Tuesday, February 26, 2008
NOESY vs ROESY for Large Molecules.
NOESY experiments work well for molecules of very low and very high molecular weight. They do not work well for molecules with molecular weights of approximately 1000 - 2000 g/mol at typical field strengths, where the NOE's are very close to zero. A ROESY experiment can be used to get NOE information for molecule in this intermediate molecular mass regime. For high molecular weight molecules a NOESY and a ROESY experiment will give very similar results with the exception that the cross peaks will be in phase with respect to the diagonals for a NOESY and 180 degrees out of phase with the diagonals in the case of a ROESY. The figure below shows both a NOESY and a ROESY for gramacidin at 300 MHz The red contours are negative and the black contours are positive.
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4 comments:
This is good to know about this diff but it should also contains type of diff with respect to chemical information...
As it is stated in the test, they basically give the same chemical information, but due to aquisition method, each one of them is more appropiate for different systems (molecules, depending on molecular weigh).
By looking at those two spectra there are cross peaks (NH-NH Region) in NOESY but those are not in the ROESY can I get the information why those peaks are missing in ROESY?
Dear Unknown.
The cross peaks between NH protons are due to chemical exchange. I suspect that the mixing times in the NOESY and ROESY spectra are not the same such that they are more intense in the NOESY compared to the ROESY.
Glenn
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