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.
The solubility and acid–base properties of the antibacterial Ofloxacin were studied in aqueous solutions of sodium chloride at a single ionic strength value (
I
= 0.15 mol·dm
−3
) and different ...temperatures. Hydronation constants were investigated at
T
= 288.15, 298.15, 310.15 and 318.15 K by potentiometric and UV-spectrophotometric titrations. From the distribution of the different hydronated/dehydronated Ofloxacin species, it was observed that at physiological pH, the neutral HL
0
(zwitterion) species has a mole fraction percentage of ~ 85%. A lowering trend of the hydronation constants with increasing
T
/K was observed and the standard enthalpy, entropy and the Gibbs energy of hydronation were also calculated. The solubility (
S
T
), investigated at
T
= 288.15, 295.15, 310.15 K, was determined by UV-spectrophotometric measurements by using the calibration straight line method. Absorbance values of the standard Ofloxacin solutions and of the saturated solutions were measured at two wavelengths (
λ
= 287 nm and 331.5 nm), and the concentration of Ofloxacin was calculated from the slope of the straight lines. The concentration of Ofloxacin neutral species (
S
0
) was calculated from simple mass balance equations, by using the free hydrogen ion concentration of the saturated solutions and hydronation constants determined at the same ionic strength and temperature of the solubility measurements. From the experimental results, it was possible to observe a different effect of the temperature on solubility and hydronation constants. In the first case, the solubility increases almost linearly with the increase of the temperature, while the hydronation constants decrease by about 0.2 logarithmic units passing from
T
= 288.15 to 318.15 K. By using a Van’t Hoff equation as modified by Apelblat, the standard enthalpy, entropy and the Gibbs energy of solution were calculated by the slope and the intercept of the straight lines obtained by fitting ln
x
against 1/
T
, where
x
is the solubility of Ofloxacin expressed as mole fraction. By using an approach reported in the literature, calculated hydronation constants were obtained at different ionic strengths (up to 1.0 mol⋅dm
−3
) and at the same temperatures experimentally investigated. Successively, by means of a Debye–Hückel type equation, the corresponding hydronation constants at infinite dilution and the parameters for the dependence on the ionic strength were calculated, as well as the enthalpy change values of hydronation at infinite dilution. A very good agreement was obtained from the comparison of the hydronation constants and solubility of Ofloxacin here determined and those reported in pure water in the literature.
In this paper, the thermodynamic properties of the complex species of the Gantrez (Trade Mark product) copolymers of different molecular weights (AN169, S97, and S95) with different divalent (Ca2+, ...Mg2+, Sn2+, and Zn2+) metal cations in NaCl aqueous solutions at different ionic strengths and temperatures were studied by a potentiometric technique. Investigations were carried out in wide ranges of metal to ligand molar concentration ratios up to basic pH values. For the simple metal-Gantrez systems, fairly similar speciation models were obtained, independent of the experimental conditions; the main differences are due to the formation of a ternary MLOH species (M = metal ion, L = Gantrez ligand) or to the final pH value of the titrations, determined by the formation in some cases (i.e., for Sn2+ investigations) of a sparingly soluble species. The stability trend of the species was: Sn2+ ≫ Zn2+ > Ca2+ ≈ Mg2+. For Gantrez S95, the interactions with Zn2+ and Sn2+ were also investigated in a solution containing different amounts of fluoride, in order to investigate the formation of mixed metal–ligand′–ligand′′ species. The dependence of the stability constants on ionic strength and temperature was modeled by means of modified Debye–Hückel equations. From the gradient of stability constants with respect to temperature, rough enthalpy and entropy change values for the formation of the species were calculated, with results that the entropic contribution is the driving force of reactions. The sequestering ability of the three Gantrez ligands, evaluated by means of the pL0.5 parameter, allowed us to highlight a net higher ability of Gantrez ligands to sequester Sn2+ with respect to the other metal ions (about 3–4 orders of magnitude).
