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.

Design and Development of Fluorinated and Biocide-Free Sol-Gel Based Hybrid Functional Coatings for Anti-Biofouling/Foul-Release Activity.

Biofouling has destructive effects on shipping and leisure vessels, thus producing severe problems for marine and naval sectors due to corrosion with consequent elevated fuel consumption and higher maintenance costs. The development of anti-fouling or fouling release coatings creates deterrent surfaces that prevent the initial settlement of microorganisms. In this regard, new silica-based materials were prepared using two alkoxysilane cross-linkers containing epoxy and amine groups (i.e., 3-Glycidyloxypropyltrimethoxysilane and 3-aminopropyltriethoxysilane, respectively), in combination with two functional fluoro-silane (i.e., 3,3,3-trifluoropropyl-trimethoxysilane and glycidyl-2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecafluorononylether) featuring well-known hydro repellent and anti-corrosion properties. As a matter of fact, the co-condensation of alkoxysilane featuring epoxide and amine ends, also mixed with two opportune long chain and short chain perfluorosilane precursors, allows getting stable amphiphilic, non-toxic, fouling release coatings. The sol-gel mixtures on coated glass slides were fully characterized by FT-IR spectroscopy, while the morphology was studied by scanning electron microscopy (SEM), and atomic force microscopy (AFM). The fouling release properties were evaluated through tests on treated glass slides in different microbial suspensions in seawater-based mediums and in seawater natural microcosms. The developed fluorinated coatings show suitable antimicrobial activities and low adhesive properties; no biocidal effects were observed for the microorganisms (bacteria).

Lipids in Archaeological Pottery: A Review on Their Sampling and Extraction Techniques.

Several studies have been performed so far for the effective recovery, detection and quantification of specific compounds and their degradation products in archaeological materials. According to the literature, lipid molecules are the most durable and widespread biomarkers in ancient pottery. Artificial ageing studies to simulate lipid alterations over time have been reported. In this review, specific lipid archaeological biomarkers and well-established sampling and extraction methodologies are discussed. Although suitable analytical techniques have unraveled archaeological questions, some issues remain open such as the need to introduce innovative and miniaturized protocols to avoid extractions with organic solvents, which are often laborious and non-environmentally friendly.

Thermodynamic Solution Properties of a Biodegradable Chelant (L-glutamic-N,N-diacetic Acid, L-GLDA) and Its Sequestering Ability toward Cd2.

The thermodynamics of the interaction of L-glutamic-N,N-diacetic acid (GLDA) with protons was studied potentiometrically at different temperatures, ionic strengths and ionic media. Four protonation constants and corresponding enthalpy changes occurred at infinite dilution together with temperature and ionic strength coefficients. The medium effect was also interpreted in terms of the formation of weak complexes between the ligand and the cations of supporting electrolytes, resulting in a greater tendency of GLDA to chemically interact with Na+ rather than K+ and, in turn, (CH3)4N+. Formation constants of GLDA with Cd2+ were determined in NaCl(aq) at different ionic strength values. Five complex species were found, namely CdL2-, CdHL-, CdH2L0(aq), Cd2L0(aq), and Cd(OH)L3-, whose formation constant values at infinite dilution were log ß = 12.68, 17.61, 20.76, 17.52, and 1.77, respectively. All the species results were relevant in the pH range of natural waters, although the Cd2L0(aq) was observed only for CCd ≥ CGLDA and concentrations of >0.1 mmol dm-3. The sequestering ability of GLDA toward Cd2+, evaluated by means of pL0.5, was maximum at pH~10, whereas the presence of a chloride containing a supporting electrolyte exerted a negative effect. Among new generation biodegradable ligands, GLDA was the most efficient in Cd2+ sequestration.

Bifunctional 3-Hydroxy-4-Pyridinones as Potential Selective Iron(III) Chelators: Solution Studies and Comparison with Other Metals of Biological and Environmental Relevance.

