Advanced versions of COSY sequence

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faq_user
Posts: 49
Joined: Tue Jul 13, 2021 8:33 am

Advanced versions of COSY sequence

Post by faq_user »

I had 2 questions regarding some Earth-field multidimensional NMR experiments in SPINACH:

1) Is there a way to perform a COSY experiment with 2 or more heteronuclei? It would be akin to the following paper (10.1016/j.jmr.2006.06.027), in which both (or more) heteronuclei are excited with the same pulse. At present it seems that the COSY experiment is limited to a single nucleus.

2) Is there a way to perform a J-resolved NMR experiment? The NMR experiment is similar to a COSY experiment, except instead of a 90-t-90-acquire, the pulse sequence is 90-1/2t-180-1/2t-acquire. I have tried to modify the COSY experiment, but I am unsure of how to implement a 180 pulse in the middle of the t1 evolution. Is there a quick solution to this?
kuprov
Posts: 72
Joined: Mon Mar 29, 2021 4:26 pm

Re: Advanced versions of COSY sequence

Post by kuprov »

1. Of course, but you need to change the pulse operators and the initial condition to match the Earth field situation. The initial density matrix should now be gamma-weighted

sum{gamma_n*Lz_n}

where gamma_n are magnetogyric ratios and Lz_n are the Lz states on each spin type. The same should be done with the pulse operators, except the Lz_n should be received from the operator.m function.

Just open the cosy.m file and make the replacements. There will be no such thing as a 90-degrees pulse anymore, of course – every nucleus type will be rotated by its own angle.

2. Yes, we have a shortcut implemented for precisely this situation – it often occurs in heteronuclear experiments such as HSQC (see Line 88 in hsqc.m). First it runs all increments to half-time (‘trajectory’ option), then applies the pulse, and then runs all increments again, each for the appropriate time (‘refocus’ option). Further details here:

http://spindynamics.org/wiki/index.php? ... volution.m
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