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Friday, May 15, 2009

The Selective 1D Gradient NOESY

Many students run very long 2D NMR experiments to find one particular piece of information. This is especially true for 2D NOESY experiments where perhaps only a single NOE correlation is sought. Depending on the amount of compound available, 2D NOESY measurements often take hours or tens of hours to acquire and can cost alot of money in instrument user fees. Many people do not realize that there are selective 1D analogs to the non selective 2D experiments. These 1D experiments rely on shaped pulses for selective excitation and take only a small fraction of the time required to run the comparable non selective 2D experiment. Previously I have posted entries in this BLOG on the very useful 1D selective gradient TOCSY experiment. The figure below demonstrates the use of the 1D selective gradient NOESY experiment for bis(phenylthio)methane compared to the standard proton NMR spectrum. In this case, the methylene protons were selectively irradiated and the NOE's were observed on the phenyl rings. The experiment took less than 5 minutes to acquire.

4 comments:

Manoj said...

we always put gradient value in percentage How to calculate those value in Tesla/meters?

Thanks

Glenn Facey said...

Dear Manoj,

Thank you for your comment. You must calibrate the gradient strengths on your spectrometer to know the strength in Tesla/m. One way of doing this is described here:

http://u-of-o-nmr-facility.blogspot.com/2008/03/gradient-calibration-1d-mri.html

Glenn

Anonymous said...

Glenn, hello!

There is an interesting pulse program in the topspin library selnorgzs. It contains adiabatic shape pulse at the end of the sequence. I understand that is for elimination of COSY artifacts in the resulting spectrum. It is very useful for small molecules. Have you ever calibrated this adiabatic pulse.

Glenn Facey said...

Anonymous,
I think you are referring to the selnogpzs sequence. I have not calibrated this the adiabatic pulse but I believe you can do it within the shape tool based on the hard pulse duration and power level.
Glenn