Structures, hydrolysis, stabilities of palladium(II) complexes containing biologically active ligands and species distribution in aqueous solution

Abstract

[PdACl(2)](n-1)H2O complexes {A: 1,10-phenanthroline (phen), 4-methyl-phenanthroline (4-mphen), 5-methyl-1,10-phenanthroline (5-mphen), 4,7-dimethyl-1,10-phenanthroline (dmphen), 3,4,7,8-tetramethyl-1,10-phenanthroline (tmphen)} were synthesized and characterized by CHN elemental analysis, ATR-FT-MIR and ATR-FT-FIR, H-1 NMR and C-13 NMR spectral measurements. n is the number of crystal water molecules in the complexes. The n value for the complexes [Pd(phen)Cl-2], [Pd(4-mphen)Cl-2] and [Pd(5-mphen)Cl-2] is 1; for the complex [Pd(tmphen)Cl-2]H2O is 2; for the complex [Pd(dmphen)Cl-2]2H(2)O is 3. [PdACl(2)](n-1)H2O complexes were converted into aqua complexes derived from 1,10-phenanthroline, [PdA(H2O)(2)](2+), and investigated [PdAB](+) mixed ligand complexes formed between [PdA(H2O)(2)](2+) complexes and amino acids {B: glycine (gly) and tyrosine (tyr)}. Protonation constants of the gly and tyr, the acid dissociation constants of the coordinated water molecules in [PdA(H2O)(2)](2+) complexes and the stepwise stability constant of the [PdAB](+) mixed ligand complexes were determined in aqueous 0.1 M KNO3 ionic media at 298.15 K by potentiometric methods. The protonation constants of ligands, the acid dissociation constants of aqua complexes and the stepwise stability constants of mixed ligand complexes were calculated from the potentiometric data using the "BEST" software package. The concentration distribution of the various species formed in aqueous solution was obtained using the "SPE" software package under the experimental conditions described. The order of stepwise stability of the mixed ligand complexes in terms of the gly and tyr was [Pd(tmphen)(gly/tyr)](+) > [Pd(dmphen)(gly/tyr)](+) > [Pd(4-mphen)(gly/tyr)](+) > [Pd(phen) (gly/tyr)](+) > [Pd(5-mphen)(gly/tyr)](+). This study could contribute to a better understanding of the behavior of the palladium(II) complexes in biological systems.