Practical considerations for the acquisition of ultra-wideline 14N NMR spectra

Stanislav L Veinberg; Austin W Lindquist; Michael J Jaroszewicz; Robert W Schurko

doi:10.1016/j.ssnmr.2016.12.008

Practical considerations for the acquisition of ultra-wideline ¹⁴N NMR spectra

Solid State Nucl Magn Reson. 2017 Jul-Aug:84:45-58. doi: 10.1016/j.ssnmr.2016.12.008. Epub 2016 Dec 21.

Authors

Stanislav L Veinberg¹, Austin W Lindquist¹, Michael J Jaroszewicz¹, Robert W Schurko²

Affiliations

¹ Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario, Canada N9B 3P4.
² Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario, Canada N9B 3P4. Electronic address: schurko@uwindsor.ca.

PMID: 28130009
DOI: 10.1016/j.ssnmr.2016.12.008

Abstract

Several considerations for the acquisition, processing, and analysis of high quality ultra-wideline (UW) ¹⁴N solid-state NMR (SSNMR) powder patterns under static conditions are discussed. It is shown that the ¹⁴N quadrupolar parameters may be determined accurately using the frequencies of only two discontinuities in ¹⁴N NMR powder patterns that are dominated by the first-order quadrupolar interaction, thereby eliminating the need for the acquisition of the entire pattern and concomitantly reducing experimental time. A framework for utilizing the WURST-CPMG pulse sequence to improve the efficiency of UW ¹⁴N SSNMR experiments is explored in two parts: (i) a systematic investigation of the design and parameterization of the WURST pulse is presented, and (ii) the development of the practical aspects of CPMG refocusing for the acquisition of UW ¹⁴N SSNMR powder patterns is discussed, with a focus on maximizing both signal-to-noise and resolution, and minimizing spectral distortions. Finally, a strategy is demonstrated that allows for the measurement of the ¹⁴N quadrupolar parameters for any nitrogen moiety whose quadrupolar coupling constant falls within the range 0.8≤|C_Q|≤1.5MHz, by acquiring only two ¹⁴N NMR sub-spectra at strategically located transmitter frequencies; these results are compared to full powder patterns which are acquired using frequency-stepped methods. The methodologies and practical considerations outlined herein are not only useful for the rapid acquisition of UW ¹⁴N NMR spectra, but may also be modified and applied for UW NMR of a plethora of quadrupolar and spin-1/2 nuclides.

Keywords: CPMG; Frequency-swept pulses; Nitrogen-14; Pulse parameterization; Spin-1; Ultra-wideline; WURST.

Publication types

Research Support, Non-U.S. Gov't