@article {383,
	title = {Investigation of slow molecular motions and chemical exchange in the high loaded form of p-xylene in ZSM-5 by two-dimensional C-13 solid-state NMR exchange experiments},
	journal = {Journal of Physical Chemistry B},
	volume = {106},
	number = {9},
	year = {2002},
	note = {ISI Document Delivery No.: 531ENTimes Cited: 6Cited Reference Count: 37},
	month = {Mar},
	pages = {2261-2268},
	type = {Article},
	abstract = {The slow molecular motions and exchange processes in the high loaded form of p-xylene in zeolite ZSM-5 have been investigated by a variety of solid-state NMR techniques. The C-13 CP MAS NMR spectra of [13C, CH3] p-xylene show four resonances in the slow exchange limit, reflecting the four inequivalent methyl positions in the two organic molecules in the asymmetric unit. From the known assignment of the silicon resonances in the MAS NMR spectrum, the four carbon signals were assigned from the cross-correlations in a H-1/C-13/ Si-29 2D CP TEDOR experiment. Using this information, the chemical exchange processes between the methyls was invesitgated by a series of 2D CP NOESY experiments with different mixing times at different temperatures. Two types of processes were identified: intramolecular exchanges with activation energies of 65 +/- 2 kJ/m for the molecule in the zigzag channel and 56 +/-13 kJ/m for the molecule in the straight channel (the substantial error in the latter value reflecting the very limited temperature range over which measurements can be made). There is also intermolecular exchange between the two molecules with a much higher energy barrier. Possible mechanisms for the exchanges and the implications of slow motional processes for the use of solid-state NMR for the determination of sorbate/frame work structures are discussed.},
	keywords = {DOUBLE-RESONANCE NMR, NA-A ZEOLITE, SPECTROSCOPY, XENON DYNAMICS},
	isbn = {1520-6106},
	url = {<Go to ISI>://000174403200022},
	author = {Fyfe, C. A. and Diaz, A. C.}
}
@article {4815,
	title = {Investigation of the viability of solid-state NMR distance determinations in multiple spin systems of unknown structure},
	journal = {Journal of Physical Chemistry B},
	volume = {104},
	number = {1},
	year = {2000},
	note = {ISI Document Delivery No.: 283BJTimes Cited: 26Cited Reference Count: 37},
	month = {Jan},
	pages = {48-55},
	type = {Article},
	abstract = {This paper presents theoretical rotational-echo double-resonance (REDOR) and transferred-echo double-resonance (TEDOR) curves calculated for several three-spin systems and explores the potential for determining reliable distances in multiple-spin systems of unknown geometry. These NMR techniques can provide distances which compare very well with those obtained by X-ray diffraction if the samples contain isolated heteronuclear (IS) spin pairs and are currently being used in structural investigations of solids including peptides, polymers, and inorganic materials. The situation is less clear when small clusters of spins (e.g., INS systems) are present, and although the multispin dephasing can be calculated, very few examples have been reported in the literature. In most cases the spin system geometry was known before analysis of the NMR data, thus it is unclear whether reliable distances can be determined when the geometry of the spin system is completely unknown. To investigate the uniqueness of distance determinations from fitting of multispin REDOR and TEDOR data, the theoretical dephasing was calculated for a selection of I2S systems. The effects of varying the two I-S dipolar couplings and the I-A-S-I-B angle, zeta, were studied. The full range of zeta (0 degrees less than or equal to zeta less than or equal to 180 degrees) was considered, and the magnitudes of the dipolar couplings selected are typical of couplings expected for commonly studied nuclei. A variation of 10 degrees or more is required to effect a noticeable change and the dephasing is identical for zeta and 180 degrees - zeta. The most distinctive behavior is observed when zeta is small (or close to 180 degrees), otherwise there are quite minor differences. Spin systems with quite different geometries may exhibit very similar dephasing, and in some cases the curves are identical to those for an isolated IS spin pair. These calculations indicate that it is highly unlikely that reliable distances can be obtained directly from REDOR and TEDOR experiments on multiple spin systems when the number of spins and their geometrical arrangement is completely unknown. Furthermore, it is possible to obtain incorrect distances if isolated spin pairs are assumed and multiple spins are present.},
