The ge-2D NOESY experiment allows to obtain a 2D NOESY spectrum with two scans per t₁ increment provided that the S/N ratio is adequate. The main advantage of such approach is the large reduction in the total acquisition time compared with a conventional 2D NOESY experiment. The NOESY experiment permits to trace out through-space proton-proton connectivities via dipolar couplings or exchange processes.
 

Easy implementation on any AVANCE spectrometer equipped with pulsed field gradients.

2D NOESY experiments must be recorded in a  phase sensitive mode. For this reason, gradients are usually incorporated as a purging method (similar to homospoil pulses) to reduce the needed phase cycle. Recently it has been shown that the application of a low-intensity gradient during the entire mixing period in a regular NOESY experiment reduces the phase cycle to 2 scans per increment t1 ( 96JMRA119-123 ). Similar results are obtained if a PFG-180º-PFG cluster (the PFGs with opposite intensity for dephasing purposes) is incorporated at the middle of the mixing period. In such cases, phase-sensitive 2D NOESY maps can be quickly obtained for concentrated samples in reduced times without unwanted sensitivity losses due to coherence selection and difussion effects. Other possible alternatives use the echo-antiecho approach ( 97JMR145-125 ) or an strong spin-lock or a z-filter pulse prior to acquisition ( 94JMRA263-109 , 95JACS6064 , and 97JMR145-125 ). 2D NOESY experiments can include gradient-based  solvent suppression schemes as, for instance, the WATERGATE  ( 92JB661 , 95JB327 , 96JB169 , and 96JACS3531 ) or DPFGE ( 96JMRB82-112 and 97JMR93-129 ) schemes optionally combined with a water-flip-back pulse prior to acquisition and the WET scheme during the preparation period ( 95JMRA295-117 ). Modified WATERGATE and DPFGE schemes for multiple-solvent suppression ( 96JMRB124-110 and 98JB437 ) purposes can also be included.

The NOESY pulse sequence can also be used to study dynamic or chemical exchange processes (see ge-2D EXSY experiment).

This experiment is acquired an processed using the same experimental conditions as described for its phase cycle version. The only difference is the presence of the gradients. Thus, the user only need to define the strength, duration, shape of the gradients and the recovery delay. More details on practical implementation of ge-2D NOESY experiments on AVANCE spectrometers can be found in

Tutorials: 2D homonuclear experiments

Tutorials: 2D gradient-based homonuclear experiments

Tutorials: 2D gradient-based homonuclear experiments in H₂O

The ge-2D NOESY experiment is usually recorded in routine and automation modes with minor required modifications if a predefined parameter set is available. The most important parameter to consider is the duration of the mixing time.

List of available gradient-enhanced NOESY pulse programs for AVANCE spectrometers.

In a NOESY spectrum, cross-peaks correlate chemical shifts between homonuclear spins via dipolar coupling or exchange processes.

Related experiments:

2D homonuclear experiments

2D gradient-based homonuclear experiments