Select a reasonable NOESY mixing time given MW, B, viscosity?

i like this post (click again to cancel)

i dont like this post (click again to cancel)

remove favorite mark from this question (click again to restore mark)

Is there a formula that would suggest a reasonable starting value for the mixing time based on the molecular weight, magnet field strength and solvent viscosity?

Would anyone recommend some publication on the subject?

Thanks!

noesy experiment-setup

asked Aug 16 '09 at 14:47

Evgeny Fadeev
577●1

2 Answers:

oldest newest most voted

i like this answer (click again to cancel)

i dont like this answer (click again to cancel)

the author of the question has selected this answer as correct

A mixing time that is about 1/3 to 1/2 of T1 will give maximum NOE. To estimate distances you need to be in the linear region of the transfer, or fit an entire mixing series. To get data in the linear region us a mixing time that is about 5% of T1.

Since there is no hard relationsip betwen T1 and Mw or viscosity there is no equation such as the one you are asking for. There may be approximations which are true within a limited family of polymers, but there is no general realationship.

link

answered Aug 18 '09 at 12:29

dare
61●1

There IS a relationship between T1 and correlation time which in turn is dependent on MW and viscosity. You may obtain a rough estimate of T1 using the following relationships.

The relationship between rotational correlation time and T1 is given by the Bloembergen, Purcell and Pound equation (BPP equation) see (relaxation time section in

http://en.citizendium.org/wiki/Nmr_spectroscopy#NMR_spectroscopy:_Observable_parameters ).

The correlation time can be estimated from knowledge of MW and viscosity as follows:

Assuming a spherical shape, the radius of hydration rh = ((MW)^0.44)/1.5

Use this radius, rh, to calculate volume of hydration, Vh.

According to the Stokes-Einstein relation, the rotational diffusion coefficient Dr = k*T/(6*Vh*viscosity)

And Rotational correlation time tau_r = 1/(6*Dr)

Therefore, rotational correlation tau_r = Vh*viscosity/(k*T)

k=Boltzmann constant and T=Temperature

References:

Cantor and Schimmel : Biophysical Chemistry
M.Goldman : Quantum description of high-resolution NMR in liquids.

link

answered Feb 11 '10 at 21:28

sekhar Talluri
621

updated Feb 12 '10 at 12:32

Evgeny Fadeev
577●1

Dr. Talluri, I've added little fixes to formatting so that equations show better. - Evgeny Fadeev (Feb 12 '10 at 12:33)

Here (once you log in) you will be able to sign up for the periodic email updates about this question.

Your answer

Please start posting your answer anonymously - your answer will be saved within the current session and published after you log in or create a new account. Please try to give a good answer, for discussions, please use comments and please do remember to vote (login to vote)

toggle preview

Tags:

noesy ×26
experiment-setup ×11

Asked: Aug 16 '09 at 14:47

Seen: 10,942 times

Last updated: Feb 12 '10 at 12:32

Related questions