The selective ge-1D NOESY experiment permits to obtain high-quality selective 1D NOESY spectra from which accurate NOE enhancements can be easily extracted and analyzed.

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

The selective ge-1D NOESY experiment consists of three parts:

Selective excitation of the selected resonance using the SPFGE block or the DPFGE block.

Mixing period consisting of the basic 90º(1H)-delay-90º(1H) block  for in-phase polarization transfer to other spins via NOE. Purging gradients are usually applied during the mixing period in order to remove any residual tranverse magnetization (see NOESY Block).

Proton detection as usual.

Gradients can be incorporated in this basic scheme in two different ways depending if a refocusing gradient is inserted before acquisition. If is is not incorporated, EXORCYCLE must be applied on a selective 180º pulse of the SPFGE or DPFGE scheme. If it is incorporated, ultra clean 1D spectra are obtained without need of phase cycling but half of the signal is lost with compared to a non-refocused experiment (coherence selection of N- or P-type data as a function of the intensity of this refocusing gradient. This is the GOESY experiment). In the last option, diffusion and convection effects can be an extra source of undesired loss of sensitivity.

The first published version of the selective ge-1D NOESY experiment ( 94JACS6037 ) used a SPFGE scheme as a selective excitation and the refocusing gradient for coherence selection (GOESY experiment). Although ultra clean NOE spectra are acquired under such conditions, sensitivity losses due to coherence selection ( 96JMRA295-119 ), and to diffusion and convection effects ( 98JMR13-132 ) can be undesired. Improved versions of the gradient-selected NOESY experiment uses the SPFGE ( 97JMR302-125 ) and DPFGE ( 95JACS4199 , 97JMR302-125 , and 96JMRA295-119 ) schemes as a initial selective excitation block. In these cases, a minimum two-step phase cycle is needed but high-quality spectra are equally obtained.

The selective ge-1D COSY experiment can be run with minor changes from a predefined parameter set. The best option is the version which uses a SPFGE or DPFGE scheme as a selective excitation and the refocusing gradient is omitted. Two important parameters to consider are:

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

Optimization of the mixing period as a function of the sample under study.

 For further details on practical implementation on AVANCE spectrometers see Tutorial: selective ge-1D NOESY experiment .

In selective 1D NOESY spectra, through-space connectivities from a selected spin can be trace-out in a very simple way. The use of gradients allows to obtain a clean, artefact-free spectrum in a short time from which careful analysis of the multiplets can be done. Sometimes, undesired anti-phase contributions can be present due to zero-quantum or SPT effects.

This same sequence can be used to monitor dynamic processes as, for instance, chemical exchange, solvent-solute interactions ... (see ge-1D selective ge-1D EXSY experiment).

The selective ge-1D COSY experiment can be used as a starting building block in more sophisticated experiments. See the doubly-selective ge-1D NOESY-TOCSY experiment as an example.