Nuclear Magnetic Relaxation Rate Research Articles

Simulation and analysis of 13C spin-rotation nuclear magnetic resonance relaxation rates of methyl groups

This work analyzes the nuclear spin–rotation contribution to the nuclear magnetic resonance relaxation of methyl groups from 10 rigid compounds (eight benzene derivatives with one, two, or three methyl groups and two bicyclic molecules) with internal rotation axes not aligned to the smallest molecular moment of inertia via molecular dynamics simulation and ab initio calculation. The molecular dynamics simulation and ab initio calculation of nuclear spin-rotation coupling constants reproduce the experimental behavior in selected systems. The presented methodology can help in the analysis and interpretation of experimental relaxation data.

Ultrasound and magnetic resonance imaging–based investigation of the role of perfusion and oxygen availability in menstrual pain

BackgroundThe mechanisms responsible for menstrual pain are poorly understood. However, dynamic noninvasive pelvic imaging of menstrual pain sufferers could aid in identifying therapeutic targets and in testing novel treatments. ObjectiveTo study the mechanisms responsible for menstrual pain, we analyzed ultrasonographic and complementary functional Magnetic Resonance Imaging (fMRI) parameters in dysmenorrhea sufferers and pain-free controls under multiple conditions. Study DesignWe performed fMRI on participants with and without dysmenorrhea during menses and non-menses. To clarify whether regional changes in oxygen availability and perfusion occur, fMRI R2* measurements were made of the endometrium and myometrium. R2* measurements are calculated nuclear magnetic resonance relaxation rates sensitive to the paramagnetic properties of oxygenated and deoxygenated hemoglobin. We also compared parameters before and after an analgesic dose of naproxen sodium. In addition, we performed similar measurements with Doppler ultrasonography to identify whether changes in uterine arterial velocity occurred during menstrual cramping in real time. Mixed model statistics were performed to account for within-subject effects across conditions. Corrections for multiple comparisons were made with a false discovery rate adjustment. ResultsDuring menstruation, a notable increase in R2* values, indicative of tissue ischemia, was observed in both the myometrium (beta ± standard error of the mean: 15.74 ± 2.29 s-1, p = 0.001, q = 0.002) and the endometrium (26.37 ± 9.33 s-1, p = 0.005, q = 0.008) among participants experiencing dysmenorrhea. A similar increase was noted in the myometrium (28.89 ± 2.85 s-1, p = 0.001, q = 0.002) and endometrium (75.50 ± 2.57 s-1, p = 0.001, q = 0.003) among pain-free controls. Post-hoc analyses revealed that R2* values during menstruation were significantly higher than those in participants with dysmenorrhea (Myometrium: p = 0.008, Endometrium: p = 0.043). Whereas naproxen sodium increased endometrial R2* in participants with dysmenorrhea (48.29 ± 15.78 s-1,p = 0.005, q = 0.008), it decreased myometrial R2*in pain-free controls. Doppler findings were consistent with fMRI (-8.62 ± 3.25 s-1, p = 0.008, q = 0.011). The pulsatility index (-0.42 ± 0.14, p = 0.004, q = 0.004) and resistance index (-0.042 ± 0.012, p = 0.001, q = 0.001) decreased during menses compared with non-menses, and effects were significantly reversed by naproxen sodium. Naproxen sodium had the opposite effect in pain-free controls. There were no significant real-time changes in the pulsatility index, resistance index, peak systolic velocity, or minimum diastolic velocity during episodes of symptomatic menstrual cramping. ConclusionsfMRI and Doppler metrics suggest participants with dysmenorrhea have better perfusion and oxygen availability than pain-free controls. Naproxen sodium's therapeutic mechanism is associated with relative reductions in uterine perfusion and oxygen availability. An opposite pharmacological effect was observed in pain-free controls. During menstrual cramping, there is insufficient evidence of episodic impaired uterine perfusion. Thus, prostaglandins may have protective vasoconstrictive effects in pain-free controls and opposite effects among participants with dysmenorrhea.

Nuclear Magnetic Resonance Studies of Bicontinuous Liquid Crystalline Phases of Cubic Symmetry: Transport Properties from 2H Nuclear Magnetic Resonance Relaxation Rates.

