Showing papers on "Proton spin crisis published in 1985"
171 citations
78 citations
TL;DR: In this paper, field cycling and conventional proton relaxation spectroscopy in the frequency range 104 ≤ v ≤ 3·108 Hz have been applied to diverse lyophilized and D2O-hydrated globular proteins and poly-L-alanine.
Abstract: Field-cycling and conventional proton relaxation spectroscopy in the frequency range 104 ≤ v ≤ 3·108 Hz have been applied to diverse lyophilized and D2O-hydrated globular proteins and poly-L-alanine. An overall T 1-dispersion T 1 ∼ v 0.75±0.05 has been found.This v 3/4-law is tentatively interpreted by a double-diffusive fluctuation mechanism.
32 citations
TL;DR: This article showed that des correlations de deplacements heteronucleaires peuvent etre realisees par le transfert "inverse" de polarisation, du carbone 13 au proton.
30 citations
TL;DR: In this paper, the proton spin-flip transitions in Mo(V) EPR spectra of the different reduced forms of the enzymes xanthine oxidase and sulfite oxidase have been examined.
27 citations
TL;DR: Observations d'une relaxation spin-reseau rapide dans le phase incommensurable superieure, du fait d'excitation a basse frequence T 1 −1 est proportionnel a T 413 ω −113.
Abstract: Observations d'une relaxation spin-reseau rapide dans le phase incommensurable superieure, du fait d'excitation a basse frequence (phasons): T 1 −1 est proportionnel a T 413 ω −113 (1ere observation d'une variation de T 1 avec la frequence de Larmor dans une phase incommensurable). Pics de T 1 −1 dans la phase incommensurable inferieure. Activation thermique du mouvement
27 citations
TL;DR: In this paper, the effects of rotational tunnelling on the proton spin-lattice relaxation were studied in (NH4)>ZnCl4 as functions of both temperature and the resonance frequency.
Abstract: Effects of rotational tunnelling on the proton spin-lattice relaxation were studied in (NH4)>ZnCl4 as functions of both temperature and the resonance frequency. Several tunnelling-related TI minima were found. At 20 K the tunnel frequencies were deduced to be 13 MHz, 24.5 MHz, 37 MHz and 51.5 MHz corresponding to the separation between the nondegenerate and the doubly degenerated T levels, to the T-A splittings and to the E-A splitting, respectively. The smallest tunnel frequency (13 MHz) was observed to branch into two above 20 K. The higher frequency branch could not be detected above 26 K because of a broadening of the corresponding TI minimum. The broadening suggests a presence of two motions which was supported by experiments on the spin-lattice relaxation of the dipolar energy.
23 citations
TL;DR: In this article, the authors measured the temperature dependence of the proton spin-lattice relaxation time in glycerol in the temperature range 5-300 K using solitons.
Abstract: We have measured the temperature dependence of the proton spin-lattice relaxation time ${\mathit{T}}_{1}$ in glycerol in the temperature range 5--300 K. The lattice dynamics responsible for the relaxation in the range 5T160 K is calculated using solitons with a formation energy \ensuremath{\Delta}/k=1 K. In the range 220T300 K the dynamics of the lattice includes solitons with a formation energy \ensuremath{\Delta}/k=4200 K and these are used to calculate the relaxation of the protons. In both temperature ranges the heat capacity, thermal expansion, and heat conduction are calculated using the same parameters for the soliton representation as were used to calculate the temperature dependence of the proton spin-lattice relaxation time. Discontinuities in the thermal properties at the glass transition temperature ${\mathit{T}}_{\mathit{g}}$ are attributed to an effective-mass change of the low-energy solitons. This work was conducted to test, with the use of nuclear magnetic resonance, some recent ideas in the dynamics of amorphous materials.
13 citations
TL;DR: Performing the relay from the heteronucleus to the proton spin system is preferable to the conventional heteronuclear RCT sequence (H → H → X) since the ultimate detection of proton rather thanheteronuclear magnetization affords an increase in the sensitivity of the experiment.