In this paper, the sequestering ability of amoxicillin and ampicillin toward Mg2+ in NaCl aqueous solutions at different ionic strengths I = (0 to 1.0) mol·kg–1 and temperatures of T = (288.15 to ...318.15) K was investigated by potentiometry (ISE-H+, glass electrode). The complex formation constants determined at different ionic strengths and temperatures were modeled by means of the Debye–Hückel equation and the Specific ion Interaction Theory (SIT). From the results, a weak ability of the two penicillins to bind the metal ion can be observed; in fact, the stability constants of the ML species (M = Mg2+ and L = amoxicillin or ampicillin) are log β = 4.348 and 3.242 at infinite dilution and T = 298.15 K, respectively. The dependence of the formation constants on the temperature was modeled by means of a van’t Hoff equation, which allowed us to calculate the enthalpy and entropy change values of formation of each species. The sequestering ability of amoxicillin and ampicillin toward Mg2+ in the different experimental conditions (pH, ionic strength, temperature) was quantified by means of a sigmoid equation and of the pL0.5 parameter. The pL0.5 values reflect the low stability constant values of the species; as an example at I = 0.15 mol·kg–1, pH = 7.4, and T = 298.15 K, we have pL0.5 = 2.52 and 2.78, for Mg2+/amox2− and Mg2+/amp− systems, respectively.
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
+2
j
−3)
and Ca
j
H
i
(GSH)
(
i
+2
j
−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.
In this paper, new potentiometric, calorimetric, and voltammetric measurements are reported to model the behavior of d-gluconic acid in aqueous NaCl(aq) and NaNO3(aq) ionic media at different ionic ...strengths and temperatures (283.15 ≤ T/K ≤ 318.15) also in the presence of Sn2+ and Zn2+. The protonation constants of d-gluconic acid (Gluc– in its deprotonated form) in NaCl(aq) and NaNO3(aq) are very similar. The dependence on ionic strength of the protonation constant was modeled by means of the extended Debye–Hückel type equation, the Specific ion Interaction Theory (SIT) and a weak interaction model. At infinite dilution and T = 298.15 K, the thermodynamic parameters for the proton binding reaction, determined by direct calorimetric titrations and temperature gradients of protonation constants, are log K H0 = 3.709 ± 0.004, ΔG 0 = −21.18 ± 0.01 kJ mol–1, ΔH 0 = −4.56 ± 0.04 kJ mol–1, and TΔS 0 = 16.6 ± 0.1 kJ mol–1, indicating that the reaction is exothermic and entropic in nature. Potentiometric and voltammetric measurements on the Sn2+ and Zn2+/Gluc– systems allowed us to determine the MGluc + species for both systems at different ionic strengths, together with the Sn(Gluc)2 and Sn(OH)Gluc species. The values of the formation constant of the SnGluc+ species are higher than the corresponding ZnGluc+. During the experiments, the precipitation of insoluble species was evidenced at pH ≥ 4.0 for Sn2+/Gluc– and pH ≥ 7.0 for Zn2+/Gluc–. The stoichiometry of the precipitates was established by means of thermogravimetric analysis, and the solubility of the two salts, Sn(OH)Gluc(s) and Zn(Gluc)2(s), was determined in pure water, in NaCl and in NaNO3 aqueous media. In pure water, the total solubility is S T = 0.262 ± 0.001 and 0.082 ± 0.006 mol kg–1 for the ZnGluc2 and Sn(OH)Gluc, respectively. Calorimetric measurements were performed to determine the enthalpy changes of the gluconate protonation and Sn2+ complex formation constants at different ionic strengths. The effect of two anions, as fluoride and citrate, on the stability of the Sn2+/Gluc– species was studied by means of potentiometric measurements at I = 0.15 and 1.02 mol kg–1, and it was found that the formation of mixed complexes is thermodynamically favored.
