Spin-lattice Relaxation Studies Research Articles

Dynamic of binary molecular systems-Advantages and limitations of NMR relaxometry.

1H spin-lattice relaxation studies have been performed for binary systems, including glycerol as the first component and alanine, glycine, and aspartic acid (with different levels of deuteration) as the second one. The relaxation studies have been performed in the frequency range from 10kHz to 10MHz vs temperature. A theoretical framework, including all relevant 1H-1H and 1H-2H relaxation pathways, has been formulated. The theory has been exploited for a thorough interpretation of a large set of the experimental data. The importance of the 1H-2H relaxation contributions has been discussed, and the possibility of revealing dynamical properties of individual liquid components in binary liquids has been carefully investigated. As far as the dynamical properties of the specific binary liquids, chosen as an example, are considered, it has been shown that in the presence of the second component (alanine, glycine, and aspartic acid), both molecular fractions undergo dynamics similar to that of glycerol in bulk.

Relationship between macroscopic properties of honey and molecular dynamics – temperature effects

1H spin-lattice relaxation studies of different kinds of honey have been performed in a broad frequency range, versus temperature. On the basis of the extensive data set, translation diffusion coefficients and rotational correlation times of water molecules confined in the sugar matrix have been determined. It has turned out that the translation dynamics is of three-dimensional (isotropic) character and its by three orders of magnitude slower compared to water in bulk. This scenario established on the molecular level has been compared with the picture of translation diffusion obtained from viscosity measurements. Systematic discrepancies have been observed for all kinds of honey and their origin has been explained. Activation energies of the translational and rotational motion and ratios between the translational and rotational correlational times have been determined and discussed in the context of the properties of supercooled liquids.

The3He nuclear magnetic relaxation in nematically ordered Al2O3 aerogels: effects of 4He and nitrogen pre-plating

The results of 3He gas pulsed NMR spin–lattice relaxation study in high-porosity (84.9%–97.9%) nematically ordered Al2O3 aerogels at 1.5 and 4.2 K are presented. The linear dependence of T 1 on gas pressure is observed in aerogels that are pre-plated by helium-4. Nitrogen pre-plating prior to helium-4 pre-plating weakly decreases the 3He gas spin–lattice relaxation rate. A few possible mechanisms plausibly involved in 3He nuclear magnetic relaxation in aerogels are considered. The suggested nuclear spin–lattice relaxation model due to some magnetically ‘dirty’ aerogel fibers allows to estimate the effective mean free path of 3He atoms in aerogel.

Solid-State NMR Spectroscopy Study of Molecular Dynamics of Pyridine 1-Oxide Encapsulated in p-tert-Butylcalix[4]arene.

The mixture of guests 25% pyridine 1-oxide (PNO) and 75% nitrobenzene (NB) encapsulated in a host cavity of p-tert-butylcalix[4]arene (p-tBC) is a suitable system for the study of intermolecular weak interactions, and the preferred orientation of the guest molecules within the host was derived. Variable temperature deuterium nuclear magnetic resonance line shape and spin-lattice relaxation studies were performed on three samples of 25% PNO as a guest (selectively and entirely deuterated) with 75% NB encapsulated in p-tBC as a host system. It is found that the PNO molecular motion supports the two-site jump model and is highly mobile throughout the temperature range from -130 to 20 °C. PNO reorients about its C2 molecular symmetry axis followed by reorientation around the compound's C4 axis of symmetry of a host. Calculation showed that besides precise molecular jumping, the guest also experiences the vibrational motion with a variation angle dispute about 15°. The correlation times for the molecular guest motion and two-dimensional exchange spectroscopy confirmed a fast exchange limit inside the cavity. These molecular dynamics follow an Arrhenius behavior motion from which the small activation energy is delivered that strongly suggests a relatively weak intermolecular interaction between the host and guest species. PNO has definite dipole orientational motion in the cavity where its aromatic covalent bond structure minimizes contact with the host p-tert-butyl groups. Experimentally found, PNO-d5 deuterons in the single crystal collapse at 55 and 125° at ambient temperature. The first splitting of 124 kHz belongs to D3(D5), the second splitting of 100 kHz belongs to D2(D6), and the last splitting of 52 kHz belongs to D4 of the ring of PNO inside the p-tBC.

