Theoretical Studies on the Binding of Cd~（2＋） to Uracil and Its Thio-derivatives

摘要

The interaction of Cd2+ with uracil,2-thiouracil,4-thiouracil and 2,4-dithiouracil have been investigated by the density functional theory(DFT) calculations.For uracil and 2,4-dithiouracil,where the two basic sites are the same,Cd2+ attachment to the heteroatom at position 4 is preferred.However,for the systems where both types of basic centers,a carbonyl and a thiocarbonyl groups,are present,Cd2+ association with sulfur is favorable.The enhanced stability of these enolic and thiol forms comes from Cd2+ interaction with two basic sites simultaneously,which thereby triggers a significant aromatization of the ring.More significantly,the Cd2+ binding energy with uracil and its thio-derivatives is larger than the tautomerization barriers connecting the diketo-like forms with the corresponding enolic-like tautomers.Consequently,when associated with Cd2+,all tautomers are energetically accessible and should be observed in the gas phase.