Nuclear Magnetic Relaxation Research Articles

2H NMR study on temperature-dependent water dynamics in amino-acid functionalized silica nanopores.

We prepare various amino-acid functionalized silica pores with diameters of ∼6 nm and study the temperature-dependent reorientation dynamics of water in these confinements. Specifically, we link basic Lys, neutral Ala, and acidic Glu to the inner surfaces and combine 2H nuclear magnetic resonance spin-lattice relaxation and line shape analyses to disentangle the rotational motions of the surfaces groups and the crystalline and liquid water fractions coexisting below partial freezing. Unlike the crystalline phase, the liquid phase shows reorientation dynamics, which strongly depends on the chemistry of the inner surfaces. The water reorientation is slowest for the Lys functionalization, followed by Ala and Glu and, finally, the native silica pores. In total, the rotational correlation times of water at the different surfaces vary by about two orders of magnitude, where this span is largely independent of the temperature in the range ∼200-250 K.

Expanding the Ligand Classes Used for Mn(II) Complexation: Oxa-aza Macrocycles Make the Difference.

We report two macrocyclic ligands based on a 1,7-diaza-12-crown-4 platform functionalized with acetate (tO2DO2A2−) or piperidineacetamide (tO2DO2AMPip) pendant arms and a detailed characterization of the corresponding Mn(II) complexes. The X−ray structure of [Mn(tO2DO2A)(H2O)]·2H2O shows that the metal ion is coordinated by six donor atoms of the macrocyclic ligand and one water molecule, to result in seven-coordination. The Cu(II) analogue presents a distorted octahedral coordination environment. The protonation constants of the ligands and the stability constants of the complexes formed with Mn(II) and other biologically relevant metal ions (Mg(II), Ca(II), Cu(II) and Zn(II)) were determined using potentiometric titrations (I = 0.15 M NaCl, T = 25 °C). The conditional stabilities of Mn(II) complexes at pH 7.4 are comparable to those reported for the cyclen-based tDO2A2− ligand. The dissociation of the Mn(II) chelates were investigated by evaluating the rate constants of metal exchange reactions with Cu(II) under acidic conditions (I = 0.15 M NaCl, T = 25 °C). Dissociation of the [Mn(tO2DO2A)(H2O)] complex occurs through both proton− and metal−assisted pathways, while the [Mn(tO2DO2AMPip)(H2O)] analogue dissociates through spontaneous and proton-assisted mechanisms. The Mn(II) complex of tO2DO2A2− is remarkably inert with respect to its dissociation, while the amide analogue is significantly more labile. The presence of a water molecule coordinated to Mn(II) imparts relatively high relaxivities to the complexes. The parameters determining this key property were investigated using 17O NMR (Nuclear Magnetic Resonance) transverse relaxation rates and 1H nuclear magnetic relaxation dispersion (NMRD) profiles.

Probing hydrocarbon dynamics at asphaltene/maltene interfaces for the global characterization of bitumen

Hypothesis.The objective is to noninvasively probe the local hydrocarbon dynamics at asphaltene/maltene interfaces to reveal the global characteristics of bitumen at increasing temperatures and under various mechanical constraints.Experiments.We propose multidimensional (1D and 2D) nuclear magnetic relaxation (NMR) experiments to characterize the dynamic properties of hydrocarbons for a set of bitumen from 40 to 180 °C. The convergence towards universal theoretical modelling of NMR relaxation experiments gives a comprehensive understanding of hydrocarbon transport in these very weakly permeable samples. Moreover, a multivariate statistical analysis allows for correlating these NMR relaxation data for all bitumen samples to the main empirical parameters by qualifying the bitumen grading, such as the penetrability, softening and fragility points over a large range of temperatures.Findings.These new experimental and theoretical multiscale approaches link hydrocarbon interfacial dynamics to the global characteristics of various bitumen types. This is critical for grading these universally encountered materials.

Similarities and Differences among Protein Dynamics Studied by Variable Temperature Nuclear Magnetic Resonance Relaxation.

