Deuterium MAS NMR Studies of Dynamics on Multiple Timescales: Histidine and Oxalic Acid (original) (raw)
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Solid-state deuterium NMR investigation of internal motion in 2'-deoxythymidine
Journal of the American Chemical Society, 1988
molecules it is expected that the extreme narrowing limit holds. Our experiments with the two isotopes of chlorine provide a test for whether exchange is slow. If the line width were controlled by slow exchange, transverse relaxation should be essentially independent of the isotopic identity. The ratio of 35Cl and 37Cl line widths should then be unity.I2 On the other hand, if exchange is fast, the ratio of line widths should go as the square of the ratio of quadrupole moments (1 .262 = 1 .6).99'23'3 Indeed, except for the lowest concentration, the ratio of line widths is in the range 1.6-1.9. Thus, throughout the range of concentrations, exchange between free and associated perchlorate is fast. A possible alternative explanation, that the line broadening derives from exchange between environments with a very large chemical shift difference, is excluded by the observation of only a 38 ppm chemical shift difference between the species. We may conclude that each perchlorate ion must visit a silyl cation many times on the time scale of transverse relaxation, even at 0.584 M.14
Journal of The American Oil Chemists Society, 1992
Deuterium nuclear magnetic resonance (NMR) quadrupole echo spectra of deuterated acyl chains and the glyceryl moiety of tripalmitin were found to depend on the crystal form. At 20°C, which is below melting points, line shapes indicate that molecular motions in theβ form (triclinic subcell) are more restricted than inβ′ (orthorhombic) orα (hexagonal). Motional rates in excess of about 20 kHz are responsible for the line shapes. Spin-lattice relaxation, sensitive to motional frequencies in the tens of megahertz range, is much faster for methyl (CD2) groups inα orβ′ than inβ, indicating that fast motions are also governed by crystal form. General theoretical considerations suggest that motion of methylene groups is dynamically heterogeneous and that motion of methyl (CD3) groups may be averaged by motions other than rotation about the terminal C-C bond. The isothermal solid-state transition fromα toβ, induced by increasing the temperature to 35°C, was accompanied by NMR lineshape changes consistent with immobilization. The reversible transition ofα to “sub-α” upon cooling, accompanied by orthorhombic-like Bragg spacings and other changes in the X-ray pattern and by corresponding changes in the infrared spectrum, also produced a marked restriction in NMR-detected mobility of the kind seen inβ′ relative toα. The advantages of2H NMR for studies of motions and transitions in solid glycerides are discussed.
Protein Dynamics in the Solid State from 2 H NMR Line Shape Analysis: A Consistent Perspective
Deuterium line shape analysis of CD 3 groups has emerged as a particularly useful tool for studying microsecond−millisecond protein motions in the solid state. The models devised so far consist of several independently conceived simple jump-type motions. They are comprised of physical quantities encoded in their simplest form; improvements are only possible by adding yet another simple motion, thereby changing the model. The various treatments developed are case-specific; hence comparison among the different systems is not possible. Here we develop a new methodology for 2 H NMR line shape analysis free of these limitations. It is based on the microscopic-order-macroscopic-disorder (MOMD) approach. In MOMD motions are described by diffusion tensors, spatial restrictions by potentials/ordering tensors, and geometric features by relative tensor orientations. Jump-type motions are recovered in the limit of large orientational potentials. Model improvement is accomplished by monitoring the magnitude, symmetry, and orientation of the various tensors. The generality of MOMD makes possible comparison among different scenarios. CD 3 line shapes from the Chicken Villin Headpiece Subdomain and the Streptomyces Subtilisin Inhibitor are used as experimental examples. All of these spectra are reproduced by using rhombic local potentials constrained for simplicity to be given by the L = 2 spherical harmonics, and by axial diffusion tensors. Potential strength and rhombicity are found to be ca. 2− 3 k B T. The diffusion tensor is tilted at 120° from the C−CD 3 axis. The perpendicular (parallel) correlation times for local motion are 0.1−1.0 ms (3.3−30 μs). Activation energies in the 1.1−8.0 kcal/mol range are estimated. Future prospects include extension to the 2 H relaxation limit, application to the 15 N and 13 C NMR nuclei, and accounting for collective motions and anisotropic media.