The ternary system didodecyltrimethylammonium bromide, 1-decanol, and water forms an extended reversed continuous phase of cubic symmetry at 25 °C. The cubic phase belongs to the space group Im3m, as shown by small-angle X-ray experiments. We present extensive deuterium NMR relaxation data from this cubic phase for 1-decanol, deuterated at the carbon adjacent to the hydroxyl carbon position. 2H spin-lattice (R1) and spin-spin (R2) relaxation rates were measured over the existence region of the cubic phase, which extends from 0.2 to 0.6 in volume fraction of the dividing bilayer surface of the cubic phase. The data are interpreted with an existing theoretical framework for NMR spin relaxation in bicontinuous cubic phases, which takes its starting point in the description of bicontinuous phases using periodic minimal surfaces. Specifically, we obtain the self-diffusion coefficient over the minimal surface in one unit cell for 1-decanol. We also present pulsed field gradient NMR-derived self-diffusion data for didodecyltrimethylammonium bromide and compare the two sets of data. The diffusion data for both components show a mild, if any, dependence on the volume fraction of the bilayer surface. Furthermore, we present diffusion data for the water component in the cubic phase. Finally, we discuss the influences of the choice of the value of the product of the deuterium quadrupole constant and the order parameter S. Within the framework of the model used to analyze the relaxation data, a value for this parameter is required. As an initial value, we rely on measurements of deuterium quadrupolar splittings from deuterated decanol in an anisotropic phase.

Nuclear spin relaxation in aqueous paramagnetic ion solutions.

A Brownian shell model describing the random rotational motion of a spherical shell of uniform particle density is presented and validated by molecular dynamics simulations. The model is applied to proton spin rotation in aqueous paramagnetic ion complexes to yield an expression for the Larmor-frequency-dependent nuclear magnetic resonance spin-lattice relaxation rate T_{1}^{-1}(ω) describing the dipolar coupling of the nuclear spin of the proton with the electronic spin of the ion. The Brownian shell model provides a significant enhancement to existing particle-particle dipolar models without added complexity, allowing fits to experimental T_{1}^{-1}(ω) dispersion curves without arbitrary scaling parameters. The model is successfully applied to measurements of T_{1}^{-1}(ω) from aqueous manganese(II), iron(III), and copper(II) systems where the scalar coupling contribution is known to be small. Appropriate combinations of Brownian shell and translational diffusion models, representing the inner and outer sphere relaxation contributions, respectively, are shown to provide excellent fits. Quantitative fits are obtained to the full dispersion curve of each aquoion with just five fit parameters, with the distance and time parameters each taking a physically justifiable numerical value.

Electrical conductivity and nuclear magnetic resonance relaxation rate of Eliashberg superconductors in the weak-coupling limit

Electrical conductivity is an important transport response in superconductors, enabling clear signatures of dynamical interactions to be observed. Of primary interest in this paper is to study characteristics of the electron-phonon interaction in weak-coupling Eliashberg theory (Eth), and to note the distinctions with Bardeen-Cooper-Schrieffer (BCS) theory. Recent analysis of weak-coupling Eth has shown that while there are modifications from the BCS results, certain dimensionless ratios are in agreement. Here we show that the conductivities in BCS theory and Eth fundamentally differ, with the latter having an imaginary gap component that damps a divergence. We focus on the dirty limit, and for both BCS theory and Eth we derive expressions for the low-frequency limit of the real conductivity. For Eth specifically, there are two limits to consider, depending on the relative size of the frequency and the imaginary part of the gap. In the case of identically zero frequency, we derive an analytical expression for the nuclear magnetic resonance relaxation rate. Our analysis of the conductivity complements the previous study of the Meissner response and provides a thorough understanding of weak-coupling Eth.

Nuclear spin relaxation rate of nonunitary Dirac and Weyl superconductors

Nonunitary superconductivity has attracted renewed interest as a novel gapless phase of matter. In this study, we investigate the superconducting gap structure of nonunitary odd-parity chiral pairing states in a superconductor involving strong spin-orbit interactions. By applying a group theoretical classification of chiral states in terms of discrete rotation symmetry, we categorized all possible point-nodal gap structures in nonunitary chiral states into four types in terms of the topological number of nodes and node positions relative to the rotation axis. In addition to conventional Dirac and Weyl point nodes, we identify a type of Dirac point nodes unique to nonunitary chiral superconducting states. Such a Dirac point node is a nodal point of two pseudospin excitations, but the dispersions around it depend on the pseudospin. The node type can be identified experimentally based on the temperature dependence of the nuclear magnetic resonance longitudinal relaxation rate. The implication of our results for a nonunitary odd-parity superconductor in ${\mathrm{UTe}}_{2}$ is also discussed.

