Friday, September 03, 2010

Oh, Sugar

I have good news! With a minimal simplification of my INADEQUATE filter I have been able to rescue the last cross-peak of cholesterol. It had been rejected because too near to the diagonal. I changed the code saying: "if it's on the diagonal, it is bad; if it's just near, let's accept it". So it is possible to have the perfect INADEQUATE of cholesterol, with all the expected cross-peaks IN and everything else OUT.
Yesterday I received another INADEQUATE spectrum, this time of sucrose. The S/N is still high enough to make my filter unnecessary. If I play with the contour plot all the noise disappears while the 12 carbon atoms and their 10 bonds remain. Only a spurious peak remains at the coordinates 103.7;-22.9. I have not received the 1-D external projection, so I created it artificially. The spectral width is the same in both dimension (instead of being doubled for the DQF axis). The consequence is that two cross-peaks fall just on the boundary and are partially folded. This is the spectrum:

I have applied the filter with the same parameters used for the cholesterol (C-C coupling; linewidths in the two dimensions) while the threshold corresponds to the above plot. The result is perfect. All the cross-peaks are resolved and they are all present. Nothing else survives.

This time all the peaks are regular anti-phase doublets. The Js are generally larger than in cholesterol.
Click on the thumbnails to see the full-size pictures. There is an expansion to help counting the correct number of cross-peaks.
Do you want to send another spectrum? I can clean it for free. Remember to enclose the 13-C of the same sample.


At 12:27 PM, Anonymous Anonymous said...

Is the filter available for download? Also it would be helpful to have some example files on which beginners could learn the correct routine for processing classic 2D spectra: INADEQUATE, COSY, NOESY, etc.

At 1:19 PM, Blogger old swan said...

The filter, in its present experimental form, has been embedded into versions 3.6 of iNMR and iNMR reader.
Friends of mine gave me collections of nice spectra of strychnine. I don't know why this poison is such a favorite. I don't know if I can share them. A vast public collection is available at:


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