Binding ability of glutathione towards alkyltin(IV) compounds in aqueous solution

Towards a rational design of materials for the removal of environmentally relevant cations: polymer inclusion membranes (PIMs) and surface-modified PIMs for Sn2+ sequestration in aqueous solution

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.

Ca2+ Complexation With Relevant Bioligands in Aqueous Solution: A Speciation Study With Implications for Biological Fluids

A speciation study on the interaction between Ca2+ and ligands of biological interest in aqueous solution is reported. The ligands under study are l-cysteine (Cys), d-penicillamine (PSH), reduced glutathione (GSH), and oxidized glutathione (GSSG). From the elaboration of the potentiometric experimental data the most likely speciation patterns obtained are characterized by only protonated species with a 1:1 metal to ligand ratio. In detail, two species, CaLH2 and CaLH, for systems containing Cys, PSH, and GSH, and five species, CaLH5, CaLH4, CaLH3, CaLH2, and CaLH, for system containing GSSG, were observed. The potentiometric titrations were performed at different temperatures (15 ≤ t/°C ≤ 37, at I = 0.15 mol L-1). The enthalpy and entropy change values were calculated for all systems, and the dependence of the formation constants of the complex species on the temperature was evaluated. 1H NMR spectroscopy, MALDI mass spectrometry, and tandem mass spectrometry (MS/MS) investigations on Ca2+-ligand solutions were also employed, confirming the interactions and underlining characteristic complexing behaviors of Cys, PSH, GSH, and GSSG toward Ca2+. The results of the analysis of 1H NMR experimental data are in full agreement with potentiometric ones in terms of speciation models and stability constants of the species. MALDI mass spectrometry and tandem mass spectrometry (MS/MS) analyses confirm the formation of Ca2+-L complex species and elucidate the mechanism of interaction. On the basis of speciation models, simulations of species formation under conditions of some biological fluids were reported. The sequestering ability of Cys, PSH, GSH, and GSSG toward Ca2+ was evaluated under different conditions of pH and temperature and under physiological condition.

A mass spectrometry-based approach gives new insight into organotin-protein interactions

In this study, the combination of speciation analysis and native mass spectrometry is presented as a powerful tool to gain new insight into the diverse interactions of environmentally relevant organotin compounds (OTCs) with proteins. Analytical standards of model proteins, such as β-lactoglobulin A (LGA), were thereby incubated with different phenyl- and butyltins. For adduct identification and characterization, the incubated samples were analyzed by inductively coupled plasma-mass spectrometry (ICP-MS) and electrospray ionization-mass spectrometry (ESI-MS) in combination with size exclusion chromatography (SEC). It allowed for a mild separation, which was most crucial to preserve the acid-labile organotin-protein adducts during their analyses. The binding of triorganotin compounds, such as triphenyltin, was shown to be sulfhydryl-directed by using cysteine-specific protein labeling. However, the sole availability of reduced cysteine residues in proteins did not automatically enable adduct formation. This observation complements previous studies and indicates the necessity of a highly specific binding pocket, which was identified for the model protein LGA via enzymatic digestion experiments. In contrast to triorganotins, their natural di- and mono-substituted degradation products, such as dibutyltin, revealed to be less specific regarding their binding to several proteins. Further, it also did not depend on reduced cysteine residues within the protein. In this context, they can probably act as linker molecules, interconnecting proteins, and leading to dimers and probably to higher oligomers. Furthermore, dibutyltin was observed to induce hydrolysis of the protein's peptide backbone at a specific site. Concerning unknown long-term toxic effects, our studies emphasize the importance of future studies on di- and mono-substituted OTCs.

