title: Practical considerations for the acquisition of ultra-wideline14N NMR spectra.
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 the14N quadrupolar parameters may be determined accurately using the frequencies of only two discontinuities in14N 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 UW14N 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 UW14N 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 the14N quadrupolar parameters for any nitrogen moiety whose quadrupolar coupling constant falls within the range 0.8≤|CQ|≤1.5MHz, by acquiring only two14N 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 UW14N NMR spectra, but may also be modified and applied for UW NMR of a plethora of quadrupolar and spin-1/2 nuclides.
authors.affiliation: Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario, Canada N9B 3P4.
authors.forename: Stanislav L
authors.initials: SL
authors.lastname: Veinberg
authors.affiliation: Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario, Canada N9B 3P4.
authors.forename: Austin W
authors.initials: AW
authors.lastname: Lindquist
authors.affiliation: Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario, Canada N9B 3P4.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Jaroszewicz
authors.affiliation: Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario, Canada N9B 3P4. Electronic address: schurko@uwindsor.ca.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Schurko
keywords: CPMG; Frequency-swept pulses; Nitrogen-14; Pulse parameterization; Spin-1; Ultra-wideline; WURST