Bonding mechanism of cisplatin with DNA has been studied by CNDO/2 calculation. The computed results of the six models considered indicated that form the point of view of overlap population QAB and two atoms energy EAB, the most favorable bonding from was that between cisplatin and two N7 atoms, each from one of the two guanines to form ((NH3)2PtG2)2+. Thus, intrastrand cross-linkage mechanism which had been proposed before by some authors was confirmed by our calculation. Chelation mechanism could not completely be excluded. Under certain conditions, it was possible for cisplatin to combine with a guanine through its N7 and O to form a chelate, but it was unstable as compared with((NH3)2PtG2)2+. Although the intrastrand cross-linkage mechanism is favored by our calculation, the way such a mode of combination hampers replication of DNA remains to be solved.

Key words: DEOXYRIBONUCLEIC ACID, ANTICARCINOGEN, CALCULATION, CHLORO COMPLEX, PLATINUM COMPLEX, CNDO APPROXIMATION, CHEMICAL BONDS, MOLECULAR ORBITAL THEORY, AMMINE COMPLEX