The selective ge-1D COSY experiment permits to obtain high-quality selective 1D COSY spectra from which COSY patterns can be easily extracted and analyzed in terms of coupling constant values.

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

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

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

Evolution of homonuclear J-couplings during an optimized delay followed by a mixing pulse for anti-phase polarization transfer to other spins (see COSY 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 (selection of N- or P-type data as a function of the intensity of this refocusing gradient).

The first published version of the selective ge-1D COSY experiment ( 94MRC107 ) used a single (90º or 270º) gaussian pulse as a selective excitation and the refocusing gradient for coherence selection. This same scheme was applied to record selective ge-1D 13C-COSY spectra on 13C-labeled molecules ( 94MRC665 ). Improved versions of the gradient-selected COSY experiment uses the SPFGE ( 95JMRA120-113 , 96JMRB124-110 , and 96JMRB183-111 ) schemes as a initial selective excitation block. In this way, spectra can be also obtained from water solutions without the need of saturating the strong solvent signal.

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 J-coupling delay as a function of 1/(2*J(HH)), in order to get the anti-phase magnetization of the selected proton suitable for transfer polarization.

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

In 1D COSY spectra, all coupled protons appear in antiphase pattern with respect to the active coupling of the selected proton and in-phase pattern with respect to all other passive couplings. 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.

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