QUANTUM CHEMICAL STUDY OF CISPLATIN-WATER COMPLEXES: AN INVESTIGATION OF ELECTRON CORRELATION EFFECTS

Abstract

The interaction of cisplatin ([ Pt(NH3)2Cl2] ) with water was studied for distinct complexation modes aiming to investigate the level of calculation required to describe transition metal complexes of biological relevance, where large scale ab initio post-Hartree-Fock calculations are usually precluded. Coupled Cluster (CCSD(T)) single point calculations employing MP2 and MP4(SDQ) optimized geometries and good quality basis sets, using effective core potential for platinum atom, are reported as well as Density Functional Theory (DFT) results employing various exchange-correlation functional. The importance of electron correlation effects for the calculation of interaction energies is discussed. The extension of correlation energy recovered by DFT was assessed considering the CCSD(T) results as reference. The recently developed M06-2x functional showed the best overall agreement with CCSD(T) calculations. The relative importance of the electrostatic and dispersion contributions to the interaction energy was estimated with the aid of the atoms in molecules theory and also using an empirical approach based on the multipole expansion method. It was found a strong dependence of the energy contributions on the spatial orientation of water and cisplatin monomers, with the electrostatic contribution dominating the interaction energy for the lowest energy equilibrium structures.