Understanding and describing the dynamics of proteins is one of the major challenges in biology. Here, we use multifield variable-temperature NMR longitudinal relaxation (R1) measurements to determine the hierarchical activation energies of motions of four different proteins: two small globular proteins (GB1 and the SH3 domain of α-spectrin), an intrinsically disordered protein (the C-terminus of the nucleoprotein of the Sendai virus, Sendai Ntail), and an outer membrane protein (OmpG). The activation energies map the motions occurring in the side chains, in the backbone, and in the hydration shells of the proteins. We were able to identify similarities and differences in the average motions of the proteins. We find that the NMR relaxation properties of the four proteins do share similar features. The data characterizing average backbone motions are found to be very similar, the same for methyl group rotations, and similar activation energies are measured. The main observed difference occurs for the intrinsically disordered Sendai Ntail, where we observe much lower energy of activation for motions of protons associated with the protein-solvent interface as compared to the others. We also observe variability between the proteins regarding side chain 15N relaxation of lysine residues, with a higher activation energy observed in OmpG. This hints at strong interactions with negatively charged lipids in the bilayer and provides a possible mechanistic clue for the "positive-inside" rule for helical membrane proteins. Overall, these observations refine the understanding of the similarities and differences between hierarchical dynamics in proteins.

Mn2+ Complexes with Pyclen-Based Derivatives as Contrast Agents for Magnetic Resonance Imaging: Synthesis and Relaxometry Characterization.

Magnetic resonance imaging (MRI) has a leading place in medicine as an imaging tool of high resolution for anatomical studies and diagnosis of diseases, in particular for soft tissues that cannot be accessible by other modalities. Many research works are thus focused on improving the images obtained with MRI. This technique has indeed poor sensitivity, which can be compensated by using a contrast agent (CA). Today, the clinically approved CAs on market are solely based on gadolinium complexes that may induce nephrogenic systemic fibrosis for patients with kidney failure, whereas more recent studies on healthy rats also showed Gd retention in the brain. Consequently, researchers try to elaborate other types of safer MRI CAs like manganese-based complexes. In this context, the synthesis of Mn2+ complexes of four 12-membered pyridine-containing macrocyclic ligands based on the pyclen core was accomplished and described herein. Then, the properties of these Mn(II) complexes were studied by two relaxometric methods, 17O NMR spectroscopy and 1H NMR dispersion profiles. The time of residence (τM) and the number of water molecules (q) present in the inner sphere of coordination were determined by these two experiments. The efficacy of the pyclen-based Mn(II) complexes as MRI CAs was evaluated by proton relaxometry at a magnetic field intensity of 1.41 T near those of most medical MRI scanners (1.5 T). Both the 17O NMR and the nuclear magnetic relaxation dispersion profiles indicated that the four hexadentate ligands prepared herein left one vacant coordination site to accommodate one water molecule, rapidly exchanging, in around 6 ns. Furthermore, it has been shown that the presence of an additional amide bond formed when the paramagnetic complex is conjugated to a molecule of interest does not alter the inner sphere of coordination of Mn, which remains monohydrated. These complexes exhibit r1 relaxivities, large enough to be used as clinical MRI CAs (1.7-3.4 mM-1·s-1, at 1.41 T and 37 °C).

Manganese(III) porphyrin oligomers as high-relaxivity MRI contrast agents

Manganese(III) porphyrins (MnIIIPs) as MRI contrast agents (CAs) have drawn particular attention due to their high longitudinal relaxivity (r1) and unique biodistribution. In this work, two MnIIIP-based oligomers, MnPD and MnPT, were designed to further improve the relaxivity with ease of synthesis. The two compounds were fully characterized and their nuclear magnetic relaxation dispersion (NMRD) profiles were acquired with a fast field cycling NMR relaxometer. Both of the compounds exhibited extended high molar r1 at high fields, higher than that of Gd-DTPA, the first clinical gadolinium(III)-based MRI CA. The r1 value of per manganese atom increased with the increasing number of MnIIIP building blocks, suggesting rotational correlation time (τR) played dominant role in the r1 dispersion. The toxicity of the two MnIIIPs and the imaging effectiveness were estimated in vitro and in vivo. With good biocompatibility, significant contrast enhancement, and complete excretion in 24 h, MnPD and MnPT are both promising for high field clinical applications. The applied strategy also potentially provided a facile approach for creation of more MnIIIP oligomer as efficient T1 MRI CAs.

