The influence of Cd2+ on nucleobases and base pairing has been studied systematically using high-level DFT method. Cd2+ strongly interacts with adenine (A), changing tautomer structures and affecting the tautomer equilibrium whereas the Cd2+-thymine (T) interaction barely shifts the equilibrium of T tautomers. The isoenergy of metal-bridged A-Cd2+-T base pair complexes in the same binding pattern reveals the absence of interaction between A and T. The effects of Cd2+ in H-bond base pairing have also been discussed to further understand the possible schemes in cadmium induced DNA mutations. (C) 2008 Elsevier B.V. All rights reserved.