Re: water T1

THOMAS OCONNELL (tmoc@email.unc.edu)
Fri, 30 Apr 1999 14:57:43 -0400 (EDT)

Another possible source of nonexponential behavior in a 90%H2O sample
would be radiation damping. In addition to the inherent relaxation
behavior of the water, the magnitude of radiation damping will change as
differing amounts of transverse magnetization are present at the start of
detection. One simple way to test this would be to try this expt with the
probe slightly detuned.

cheers,
Tom
_________________________________________________________________
Thomas M. O'Connell
Asst. Professor of Medicinal Chemistry email: toconnell@unc.edu
School of Pharmacy CB #7360 phone: 919-966-2956
University of North Carolina fax : 919-966-0204
Chapel Hill, NC 27599

On Fri, 30 Apr 1999, David Naugler wrote:

> From: Maura & Gautam <mustard@cal.vsnl.net.in>
>
> > Dear All:
> >
> > Recently I was approached by a fellow researcher about a collaboration
> > where he wants me to measure the T1 of water in leaves of rice plant. In
> > the literature, the measured T1 has been used to identify the "mobility"
> > of water in the leaf which is related to the "availability" of water to the
> > plant. For example, it has been shown that the T1 can be related to
> > droughts or that in drought resistant variety it has some unique signature.
> >
> > Anyway, before trying to perform the actual experiment with leaves, I
> > tried to measure the T1 value of a 90%H20/10%D20 solution, and to my
> > surprise, in a standard inverse-recovery experiment, I observed a
> > sigmoidal rise of water signal as a function of Tau (instead of an exponential
> > growth). I feel that since I am dealing with a huge solvent peak,
> > either some special trick is needed to measure the T1 or that there is
> > something special about H20.
> >
> > I looked around for an answer but failed. Would one of you be able to
> > shed some light so that I can finish this simple experiment?
> >
> > best regards,
> >
> > Gautam Basu
>
>
> I think you will only see a simple exponential if there is only one relaxation
> pathway and only one relaxing species. In a 90%H20/10%D20 solution you will have
> ~80% H2O and ~10% HDO (a statistical mixture) and if you did not degas there are
> at least two relaxation pathways. As I understand it, it gets worse with
> biological preparations. In "An evaluation of the hydration of lysosyme by an
> NMR titration method", By G.D. Fullerton et al. Biochem. Biophys. Acta 8969
> (1986) p230-246, the authors observed several different types of bound water and
> multiexpontial decays.
>
> David Naugler
> Institute of Molecular Biology and Biochemistry
> Simon Fraser University
>
>