A Systematic ab Initio Study of the Hydration of Selected Palladium Square-Planar Complexes. A Comparison with Platinum Analogues

Abstract

The hydration surface of four palladium square-planar complexes (neutral cis-dichlorodiamminepalladium PdCl 2 (NH 3 ) 2, neutral trans-dichlorodiamminepalladium PdCl 2 (NH 3 ) 2 , tetraamminepalladium cation [Pd-(NH 3 ) 4 ] 2+ , and tetrachloropalladium anion [PdCl 4 ] 2-) has been examined by advanced quantum-chemical calculations. Preliminary geometry optimizations were carried out using the second-order Møller-Plesset level of theory with frozen core approximation, utilizing the 6-31G* basis set for H, N, O, and Cl atoms. Pd was described with the Stuttgart relativistic pseudopotential with a basis set of corresponding quality for the explicitly treated electrons. Final reoptimization of all the species considered in the hydration scheme was done at the MP2 (full) level. Then, the reaction surfaces of the structures localized by optimizations were constructed utilizing the MP4 single-point evaluations with additional inclusion of diffuse functions. The computed results were compared with corresponding data of analogous platinum complexes. The Pd and Pt energy surfaces resemble each other to a surprisingly large extent. Practically all qualitative trends, such as cis/trans energy ordering, are identical, and the solvation energies of Pd and Pt species differ only by a few (at most 10) kcal/mol. Concerning the markedly different biochemical and pharmacological roles of Pt-and Pd-based compounds, our basic conclusion is that the difference between cisplatin and analogous palladium complexes cannot be rationalized considering the energetics (thermodynamic properties) of hydration because these properties do not differ significantly.

Cisplatin interaction with cysteine and methionine, a theoretical DFT study

“…This work can be considered as an extension of our previous studies on platinum activation [17,18,69,70] and platinum interaction with DNA bases and base pairs [71][72][73][74][75].…”

Cisplatin interaction with amino acids cysteine and methionine from gas phase to solutions with constant pH

“…In our group this problem was also studied and the results were compared to hydrolysis of trans Pt(II) complexes and palladium analogs Zeizinger et al, 2001). Comparison of the rate of hydrolysis of cis-and trans-complexes was done also by Tsipis et al (2002).…”

Geometrical Characteristics and Reactivities of Tetracoordinated Pd Complexes: Mono- and Bidentate Ligands and Charged and Uncharged Ligands

“…Our calculated charges are similar to the previously reported theoretical results. 19 The absolute values of the atomic charges calculated at the B3P86/lanl2dz levels are smaller than the corresponding values at any other level. In the Pd complexes, the charge values of the Pd(II) and P atoms are positive, whereas those of the other atoms are negative.…”