This work is focused on the design and preparation of polymer inclusion membranes (PIMs) for potential applications for stannous cation sequestration from water. For this purpose, the membranes have ...been synthesized employing two polymeric matrices, namely, polyvinylchloride (PVC) and cellulose triacetate (CTA), properly enriched with different plasticizers. The novelty here proposed relies on the modification of the cited PIMs by selected extractants expected to interact with the target cation in the membrane bulk or onto its surface, as well as in the evaluation of their performances in the sequestration of tin(II) in solution through chemometric tools. The composition of both the membrane and the solution for each trial was selected by means of a D-Optimal Experimental Design. The samples such prepared were characterized by means of TG-DTA, DSC, and static contact angles investigations; their mechanical properties were studied in terms of tensile strength and elastic modulus, whereas their morphology was checked by SEM. The sequestering ability of the PIMs toward stannous cation was studied by means of kinetic and isotherm experiments using DP-ASV. The presence of tin in the membranes after the sequestration tests was ascertained by μ-ED-XRF mapping on selected samples.
This contribution reports the results of an investigation on the speciation of various lanthanoid(III) cations (Ln3+), namely, La3+, Nd3+, Sm3+, Eu3+, Gd3+, Dy3+, and Yb3+, in the presence of ...reduced glutathione (or simply glutathione, GSH), in NaCl(aq) at I = 0.15 mol·dm–3 and T = 298.15 K. GSH forms in all cases the same four species, namely, Ln(GSH)H3, Ln(GSH)H2, Ln(GSH)H, and Ln(GSH)OH, whose stability depends on the type of lanthanoid, although it is also possible to consider an average stability for a generic lanthanoid, at least for the protonated species. Measurements at different temperatures and ionic strengths for the La3+/GSH and Gd3+/GSH systems have also been performed, to evaluate their effect on the speciation of both GSH and the Ln3+ cations. The dependence of the determined stability constants on I and T has been modeled by an extended Debye–Hückel type and by the van’t Hoff equations. In this last case, the formation enthalpy changes of La3+/GSH species have also been determined. The stability constants obtained have been therefore used to quantify the sequestering ability of GSH toward the investigated cations, in different pH, ionic strength, and temperature conditions, by the calculation of several pL0.5 parameters. Their analysis showed that, generally, the sequestering ability of GSH increases with increasing pH and decreases with increasing temperature, while the ionic strength has only a small effect. Finally, results obtained may be exploited for the evaluation of the speciation (and, therefore, of the sequestration) of any Ln3+ cations in the presence of GSH in different conditions of T and I, like those featuring many natural waters and biological fluids.
The current work investigates the protonation constants of gabapentin (GP), 2-1-(aminomethyl)cyclohexylacetic acid and the stability constants for the binding of GP to Ca
2+
and Mg
2+
in a wide range ...of temperature and ionic strength conditions 283.15 ≤
T
/K ≤ 318.15 and ionic strengths of NaCl(aq), 0.12 ≤
I
/mol·dm
−3
≤ 4.84. The pH-potentiometric titration method was applied for gathering experimental data and determination of solution equilibrium constants. The Δp
K
method was used for the determination of calcium and magnesium stability constants due to the low values which were predicted. A Debye–Hückel type equation, Specific Ion Interaction Theory, Pitzer and van’t Hoff equations were used for the modeling of ionic strength and temperature effects. Two species, ML and MHL, were found according to the best model for Ca
2+
and Mg
2+
. Both protonation processes are exothermic based on the enthalpy values at 298.15 K and infinite dilution. A case study has been performed taking into account the speciation of GP in seawater.
1,2,3,4,5,6 hexakis (di-hydrogen phosphate) myo-inositol, best known as phytic acid, is a very important molecule from a biological, environmental and technological point of view. For a thorough ...understanding of phytate properties and the mechanisms involving this ligand, a careful study of its acid–base behavior and of the formation and stability of its complexes in solution is necessary. Unfortunately, regarding the thermodynamic data on phytate complexes in solution, some are lacking, while some others exhibit large discrepancies between different authors. This motivated a detailed evaluation of the literature on this topic, aimed at identifying the most accurate data on phytate coordination chemistry in solution. This review presents the results of this, reporting and analyzing the most significant thermodynamic parameters published for both phytate protonation and complex formation with several metal and organometal cations, as well as polyammonium ligands.