Complexation of As(III) by phosphonate ligands in aqueous fluids: Thermodynamic behavior, chemical binding forms and sequestering abilities

In recent years, the contamination of water by arsenic reached alarming levels in many countries of the world, attracting the interest of many researchers engaged in testing methodologies able to remove this harmful pollutant. An important aspect that must be taken into consideration is the possibility to find arsenic in different chemical forms which could require different approaches for its removal. At this aim, a speciation analysis appears to be crucial for better understanding the behavior of arsenic species in aqueous solutions, especially in presence of compounds with marked chelating properties. Phosphonates can be identified as good sequestering agents and, at this purpose, this manuscript intends to investigate the interaction of As(III) with three phosphonic acids derived from nitrilotriacetic acid (NTA) by replacements of one (N-(Phosphonomethyl) iminodiacetic acid, NTAP), two (N,N-Bis-(phosphonomethyl) glycine, NTA2P) and three (Nitrilotri(methylphosphonic acid), NTA3P) carboxylic groups with the same number of phosphonate groups. An in-depth potentiometric and calorimetric investigation allowed to determine speciation models featured by simple ML, MLH_i and ML(OH) species. A complete thermodynamic characterization of the systems is reported together with the definition of coordination mode by mass spectrometry measurements. On the light of the speciation models, the possibility of using these ligands in arsenic removal techniques was assessed by determining the pL_0.5 (the concentration of ligand able to remove the 50% of metal ion present in trace). All ligands show a good sequestering ability, in particular under the conditions of fresh water, following the trend NTA3P > NTA2P > NTAP.

Interaction of Ampicillin and Amoxicillin with Mn2+: A Speciation Study in Aqueous Solution

A potentiometric and UV spectrophotometric investigation on Mn²⁺-ampicillin and Mn²⁺-amoxicillin systems in NaCl aqueous solution is reported. The potentiometric measurements were carried out under different conditions of temperature (15 ≤ t/°C ≤ 37). The obtained speciation pattern includes two species for both the investigated systems. More in detail, for system containing ampicillin MLH and ML species, for that containing amoxicillin, MLH₂ and MLH ones. The spectrophotometric findings have fully confirmed the results obtained by potentiometry for both the systems, in terms of speciation models as well as the stability constants of the formed species. Enthalpy change values were calculated via the dependence of formation constants of the species on temperature. The sequestering ability of ampicillin and amoxicillin towards Mn²⁺ was also evaluated under different conditions of pH and temperature via pL_0.5 empirical parameter (i.e., cologarithm of the ligand concentration required to sequester 50% of the metal ion present in traces).

Study of Al3+ interaction with AMP, ADP and ATP in aqueous solution

The interaction of Al³⁺ and nucleotide ligands, namely adenosine-5'-monophosphate, (AMP), adenosine-5'-diphosphate, (ADP), adenosine-5'-triphosphate, (ATP), has been studied in aqueous solution at T = 298.15 K and I = 0.15 mol L^-1 in NaCl (only for Al³⁺-ATP system at I = 0.1 mol L^-1). Formation constants and speciation models for the species formed are discussed on the basis of potentiometric results. The speciation models found for the three systems include ML and ML₂ species in all the cases, and for Al³⁺-ADP and ATP systems, MLH, MLOH and ML₂OH species as well. The formation constant value for ML species shows the trend, AMP < ADP < ATP. ¹H NMR spectroscopy was also employed for the study of Al³⁺-ATP system. The ¹H NMR results are in agreement with the speciation model obtained from analysis of potentiometric titration data, confirming the stabilities of the main species. Enthalpy change values were obtained by titration calorimetry; for the main Al³⁺-ATP species (at T = 298.15 K and I = 0.1 mol L^-1 in NaCl), they resulted always higher than zero, as typical for hard-hard interactions. The dependence of formation constants on ionic strength over the range I = 0.1 to 1 mol L^-1 in NaCl is also reported for Al³⁺-ATP system. The sequestering ability of the nucleotides under study towards Al³⁺ was also evaluated by the empirical parameter pL_0.5.

Thermodynamic parameters for the protonation and the interaction of arsenate with Mg2+, Ca2+ and Sr2+: Application to natural waters

Thermodynamic parameters for the protonation of AsO₄^3- and for the interaction with Mg²⁺, Ca²⁺ and Sr²⁺ were reported, comprehensive also of their dependence on ionic strength, considering the 0.1 ≤ I ≤ 1 M range and using NaCl as background salt. The same speciation models were obtained for Mg²⁺, Ca²⁺ and Sr²⁺ systems, with the formation of three different species: ML, MLH and MLH₂ (L = AsO₄^3-). Mono- and di-protonated species were very weak, with formation constant values (log K) ranging from 1.45 to 3.23. In order to have a complete picture of thermodynamic properties of the systems under study and to fill the shortage of thermodynamic data on arsenate complex systems, the ligand protonation and metal complex enthalpies were also determined by calorimetric titrations, at t = 25 °C and in NaCl at I = 0.7 M (for H⁺-AsO₄^3- species also at I = 0.1 M). On the light of the proposed speciation models, examples of As(V) distribution in some natural waters are reported.