Association Equilibria of Organo-Phosphoric Acids with Imines from a Combined Dielectric and Nuclear Magnetic Resonance Spectroscopy Approach.

Aggregates formed between organo-phosphoric acids and imine bases in aprotic solvents are the reactive intermediates in Brønsted acid organo-catalysis. Due to the strong hydrogen-bonding interaction of the acids in solution, multiple homo- and heteroaggregates are formed with profound effects on catalytic activity. Yet, due to the similar binding motifs—hydrogen-bonds—it is challenging to experimentally quantify the abundance of these aggregates in solution. Here we demonstrate that a combination of nuclear magnetic resonance (NMR) and dielectric relaxation spectroscopy (DRS) allows for accurate speciation of these aggregates in solution. We show that only by using the observables of both experiments heteroaggregates can be discriminated with simultaneously taking homoaggregation into account. Comparison of the association of diphenyl phosphoric acid and quinaldine or phenylquinaline in chloroform, dichloromethane, or tetrahydrofuran suggests that the basicity of the base largely determines the association of one acid and one base molecule to form an ion-pair. We find the ion-pair formation constants to be highest in chloroform, slightly lower in dichloromethane and lowest in tetrahydrofuran, which indicates that the hydrogen-bonding ability of the solvent also alters ion-pairing equilibria. We find evidence for the formation of multimers, consisting of one imine base and multiple diphenyl phosphoric acid molecules for both bases in all three solvents. This subsequent association of an acid to an ion-pair is however little affected by the nature of the base or the solvent. As such our findings provide routes to enhance the overall fraction of these multimers in solution, which have been reported to open new catalytic pathways.

Evaluation of the ex vivo liver viability using a nuclear magnetic resonance relaxation time-based assay in a porcine machine perfusion model

There is a dearth of effective parameters for selecting potentially transplantable liver grafts from expanded-criteria donors. In this study, we used a nuclear magnetic resonance (NMR) relaxation analyzer-based assay to assess the viability of ex vivo livers obtained via porcine donation after circulatory death (DCD). Ex situ normothermic machine perfusion (NMP) was utilized as a platform for viability test of porcine DCD donor livers. A liver-targeted contrast agent, gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid (Gd-EOB-DTPA), was injected into the perfusate during NMP, and the dynamic biliary excretion of the Gd-EOB-DTPA was monitored by measuring the longitudinal relaxation time (T1). The longitudinal relaxation rate (R1) of the bile was served as a parameter. The delay of increase in biliary R1 during early stage of NMP indicated the impaired function of liver grafts in both warm and cold ischemia injury, which was correlated with the change of alanine aminotransferase. The preservative superiority in cold ischemia of dual hypothermic oxygenated machine perfusion could also be verified by assessing biliary R1 and other biochemical parameters. This study allows for the dynamic assessment of the viability of porcine DCD donor livers by combined usage of ex situ NMP and NMR relaxation time based assay, which lays a foundation for further clinical application.

Estimating the nuclear magnetic resonance surface relaxivity of Eocene sandstones: A comparison of different approaches

Nuclear magnetic resonance (NMR) relaxometry typically involves the analysis of a relaxation time distribution. The surface relaxivity ([Formula: see text]) is the key parameter that relates the relaxation time to the pore radius. Only a good estimate of the surface relaxivity enables a reliable determination of the pore radius distribution in a rock or sediment sample. A wide variety of approaches for the estimation of [Formula: see text] has been proposed; however, the accuracy of [Formula: see text] determination approaches has rarely been checked. We have compared different approaches of [Formula: see text] determination for a set of Eocene sandstone samples. Most approaches based on a weighted logarithmic mean of relaxation times or the peak relaxation time result in significant underestimation of [Formula: see text]. However, the correct weighting of the set of relaxation times has proven to be a crucial approach in [Formula: see text] determination. The consequent application of geometric rules suggests the application of the weighted harmonic mean ([Formula: see text]). The specific surface area per unit pore volume ([Formula: see text]), which results from the gas adsorption method, is another crucial parameter in most approaches for [Formula: see text] estimation. The quantities [Formula: see text] and [Formula: see text] depend on the resolution of the used method. Applying the fractal theory, we adopt an approach that performs an upscaling of [Formula: see text] to the resolution of the NMR relaxometry. Using equal resolution for [Formula: see text] and [Formula: see text], we obtain more reliable [Formula: see text] estimates. The resulting [Formula: see text] values are comparable with the ones determined by using the median relaxation time from NMR and the median pore-throat radius from the mercury injection capillary pressure method.