	keywords = {COMPLEX, DOUBLE-RESONANCE NMR, ECHO DOUBLE-RESONANCE, NMR, NUCLEI, QUADRUPOLAR, REDOR, ROTATIONAL-ECHO, zeolites},
	isbn = {1089-5647},
	url = {<Go to ISI>://000085256000007},
	author = {Fyfe, C. A. and Lewis, A. R.}
}
@article {4702,
	title = {Ordering of silicate layers by hydrogen-bonding networks: Solid state NMR investigation of the perfect three-dimensional registration in the layer silicate RUB-18},
	journal = {Journal of Physical Chemistry B},
	volume = {103},
	number = {29},
	year = {1999},
	note = {ISI Document Delivery No.: 222CMTimes Cited: 24Cited Reference Count: 12},
	month = {Jul},
	pages = {5933-5938},
	type = {Article},
	abstract = {Solid state H-1 and Si-29 NMR spectroscopies were applied to the layer silicate RUB-18 in order to investigate the hydrogen bonding network providing the three-dimensional ordering of the silicate layers. Two H-1 NMR signals corresponding to water molecules and strongly hydrogen-bonded silanol groups were resolved, the relative intensities of which are in good agreement with the recently proposed structure. By means of two-dimensional heteronuclear correlation NMR, the protons in hydroxyl groups are clearly identified as the source of polarization transfer to the Si-29 nuclei of the silicate layer. The dynamics of the exchange process between the protons in hydroxyl groups and those in the water molecules were investigated by two-dimensional H-1 exchange spectroscopy, giving insight into the nature of the exchange process-chemical exchange or spin diffusion. In addition, the ratio of exchanging protons of the two species has been found to differ from the stoichiometric ratio. Si-29 cross-polarization/magic angle spinning (CP MAS) NMR spectra taken at temperatures down to 140 K lead to enhanced resolution in the spectral region of Q(4) silicons, whereas the signal from Q(3) silicons remains unaffected. The potential applicability of solid-state NMR methods for measuring internuclear distances in this material is discussed.},
	keywords = {DOUBLE-RESONANCE NMR},
	isbn = {1089-5647},
	url = {<Go to ISI>://000081765900004},
	author = {Wolf, I. and Gies, H. and Fyfe, C. A.}
}
@article {3979,
	title = {F-19/Si-29 distance determinations in fluoride-containing octadecasil from solid-state NMR measurements},
	journal = {Journal of the American Chemical Society},
	volume = {119},
	number = {50},
	year = {1997},
	note = {ISI Document Delivery No.: YN229Times Cited: 48Cited Reference Count: 76},
	month = {Dec},
	pages = {12210-12222},
	type = {Article},
	abstract = {In the present work we report results from CP, REDOR, and TEDOR NMR experiments carried out to locate the fluoride anions within the three-dimensional framework of the silicate octadecasil. Accurate Si-F distances were obtained-through measurements of the F-19/Si-29 dipolar couplings from these experiments. Weighted, nonlinear least-squares fittings of the REDOR and TEDOR data for the silicons in the D4R units gave an average value of D = 1150 +/- 50 Hz from which the Si-F interatomic distance was calculated to be 2.69 +/- 0.04 Angstrom. This distance is in excellent agreement with the value of 2.63 Angstrom reported from the X-ray determined single crystal structure-and confirms that the F- anions are located inside the D4R units. Calculations and fittings of the REDOR and TEDOR data for the silicons not in the D4R gave = 120 +/- 20 Hz when the specific geometrical (tetrahedral) arrangement of the multiple equivalent fluoride anions surrounding the Si nuclei in these T-2 sites was taken into account. This yields a Si-F distance of 5.7 +/- 0.4 Angstrom, compared to the value 5.69 Angstrom obtained from the diffraction measurements. Factors influencing the selection of the optimum experiments to perform in different situations and the dependence of the results on experimental variables are discussed. These studies clearly establish the viability and reliability of F-19/Si-29 REDOR and TEDOR NMR experiments to obtain distance information which can be used to determine the precise location of fluorine-containing species within such framework structures or in suitable cases to assist in the determination of the framework structure itself where it is unknown.},
