Palladium(II) Complexes Containing Mixed Nitrogen-Sulphur Donor Ligands: Interaction of [Pd(Methionine Methyl Ester)(H2O)2](2+) with Biorelevant Ligands.

Mohamed M Shoukry,Sameya M T Ezzat

doi:10.1155/2014/382646

Abstract

Pd(MME)Cl2 complex (MME = methionine methyl ester) was synthesised and characterized by physicochemical measurements. The reaction of [Pd(MME)(H2O)2]2+ with amino acids, peptides, or dicarboxylic acids was investigated at 25°C and 0.1 M ionic strength. Amino acids and dicarboxylic acids form 1 : 1 complexes. Peptides form both 1 : 1 complexes and the corresponding deprotonated amide species. The stability of the complexes formed was determined and the binding centres of the ligands were assigned. Effect of solvent on the stability constant of Pd(MME)-CBDCA complex, taken as a representative example, shows that the complex is more favoured in a medium of low dielectric constant. The concentration distribution diagrams of the complexes were evaluated.

Highlights

ExperimentalThe pKw in dioxane-water solution was determined as described previously [16, 17]
Effect of solvent on the stability constant of Pd(MME)-CBDCA complex, taken as a representative example, shows that the complex is more favoured in a medium of low dielectric constant
From comparing the IR spectrum of MME and Pd(MME)Cl2 complex, the stretching vibration of NH group of methionine methyl ester located at 2954 cm−1 is broadened in the complex spectrum due to coordination by the amino group

Summary

Experimental

The pKw in dioxane-water solution was determined as described previously [16, 17]. For this purpose, various amounts of standard NaOH solution were added to a solution containing 0.1 M NaNO3. The acid dissociation constants of the ligands were determined by titrating mmole samples of each with standard NaOH solutions. Ligands were converted into their protonated form with standard HNO3 solutions. Were determined by titrating 1 mmole of complex with standard 0.05 M NaOH solution. The formation constants of the complexes were determined by titrating solution mixtures of [Pd(MME)(H2 O)2 ]2+ (1 mmole) and the ligand in the concentration ratio of 1 : 1 for amino acids, peptides, and dicarboxylic acids. The concentration distribution diagrams were obtained with the program SPECIES [22] under the experimental condition used

Results and Discussion

Complex Formation Equilibria Involving Dicarboxylic

Conclusion