@article {428, title = {Application of rotational resonance to inhomogeneously broadened systems}, journal = {Chemical Physics Letters}, volume = {251}, year = {1996}, note = {Chem Phys LettUd924Times Cited:17Cited References Count:28}, month = {Mar 22}, pages = {223-229}, abstract = {

A protocol is presented for the determination of internuclear distances using rotational-resonance magnetization-exchange NMR in systems with inhomogeneously broadened lines. Non-linear least-square fitting procedures are used to obtain the distance, the inhomogeneous broadening, the zero-quantum relaxation time, and error estimates for these parameters. We apply this procedure to a biological system of unknown structure.

}, keywords = {nmr}, isbn = {0009-2614}, doi = {Doi 10.1016/0009-2614(96)00098-X}, url = {://WOS:A1996UD92400015}, author = {Heller, J. and Larsen, R. and Ernst, M. and Kolbert, A. C. and Baldwin, M. and Prusiner, S. B. and Wemmer, D. E. and Pines, A.} } @article {430, title = {Isotropic second-order dipolar shifts in the rotating frame}, journal = {Journal of Chemical Physics}, volume = {104}, year = {1996}, note = {J Chem PhysUm909Times Cited:9Cited References Count:44}, month = {Jun 1}, pages = {8258-8268}, abstract = {

An experiment is described that utilizes the truncation of the Hamiltonian in the rotating frame by a radio-frequency field designed to yield an isotropic shift for the dipolar coupling. This approach allows the measurement of a normally orientation-dependent coupling constant by a single isotropic value. The dipolar isotropic shift is closely related to the field-dependent chemical shift in solids due to the second-order dipolar perturbation observed in magic-angle spinning experiments. In the rotating frame, larger shifts of up to 1000 Hz can be observed for the case of a one-bond C-H coupling compared to a shift of a few Hertz in the laboratory-frame experiment. In addition to the isotropic shift, a line broadening due to the P-4(cos beta) terms is observed when the experiment is carried out under magic-angle sample spinning (MAS) conditions, leading to the requirement of higher-order averaging such as double rotation (DOR) for obtaining narrow lines. As an application of this new experiment the separation of CH, CH2, and CH3 groups in a 2D spectrum under MAS is demonstrated. Implemented under DOR it could be used as a technique to select carbon atoms according to the number of directly attached protons. (C) 1996 American Institute of Physics.

}, keywords = {spins}, isbn = {0021-9606}, doi = {Doi 10.1063/1.471579}, url = {://WOS:A1996UM90900008}, author = {Ernst, M. and Kolbert, A. C. and Schmidt-Rohr, K. and Pines, A.} } @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 = {

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.

}, keywords = {waltz-16}, isbn = {0021-9606}, doi = {Doi 10.1063/1.472224}, url = {://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 = {

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.

}, keywords = {alpha-helices}, isbn = {0961-8368}, url = {://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.} } @article {441, title = {Magnetic-Resonance Evidence for Metallic State in Highly Conducting Polyaniline}, journal = {Synthetic Metals}, volume = {69}, year = {1995}, note = {Synthetic MetQl601Times Cited:9Cited References Count:12}, month = {Mar 1}, pages = {243-244}, abstract = {

Polyaniline doped with camphor sulfonic acid (PANI-CSA) has been shown to yield a material which, after processing from solutions in meta-cresol, exhibit a temperature independent magnetic susceptibility down to 50K. Below 50K a Curie like contribution sets in. We also report C-13 NMR experiments which clearly show that the C-13 spin lattice relaxation rates obey the Korringa relation for relaxation via the hyperfine coupling to conduction electrons.

}, keywords = {polymers}, isbn = {0379-6779}, doi = {Doi 10.1016/0379-6779(94)02435-2}, url = {://WOS:A1995QL60100097}, author = {Sariciftci, N. S. and Kolbert, A. C. and Cao, Y. and Heeger, A. J. and Pines, A.} } @article {463, title = {Measurement of Internuclear Distances by Switched Angle Spinning Nmr}, journal = {Journal of Physical Chemistry}, volume = {98}, year = {1994}, note = {J Phys Chem-UsPc619Times Cited:11Cited References Count:20}, month = {Aug 18}, pages = {7936-7938}, abstract = {

Dipolar switched angle spinning, an NMR technique due to Terao et al. [Terao, T.; Miura H.; Saika, A, J. Chem. Phys. 1986, 85, 3816], has been used to measure C-13-C-13 distances in the solid state. The experiment involves rotation of the sample at two different angles during different periods of a two-dimensional experiment. An evolution period with off-magic-angle spinning and chemical shift refocusing, followed by detection of the signal under magic angle spinning, yields scaled Pake patterns in omega(1), correlated with their isotropic shifts in omega(2) allowing the high-resolution measurement of dipolar couplings. We demonstrate this experiment on samples of doubly C-13 labeled zinc acetate and a 14 amino acid peptide, in which we show that under optimal conditions distances of up to 5 Angstrom may be measured.

}, keywords = {protein}, isbn = {0022-3654}, doi = {Doi 10.1021/J100084a003}, url = {://WOS:A1994PC61900003}, author = {Kolbert, A. C. and Grandinetti, P. J. and Baldwin, M. and Prusiner, S. B. and Pines, A.} }