Dynamics of Ionic Liquids in Confinement by Means of NMR Relaxometry-EMIM-FSI in a Silica Matrix as an Example.

1H and 19F spin–lattice relaxation studies for 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide in bulk and mesoporous MCM-41 silica matrix confinement were performed under varying temperatures in a broad range of magnetic fields, corresponding to 1H resonance frequency from 5Hz to 30MHz.A thorough analysis of the relaxation data revealed a three-dimensional translation diffusion of the ions in the bulk liquid and two-dimensional diffusion in the vicinity of the confining walls in the confinement. Parameters describing the translation dynamics were determined and compared. The rotational motion of both kinds of ions in the confinement was described by two correlation times that might be attributed to anisotropic reorientation of these species.

Reorientation Times for Solid-State Electrolyte Solvents and Electrolytes from NMR Spin-Lattice Relaxation Studies.

Ionic and molecular plastic crystals have been studied recently as solid electrolytes or solvents, but the specific role of molecular reorientation has not been clarified. We use NMR spin-lattice relaxation times (T1 minima) to compare the time scale for magnetic fluctuations in a plastic crystal solvent to the molecular reorientation times, as established by dielectric spectroscopy. We focus on a mixture of succinonitrile and glutaronitrile, in which the rotationally disordered phase is stabilized against crystallization. Reorientation times can then be studied over 13 orders of magnitude, down to the glass transition temperature at 144 K. For each nucleus, 1H and 13C, the most probable magnetic fluctuation time is found to be slightly shorter than the reorientation time, but with practically indistinguishable temperature dependence. This facilitates investigation of the relation of solvent reorientation to ion conductivity relaxation times in ionic conducting systems in which the conductivity swamps the dielectric signature of solvent reorientation.

35 Cl NQR frequency and spin lattice relaxation study in 3,4-dichloronitrobenzene as a function of temperature and pressure.

35 Cl NQR frequency and spin lattice relaxation time in 3,4-dichloronitrobenzene have been measured as a function of temperature and pressure. Two NQR signals were observed in the temperature range 77 to 300K and pressure up to 5.1kbar at 300K. The contributions to the relaxation from the torsional motion of the molecule and reorientational motion of the nitro group have been analyzed on the basis of the Woessner and Gutowsky model. The temperature dependence of the average torsional lifetimes of the molecules, transition probabilities, and the activation energy for the reorientation of the nitro group was estimated. The pressure dependence of the NQR frequency in 3,4-Dichloronitrobenzene shows a nonlinear increase in NQR frequency with increase in pressure, indicating increased contribution from the static effects at higher pressures. A thermodynamic analysis of the data was carried out to determine the constant-volume temperature coefficients of the NQR frequency. The spin-lattice relaxation was found to be weakly dependent on pressure.

Quadrupole relaxation enhancement and polarisation transfer in DMSO solution of [Bi(NO3)3(H2O)3]*18-crown-6 in solid state

ABSTRACT1H spin-lattice relaxation studies have been performed for pure [Bi(NO3)3(H2O)3]*18-crown-6 in powder and its solution in dimethyl sulfoxide (DMSO). The experiments have been carried out in the frequency range of 10 kHz–30 MHz and the temperature range of 240–277 K; at 277 K the solution is already frozen. The 1H relaxation of pure [Bi(NO3)3(H2O)3]*18-crown-6 has been interpreted in terms of three dynamical processes. Quadrupole Relaxation Enhancement effects have been observed in the frozen DMSO solution of [Bi(NO3)3(H2O)3]*18-crown-6. The specific mechanisms of the 1H spin-lattice relaxation enhancement have been discussed distinguishing between effects caused by time independent (residual) and fluctuating 1H-209Bi dipole-dipole interactions.

