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The interaction of diethylltin(IV) (DET) and divinyltin(IV) (DVT) with 1-(2-aminoethyl)-pyrrolidine (AEPY) was investigated using potentiometric technique at ionic strength of 0.1 mol dm −3 NaNO 3 . The hydrolysis constants of diethyltin(IV) and divinyltin(IV) cations and the stepwise formation constants of the complexes formed in solution were calculated at different temperatures and in solutions of dioxane-water solutions of different compositions. The stoichiometry and stability constants for the complexes formed were reported. The results showed the formation of 1:1 complex and the corresponding hydroxo complexes. The concentration distributions of the various complex species were evaluated as a function of pH. The thermodynamic parameters ΔH° and ΔS° calculated from the temperature dependence of the equilibrium constants were investigated for DET and DVT complexes with AEPY. The equilibrium constant for the displacement of 1-(2-aminoethyl)-pyrrolidine coordinated to diorganotin(IV) by thymine and thymidine as representative examples of DNA constituents was calculated from calculations based upon equilibrium properties. The results are expected to contribute to the chemistry of tin(IV) based anticancer agents. [ABSTRACT FROM AUTHOR]

Protonation constants of novel thiosemicarbazones including 2-(1-(2-phenyl-hydrazono)-propan-2-ylidene) hydrazine-carbothioamide (TPHP) and N -methyl-2-(1-(2-phenyl-hydrazono)-propan-2-ylidene)hydrazinecarbo-thioamide (MTPHP) ligands and their corresponding metal-ligand formation constants with Cu(II), Ni(II), Mn(II) and Co(II) ions were determined at 15 °C, 25 °C and 35 °C in 50% DMSO solution at I = 0.1 mol·dm − 3 NaNO 3 . The stability order of complexes with reference to the metal ions has been followed this order Cu(II) > Ni(II) > Co(II) > Mn(II) in concord with the Irving-Williams stability order. Also, chemical equilibrium studies indicated that substitution of hydrogen in thiosemicarbazone (TPHP) by methyl group causes lowering of acidity as a result of the electron-releasing effect of the methyl group in the substituted amino group of the thiosemicarbazide moiety. The speciation of different species in solution has been evaluated as a function of pH. Additionally, the effect of temperature on protonation of thiosemicarbazone ligands and formation of their M(II)-thiosemicarbazone complexes was investigated. The thermodynamic parameters (ΔH, ΔS and ΔG) were calculated and discussed. It was found that both log K 1 and –ΔH 1 , for M(II)-thiosemicarbazone complexes are somewhat larger than log 10 K 2 and –ΔH 2 , indicating a change in the dentate character of these ligands from tridentate (SNN-donors) in 1:1 chelates to bidentate (SN-donors) in 1:2; M:L chelates. Also, the lower values of log 10 K 2 and –ΔH 2 than log K 1 and –ΔH 1 may be attributed to steric hindrance produced by the entrance of a second molecule. [ABSTRACT FROM AUTHOR]

Binary and ternary complex formation equilibria of copper(II) with imidazole-4-acetic acid (IMA) and some aromatic amino acids such as tryptophan and phenylalanine have been studied from 15 to 45 °C by potentiometric titration. The pH-titrations of the reaction mixtures have shown 1:1:1 (Cu:IMA:amino acid) ternary complex formation. The stability of mixed-ligand complexes was quantitatively compared with the stability of the binary complexes as Δlog K, Δlog β and log X parameters. The speciation of different species in solution has been evaluated as a function of pH. The effect of temperature on protonation of the ligands and formation of mixed ligand complexes was investigated. Thermodynamic parameters were calculated and are discussed. The effect of solvent of the protonation of IMA and Cu-IMA complex formation was also investigated and discussed. Additionally, the stoichiometric protonation constants (log β) of imidazole-4-acetic acid and its binary Cu(II)-IMA complexes were determined potentiometrically over a wide range of solvent composition. [ABSTRACT FROM AUTHOR]

The interaction of DET (diethyltin(IV)) and DVT (divinyltin(IV)) with 1-(2-aminoethyl)piperazine (AEP) was investigated potentiometrically at different temperatures in 0.1 mol·dm NaNO. The hydrolysis constants of diethyltin(IV) and divinyltin(IV) cations and the stepwise formation constants of the complexes formed in solution were calculated at different temperatures and in solutions of dioxane-water solutions of different compositions. The stoichiometries and stability constants for the complexes formed are reported. The results show formation of 1:1 complexes and the corresponding hydroxide complexes. The concentration distributions of the various complex species were evaluated as a function of pH. The thermodynamic parameters Δ H° and Δ S° calculated from the temperature dependence of the equilibrium constants were investigated for DET and DVT complexes with AEP. [ABSTRACT FROM AUTHOR]

Proton-ligand association constants of imidazole-4-acetic acid (IMA) were determined potentiometrically in aqueous solution at different temperatures in the range 15-35 °C. The stepwise stability constants of IMA with some selected bivalent transition metal ions were also determined in 0.1 mol·dm NaNO. The stability of the complexes follows the trend Cu > Ni > Co > Mn, which is in agreement with the Irving-Williams order of the metal ions. The thermodynamic parameters for Cu(II)-IMA complex formation were derived and discussed. The ternary complexes Cu(IMA)L (IMA = imidazole-4-acetic acid, HL = amino acid, amides or DNA constituents) have been investigated. Ternary complexes of amino acids or amides are formed by a simultaneous mechanism. Amino acids form the complex Cu(IMA)L, whereas amides form two complex species Cu(IMA)L and Cu(IMA)(LH). The DNA constituents form both 1:1 and 1:2 complexes. The stabilities of ternary complexes are quantitatively compared with their corresponding binary complexes. The concentration distribution of the complexes in solution was evaluated as a function of pH. [ABSTRACT FROM AUTHOR]

