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The interaction of dibutyltin(IV) dichloride (DBT) with 1,4-diazacycloheptane (homopiperazine, HP) was investigated. In solutions, the complexes formed a 1:1 complex, its protonated and hydrolyzed forms. The formation constants of the complexes and thermodynamic parameters as ΔH° and ΔS° were estimated. The optimization of the structure of the (Bu)2Sn(HP)Cl2 complex reveals that the tin is six-coordinate in a distorted octahedral geometry, where the two nitrogen atoms of homopiperazine and the two chloride ions are in one plane. The solid (Bu)2Sn(HP)Cl2 complex with homopiperazine was synthesized, and the composition was assigned by elemental micro-analysis and mass spectrum. The complex was investigated by infrared, mass spectra, and thermal measurements. The ligand and its complex were tested against antimicrobial Staphylococcus aureus (+ve), Escherichia coli (−ve), and antifungal Candida albicans and Aspergillus flavus. Anticancer activities of homopiperazine and its dibutyltin(IV) complex were tested against breast cancer cell lines. The molecular docking investigations were performed to know the possible modes of binding to the most active sites of the breast cancer oxidoreductase receptor and those of Escherichia coli. [ABSTRACT FROM AUTHOR]

This review article presents an overview of the equilibrium studies on Pd-amine complexes with bio-relevant ligands in reference to their antitumor activity. Pd(II) complexes with amines of different functional groups, were synthesized and characterized in many studies. The complex formation equilibria of Pd(amine)2+ complexes with amino acids, peptides, dicarboxylic acids and DNA constituents, were extensively investigated. Such systems may be considered as one of the models for the possible reactions occurring with antitumor drugs in biological systems. The stability of the formed complexes depends on the structural parameters of the amines and the bio-relevant ligands. The evaluated speciation curves can help to provide a pictorial presentation of the reactions in solutions of different pH values. The stability data of complexes with sulfur donor ligands compared with those of DNA constituents, can reveal information regarding the deactivation caused by sulfur donors. The formation equilibria of binuclear complexes of Pd(II) with DNA constituents was investigated to support the biological significance of this class of complexes. Most of the Pd(amine)2+ complexes investigated were studied in a low dielectric constant medium, resembling that of a biological medium. Investigations of the thermodynamic parameters reveal that the formation of the Pd(amine)2+ complex species is exothermic. [ABSTRACT FROM AUTHOR]

The reaction of dimethyltin(IV) dichloride (DMT) with homopiperazine (HPIP) was studied. The equilibria of the complexes formed in solution were investigated. The complexes detected are of 1:1 stoichiometry in addition to the protonated and hydrolysed species. The complex formation constants were determined by the use of potentiometric technique and the non-linear computer program Miniquad-75. The dielectric constant effect of the reaction medium on the formation of the complexes was investigated. Formation constants of the complexes were determined at different temperatures and the thermodynamic parameters as ΔH° and ΔS° were estimated and discussed. The ternary complexes of dimethyltin(IV) with HPIP and DNA constituents are formed by a simultaneous mechanism. Their formation constants were determined. The speciation diagrams of the binary and mixed-ligand complexes were evaluated. [ABSTRACT FROM AUTHOR]

[Pd(BHEP)Cl2] and [Pd(BHEP)(CBDA)] complexes, where BHEP = 1,4-bis(2-hydroxyethyl)piperazine and CBDA = cyclobutanedicarboxylate, were synthesized and characterized. [Pd(BHEP) (CBDA)] crystallizes in space group P21, a = 9.5740(8) Å, b = 9.4700(7) Å, c = 9.7890(10) Å, α = 90.00°, β = 113.360(5)°, γ = 90.00°, V = 814.78(13) Å3, Z = 2. The palladium center has a typical square planar geometry with tetrahedral distortion. DFT calculations show good agreement between theoretical and X-ray data. The stability constants and stoichiometry of the complexes formed between various dicarboxylic acids and [Pd(BHEP)(H2O)2]2+ were studied. Dicarboxylic acids form 1:1 and protonated complexes. Inosine forms 1:1, 1:2 and the protonated form of 1:1 complexes. The temperature effect on the formation constant of the cyclobutanedicarboxylate complex was investigated. The hydrolysis of [Pd(BHEP)(H2O)2]2+ and complex formation with cyclobutanedicarboxylic acid are exothermic processes. [ABSTRACT FROM AUTHOR]

