Equilibrium Studies on Pd(II)–Amine Complexes with Bio-Relevant Ligands in Reference to Their Antitumor Activity

Abstract

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.

From Simple Palladium(II) Monomers to 2D Heterometallic Sodium–Palladium(II) Coordination Networks with 2-Halonicotinates

“…In line with the stated objectives, we have prepared 2D heterometallic sodium−palladium(II) coordination polymers with 2-halonicotinates (2-Clnic − and 2-Brnic (2), and palladium(II) monomers with the neutral 2-chloronicotinic and 2-bromonicotinic acid ligands, PdCl 2 (2- (4). The experimental findings were rationalized by DFT calculations.…”

“…1,2 These complexes are usually kinetically more labile than their platinum(II) analogues in aqueous solutions, 3 causing their hydrolysis to be faster and enabling the hydrolyzed complexes to be more efficient in reaching pharmacological targets. 4,5 Hence, palladium(II) complexes could be better models for studying their interactions with the biologically important ligands in vivo. These interactions with target molecules, e.g., tumor DNA, are crucial for the successful antitumor activity of palladium(II) complexes.…”

“…These interactions with target molecules, e.g., tumor DNA, are crucial for the successful antitumor activity of palladium(II) complexes. 4 It is believed that a cis−trans isomerization of palladium(II) complexes in solution, promoted by a fast palladium(II) hydrolysis, hinders the antitumor efficiency of the usually active cis isomers. 6 Therefore, the synthetic protocols that would prevent palladium(II) complexes isomerization by the introduction of a strongly coordinated N atom from the main ligand (e.g., nicotinate) and an appropriate leaving group (e.g., halide ion) are of an increasing interest.…”

“…Palladium­(II) coordination compounds often show pronounced biological properties, e.g. , antitumor activity resembling cisplatin. , These complexes are usually kinetically more labile than their platinum­(II) analogues in aqueous solutions, causing their hydrolysis to be faster and enabling the hydrolyzed complexes to be more efficient in reaching pharmacological targets. , Hence, palladium­(II) complexes could be better models for studying their interactions with the biologically important ligands in vivo . These interactions with target molecules, e.g.…”

“…These interactions with target molecules, e.g. , tumor DNA, are crucial for the successful antitumor activity of palladium­(II) complexes . It is believed that a cis – trans isomerization of palladium­(II) complexes in solution, promoted by a fast palladium­(II) hydrolysis, hinders the antitumor efficiency of the usually active cis isomers .…”