Subject: Re: Fw: [nmr_sparky] distance constraints in 13C-edited spectra
From: Víctor Sánchez Pedregal
Date: Nov 24 8:49 AM

Previous: 308 Next: 310


Shouldnt one calibrate NOE-based distances independently in each spectrum?
I do not expect the 13C-edited and 15N-edited NOESYs to have necessarily the same absolute peak intensities. There is some relaxation during the t1 or t2 evolution times. Moreover, the magnetization that relaxes during t1 is either transverse 13C or transverse 15N, that probably have different rates. I have not calculated it quantitatively (somebody has?) but I guess that this explains part of the difference.
In addition, if selective pulses are used, the efficiency is never 100% and magnetization is not 100% transferred to the next product operator after the pulse. Most probably, these unwanted losses are different for the two NOESYs.
The overall duration of the pulse sequences may be different for C- and N-edited NOESYs. Relaxation operates all the time.
INEPT steps are never perfect (relaxation and use of an average compromise delay ~1/4J) and the degree of imperfection may be different for C and for N.
Victor



----- Mensaje original ----

De: Betty Swanson betswanso@...

Para: nmr_sparky@yahoogroups.com

Enviado: viernes, 24 de noviembre, 2006 4:42:21

Asunto: Re: Fw: [nmr_sparky] distance constraints in 13C-edited spectra



Dear Mandar and Eiso,

I asked our NMR spectroscopist regarding the relatively weaker intensities of all cross-peaks in 13C-edited spectra (when compared with 15N-edited spectra). According to him the pulse sequence used was fine and he doesn’t know the cause of this problem. Anyway, thanks you both for your suggestions.






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