1H Relaxation Research Articles

Effect of Exchange Dynamics on the NMR Relaxation of Water in Porous Silica.

The interaction of molecules, in particular, water, with solid interfaces has been studied by a multitude of methods, among them nuclear magnetic resonance spin relaxation. The frequency dependence of the relaxation times follows patterns that have been interpreted in terms of the molecular orientation and dynamics. Several different model approaches could successfully explain limiting cases of 1H relaxation dispersion in systems with rigid surfaces such as silica gel or glass, but none of them can reproduce the relaxation of both 1H and 2H nuclei, which differ in their respective relaxation mechanisms, dipolar vs quadrupolar. From detailed studies of the dynamics of hydration of water in biological materials, the importance of hydrogen and molecular exchange to the longitudinal relaxation time of T1 was demonstrated. In this work, exchange times of both H2O and D2O in hydrophilic silica gel are varied in a controlled fashion in a wide range using disodium hydrogen phosphate, and the effect of physical exchange on spin relaxation is quantified for the first time in such systems using the exchange-mediated reorientation model.

Translational Dynamics of Cations and Anions in Ionic Liquids from NMR Field Cycling Relaxometry: Highlighting the Importance of Heteronuclear Contributions.

NMR field cycling relaxometry is a powerful method for determining the rotational and translational dynamics of ions, molecules, and dissolved particles. This is in particular true for ionic liquids (ILs) in which both ions carry NMR sensitive nuclei. In the IL triethylammonium bis(trifluoromethanesulfonyl)imide ([TEA][NTf2]), there are 1H nuclei at the [TEA]+ cations and 19F nuclei at the [NTf2]- anions. Moreover, the high viscosity of this IL leads to frequency-dependent relaxation rates, leaving the so-called extreme narrowing regime. Both the rotational and the translational dynamics of the constituents of ILs can be obtained by separating the contributions of intra- and intermolecular relaxation rates. In particular, the translational dynamics can be obtained separately by applying the so-called "low-frequency approach" (LFA), utilizing the fact that the change in the total relaxation rates at low frequencies results solely from translational motions. However, for systems containing multiple NMR active nuclei, heteronuclear interactions can also affect their relaxation rates. For [TEA][NTf2], the intermolecular relaxation rate is either the sum of 1H-1H cation-cation and 1H-19F cation-anion interactions or the sum of 19F-19F anion-anion and 19F-1H anion-cation interactions. Due to the lack of available experimental information, the 1H-19F heteronuclear intermolecular contribution has often been neglected in the past, assuming it to be negligible. Employing a suitable set of ILs and by making use of isotopic H/D substitution, we show that the 1H-19F heteronuclear intermolecular contribution in fact cannot be neglected and that the LFA cannot be applied to the total 1H and total 19F relaxation rates.

Small, Fluorinated Mn2+ Chelate as an Efficient 1H and 19F MRI Probe.

We explore the potential of fluorine-containing small Mn2+ chelates as alternatives to perfluorinated nanoparticles, widely used as 19F MRI probes. In MnL1, the cyclohexanediamine skeleton and two piperidine rings, involving each a metal-coordinating amide group and an appended CF3 moiety, provide high rigidity to the complex. This allows for good control of the Mn-F distance (rMnF=8.2±0.2 Å determined from 19F relaxation data), as well as for high kinetic inertness (a dissociation half-life of 1285 h is estimated for physiological conditions). The paramagnetic Mn2+ leads to a ~150-fold acceleration of the longitudinal 19F relaxation, with moderate line-broadening effect, resulting in T2/T1 ratios of 0.8 (9.4 T). Owing to its inner sphere water molecule, MnL1 is a good 1H relaxation agent as well (r1=5.36 mM-1 s-1 at 298 K, 20 MHz). MnL1 could be readily visualized in 19F MRI by using fast acquisition techniques, both in phantom images and living mice following intramuscular injection, with remarkable signal-to-noise ratios and short acquisition times. While applications in targeted imaging or cell therapy monitoring require further optimisation of the molecular structure, these results argue for the potential of such small, monohydrated and fluorinated Mn2+ complexes for combined 19F and 1H MRI detection.

