, and SEM-EDX techniques were used to characterize the adsorbent materials. The mechanism of metal ions adsorption was explained on the basis of the results obtained by the metal ions speciation study and the characterization of materials.

Speciation of phytate ion in aqueous solution. Protonation constants and copper(II) interactions in NaNO3aq at different ionic strengths.

The acid base behavior of phytate has been studied (at t=25 degrees C by potentiometry, ISE-H+ glass electrode) in NaNO3aq at different ionic strengths (0.1 < or = I/mol L(-1) < or = 1.0). The interactions with copper(II) were investigated in the same experimental conditions in different metal to ligand (Phy) ratios (1:1 < or = Cu2+ :Phy < or = 4:1), by using both ISE-H+ and ISE-Cu2+ electrodes. Phytate acid base behavior in sodium nitrate is very similar to that in sodium chloride, previously investigated. In the experimental conditions adopted, the formation of three CuiHjPhy(12-2i-j)- species is observed: the mononuclear CuH4Phy6- and CuH5Phy5-, and the dinuclear Cu2H5Phy3-. Analysis of complex formation constants at different ionic strengths reveals that both ISE-H+ and ISE-Cu2+ electrodes gave, within the experimental error, analogous values. Dependence of complex formation constants on ionic strength was modeled by EDH (Extended Debye-Hückel) and SIT (Specific ion Interaction Theory) equations. The sequestering ability of phytate toward copper(II) has been evaluated by the calculation of pL50 (the total ligand concentration, as -log CL, able to bind 50% of metal cation), an empirical parameter already proposed for an objective "quantification" of this ability. A thorough analysis of literature data on phytate-copper(II) complexes has been performed.

Dioxouranium(VI)-carboxylate complexes. Speciation of UO2(2+)-1,2,3-propanetricarboxylate system in NaCl(aq) at different ionic strengths and at t=25 degrees C.

The formation constants of dioxouranium(VI)-1,2,3-propanetricarboxylate [tricarballylate (3-), TCA] complexes were determined in NaCl aqueous solutions at 0 < or = I/mol L(-1) < or = 1.0 and t=25 degrees C, by potentiometry, ISE-[H+] glass electrode. The speciation model obtained at each ionic strength includes the following species: ML-, MLH0, ML2(4-) and ML2H3- (M = UO2(2+) and L = TCA). The dependence on ionic strength of protonation constants of 1,2,3-propanetricarboxylate and of the metal-ligand complexes was modeled by the SIT (Specific ion Interaction Theory) approach and by the Pitzer equations. The formation constants at infinite dilution are [for the generic equilibrium p UO22+ + q (L3-) + r H+ = (UO2(2+))p(L)qHr(2p-3q+r); betapqr]: log beta110 = 6.222 +/- 0.030, log beta111 = 11.251 +/- 0.009, log beta121 = 7.75 +/- 0.02, log beta121 = 14.33 +/- 0.06. The sequestering ability of 1,2,3-propanetricarboxylate towards UO2(2+) was quantified by using a sigmoid Boltzman type equation.

Speciation of phytate ion in aqueous solution. Trimethyltin(IV) interactions in self medium.

In this paper the results of a potentiometric (ISE-[H+] glass electrode) investigation at t = 25 degreesC on the complexing ability of phytate towards trimethyltin(IV) (tmt) and on the acid-base properties of tmt at high metal concentration (0.050 and 0.075 mol L(-1)) are reported. First we determined the hydrolytic constants of tmt in aqueous solution without further addition of background salt (self medium); in these experimental conditions we verified the formation of the following hydrolytic species: tmt(OH)0, tmt(OH)2(-) and the binuclear species (tmt)2(OH)(+). Successively, we studied the complex formation constants obtained from the interaction of phytate anion with tmt in the same experimental conditions of hydrolytic measurements; the speciation model obtained takes into account several polynuclear species (tmtH5Phy(6-); tmt2H5Phy(5-); tmt3H4Phy(5-); tmt3H5Phy(4-); tmt4H6Phy(2-); tmtsHPhy(6-)). A comparison with literature data is reported too.

Modeling ATP protonation and activity coefficients in NaClaq and KClaq by SIT and Pitzer equations.

The acid-base properties of Adenosine 5'-triphosphate (ATP) in NaCl and KCl aqueous solutions at different ionic strengths (0

Speciation of phytate ion in aqueous solution. Sequestering ability toward mercury(II) cation in NaClaq at different ionic strengths.

As a contribution to understanding the speciation of mercury in the environment and to the study of the sequestering ability of phytate (Phy) toward heavy metal and organometal cations, this paper describes the results of an investigation (at t = 25 degrees C by potentiometry, ISE-H+ glass electrode) of its interactions with mercury(II) cation in NaCl aqueous solutions at different ionic strengths (I = 0.15 and 1.0 mol L(-1)), in the pH range 2.5 < or = pH < or = 9.5 and considering metal-to-ligand ratios of 1:1 < or = Hg/Phy < or = 4:1. The formation of 11 HgiHjPhy(12-2i-j)(- species with i = 1 and 0 < or = j < or = 7 and i = 2 and 0 < or = j < or = 2 was observed. Their complex formation constant values proved to be fairly dependent on ionic strength. The speciation of phytic acid and mercury(II) is also dependent on the metal-to-ligand ratio; the dependence of the stability of phytate-mercury(II) species on the phytate protonation step was modeled, and an empirical predictive relationship was proposed. From the results obtained, phytate has very good sequestering ability toward Hg2+, even in the presence of considerable excesses of chloride ion, that is, another ligand strongly interacting with mercury; this supports future studies both on the use of plants that naturally synthesize it for phytoremediation purposes and on its direct application in remediation techniques.

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.