Hi Sébastien, The field dependence you note is expected for J(wN) and J(wH), because the frequencies wN and wH are of course field dependent, and J(w) decreases with increasing frequency. Field dependence in J(0) is not expected, however. In fact I often use the consistency of J(0) across datasets as a check on the quality of the data - any variation in J(0) across datasets, irrespective of field, is an indication of inconsistencies in the data. If you are seeing inconsistency in J(0), then there are any number of possible problems that might contribute. Changes in sample temperature in the various magnets and sample instability (aggregation or proteolytic degredation, eg) both tend to affect J(0) by changing the apparent rotational diffusion of the molecule; imperfect water supression causes errors in relaxation measurements, etc ... Hope this helps, Chris On Tue, 2006-12-12 at 11:34 -0500, Sebastien Morin wrote:
Hi everyone I got a question concerning the treatment of Rex in reduced spectral density mapping as implemented in relax... My data include R1, R2 and {1H}15N-NOE at three magnetic fields (500, 600 and 800 MHz). When proceeding to the reduced spectral density mapping, I obtain J at three values (0, wN and wH). However, a slight trend is observable between those extracted values, i.e. the values from data at 500 MHz are higher than those at 600, which are higher than those at 800... Is it normal ? Is there a way to extract the contribution from Rex (conformational exchange, slow us-ms timescale motions) from my data using reduced spectral density mapping at those three fields ? Thanks !! Sébastien :)