The ge-2D HSQC-NOESY experiment is the gradient-enhanced version of the conventional 2D HSQC-NOESY experiment in which coherence selection is achieved by means of PFG. Thus, clean 2D HSQC-NOESY spectra can be recorded with two scans per t1 increment without need for phase cycle when sample concentration is high. 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 HSQC-NOESY data can be acquired using the same principles discussed for the phase-sensitive ge-2D HSQC pulse sequence using a modified sequence incorporating a z-filter ( 97MRC199 ) or using the echo-antiecho approach. The basic ge-2D HSQC-NOESY pulse sequence can be derived by inserting a NOESY block (90º(1H)-mixing time-90º(1H))) 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.

A modified 1H-15N HSQC-NOESY experiment has been proposed to detect NOEs involving exchange-broadened amino protons from which standard NOESY cross-peaks were not observed. The transfer is effectively achieved by application of s train of closely spaced 180 echo pulses like CPMG pulse train ( 95JACS11043 ). Gradients are included to select zz magnetization and Watergate scheme is used to suppress solvent resonance.

The X-coupled ge-2D HSQC-NOESY experiment ( 97MRC199 ) has been applied to detect NOEs between chemically equivalent or accidentally overlapped protons (for instance, study of symmetrical molecules).

The ge-2D HSQC-NOESY experiment is usually 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 HSQC-NOESY experiments on AVANCE spectrometers can be found in

Tutorials: 2D inverse experiments

Tutorials: 2D gradient-based inverse experiments

The HSQC-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) (HSQC block) and via 1H-1H NOE enhancement (NOESY block).

Related experiments:

2D Inverse experiments

2D Inverse gradient-enhanced experiments