Proton-detected 15N-1H dipolar coupling/1H chemical shift correlation experiment for the measurement of NH distances in biological solids under fast MAS solid-state NMR

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2021-12-28
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Nehra, Ekta
Sehrawat, Neelam
Kobayashi, Takeshi
Nishiyama, Yusuke
Pandey, Manoj Kumar
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Iowa State University Digital Repository, Ames IA (United States)
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Ames National Laboratory

Ames National Laboratory is a government-owned, contractor-operated national laboratory of the U.S. Department of Energy (DOE), operated by and located on the campus of Iowa State University in Ames, Iowa.

For more than 70 years, the Ames National Laboratory has successfully partnered with Iowa State University, and is unique among the 17 DOE laboratories in that it is physically located on the campus of a major research university. Many of the scientists and administrators at the Laboratory also hold faculty positions at the University and the Laboratory has access to both undergraduate and graduate student talent.

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Measurement of distances from dipolar couplings is essential for structural characterization, refinement and validation using the solid-state nuclear magnetic resonance (ssNMR) spectroscopy. Particularly, knowledge about NH dipolar interactions in biological solids is important for understanding the hydrogen (H)-bonding interactions, molecular geometry and spin dynamics. In this regard, we have proposed a proton-detected two-dimensional (2D) 15N-1H dipolar coupling/1H chemical shift correlation experiment using the C-symmetry based windowless recoupling of chemical shift anisotropy (ROCSA) in combination with the DIPSHIFT pulse-based method for the measurement of short NH distances in the isotopically labeled and naturally abundant biological solids at fast magic angle spinning (MAS) rates (40–70 kHz). Our proposed method results in undistorted recoupled 15N-1H dipolar coupling powder lineshapes that are free from the recoupled 1H CSA contributions under the 15N evolution, a feature that is essential for the measurement of NH distances with improved accuracy (± 500 Hz in terms of the NH dipolar couplings). The pulse sequence developed in the present study is also insensitive to the 1H–1H homonuclear dipolar interactions, relaxation effects owing to its constant-time implementation, and t1-noise from the fluctuations in the MAS.
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This article is published as Nehra, Ekta, Neelam Sehrawat, Takeshi Kobayashi, Yusuke Nishiyama, and Manoj Kumar Pandey. "Proton-detected 15N-1H dipolar coupling/1H chemical shift correlation experiment for the measurement of NH distances in biological solids under fast MAS solid-state NMR." Journal of Magnetic Resonance Open 10 (2022): 100028. DOI: 10.1016/j.jmro.2021.100028. Copyright 2021 The Authors. Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0). DOE Contract Number(s): AC02-07CH11358; ECR/2017/000713; 20K05483; JPMJMI17A2. Posted with permission.
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