1H spin–lattice relaxation in water solution of 209Bi counterparts of Gd3+contrast agents

ABSTRACT1H spin–lattice relaxation studies of water solutions of Bismuth-ethylenediamine-tetraacetic acid (Bi-EDTA), Bismuth-ethylenediamine-tetrakis(methylenephosphonic) acid (Bi-EDTP), Bismuth-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (Bi-DOTA), Bismuth-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylenephosphonic acid) (Bi-DOTP) and Bismuth-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (Bi-DO3A) have been performed in order to compare Quadrupole Relaxation Enhancement (QRE) effects with Paramagnetic Relaxation Enhancement (PRE) from the perspective of exploiting the first one as a novel contrast mechanism for Magnetic Resonance Imaging (MRI). The selected compounds can be considered as 209Bi counterparts of Gd3+ complexes. The relaxation experiments have been performed in a broad frequency range of 5 kHz–30 MHz. The relaxation contribution associated with QRE has been extracted from the data and compared with PRE. Similarities and differences between the two effects have been discussed.

Spin-Lattice Relaxation of Hyperpolarized Metronidazole in Signal Amplification by Reversible Exchange in Micro-Tesla Fields.

Simultaneous reversible chemical exchange of parahydrogen and to-be-hyperpolarized substrate on metal centers enables spontaneous transfer of spin order from parahydrogen singlet to nuclear spins of the substrate. When performed at sub-micro-Tesla magnetic field, this technique of NMR Signal Amplification by Reversible Exchange in SHield Enables Alignment Transfer to Heteronuclei (SABRE-SHEATH). SABRE-SHEATH has been shown to hyperpolarize nitrogen-15 sites of a wide range of biologically interesting molecules to a high polarization level (P > 20%) in one minute. Here, we report on a systematic study of 1H, 13C and 15N spin-lattice relaxation (T1) of metronidazole-13C2-15N2 in SABRE-SHEATH hyperpolarization process. In micro-Tesla range, we find that all 1H, 13C and 15N spins studied share approximately the same T1 values (ca. 4 s at the conditions studied) due to mixing of their Zeeman levels, which is consistent with the model of relayed SABRE-SHEATH effect. These T1 values are significantly lower than those at higher magnetic (i.e. the Earth's magnetic field and above), which exceed 3 minutes in some cases. Moreover, these relatively short T1 values observed below 1 micro-Tesla limit the polarization build-up process of SABRE-SHEATH- thereby, limiting maximum attainable 15N polarization. The relatively short nature of T1 values observed below 1 micro-Tesla is primarily caused by intermolecular interactions with quadrupolar iridium centers or dihydride protons of the employed polarization transfer catalyst, whereas intramolecular spin-spin interactions with 14N quadrupolar centers have significantly smaller contribution. The presented experimental results and their analysis will be beneficial for more rational design of SABRE-SHEATH (i) polarization transfer catalyst, and (ii) hyperpolarized molecular probes in the context of biomedical imaging and other applications.

Study of H1 spin lattice relaxation and dielectric relaxation in Poly(propylene glycol) system

Proton NMR spin-lattice relaxation time (T1) and dielectric relaxation time (τ0) have been used to correlate the experimental and calculated values of T1 for Poly (propylene glycol) at 300 K. Also, the contributions of dielectric relaxation time (τ0) of each constituent group of PPG-425 to the effective dielectric relaxation time due to the whole chain of the polymer have been calculated using NMR spin–lattice relaxation time. The H1 NMR data and dielectric data of Poly (propylene glycol) HO [CH(CH3)CH2O]nH with number average molecular weight 425 (n = 7) g mol−1have been used to understand the conformation and basic mechanism of relaxation in polymer in its pure liquid state. Conformational analysis using Hartree-Fock formalism was performed for the polymer of n = 7 and the average bond distances obtained from the computation were used to assign NMR relaxation times to specific subgroups. Free energy and enthalpy of activation associated with methyl and other groups in the chain of PPG molecules have been calculated. BPP (Bloembergen Purcell Pound) model gives better correlation for molecular tumbling motion for PPG-425 in pure liquid state than Kubo & Tomita equation.

Spin-lattice relaxation studies on deep eutectic solvent/Choliniumtetrachloroferrate mixtures: Suitability of DES-based systems towards magnetic resonance imaging studies.

