The 2D RELAY experiment is an extension of the 2D COSY experiment that allows to identify a full coupled spin network in a stepwise fashion so that with each further step the topology of the spin system and the signal assignments can usually be determined unambiguously. Thus, for instance, given a AMX system with J(AM), J(MX) different to 0 and J(AX)=0, the RELAY spectrum will show COSY cross-peaks due to AM and MX couplings, and RELAY cross-peak at the AX site.

Easy implementation on any AVANCE spectrometer.

In the basic pulse sequence of the 2D RELAY experiment (  82JACS3731 and  83JMR151-55 ), a fixed mixing period and a final coherence transfer pulse (delay-180º-delay-90º block) is added to the classical two-pulse COSY pulse sequence (see RELAY block) . In this way, magnetization is transfered from a directly coupled spins to the next neighbor of each. The RELAY experiment can be extended to multiple-steps by the insertion of successive RELAY building-blocks which must be individually optimized. The mixing time can also be incremented in concert with the variable evolution period

Pulsed field gradient can also be incorporated in this experiment (see ge-2D RELAY experiment).

The 2D RELAY can be recorded in routine/automation modes. The experimental set-up procedure is exactly as described for the conventional 2D COSY experiment. The fixed evolution period is the most important parameter to consider and must be optimized to 1/2*J(HH) (  85JMR306-61 ). Of course, relaxation will limit how many steps can be carried out in practice. More details on practical implementation of 2D RELAY 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

A RELAY spectrum displays the same information than a COSY spectrum. However, it is highly advisable to run a previous COSY experiment in order to distinguish relayed from direct connectivities in the RELAY spectrum. The RELAY cross-peaks will show the typical antiphase pattern with respect to the active coupling as found in COSY-type experiments. In a multistep relay experiment, correlation signals for all intermediate steps will usually be observed as well.

General Reading:

Relaxation effects of chemical exchange ( 96ENC4120 )

Relayed coherences can also be established using the 2D TOCSY experiment.

Related experiments:

2D homonuclear experiments

2D gradient-based homonuclear experiments