Dear AMMRL,
Thanks to all for the many responses to my original query below. The
consensus of responses was that we are seeing free ammonium ion, which due
to its highly symmetrical N14 environment leads to slow quadrupolar
relaxation and observable N14-proton couplings. When I gave this info to
the grad student he said well yes actually he did expect free ammonium ion
in his sample.
Another case solved....thanks to AMMRL.
Jeff de Ropp
>***********
>
>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 Sat Jun 02 2007 - 08:06:44 MST