This study has been undertaken with an aim to investigate the suitability of the deep eutectic solvents (DES)-based systems for magnetic resonance imaging studies. DESs are used to develop the systems, keeping in mind the fact that these are relatively less toxic than ionic liquids, and hence, DES based magnetic compound is expected to be relatively less toxic than magnetic ionic liquids. In this work, spin-lattice (T1 ) relaxation measurements are carried out in the binary mixtures of deep eutectic solvent with a paramagnetic component choliniumtetrachloroferrate ([Ch][FeCl4 ]). Two cholinium ion based DESs, namely ethaline and glyceline have been used for this study. For both ethaline/[Ch][FeCl4 ] and glyceline/[Ch][FeCl4 ], T1 is observed to vary significantly with very low concentration of [Ch][FeCl4 ]. Such an observation can arise due to the high degree of paramagnetic coupling between DESs and [Ch][FeCl4 ]. The results advocate the suitability of both ethaline/[Ch][FeCl4 ] and glyceline/[Ch][FeCl4 ] mixture as a potential T1 contrast agent. Interestingly, when the experiments are carried out in aqueous medium, significant lowering of T1 of water proton with very low concentration of ethaline/[Ch][FeCl4 ] and glyceline/[Ch][FeCl4 ] is observed. This study demonstrates that the present systems can act as a suitable T1 contrast agent.

Nuclear magnetic resonance and nuclear spin relaxation in AlAs quantum well probed by ESR

The study of nuclear magnetic resonance and nuclear spin-lattice relaxation was conducted in an asymmetrically doped to $n\sim1.8\times10^{11}$ cm$^{-2}$ 16 nm AlAs quantum well grown in the $[001]$-direction. Dynamic polarization of nuclear spins due to the hyperfine interaction resulted in the so-called Overhauser shift of the two-dimensional conduction electron spin resonance. The maximum shifts achieved in the experiments are several orders of magnitude smaller than in GaAs-based heterostructures indicating that hyperfine interaction is weak. The nuclear spin-lattice relaxation time extracted from the decay of Overhauser shift over time turned out to depend on the filling factor of the two-dimensional electron system. This observation indicates that nuclear spin-lattice relaxation is mostly due to the interaction between electron and nuclear spins. Overhauser shift diminishes resonantly when the RF-radiation of certain frequencies was applied to the sample. This effect served as an indirect, yet powerful method for nuclear magnetic resonance detection: NMR quadrupole splitting of $^{75}$As nuclei was clearly resolved. Theoretical calculations performed describe well these experimental findings.

NMR spin-lattice relaxation study of 7Li and 93Nb nuclei in Ti- or Fe-doped LiNbO3:Mg single crystals

In this study, to understand the effects of paramagnetic impurities, we investigated the temperature dependent of the spin-lattice relaxation times of pure LiNbO3, LiNbO3:Mg, LiNbO3:Mg/Ti, LiNbO3:Mg/Fe, and LiNbO3:Mg/Fe (thermally treated at 500°C) single crystals. The results for the LiNbO3:Mg single crystals doped with Fe3+ or Ti3+ are discussed with respect to the site distribution and atomic mobility of Li and Nb. In addition, the effects of a thermal treatment on LiNbO3:Mg/Fe single crystals were examined based on the T1 analysis of 7Li and 93Nb. It was found that the presence of impurities in the crystals induced systematic changes of activation energies concerning atomic mobility.

Effect of H bond removal and changes in the position of the iron-sulphur head domain on the spin-lattice relaxation properties of the [2Fe-2S](2+) Rieske cluster in cytochrome bc(1).

