Measurement of weak heteronuclear (13C–1H) Overhauser effects involving carbons not directly bonded to protons

Although proton detected heteronuclear Overhauser effect spectroscopy is known to be an efficient tool for probing molecular structure and dynamics, it is shown that, in practice, the method fails for observing weak 13C–1H heteronuclear Overhauser effect when the considered carbon-13 (in natural abundance) is not directly bonded to proton(s). Such a weak heteronuclear Overhauser effect has been successfully measured using a modified pulse sequence made of a selective TOCSY block followed by a classical (carbon-13 observation) one-dimensional HOESY sequence. The potentialities of this tool have been illustrated by the confirmation of the preferential conformation of uridine in water.