Small, Fluorinated Mn2+ Chelate as an Efficient 1H and 19F MRI Probe

AbstractWe explore the potential of fluorine‐containing small Mn2+ chelates as alternatives to perfluorinated nanoparticles, widely used as 19F MRI probes. In MnL1, the cyclohexanediamine skeleton and two piperidine rings, involving each a metal‐coordinating amide group and an appended CF3 moiety, provide high rigidity to the complex. This allows for good control of the Mn−F distance (rMnF=8.2±0.2 Å determined from 19F relaxation data), as well as for high kinetic inertness (a dissociation half‐life of 1285 h is estimated for physiological conditions). The paramagnetic Mn2+ leads to a ~150‐fold acceleration of the longitudinal 19F relaxation, with moderate line‐broadening effect, resulting in T2/T1 ratios of 0.8 (9.4 T). Owing to its inner sphere water molecule, MnL1 is a good 1H relaxation agent as well (r1=5.36 mM−1 s−1 at 298 K, 20 MHz). MnL1 could be readily visualized in 19F MRI by using fast acquisition techniques, both in phantom images and living mice following intramuscular injection, with remarkable signal‐to‐noise ratios and short acquisition times. While applications in targeted imaging or cell therapy monitoring require further optimisation of the molecular structure, these results argue for the potential of such small, monohydrated and fluorinated Mn2+ complexes for combined 19F and 1H MRI detection.

Albumin nanoparticle electrostatically loaded with highly anionic Gd-thiacalixarene complex for MRI-guided neutron capture therapy

As a neutron capture therapy (NCT) agent, 157Gd garners significant attention due to the largest neutron capture cross section, emission of γ rays and Auger electrons, and facilitation of magnetic resonance imaging-guided NCT. Owing to its high kinetic stability, 1H relaxivity, and facile conjugation to albumin via electrostatic interactions, the negatively charged Gd3TCAS2 complex {TCAS = thiacalix[4]arene-p-tetrasulfonate (TCAS)} was incorporated into albumin nanoparticles (ANPs) in various configurations, including shell, core, and core-shell types, contingent on the positioning of Gd3TCAS2 within the ANP. The characteristics of the ANPs optimized with respect to loading capacity (LC) were explored, all of which demonstrated particle sizes suitable for passive delivery. The LC of Gd3TCAS2 per ANP increased in the following order: shell (1.1 %) < core (1.4 %) < core-shell (8.1 %). The leakage of Gd3TCAS2 after 7 d of storage was approximately 2 % for all ANPs, indicating stable Gd3TCAS2 loading. The 1H relaxivity (e.g., core-shell: r1 = 10.7 mM–1s–1) surpassed that of the Gd3TCAS2 complex alone (3.15 mM–1s–1). The luminescence emanating from Tb in MCF-7 cells co-cultured with Tb3TCAS2-loaded ANPs corroborated this cellular uptake. Gd uptake into MCF-7 cells via Gd3TCAS2-loaded ANPs was most pronounced for core-shell ANP at 1.33 ± 0.06 nmol/106 cells. The cytotoxicity of Gd3TCAS2-loaded ANPs was mitigated compared to free Gd3TCAS2 (CC50 = 52 µM), with shell and core-shell ANPs demonstrating nearly 100 % cell survival even at 50 µM. Cell viability post thermal neutron irradiation revealed the highest NCT efficacy for free Gd3TCAS2, attributed to its elevated cellular uptake (15.71 ± 0.57 nmol/106 cells). Core-shell ANP also exhibited a notable reduction in cell viability relative to the control, validating their potential as a promising GdNCT agent.

Deuterium spin relaxation of fractionally deuterated ribonuclease H using paired 475 and 950MHz NMR spectrometers.

Deuterium (2H) spin relaxation of 13CH2D methyl groups has been widely applied to investigate picosecond-to-nanosecond conformational dynamics in proteins by solution-state NMR spectroscopy. The B0 dependence of the 2H spin relaxation rates is represented by a linear relationship between the spectral density function at three discrete frequencies J(0), J(ωD) and J(2ωD). In this study, the linear relation between 2H relaxation rates at B0 fields separated by a factor of two and the interpolation of rates at intermediate frequencies are combined for a more robust approach for spectral density mapping. The general usefulness of the approach is demonstrated on a fractionally deuterated (55%) and alternate 13C-12C labeled sample of E. coli RNase H. Deuterium relaxation rate constants (R1, R1ρ, RQ, RAP) were measured for 57 well-resolved 13CH2D moieties in RNase H at 1H frequencies of 475MHz, 500MHz, 900MHz, and 950MHz. The spectral density mapping of the 475/950MHz data combination was performed independently and jointly to validate the expected relationship between data recorded at B0 fields separated by a factor of two. The final analysis was performed by jointly analyzing 475/950MHz rates with 700MHz rates interpolated from 500/900MHz data to yield six J(ωD) values for each methyl peak. The J(ω) profile for each peak was fit to the original (τM, Sf2, τf) or extended model-free function (τM, Sf2, Ss2, τf, τs) to obtain optimized dynamic parameters.

