Gradient Selected Phase-sensitive HMQC

Differences between HSQC and HMQC

Similiar to 1H-13C HSQC, HMQC reveals through-bond correlations between 1H and one-bond connected heteronucleus such as 13C. The differences between the two experiments are: (1) HSQC sequence involves more pulses, potentially making pulse calibration more important, and (2) more significantly, the HMQC spectrum also shows through-bond 1H-1H couplings along the indirect (13C) dimension because both 1H and 13C are in the XY plane during 13C evolution. In a HSQC, the 1H-1H couplings are absent because all 1H's are along Z-axis during the single quantum 13C coherencee evolution. These 1H-1H couplings are often small and only obvious when the resolution is good along the indirect dimension. But some peak broadening along the 13C dimension is expected in a HMQC.

Becuase the HMQC sequence retains the 1H-1H coupling along the 13C dimension, the splitting of the peaks along 13C dimension can be used to estimate a major 1H-1H coupling constant if shaprness allows an accurate measurement. However, several couplings may be involved, leading to a complex peak profile and rendering this method less useful in measuring 1H-1H J couplings in many situations.

The following figure is the gradient based 2D 1H-13C HMQC pulse sequence with the main parameters displayed (NMR500).

gHMQC Sequence

Procedure (on NMR500)

Default parameters

The default setting (modified from Varian's default values) in our parameter set uses the following for a quick 2D experiment:

Data Processing

You can use vnmrJ to process the data, but vnmrJ's graphics display for 2D spectrum leaves much to be desired. A separate program is strongly recommended for detailed processing and analysis.

One of the most widely used free processing/display software package for multi-dimensional NMR data processing is nmrPipe/nmrDraw. This program package has been installed on NMR500 and the data station. Follow this procedure to process data with nmrPipe/nmrDraw.

Example spectrum collected on NMR500

Sample: Strychnine at ~ 25mg/mL (~ 100mM) in cdcl3
  • Data collected October 2010 (~20 mins with nt=4)
  • Processed and displayed with nmrPipe/nmrDraw

Strychnine 1H-13C gHMQC

Strychnine gHMQC

H. Zhou Updated Oct 2010