Dear AMMRL,
Over the years we have run proton spectra of large numbers of samples with
NH and NH2 groups such as peptide samples in DMSO and have never observed
N14-proton couplings, which I assume is due to the loss of multiplet
structure for spins that are scalar coupled to quadrupolar nuclei (assuming
relaxation is fast compared to J).
However a graduate student here has a sample of polymethacrylamide in
d6-DMSO. The molecular weight is around 1,500. In the room temperature
proton spectrum he sees three peaks in the ratio of 1:1:1 at the expected
chemical shift of the amide. The J value of ~50 Hz fits what one would
expect for N14-H coupling.
Is it reasonable to attribute the multiplet to N14-H coupling?
If so what is different about this sample that makes the coupling
observable, for example is T2 relaxation significantly slowed? And why?
Perhaps I am missing something very obvious but in any event your insights
would be appreciated.
Jeff
Jeffrey S. de Ropp, Ph.D.
NMR Facility
UC Davis
One Shields Avenue
Davis CA 95616
jsderopp_at_ucdavis.edu
530-752-7677 office
530-752-6480 MS1-D Lab
530-752-5682 600 MHz Lab
530-754-8238 Chem NMR Lab
530-752-3516 Fax
NMR Facility Web site URL is:
http://www.nmr.ucdavis.edu/
Received on Tue May 29 2007 - 10:03:20 MST