The binding ability of five bifunctional 3-hydroxy-4-pyridinones towards Cu2+ and Fe3+ was studied by means of potentiometric and UV-Vis spectrophotometric measurements carried out at I = 0.15 mol L-1 in NaCl(aq),T = 298.15 K and 310.15 K. The data treatments allowed us to determine speciation schemes featured by metal-ligand species with different stoichiometry and stability, owing to the various functional groups present in the 3-hydroxy-4-pyridinones structures, which could potentially participate in the metal complexation, and in the Cu2+ and Fe3+ behaviour in aqueous solution. Furthermore, the sequestering ability and metal chelating affinity of the ligands were investigated by the determination of pL0.5 and pM parameters at different pH conditions. Finally, a comparison between the Cu2+ and Fe3+/3-hydroxy-4-pyridinones data herein presented with those already reported in the literature on the interaction of Zn2+ and Al3+ with the same ligands showed that, from the thermodynamic point of view, the 3-hydroxy-4-pyridinones are particularly selective towards Fe3+ and could therefore be considered promising iron-chelating agents, also avoiding the possibility of competition, and eventually the depletion, of essential metal cations of biological and environmental relevance, such as Cu2+ and Zn2+.

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.

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.

Speciation Studies of Bifunctional 3-Hydroxy-4-Pyridinone Ligands in the Presence of Zn2+ at Different Ionic Strengths and Temperatures.

The acid-base properties of two bifunctional 3-hydroxy-4-pyridinone ligands and their chelating capacity towards Zn2+, an essential bio-metal cation, were investigated in NaCl aqueous solutions by potentiometric, UV-Vis spectrophotometric, and 1H NMR spectroscopic titrations, carried out at 0.15 ≤ I/mol -1 ≤ 1.00 and 288.15 ≤ T/K ≤ 310.15. A study at I = 0.15 mol L-1 and T = 298.15 K was also performed for other three Zn2+/Lz- systems, with ligands belonging to the same family of compounds. The processing of experimental data allowed the determination of protonation and stability constants, which showed accordance with the data obtained from the different analytical techniques used, and with those reported in the literature for the same class of compounds. ESI-MS spectrometric measurements provided support for the formation of the different Zn2+/ligand species, while computational molecular simulations allowed information to be gained on the metal-ligand coordination. The dependence on ionic strength and the temperature of equilibrium constants were investigated by means of the extended Debye-Hückel model, the classical specific ion interaction theory, and the van't Hoff equations, respectively.

Analytical assessment to develop innovative nanostructured BPA-free epoxy-silica resins as multifunctional stone conservation materials.

Bisphenol A (BPA)-free epoxy resins, synthesized from low molecular weight cycloaliphatic compounds, may represents promising materials for stone conservation due to their very appealing and tunable physico-chemical properties, such as viscosity, curing rate and penetration ability, being also easy to apply and handle. Furthermore, alkoxysilanes have been widely employed as inorganic strengtheners since they are easily hydrolysed inside lithic substrates affording SiO linkages with the stone matrix. Taking into account the advantages of these two classes of materials, this work has been focused on the development of innovative conservation materials, based on hybrid epoxy-silica BPA-free resins obtained by reaction of 1,4-cycloexanedimethanol diglycidylether (CHDM-DGE) with various siloxane precursors, i.e. glycidoxypropylmethyldiethoxysilane (GPTMS), tetraethyl orthosilicate (TEOS) and isobutyltrimethoxysilane (iBuTMS), using the 1,8-diaminooctane (DAO) as epoxy hardener. Thanks to Raman spectroscopy the synthesis processes have been successfully monitored, allowing the identification of oxirane rings opening as well as the formation of the cross-linked organic-inorganic networks. In accordance with the spectroscopic data, the thermal studies carried out by TGA and DSC techniques have pointed that GPTMS is a suitable siloxane precursor to synthesize the most stable samples against temperature degradation. GPTMS-containing resins have also shown good performances in the dynamic mechanical analysis (DMA) and in contact angle investigations, with values indicating considerable hydrophobic properties. SEM analyses have highlighted a great homogeneity over the entire observed areas, without formations of clusters and/or aggregates bigger than 45 µm, for the cited materials, confirming the efficiency of GPTMS as coupling agent to enhance the organic/inorganic interphase bonding. The variations provided by the incorporation of nanostructured titania, specifically synthesized, inside the epoxy-silica hybrids have been also evaluated. According to all the collected results, the hybrid materials here reported have proven to be promising multifunctional products for potential application in the field of stone conservation.

