Effects of Substituents on the Binding Energy in Hydrogen-bonded Complexes Containing Adenine and Thymine

The optimal structures and binding energies of seventeen substitutional thymine and adenine hydrogen-bonded complexes were obtained theoretically and the effects of substituents on the binding energies were explored. The calculation results show that the interaction between trifluridine and adenine is stronger than that between thymine and adenine. This conclusion is in agreement with the fact that the association of trifluridine and adenine has precedence over the association of thymine and adenine. Compared with CF3 three stronger electron withdrawing groups(SO3H, CN and NO2) can increase the binding energy between thymine and adenine, suggesting that the thymine substituted by these three groups may also provide a potential anticancer application. Atoms in molecules theory and the natural bond orbital analysis indicate that N-H center dot center dot center dot N hydrogen bon-ding is the strongest, N-H-center dot center dot center dot O=C is stronger, while C-H center dot center dot center dot O=C is the weakest. Atoms in molecules theory and the natural bond orbital analysis also indicate that the orbital overlap interactions play a significant role in these hydrogen bonds.