title: 14N Solid-State NMR Spectroscopy of Amino Acids.
abstract: 14N ultra-wideline solid-state NMR (SSNMR) spectra were obtained for 16 naturally occurring amino acids and four related derivatives by using the WURST-CPMG (wideband, uniform rate, and smooth truncation Carr-Purcell-Meiboom-Gill) pulse sequence and frequency-stepped techniques. The14N quadrupolar parameters were measured for the sp3nitrogen moieties (quadrupolar coupling constant, CQ, values ranged from 0.8 to 1.5 MHz). With the aid of plane-wave DFT calculations of the14N electric-field gradient tensor parameters and orientations, the moieties were grouped into three categories according to the values of the quadrupolar asymmetry parameter, ηQ: low (≤0.3), intermediate (0.31-0.7), and high (≥0.71). For RNH3+moieties, greater variation in N-H bond lengths was observed for systems with intermediate ηQvalues than for those with low ηQvalues (this variation arose from different intermolecular hydrogen-bonding arrangements). Strategies for increasing the efficiency of14N SSNMR spectroscopy experiments were discussed, including the use of sample deuteration, high-power1H decoupling, processing strategies, high magnetic fields, and broadband cross-polarization (BRAIN-CP). The temperature-dependent rotations of the NH3groups and their influence on14N transverse relaxation rates were examined. Finally,14N SSNMR spectroscopy was used to differentiate two polymorphs of l-histidine through their quadrupolar parameters and transverse relaxation time constants. The strategies outlined herein permitted the rapid acquisition of directly detected14N SSNMR spectra that to date was not matched by other proposed methods.
authors.affiliation: Department of Chemistry and Biochemistry, University of Windsor, 401 Sunset Avenue, Windsor, Ontario, N9B 3P4, Canada.
authors.forename: Stanislav L
authors.initials: SL
authors.lastname: Veinberg
authors.affiliation: Department of Chemistry and Biochemistry, University of Windsor, 401 Sunset Avenue, Windsor, Ontario, N9B 3P4, Canada.
authors.forename: Zachary W
authors.initials: ZW
authors.lastname: Friedl
authors.affiliation: Department of Chemistry and Biochemistry, University of Windsor, 401 Sunset Avenue, Windsor, Ontario, N9B 3P4, Canada.
authors.forename: Austin W
authors.initials: AW
authors.lastname: Lindquist
authors.affiliation: Department of Chemistry and Biochemistry, University of Windsor, 401 Sunset Avenue, Windsor, Ontario, N9B 3P4, Canada.
authors.forename: Brianna
authors.initials: B
authors.lastname: Kispal
authors.affiliation: Department of Chemistry and Biochemistry, University of Windsor, 401 Sunset Avenue, Windsor, Ontario, N9B 3P4, Canada.
authors.forename: Kristopher J
authors.initials: KJ
authors.lastname: Harris
authors.affiliation: Institute for Frontier Materials, Deakin University, Waurn Ponds Campus, Geelong, Victoria, 3220, Australia.
authors.forename: Luke A
authors.initials: LA
authors.lastname: O'Dell
authors.affiliation: Department of Chemistry and Biochemistry, University of Windsor, 401 Sunset Avenue, Windsor, Ontario, N9B 3P4, Canada.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Schurko
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D009584:Nitrogen / Q000737:chemistry
chemical_list: D000596:Amino Acids; D009584:Nitrogen
keywords: NMR spectroscopy; amino acids; hydrogen bonding; nitrogen; polymorphism