Here, comparative electron spin-lattice relaxation studies of the 2Fe-2S iron-sulphur (Fe-S) cluster embedded in a large membrane protein complex - cytochrome bc1 - are reported. Structural modifications of the local environment alone (mutations S158A and Y160W removing specific H bonds between Fe-S and amino acid side chains) or in combination with changes in global protein conformation (mutations/inhibitors changing the position of the Fe-S binding domain within the protein complex) resulted in different redox potentials as well as g-, g-strain and the relaxation rates (T1(-1)) for the Fe-S cluster. The relaxation rates for T < 25 K were measured directly by inversion recovery, while for T > 60 K they were deduced from simulation of continuous wave EPR spectra of the cluster using a model that included anisotropy of Lorentzian broadening. In all cases, the relaxation rate involved contributions from direct, second-order Raman and Orbach processes, each dominating over different temperature ranges. The analysis of T1(-1) (T) over the range 5-120 K yielded the values of the Orbach energy (EOrb), Debye temperature θD and Raman process efficiency CRam for each variant of the protein. As the Orbach energy was generally higher for mutants S158A and Y160W, compared to wild-type protein (WT), it is suggested that H bond removal influences the geometry leading to increased strength of antiferromagnetic coupling between two Fe ions of the cluster. While θD was similar for all variants (∼107 K), the efficiency of the Raman process generally depends on the spin-orbit coupling that is lower for S158A and Y160W mutants, when compared to the WT. However, in several cases CRam did not only correlate with spin-orbit coupling but was also influenced by other factors - possibly the modification of protein rigidity and therefore the vibrational modes around the Fe-S cluster that change upon the movement of the iron-sulphur head domain.

Multigap superconductivity in locally noncentrosymmetric SrPtAs: AnAs75nuclear quadrupole resonance investigation

We report detailed $^{75}$As-NQR investigations of the locally non-centrosymmetric superconductor SrPtAs. The spin-lattice relaxation studies prove weakly coupled multi-gap superconductivity. The Hebel-Slichter peak, a hallmark of conventional superconductivity, is strongly suppressed, which points to an unconventional superconducting state. The observed behavior excludes a superconducting order parameter with line nodes and is consistent with proposed $f$-wave and chiral $d$-wave order parameters.

Li Ion Self-Diffusion in Metastable Li15Si4 prepared from Monocrystalline Si — an Ex Situ 7Li NMR Relaxometry Study

New energy systems became one of the basic needs in modern society. The explosive increase of portable electronic devices, such as cell phones, laptop computers etc., and the storage of electricity from renewable resources calls for reliable batteries with extraordinary capacities. For this purpose, tremendous research effort has been devoted to novel high-capacity electrode materials.Silicon containing electrodes are one of the most promising anode materials, not only due to their extremely large theoretical charge capacity but also owing to the availability of state-of-the-art fabrication methods. To overcome, however, the hurdles of Si-based batteries an in-depth understanding of the fundamental ion transport processes in such systems is expected to be highly useful. In the past, mainly macroscopic electrochemical methods have been used to estimate Li ion diffusivities in amorphous Si and metastable Li15Si4. By comparing the studies published so far, in some cases the resulting diffusivities differ from each other by many orders of magnitude. In the present contribution, we used an atomic-scale technique to probe Li self-diffusion parameters viz time-domain nuclear magnetic resonance (NMR) relaxometry.Here, temperature-variable 7Li NMR relaxometry is known to be a powerful tool for the investigation of Li ion dynamics in crystalline as well as amorphous solids and enables, in the ideal case, direct access to both Li+ jump rates and activation energies [1-3]. For that purpose, half-cells of boron doped, monocrystalline Si (100) on Cu were cycled at 20 mV vs. Li/Li+ (2.5 cycles) with charge cut-off and current limitation. X-ray powder diffraction confirmed the formation of phase pure crystalline, metastable Li15Si4. The samples prepared are also expected to contain amorphous Si. 7Li NMR line shape measurements point to heterogeneous dynamics with relatively fast Li ions at temperatures well below 20 °C. A comprehensive NMR spin-lattice relaxation (SLR) study including both measurements in the laboratory (R 1, 116 MHz) and the rotating frame of reference (R 1ρ, 20 kHz) was used to deduce microscopic Li ion diffusion parameters. Fortunately, the temperature variable R 1ρ rates recorded at locking frequencies in the kHz range reveal a diffusion induced rate peak when the rates are plotted versus inverse temperature 1/T in an Arrhenius diagram. From the low-temperature flank of this peak an activation energy of 0.55(5) eV can be estimated. Moreover, the position of the maximum on the 1/T-axis leads to a Li jump rate of approximately 2.5 × 105 1/s at –30 °C. According to the Einstein-Smoluchowski equation this corresponds to a Li ion self-diffusion coefficient in the order of 10–11 cm2/s which points to relatively fast Li diffusivity in the sample studied, see also ref. [4]. For comparison, ongoing NMR studies also include the investigation of a completely amorphous Si sample prepared by electrochemical reaction with Li as described above. Acknowledgement Financial support by the Federal Ministry of Economy, Family and Youth and the National Foundation for Research, Technology and Development is gratefully acknowledged.