A Needless but Interesting Controversy with Pedagogical Overtones

A decade ago four independent groups, using four independent methods, reported the unanticipated and still surprising result that the bending modulus KC of bilayers of DOPC, unlike other standard lipids, does not increase with addition of cholesterol. A recent paper, using neutron spin echo (NSE) and nuclear magnetic resonance relaxation times (NMRτ), reports that the bending modulus of DOPC increases three fold with increasing cholesterol concentration up to 50%. It would appear that this has become a controversial topic. This controversy is needless because NSE and NMRτ do not measure the bending modulus as it has been defined for decades. Each measures important, complementary, properties that could enrich our understanding of bilayer properties, notably membrane viscosity and location of the neutral plane employed in membrane mechanics. The resolution of this controversy rests on elucidating the difference between measurements on a system in equilibrium that lead directly to equilibrium properties like the bending modulus, and measurements on the same equilibrium system that lead to more complex results involving both static moduli and transport properties. While the difference between static and non-equilibrium quantities is well understood in the physical sciences and statistical thermodynamics, this emerging controversy seems to warrant a pedagogical reminder.

Single Base-Pair Conformational Switch Modulates miR-34a Targeting of Sirt1 mRNA

MicroRNAs (miRNAs) regulate numerous messenger RNAs levels and translation, via binding to the protein Argonaute (Ago). The base pairing between the miRNA and mRNA in the seed region governs target selection and repression efficiency. Biochemical studies and X-ray crystallography structures elucidated the role of Ago and miRNA in this complex, however, structural information on the miRNA-mRNA duplex and its dynamics are still missing. We employ Nuclear Magnetic Resonance R1ρ Relaxation Dispersion and molecular simulations to study the structure and dynamics of miR-34a binding to mRNA of Sirt1, regulating p53 activity. We reveal a switching mode based on a single base pair rearrangement in the miRNA-mRNA duplex, elongating the 6/7mer seed to an 8mer seed. The base pair switch correlates with changing in overall structure of these conformers, which, in hAgo2, indicates two distinct binding modes and the stabilization of the minor conformer exhibit enhanced target repression in cells, shown by luciferase reporter assay. This change in activity indicates that the conformational switch in the miRNA-mRNA duplex can push the complex from an initial “screening” state to an “active” state. Our observations tie together current understanding of the step-wise miRNA target recognition process and shed light on the role of miRNA binding to mRNA beyond the seed.

Membrane Deformation Modulated by Hydration and Cholesterol Unveiled by Solid-State 2H NMR Spectroscopy

