The 2D HMQC-COSY experiment is an hybrid inverse experiment consisting of an initial HMQC pulse train and one or several RELAY building blocks. In the first step, magnetization is transferred from the X nucleus (13C or 15N) to the directly-bonded proton nuclei via ¹J(CH). In the second step, such magnetization is step-wise propagated through the whole coupled homonuclear spin network via J(HH). Similar results are obtained from the analog 2D HSQC-COSY experiment.
 

Easy implementation on any AVANCE spectrometer equipped with an inverse probehead.

The basic sequence of the 2D HMQC-COSY experiment is based on the four-pulse 2D HMQC experiment in which a 90º proton pulse is inserted prior to acquisition ( 85JMR145-62 and 88FEBS17 ). This version does not provide for heteronuclear decoupling during acquisition. In a better alternative, a BIRD-recovery cluster is used as a preparation period in order to reduce the large unwanted 1H-X (typically, 12C or 14N) magnetization and a refocusing period is optionally included ( 86JMR375-69 ).

A very related sequence has also been proposed ( 86JMR546-69 ). Improved results can be obtained from the gradient enhanced version (see ge-2D HMQC-COSY experiment).

The 2D HMQC-COSY experiment can be recorded in routine/automation modes. The experiment is basically optimized as described for the 2D HMQC experiment. More details on practical implementation of 2D HMQC-COSY experiments on AVANCE spectrometers can be found in

Tutorials: 2D inverse experiments

Tutorials: 2D gradient-based inverse experiments

The HMQC-COSY spectrum correlates chemical shifts of heteronucleus X (F1 dimension) and protons (F2 dimension) via the direct heteronuclear coupling ¹J(XH). Two different cross-peaks are present for each X resonance: The direct 1H-X connectivites (HMQC cross-peak) and the relayed 1H-X connectivity due to the cumulative transfer ¹J(XH)+J(HH). In the case of more relayed steps are included to the pulse sequence, magnetization is propagated to the whole proton spin network and, therefore, more relayed peaks will be detected. However, a 2D HMQC-TOCSY experiment can be preferred for this purpose.

Comparison of different 2D inverse correlations have been carried out ( 90JMR488-87 ).

Related experiments:

2D Inverse experiments

2D Inverse gradient-enhanced experiments