A theoretical study on the effect of “bound” water on the proton chemical shifts of the nucleic acid bases

摘要

Computations are performed on the proton chemical shifts due to hydrogen bonding between the purine and pyrimidine bases of the nucleic acids and water molecules of their first hydration shell. The water molecules should produce measurable shifts essentially for protons of the bases located close to the site of interaction. For the imino protons of the bases G–N₁H and U–N₃H participating in hydrogen bonding, the calculated Δδ is larger for the interaction of a base with a complementary base than for its interaction with water. Base pairing will thus produce a downfield shift in water but the measured Δδ due to pairing in this solvent will be smaller than in an inert solvent. Also, the chemical shift difference between G–N₁H and U–N₃H in water will be larger if the molecules are engaged in pairs than if they are not.