scholarly journals Methyl Group Rotation and Tunnellingin Crystals of 5-Membered Ring Molecules

1988 ◽  
Vol 43 (1) ◽  
pp. 35-42 ◽  
Author(s):  
A.-S. Montjoie ◽  
W. Müller-Warmuth ◽  
Hildegard Stiller ◽  
J. Stanislawski
Keyword(s):  
Elevated Temperatures ◽  
Inelastic Neutron Scattering ◽  
Relaxation Times ◽  
Nmr Relaxation ◽  
Lattice Relaxation ◽  
Inelastic Neutron ◽  
Spin Lattice Relaxation ◽  
Relaxation Rates ◽  
Quantum Tunnelling ◽  
Spin Lattice

Abstract1H NMR spin-lattice relaxation times T1 and -if accessible -level-crossing peaks and inelastic neutron scattering spectra have been measured for solid 2-and 3-methylfuran, 2-and 3-methylthiophene, 3-and 4-methylpyrazole, 1-methylimidazole, and 5-methylisoxazole. From the tunnel splittings, the torsional excitations and the NMR relaxation rates, the molecular dynamics of the methyl rotators has been evaluated between the limits of quantum tunnelling at low temperatures and thermally activated random reorientation at elevated temperatures.

Boron-11, boron-10, and nitrogen-14 NMR relaxation rates and quadrupole coupling constants in BH3NH3

1992 ◽  
Vol 70 (9) ◽  
pp. 2420-2423 ◽  
Author(s):  
Glenn H. Penner ◽  
Stephen I. Daleman ◽  
Angela R. Custodio
Keyword(s):  
Relaxation Times ◽  
Nmr Relaxation ◽  
Lattice Relaxation ◽  
Coupling Constants ◽  
Spin Lattice Relaxation ◽  
Relaxation Rates ◽  
Orbital Theory ◽  
Spin Lattice ◽  
Quadrupolar Coupling ◽  
Field Gradients

The 11B, 10B, and 14N spin–lattice relaxation times (T1) for aqueous solutions of BH3NH3 were measured by NMR spectroscopy. The results of this investigation are consistent with the nuclear quadrupolar coupling constants reported in previous nuclear quadrupolar resonance and microwave studies. The activation energy associated with rotational reorientation of BH3NH3 in aqueous solution is 11.7 ± 0.6 kJ/mol. Electric field gradients were calculated at various levels of abinitio molecular orbital theory, in order to obtain theoretical 14N and 11B quadrupolar coupling constants. At the highest level of calculation (CI(SD)/6-31G**//MP2/6-31G**), these are in agreement with recently reported microwave results but not with previously reported NQR experiments.

Ionic mobility in Nasicon-type LiMIV2(PO4)3 materials followed by 7Li NMR spectroscopy.

2011 ◽  
Vol 1313 ◽  
Author(s):  
K. Arbi ◽  
I. Sobrados ◽  
M. Hoelzel ◽  
A. Kuhn ◽  
F. Garcia-Alvarado ◽  
...  
Keyword(s):  
Nmr Spectroscopy ◽  
Impedance Spectroscopy ◽  
Nmr Relaxation ◽  
Lattice Relaxation ◽  
Ionic Mobility ◽  
Spin Lattice Relaxation ◽  
Pulse Field ◽  
Relaxation Rates ◽  
Arrhenius Behavior ◽  
Spin Lattice

AbstractLithium mobility in LiM2(PO4)3 compounds, with M= Ge, Ti, Sn, Zr and Hf, has been investigated by 7Li Nuclear Magnetic Resonance (NMR) spectroscopy in the temperature range 100-500 K. From the analysis of 7Li NMR quadrupole interactions (CQ and η parameters), Li sites occupancy and exchange processes between structural sites have been studied. Below 250K, Li ions are preferentially located at M1 sites in rhombohedral phases, but occupy M12 sites in triclinic ones. At increasing temperatures, Li mobility has been deduced from spin-spin () and spin-lattice relaxation () rates. In this analysis, the presence of two relaxation mechanisms in plots has been associated with departures of conductivity from the Arrhenius behavior. At high temperatures, residence times at M12−T11−T11−T1 and M12 sites become similar and conductivity significantly increase. This superionic state can be achieved by enlarged order-disorder transformations in rhombohedral phases, or by sharp first order transitions in triclinic ones. Results described in the LiTi2(PO4)3 sample have been compared with those obtained in rhombohedral Li1+xTi2-xAlx(PO4)3 and LiTi2-xZrx(PO4)3 series showing respectively higher and lower conductivities. In the case of Li1.2Ti1.8Al0.2(PO4)3, displaying the highest reported conductivity, NMR results are discussed in relation with those obtained by Neutron Diffraction (ND) and Impedance Spectroscopy (IS). Diffusion coefficients determined by NMR Pulse Field Gradient (PFG) technique are similar to those deduced from Impedance Spectroscopy and NMR relaxation data.