Development of Spin Fluctuations under the Presence of d-wave Bond Order in Cuprate Superconductors

In cuprate superconductors, superconductivity appears below the CDW transition temperature $T_{CDW}$. However, many-body electronic states under the CDW order are still far from understood. Here, we study the development of the spin fluctuations under the presence of $d$-wave bond order (BO) with wavevector $q=(\pi/2,0),(0,\pi/2)$, which is derived from the paramagnon interference mechanism in recent theoretical studies. Based on the $4 \times 1$ and $4 \times 4$ cluster Hubbard models, the feedback effects between spin susceptibility and self-energy are calculated self-consistently by using the fluctuation-exchange (FLEX) approximation. It is found that the $d$-wave BO leads to a sizable suppression of the nuclear magnetic relaxation rate $1/T_1$. In contrast, the reduction in $T_c$ is small, since the static susceptibility $\chi^s(Q_s)$ is affected by the BO just slightly. It is verified that the $d$-wave BO scenario is consistent with the experimental electronic properties below $T_{CDW}$.

Rechargeable Thin‐Film Lithium Microbattery Using a Quasi‐Solid‐State Polymer Electrolyte

AbstractA thin‐film microbattery was designed after synthesizing a unique gel polymer electrolyte (GPE), using polyvinylidene fluoride‐co‐hexafluoropropylene (PVdF‐HFP) and cross‐linked poly(ethylene oxide) (PEO), with an ionic liquid and salt (LiTFSI) mixture. The polymers resulted in a semi‐interpenetrated polymer network (semi‐IPN), hosting an ionic liquid (IL)/salt mixture, and thus exhibited high ionic conductivity and excellent mechanical properties. Nuclear magnetic resonance (NMR) diffusion measurements and relaxation rates analysis highlighted the existence of interactions between Li+ ions and oxygen within the polymers, preventing electrolyte leakage and ensuring excellent mechanical strength which enabled a unique quasi‐solid electrolyte. Such mechanical strength and chemical stability made this electrolyte to be first ever reported GPE to withstand thermal evaporation deposition and hence direct deposition of lithium metal. The electrolyte could be shaped as self‐standing thin films, and thus worked as both separator and electrolyte in a thin‐film lithium microbattery. The thin‐film microbattery exhibited excellent performances showing no short‐circuit current, an open circuit voltage of ∼3.0 V, higher nominal voltage plateau, lower equivalent series resistance by comparison to a thin‐film microbattery designed in conventional way with a popular ceramic electrolyte LiPON.

Continuous Matrix Product Operator Approach to Finite Temperature Quantum States.

We present an algorithm for studying quantum systems at finite temperature using continuous matrix product operator representation. The approach handles both short-range and long-range interactions in the thermodynamic limit without incurring any time discretization error. Moreover, the approach provides direct access to physical observables including the specific heat, local susceptibility, and local spectral functions. After verifying the method using the prototypical quantum XXZ chains, we apply it to quantum Ising models with power-law decaying interactions and on the infinite cylinder, respectively. The approach offers predictions that are relevant to experiments in quantum simulators and the nuclear magnetic resonance spin-lattice relaxation rate.

Design of a fast field-cycling magnetic resonance imaging system, characterization and methods for relaxation dispersion measurements around 1.5 T.

The dependence of the nuclear magnetic resonance relaxation rate on the magnetic field has been widely studied, in particular, in biomedical areas with the objectives to better understand the underlying microscopic mechanisms in tissues and provide biomarkers of diseases. By combining fast-field cycling (FFC) and magnetic resonance imaging (MRI), it is possible to provide localized relaxation dispersion measurements in heterogeneous systems with recent demonstrations in solutions, biological samples, human beings, and small animals. We report here the developments and performances of a device designed for small animal FFC-MRI comprising a resistive insert technology operating inside a 1.5 T MRI system. Specific measurement methods were developed to characterize the system efficiency, response time, homogeneity, stability, and compensation. By adding a non-linear element in the system and using a dual amplifier strategy, it is shown that large field offsets can be produced during relaxation periods while maintaining precise field control during detection periods. The measurement of longitudinal nuclear magnetic relaxation dispersion (NMRD) profiles in the range of 1.08 T-1.92 T is reported, essentially displaying a linear variation in this range for common MRI contrast agents. The slopes of both the longitudinal and transverse relaxation dispersion profiles at 1.5 T are measured and validated, extending the capabilities of previous approaches. The performances of a longitudinal relaxation dispersion mapping method are finally reported, opening the way to quantitative preclinical dispersion imaging studies at a high FFC-MRI field.

Distribution of Gadolinium in Rat Heart Studied by Fast Field Cycling Relaxometry and Imaging SIMS.

