Thermodynamic and spectroscopic study of the binding of dimethyltin(IV) by citrate at 25 °C

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.

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).

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.

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.