Phospholipid membranes are biological liquid crystals in which intermolecular interactions at mesoscopic length scales play key roles in the emergence of membrane physical properties like structure and rigidity. Such interactions modulated by membrane hydration [1] and cholesterol [2] have been investigated using solid-state 2H NMR spectroscopy. The average structure is manifested by the lineshapes through principal values of static or residual coupling tensors due to quadrupolar interactions. The residual quadrupolar couplings (RQCs) yield segmental order parameters for the individual acyl segments (i), providing average membrane properties such as bilayer thickness, area/lipid, and spontaneous curvature [3]. We show that membrane dehydration and increased cholesterol content result in greater RQCs, indicative of membrane thickening. Elastic membrane deformations are exhibited as collective order-director fluctuations (ODF) contributing to the nuclear magnetic relaxation. At mesoscopic length scales the thermal fluctuations connect to membrane mechanical properties via the fluctuation-dissipation theorem. Model-free interpretation of the functional dependence of spin-lattice relaxation rates, R1Z, on segmental order parameters (square-law) reveals emergent material properties in the liquid-crystalline state. The R1Z relaxation dispersion and temperature dependence of square-law plots indicate a nematic-like membrane hydrocarbon core. Solid-state 2H NMR relaxation studies demonstrate that both dehydration and increased cholesterol content in the membrane lead to decreased slopes of square-law plots, indicating an increase in membrane bending rigidity, consistent with neutron spin-echo (NSE) measurements. Analogous 2H NMR studies with various membrane lipid compositions and peptide-reconstituted membranes have addressed lipid-mediated cell signaling and lipid-protein interactions. Molecular dynamics simulations provide further insights on the correspondence of the solid-state NMR and NSE results. [1] K.J. Mallikarjunaiah et al. (2019) Phys. Chem. Chem. Phys. 21, 18422. [2] S. Chakraborty et al. (2020) Proc. Natl. Acad. Sci. 117, 21896. [3] Mallikarjunaiah et al. (2011) Biophys. J. 100, 98.

Gd3+ Complexes Conjugated to Cyclodextrins: Hydroxyl Functions Influence the Relaxation Properties

In the search for improvement in the properties of gadolinium-based contrast agents, cyclodextrins (CDs) are interesting hydrophilic scaffolds with high molecular weight. The impact of the hydrophilicity of these systems on the MRI efficacy has been studied using five β-CDs substituted with DOTA or TTHA ligands which, respectively, allow for one (q = 1) or no water molecule (q = 0) in the inner coordination sphere of the Gd3+ ion. Original synthetic pathways were developed to immobilize the ligands at C-6 position of various hydroxylated and permethylated β-CDs via an amide bond. To describe the influence of alcohol and ether oxide functions of the CD macrocycle on the relaxation properties of the Gd3+ complexes, 1H Nuclear Magnetic Relaxation Dispersion (NMRD) profiles, and 17O transverse relaxation rates have been measured at various temperatures. The differences observed between the hydroxylated and permethylated β-CDs bearing non-hydrated GdTTHA complexes can be rationalized by a second sphere contribution to the relaxivity in the case of the hydroxylated derivatives, induced by hydrogen-bound water molecules around the hydroxyl groups. In contrast, for the DOTA analogs the exchange rate of the water molecule directly coordinated to the Gd3+ is clearly influenced by the number of hydroxyl groups present on the CD, which in turn influences the relaxivity and gives rise to a very complex behavior of these hydrophilic systems.

Influence of Refrigerated Storage on Water Status, Protein Oxidation, Microstructure, and Physicochemical Qualities of Atlantic Mackerel (Scomber scombrus).

Moisture migration, protein oxidation, microstructure, and the physicochemical qualities of Atlantic mackerel during storage at 4 °C and 0 °C were explored in this study. Three proton components were observed in mackerel muscle using low-field nuclear magnetic resonance relaxation, which were characterized as bound water, immobilized water, and lipid. The relaxation peak of immobilized water shifted to a shorter relaxation time and its intensity decreased with the proceeding of the storage process. T1 and T2 weighted images obtained by magnetic resonance imaging showed a slightly continuous decrease in the intensity of water. The significant decrease in sulfhydryl (SH) content and the increase in carbonyl group (CP) content, disulfide bond content, and hydrophobicity revealed the oxidation of protein during storage. The contents of α-helixes in proteins decreased while that of random coils increased during storage, which suggested changes in the secondary structure of mackerel protein. The storage process also caused the contraction and fracture of myofibrils, and the granulation of endolysin protein. In addition, the drip loss, total volatile basic nitrogen (TVB-N), thiobarbituric acid-reactive substances (TBARS) value, and b* value increased significantly with the storage time.

Conformational Dynamics of Deubiquitinase A and Functional Implications.

