The selective 1D RELAY experiment allows to obtain 1D RELAY spectra from which the typical COSY patterns can be easily extracted and analyzed in terms of coupling constant values. The experiment is a single extension of the selective 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). Improved results are obtained from the gradient-based selective ge-1D RELAY experiment.

Easy implementation on AVANCE spectrometers with selective excitation using shaped pulses.

The selective ge-1D RELAY experiment consists of the following parts:

Selective excitationof the selected resonance.

Evolution of homonuclear J-couplings of the selected spin during an optimized delay followed by a mixing 90º pulse for anti-phase polarization transfer to other spins (see COSY Block).

These other spins 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 evolution and polarization transfer 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.

Several approaches have been reported:

• The first published version of the selective 1D COSY experiment ( 86JMR106-70 ) used a single (90º or 270º) gaussian pulse as a selective excitation. A DANTE pulse train ( 87TL3331 , 92JMR153-98 , and 96CONC119 ) has also been used.
• Using a chemical-shift-selective filter (CSSF) ( 91TET3535 and 93JB367 ).
• Using the DICE approach ( 90JMR331-87 ).
• The experiment has also been applied to ¹³C nuclei using ¹³C-labeled compounds ( 90MRC149 ).
• Use of pulsed-field gradients (see selective ge-1D RELAY experiment).

The selective 1D RELAY experiment can be run with minor changes from a predefined parameter set. Detailed description of the experiment can be found in the original publication ( 86JMR106-70 ). Two important parameters to consider are:

Selectivity of the selective excitation 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 the anti-phase magnetization of the selected and intermediate protons suitable for transfer polarization.

For further details on practical implementation of selective 1D RELAY experiments on AVANCE spectrometers see Tutorial: selective 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 selective 1D TOCSY experiment offers some advantages with compared to RELAY experiments when spin subsystems want to be trace out.

The selective 1D RELAY experiment can be the starting block of more sophisticated pseudo-3D experiments as:

• Selective 1D RELAY-RELAY ( 93JB367 ).
• Selective 1D RELAY-TOCSY ( 93JB367 ).
• Selective 1D RELAY-NOESY ( 92JMR153-98 , 93JB367 and 96CONC119 ).
• Selective 1D RELAY-ROESY experiment ( 93JB367 ).

An excellent review describing selective excitation in 1D and multidimensional NMR experiments was published ( 91MRC527 ).