title: Efficient polarization transfer between spin-1/2 and ¹⁴N nuclei in solid-state MAS NMR spectroscopy.
abstract: Polarization transfer between spin-1/2 nuclei and quadrupolar spin-1 nuclei such as (14)N in solid-state NMR is severely challenged by the typical presence of large quadrupole coupling interactions. This has effectively prevented the use of the abundant (14)N spin as a probe to structural information and its use as an element in multi-dimensional solid-state NMR correlation experiments for assignment and structural characterization. In turn, this has been a contributing factor to the extensive use of isotope labeling in biological solid-state NMR, where (14)N is replaced with (15)N. The alternative strategy of using the abundant (14)N spins calls for methods enabling efficient polarization transfer between (14)N and its binding partners. This work demonstrates that the recently introduced (RESPIRATION)CP transfer method can be optimized to achieve efficient (1)H ↔(14)N polarization transfer under magic angle spinning conditions. The method is demonstrated numerically and experimentally on powder samples of NH4NO3 and L-alanine.
authors.affiliation: Center for Insoluble Protein Structures (inSPIN), Interdisciplinary Nanoscience Center (iNANO), and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, DK-8000 Aarhus C, Denmark.
authors.forename: Kristoffer
authors.initials: K
authors.lastname: Basse
authors.affiliation: Center for Insoluble Protein Structures (inSPIN), Interdisciplinary Nanoscience Center (iNANO), and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, DK-8000 Aarhus C, Denmark.
authors.forename: Sheetal Kumar
authors.initials: SK
authors.lastname: Jain
authors.affiliation: Center for Insoluble Protein Structures (inSPIN), Interdisciplinary Nanoscience Center (iNANO), and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, DK-8000 Aarhus C, Denmark.
authors.forename: Oleg
authors.initials: O
authors.lastname: Bakharev
authors.affiliation: Center for Insoluble Protein Structures (inSPIN), Interdisciplinary Nanoscience Center (iNANO), and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, DK-8000 Aarhus C, Denmark. Electronic address: ncn@inano.au.dk.
authors.forename: Niels Chr
authors.initials: NC
authors.lastname: Nielsen
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008956:Models, Chemical; D009584:Nitrogen / Q000032:analysis* / Q000737:chemistry*; D013113:Spin Labels
chemical_list: D013113:Spin Labels; D009584:Nitrogen
keywords: 14N; CP; Magic-angle spinning; Polarization transfer; Solid-state NMR