The ge-2D EXSY experiment allows to obtain a 2D EXSY spectrum with two scans per t1 increment provided that the S/N ratio is adequate to study dynamic or chemical exchange processes. The main advantage of such approach is the large reduction in the total acquisition time compared with a conventional 2D EXSY experiment. Basically, the EXSY experiment uses the same pulse sequences for the NOESY or ROESY experiments.

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

Although 2D EXSY experiments must be recorded in a phase sensitive mode, the original publication included PFGs for coherence selection ( 92JMR419-97 ). However, PFGs are usually incorporated as a purging method (similar to homospoil pulses) to remove unwanted magnetization and 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/EXSY 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 EXSY 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 ). Similar to 2D NOESY experiments, 2D EXSY experiments can include gradient-based  solvent suppression schemes as, for instance, the WATERGATE  ( 92JB661 , 95JB327 , and 96JB15-8 ) or DPFGE ( 96JMRB82-112 ) schemes optionally combined with a water-flip-back pulse prior to acquisition. Modified WATERGATE and DPFGE schemes for multiple-solvent suppression ( 96JMRB124-110 , and 98JB437 ) purposes can also be included.

An excellent review analyzing several 1D and 2D EXSY experiments to study solvent-solute interactions have been published ( 97PROG259 ).

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 EXSY experiment can be recorded with minor required modifications if a predefined parameter set is available. In principle, 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