regarding REDOR simulations

[Rajeswari Mulakalapalli]

Hi, 

I need a help regarding REDOR simulations. Example program of REDOR says that the internuclear distance is sufficient to calculate dipolar coupling between a pair of spins. Instead of giving distance, I have used the coordinate file in the program for a pair of spins. The resulting dephasing curve  for the coordinate file and the internuclear distance are not matching even though the dipolar coupling from both is same. I do not understand why it is happening like this? Can anybody help me to understand this problem.

Thank you
regards
Rajeswari

[Mikhail Veshtort]

Hi Rajeswari,

Most likely this happens because of an incorrect powder averaging scheme you are using.

In the REDOR example, the atomic coordinates of the spins are indeed given through specifying the interatomic distance. In this case, the nuclei are automatically placed on the z axis of the coordinate system. This symmetry allows using the beta+gamma averaging scheme in that example. Using the same averaging scheme with a spin pair that is not aligned along z axis would be error.

Best regards,

Mikhail

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[Rajeswari]

Hi Mikhail,

Thank you for your immediate reply. Do I need to do averaging over three angles when I use coordinate file. I tried this for a pair of spins using a100b200 scheme with 20 gamma angles. It is working fine. When I take more than one pair (Ex; Alanine,3-13C, 1-15N) it is still working but the dephasing curve is not smooth like a single pair case. I am not understanding why it is happening like this in multiple pair case. I am doing selective excitation in the middle of the REDOR block to select  a particular pair for which I want to find the distance. Can you help me to solve this problem.

Thank you

Regards

Rajeswari

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******************************************
Dr. M. Rajeswari
Post Doctoral Visiting Scientist
Department of Chemical Sciences
Tata Institute of Fundamental Research 

Mumbai
India
*******************************************

[Mikhail Veshtort]

Hi Rajeswari,

You do need averaging over all three angles in the general case.

The dephasing (or exchange) curves that do not look smooth may result from insufficiently fine powder averaging, but this may also be their actual natural appearance. In your case, it is possible that other spins (that you did not select) are also contributing to the dephasing because the selective pulse is not perfect. But you will have to figure out these things yourself.

Best regards,

Mikhail