Comprehensive ab initio quantum mechanical and molecular orbital (MO) analysis of cisplatin: Structure, bonding, charge density, and vibrational frequencies

We carried out an extensive series of ab initio quantum mechanical (QM) cal culations using pure effective core potential (ECP) and hybrid Hartree-Fock (HF)/ECP basis sets, including various electron correlation treatments up to the MP4 level on cis-diamminedichloroplatinum(II), cisplatin, an importa nt anticancer drug. The optimized geometric parameters and vibrational freq uencies of cisplatin were compared with the experimental values, and the ef fects of varying basis sets and correlation (MP level) treatments on the ge ometric parameters and vibrational frequencies were analyzed. We also prese nt a detailed description of the bonding in cisplatin using qualitative MO analysis to characterize the key intramolecular interactions in cisplatin. The calculated molecular electrostatic potential (MEP), and the electrostat ic potential (ESP) charges for cisplatin were used to identify regions of e lectrophilic and nucleophilic character. The charge density and the Laplaci an of charge density of cisplatin were calculated to determine its bonding relationships. Using basis set performance, we identified two hybrid basis sets (HF/6-311G* and MP2/6-311G*) as basis sets of choice for studying cisp latin's molecular properties. Furthermore, we recommend a hybrid ECP/HF app roach with electron correlation for the most accurate physicochemical and e lectronic description of cisplatin and related compounds. (C) 1999 John Wil ey & Sons, Inc.