Range and sensitivity of 17O nuclear spin-lattice relaxation as a probe of aqueous electrolyte dynamics.

The study of electrolytic solutions is of relevance in many research fields, ranging from biophysics, materials, and colloid science to catalysis and electrochemistry. The dependence of solution dynamics on the nature of electrolytes and their concentrations has been the subject of many experimental and computational studies, yet it remains challenging to obtain a full understanding of the factors that govern solution behavior. Here, we provide additional insights into the behavior of aqueous solutions of alkali chlorides by combining 17O relaxation data with diffusion and viscosity data and contrast their behavior with 1H nuclear magnetic resonance relaxation data. The main findings are that 17O relaxation correlates well with viscosity data but not with diffusion data, while 1H relaxation correlates with neither. Certain ionic trends match known ion-specific series behavior, especially at high concentrations. Notably, we also examine the ranges of the interactions and conclude that the majority of the effects are tied to local water reorientation dynamics.

Dynamics of ionic liquids by means of nuclear magnetic resonance relaxation - overview of theoretical approaches.

This paper presents a comprehensive overview of the spin relaxation theory needed for exploring nuclear magnetic resonance (NMR) relaxometry to study the dynamical properties of ionic liquids. The term NMR relaxometry refers to relaxation experiments performed over a wide range of magnetic fields (resonance frequencies). In this way, dynamical processes occurring on timescales from milliseconds to nanoseconds can be studied, including translational and rotational dynamics of both types of ions (cations and anions). In order to take advantage of the remarkable experimental possibilities, appropriate theoretical models linking relaxation properties with ionic motion are needed. With the aim of providing such theoretical tools, 1H and 19F relaxation models for ionic liquids have been reviewed and their applications have been illustrated by several examples. The presented models are valid for an arbitrary magnetic field, include all relevant relaxation pathways and allow to extract detailed information about the translational and rotational dynamics of the ions. On the basis of the theoretical models, formulas allowing a straightforward determination of the translational diffusion coefficients of cations and anions from combined 1H and 19F relaxation studies have been derived and discussed in detail.

Catalytic Cracking of 1,3,5‐Triisopropylbenzene and Low‐Density Polyethylene over Hierarchical Y Zeolites and Al‐SBA‐15

AbstractCatalytic cracking of high molecular weight hydrocarbons underpins the production of fossil fuels from petroleum vapour and the recycling of polyolefin waste plastic. However, thermal cracking over conventional microporous solid acids is hindered by poor mass‐transport. Here we explore the performance of hierarchical H−Y zeolites and Al‐SBA‐15 for the catalytic cracking of 1,3,5‐triisopropylbenzene (1,3,5‐TIPB) and low‐density polyethylene (LDPE) in a continuous fixed‐bed flow reactor. Dealumination by acid washing was used to create hierarchical mesoporosity in H−Y zeolite and modify the solid acidity. Physicochemical properties were studied by X‐ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), gas adsorption, in‐situ Fourier transform infrared (FTIR), ex‐situ pyridine DRIFT, 29Si and 27Al nuclear magnetic resonance (NMR), and 1H relaxation and pulsed field gradient (PFG) NMR diffusion studies. Despite weakening acidity, the introduction of hierarchical porosity promotes deep cracking of both feedstocks; HNO3 dealuminated H−Y produces five times more cumene and benzene from 1,3‐5‐TIPB, and 33 % more benzene and xylenes from LDPE, than the parent H−Y.

