Dear friends,
Thank you so much for all the quick and insightful responses. Nearly everyone points out that it is the ZQC cross peak, it is only a "problem" with small molecules when the linewidth is very narrow and the couplings are strong, and nothing to do with the parameter settings. All suggest to use sort of randomized mixing time to suppress these artifacts, however, the t1 noise may penalize the spectrum. A few suggested ROESY which should not have the ZQC peaks.
It does not affect my structural analysis. These peaks are well separated from all other NOE peaks. I just thought that I could use the two methylene protons as internal distance calibration if I can get a good NOE on them, so that I can compare the distance constraints obtained with Mardigras.
I am taking the liberty to ask for another question: I agree with Marcus in that the selective NOESY1D gives wonderful spectra in my INOVA (I am sure Bruker's or other Vendor's can give wonderful results too). For small molecules, is it valid if I use NOESY1D or ROESY1D to run at different mixing time, integrate the NOE, and use these build-up rate for my distance constraints calculations, rather than use NOESY? Suppose I don't have to worry about overlapping. I think the selective NOESY1D is steady-state, which is probably not valid for distance constraints, but I would like to know for sure.
Thank you very much and you all have a wonderful weekend.
Wei Li
Received on Fri Jan 31 2003 - 11:03:27 MST