@article {434, title = {Rotational diffusion measurements of suspended colloidal particles using two-dimensional exchange nuclear magnetic resonance}, journal = {Journal of Chemical Physics}, volume = {104}, year = {1996}, note = {J Chem PhysTn837Times Cited:13Cited References Count:24}, month = {Jan 8}, pages = {509-520}, abstract = {

We present here an experimental and theoretical study of the application of two-dimensional exchange nuclear magnetic resonance spectroscopy (NMR) to the investigation of the rotational diffusion of colloidal particles. The theoretical discussion includes the nature of the NMR frequency time-correlation function where the NMR interaction is represented by the chemical shift anisotropy (CSA). Time-correlation functions for the isotropic rotational diffusion of a suspension of colloidal particles containing single and multiple sites are derived in addition to time-correlation functions for the rotational diffusion of a suspension of symmetric top particles containing an isotropic distribution of a single CSA interaction. Simulations of two-dimensional exchange spectra for particles undergoing isotropic rotational diffusion are presented. We performed two-dimensional exchange NMR experiments on a colloidal suspension of spherical poly(methyl methacrylate) (PMMA) particles which were synthesized with a 20\% enrichment in C-13 at the carbonyl site. Rotational diffusion time-correlation functions determined from the experimental exchange spectra are consistent with the composition of the colloidal suspension. Detailed explanations of the syntheses of the enriched methyl C-13-(carbonyl)-methacrylate monomer and the small quantities of 20\% enriched C-13-(carbonyl)-poly(methyl methacrylate) microspheres used for this study are presented. (C) 1996 American Institute of Physics.

}, keywords = {scattering}, isbn = {0021-9606}, doi = {Doi 10.1063/1.470847}, url = {://WOS:A1996TN83700009}, author = {Barrall, G. A. and Schmidt-Rohr, K. and Lee, Y. K. and Landfester, K. and Zimmermann, H. and Chingas, G. C. and Pines, A.} } @article {449, title = {C-13 Chemical-Shift Tensor Correlation Via Spin-Diffusion in Solid Tropolone Using Switched-Angle Spinning Spectroscopy}, journal = {Journal of Chemical Physics}, volume = {103}, year = {1995}, note = {J Chem PhysTh657Times Cited:7Cited References Count:42}, month = {Dec 8}, pages = {9844-9854}, abstract = {

In switched-angle spinning spectroscopy (SAS) a sample is spun about different angles, beta, relative to the magnetic field, during various periods of the experiment. In the present work, SAS is combined with two-dimensional exchange spectroscopy in order to correlate carbon-13 chemical shift tensors of the carbonyl (1) and hydroxyl (2) carbons of tropolone. Experiments were performed on a sample enriched to 25 at. \% in each of these sites (at different molecules). At this level of enrichment the dominant exchange mechanism between the two sites involves spin diffusion, The experiment consists of a preparation period during which the sample spins at the magic angle and the magnetization of one of the sites is quenched by means of a selective pulse sequence. During the rest of the experiment the sample spins with its axis away from the magic angle except for a short period just before the detection where the axis is switched to the magic angle in order to select the magnetization to be detected. Experiments were performed for all four possible combinations of the initial and final magnetizations, thus providing chemical shift correlations between carbons 1,1\&$\#$39;,2, and 2\&$\#$39; in the two magnetically inequivalent (but symmetry related) molecules in the unit cell. Combining these results with the known crystal structure of tropolone (neglecting a small tilt between the perpendicular to the molecular plane and the crystallographic c-axis) provides information on the orientation and magnitude of the chemical shift tensors of the two types of carbons, The principal values (in ppm) are sigma(xx)(1)=65, sigma(yy)(1)=33, sigma(zz)(1)=-98, sigma(xx)(2)=77, sigma(yy)(2)=17, and sigma(zz)(2)=-94. Assuming sigma(zz) to be perpendicular to the molecular plane, the orientations of the sigma(yy) s\&$\#$39; are 12 degrees off the C-1=0 bond (toward the hydroxyl carbon) for carbon 1 and 10 degrees off the C-3=C-2 bond (away from the carbonyl carbon) for carbon 2. (C) 1995 American Institute of Physics.

