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The stoichiometry and stability constants of the complexes formed between [Pd(MAMP)(HO)] and various biologically relevant ligands containing different functional groups were investigated. The ligands used are amino acids, peptides and DNA constituents. The results show the formation of 1:1 complexes with amino acids and peptides and the corresponding deprotonated amide species. Structural effects of peptides on amide deprotonation were investigated. The purine and pyrimidine bases uracil, uridine, cytosine, inosine, inosine 5′-monophosphate (5′-IMP) and thymine form 1:1 and 1:2 complexes. The concentration distribution of the various complex species was calculated as a function of pH. The effect of chloride ion concentration on the formation constant of CBDCA with Pd(MAMP) was also reported. The results show ring opening of CBDCA and monodentate complexation of the DNA constituent with the formation of [Pd(MAMP)(CBDCA-O)DNA], where (CBDCA-O) represents cyclobutane dicarboxylate coordinated by one carboxylate oxygen. The equilibrium constant of the displacement reaction of coordinated inosine, as a typical DNA constituent, by SMC and/or methionine was calculated. The results are expected to contribute to the chemistry of antitumor agents. The calculated parameters of the optimized complexes support the measured formation constants. [ABSTRACT FROM AUTHOR]

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]

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 protonation constants of some α-amino acids (glycine (Gly), l-alanine (Ala), l-valine (Val), l-serine (Ser), l-leucine (Leu) and l-isoleucine (Ile)) were studied in water and DMSO-water solution mixtures containing 30, 50 and 70 vol-% DMSO; in addition the complex formation equilibria of their copper(II) complexes were studied by potentiometric technique using a combined pH electrode system calibrated in concentration units of the hydrogen ion at 25 ± 0.1 °C under a nitrogen atmosphere, and at an ionic strength of 0.10 mol·dm NaNO. The protonation constants and the overall stability constants of copper(II) complexes were influenced by changes in solvent composition, and their variations are discussed in terms of solvent and structural properties. [ABSTRACT FROM AUTHOR]

Binary and mixed-ligand complexes of zinc(II) involving 2-(aminomethyl)-benzimidazole (AMBI) and amino acids, peptides (HL) or DNA constituents have been investigated. Ternary complexes of amino acids or peptides are formed simultaneously. Amino acids form the complex Zn(AMBI)L, whereas amides form two complex species Zn(AMBI)L and Zn(AMBI)(LH). The ternary complexes of zinc(II) with AMBI and DNA are formed in a stepwise process, whereby binding of zinc(II) to AMBI is followed by ligation of the DNA constituents. The stability of ternary complexes is quantitatively compared with their corresponding binary complexes in terms of the parameters Δlog K, log β and log X. The effect of the side chains of amino acid ligands (Δ) on complex formation is discussed. The values of Δlog K indicated 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 evidence for a stacking interaction between the aromatic moiety of AMBI and the aromatic side chains of the bio-active ligands. The concentration distributions of various species formed in solution were also evaluated as a function of the pH. [ABSTRACT FROM AUTHOR]

A comprehensive review of organotin(IV) hydrolysis and complex formation equilibria with amino acids, peptides and DNA constituents is presented with special reference to solution and coordination chemistry studies. The review focuses on results obtained in the author's laboratory and related work of other groups. Also, published studies on these complexes were reviewed with emphasis on their biological aspects. [ABSTRACT FROM AUTHOR]

Binary and ternary complexes of zinc(II) involving nitrilo-tris(methyl phosphonic acid (H6A) and amino acids, peptides (HL), or DNA constituents have been investigated. The stoichiometry and stability constants for the complexes formed are reported. The results show that ternary complexes are formed in a stepwise manner whereby nitrilo-tris(methylphosphonic acid) binds to zinc(II), which is then followed by coordination of an amino acid, peptide or DNA. Zinc(II) was found to form ZnA and ZnAH n complex species where n=3, 2 or 1. The stabilities of the ternary complexes are compared with the stabilities of their corresponding binary complexes. The concentration distributions of the various complex species have been evaluated. The kinetics of the base hydrolysis of glycine methyl ester in the presence of Zn(II)-NTP complexes was studied in aqueous solution using a pH-stat technique. The p Ka for ionization of the coordinated water molecule is 9.14 as determined from the kinetic results, while direct potentiometric titration of the complex [Zn(NTP)(H2O)] gave 9.98 (±0.02). The rate constant for the intramolecular attack of coordinated hydroxide on the ester is k=(2.65×10−4±0.003) dm3⋅mol−1⋅s−1. [ABSTRACT FROM AUTHOR]