2H and 13C nuclear spin relaxation unravels dynamic heterogeneities in deep eutectic solvents of ethylene glycol, glycerol, or urea with choline chloride

Using deuteron spin-lattice and spin-spin relaxometry, the reorientational dynamics of ethaline (choline chloride/ethylene glycol) and reline (choline chloride/urea) are studied in a component-selective, isotope-edited manner over a wide temperature range, thereby complementing previous work on glyceline (choline chloride/glycerol). Differences in the hydrogen bond propensities effectuate that in reline and glyceline, the choline ions move faster than the hydrogen bond donors, glycerol and urea; in ethaline, the ethylene glycol molecules are reorienting faster. For glyceline and reline, the increase in the corresponding time scale ratio indicates a pronounced strengthening of the glycerol and urea networks upon cooling, while in ethaline, the time scale ratio remains essentially constant. For the three deep eutectic solvents, a comparison of the present component-selective results with the dielectric time constants shows that the latter are primarily sensitive to the dynamics of the respective hydrogen bond donors. In a Walden-type plot, the reorientation rates, selectively determined for the hydrogen bond donors and acceptors, are compared with their conductivity and fluidity, revealing that the dynamics of the choline ions relate most directly to the charge transport.

Precision measurements of relaxation rates of degenerate 1H transitions in methyl groups of small proteins

An NMR experiment is designed for accurate and robust measurement of transverse relaxation rates of degenerate 1H transitions in selectively 13CH3-labeled, deuterated small proteins. The measurement is based on the use of acute (<90°) angle 1H radio-frequency pulses and relies on selection of the slow- and fast-relaxing components of methyl magnetization following the relaxation period in separate experiments. The R2 decay series recorded with selection of the fast-relaxing components serves as a useful complement to the R2 series acquired with selection of the slow-relaxing part, and permits the extension of the range of relative contributions of the fast- and slow-relaxing parts to apparent signal decay. The approach is experimentally verified on 13CH3 methyl groups of the ILV-{13CH3}-labeled protein ubiquitin at 10 °C and 25 °C. The obtained methyl 1H relaxation rates are in remarkably good agreement with the values obtained from well-established NMR techniques.

Effect of Magnetic Anisotropy on the 1H NMR Paramagnetic Shifts and Relaxation Rates of Small Dysprosium(III) Complexes.

We present a detailed analysis of the 1H NMR chemical shifts and transverse relaxation rates of three small Dy(III) complexes having different symmetries (C3, D2 or C2). The complexes show sizeable emission in the visible region due to 4F9/2 → 6HJ transitions (J = 15/2 to 11/2). Additionally, NIR emission is observed at ca. 850 (4F9/2 → 6H7/2), 930 (4F9/2 → 6H5/2), 1010 (4F9/2 → 6F9/2), and 1175 nm (4F9/2 → 6F7/2). Emission quantum yields of 1-2% were determined in aqueous solutions. The emission lifetimes indicate that no water molecules are present in the inner coordination sphere of Dy(III), which in the case of [Dy(CB-TE2PA)]+ was confirmed through the X-ray crystal structure. The 1H NMR paramagnetic shifts induced by Dy(III) were found to be dominated by the pseudocontact mechanism, though, for some protons, contact shifts are not negligible. The analysis of the pseudocontact shifts provided the magnetic susceptibility tensors of the three complexes, which were also investigated using CASSCF calculations. The transverse 1H relaxation data follow a good linear correlation with 1/r6, where r is the distance between the Dy(III) ion and the observed proton. This indicates that magnetic anisotropy is not significantly affecting the relaxation of 1H nuclei in the family of complexes investigated here.

Hydration and Mobility of Alkaline Metal Cations in Sulfonic Cation Exchange Membranes.

The interconnection of ionogenic channel structure, cation hydration, water and ionic translational mobility was revealed in Nafion and MSC membranes based on polyethylene and grafted sulfonated polystyrene. A local mobility of Li+, Na+ and Cs+ cations and water molecules was estimated via the 1H, 7Li, 23Na and 133Cs spin relaxation technique. The calculated cation and water molecule self-diffusion coefficients were compared with experimental values measured using pulsed field gradient NMR. It was shown that macroscopic mass transfer is controlled by molecule and ion motion near sulfonate groups. Lithium and sodium cations whose hydrated energy is higher than water hydrogen bond energy move together with water molecules. Cesium cations in possession of low hydrated energy are directly jumping between neighboring sulfonate groups. Cation Li+, Na+ and Cs+ hydration numbers (h) in membranes were calculated from 1H chemical shift water molecule temperature dependences. The values calculated from the Nernst-Einstein equation and the experimental conductivity values were close to each other in Nafion membranes. In MSC membranes, calculated conductivities were one order of magnitude more compared to the experimental ones, which is explained by the heterogeneity of the membrane pore and channel system.