Spin–lattice relaxation and hydrodynamical rotation of triphenylene

1977 ◽  
Vol 55 (20) ◽  
pp. 3602-3608 ◽  
Author(s):  
Roderick E. Wasylishen ◽  
Brian A. Pettitt ◽  
Werner Danchura
Keyword(s):  
Nmr Relaxation ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Relaxation Rates ◽  
Hindered Rotation ◽  
Spin Lattice ◽  
Slip Boundary ◽  
The Times ◽  
Dynamic Rotation ◽  
C Nmr

The viscosity and temperature dependence of 1H, 2H, and 13C nmr relaxation rates of triphenylene were investigated. The observed η/T dependence of the reorientation correlation time, τc, is compared with that derived from the work of Hu and Zwanzig based on hydro–dynamic rotation with 'stick' and 'slip' boundary conditions. In the hydrodynamic regime,τ = Cη/T. The observed slope, Cexperimental, is 6.2 ± 2 ns K/cP and the calculated values are Cslip = 4.1 ± 0.6 ns K/cP and Cstick = 31.0 ± 3.1 ns K/cP. These data imply that the reorientation of triphenylene obeys a near-slip condition. That is, rotation in the plane of the molecule encounters little resistance, but rotation of the plane of the molecule is resisted by shear forces in the solvent displaced during rotation. Expressions are given for Boltzmann-averaged free rotation times and comparisons are made with the η = 0 intercept and the times for slightly hindered rotation.

scholarly journals Possibilities of proton magnetic resonance in determination the cellulose crystallinity

2019 ◽  
Vol 59 (8) ◽  
pp. 116-123
Author(s):  
Yury B. Grunin ◽  
◽  
Maria S. Ivanova ◽  
Keyword(s):  
Relaxation Time ◽  
Relaxation Times ◽  
Nmr Relaxation ◽  
Lattice Relaxation ◽  
Active Surface ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Cellulose Crystallinity ◽  
Spin Lattice ◽  
Free Induction

A layered model of the structural organization of macrofibrils of native cellulose, consisting of microfibrils, which include elementary fibrils, has been developed. A feature of the proposed model is the presence of slit-like pores between the crystalline elements of cellulose. It was found that, on average, each water molecule interacts with one glucose residue of the surface chains of cellulose with the formation of hydrogen bonds in the framework of monolayer adsorption. This allows to establish a correlation between the cellulose crystallinity and the capacity of the adsorption water monolayer on its active surface. Based on the condition of rapid molecular exchange between the adsorption water layers in the framework of the Bloembergen-Purcell-Pound theory, an approach is proposed for determination the capacity of water monolayer. The obtained values are consistent with the results of solving the Brunauer-Emmett-Teller equation for the adsorption isotherm of water on the active surface of cellulose. The Fourier transform of the free induction decay signal of cellulose allows to estimate its crystallinity at various moisture contents. Methods have been developed for assessing the crystallinity of different types of dry cellulose based on NMR relaxation parameters — spin-lattice relaxation time and spin-spin relaxation time. Using the method of deuteration of cellulose, the relaxation times of its crystalline regions were determined. The results of preliminary studies showed that the crystallinity of cotton cellulose is higher in comparison with the same parameter of woody types of cellulose. A comparison of the literature and the data we obtained using 1H-NMR relaxation confirmed the possibility of utilizing the developed methods to solve the tasks of scientific research and conducting quality control of cellulosic materials at specialized enterprises.

scholarly journals Hydrogen Vacancy Diffusion Parameters in ScH2-x and ScD2-x from 45Sc Spin-Lattice Relaxation Time Measurements

1985 ◽  
Vol 40 (3) ◽  
pp. 222-228
Author(s):  
M. Jerosch-Herold ◽  
L.-T. Lu ◽  
D. R. Torgeson ◽  
D. T. Peterson ◽  
R. G. Barnes ◽  
...  
Keyword(s):  
Inelastic Neutron Scattering ◽  
Lattice Relaxation ◽  
Inelastic Neutron ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Vacancy Diffusion ◽  
Arrhenius Behavior ◽  
Spin Lattice ◽  
Diffusion Parameters ◽  
Hydrogen Deuterium

The temperature dependence of the nuclear spin-lattice relaxation rate R1 of 45Sc has been measured in scandium dihydrides and dideuterides. These data are satisfactorily accounted for by two contributions to R1, R1e due to conduction electrons, and R1Q due to quadrupole interaction fluctuations resulting from vacancy diffusion on the hydrogen (deuterium) sublattice. Describing these fluctuations by a Lorentzian spectral density and Arrhenius behavior for the vacancy hopping, analysis of the data yields values of the Korringa product A = T/R1e and the activation energy Ea and attempt frequency v0 for vacancy-diffusion. In contrast to v0 values based on proton measurements, the 45Sc results agree satisfactorily with the value based on inelastic neutron scattering measurements of hydrogen optic mode vibration frequencies, v0 ≅ 2 x 1014s-1. We conclude that hydrogen-hydrogen interactions are responsible for the lower v0 values derived from proton R1 measurements.