Exploring various ligand classes for the efficient sequestration of stannous cations in the environment.

Metal pollution, coming from both natural and anthropogenic sources, has become one of the most serious environmental problems. Various strategies have been tested with the aim of removing heavy metals from environment. In this contribution, containing a robust experimental work together with a critical literature analysis, the sequestering ability of a variety of ligands towards Sn2+ cation will be evaluated in the conditions of several natural fluids, i.e. sea water, fresh water, human blood plasma, urine and saliva. 13 structural and 11 thermodynamic descriptors will be selected for a total of thirty-eight molecules belonging to different classes (carboxylic acids, amines, amino acids, phosphonates, polyelectrolytes etc. …). For the filling of those missing data relative to the 11 thermodynamic descriptors, different strategies will be adopted, including simple correlations and Nipals algorithm. The evaluation of the sequestering ability of the ligands is assessed in terms of estimation of pL0.5 (total concentration of ligand required to bind the 50% of metal in solution), an empirical parameter that takes into account all the side reactions in solutions and does not depend on the speciation scheme. Partial least square calculations were performed to model the pL0.5 and to determine its correlation with the abovementioned descriptors. The possibility to design and build up new tailor-made molecules capable of effectively sequester Sn2+ in various conditions is crucial for practical applications in biosphere, hydrosphere and lithosphere.

Bifunctional 3-hydroxy-4-pyridinones as effective aluminium chelators: synthesis, solution equilibrium studies and in vivo evaluation.

This paper reports the results on the study of a set of synthesized bifunctional 3-hydroxy-4-pyridinones chelators as potential aluminium sequestering agents. They were N-functionalized with alkyl-amino, -carboxylic and -(amino-carboxylic) groups, envisaging the improvement of the Al3+ sequestering capacity, in comparison with the marketed chelating drug deferiprone. The main focus of this work was given to the assessment of their binding ability towards Al3+, which was studied by potentiometric and UV-Vis spectrophotometric measurements carried out at T = 298.15 K. The speciation models were characterized by AlpLqHr(3p+r-qz) species with different stoichiometry. Depending on ligand side-chain structures and on their thermodynamic properties, different trends of stability was found. Furthermore, the sequestering ability of the ligands towards Al3+ was investigated by the calculation of pL0.5 values at different experimental conditions. These results clearly indicate that the presence of amino-carboxylic groups in the ligands increases the sequestering ability towards Al3+. The in silico evaluation of pharmacokinetic descriptors indicated no violation to the Lipinski's rule and drug-likeness properties. Furthermore, the in vivo bioassays on a model of metal-overload mice showed for three investigated ligands a higher metal-sequestering capacity than for the chelating drug deferiprone, thus suggesting their potential interest as Al-chelating drug candidates.

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 pL0.5.

Novel Luminescent Ionic Adducts Based on Pyrene-1-sulfonate.

The potential of pyrene-1-sulfonate to act as an emitting anion for the development of ionic liquids is explored here. Amphiphilic trimethylpropylammonium hepta(isooctyl)octasilsesquioxane and conventional imidazolium, namely, 1-vinyl-3-hexyl-, 1-vinyl-3-decyl-, and 1-methyl-3-decyl-imidazolium, featuring moderate alkyl chain length substituents, have been chosen as countercations. The new species have been synthesized via simple metathesis reactions involving pyrene-1-sulfonate sodium salt and the appropriate halide cation precursors. Their thermal behavior has been investigated by thermogravimetric and differential scanning calorimetry at different scanning rates. According to this latter technique, only the trimethylpropylammonium hepta(isooctyl)octasilsesquioxane pyrenesulfonate adduct, displaying a reversible glass transition at -4.2 °C, may be classified as an ionic liquid. All pyrene-1-sulfonate imidazolium-based ion pairs are crystalline solids with the melting point just above 100 °C that produce very complex, nonreversible, and scanning rate-dependent thermograms, very likely arising from polymorphism phenomena. Such a behavior may be attributed to the pyrene-1-sulfonate polycyclic system, which in solution, as confirmed through spectroscopic characterization, displays a general attitude in promoting supramolecular structures via cation interactions. Emission lifetime measurements on the emitting fluorophore reveal that there are at least two different active species, whereas light scattering measurements show the presence of aggregates with hydrodynamic radii depending on the medium and adduct concentration. Tests aimed at investigating the potential of these novel pyrene-1-sulfonate salts in functionalization/exfoliation of graphite flakes are also reported here.