Journal of Physical Chemistry B, 2015
Deuterium line shape analysis from mobile C−D and C−CD 3 groups has emerged as a particularly useful tool for studying dynamics in the solid state. The theoretical models devised so far consist typically of sets of independent dynamic modes. Each such mode is simple and usually casespecific. In this scenario, model improvement entails adding yet another mode (thereby changing the overall model), comparison of different cases is difficult, and ambiguity is unavoidable. We recently developed the microscopic order macroscopic disorder (MOMD) approach as a single-mode alternative. In MOMD, the local spatial restrictions are expressed by an anisotropic potential, the local motion by a diffusion tensor, and the local molecular geometry by relative (magnetic and model-related) tensor orientations, all of adjustable symmetry. This approach provides a consistent method of analysis, thus resolving the issues above. In this study, we apply MOMD to PS-adsorbed LKα14 peptide and dimethylammonium tetraphenylborate (C−CD 3 and N−CD 3 dynamics, respectively), as well as HhaI methyltransferase target DNA and phase III of benzene-6-hexanoate (C−D dynamics). The success with fitting these four disparate cases, as well as the two cases in the previous report, demonstrates the generality of this MOMD-based approach. In this study, C−D and C− CD 3 are both found to execute axial diffusion (rates R ⊥ and R ∥) in the presence of a rhombic potential given by the L = 2 spherical harmonics (coefficients c 0 2 and c 2 2). R ⊥ (R ∥) is in the 10 2 −10 3 (10 4 −10 5) s −1 range, and c 0 2 and c 2 2 are on the order of 2−3 k B T. Specific parameter values are determined for each mobile site. The diffusion and quadrupolar tensors are tilted at either 120°(consistent with trans−gauche isomerization) or nearly 110.5°(consistent with methyl exchange). Future prospects include extension of the MOMD formalism to include MAS, and application to 15 N and 13 C nuclei.
Solid State Nuclear Magnetic Resonance, 2018
We report on a new approach to the analysis of dynamic NMR lineshapes from polycrystalline (i.e., macroscopically disordered) samples in the presence of Magic Angle Spinning (MAS). This is an application of the Stochastic Liouville Equation developed by Freed and co-workers for treating restricted (i.e., microscopically ordered) motions. The 2 H nucleus in an internally-mobile C-CD 3 moiety serves as a prototype probe. The acronym is 2 H/MOMD/MAS, where MOMD stands for "microscopic-order-macroscopic-disorder." The key elements describing internal motions-their type, the local spatial restrictions, and related features of local geometry-are treated in MOMD generally, within their rigorous three-dimensional tensorial requirements. Based on this representation a single physically well-defined model of local motion has the capability of reproducing experimental spectra. There exist other methods for analyzing dynamic 2 H/MAS spectra which advocate simple motional modes. Yet, to reproduce satisfactorily the experimental lineshapes, one has either to use unusual parameter values, or combine several simple motional modes. The multi-simple-mode reasoning assumes independence of the constituent modes, features ambiguity as different simple modes may be used, renders inter-system comparison difficult as the overall models differ, and makes possible model-improvement only by adding yet another simple mode, i.e., changing the overall model. 2 H/MOMD/MAS is free of such limitations and inherently provides a clear physical interpretation. These features are illustrated. The advantage of 2 H/MOMD/MAS in dealing with sensitive but hardly investigated slow-motional lineshapes is demonstrated by applying it to actual experimental data. The results differ from those obtained previously with a two-site exchange scheme that yielded unusual parameters.