The interaction of trimethyltin(IV) (TMT) with imino-bis(methylphosphonic acid) (IDP), abbreviated as HL, was investigated at 25 °C and at ionic strength 0.1 mol⋅dm (NaNO) using a potentiometric technique. The formation constants of the complexes formed in solution were calculated using the nonlinear least-squares program MINIQUAD-75. The stoichiometry and stability constants are reported for the complexes formed. The results show the formation of 110, 111, 112 and 11-1 complexes for the TMT-IDP system. The concentration distribution of the various complex species was evaluated. The effect of dioxane as a solvent, on both the protonation constants and the formation constants of trimethyltin(IV) complexes with IDP, is discussed. The thermodynamic parameters Δ H and Δ S calculated from the temperature dependence of the equilibrium constants were evaluated. The effect of ionic strength on the protonation constants of IDP is also discussed. [ABSTRACT FROM AUTHOR]

Thermodynamic parameters for protonation of 1,4-bis(3-aminopropyl)-piperazine (BAPP) and itsmetal complexation with some divalent metal ions were determined in aqueous solution at constant ionic strength (0.1M NaNO3) using a potentiometric technique. The order of -ΔG0 and -ΔH0 was found to obey Co2+ < Ni2+ < Cu2+ > Zn2+, in accordance with the Irving-Williams order. The formation equilibria of zinc (II) complexes and the ternary complexes Zn(BAPP)L, where L = amino acid, amides, or DNA constituents), have been investigated. Ternary complexes are formed by a simultaneous mechanism. The concentration distribution of the complexes in solution was evaluated as a function of pH. Stoichiometry and stability constants for the complexes formed are reported and discussed. The stability of ternary complexes was quantitatively compared with their corresponding binary complexes in terms of the parameter Δlog K. [ABSTRACT FROM AUTHOR]

Abstract: The formation equilibria of copper(II) complexes and the ternary complexes Cu(PDC)L (PDC=2,6-bis-(hydroxymethyl)-pyridine, HL=amino acid, amides or DNA constituents) have been investigated. Ternary complexes are formed by a simultaneous mechanism. The results showed the formation of Cu(PDC)L, Cu(PDC, H−1)(L) and Cu(PDC, H−2)(L) complexes. The concentration distribution of the complexes in solution is evaluated as a function of pH. The effect of dioxane as a solvent on the protonation constant of PDC and the formation constants of Cu(II) complexes are discussed. The thermodynamic parameters and calculated from the temperature dependence of the equilibrium constants are investigated. [Copyright &y& Elsevier]

The interaction of diethyltin(IV), DET, with selected bioligands having a variety of model functional groups was investigated at 25 °C and ionic strength 0.1 mol·dm −3 NaCl using the potentiometric technique. The hydrolysis constants of the DET cation and the formation constants of the complexes formed in solution were calculated using the MINIQUAD-75 program. The stoichiometry and stability constants for the complexes formed are reported. The results show the formation of 1:1 and 1:2 complexes with amino acids and DNA constituents. The dicarboxylic acids form 1:1 complexes. The peptides form both 110 complexes and the corresponding deprotonated amide species [Et 2Sn(LH −1)] (11-1). The participation of different ligand functional groups in binding to organotin is discussed. The concentration distributions of the various complex species were evaluated as a function of pH. The standard thermodynamic parameters Δ H° and Δ S°, calculated from the temperature dependence of the equilibrium constants, were investigated for the interaction of DET with thymine as a representative example of DNA constituents. The effect of ionic strength and solvent on hydrolysis constants of DET, protonation equilibria of thymine and its complex formation with DET were investigated and discussed. [ABSTRACT FROM AUTHOR]

As a model for forecasting the ligand properties of antibiotics in living organisms , formation equilibria of binary and ternary Cu(II) complex with Cephradine (Cep) antibiotic in presence of α-alanine (α-Ala) and β-alanine (β-Ala) amino acids have been studied using the potentiometric titrations. Many factors were investigated like the formation constant, protonation constant, composition and stabilities of the species formed with copper(II) ions in water and water-ethanol solutions of different compositions. The thermodynamics were calculated and the data clarified. The pH-titrations of the reaction mixtures have been revealed 1:1:1 (Cu:Cep:amino acid (AA)) ternary complex formation. By aid of Δ log 10 K , Δ log 10 β and log 10 X parameters, quantitative matching of the stability of mixed-ligand complexes and the stability of the binary complexes was done. Investigations of the stability of the ternary complexes relative to their corresponding binary complexes indicated that formation of ternary complexes is more preferable than binary metal complexes. The obtained data from protonation of the investigated cephradine antibiotic and β-Ala/α-Ala amino acids and their complex formation equilibria will be a significant contribution to workers carrying out mechanistic studies in biological media. • Studying the Formation equilibria of binary and ternary Cu(II) complex with Cephradine (Cep) antibiotic in presence of amino acids. • (logβ) were determined potentiometrically along a broad range of solvent composition. • The speciation of different species in solution was assessed. • The effect of temperature on protonation of ligands and formation of mixed-ligand complexes was studied. [ABSTRACT FROM AUTHOR]