Binary fluids in mesoporous materials: Phase separation studied by NMR relaxation and diffusion

Relaxation and diffusion measurements were carried out on single and binary liquids filling the pore space of controlled porous glass Vycor with an average pore size of about 4 nm. The dispersion of the longitudinal relaxation time T1 is discussed as a means to identify liquid-surface interaction based on existing models developed for metal-free glass surfaces. In addition, the change of T1 and T2 with respect to their bulk values is discussed, in particular T2 serves as a probe for the strength of molecular interactions. As the native glass surface is polar and contains a large amount of hydroxyl groups, a pronounced interaction of polar and protic adsorbate liquids is expected; however, the T1 dispersion, and the corresponding reduction of T2, are also observed for non-polar liquids such as alkanes and cyclohexane. Deuterated liquids are employed for simplifying data analysis in binary systems, but also for separating the respective contributions of intra- and intermolecular interactions to the overall relaxation rate. Despite the lack of paramagnetic impurities in the glass material, 1H and 2H relaxation dispersions of equivalent molecules are frequently found to differ from each other, suggesting intermolecular relaxation mechanisms for the 1H nuclei. The variation of the T1 dispersion when comparing single and binary systems gives clear evidence for the preferential adsorption of one of the two liquids, suggesting complete phase separation in several cases. Measurement of the apparent tortuosity by self-diffusion experiments supports the concept of a local variation of sample composition within the porespace.

Identification of Natural Products Inhibiting SARS-CoV-2 by Targeting Viral Proteases: A Combined in Silico and in Vitro Approach.

In this study, an integrated in silico-in vitro approach was employed to discover natural products (NPs) active against SARS-CoV-2. The two SARS-CoV-2 viral proteases, i.e., main protease (Mpro) and papain-like protease (PLpro), were selected as targets for the in silico study. Virtual hits were obtained by docking more than 140,000 NPs and NP derivatives available in-house and from commercial sources, and 38 virtual hits were experimentally validated in vitro using two enzyme-based assays. Five inhibited the enzyme activity of SARS-CoV-2 Mpro by more than 60% at a concentration of 20 μM, and four of them with high potency (IC50 < 10 μM). These hit compounds were further evaluated for their antiviral activity against SARS-CoV-2 in Calu-3 cells. The results from the cell-based assay revealed three mulberry Diels-Alder-type adducts (MDAAs) from Morus alba with pronounced anti-SARS-CoV-2 activities. Sanggenons C (12), O (13), and G (15) showed IC50 values of 4.6, 8.0, and 7.6 μM and selectivity index values of 5.1, 3.1 and 6.5, respectively. The docking poses of MDAAs in SARS-CoV-2 Mpro proposed a butterfly-shaped binding conformation, which was supported by the results of saturation transfer difference NMR experiments and competitive 1H relaxation dispersion NMR spectroscopy.

Investigating bone resorption in Atlantic herring fish intermuscular bones with solid-state NMR.

Bones are connective tissues mainly made of collagen proteins with calcium phosphate deposits. They undergo constant remodeling, including destroying existing bones tissues (known as bone resorption) and rebuilding new ones. Bone remodeling has been well-described in mammals, but it is not the case in fish. Here, we focused on the mobile phase of the bone vascular system by carefully preserving moisture in adult Atlantic herring intermuscular bones. We detected pore water with high ionic strength and soluble degraded peptides whose 1H-transverse relaxation times, T2s, exceed 15 milliseconds. With favorable T2s, we incorporated a solution state spinlock scheme into the INEPT techniques to unequivocally demonstrate collagen degradation. In addition, we detected a substantial amount of inorganic phosphate in solution with 31P-NMR in the considerable background of solid hydroxyapatite calcium phosphate by saturation recovery experiment. It is consistent with the idea that bone resorption degrades bone collagen and releases calcium ions and phosphate ions in the pore water with increased ionic strength. Our report is the first to probe the resorption process in the heterogenous bone microstructure with a rigorous characterization of 1H and 13C relaxation behavior and direct assignments. In addition, we contribute to the fish bones literature by investigating fish bone remodeling using NMR for the first time.

