Azza A. Shoukry

Complex formation reactions between [Pd(piperazine)(H2O)2]2+ and biorelevant ligands: synthesis and equilibrium constants

[Pd(pip)Cl2], [Pd(pip)(cbdca)] ⋅ 2H2O, and [Pd(pip)(malonate)] ⋅ 2H2O complexes were synthesized and characterized, where pip is piperazine and cbdca is cyclobutanedicarboxylate. The stoichiometry and stability of the complexes formed between [Pd(pip)(H2O)2]2+ and various biologically relevant ligands (amino acids, peptides, DNA constituents, and dicarboxylic acids) were investigated at 25°C and 0.1 M ionic strength. The stability constant of the complexes formed in solution was determined and the binding centers of the ligands were assigned. The concentration distribution diagrams of the complexes were evaluated.

Coordination properties of N,O-carboxymethyl chitosan (NOCC). Synthesis and equilibrium studies of some metal ion complexes. Ternary complexes involving Cu(II) with (NOCC) and some biorelevant ligand

In the present study, the acid-base equilibria of N,O-carboxymethy chitosan abbreviated as (NOCC), is investigated. The complex formation equilibria with the metal ions Cu(II), Ni(II), Co(II), Mn(II), and Zn(II) are investigated potentiometrically. The stability constant values of the binary and ternary complexes formed in solution were determined and the binding centers of the ligands were assigned. The relationships between the properties of the studied central metal ions as ionic radius, electronegativity, atomic number, and ionization potential, and the stability constants of the formed complexes were investigated in an effort to give information about the nature of chemical bonding in complexes and make possible the calculation of unknown stability constants. Cu(II), Ni(II), and U(VI) complexes with NOCC are isolated as solid complexes and characterized by conventional chemical and physical methods. The structures of the isolated solid complexes are proposed on the basis of the spectral and magnetic studies. The ternary copper(II) complexes involving NOCC and various biologically relevant ligands containing different functional groups, as amino acids and DNA constituents are investigated. The stability constants of the complexes are determined and the concentration distribution diagrams of the complexes are evaluated.

Kinetics of base hydrolysis of α-amino acid esters catalyzed by palladium(II) piperazine complex

AbstractThe kinetics of base hydrolysis of glycine, histidine, and methionine methyl esters in the presence of [Pd(pip)(H2O)2]2+ complex, where pip is piperazine, is studied in aqueous solutions, at T = 25°C, and I = 0.1 mol dm−3. The rate of ester hydrolysis for glycine methyl ester is studied at different temperature and dioxane/water solutions of different compositions. The kinetic data are fit under the assumption that the hydrolysis proceeds in one step. The activation parameters for the base hydrolysis of the complexes are evaluated

Kinetics and mechanism of the substitution behaviour of Pd(II) piperazine complexes with different biologically relevant nucleophiles

The interaction of the palladium(II) complex [Pd(Pip)(H2O)2]2+, where Pip is piperazine, with a series of biologically relevant nucleophiles including guanosine-5′-monophosphate, L-methionine and thiourea was studied under pseudo-first-order conditions as a function of nucleophile concentration and temperature, using UV-Vis spectrophotometric and stopped-flow techniques. The reactions were found to occur in two subsequent steps. For the sulfur donor containing nucleophiles thiourea and L-methionine, a third reaction step, the displacement of the labilized amine, as a result of the strong trans-effect of S-donor ligands, was observed. The activation parameters for all reactions studied suggest an associative substitution mechanism.