Deubiquitinase A (DUBA) belongs to the ovarian tumor family of deubiquitinating enzymes and was initially identified as a negative regulator of type I interferons, whose overproduction has been linked to autoimmune diseases. The deubiquitinating activity of DUBA is positively regulated by phosphorylation at a single serine residue, S177, which results in minimal structural changes. We have previously shown that phosphorylation induces a two-state conformational equilibrium observed only in the active form of DUBA, highlighting the functional importance of DUBA dynamics. Here, we report the conformational dynamics of DUBA on the microsecond-to-millisecond time scales characterized by nuclear magnetic resonance relaxation dispersion experiments. We found that motions on these time scales are highly synchronized in the phosphorylated and nonphosphorylated DUBA. Despite the overall similarity of these two forms, different dynamic properties were observed in helix α1 and the neighboring regions, including residue S177, which likely contribute to the activation of DUBA by phosphorylation. Moreover, our data suggest that transient unfolding of helix α6 drives the global conformational process and that mutations can be introduced to modulate this process, which provides a basis for future studies to define the exact functional roles of motions in DUBA activation and substrate specificity.

Research of the chemical composition peculiarities of food additives – vegetable lecithins for the development of methods for assessing their quality

Lecithins are widely used in the food industry as food additives. In this regard, the requirements for the lecithins quality are quite high, and the development of the rapid determination methods of their quality indicators, including the acid value, is an urgent task. The article presents research of the peculiarities of vegetable lecithins chemical composition for the development of a method for determining their acid value using the pulsed nuclear magnetic relaxation (NMR) method. It was found that the studied lecithins differ significantly in the content of individual phospholipid groups exhibiting acidic properties. As a result of the research of the fatty acid composition of the lecithins acetone-soluble fractions, it was found that the highest total content of monounsaturated fatty acids is a characteristic of sunflower oleic type lecithins (81.3 %) and rapeseed lecithins (66.3 %), and polyunsaturated fatty acids – sunflower linoleic type lecithins (63.6 %) and soybean lecithins (67.7 %). Researches of the NMR characteristics of lecithins with the introduction of carbon tetrachloride (CCl4) have been carried out. It was found that the redistribution of component composition in the “lecithin-CCl4” system occurs at different ratios for each type of lecithin, which is due to their chemical composition peculiarities.

Using nuclear magnetic resonance proton relaxation to probe the surface chemistry of carbon 2D materials.

Nanomaterials exhibit a high surface-area-to-mass ratio, making surface properties key to optimising product performance. However, characterising surfaces at the nanoscale is difficult to achieve, especially as nanomaterials are often in liquid dispersions. Herein, we demonstrate the use of nuclear magnetic resonance proton relaxation for rapid characterisation of the surface chemistry of graphitic materials.

Fast Li Ion Dynamics in the Mechanosynthesized Nanostructured Form of the Solid Electrolyte Li3YBr6

The Y-halides Li3YBr6 and Li3YCl6 have recently gained considerable attention as they might be used as ceramic electrolytes in all-solid-state batteries. Such materials need to show sufficiently high ionic conductivities at room temperature. A thorough investigation of the relationship between ion dynamics and morphology, defect structure, and size effects is, however, indispensable if we want to understand the driving forces behind Li ion hopping processes in these ternary compounds. Li3YBr6 can be prepared by conventional solid-state synthesis routes. Nanostructured Li3YBr6 is, on the other hand, directly available by mechanosynthesis under ambient conditions. The present study is aimed at shedding light on the question of whether (metastable) mechanosynthesized Li3YBr6 might serve as a sustainable alternative to annealed Li3YBr6. For this purpose, we studied the impact of structural disorder on ionic transport by combining mechanosynthesis with soft-annealing steps to prepare Li3YBr6 in two different morphologies. While structural details were revealed by X-ray powder diffraction and by high-resolution 6Li and 79Br magic angle spinning nuclear magnetic resonance (NMR) spectroscopy, broadband impedance measurements in conjunction with time-domain 7Li NMR relaxation measurements helped us to characterize Li+ dynamics over a wide temperature range. Interestingly, for Li3YBr6, annealed at 823 K, we observed a discontinuity in conductivity at temperatures slightly below 273 K, which is almost missing for nano-Li3YBr6. This feature is, however, prominently seen in NMR spectroscopy for both samples and is attributed to a change of the Li sublattice in Li3YBr6 Although a bit lower in ionic conductivity, the nonannealed samples, even if obtained after a short milling period of only 1 h, shows encouraging dynamic parameters (0.44 mS cm–1, Ea = 0.34 eV) that are comparable to those of the sample annealed at high temperatures (1.52 mS cm–1, Ea = 0.28 eV). 7Li nuclear magnetic relaxation, being solely sensitive to Li+ hopping processes on shorter length scales, revealed highly comparable Li+ self-diffusion coefficients on the order of 10–12 m2 s–1, which we extracted directly from purely diffusion-controlled 7Li NMR rate peaks. Spin-lock 7Li NMR reveals a change from uncorrelated to correlated dynamics at temperatures as low as 220 K.

