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Tuesday, November 20, 2018

NOAH - Faster 2D Data Collection

NMR users typically run 1H, 13C, COSY, HSQC, HMBC and NOESY spectra to elucidate the structures of small molecules. Even with cryogenically cooled probes and pulsed field gradient accelerated methods, collecting 2D spectra can be quite time consuming. For concentrated samples, each 2D experiment will typically take minutes to tens of minutes to collect. Much of this time is the result of waiting for T1 relaxation in each of the experiments. Recently, Kupce and Claridge1,2 have developed a technique using standard NMR hardware where multiple 2D methods are concatenated in a single super pulse sequence employing a single relaxation delay. They have called the technique NOAH (NMR by Ordered Acquisition using 1H detection) The time saving of the NOAH technique compared to individually collected 2D spectra results from waiting a single relaxation delay for all experiments rather than a single relaxation delay for each separately acquired spectrum. The data for each spectrum is acquired in separate memory blocks which are separated after data collection allowing the data for each 2D method to be processed individually. The data can also be processed in automation. The authors have kindly made this method accessible to all Bruker users through the Bruker User Library which contains pulse sequences, parameter sets, automation scripts and detailed instructions. The left-hand panel of the figure below shows the 600 MHz HMBC, Ed-HSQC and COSY spectra obtained from the NOAH-3 BSC (HMBC, HSQC, COSY) pulse sequence for sucrose in DMSO-d6.  The right-hand panel shows separately acquired 2D data sets for comparison.
The NOAH spectra were obtained from the raw concatenated data with the automation script provided. The high quality NOAH-3 data using 2 scans, 256 increments and a 2 second relaxation delay, took only 24 minutes to acquire in comparison to the separately acquired 2D spectra obtained with similar parameters, which took a total of 59 minutes to acquire. This represents a time saving of 35 minutes or 59%. It should also be noted that the data from the NOAH-3 BSC sequence is of comparable quality to that of the individually collected spectra.

1. Eriks Kupce and Tim D. W. Claridge.  Chem. Commun. 54, 7139 (2018).
2. Eriks Kupce and Tim D. W. Claridge. Angew. Chem. Int. Ed., 56, 11779 (2017).