	keywords = {3-DIMENSIONAL LATTICE CONNECTIVITIES, CROSS-POLARIZATION, CRYSTAL-STRUCTURE, DOUBLE-RESONANCE NMR, INTERATOMIC DISTANCE, MICROPOROUS, MOLECULAR-SIEVE, P-DICHLOROBENZENE, ROTATIONAL-ECHO, SINGLE-CRYSTAL, SOLIDS},
	isbn = {0002-7863},
	url = {<Go to ISI>://000071146000024},
	author = {Fyfe, C. A. and Lewis, A. R. and Chezeau, J. M. and Grondey, H.}
}
@article {3338,
	title = {INEPT EXPERIMENTS IN SOLID-STATE NMR},
	journal = {Journal of the American Chemical Society},
	volume = {117},
	number = {41},
	year = {1995},
	note = {ISI Document Delivery No.: TB353Times Cited: 38Cited Reference Count: 16},
	month = {Oct},
	pages = {10397-10398},
	type = {Note},
	keywords = {DOUBLE-RESONANCE NMR, ENHANCEMENT, HELICAL PEPTIDE, INTERATOMIC DISTANCE, NUCLEI, POLARIZATION TRANSFER, QUADRUPOLAR, REDOR, SIGNALS, VPI-5},
	isbn = {0002-7863},
	url = {<Go to ISI>://A1995TB35300031},
	author = {Fyfe, C. A. and Wongmoon, K. C. and Huang, Y. and Grondey, H.}
}
@article {3042,
	title = {INCREASED EFFICIENCY OF COHERENCE TRANSFER IN CROSS-POLARIZATION NMR FROM QUADRUPOLAR NUCLEI - DYNAMIC-ANGLE CROSS-POLARIZATION},
	journal = {Journal of Physical Chemistry},
	volume = {98},
	number = {8},
	year = {1994},
	note = {ISI Document Delivery No.: MY355Times Cited: 9Cited Reference Count: 26},
	month = {Feb},
	pages = {2139-2142},
	type = {Article},
	abstract = {In this work we describe the increased efficiency obtained in solid-state coherence-transfer NMR experiments involving quadrupolar nuclei by carrying out cross-polarization while the sample is spinning along an axis parallel to the magnetic field. After the cross-polarization step, the spinning axis is rapidly switched to the {\textquoteright}{\textquoteright}magic angle{\textquoteright}{\textquoteright} for detection of a high-resolution free induction decay from the target nuclei. The increased efficiency of the cross-polarization process, coupled with the superior resolution available from magic-angle sample spinning, is useful for obtaining high-resolution NMR spectra of slowly-relaxing spin species in condensed phases. A specific example illustrating this method is drawn from the cross-polarization of magnetization from aluminum-27 spins to phosphorus-31 spins in the large-pore aluminophosphate VPI-5.},
	keywords = {DOUBLE-RESONANCE NMR, MOLECULAR-SIEVE VPI-5, PROTON-ENHANCED NMR, SOLIDS},
	isbn = {0022-3654},
	url = {<Go to ISI>://A1994MY35500028},
	author = {Fyfe, C. A. and Wongmoon, K. C. and Grondey, H. and Mueller, K. T.}
}
@article {7239,
	title = {DIPOLAR DEPHASING BETWEEN QUADRUPOLAR AND SPIN-1/2 NUCLEI - REDOR AND TEDOR NMR EXPERIMENTS ON VPI-5},
	journal = {Chemical Physics Letters},
	volume = {199},
	number = {1-2},
	year = {1992},
	note = {ISI Document Delivery No.: JV107Times Cited: 64Cited Reference Count: 21},
	month = {Oct},
	pages = {198-204},
	type = {Article},
	abstract = {In this work we examine the use of dipolar-dephasing magic-angle spinning NMR to study mixed pairs of quadrupolar and spin-1/2 nuclei in solids. Dipolar connectivities are examined in both directions between the Al-27(I=5/2) and P-31(I=1/2) spins in the very large pore aluminophosphate VPI-5, which is considered representative of a range of inorganic framework materials. Rotational-echo double-resonance (REDOR) and transferred-echo double-resonance (TEDOR) experiments are demonstrated, as well as a two-dimensional extension of the TEDOR experiment. These experiments restore the heteronuclear dipolar coupling under MAS conditions via a train of radiofrequency pulses, thereby providing information about connectivities and distances between coupled nuclei in these inorganic solids.},
	keywords = {ANGLE, COUPLINGS, DOUBLE-RESONANCE NMR, MAGIC, MAGNETIC-RESONANCE, SOLIDS, SPECTROSCOPY, TWO-DIMENSIONAL NMR},
	isbn = {0009-2614},
	url = {<Go to ISI>://A1992JV10700030},
	author = {Fyfe, C. A. and Mueller, K. T. and Grondey, H. and Wongmoon, K. C.}
}
