@article {431,
	title = {Second-order recoupling of chemical-shielding and dipolar-coupling tensors under spin decoupling in solid-state NMR},
	journal = {Journal of Chemical Physics},
	volume = {105},
	year = {1996},
	note = {J Chem PhysVd768Times Cited:55Cited References Count:53},
	month = {Sep 1},
	pages = {3387-3397},
	abstract = {<p>The source of the residual line broadening in continuous-wave (cw) decoupled spectra under magic-angle sample spinning conditions is reexamined. It is shown that an important contribution to the line broadening comes from a second-order recoupling of the heteronuclear dipolar-coupling tensor and the chemical-shielding tensor of the irradiated spin. Such an interference between the two tensors leads to a sum of a zeroth-rank, a second-rank, and a fourth-rank tensor component in the Hamiltonian. The zeroth-rank and the fourth-rank tensor components are not averaged out under magic-angle sample spinning (MAS) conditions, requiring the use of higher-order averaging such as double rotation (DOR) for obtaining narrow lines. This broadening is distinctly different from off-resonance decoupling effects which transform as a second-rank tensor and can be averaged out by MAS. The properties of this second-order recoupling as a source of structural information are explored, and the conditions for removing the broadening in systems with weak homonuclear dipolar-coupling networks are discussed. (C) 1996 American Institute of Physics.</p>
},
	keywords = {waltz-16},
	isbn = {0021-9606},
	doi = {Doi 10.1063/1.472224},
	url = {<Go to ISI>://WOS:A1996VD76800005},
	author = {Ernst, M. and Bush, S. and Kolbert, A. C. and Pines, A.}
}
@article {429,
	title = {Solid-state NMR studies of the prion protein H1 fragment},
	journal = {Protein Science},
	volume = {5},
	year = {1996},
	note = {Protein SciVa138Times Cited:74Cited References Count:53},
	month = {Aug},
	pages = {1655-1661},
	abstract = {<p>Conformational changes in the prion protein (PrP) seem to be responsible for prion diseases. We have used conformation-dependent chemical-shift measurements and rotational-resonance distance measurements to analyze the conformation of solid-state peptides lacking long-range order, corresponding to a region of PrP designated H1. This region is predicted to undergo a transformation of secondary structure in generating the infectious form of the protein. Solid-state NMR spectra of specifically C-13-enrrched samples of H1, residues 109-122 (MKHMAGAAAAGAVV) of Syrian hamster PrP, have been acquired under cross-polarization and magic-angle spinning conditions. Samples lyophilized from 50\% acetonitrile/50\% water show chemical shifts characteristic of a beta-sheet conformation in the region corresponding to residues 112-121, whereas samples lyophilized from hexafluoroisopropanol display shifts indicative of alpha-helical secondary structure in the region corresponding to residues 113-117. Complete conversion to the helical conformation was not observed and conversion from alpha-helix back to beta-sheet, as inferred from the solid-state NMR spectra, occurred when samples were exposed to water. Rotational-resonance experiments were performed on seven doubly C-13-labeled H1 samples dried from water. Measured distances suggest that the peptide is in an extended, possibly beta-strand, conformation. These results are consistent with the experimental observation that PrP can exist in different conformational states and with structural predictions based on biological data and theoretical modeling that suggest that H1 may play a key role in the conformational transition involved in the development of prion diseases.</p>
},
	keywords = {alpha-helices},
	isbn = {0961-8368},
	url = {<Go to ISI>://WOS:A1996VA13800019},
	author = {Heller, J. and Kolbert, A. C. and Larsen, R. and Ernst, M. and Bekker, T. and Baldwin, M. and Prusiner, S. B. and Pines, A. and Wemmer, D. E.}
}
