Applications of cryogenic NMR probe technology to long‐range 1H‐15N 2D NMR studies at natural abundance

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Abstract
The development of new NMR probe technologies has been an active area of research effort for the past decade. Recently, cryogenically cooled NMR probes have been the subject of considerable interest in the light of the large gains in sensitivity and hence savings in spectrometer time that can be realized by utilizing this technology. With low gamma nuclides, such as 15N, time savings may be less of an issue than the ability to work with available samples rather than having to isolate additional material for analysis. Results of 5–10 Hz optimized CIGAR‐HMBC 1H–15N experiments at natural abundance obtained using a 5 mm Varian 1H–15N Cryo‐Q NMR probe are compared with those from a 3 mm gradient inverse triple resonance probe using a 2 mg sample of the oxazolidinone antibiotic eperezolid in a 3 mm NMR tube. Using the cryogenic NMR probe, a 1H–15N CIGAR‐HMBC spectrum in which most previously reported long‐range couplings are observed was recorded in ∼10 min; almost all of the expected long‐range responses were observed within 26 min. Acquiring the same data set with identical parameters using a conventional 3 mm gradient inverse triple resonance probe gave data that were of substantially lower quality. Acquiring data comparable to the 26 min cryogenic probe data with the conventional 3 mm probe required ∼4 h to observe all of the responses and ∼18 h to obtain a spectrum with a signal‐to‐noise ratio comparable to the data set acquired with the cryogenic NMR probe. Copyright © 2001 John Wiley & Sons, Ltd.