Re: R2 from R1rho & R1Re: R2 from R1rho & R1On 26/03/14 13:39, Edward d'Auvergne wrote:
Hi, The key here is what is meant by R2. There are many different definitions. In relax, the parameter name R2 is defined as: - In the standard relaxation equations, spin-spin relaxation component. I.e. the part influenced by the spectral density function J(w). - Again in the standard relaxation equations, R2 is used for R2*, where R2* = R2 + Rex. R2* is also defined differently if you look at the exponential decay curves or if you looking at peak widths (for the later there are additional factors broadening the peaks which add to the R2* equation). - For relaxation dispersion, R2 is currently defined as R1rho', i.e. just the parts influenced by the spectral density function. Here R1rho' is the on-resonance part of R1rho, excluding exchange. R2 = R1rho' + Rex could also be defined, which is probably what you are after. The value of R1rho' + Rex has been named many different things by the field and there seems to be no consensus. I have discussed this with Troels at http://thread.gmane.org/gmane.science.nmr.relax.devel/5119/focus=5207. This is a long thread with many discussions about implementing this as an automatically calculated parameter - which in the end would be a great feature. So which R2 value are you after? Regards, Edward
Hi Edward, Principally I am looking for pure R2 without Rex contribution. Currently we are using some home made scripts which basically are using equation 20 in Palmer, Massi, 2006 (PMID 16683750). So for the technical side, how do I proceed in relax? Do I need to fix the decay for R1 and R1rho and then calculate R2 or just fit R1 and use my raw intensities from the R1rho measurements for the R2 calculation? Thanks, Justin -- Justin Lecher Institute of Complex Systems ICS-6 Structural Biochemistry Research Centre Juelich 52425 Juelich, Germany phone: +49 2461 61 2117
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