The ge-2D HMQC-NOESY experiment is the gradient-enhanced version of the conventional 2D HMQC-NOESY experiment in which coherence selection is achieved by means of PFG. Thus, clean 2D HMQC-NOESY spectra can be recorded with two scans per t1 increment without need for phase cycle. Other advantages are the optimal dynamic range, improved water and artefact suppression, and reduced t1 noise in the minimally required experiment time.

Easy implementation on any AVANCE spectrometer equipped with pulsed field gradients (PFGs) and inverse probehead.

Phase-sensitive ge-2D HMQC-NOESY data can be acquired using the echo-antiecho approach. The sequence can be derived from the basic phase-sensitive ge-2D HMQC pulse sequence using the echo-antiecho approach by inserting a NOESY block (90º(1H)-mixing period-90º(1H) cluster) just prior to the refocusing gradient. Thus, defocusing gradients are usually applied during the variable evolution period and the refocusing gradient is applied between the NOESY block and acquisition. In order to obtain phase-sensitive data, the intensity of this refocusing gradient is inverted on alternate scans.

The ge-2D HMQC-NOESY experiment can be recorded in routine/automation modes and minor changes are required if a predefined parameter set is available. Important parameters to consider:

• The user need to define the strength, duration, shape of the gradients and the recovery delay.
• Offset and spectral widths in each dimension.
• Optimization of the NOESY mixing time.

More details on practical implementation of ge-2D HMQC-NOESY experiments on AVANCE spectrometers can be found in

Tutorials: 2D inverse experiments

Tutorials: 2D gradient-based inverse experiments

The HMQC-NOESY spectrum correlates chemical shifts of heteronucleus X (F1 dimension) and protons (F2 dimension). The effective suppression of unwanted 1H-12C or 1H-14N magnetization by means of PFGs allows to obtain ultra-clean 2D spectra from which clear analysis can be done. Two different cross-peaks re present:

• Strong direct heteronuclear correlations.
• Heteronuclear NOE correlations arising of two added mechanisms: via 1J(CH) (HMQC block) and via 1H-1H NOE (NOESY block).

Related experiments:

2D Inverse experiments

2D Inverse gradient-enhanced experiments