12 citations
TL;DR: In this article, a model for independent modulations of dipolar and zero field splitting (zfs) interactions is considered and the proton relaxation rates are directly calculated from the approach of solving stochastic Liouville equation for slow-motional ESR relaxations.
Abstract: Proton NMR relaxation in paramagnetic systems of S=3/2 with electron spin relaxation in slow‐motional region is examined. The proton relaxations arising from the modulations of scalar, dipolar, and scalar–dipolar cross interactions from paramagnetic spin by slow molecular motion together with their field dependence, the variation of zero field splitting (zfs) interaction, and internal rotation interference are investigated. The overall reorientational motion of the complex presumably gives rise to the fluctuation of zfs interaction. The model for independent modulations of dipolar and zfs interactions is considered also. The proton relaxation rates are directly calculated from the approach of solving stochastic Liouville equation for slow‐motional ESR relaxations. Slow‐motional effects on individual proton relaxation rates are discussed. The final results are appropriately modified to incorporate the influence of internal rotation for proton. The field‐dependent methyl proton relaxation rates in tris‐acet...
11 citations
TL;DR: In this paper, a kinetic model of three-dimensional-coupled Ising chains is applied to study the proton spin-lattice relaxation rates in a quasi-one-dimensional solid.
Abstract: A kinetic model of three-dimensionally-coupled Ising chains is applied to study the proton spin-lattice relaxation rates in ${\mathrm{H}}_{2}$${\mathrm{C}}_{4}$${\mathrm{O}}_{4}$. Good agreement with the experimental proton spin-lattice relaxation rates implies the validity of the model in visualizing ${\mathrm{H}}_{2}$${\mathrm{C}}_{4}$${\mathrm{O}}_{4}$ as a quasi-one-dimensional solid.
TL;DR: In this paper, an extensive set of measurements of the proton spin longitudinal relaxation time T1 for molecular hydrogen diluted in argon was presented, carried out at 18.975 MHz.
Abstract: An extensive set of measurements of the proton spin longitudinal relaxation time T1 for molecular hydrogen diluted in argon is presented. These measurements, carried out at 18.975 MHz, establish th...
TL;DR: In this article, all the available experimental data (cross sections, projectile and target polarizations, polarization transfer coefficients) on p-3 He elastic scattering up to ~10 MeV are analyzed on a unified basis in the framework of a separable potential model.
TL;DR: In this paper, it was shown that the proton-proton spin-spin coupling in methane is very sensitive to the interbond angle involving the coupled protons, which leads to the prediction of primary isotope effects on 2J(H,H) in agreement with experimental results for geminal deuterium isotope effect in related compounds.
Abstract: Calculation shows that the proton–proton spin–spin coupling in methane is very sensitive to the interbond angle involving thecoupled protons, a result which leads to the prediction of primary isotope effects on 2J(H,H) in agreement with experimental results for geminal deuterium isotope effects in related compounds.
TL;DR: In this paper, hyperfine interaction, proton spin relaxation and dynamic spin polarization were determined for the radical cation salts of fluoranthene: (FA)+ 2;PF− 6, and (FA+ 2:SbF6 −, by observation of...
Abstract: Hyperfine interaction, proton spin relaxation and dynamic proton spin polarization were determined for the radical cation salts of fluoranthene: (FA)+ 2;PF− 6, and (FA)+ 2:SbF6 −, by observation of...
TL;DR: In this paper, the proton spin-lattice relaxation time of a CH 2 D 2 molecule was calculated and the dependence of the relaxation efficiency on the site symmetry was examined.
Abstract: The proton spin-lattice relaxation time of a CH 2 D 2 molecule is calculated. The tunnel splittings are assumed to be much larger than the Zeeman energy. The dependence of the relaxation efficiency on the site symmetry is examined. The results are compared with experimental T 1 values in the solid phases of CH 2 D 2 . Contrary to CH 4 and CD 4 , the symmetry of the crystal field has no influence on the relaxation rate. The calculated relaxation rate is lower than experimentally observed, which indicates that some of the energy levels coincide.