Synthesis, DNA binding and complex formation reactions of 3-amino-5,6-dimethyl-1,2,4-triazine with Pd(II) and some selected biorelevant ligands

With the purpose of studying the binding behavior of Pd(II) complexes with DNA as the main biological target, and their ability to penetrate reasonably into tumour cells and destroy their replication ability, Pd(ADT)Cl2 complex was synthesized and characterized, where ADT is 3-amino-5,6-dimethyl-1,2,4-triazine. Stoichiometry and stability constants of the complexes formed between various biologically relevant ligands (amino acids, amides, DNA constituents, and dicarboxylic acids) and [Pd(ADT)(H2O)2](2+) were investigated at 25°C and at constant 0.1moldm(-3) ionic strength. The concentration distribution diagrams of the various species formed are evaluated. Further investigation of the binding properties of the diaqua complex [Pd(ADT)(H2O)2](2+) with calf thymus DNA (CT-DNA) was investigated by UV-vis spectroscopy. The intrinsic binding constants (Kb) calculated from UV-vis absorption studies was calculated to be 2.00×10(3)moldm(-3). The calculated (Kb) value was found to be of lower magnitude than that of the classical intercalator EB (Ethidium bromide) (Kb=1.23(±0.07)×10(5)moldm(-3)) suggesting an electrostatic and/or groove binding mode for the interaction with CT-DNA. Thermal denaturation has been systematically studied by spectrophotometric method and the calculated ΔTm was nearly 5°C, supporting the electrostatic and/or groove binding mode for the interaction between the complex and CT-DNA.

Kinetics and mechanism for the substitution reactions of monoaquamonochloro-(piperazine) palladium (II) complex with L-methionine and thiourea in aqueous solution

AbstractThe interaction of the palladium(II) complex [Pd(Pip)Cl(H2O)] + , where Pip is piperazine, with the sulphur donor nucleophiles; L-methionine (L-Met), and thiourea (tu) was studied under pseudo-first-order conditions as a function of nucleophile concentration and temperature, using UV-Visible spectrophotometric and stopped-flow techniques. Two consecutive reaction steps were observed for the substitution process with L-methionine. For the substitution with thiourea, a third reaction step, the displacement of the labilized amine, as a result of the strong trans-effect of thiourea ligand was observed. 1HNMR spectroscopy was used to follow the substitution of the ligand by thiourea. The activation parameters for all reactions studied suggest an associative substitution mechanism. Graphical AbstractThe interaction of the monoaquamonochloro-(piperazine) Palladium (II) complex [Pd(Pip)Cl(H2O)] + , where Pip is piperazine, with the sulphur donor nucleophiles; L-methionine (L-Met), and thiourea (tu) was studied under pseudo-first-order conditions as a function of nucleophile concentration and temperature, using UV-Visible spectrophotometric and stopped-flow techniques. Two consecutive reaction steps were observed for the substitution process with L- methionine. For the substitution with thiourea, three reaction steps were observed.

Synthesis, characterization, mixed-ligand complex formation reactions, and equilibrium studies of Co(II) with 2,2′-dipyridylamine and some selected biorelevant ligands

Binary and ternary cobalt(II) complexes involving 2,2′-dipyridylamine and various biologically relevant ligands containing different functional groups are investigated. The ligands used are dicarboxylic acids, amino acids, and DNA unit constituents. The ternary complexes are formed by simultaneous reactions. The results showed the formation of 1:1 complexes with amino acids and dicarboxylic acids. The effect of chelate ring size of the dicarboxylic acid complexes on their stability constants was examined. The stability of ternary complexes formed with dicarboxylic acids was quantitatively compared with their corresponding binary complexes in terms of the ∆log10K parameters. The concentration distribution of the complexes in solution was evaluated. The solid complexes of Co(II) dipyridylamine cyclobutane-1,1-dicarboxylate, or malonate, oxalate, and succinate have been synthesized and characterized by elemental analysis, infrared spectra, magnetic, and conductance measurements. Spectroscopic studies and Meff values suggest a tetrahedral geometry for the cobalt(II) complexes. The effect of temperature on the formation constant of the complexes was studied, and the thermodynamic parameters were calculated. Formation of the metal complexes has been found to be spontaneous, exothermic, and entropically favorable.Graphical Abstract