Ionic Dynamics in Plastic Crystal KNO2 Studied by 39K and 15N NMR

1994 ◽  
Vol 49 (1-2) ◽  
pp. 247-252 ◽  
Author(s):  
Motoko Kenmotsu ◽  
Hisashi Honda ◽  
Hiroshi Ohki ◽  
Ryuichi Ikeda ◽  
Tomoki Erata ◽  
...  
Keyword(s):  
Intermediate Phase ◽  
Relaxation Times ◽  
Nmr Relaxation ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
15N Nmr ◽  
Temperature Phase ◽  
Self Diffusion ◽  
Spin Lattice

AbstractThe spin-lattice relaxation time of 39K NMR observed in the low-temperature phase (T<264.1 K) of KNO2 is explained by the quadrupole mechanism contributed from a newly found NO2- motion. The in-plane C3 reorientation and the overvall NO2 rotation as well as the self-diffusion were shown in the intermediate phase (T ≤ 314.7 K) and the high-temperature plastic phase (T < melting point: 710 K), respectively, by observing 39K and 15N NMR relaxation times and 15N lineshapes.

scholarly journals Permeation of small molecules into the cavity of ferritin as revealed by proton nuclear magnetic resonance relaxation

1995 ◽  
Vol 307 (1) ◽  
pp. 253-256 ◽  
Author(s):  
D Yang ◽  
K Nagayama
Keyword(s):  
Relaxation Times ◽  
Nmr Relaxation ◽  
Maximum Size ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Proton Nuclear Magnetic Resonance ◽  
Ferric Ions ◽  
Spin Lattice ◽  
Resonance Relaxation ◽  
Pass Through

The NMR relaxation technique was used to investigate the permeation of molecules into the cavity of ferritin. Spin-lattice relaxation times in the rotating frame of various probe molecules were measured for solutions of recombinant horse L-apoferritin without iron and horse spleen apoferritin with very small amounts of ferric ions. The results show that molecules larger than the size of the ferritin channels can pass through the channels into the ferritin interior, and that the maximum size of molecules for the permeation is smaller than maltotriose.

89Y AND 63Cu NMR-NQR AND SUSCEPTIBILITY STUDY OF UNDERDOPED SUPERCONDUCTING Y1-xCaxBa2Cu3O6.1

2000 ◽  
Vol 14 (25n27) ◽  
pp. 2797-2802 ◽  
Author(s):  
A. CAMPANA ◽  
P. CARRETTA ◽  
M. CORTI ◽  
A. LASCIALFARI ◽  
A. RIGAMONTI ◽  
...  
Keyword(s):  
Magnetic Moments ◽  
Nmr Relaxation ◽  
Lattice Relaxation ◽  
Superconducting Phase ◽  
Spin Fluctuations ◽  
Spin Lattice Relaxation ◽  
Freezing Process ◽  
Relaxation Rates ◽  
Spin Lattice ◽  
Spin Freezing

89 Y NMR relaxation has been used to study the spin freezing process in Y 1-x Ca x Ba 2 Cu 3 O 6.1. Substituting Ca 2+ for Y 3+ in the parent antiferromagnetic YBa 2 Cu 3 O 6.1 leads the system in the underdoped superconducting phase. In the normal state of the sample at x=0.15 the spin-lattice relaxation rate, which is not affected by the antiferromagnetic correlation of the Cu 2+ magnetic moments, still evidences a decrease of (1/ T 1 T ) on cooling, indicative of a pseudo-gap opening in the density of states around the Fermi energy. The most relevant result is found in the superconducting phase, where the recovery of the 89 Y NMR signal displays two distinct laws, pointing out different relaxation mechanisms without common spin temperature. One exponential recovery law yields a decay rate which decreases on cooling, as expected in the superconducting phase. The second relaxation process turns out to be described by a stretched exponential, with fast relaxation rates, strongly increasing on cooling, with a characteristic spin fluctuations frequency reaching the 20 MHz range at about 8 K. This observation is interpreted as the direct experimental evidence of the coexistence, at mesoscopic level, of superconductive and spin-glass like phases, the spin freezing process being described by the fast rate of the nuclear relaxation.

Application of the relaxation reagent Gd(FOD)3 (1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedionate)gadolinium(III) in 1H NMR spectroscopy of adamantoid compounds

1979 ◽  
Vol 44 (2) ◽  
pp. 533-541
Author(s):  
Jiří Karhan ◽  
Milan Hájek ◽  
Zbyněk Ksandr ◽  
Luděk Vodička
Keyword(s):  
Nmr Spectroscopy ◽  
Structure Analysis ◽  
1H Nmr Spectroscopy ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Shift Reagent ◽  
Spin Lattice Relaxation ◽  
Reagent Concentration ◽  
Relaxation Rates ◽  
Spin Lattice

This spin-lattice relaxation times T1 of protons in the presence of the shift reagent Eu(FOD)3-D27 and the relaxation reagent Gd(FOD)3 were employed for the structure analysis of 1-adamantanol, 4-diamantanol, adamantanone, and 2,2-dioxy-2-thiaadamantane. The structure models of the complex adducts of the substrates with Gd(FOD)3 are discussed. The dependence of the corrected spin-lattice relaxation rates on the relaxation reagent concentration is linear only in the region of low concentration.

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