High-Field (3.4 T) Electron Paramagnetic Resonance, 1H Electron-Nuclear Double Resonance, ESEEM, HYSCORE, and Relaxation Studies of Asphaltene Solubility Fractions of Bitumen for Structural Characterization of Intrinsic Carbon-Centered Radicals

Petroleum asphaltenes are considered the most irritating components of various oil systems, complicating the extraction, transportation, and processing of hydrocarbons. Despite the fact that the paramagnetic properties of asphaltenes and their aggregates have been studied since the 1950s, there is still no clear understanding of the structure of stable paramagnetic centers in petroleum systems. The paper considers the possibilities of various electron paramagnetic resonance (EPR) techniques to study petroleum asphaltenes and their solubility fractions using a carbon-centered stable free radical (FR) as an intrinsic probe. The dilution of asphaltenes with deuterated toluene made it possible to refine the change in the structure at the initial stage of asphaltene disaggregation. From the measurements of samples of bitumen, a planar circumcoronene-like model of FR structure and FR-centered asphaltenes is proposed. The results show that EPR-based approaches can serve as sensitive numerical tools to follow asphaltenes' structure and their disaggregation.

Quantitative Multistate Binding Model of Silica Nanoparticle-Protein Interactions Obtained from Multinuclear Spin Relaxation.

Nanoparticle-assisted NMR spin relaxation (NASR), which makes internal protein dynamics in solution directly observable on nanosecond to microsecond time scales, has been applied to different nuclei and relaxation processes of the same protein system. A model is presented describing the transient interaction between ubiquitin and anionic silica nanoparticles for the unified interpretation of a wealth of experimental data including 2H, 13C, and 15N relaxation of methyl side chain and backbone moieties. The best model, implemented using a stochastic Liouville equation, describes the exchange process via an intermediary encounter state between free and fully nanoparticle-bound protein. The implication of the three-state binding model on the interpretation of NASR data is discussed.

Radical-Induced Low-Field 1H Relaxation in Solid Pyruvic Acid Doped with Trityl-OX063.

In dynamic nuclear polarization (DNP), radicals such as trityl provide a source for high nuclear spin polarization. Conversely, during the low-field transfer of hyperpolarized solids, the radicals' dipolar or Non-Zeeman reservoir may act as a powerful nuclear polarization sink. Here, we report the low-temperature proton spin relaxation in pyruvic acid doped with trityl, for fields from 5 mT to 2 T. We estimate the heat capacity of the radical Non-Zeeman reservoir experimentally and show that a recent formalism by Wenckebach yields a parameter-free, yet quantitative model for the entire field range.

Modeling Molecular Interactions with Wetting and Non-Wetting Rock Surfaces by Combining Electron Paramagnetic Resonance and NMR Relaxometry.

Three types of natural rocks─Bentheimer and Berea sandstones, as well as Liège Chalk─have been aged by immersion in a bitumen solution for extended periods of time in two steps, changing the surface conditions from water-wet to oil-wet. NMR relaxation dispersion measurements were carried out on water and oil constituents, with saturated and aromatic molecules considered individually. In order to separate the different relaxation mechanisms discussed in the literature, 1H and 19F relaxation times were compared to 2H for fully deuterated liquids: while 2H relaxes predominantly by quadrupolar coupling, which is an intramolecular process, the remaining nuclei relax by dipolar coupling, which potentially consists of intra- and intermolecular contributions. The wettability change becomes evident in an increase of relaxation rates for oil and a corresponding decrease for water. However, this expected behavior dominates only for the spin-lattice relaxation rate R1 at very low field strengths and for the spin-spin relaxation rate R2, while high-field longitudinal relaxation shows a much weaker or even reverse trend. This is attributed in part to a change of radical concentration on the pore surface upon coverage of the native rock surface by bitumen as well as by the change of surface chemistry and roughness. EPR and DNP measurements quantify the change of volume vs surface radical concentration in the rocks, and an improved understanding of the role of relaxation via paramagnetic centers is obtained. By means of comparing different fluids and nuclei in combination with a defined wettability change of natural rocks, a refined model for molecular dynamics in conjunction with NMR relaxation dispersion is proposed.