}, keywords = {spectra}, isbn = {0021-9606}, doi = {Doi 10.1063/1.469951}, url = {://WOS:A1995TH65700040}, author = {Larsen, R. G. and Lee, Y. K. and He, B. and Yang, J. O. and Luz, Z. and Zimmermann, H. and Pines, A.} } @article {448, title = {Linear Prediction with Singular-Value Decomposition for Removing Phase Artifacts in 2d Vacsy Spectra}, journal = {Journal of Magnetic Resonance Series A}, volume = {112}, year = {1995}, note = {J Magn Reson Ser AQd079Times Cited:8Cited References Count:20}, month = {Jan}, pages = {112-117}, keywords = {signals}, isbn = {1064-1858}, doi = {Doi 10.1006/Jmra.1995.1018}, url = {://WOS:A1995QD07900018}, author = {Lee, Y. K. and Vold, R. L. and Hoatson, G. L. and Lin, Y. Y. and Pines, A.} } @article {461, title = {3-Dimensional Variable-Angle Nuclear-Magnetic-Resonance Exchange Spectroscopy without Rotor Axis Hopping}, journal = {Journal of Chemical Physics}, volume = {101}, year = {1994}, note = {J Chem PhysNy002Times Cited:12Cited References Count:48}, month = {Aug 1}, pages = {1852-1864}, abstract = {

Slow, large-amplitude chain motions play an important role in determining the macroscopic mechanical properties of polymers. Although such motions have been studied quantitatively by two-dimensional (2D) nuclear: magnetic resonance (NMR) exchange experiments, overlapping anisotropic patterns hamper spectral analysis, and limit applications. Variable angle correlation spectroscopy (VACSY) has proven useful in resolving such problems for rapidly spinning samples by separating anisotropic spectral patterns according to isotropic chemical shifts. In a previous study [J. Am. Chem. Sec. 115, 4825 (1993)], we described a three-dimensional (3D) NMR experiment that incorporates; the VACSY method and a hop of the rotor axis to correlate the isotropic chemical shifts to 2D anisotropic exchange patterns. The hop of the rotor axis, however, presents experimental difficulties and limits the range of motional rates that may be studied. We present in this paper a new 3D VACSY exchange experiment that obtains the same correlations without the need for the rotor axis hop. A series of 2D exchange spectra are recorded with the sample spinning at different rotation axis angles.\&$\#$39; Then using the scaling of the anisotropic frequency at the different angles, we construct the data onto a 3D matrix so that a Fourier transformation directly yields the desired correlations. The technique is applied to C-13 exchange NMR to study the slow molecular motion of ordered isotactic polypropylene.

}, keywords = {distributions}, isbn = {0021-9606}, doi = {Doi 10.1063/1.467696}, url = {://WOS:A1994NY00200011}, author = {Lee, Y. K. and Emsley, L. and Larsen, R. G. and Schmidt-Rohr, K. and Hong, M. and Frydman, L. and Chingas, G. C. and Pines, A.} } @article {478, title = {Pure-Absorption-Mode Lineshapes and Sensitivity in 2-Dimensional Dynamic-Angle Spinning Nmr}, journal = {Journal of Magnetic Resonance Series A}, volume = {103}, year = {1993}, note = {J Magn Reson Ser ALj625Times Cited:98Cited References Count:20}, month = {Jun 1}, pages = {72-81}, keywords = {nuclei}, isbn = {1064-1858}, doi = {Doi 10.1006/Jmra.1993.1132}, url = {://WOS:A1993LJ62500010}, author = {Grandinetti, P. J. and Baltisberger, J. H. and Llor, A. and Lee, Y. K. and Werner, U. and Eastman, M. A. and Pines, A.} } @article {477, title = {Side-Band Patterns in Dynamic-Angle-Spinning Nmr}, journal = {Journal of Magnetic Resonance Series A}, volume = {102}, year = {1993}, note = {J Magn Reson Ser AKz480Times Cited:19Cited References Count:26}, month = {Apr}, pages = {195-204}, keywords = {samples}, isbn = {1064-1858}, doi = {Doi 10.1006/Jmra.1993.1091}, url = {://WOS:A1993KZ48000011}, author = {Grandinetti, P. J. and Lee, Y. K. and Baltisberger, J. H. and Sun, B. Q. and Pines, A.} } @article {480, title = {Variable-Angle 3-Dimensional Exchange Nuclear-Magnetic-Resonance Spectroscopy for the Study of Molecular-Motion in Complex Solids}, journal = {Journal of the American Chemical Society}, volume = {115}, year = {1993}, note = {J Am Chem SocLf062Times Cited:14Cited References Count:23}, month = {Jun 2}, pages = {4825-4829}, abstract = {