Rotational correlation times, diffusion coefficients and quadrupolar peaks of the protic ionic liquid ethylammonium nitrate by means of 1H fast field cycling NMR relaxometry

The protic ionic liquid (PIL) ethylammonium nitrate (EAN) is characterized by hydrogen bonding between the NH bonds of the cations and the oxygen atoms of the anions. The three-dimensional H-bond network of EAN very much resembles that of water. Although this first ionic liquid is known for more than 100 years, there is still lack of information about the rotational and translational dynamics, and how both are related to each other. For that purpose, we measured the 1H nuclear magnetic relaxation dispersion curves (NMRD) of EAN by means of Fast Field Cycling (FFC) NMR relaxometry. We were able to analyze the measured 1H spin-lattice relaxation rates R1 covering a large temperature range between 248 and 333 K simultaneously. Applying the well-known Bloembergen-Purcell-Pound (BPP) approach, we decomposed the total relaxation rates into intramolecular and intermolecular contributions, describing the rotational and translational dynamics of the ethylammonium cation. Here, we report rotational correlation times, τR, and translational diffusion coefficients, DT, both derived from the total 1H spin-lattice relaxation rates as a function of temperature and frequency. Self-diffusion coefficients, DT, were also determined from the total relaxation rates in the low frequency range, wherein only the intermolecular relaxation contribution is frequency dependent. Then, DT results from the slope of a linear fit of the spin-lattice relaxation rate R1 as a function of the square root of frequency, ν. The diffusion coefficients obtained from both methods are in good agreement with self-diffusion coefficients measured by pulsed-field-gradient (PFG) NMR. The rotational correlation times, τR, derived from the intramolecular 1H relaxation contribution were compared to correlation times obtained from high-field NMR deuteron relaxation experiments, dielectric spectroscopy (DS) and femto-second-infrared (fs-IR) spectroscopy. For EAN, we also observed a local enhancement of the 1H spin-lattice relaxation rates R1 at high frequencies. This so-called quadrupole relaxation enhancement (QRE) results from the interference of the Zeeman transition energy of the 1H spins and the energy difference of two levels of the quadrupole 14N nuclei. QRE is usually known for solids, but rarely for the liquid state as observed here for EAN. Overall, we show that FFC relaxometry provides access to rotational correlation times, translational diffusion coefficients and quadrupole relaxation enhancement at the same time.

Nuclear Magnetic Relaxation Time near the Compensation Temperature in a Ferrimagnetic Insulator

The nuclear magnetic relaxation time $T_1$ in ferrimagnetic insulators is calculated by a Raman process of hyperfine interaction with a meanfield approximation. It is found that the 1/$T_1$ on one site rapidly increases near the compensation temperature $T_0$, whereas that on another site does not increase up to Curie temperature $T_c$. This is due to that the band width of soft magnon becomes comparable to $T_0$. The increasing behavior of 1/$T_1$ below $T_c$ is found also in another type ferrimagnet, which shows hump structure in the temperature dependence of magnetization instead of compensation. Also in this case, we find the rapid increase of 1/$T_1$ below $T_c$, even though the magnetization does not show the compensation. Such a coexistence of soft and hard magnons will lead to remarkable properties of ferrimagnet.