Proton-ligand association constants of 1-benzoyl(1,2,4-triazol-3-yl)thiourea (BTTU) and its complex formation constants with some bivalent metal ions Ni(II), Co(II), Mn(II), Zn(II), and Cu(II), have been determined potentiometrically in 50% EtOH–H2O and 0.1 M NaNO3. The complexes formed in solution have a stoichiometry of 1:1 and 1:2 [M:L], where M represents the metal ion and L the BTTU ligand. The corresponding thermodynamic parameters are derived and discussed. The complexes are stabilized by enthalpy changes and the results suggest that complexation is an enthalpy-driven process. The effects of metal ion, ionic radius, electronegativity, and nature of ligand on the formation constants are discussed. The formation constants of the complexes with 3d transition metals follow the order Mn2+ < Co2+ < Ni2+ < Cu2+ > Zn2+. The metal complexes were synthesized and characterized by elemental analyses, conductance, IR,1H NMR, and magnetic measurements. The low magnetic moment of 0.11 BM for the Cu(II) complex is suggestive of dimerization through Cu–Cu interaction. The concentration distribution diagrams of the complexes were evaluated. The ligands and their metal complexes have been screenedin vitroagainst some bacteria and fungi. [ABSTRACT FROM AUTHOR]

The [Pd(AEMP)Cl2] complex [AEMP = 2-(2-aminoethyl)-1-methylpyrrolidine] was prepared and characterized by single-crystal X-ray diffraction and spectroscopic analyses. The structure of the complex was found to be square-planar with some distortion. The geometric optimizations of the ligand and complex were performed with the DFT/B3LYP method by using Gaussian 09. The stoichiometry and stability constants of the complexes formed in the reaction of [Pd(AEMP)(H2O)2]2+ with dicarboxylic acids and DNA constituents were investigated at 0.1 m ionic strength and 25 °C. The results show that both DNA constituents and cyclobutanedicarboxylate (CBDCA) coordinate to [Pd(AEMP)(H2O)2]2+ to form the quaternary complex [Pd(AEMP)(CBDCA-O)DNA], where CBDCA-O represents cyclobutanedicarboxylate coordinated through one carboxylate oxygen atom to the PdII center. The speciation concentration distributions in solution were evaluated. The biological activity for DNA cleavage and cytotoxicity of the [Pd(AEMP)Cl2] complex was studied. [ABSTRACT FROM AUTHOR]

[Pd(BHEP)Cl2] (BHEp = 1,4-bis(2-hydroxyethyl)piperazine) was synthesized and characterized. The palladium center has a typical square-planar geometry with a tetrahedral distortion. The alcohol groups of the ligand do not participate in binding to Pd(II). The DFT/B3LYP method was used for geometric optimization of the ligand and the complex using the Gaussian 09 program and compared with experimental results. The stoichiometry and stability constants of the complexes formed between [Pd(BHEP)(H2O)2]2+and some selected amino acids, peptides, and DNA constituents were investigated at 25 °C and 0.1 M ionic strength. The binuclear complex [(H2O)(BHEP)Pd(Bip)Pd(BHEP)(H2O)]4+was detected, where Bip = 4,4′-bipiperidine. Inosine, uracil, and thymine interact with the binuclear complex via substitution of both coordinated water molecules. The potentiometric results were complimented by spectroscopic measurements. The concentration distribution diagrams of the various species formed were evaluated. [ABSTRACT FROM AUTHOR]

Highlights: [•] Transition metal complexes with cetirizine (CTZ) were synthesized and characterized. [•] Protonation equilibria were calculated for (CTZ) and thermodynamics were discussed. [•] Complex formation equilibria and speciation of binary M(II)–CTZ were investigated. [•] The biological activity of the free CTZ and its metal-chelates were investigated. [ABSTRACT FROM AUTHOR]

Abstract: In the present study, a new hydrazone ligand (2-((2-phthalazin-1-yl)hydrazono)methyl)phenol) prepared by condensation of hydralazine (1-Hydralazinophthalazine) with salicylaldehyde (SAH). The synthesized SAH-hydrazone and its metal complexes have been characterized by elemental analyses, IR, 1H NMR, solid reflectance, magnetic moment, molar conductance, mass spectra, UV–vis and thermal analysis (TGA). The analytical data of the complexes show the formation of 1:1 [M:L] ratio, where M represents Ni(II), Co(II) and Cu(II) ions, while L represents the deprotonated hydrazone ligand. IR spectra show that SAH is coordinated to the metal ions in a tridentate manner through phthalazine-N, azomethine-N and phenolic-oxygen groups. The ligand and their metal chelates have been screened for their antimicrobial activities using the disc diffusion method against the selected bacteria and fungi. Proton-ligand association constants of (SAH) and the stepwise stability constants of its metal complexes are determined potentiometrically in 0.1M NaNO3 at different temperatures and the corresponding thermodynamic parameters were derived and discussed. The order of −ΔG° and −ΔH° were found to obey Mn2+

