Hydration structure of uracil as studied by 1D and 2D heteronuclear Overhauser spectroscopy: evidence for the formation of a trihydrate in the first solvation shell

The intermolecular heteronuclear Overhauser effect (HOE) between water and uracil has been measured. Steady-state 13C, 1H nuclear Overhauser effect (NOE) results show that the first solvation shell includes three water molecules. Transient 13C, 1H and 15N, 1H 2D HOESY experiments as well as 1H NOESY experiments give further evidence for the formation of a cyclic trihydrate as obtained by three bridge hydrogen-bonding between the three water molecules and the two amide groups of the uracil. The trihydrate has only a very short life-time as compared to the rotational correlation time of the free uracil molecule which remains the tumbling species in the water–DMSO solution.