Research on microcirculatory alterations in human heart disease is essential to understand the genesis of myocardial contractile dysfunction and its evolution towards heart failure. The use of contrast agents in magnetic resonance imaging is an important tool in medical diagnostics related to this dysfunction. Contrast agents significantly improve the imaging by enhancing the nuclear magnetic relaxation rates of water protons in the tissues where they are distributed. Gadolinium complexes are widely employed in clinical practice due to their high magnetic moment and relatively long electronic relaxation time. In this study, the behavior of gadolinium ion as a contrast agent was investigated by two complementary methods, relaxometry and secondary ion mass spectrometry. The study examined the distribution of blood flow within the microvascular network in ex vivo Langendorff isolated rat heart models, perfused with Omniscan® contrast agent. The combined use of secondary ion mass spectrometry and relaxometry allowed for both a qualitative mapping of agent distribution as well as the quantification of gadolinium ion concentration and persistence. This combination of a chemical mapping and temporal analysis of the molar concentration of gadolinium ion in heart tissue allows for new insights on the biomolecular mechanisms underlying the microcirculatory alterations in heart disease.

NMR diagnosis of pseudo-scalar superconductivity in 3D Dirac materials

Recently observed 4π periodic Andreev bound states in 3D Dirac materials are attributed to conventional superconducting pairing. Our alternative explanation in terms of a novel form of parity breaking pseudo-scalar superconducting order can be sharply diagnosed by nuclear magnetic resonance relaxation rate. The left–right symmetry breaking of the pseudo-scalar superconductivity can be directly probed as an anti-peak structure below TC in sharp contrast to the conventional Hebel–Slichter peak.

Impurity Effects in Nodal Extendeds- and Nodelessd-Wave Superconductors: Gap Symmetry of BiS2-Based Layered Superconductors

In BiS$_2$-based layered superconductors,the existence of gap nodes on Fermi-surface curves has been suggested from angle-resolved photoemission spectroscopy measurements, whereas the conventional $s$-wave gap has been proposed from measurements of superfluid density and thermal conductivity. To reconcile these two distinct experimental results of the gap node, we investigate nonmagnetic impurity effects in the superconductor with a disconnected pocketlike Fermi-surface structure. Then, we claim that the seemingly contradictory situation concerning the gap node is resolved by a concept of dirty nodal extended $s$-wave superconductivity. Provided that it is unnecessary to consider the nodes of the gap, at first glance, the conventional $s$-wave gap seems to be a unique solution, but in the pocketlike Fermi-surface topology, a nontrivial possibility of a nodeless $d$-wave superconductor is pointed out. To clarify the gap symmetry, we propose to perform experiments on nuclear magnetic relaxation rate $T_{1}^{-1}$ in BiS$_2$-based layered superconductors.

Nuclear magnetic relaxation and Knight shift due to orbital interaction in Dirac electron systems

We study the nuclear magnetic relaxation rate and Knight shift in the presence of the orbital and quadrupole interactions for three-dimensional Dirac electron systems (e.g., bismuth–antimony alloys). By using recent results of the dynamic magnetic susceptibility and permittivity, we obtain rigorous results of the relaxation rates (1/T1)orb and (1/T1)Q, which are due to the orbital and quadrupole interactions, respectively, and show that (1/T1)Q gives a negligible contribution compared with (1/T1)orb. It is found that (1/T1)orb exhibits anomalous dependences on temperature T and chemical potential μ. When μ is inside the band gap, (1/T1)orb∼T3log(2T/ω0) for temperatures above the band gap, where ω0 is the nuclear Larmor frequency. When μ lies in the conduction or valence bands, (1/T1)orb∝TkF2log(2vFkF/ω0) for low temperatures, where kF and vF are the Fermi momentum and Fermi velocity, respectively. The Knight shift Korb due to the orbital interaction also shows anomalous dependences on T and μ. It is shown that Korb is negative and its magnitude significantly increases with decreasing temperature when μ is located in the band gap. Because the anomalous dependences in Korb is caused by the interband particle-hole excitations across the small band gap while (1/T1)orb is governed by the intraband excitations, the Korringa relation does not hold in the Dirac electron systems.

Coherence Factors and Quantum Interferences in Excitonic Condensation of Ta2NiSe5

In order to elucidate whether Ta2NiSe5 is in an excitonic condensation state or not, we study macroscopic quantum interferences in ultrasonic attenuation rate and nuclear magnetic resonance relaxation rate. Using the three-chain model describing the excitonic condensation of Ta2NiSe5, we demonstrate analytically that the ultrasonic attenuation rate shows a characteristic peak just below the transition temperature of the excitonic condensation, while the nuclear magnetic resonance relaxation rate shows a rapid drop. In particular, we find that the constructive interference originates from the hybridization between the conduction and valence bands induced by an external field.