01 Jan 1985
TL;DR: In this article, the proton spin-lattice relaxation rate T 1-1 of powdered pentamethylbenzene has been measured in the temperature range 4-80K, at two spectrometer frequencies, 40 and 60 MHz.
Abstract: The proton spin-lattice relaxation rate T1-1 of powdered pentamethylbenzene has been measured in the temperature range 4-80K, at two spectrometer frequencies, 40 and 60 MHz. The measurements are analysed using a simplified coupled relaxation theory of methyl groups. Coupling between the Zeeman and tunnel energies, indicated by the appearance of a tunnelling frequency nu t was used to interpret the data, two distinct correlation times for methyl group reorientation being found necessary.
TL;DR: In this article, the proton spin-lattice relaxation rate 1/T 1 in solid thioacetamide was measured between 28.5 K and 200 K at two Larmor frequencies, 11.4 MHz and 25 MHz.
Abstract: The proton spin-lattice relaxation rate 1/ T 1 in solid thioacetamide were measured between 28.5 K and 200 K at two Larmor frequencies, 11.4 MHz and 25 MHz. The temperature dependence of 1/ T 1 was characterized by three maxima, two maxima observed around 90 K and 37 K showing the frequency dependence and the frequency independent one at 44 K. Taking into account two crystal-lographically inequivalent thioacetamide molecules, the temperature and Larmor frequency dependence of 1/ T 1 was explained by the contribution from the quantum mechanical and classical limit of tunneling rotation of the methyl groups around their C 3 axes.
TL;DR: In this paper, the critical relaxation rate T1-1 for proton NMR in hydrogen-bonded crystals is calculated and the influence of groundstate symmetry and the range of interaction on the critical temperature dependence of T1 is examined for uniaxial systems.
Abstract: On the basis of an explicit calculation of the critical relaxation rate T1-1 for proton NMR in hydrogen bonded crystals, the influence of the groundstate symmetry and the range of interaction on the critical temperature dependence of T1 is examined for uniaxial systems. Furthermore an evaluation of T1 in squaric acid is presented which gives new information on the jumping rate of the proton in the hydrogen bond.
TL;DR: In this article, the reorientation of proton spin polarization as a result of scattering from a 0 + target is studied in a distorted-wave formulation using the momentum helicity representation.
TL;DR: In this article, a model was developed to describe spin-spin asymmetries in electron-proton elastic scattering and applied to predict proton spin spin spin asymmetry in a perturbative QCD scheme.
Abstract: We consider a model previously developed to describe spin-spin asymmetries is proton-proton large angle elastic scattering and apply it to predict proton spin-spin asymmetries in electron-proton elastic scattering. Our results differ from those commonly expected in a perturbative QCD scheme. The measurement of the spin asymmetries would provide a direct measurement of the two proton elastic form factors and a clean further test of our mechanism.
TL;DR: In this article, experimental evidence was presented for the occurrence of a nuclear dipolar magnetic ordering of the proton spins in Ca(OH)2 at positive spin temperature in a high externally applied magnetic field H0.
Abstract: Experimental evidence is presented for the occurrence of a nuclear dipolar magnetic ordering of the proton spins in Ca(OH)2 at positive spin temperature in a high externally applied magnetic field H0 The ordering was produced by dynamic nuclear polarisation (DNP) and adiabatic demagnetisation in the rotating frame (ADRF) From simultaneous measurement of the entropy and the dipolar energy the authors determined the dipolar temperature of the proton spin system after the ADRF Furthermore an analysis of the NMR absorption lineshape was made From this analysis of the NMR lineshape and from measurements of the transverse susceptibility as a function of the dipolar energy and the temperature they conclude that a transverse magnetic ordering with a helical structure is created during the ADRF
Abstract: ENDOR spectra of di-t-butyl nitroxide have been observed at −90 °C in heptane. Two ENDOR lines near the free proton frequency had different absorption intensities and their line-shape showed a clear dependence on the nitrogen spin quantum number. This indicates an important spin cross relaxation by the nitrogen nucleus in the proton spin system and suggests a negative sign of the proton hyperfine coupling constant.