RSC Advances, 2019
NMR spectroscopy at two magnetic field strengths was employed to investigate the dynamics of dimethylimidazolium dimethylphosphate ([C 1 C 1 IM][(CH 3) 2 PO 4 ]). [C 1 C 1 IM][(CH 3) 2 PO 4 ] is a low-melting, halogen-free ionic liquid comprising of only methyl groups. 13 C spin-lattice relaxation rates as well as self-diffusion coefficients were measured for [C 1 C 1 IM][(CH 3) 2 PO 4 ] as a function of temperature. The rotational correlation times, s c , for the cation and the anion were obtained from the 13 C spin-lattice relaxation rates. Although from a theoretical point of view cations and anions are similar in size, they show different reorientation mobilities and diffusivities. The self-diffusion coefficients and the rotational correlation times were related to the radii of the diffusing spheres. The analysis reveals that the radii of the cation and the anion, respectively, are different from each other but constant at temperatures ranging from 293 to 353 K. The experimental results are rationalised by a discrete and individual cation and anion diffusion. The [(CH 3) 2 PO 4 ] À anion reorients faster compared to the cation but diffuses significantly slower indicating the formation of anionic aggregates. Relaxation data were acquired with standard liquid and magic-angle-spinning NMR probes to estimate residual dipolar interactions, chemical shift anisotropy or differences in magnetic susceptibility within the sample.
Journal de Physique, 1984
2014 Le temps de relaxation spin-réseau T1 et l'effet nucléaire Overhauser des trois carbones distincts du cyclopentène ont été mesurés en RMN du 13C entre 220 et 300 K, afin d'étudier la dynamique d'inversion de cette molécule en phase liquide. Les données ont d'abord été analysées dans l'hypothèse d'une diffusion rotationnelle du cyclopentène considéré comme un rotateur asymétrique rigide. La rotation la plus lente se produirait alors autour du pseudoaxe C5 avec des différences importantes entre les valeurs des trois constantes de diffusion rotationnelle. Ces conclusions semblent avoir peu de sens physique. De plus, elles sont en désaccord avec celles déduites d'études par infrarouge, Raman et diffusion des neutrons. Le mouvement d'inversion du cycle a donc été considéré ensuite comme un mécanisme efficace de relaxation du 13C. Bien que le nombre de paramètres nécessaire pour décrire les mouvements externes et internes excède le nombre d'informations expérimentales disponibles, on peut montrer que la molécule exécute environ (5 ± 4). 1012 sauts par seconde à 300 K entre ses deux conformations équivalentes, pliées selon un angle de 25 à 30°. L'énergie d'activation associée à ce processus semble assez faible puisque la fréquence de saut est encore de l'ordre de (1 ± 0,5).1012 s-1 à 220 K. D'autre part, la rotation d'ensemble de la molécule apparaît pratiquement isotrope en accord avec les conclusions des études optiques et neutroniques. On trouve Dr = (0,22 ± 0,02).1012 s-1 à 300 K et une énergie d'activation de 5,1 kJ. mole-1. Abstract. 2014 The 13C NMR spin-lattice relaxation time T1 and Nuclear Overhauser Effect (NOE) of the three distinct carbons of cyclopentene have been measured between 220 and 300 K in order to obtain some information about the ring-puckering motion in the liquid state. The data are first analysed under the hypothesis that the rotational diffusion of cyclopentene resembles that of a rigid asymmetric top. The slower rotation is then calculated to occur around the pseudo-C5 axis and large differences are found between the three rotational diffusion constants Dxx, Dyy, Dzz. These results seem to have little physical meaning. Furthermore they do not agree with those obtained by infrared, Raman and quasielastic neutron scattering. Therefore the ring-puckering motion has to be considered as an efficient 13C relaxation mechanism. Although parameters needed to describe both external and internal motions cannot all be determined from the information available one can qualitatively show that at 300 K the molecule executes about (5 ± 4). 1012 jumps s-1 between its two equivalent bent conformations characterized by a puckering angle of 25 to 30°. The activation energy associated with this process seems to be low since the jump rate is still about (1 ± 0.5). 1012 s-1 at 220 K. On the other hand, the whole molecule rotation is found to be nearly isotropic in agreement with the conclusions of the optical and neutron spectroscopies Dr = (0.22 ± 0.02).1012 s-1 at 300 K with an activation energy of 5.1 kJ. mole-1.