Abstract: Pd(DHP)Cl2 and Pd(DHP)(CBDCA) complexes (DHP=1,3-diamino-2-hydroxopropane and CBDCA=1,1-cyclobutanedicarboxylate), were synthesized and characterized by elemental analysis, IR and NMR spectral measurements. The coordination of [Pd(DHP)(H2O)2]2+ with some selected bio-relevant ligands, containing different functional groups was investigated. The ligands used are amino acids, peptides, DNA constituents and dicarboxylic acids. Stoichiometry and stability constants of the complexes formed are reported at 25°C and 0.1M ionic strength. The results show the formation of 1:1 complexes with amino acids and dicarboxylic acids. DNA constituents form 1:1 and 1:2 complexes. Peptides form both 1:1 complexes and the corresponding deprotonated amide species. The effect of chloride ion concentration and dioxane on the acid dissociation constants of 1,1-cyclobutane dicarboxylic acid (CBDCAH2) and the formation constant of its complex with Pd(DHP)2+ was reported. The equilibrium constants for the displacement of coordinated ligands as uracil, glycine or methionine by cysteine are calculated. The results are expected to contribute to the chemistry of antitumour agents. [Copyright &y& Elsevier]

Abstract: Formation equilibria of copper(II) complexes of 2-(aminomethyl)-benzimidazole (AMBI) and the ternary complexes Cu(AMBI)L (L=amino acid, amide, dicarboxylic acid 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(AMBI)L, whereas amides form two complex species Cu(AMBI)L and Cu(AMBI)(LH−1). The ternary complexes of copper(II) with AMBI and dicarboxylic acids or DNA units are formed by a stepwise mechanism, whereby binding of copper(II) to AMBI is followed by ligation of the dicarboxylic acids or DNA components. The values of Δ log K indicate that the ternary complexes containing aromatic amino acids are significantly more stable than the complexes containing alkyl- and hydroxyalkyl-substituted amino acids. This may be taken as an evidence for a stacking interaction between the aromatic moiety of AMBI and the aromatic side chains of the bio-active ligands. The solid complexes Cu(AMBI)L where L=1,1-cyclobutanedicarboxylic acid (CBDCA) and malonic acid were separated and identified by elemental analysis and infrared spectroscopy and magnetic moment. The decomposition course and steps for the isolated complexes were analyzed and the kinetic parameters of the non-isothermal decomposition were calculated. The hydrolysis of glycine methyl ester (MeGly) is catalyzed by the Cu(AMBI)2+ complex. The kinetic data is fitted assuming that the hydrolysis reaction proceeds in two steps. The first step, involving coordination of the amino acid ester by the amino and carbonyl groups, is followed by rate-determining attack by OH− ion. The second step involves the equilibrium formation of the hydroxo-complex Cu(AMBI)(MeGly)(OH) followed by intramolecular OH− attack. [Copyright &y& Elsevier]

Abstract: Schiff base ligand, 1,4-bis[(2-hydroxybenzaldehyde)propyl]piperazine (BHPP), and its Cu(II), Ni(II) and Co(II) metal complexes were synthesized and characterized by elemental analysis, magnetic susceptibility, molar conductance and spectral (IR and UV–vis) studies. The ground state of BHPP ligand was investigated using the BUILDER module of MOE. Metal complexes are formed in the 1:1 (M:L) ratio as found from the elemental analysis and found to have the general formula [ML]·nH2O, where M=Co(II), Ni(II) and Cu(II), L=BHPP. In all the studied complexes, the (BHPP) ligand behaves as a hexadentate divalent anion with coordination involving the two azomethine nitrogen’s, the two nitrogen atoms of piperazine ring and the two deprotonated phenolic OH-groups. The magnetic and spectral data indicates octahedral geometry of metal(II) complexes. The ligand and their metal chelates have been screened for their antimicrobial activities using the disc diffusion method against the selected bacteria and fungi. They were found to be more active against Gram-positive than Gram-negative bacteria. Protonation constants of (BHPP) ligand and stability constants of its Cu2+, Co2+ and Ni2+ complexes were determined by potentiometric titration method in 50% DMSO–water solution at ionic strength of 0.1M sodium nitrate. It has been observed that the protonated Schiff base ligand (BHPP) have four protonation constants. The divalent metal ions Cu2+, Ni2+ and Co2+ form 1:1 complexes. [Copyright &y& Elsevier]