Relaxation (NMR)

About: Relaxation (NMR) is a research topic. Over the lifetime, 29342 publications have been published within this topic receiving 689851 citations.

What Can Really Be Learned from Dielectric Spectroscopy of Protein Solutions? A Case Study of Ribonuclease A

Abstract: We report on a dielectric relaxation study of aqueous solutions of ribonuclease A at 298.15 K as a function of protein concentration between 0.5 and 6 wt % in the MHz/GHz frequency range. The spectra can be decomposed into five modes of Debye type diffusive behavior. In agreement with the standard interpretation, we assign the two dominant modes at low and high frequency (β-relaxation and γ-relaxation, respectively) to protein tumbling and bulk water relaxation. We observe three further modes (δ1−δ3) between β- and γ-relaxation, in contrast to a bimodal δ-dispersion frequently reported. We attribute the high frequency part (δ3) near 40 ps to hydration water reorientation, which, in the notion of other authors, corresponds to “loosely bound water”. We argue that the existence of “tightly bound” water, often deduced from the low frequency part in the nanosecond regime (δ1), is inconsistent with a highly mobile hydration layer observed by NMR techniques and molecular dynamics (MD) simulations. On the same gr...

Magnetic Nanoparticles in Magnetic Resonance Imaging and Diagnostics

Abstract: Magnetic nanoparticles are useful as contrast agents for magnetic resonance imaging (MRI). Paramagnetic contrast agents have been used for a long time, but more recently superparamagnetic iron oxide nanoparticles (SPIOs) have been discovered to influence MRI contrast as well. In contrast to paramagnetic contrast agents, SPIOs can be functionalized and size-tailored in order to adapt to various kinds of soft tissues. Although both types of contrast agents have a inducible magnetization, their mechanisms of influence on spin-spin and spin-lattice relaxation of protons are different. A special emphasis on the basic magnetism of nanoparticles and their structures as well as on the principle of nuclear magnetic resonance is made. Examples of different contrast-enhanced magnetic resonance images are given. The potential use of magnetic nanoparticles as diagnostic tracers is explored. Additionally, SPIOs can be used in diagnostic magnetic resonance, since the spin relaxation time of water protons differs, whether magnetic nanoparticles are bound to a target or not.

Use of a water flip-back pulse in the homonuclear NOESY experiment.

Abstract: A simple modification to the WATERGATE water suppression scheme [Piotto, M., Saudek, V. and Sklenař, V. (1992) J. Biomol. NMR, 2, 661–665] is proposed. Radiation damping is used as an active element during the mixing time of a NOESY experiment, in order to obtain a reproducable state of the water magnetization at the end of the mixing time. Through the use of a water flip-back pulse and a gradient-tailored excitation scheme, we obtain both an excellent water suppression and a water magnetization close to equilibrium at the beginning of the acquisition time. We show experimentally that this modification results in a 20% gain in intensity for all signals when using a relaxation delay of 1.5 s, and also that avoiding a semisaturated state for the water magnetization allows the amide protons as well as other proton resonances to relax to equilibrium with their proper relaxation time.

Evidence for two pairing energies from nuclear spin-lattice relaxation in superconducting Ba2YCu3O7- delta.

Abstract: We report /sup 63/Cu nuclear spin-lattice relaxation data for Ba/sub 2/YC/sub 3/O/sub 7-//sub delta/ in the superconducting state obtained by nuclear quadrupole resonance in zero applied magnetic field. The temperature dependences of the relaxation rates reveal striking differences in the excitation spectra for quasiparticles on the chain-forming Cu1 and planar Cu2 lattice sites, corresponding to substantially different pairing energies for electrons on the planes and chains. Values of the gap ratio 2..delta../kT/sub c/ 8.3 and 2.4 are obtained for the Cu1 and Cu2 sites, respectively.

Critical Thermalization of a Disordered Dipolar Spin System in Diamond.

Abstract: Statistical mechanics underlies our understanding of macroscopic quantum systems. It is based on the assumption that out-of-equilibrium systems rapidly approach their equilibrium states, forgetting any information about their microscopic initial conditions. This fundamental paradigm is challenged by disordered systems, in which a slowdown or even absence of thermalization is expected. We report the observation of critical thermalization in a three dimensional ensemble of ∼10^{6} electronic spins coupled via dipolar interactions. By controlling the spin states of nitrogen vacancy color centers in diamond, we observe slow, subexponential relaxation dynamics and identify a regime of power-law decay with disorder-dependent exponents; this behavior is modified at late times owing to many-body interactions. These observations are quantitatively explained by a resonance counting theory that incorporates the effects of both disorder and interactions.