AbstractThe antitumor drugcis‐diamminedichloroplatinum(II) (cisplatin) binds preferentially to GpG and ApG sequences of DNA, forming N7,N7 intrastrand chelates. Molecular modeling of the intrastrand adducts have been handicapped, so far, by the lack of force‐field data describing the Pt–guanine and Pt–adenine binding. We usedab initiocalculations with relativistic pseudopotentials to evaluate three important parameters for the platinum–adenine model complex [Pt(NH3)3(Ade)]2+: (1) the force constant for the PtN7 bond bending out of the adenine plane; (2) the energy profile for the torsion about PtN7; (3) a set of fractional atomic charges that reproduce theab initiopotential for a number of space points placed around the adduct. A population analysis and comparative study on the tetrammine complex [Pt(NH3)4]2+have shown that for platinum adenine is a better σ‐donor than NH3, but its capacity as a π‐acceptor is weak. © 1993