Ab initio evaluation of the substitution effect of the hydrogen bond energy of the Watson-Crick type base pair between 1-methyluracil and substituted9-methyladenine derivatives

The substitution effect on hydrogen bond energy of the Watson-Crick type ba se pair between uracil and chemically modified adenine derivatives was eval uated by ab initio molecular orbital theory. Predicted hydrogen bond energi es were compared with experimental binding constants in some cases, and the calculated hydrogen bond energies correlated well with the experimental bi nding constants. Thus, ab initio calculation is an effective method to esti mate the stability of the base pair between chemically modified nucleic aci d bases. In contrast to the substitution effect in uracil on hydrogen bond energy, no remarkable trend was observed in the relation between the substi tuent in adenine derivatives and the hydrogen bond energies. The adenine de rivatives, which have a nitro group on the 8-position or an amino group on the 2-position, can form the most stable hydrogen bonds with uracil.