title: The role of (15)N CSA and CSA/dipole cross-correlation in (15)N relaxation in solid proteins.
abstract: The influence of the (15)N CSA on (15)N longitudinal relaxation is investigated for an amide group in solid proteins in powder form under MAS. This contribution is determined to be typically 20-33% of the overall longitudinal relaxation rate, at 11.74 and 16.45 T, respectively. The improved treatment is used to analyze the internal dynamics in the protein Crh, in the frame of a motional model of diffusion in a cone, using the explicit average sum approach. Significant variations with respect to the determined dynamics parameters are observed when properly accounting for the contribution of (15)N CSA fluctuations. In general, the fit of experimental data including CSA led to the determination of diffusion times (tau(w)) which are longer than when considering only an (15)N-(1)H dipolar relaxation mechanism. CSA-Dipole cross-correlation is shown to play little or no role in protonated solids, in direct contrast to the liquid state case.
authors.affiliation: Laboratoire de Chimie (UMR 5182 CNRS/ENS Lyon), Ecole Normale Supérieure de Lyon, 69364 Lyon, France.
authors.forename: Julien
authors.initials: J
authors.lastname: Sein
authors.forename: Nicolas
authors.initials: N
authors.lastname: Giraud
authors.forename: Martin
authors.initials: M
authors.lastname: Blackledge
authors.forename: Lyndon
authors.initials: L
authors.lastname: Emsley
mesh_terms: D000465:Algorithms; D007553:Isotope Labeling / Q000379:methods; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008956:Models, Chemical; D008958:Models, Molecular; D009587:Nitrogen Isotopes / Q000737:chemistry*; D011506:Proteins / Q000737:chemistry*; D013223:Statistics as Topic
chemical_list: D009587:Nitrogen Isotopes; D011506:Proteins