The selective ge-1D RELAY experiment permits to obtain high-quality selective 1D RELAY spectra from which the typical anti-phase COSY patterns can be easily extracted and analyzed in terms of coupling constant values. The experiment is a single extension of the selective ge-1D COSY experiment in which the mixing period is modified to allow step-by-step transfer polarization from the selected proton to other homonuclear spins via scalar coupling (J).

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

The selective ge-1D RELAY 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 to  anti-phase polarization transfer to a second spin as described for the COSY transfer(see COSY Block).

This second spin will show antiphase pattern with respect to the selected spin 1 and in-phase pattern for all other J-coupled spins. The incorporation of the delay-180º(1H)-delay-90º(1H) block allows the transfer polarization from this spin 2 to spin 3. This second delay is optimized as described for the COSY experiment (see RELAY Block). Multiple-step RELAY transfers can be achieved adding consecutive RELAY blocks(see Two-step RELAY 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 selective ge-1D RELAY experiment using several transfer steps has been described using the SPFGE ( 95JMRA120-113 and 96JMRB124-110 ) and DPFGE ( 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 RELAY 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.

Separate optimization of all J-coupling delays as a function of 1/(2*J(HH)), in order to get anti-phase magnetization of the selected and intermediate protons suitable for transfer polarization.

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

RELAY experiments show the same features as the analog COSY experiment. In 1D RELAY spectra, all relayed protons appear in antiphase pattern with respect to the active coupling of the last selected proton and in-phase pattern with respect to all other passive couplings. The initial and intermediate spins show mixed phases and can be difficult to analyze. 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.

 TOCSY experiments offer some advantages with compared to RELAY experiments when spin subsystems want to be trace out.