@article {335, title = {Diamagnetic clusters of paramagnetic endometallofullerenes: A solid-state MAS NMR study}, journal = {Journal of Physical Chemistry B}, volume = {108}, year = {2004}, note = {J Phys Chem B846BKTimes Cited:10Cited References Count:39}, month = {Aug 19}, pages = {12450-12455}, abstract = {

Solid powder samples of complexes of the endometallofullerenes (EMF) La@C-82 and Y@C-82 with hexamethylphosphoramide (HMPA) were studied by magic-angle spinning (MAS) NMR. We have obtained well-resolved P-31 NMR spectra and C-13 NMR spectra for both La-EMF/HMPA and Y-EMF/HMPA and La-139 spectra for the La-EMF/HMPA. The (31)p measurements on La-EMF/HMPA and Y-EMF/HMPA have revealed considerable chemical shifts of (31)p signals relative to pure HMPA. Two-dimensional exchange P-31 experiments revealed that HMPA molecules at different sites in the EMF/HMPA complex do not change positions at a time scale of up to 1 s. Both EMF samples demonstrate a vast chemical shift range for 31p of the bound HMPA molecules. In addition, the La-EMF/HMPA exhibits the enormous spreading of the chemical shifts for La-139. The experimental results suggest that paramagnetic La@C-82 and Y@C-92 in the solid state form clusters (nanoparticles) in which the exchange coupling of the EMF takes place with quenching of the most electron spins.

}, keywords = {complexes}, isbn = {1520-6106}, doi = {Doi 10.1021/Jp048610z}, url = {://WOS:000223289500027}, author = {Koltover, V. K. and Logan, J. W. and Heise, H. and Bubnov, V. P. and Estrin, Y. I. and Kareev, I. E. and Lodygina, V. P. and Pines, A.} } @article {348, title = {Reintroducing anisotropic interactions in magic-angle-spinning NMR of half-integer quadrupolar nuclei: 3D MQMAS}, journal = {Journal of the American Chemical Society}, volume = {124}, year = {2002}, note = {J Am Chem Soc591GWTimes Cited:14Cited References Count:21}, month = {Sep 11}, pages = {10652-10653}, keywords = {redor}, isbn = {0002-7863}, doi = {Doi 10.1021/Ja027043v}, url = {://WOS:000177872200011}, author = {Wi, S. and Heise, H. and Pines, A.} } @article {362, title = {Two-dimensional high-resolution NMR spectra in matched B-0 and B-1 field gradients}, journal = {Journal of Magnetic Resonance}, volume = {156}, year = {2002}, note = {J Magn Reson568UETimes Cited:15Cited References Count:26}, month = {May}, pages = {146-151}, abstract = {

In a recent publication we presented a method to obtain highly resolved NMR spectra in the presence of an inhomogeneous B-0 field with the help of a matched RF gradient. If RF gradient pulses are combined with \"ideal\" 90degrees pulses to form inhomogeneous z rotation pulses, the line broadening caused by the B-0 gradient can be refocused, while the full chemical shift information is maintained. This approach is of potential use for NMR spectroscopy in an inhomogeneous magnetic field produced by an \"ex-situ\" surface spectrometer. In this contribution, we extend this method toward two-dimensional spectroscopy with high resolution in one or both dimensions. Line narrowing in the indirect dimension can be achieved by two types of nutation echoes, thus leading to depth-sensitive NMR spectra with full chemical shift information. If the nutation echo in the indirect dimension is combined with a stroboscopic acquisition using inhomogeneous z-rotation pulses, highly resolved two-dimensional correlation spectra can be obtained in matched field gradients. Finally, we demonstrate that an INEPT coherence transfer from proton to carbon spins is possible in inhomogeneous B-0 fields. Thus, it is possible to obtain one-dimensional C-13 NMR spectra with increased sensitivity and two-dimensional HETCOR spectra in the presence of B-0 gradients of 0.4 mT/cm. These schemes may be of some value for ex-situ NMR analysis of materials and biological systems. (C) 2002 Elsevier Science (USA).

}, keywords = {echoes}, isbn = {1090-7807}, doi = {Doi 10.1006/Jmre.2002.2545}, url = {://WOS:000176562100016}, author = {Heise, H. and Sakellariou, D. and Meriles, C. A. and Moule, A. and Pines, A.} } @article {369, title = {Approach to high-resolution ex situ NMR spectroscopy}, journal = {Science}, volume = {293}, year = {2001}, note = {Science451BBTimes Cited:109Cited References Count:20}, month = {Jul 6}, pages = {82-85}, abstract = {

Nuclear magnetic resonance (NMR) experiments are typically performed with samples immersed in a magnet shimmed to high homogeneity. However, there are many circumstances in which it is impractical or undesirable to insert objects or subjects into the bore of a high-field magnet. Here we present a methodology based on an adaptation of nutation echoes that provides resolved spectra in the presence of matched inhomogeneous static and radiofrequency fields, thereby opening the way to high-resolution exsitu NMR, The observation of chemical shifts is regained through the use of multiple-pulse sequences of correlated, composite z-rotation pulses, producing resolved NMR spectra of liquid samples.

}, keywords = {echoes}, isbn = {0036-8075}, doi = {Doi 10.1126/Science.1061498}, url = {://WOS:000169780300032}, author = {Meriles, C. A. and Sakellariou, D. and Heise, H. and Moule, A. J. and Pines, A.} }