Resolving ambiguities in two-dimensional NMR spectra: the 'TILT' experiment.

Ambiguities in two-dimensional nuclear magnetic resonance spectra due to overlap are usually resolved by recording a three-dimensional version of the experiment. It is shown that a simpler solution is to record a tilted projection of the three-dimensional spectrum, derived by Fourier transformation of the time-domain signal acquired while the two evolution parameters are varied simultaneously at the appropriate rates. By avoiding the need to record the full three-dimensional spectrum, this saves an order of magnitude in measurement time. The tilt technique is illustrated by reference to degenerate responses in the TOCSY and NOESY spectra of a small protein, agitoxin, where the 1H and 15N frequencies are incremented in tandem.