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I've got a sample of about 5mg of an amino acid that is the final product of a a synthesis. Due to the long relaxation time that the carboxylic and the alpha C we only got a 200 varian Mercury instrument and we're unable to obtain those signals. I was wondering if an APT is better than DEPT, because we're only interested in this signals and i've heard the overall pulse sequence is shorter than the DEPT, increasing the number of scans in the same period of time. |
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DEPT will not work for quart 13Cs since there is no attached 1H for polarization transfer. If you have the time, I would stick the sample in the magnet and apply a 30-45 degree flip angle with a relaxation delay of ~ 1 sec and pulse on it for a few days. APT will be worse than DEPT since this is a 13C detected experiment and you must wait a full 5-10 times the 13C T1 for good spectra. If you have an inverse probe, or can get a proton pi/2 of 12-14usec or less I would try for an HMBC to detect the quart 13C's. |
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If you really want to run a dept type experiment there is a newer version the DEPTQ that does detect quaternary carbons, however sensitivity for those carbons is a bit lower than in the standard 1D carbon experiment. |
