The effect of water molecules upon the hydrogen-bonding cooperativity of three-stranded antiparallel β-sheet models

Abstract

The effect of water molecules upon the hydrogen-bonding cooperativity of three-stranded antiparallel β-sheet models has been studied by quantum chemical calculations at the MP2/6-311++G(3df,2p)//MP2/6-31G** level. Our calculation results indicate that the hydrogen-bonding lengths and the atom charge distribution are affected by the H₂O molecules, especially for those in the same amide unit directly bonded. The hydrogen-bonding cooperativity significantly increases the binding energy of the LR or SR hydrogen-bonding ring in the three-stranded β-sheet structures and the influence is also gradually increased as more H₂O molecules are added. We found that the perturbation energies are also affected as the H₂O molecules are added and this supports that the cooperative enhancement is closely related to the orbital interaction. We have also found that the charge transfer among the three diglypeptides is obviously influenced by the H₂O molecules.