Redox Potentials for Tetraplatin, Satraplatin, Its Derivatives, and Ascorbic Acid: A Computational Study

Redox potentials of the Pt(IV) complexes, such as satraplatin, tetraplatin, and several others, are determined at the density functional theory (DFT) level (with B3LYP, omega-B97XD, PBE1PBE, TPSSTPSS, M06-L, M11-L, and MN12-L functionals) and compared with post-Hartree-Fock methods MP2 and CCSD(T). Calculations are performed in water solution employing an implicit solvation model. The impact of replacement of a chloro ligand by a water molecule (hydration in the equatorial plane of the complexes) is also explored. Furthermore, an influence of solvent pH on the magnitude of the redox potentials is discussed for such hydrated complexes. The obtained results are compared with available experimental data leading to a root-mean-square deviation (RMSD) of ca. 0.23 V, using the CCSD(T)/6-31+G(d)/IEF-PCM/scaled-UAKS level. Distribution of the electron density is analyzed at the B3LYP/6-311++G(2df,2pd) level. Also, a correlation between binding energies of axial ligands and the redox potential is demonstrated. Since the Pt(IV) complexes are considered in the framework of anticancer treatment, possible reducing agents in bioenvironment are searched. From this reason, the reduction potential of different protonation states of ascorbic acid is also presented.