Transition States of Cisplatin Binding to Guanine and Adenine: ab initio Reactivity Study

Fully optimised HF and DFT transition states of cisplatin binding to adenine and guanine are presented for the first time. They have similar structure as the recently published transition states for cisplatin hydrolysis with the angle of about 70° between entering and leaving ligands and corresponding bonds prolonged up to 0.5 A. Calculated activation energies are in the range of 10.5-18 kcal/mol. The lowest activation energies were found for the binding of cis -Pt[(NH 3 ) 2 (H 2 O)(OH)] + to guanine. The role of hydrogen bonds in recognition of binding sites, stabilisation of reactants and final yields of individual cisplatin-DNA adducts is discussed.