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Quadrupolar Interactions (quadrupolar + interaction)

Distribution by Scientific Domains

Medical Sciences	66%

Selected Abstracts

Thermal relaxation and coherence dynamics of spin 3/2.

CONCEPTS IN MAGNETIC RESONANCE, Issue 2 2003

Abstract The relaxation dynamics of the spin 3/2 density operator in the presence of fluctuating and static quadrupolar interactions is reviewed. The nuclear magnetic resonance (NMR) line shapes are analyzed for any value of the static quadrupolar interaction, ranging from isotropic systems to systems exhibiting large splitting far exceeding the line widths. Pulse sequences optimized for the elimination of line broadening due to an inhomogeneous static quadrupolar interaction and for the detection of nuclei involved in slow molecular motion and/or in anisotropic, liquid crystalline environment are discussed. In Part II, the dynamics of spin 3/2 in the presence of a (pulsed) radio frequency (RF) field is reviewed. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson Part A 19A: 97,116, 2003. [source]

17O relaxation time and NMR sensitivity of cerebral water and their field dependence

MAGNETIC RESONANCE IN MEDICINE, Issue 4 2001
Xiao-Hong Zhu
Abstract 17O spin relaxation times and sensitivity of detection were measured for natural abundance H217O in the rat brain at 4.7 and 9.4 Tesla. The relaxation times were found to be magnetic field independent (T2 = 3.03 ± 0.08 ms, T = 1.79 ± 0.04 ms, and T1 = 4.47 ± 0.14 ms at 4.7T (N = 5); T2 = 3.03 ± 0.09 ms, T = 1.80 ± 0.06 ms, and T1 = 4.84 ± 0.18 ms at 9.4T (N = 5)), consistent with the concept that the dominant relaxation mechanism is the quadrupolar interaction for this nucleus. The 17O NMR sensitivity was more than fourfold higher at 9.4T than at 4.7T, for both the rat brain and a sodium chloride solution. With this sensitivity gain, it was possible to obtain localized 17O spectra with an excellent signal-to-noise ratio (SNR) within 15 s of data acquisition despite the relatively low gyromagnetic ratio of this nucleus. Such a 15-s 2D 17O-MRS imaging data set obtained for natural abundance H217O in the rat brain yielded an SNR greater than 40:1 for a ,16,l voxel. This approach was employed to measure cerebral blood flow using a bolus injection of H217O via one internal carotid artery. These results demonstrate the ability of 17O-MRS imaging to reliably map the H217O dynamics in the brain tissue, and its potential for determining tissue blood flow and oxygen consumption rate changes in vivo. Magn Reson Med 45:543,549, 2001. © 2001 Wiley-Liss, Inc. [source]

Thermal relaxation and coherence dynamics of spin 3/2.

Alignment and structural analysis of membrane polypeptides by 15N and 31P solid-state NMR spectroscopy

CONCEPTS IN MAGNETIC RESONANCE, Issue 2 2003
Burkhard Bechinger
Abstract In contrast to solution NMR spectroscopy, where complete or almost complete averaging leads to isotropic values, the anisotropic character of nuclear interactions is apparent in solid-state NMR spectra. The orientation dependence of chemical shift and dipolar or quadrupolar interactions has been used to obtain dynamic as well as angular information from polypeptides that strongly interact with phospholipid bilayers. This article illustrates the advantageous characteristics of the anisotropic 15N or 31P chemical shift interactions that in a direct manner allow one to obtain information on the alignment of helical polypeptides or of phospholipid head groups with respect to the membrane normal. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson 18A: 130,145, 2003 [source]

Studying porous materials with krypton-83 NMR spectroscopy

MAGNETIC RESONANCE IN CHEMISTRY, Issue S1 2007
Zackary I. Cleveland
Abstract This report is the first review of 83Kr nuclear magnetic resonance as a new and promising technique for exploring the surfaces of solid materials. In contrast to the spin I = 1/2 nucleus of 129Xe, 83Kr has a nuclear spin of I = 9/2 and therefore possesses a nuclear electric quadrupole moment. Interactions of the quadrupole moment with the electronic environment are modulated by surface adsorption processes and therefore affect the 83Kr relaxation rate and spectral lineshape. These effects are much more sensitive probes for surfaces than the 129Xe chemical shielding and provide unique insights into macroporous materials in which the 129Xe chemical shift is typically of little diagnostic value. The first part of this report reviews the effect of quadrupolar interactions on the 83Kr linewidth in zeolites and also the 83Kr chemical shift behavior that is distinct from that of its 129Xe cousin in some of these materials. The second part reviews hyperpolarized (hp) 83Kr NMR spectroscopy of macroporous materials in which the longitudinal relaxation is typically too slow to allow sufficient averaging of thermally polarized 83Kr NMR signals. The quadrupolar-driven T1 relaxation times of hp 83Kr in these materials are sensitive to surface chemistry, surface-to-volume ratios, coadsorption of other species on surfaces, and surface temperature. Thus, 83Kr T1 relaxation can provide information about surfaces and chemical processes in macroscopic pores and can generate surface-sensitive contrast in hp 83Kr MRI. Copyright © 2007 John Wiley & Sons, Ltd. [source]

7Li and 13C solid-state NMR spectra of lithium cuprates,

MAGNETIC RESONANCE IN CHEMISTRY, Issue 10 2006
Steffen Jost
Abstract 7Li and 13C solid-state MAS NMR spectra of three lithium cuprates with known X-ray structures,lithium([12]crown-4)2 dimethyl and diphenyl cuprate (1,2) and lithium(thf)4 -[tris(trimethylsilyl) methyl]2 cuprate (3),have been measured and analysed with respect to the quadrupolar coupling constants of lithium-7, ,(7Li), and the asymmetry parameters of the quadrupolar interactions, ,(7Li), as well as the 6, 7Li and 13C chemical shifts. The ,(7Li) values of 23, 30, and 18 kHz for 1, 2 and 3, respectively, are in line with the high symmetry around the lithium nucleus in the solvent-separated structures and may be used as reference data for this structural motif. Calculations based on charges derived from ab initio 6-31 G* HF computations using the point charge model (PCM) and the program GAMESS support the experimental findings. Copyright © 2006 John Wiley & Sons, Ltd. [source]