127I and 207Pb Solid-State NMR Spectroscopy and Nuclear Spin Relaxation in PbI2: A Preliminary Study

Lead iodide is a layered structure that experiences polytypism. The 2H polytype contains high rates of iodine vacancies but retains its stoichiometry. This characteristic feature makes it potentially useful for many practical applications. The hopping of iodine ions among vacancies is the dominant motion in the 2H polytype. We present a preliminary 127I and 207Pb solid-state nuclear magnetic resonance (NMR) spectroscopy and spin–lattice relaxation study of the 2H polytype below 400 K. We present reasonable models for the solid-state NMR results in terms of the effects of iodine hopping and lattice vibrations.

Saturation recovery electron spin–lattice relaxation studies on benzene anion radical and its derivatives: application of Kivelson–Orbach mechanism of electron spin relaxation

The role of low-lying excited states on the spin–lattice relaxation times (T1) of organic radicals has been investigated. To test the applicability of Kivelson's electric field fluctuation model (D. Kivelson, J. Chem. Phys. 45, 1324 (1966)), based on the Orbach mechanism of spin relaxation, the T1s of the anion radicals of benzene, benzene-1-d, toluene, ethyl benzene, isopropyl benzene, t-butyl benzene, p-xylene, 1,2,4-trimethyl benzene and 1,3,5-trimethyl benzene in liquid solutions, with potassium cation as the counter ion, have been measured by the pulse saturation recovery technique. The energy gap between the ground and the first excited electronic states changed with the substitutions to different extent. The spin–lattice relaxation rates showed correlation with this energy gap. Anion radicals of benzene and benzene-1-d showed the shortest T1 among the radicals studied here. A small but measurable energy splitting due to the deuterium substitution in benzene-1-d radical was obtained from the temperature dependence of T1. Spin–lattice relaxation times of benzene anion measured here decreased monotonically in the range of −60 to −125 °C, in contrast to some reported claims of very unusual temperature dependence, based on the continuous wave microwave power saturation studies. Our results also showed that the ion pairing between benzene anion and potassium cation did not significantly influence the spin–lattice relaxation times.

Nuclear Spin–Lattice Relaxation Study for 4fElectron State in CeT2Al10(T = Ru, Os, and Fe): Comparison with RKKY System NdRu2Al10

In order to uncover the \(4f\) electron state as a background for the emergence of the novel phase below \(T_{0}\) in CeT2Al10 (T = Ru, Os), the nuclear spin–lattice relaxation rate \(1/T_{1}\) in the well-localized RKKY system NdRu2Al10 was measured and compared with that in CeRu2Al10. The value of \(1/T_{1}\) in NdRu2Al10 with \(T_{\text{N}}=2.4\) K, which follows de Gennes scaling from \(T_{\text{N}}=16\) K in GdRu2Al10, shows a characteristic \(T\)-dependence for localized systems, \(1/T_{1}=a/(b+cT)\), with the constants \(a\), \(b\), and \(c\). On the other hand, in CeRu2Al10, \(1/T_{1}\) at temperatures higher than \(T^{*}\sim 60\) K also follows the same function if the Korringa relaxation is subtracted, indicating that the Ce \(4f\) electron in CeRu2Al10 is in a localized state at least down to \(T^{*}\). Below the characteristic temperature \(T^{*}\), the downward deviation of \(1/T_{1}\) from the above function might be ascribed to the beginning of Kondo coherence as proposed previously. Furthe...