The 2D HmQC (Heteronuclear Multiple-Quantum Coherence) experiment permits to obtain 2D
multiplicity-edited heteronuclear correlation spectra. Depending of the used filter HDQC (Heteronuclear Double-Quantum Experiment), HTQC (Heteronuclear Triple-Quantum Experiment), or HQQC (Heteronuclear Quadrupole-Quantum Experiment) spectra result.

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

The basic 2D HmQC pulse sequence consists of an initial DEPT pulse train for the stepwise preparation of multiple-qauntum coherences (MQCs). These MQC evolve during the variable evolution period. A 180º 1H pulse is inserted at the middle of the t1 period to remove chemical shift and heteronuclear coupling evolutions. Finally, a reverse DEPT pulse sequence creates SQC proton magnetization which is suitable for recording under carbon decoupling. Specific phase cycling will be used to select DQC, TQC ( 90JACS1279 ) or QQC ( 91JMR375-91 ). These experiment can be easily converted to a 3D experiment by adding a second building block prior to acquisition. Thus, a 3D HQQC-TOCSY experiment has been proposed ( 90JACS8599 ) to resolve assignments in crowded spectra.

A related family of experiments have also been reported under the acronym  MAXY (MAXimum-quantum correlation spectroscopY) ( 95MRC212 ) and ). Hybrid experiments have been proposed in which a COSY, TOCSY or NOESY building block can be appended to the conventional HmQC pulse train. These experiments can also be referred as MAXY-COSY, MAXY-TOCSY and MAXY-NOESY. Thus, for instance, a 2D COSY spectrum of only proton resonances belonging to I2S systems can be obtained. Improved editing results can be obtained using gradient-enhanced experiments (see ge-2D multiplicity-edited HSQC  experiment and related experiment).

The HmQC pulse scheme can be used as a starting building block in multidimensional triple-resonance experiments replacing the conventional INEPT pulse scheme in order to selectively excite XH₂ or XH₃ spin systems. This building block, called MUSIC, has been succesfully applied to obtain amino-acid selective 2D ¹H-¹⁵N correlations ( 98JMR199-131 and 99JMR34-141 ).

The 2D HmQC experiments can be recorded in routine/automation modes. The parameter set-up is very similar to the HSQC experiment. The phase cycle selects for an specific n-quantum coherence order.

The HmQC spectrum only correlates chemical shifts of heteronucleus X (F1 dimension) and protons (F2 dimension) belonging to an specific I_nS system via the direct heteronuclear coupling 1J(XH). Thus, for instance, the HQQC spectrum displays an heteronuclear correlation map of the methyl resonances.

Related experiments:

2D Inverse experiments

2D Inverse gradient-enhanced experiments