The Effects Of Water Molecules On The Hydrogen Bonds Between Uracil And Thymine

Theoretical calculations on a series of hydrogen-bonded complexes containing uracil,thymine and water molecules were carried out using MP2method. The effects of water molecule on the hydrogen bond strength were explored. The calculation results show that water molecules on the site3of uracil and thymine strengthen the hydrogen bond whereas the water molecules on the site4of uracil and thymine weaken the hydrogen bond. Natural bond orbital (NBO) analysis indicates that water molecules on the site3of uracil and thymine strengthen the second-order interaction energy between the lone pair and the antibonding orbital. Water molecules on the site4of uracil and thymine are opposite in results. And the effect of the former are more than the latter. There exists a linear relationship between the hydrogen-bond distance and the charge transfer. There also exists a linear relationship between the hydrogen-bond distance and the second-order interaction energy. Atoms in molecules (AIM) theory analysis indicates that there exists a linear relationship between the hydrogen bond strength and the electron densities at hydrogen bond critical points.