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 C-13, H-1 nuclear Overhauser effect (NOE) results show that the first solvation shell includes three water molecules. Transient C-13, H-1 and N-15, H-1 2D HOESY experiments as well as H-1 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. (C) 1998 Elsevier Science B.V.