title: Symmetry-based constant-time homonuclear dipolar recoupling in solid state NMR.
abstract: Constant-time dipolar recoupling pulse sequences are advantageous in structural studies by solid state nuclear magnetic resonance (NMR) with magic-angle spinning (MAS) because they yield experimental data that are relatively insensitive to radio-frequency pulse imperfections and nuclear spin relaxation processes. A new approach to the construction of constant-time homonuclear dipolar recoupling sequences is described, based on symmetry properties of the recoupled dipole-dipole interaction Hamiltonian under cyclic displacements in time with respect to the MAS sample rotation period. A specific symmetry-based pulse sequence called PITHIRDS-CT is introduced and demonstrated experimentally. (13)C NMR data for singly-(13)C-labeled amino acid powders and amyloid fibrils indicate the effectiveness of PITHIRDS-CT in measurements of intermolecular distances in solids. (15)N-detected and (13)C-detected measurements of intramolecular (15)N-(15)N distances in peptides with alpha-helical and beta-sheet structures indicate the utility of PITHIRDS-CT in studies of molecular conformations, especially measurements of backbone psi torsion angles in peptides containing uniformly (15)N- and (13)C-labeled amino acids.
authors.affiliation: Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0520, USA. robertty@mail.nih.gov
authors.forename: Robert
authors.initials: R
authors.lastname: Tycko
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry*; D000682:Amyloid / Q000737:chemistry*; D016229:Amyloid beta-Peptides / Q000737:chemistry; D002247:Carbon Isotopes / Q000737:chemistry; D008969:Molecular Sequence Data; D009587:Nitrogen Isotopes; D019906:Nuclear Magnetic Resonance, Biomolecular; D010446:Peptide Fragments / Q000737:chemistry; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary
chemical_list: D000596:Amino Acids; D000682:Amyloid; D016229:Amyloid beta-Peptides; D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D010446:Peptide Fragments; D010455:Peptides; C078592:amyloid beta-protein (1-40)