Hi there, I've been trying to use bruker's pseudo-3D sequence for meassuring T2 relaxation dispersion and have a problem with it: I don't see any effect of the cpmg strength on the intensities, hence R2s, as if there were no exchange for any residue... but of course I do expect some... (and I tested it against proteins for which we know there is exchange at some residues).
Initially I thought that the 180 degrees pulse on 15N could be wrong, but I checked it and it's ok. For the 180 degrees pulse doing the magic I'm using 110 us at 0.85 dB...
The constant time is 60 ms (2 parts of 30 ms each) and the cpmg field strengths were set up between 33 and 966 Hz with the rex_setup tool provided by Bruker...
I'm using a 600 MHz Bruker spectrometer with Avance II console and a standard TXI probe.
I don't see any other critical parameters... do you? Can anyone provide a sample dataset?
I'm really interested by your bruker sequence for relaxation dispersion because I don't find any at the moment...
I guess that your sequence is a constant relaxation time and relaxation compensated CPMG-HSQC.
Perhaps, the CPMG frequency range is not adequate to visualize the exchange (so increased frequency can be an issue) ? Or, the error on T2 measurement can hide the exchange process (if R2ex is small) ?
But my real question is : which sequence you use !! Because, there are no standart bruker sequence for relaxation dispersion...