Nuclear relaxation rates in the herbertsmithite kagome antiferromagnets ZnCu3(OH)6Cl2

Local spectral functions and Nuclear Magnetic Relaxation (NMR) rates, 1/T1, for the spin-half Heisenberg antiferromagnet on the Kagome Lattice are calculated using Moriyas Gaussian approximation, as well as through an extrapolation of multiple frequency moments. The temperature dependence of the calculated rates is compared with the oxygen 1/T1 NMR data in Herbertsmithite. We find that the Gaussian approximation for 1/T1 shows behavior qualitatively similar to experiments with a sharp drop in rates at low temperatures, consistent with a spin-gapped behavior. However, this approximation significantly underestimates the magnitude of 1/T1 even at room temperature. Rates obtained from extrapolation of multiple frequency moments give very good agreement with the room temperature NMR data with J = 195 +/- 20 K and hyperfine couplings determined independently from other measurements. The use of multiple frequency moments also leads to additional low frequency weight in the local structure factors. The convergence of our calculations with higher frequency moments breaks down at low temperatures suggesting the existence of longer range dynamic correlations in the system despite the very short-range static correlations.

Nuclear magnetic relaxation rates of unconventional superconductivity in doped topological insulators

We study the temperature dependence of nuclear magnetic relaxation (NMR) rates to detect a sign of topological superconductivity in doped topological insulators, such as $M$($=$Cu,Nb,Sr)$_{x}$Bi$_{2}$Se$_{3}$ and Sn$_{1-x}$In$_{x}$Te. The Hebel-Slichter coherence effect below a critical temperature Tc depends on the superconducting states predicted by a minimal model of doped topological insulators. In a nodal anisotropic topological state similar to the ABM-phase in $^{3}$He, the NMR rate has a conventional $s$-wave like coherence peak below Tc. In contrast, in a fully-gapped isotropic topological superconducting state, this rate below Tc exhibits an anti-peak profile. Moreover, in a two-fold in-plane anisotropic topological superconducting state, there is no coherence effect, which is similar to that in a chiral $p$-wave state. Thus, we reveal that the NMR rates shed light on unconventional superconductivity in doped topological insulators.

Direct Chemical Fine-Tuning of Electronic Properties in Sc2 Ir6-x Pdx B.

Crystal orbital Hamilton population (COHP) bonding analysis has predicted that ScPd3 B0.5 is the least stable compound of the entire series Sc2 Ir6-x Pdx B. Here, we report a systematic study of Sc2 Ir6-x Pdx B (x=3, 5 and 6) by means of 11 B nuclear magnetic resonance (NMR), Knight shift (K) and nuclear spin-lattice relaxation rate (1/T1 ). NMR results combined with theoretical band structure calculations provide a measure of s- and non-s-character Fermi-level density of states. We present direct evidence that the enhanced s-state character of the Fermi level density of states (DOS) in ScPd3 B0.5 reduces the strength of the B 2p and Pd 4d hybridized states across the entire Sc2 Ir6-x Pdx B series. This hybridization strength relates to the opening of a deep pseudogap in the density of states of Sc2 IrPd5 B and the chemical bonding instability of ScPd3 B0.5 . This study is an experimental realization of a chemical fine-tuning of the electronic properties in intermetallic perovskites.

Protein dynamics from nuclear magnetic relaxation.

Nuclear magnetic resonance is a ubiquitous spectroscopic tool to explore molecules with atomic resolution. Nuclear magnetic relaxation is intimately connected to molecular motions. Many methods and models have been developed to measure and interpret the characteristic rates of nuclear magnetic relaxation in proteins. These approaches shed light on a rich and diverse range of motions covering timescales from picoseconds to seconds. Here, we introduce some of the basic concepts upon which these approaches are built and provide a series of illustrations.

Inverse coherence effects in nuclear magnetic relaxation rates as a sign of topological superconductivity

We reveal that three-dimensional multi-orbital topological superconductivity can be identified by a bulk measurement, i.e., the temperature dependence of nuclear magnetic relaxation (NMR) rates. Below a critical temperature $T_{\rm c}$, the NMR rate in the topological state exhibits an anti-peak profile, which is opposite to the conventional $s$-wave state. This inversion coherence effect comes from a twist of order parameters with respect to orbital and spin degrees of freedom. Our self-consistent calculations in the model for Cu$_{x}$Bi$_{2}$Se$_{3}$ prove that the inverse coherence effect appears as a concave temperature dependence of the NMR rates. We propose that a time-reversal-invariant orbital-singlet spin-triplet topological superconductivity is characterized by the temperature dependence of the NMR rate.