Probing the Effect of Bipyridine Derivatives on the Reduction of Platinum(IV) Complexes by 5ˊ-dGMP

In previous studies, the mechanism for the reduction of tetrachloridoplatinum(IV) complex with 5ˊ-dGMP has been investigated. In this research, two platinum(IV) complexes [PtCl4(N-N)] (N-N = 4,4ˊ-dimethyl-2,2ˊ-bipyridine, A and 5,5ˊ-dimethyl-2,2ˊ-bipyridine, B) were considered and theoretically compared with PtIVdach (dach = diaminocyclohexane), by means of the Becke3LYP DFT functional calculations. The mechanism of two electron reduction was thoroughly followed for three compounds. The relative Gibbs energies for all intermediate, transition states and products were calculated and compared. LUMO-HOMO energy gap was also determined, where this energy gap was 3.5 eV in complexes A and B; and 4.5 eV in PtIVdach. The overall calculated Gibbs energy for the formation of corresponding PtII complex is 30.0 kJ mol-1 in A, 28.5 kJ mol-1 in B and 43.2 kJ mol-1 in PtIVdach. Thus compounds A and B illustrated more favorability for the proposed two electron reduction, interestingly. The results demanded that the hydrogen bonds play a critical role in the stability of intermediates and transition states in PtIVdach. The effective parameters in the mechanism were also discussed.