Potentiometric, UV and 1H NMR study on the interaction of Cu2+ with ampicillin and amoxicillin in aqueous solution

A potentiometric, UV and ¹H NMR study on Cu²⁺-ampicillin [(2S,5R,6R)-6-([(2R)-2-amino-2-phenylacetyl]amino)-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-2-carboxylic acid] and -amoxicillin [(2S,5R,6R)-6-{[(2R)-2-amino-2-(4-hydroxyphenyl)-acetyl]amino}-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-24-carboxylic acid] systems in NaCl aqueous solution at I=0.15molL^-1 and t=25°C is reported. On the basis of potentiometric results two speciation models were proposed for each system. It was found that spectrophotometric and ¹H NMR measurements are essential for selecting the most reliable speciation models. They included ML, MLOH and ML(OH)₂ species in both systems and, only for Cu²⁺-ampicillin, also MLH species. The stability constants obtained by UV and ¹H NMR titrations were comparable to the ones calculated by potentiometry. The sequestering ability of the ligands under study towards Cu²⁺ by pL_0.5 empiric parameter (ligand concentration required to sequester 50% of the metal cation present in traces) at several pH values was calculated as well. For ampicillin and amoxicillin, pL_0.5=7.19 and 6.67, respectively, at physiological pH, I=0.15molL^-1 and t=25°C were obtained.

Potentiometric, UV and 1H NMR study on the interaction of penicillin derivatives with Zn(II) in aqueous solution

The interaction of Zn(II) with ampicillin [(2S,5R,6R)-6-([(2R)-2-amino-2-phenylacetyl]amino)-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-2- carboxylic acid] and amoxicillin [(2S,5R,6R)-6-{[(2R)-2-amino-2-(4-hydroxyphenyl)-acetyl]amino}-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-24-carboxylic acid] in NaCl aqueous solution at different ionic strengths and at t=25°C was investigated by potentiometric, UV and ¹H NMR techniques. Fairly similar speciation models were obtained for the two systems. At I=0.15molL^-1, two different sets of measurements, at low and high concentrations, were carried out. For the Zn²⁺-amoxicillin system, the Zn₂L₂(OH)₂ species was obtained in the set of measurements at high concentration. The spectrophotometric and ¹H NMR results thus obtained are fully consistent with the speciation models found from potentiometric investigations, confirming the formation as well as the relative stability of the complex species. The dependence of the stability constants on the ionic strength was modeled by means of the Debye-Hückel and SIT (Specific ion Interaction Theory) approaches, and the parameter that accounts for the variation of the stability constants with the ionic strength and the specific ion interaction parameters were determined for all the ionic species. The sequestering ability of the ligands towards Zn²⁺ was evaluated by determining the pL_0.5 parameter at different ionic strengths. It resulted that the sequestering ability of ampicillin is higher of ~0.5 order of magnitude with respect to amoxicillin.

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

Complexation of various metal cations by DTPMA obtained by an efficient synthetic procedure has been investigated, assessing its sequestering ability and speciation in real systems.

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

Replacing carboxylic with phosphonic groups in NTA significantly affects the sequestering ability toward Hg²⁺, CH₃Hg⁺, Sn²⁺ and (CH₃)₂Sn²⁺.

Thermodynamic data for Pb2+and Zn2+sequestration by biologically important S-donor ligands, at different temperatures and ionic strengths

A thermodynamic picture is reported for cys–Pb²⁺, psh–Pb²⁺, gsh–Pb²⁺, and gsh–Zn²⁺systems, and equilibrium constants can be predicted for any experimental condition.