The selective ge-1D heteronuclear NOESY (HOESY or HETGOESY) experiment allows to detect heteronuclear 1H-13C NOE enhancements directly on proton spectrum in a similar way as described in this homonuclear analogue selective ge-1D NOESY experiment. PFG are used for coherence selection and, therefore, artifact free spectra are obtained without the presence of artefacts due to subtraction imperfections.

Easy implementation on AVANCE spectrometers equipped with pulsed field gradients, selective excitation using shaped pulses and inverse probehead.

The basic pulse sequence of the HETGOESY experiment ( 96MRC554 ) consists of the following parts:

• During the long relaxation period (5*T1(13C)), broadband proton decoupling is applied to improve sensitivity via heteronuclear NOE.
• A DPFGE scheme is used to achieve clean selective carbon excitation. Broadband proton decoupling is applied during the long selective pulse in order to collapse the large doublet due to 1J(CH).
• A 90º carbon pulse rotates the y-component of the dephased magnetization onto the z-axis. During the NOESY mixing time, cross-relaxation transfer magnetization of the selected carbon to protons. The final 90 proton pulse rotates any proton z-magnetization to the xy plane (see HOESY Block).
• Proton detection as usual.
• Gradients are usually applied for coherence selection purposes in natural abundance samples to obtain efficient suppression of 1H-12C magnetization.

A modified sequence is also proposed that eliminate anti-phase SPT-type signals.

The HETGOESY experiment can be run with minor changes from a predefined parameter set. Important parameters to consider are:

Selectivity of the selective inversion 13C pulse: the user must define the offset, the shape, the duration and the power level needed for a defined excitation profile.

Optimization of the relaxation period (5*T1(selected 13C)).

Optimization of the NOESY mixing time.

Set a large number of scans. This experiment suffers of its inherent insensitivity. In the original paper, 8 hours of acquisition were needed on a 50 mM gibberellic acid sample.

In the HETGOESY spectrum, only protons showing NOE enhancement to the selected carbon will be present, all other signals remain dephased. The use of gradients allows to obtain a clean, artefact-free spectrum in a short time in which perfect suppression of undesired 1H-12C magnetization is achieved with a single two-step phase cycle.