Rosario Cali

Water soluble calix[4]arenes. A thermodynamic investigation of proton complex formation

Abstract Thermodynamic parameters of protonation of calix[4]arene-p-tetra sulphonate were potentiometrically and calorimetrically determined in aqueous solution at 25 °C and I = 0.1 mol dm−3 (NaNO3). These values were compared with literature findings. ΔH° and ΔS° values reveal that the penta-anion protonation is energetically costly. In this connection the role played by hydrogen bonding and the cone conformation stabilization are critically discussed. Proton formation constants of the calix[4]arene-p-tetrasulphonate-tetra-carboxylate derivative in the cone conformation were also potentiometrically determined under the same experimental conditions.

Thermodynamic study on the formation of the cupric ion hydrolytic species

Abstract The formation constants of Cu(OH), Cu2(OH)2 and Cu3(OH)4 were determined by potentiometric measurements. The enthalpy changes were obtained by direct calorimetry. The species were individualized by statistic tests. The calculated entropy changes were correlated with the assumed structure of the species present in the solution.

Coordination properties of dialkyltin (IV) in aqueous solution. Thermodynamic study of dimethyltin (IV) complexes with l-amino acids

Abstract The complex formation of dimethyltin (IV) ([SnMe2]2+) with alanine, phenylalanine, triptophane and valine has been investigated by means of potentiometry at 25 °C and I = 0.1 mol dm−3 (KNO3). The selection of the models and the calculation of stability constants have been performed collecting a large amount of data points and using three different computer programs. This procedure has made it possible to detect the species forming in low percentages. A comparison with monodentate and bidentate systems previously studied gives an indication as to the number and the nature of the donor atoms involved in the coordination.

The formation of proton and alkali-metal complexes with ligands of biological interest in aqueous solution. Part I. Potentiometric and calorimetric investigation of H+ and Na+ complexes with citrate, tartrate and malate☆

Abstract The thermodynamic parameters for the interaction of H + and Na + with citrate, tartrate and malate are determined potentiometrically and calorimetrically in aqueous solution. The investigation is carried out at various ionic strengths and temperatures. The data obtained by direct calorimetry are reported for the first time. The species NaA and NaHA are found to exist for tartrate and malate only, whereas the species NaH 2 A is found to be present for citrate also. Simultaneous analysis of the potentiometric and calorimetric data enables the temperature and ionic strength dependence of the equilibrium parameters to be obtained for the complexes.

Thermodynamics of metal complexes with ligand—ligand interaction. Mixed complexes of copper(II) and zinc(II) with adenosine 5′-triphosphate and l-phenylalanine or l-tyrosine

Abstract Thermodynamic parameters for the formation of copper(II) and zinc(II) mixed complexes with ATP and l -phenylalanine or l -tyrosine were determined by means of potentiometric and calorimetric measurements at t = 25°C and I = 0.1 mol dm −3 (KNO 3 ) in aqueous solution. Δ G 0 , Δ H 0 and Δ S 0 values for the binary systems of the two amino acids were also determined under the same experimental conditions. On the basis of the obtained results, the occurrence of solvophobic and of other non-covalent interactions between the non-coordinating side-chain moleties of the bonded ligands has been ascertained in the investigated zinc(II) mixed complexes. For copper(II) mixed complexes, Δ G 0 , Δ H 0 and Δ S 0 values do not allow a straightforward assessment of the occurrence of stacking interaction. The origin of this difference in behaviour of the two metal ions is also discussed.

Thermodynamics of metal complexes with ligand–ligand interaction, simple and mixed complexes of copper(II) and zinc(II) with adenosine 5′-triphosphate and L-tryptophan or L-alanine

Thermodynamic parameters for the formation of simple copper(II) and zinc(II) complexes with adenosine 5′-triphosphate (ATP), L-tryptophanate (trpO), and L-alaninate (alaO) were determined by means of potentiometric and calorimetric measurements. Detailed analysis of the potentiometric data allowed reliable values of stability constants to be obtained. For the first time, the thermodynamic functions for the [M2(ATP)] species are also reported. On the basis of ΔH⊖ and ΔS⊖ changes, the structure, in aqueous solution, of the main species present in the M–ATP systems are discussed. The ΔG⊖, ΔH⊖, and ΔS⊖ values for the [M(ATP)L]3– mixed-ligand complex (L = amino-acid anion) were also determined. The larger positive AHe and the less positive ΔS⊖ accompanying formation of [M(ATP)(trpO)]3– compared with [M(ATP)(alaO)]3– are considered to indicate the presence of ligand–ligand interaction in the former complex. Further support for this is gained by comparing the differences between the ΔH⊖ and ΔS⊖values for formation of [Cu(ATP)(trpO)]3– and [Zn(ATP)(trpO)]3– and those for [Cu(ATP)(alaO)]3– and [Zn(ATP)(alaO)]3–. The presence of the stacking interaction is also discussed in relation to the geometric requirements of the metal ions.

Thermodynamics of copper(II) dicarboxylate coordination in aqueous solution

SummaryThe association of H+ and Cu2+ with malonate, maleate, succinate and phthalate ions has been investigated both potentiometrically and calorimetrically at 25° and I = 0.1 mol dm−3 (NaClO4).The structures of the complexes existing in aqueous solution are proposed on the basis of thermodynamic data.

Influence of non-covalent interactions on the thermodynamic stereoselectivity of the protonation of some dipeptides

Abstract Δ G 0 , Δ H 0 and Δ S 0 protonation values of some pairs of diastereoisomeric dipeptides have been determined by potentiometry and calorimetry in aqueous solution at 25°C and I = 0.1 mol dm −3 (KNO 3 ). On the basis of the results obtained it has been possible to assess the role played by two different non-covalent interactions, namely the electrostatic interaction and the solvophobic interaction, on the thermodynamic stereoselectivity in the proton complex formation, shown by the systems investigated.

Thermodynamics of copper(II) 2,2′-dipyridyl complexes in aqueous solution

Abstract The thermodynamic parameters for the chelation of cupric ion with 2,2′-dipyridyl have been redetermined at 25°C and I =0.1 M. Δ G values were obtained by potentiometry with a selective ion electrode and Δ H values by direct calorimetry. Similar studies have been made on the relative hydroxocomplexes. The data obtained are compared with those in the literature and the chelate effect of the heterocyclic diimine is described.

Thermodynamic study of dimethyltin(IV) complexes with nucleoside 5′-triphosphates

The complex formation of [SnMe2]2+ ion with guanosine 5′-triphosphate (GTP), inosine 5′-triphosphate (ITP), cytidine 5′-triphosphate (CTP) and tripolyphosphate(5–)(tpp) has been investigated by means of potentiometric and calorimetric measurements at 25 °C and I= 0.1 mol dm–3(KNO3). On the basis of the thermodynamic parameters, bonding details have been inferred for the main nucleotide complex species, using tpp as reference. The thermodynamic data show that the nitrogen atom [N(1)] of the bases interacts with dimethyltin in the [SnMe2L] species of GTP and ITP only.