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In the decoupled HSQC of a polypetide I see two small peaks right and left to the delta arginine signal. These peaks have the same 13C chemical shift as the arginine signal, are equidistant from it in the 1H direction and are spa rated by around 450 Hz. In another example I see the same phenomenon for the epsilon lysine signal. In this case the peaks are separated by 400 Hz and I could also compare the integrals of the two small peaks resulting in 1/200 of the bigger peak. I see these peaks both in se-HSQC and non sensitivity enhanced HSQC, and I think I can exclude that these are "COSY-peaks".

Does anyone have an explanation for this?

Thanks a lot!

asked Nov 28 '13 at 09:46

PQdotL's gravatar image


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I would guess at decoupling sidebands, which could be of the order of 1% of the intensity of the main peak. What decoupling scheme is used, and how many scans per increment? You could test by moving the decoupler frequency and seeing if the splitting changes.


answered Nov 29 '13 at 00:45

Pete%20Gierth's gravatar image

Pete Gierth

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