Although molecular motions are responsible for many of the macroscopic properties observed in solids, especially in polymers, methods for studying these processes in all but the simplest systems are scarce. In the present study we introduce a three-dimensional nuclear magnetic resonance experiment for characterizing ultraslow molecular motions in complex solid systems. The technique extracts dynamic information by resolving the two-dimensional exchange distributions that can be observed in spectra of static samples, according to the isotropic chemical shifts of individual molecular sites. These three-dimensional correlations are achieved by processing signals arising from a fast-spinning solid sample using two independent macroscopic axes of rotation as extraction parameters, an approach which becomes practical due to the simple scaling behavior of anisotropic chemical shifts with respect to the axis of sample rotation. The principles involved in this new spectroscopic technique are discussed, and the method is illustrated with an application to the analysis of motions in isotactic polypropylene.

}, keywords = {jumps}, isbn = {0002-7863}, doi = {Doi 10.1021/Ja00064a050}, url = {://WOS:A1993LF06200050}, author = {Frydman, L. and Lee, Y. K. and Emsley, L. and Chingas, G. C. and Pines, A.} } @article {496, title = {Correlation of Isotropic and Anisotropic Chemical-Shifts in Solids by 2-Dimensional Variable-Angle-Spinning Nmr}, journal = {Israel Journal of Chemistry}, volume = {32}, year = {1992}, note = {Israel J ChemKt517Times Cited:29Cited References Count:19}, pages = {161-164}, abstract = {

We describe a new solid-state nuclear magnetic resonance (NMR) technique for correlating anisotropic and isotropic chemical shifts in powdered samples. Two-dimensional (2D) NMR spectra are obtained by processing signals acquired in independent experiments for different angles between the sample spinning axis and the Zeeman magnetic field. This 2D NMR approach can therefore resolve individual static anisotropic lineshapes according to their isotropic chemical shift frequencies, without use of sudden mechanical motions or multiple-pulse irradiation schemes. Applications of the technique are illustrated with an analysis of the chemical shift anisotropy for the eight distinct C-13 sites in tyrosine.

}, keywords = {magic-angle}, isbn = {0021-2148}, url = {://WOS:A1992KT51700005}, author = {Frydman, L. and Chingas, G. C. and Lee, Y. K. and Grandinetti, P. J. and Eastman, M. A. and Barrall, G. A. and Pines, A.} } @article {499, title = {Double-Tuned Hopping-Coil Probe for Dynamic-Angle-Spinning Nmr}, journal = {Journal of Magnetic Resonance}, volume = {98}, year = {1992}, note = {J Magn ResonHz623Times Cited:29Cited References Count:13}, month = {Jun 15}, pages = {333-341}, keywords = {axis}, isbn = {0022-2364}, doi = {Doi 10.1016/0022-2364(92)90136-U}, url = {://WOS:A1992HZ62300008}, author = {Eastman, M. A. and Grandinetti, P. J. and Lee, Y. K. and Pines, A.} } @article {497, title = {Variable-Angle Correlation Spectroscopy in Solid-State Nuclear-Magnetic-Resonance}, journal = {Journal of Chemical Physics}, volume = {97}, year = {1992}, note = {J Chem PhysJr338Times Cited:90Cited References Count:28}, month = {Oct 1}, pages = {4800-4808}, abstract = {

We describe here a new solid-state nuclear-magnetic-resonance (NMR) experiment for correlating anisotropic and isotropic chemical shifts of inequivalent nuclei in powdered samples. Spectra are obtained by processing signals arising from a spinning sample, acquired in independent experiments as a function of the angle between the axis of macroscopic rotation and the external magnetic field. This is in contrast to previously proposed techniques, which were based on sudden mechanical flippings or multiple-pulse sequences. We show that the time evolution of variable-angle-spinning signals is determined by a distribution relating the isotropic frequencies of the spins with their corresponding chemical shift anisotropies. Fourier transformation of these data therefore affords a two-dimensional NMR spectrum, in which line shapes of isotropic and anisotropic interactions are correlated. Theoretical and experimental considerations involved in the extraction of this spectral information are discussed, and the technique is illustrated by an analysis of C-13 NMR anisotropy in glycine, cysteine, and p-anisic acid.

}, keywords = {axis}, isbn = {0021-9606}, doi = {Doi 10.1063/1.463860}, url = {://WOS:A1992JR33800022}, author = {Frydman, L. and Chingas, G. C. and Lee, Y. K. and Grandinetti, P. J. and Eastman, M. A. and Barrall, G. A. and Pines, A.} }