Multi-analytical methodology to diagnose the environmental impact suffered by building materials in coastal areas.

This work is focused on the development of an innovative multi-analytical methodology to estimate the impact suffered by building materials in coastal environments. With the aim of improving the in situ spectroscopic assessment, which is often based on XRF and Raman spectrometers, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was implemented in the diagnosis study. In this way, the additional benefits from DRIFT were compared to the usual in situ analyses of building materials, which often have interferences from fluorescence and reststrahlen effects. The studies were extended to the laboratory scale by µ-X-ray fluorescence (µ-XRF) cross-section mapping and ion chromatography (IC), and the IC quantitative data were employed to develop thermodynamic models using the ECOS-RUNSALT program, with the aim of rationalizing the behavior of soluble salts with variations in the temperature and the relative humidity (RH). The multi-analytical methodology allowed identification of the most significant weathering agents and classification of the severity of degradation according to the salt content. The suitability of a DRIFT portable device to analyze these types of matrices was verified. Although the Kramers-Kronig algorithm correction proved to be inadequate to decrease the expected spectral distortions, the assignment was successfully performed based on the secondary bands and intensification of the overtones and decreased the time needed for in situ data collection. In addition, the pollutants' distribution in the samples and the possible presence of dangerous compounds, which were not detected during the in situ analysis campaigns, provided valuable information to clarify weathering phenomena.

Sequestration of Aluminium(III) by different natural and synthetic organic and inorganic ligands in aqueous solution.

The speciation of Al3+ in aqueous solutions containing organic and inorganic ligands important from a biological (citrate (Cit3-), gluconate (Gluc-), lactate (Lac-), silicate (H2SiO42-), carbonate (CO32-), fluoride (F-)) and industrial (Gantrez®; polymethyl-vinyl-ether-co-maleic acids; GTZ S95 and GTZ AN169) point of view is reported. The stability constants of Al3+/Lz- complexes (Lz- = ligand with z- charge) were determined by potentiometry at T = 298.15 K and 0.10 ≤ I/M ≤ 1.00 in NaCl(aq) (in NaNO3(aq) only for Al3+/GTZ S95 and Al3+/Gluc- acid systems). For Al3+/Cit3-, Al3+/Lac- and Al3+/GTZ AN1694- systems, the investigations were also carried out at 283.15 ≤ T/K ≤ 318.15. The dependence of the thermodynamic parameters on ionic strength and temperature was modelled with a Debye-Hückel type equation. Different speciation schemes of Al3+/Lz- systems were obtained, including protonated, simple metal-ligand, polynuclear and hydrolytic mixed species. At I → 0 M and T = 298.15 K the stability trend for the AlL(3-z) species is: 14.28 ± 0.02, 13.99 ± 0.03, 10.16 ± 0.03, 3.16 ± 0.08, 2.84 ± 0.10 for GTZ S95, GTZ AN169, Cit3-, Gluc- and Lac-, respectively. From the investigations at different temperatures, it results that the entropic contribution is the driving force of the reactions. The sequestering ability of the ligands towards Al3+ was investigated determining the pL0.5 parameter at different experimental conditions, finding the following trend: Cit3- ¼ Gluc- > GTZ S954- > GTZ AN1694- > Lac- for the organic ligands, and pL0.5: F- ¼ CO32- > H2SiO42- for the inorganic ones.

Thermodynamic and spectroscopic study of Al3+ interaction with glycine, l-cysteine and tranexamic acid in aqueous solution.

