What type of molecule are you looking at?
What type of t1/t2 or t1(rho) is your molecule experiencing?
Is the water molecule or molecules directly effecting your conformation or
dynamics?
Regular organics need 1-3 second presat periods equal to 1 to 2 x T1/T2 and
100msec to 500msec mix time before the read pulse.
Organo-metallics have longer T1's but short T2's. Presat for 500 msec and
mix for 50msec to 200msec.
Bio-molecules are a matter of T1(rho).
My experience has shown that a series of these experiments is needed for
good NOE/exchange measurements by 2-D.
Try Phase_Sensitive Double Quantum NOE experiments along with presat to
futhur your water-suppression and increase spectrometer temperature 10
degrees to shorten T1effects
Worse comes to worse try 1-D presat experiments. They may give clearer
results as to NOE/exchage phenoms.
Alan Kook
NMRS & C
Austin, TX
Zhang, Weixing wrote:
> Dear All,
>
> My understanding is that pre-saturation is the original method for water
> suppression.
> Nowadays, pulsed field gradient is used exclusively for water
> suppression. I am using a
> presat 2D NOESY experiment to evaluate the performance of a NMR
> spectrometer. The
> simple pulse sequence is:
>
> relaxation_delay presaturation_delay 90 t1 90 mix 90 Acquire.
>
> I am wondering what is the minimal power (in terms of gamma-H2) and
> saturation period
> should I use to saturate the water and still get a good spectrum for a
> good spectrometer.
>
> Any suggestion is appreciated.
>
> Weixing Zhang, Ph.D.
> NMR Manager
> St. Jude Children's Research Hospital
> Department of Structural Biology
> 332 North Lauderdale Street
> Memphis, TN 38105
> Phone: (901)495-3169
> Fax: (901)495-3032
> http://www.stjude.org