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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?


asked Aug 16 '09 at 14:47

Evgeny%20Fadeev's gravatar image

Evgeny Fadeev

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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.


answered Aug 18 '09 at 12:29

dare's gravatar image


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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


  1. Cantor and Schimmel : Biophysical Chemistry

  2. M.Goldman : Quantum description of high-resolution NMR in liquids.


answered Feb 11 '10 at 21:28

sekhar%20Talluri's gravatar image

sekhar Talluri

updated Feb 12 '10 at 12:32

Evgeny%20Fadeev's gravatar image

Evgeny Fadeev

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

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