In this paper a thermodynamic and spectroscopic study on the interaction between Al3+ and glycine (Gly), l-cysteine (Cys), tranexamic acid (Tranex) is reported. Speciation models have been obtained by processing potentiometric titration data to determine stability constants of the species formed in aqueous solution at T=298.15K, 0.15≤I/molL-1≤1 in NaCl. Thermodynamic formation parameters have been obtained from calorimetric titration data, at T=298.15K, I=0.15molL-1 using NaCl as ionic medium. Al3+-Cys system was also investigated by spectrophotometric and 1H NMR measurements. 1H NMR experiments were performed on Al3+-Tranex system as well. Different speciation models have been observed for the three systems. The results showed the formation of MLH, ML and M2L2(OH)2 species for Gly, ML, M2L and MLOH for Cys, MLH and MLOH for Tranex. The formed species are quite stable, i.e. for ML, logß=7.18, 11.91 for Gly and Cys, respectively, at I=0.15molL-1 and T=298.15K. For all the systems the dependence of formation constants on ionic strength over the range 0.1-1molL-1 is reported. The sequestering ability of the ligands under study was also evaluated by pL0.5 empiric parameter. For Gly, Cys and Tranex, pL0.5=2.51, 3.74, 3.91 respectively, at pH=5, I=0.15molL-1 and T=298.15K.

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 pL0.5 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, pL0.5=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 pL0.5 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.

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

The interactions between glutathione (H3GSH) and (CH3)2Sn(2+), (CH3)3Sn(+), (C2H5)3Sn(+) and (C3H7)3Sn(+) cations were studied by potentiometry, UV spectrophotometry, (1)H NMR spectroscopy and electrospray mass spectrometry (ESI MS). Potentiometric measurements evidenced speciation models very similar for all the alkyltin(IV) cation-GSH(3-) systems, with the formation of M(GSH)(z-3), M(GSH)H(z-2) and M(GSH)H2(z-1) species [M(z+)=(CH3)2Sn(2+), (CH3)3Sn(+), (C2H5)3Sn(+), or (C3H7)3Sn(+)] and, for dimethyltin(IV) cation, also the mixed hydrolytic M(GSH)(OH)(2-) one. The equilibrium behavior in NaCl aqueous solution, at different ionic strengths and temperatures, is discussed. The stability of the species for the dimethyl and trialkyl cations is quite different. As an example, for M(GSH)(z-3), logß=13.33, 6.55, 6.44 and 5.84, for (CH3)2Sn(2+), (C3H7)3Sn(+), (C2H5)3Sn(+) and (CH3)3Sn(+), respectively (at I=0.1M and t=25°C). The speciation models and the possible structures of the complexes formed are discussed on the basis of spectroscopic and spectrometric results. The sequestering ability of glutathione towards alkyltin(IV) cations was evaluated by determining the concentration of the ligand able to complex half of the metal ion fraction (pL0.5). Glutathione shows a fairly good sequestering ability towards alkyltin(IV) cations, in 10(-3)-10(-5)M range.

Thermodynamic and spectroscopic study for the interaction of dimethyltin(IV) with L-cysteine in aqueous solution.

Thermodynamic and spectroscopic properties of the species formed by dimethyltin(IV) cation with L-cysteine (cys) were studied by potentiometric, calorimetric, UV and NMR investigations in aqueous solution. The resulting speciation model showed the formation of five complex species: (CH(3))(2)Sn(cys)H(+), (CH(3))(2)Sn(cys)(0), (CH(3))(2)Sn(cys)OH(-), (CH(3))(2)Sn(cys)(2)H(-), (CH(3))(2)Sn(cys)(2)(2-). The stability and the formation percentages, for the mononuclear mixed species in particular, are very high, in a wide pH range. Thermodynamic parameters indicate that the enthalpy values are exothermic and the enthalpic contribution to the stability is higher than entropic one. Individual UV spectra of cys and dimethyltin(IV)-cys species were calculated. Spectroscopic results of UV and (1)H NMR investigations fully confirm the speciation model. The structures calculated from NMR investigations show that all the species have an eq-(CH(3))(2)-tbp structure.