The Experts below are selected from a list of 121176 Experts worldwide ranked by ideXlab platform
Michael F Brown - One of the best experts on this subject based on the ideXlab platform.
-
chapter 17 structural dynamics of retinal in rhodopsin activation viewed by solid state 2H NMR Spectroscopy
2014Co-Authors: Michael F Brown, Andrey V StrutsAbstract:Rhodopsin is a member of the family of G-protein-coupled receptors (GPCRs) that are implicated in cellular signaling and constitute the majority of human pharmaceutical targets. Solid-state 2H NMR Spectroscopy can be used to obtain structural and dynamical information unavailable from X-ray crystallography and other biophysical methods. In this approach, site-specific 2H labels are introduced into the methyl groups of retinal that play an important role in rhodopsin function. Analysis of angular-dependent 2H NMR lineshapes for rhodopsin in aligned membranes enables determination of the average ligand conformation within the binding pocket. Solid-state 2H NMR relaxation methods further allow the investigation of light-induced changes in local ps–ns timescale motions of retinal bound to rhodopsin. In terms of a multi-scale activation mechanism, changes in retinal structure and dynamics upon photon absorption activate fluctuations of transmembrane helices H5 and H6 in rhodopsin. Allosteric interactions due to light absorption of rhodopsin are propagated from the retinal-binding pocket to the binding site of the G-protein transducin. An ensemble of substates in the Meta I–Meta II equilibrium yields the first amplification step in the visual response and may be typical for the activation mechanisms of other GPCRs in a membrane environment.
-
intermembrane forces probed by osmotic stress and solid state 2H NMR Spectroscopy
Biophysical Journal, 2012Co-Authors: Jacob J Kinnun, K J Mallikarjunaiah, Horia I Petrache, Michael F BrownAbstract:Intermembrane forces play a significant role in biological processes such as fusion, shape transformations, and lipid-protein interactions. Forces suggested to govern intermembrane interactions include van der Waals attraction, membrane undulations, hydration force, and lipid protrusions. How do the regimes of these forces overlap and how can we experimentally study them? Through use of osmolytes and dehydration we can control intermembrane spacing in liquid-crystalline DMPC-d54 membranes [1]. Measured order parameters from solid-state 2H NMR Spectroscopy allow deformations to be accessed at a molecularly resolved level [2]. Stresses from dehydration and osmotic pressure are thermodynamically equivalent, because the change in chemical potential when transferring water from the interlamellar space to the bulk water phase corresponds to an induced pressure. A unified theoretical framework predicts an ideal equation of state for the membrane system that depends inversely on the number waters per lipid as confirmed by experimental 2H NMR data [1]. Non-ideal interactions (intermembrane forces) within the membrane system are treated in terms of an osmotic coefficient. Intermembrane forces have differing temperature dependences and can be separated by the temperature variation of the osmotic coefficient. At lower osmotic pressures (larger intermembrane separation) the osmotic coefficient has a linear temperature dependence, agreeing with theoretical predictions for thermal undulations. At high pressures (smaller intermembrane separation) the osmotic coefficient becomes independent of temperature, in accord with predictions for lipid protrusions. Our evidence shows that undulations dominate at intermediate intermembrane distances and protrusions dominate at short distances. We provide a new experimental method for understanding intermembrane forces. This understanding is needed for the interpretation of membrane fusion, shape transformations, and lipid-protein interactions. [1] K.J. Mallikarjunaiah et al. (2011) Biophys. J.100, 98-107. [2] A. Leftin and M.F. Brown (2011) BBA1808, 818-839.
-
phase separation in binary mixtures of bipolar and monopolar lipid dispersions revealed by 2H NMR Spectroscopy small angle x ray scattering and molecular theory
Biophysical Journal, 2009Co-Authors: David Brownholland, Andrey V Struts, Michael F Brown, Horia I Petrache, Gabriel S Longo, Matthew J Justice, Igal Szleifer, David H ThompsonAbstract:Binary mixtures of C20BAS and POPC membranes were studied by solid-state 2H NMR Spectroscopy and small angle x-ray scattering (SAXS) over a wide range of concentrations and at different temperatures. Three specifically deuterated C20BAS derivatives—[1′,1′,20′,20′-2H4]C20BAS, [2′,2′,19′,19′-2H4]C20BAS, and [10′,11′-2H2]C20BAS—combined with protiated 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), as well as membranes containing POPC-d31 and fully protiated bolalipid, were used in NMR experiments to obtain structural information for the mixtures. The 2H NMR spectra of [10′,11′-2H2]C20BAS/POPC membrane dispersions reveal that the bolalipid is predominantly in the transmembrane conformation at high bolalipid concentrations (100, 90, and 70 mol %). At ≤50 mol % C20BAS, smaller quadrupolar couplings appear in the spectra, indicating the presence of U-shaped conformers. The proportion of U-shaped bolalipids increases as the amount of POPC in the membrane increases; however, the transmembrane component remains the dominant bolalipid conformation in the membrane even at 45°C and 10 mol % C20BAS, where it accounts for ∼50% of the bolalipid population. The large fraction of C20BAS transmembrane conformers, regardless of the C20BAS/POPC ratio, together with the findings from molecular mean-field theory calculations, suggests the coexistence of phase-separated bolalipid-rich domains and POPC-rich domains. A single lamellar repeat distance was observed in SAXS experiments corresponding to the average repeat spacing expected for C20BAS- and POPC-rich domains. These observations are consistent with the presence of microphase-separated domains in the mixed membrane samples that arise from POPC-C20BAS hydrophobic mismatch.
-
retinal conformation and dynamics in activation of rhodopsin illuminated by solid state 2H NMR Spectroscopy
Photochemistry and Photobiology, 2009Co-Authors: Michael F Brown, Koji Nakanishi, Gilmar F. Salgado, Karina Martinezmayorga, Andrey V StrutsAbstract:Solid-state NMR Spectroscopy gives a powerful avenue for investigating G protein-coupled receptors and other integral membrane proteins in a native-like environment. This article reviews the use of solid-state (2)H NMR to study the retinal cofactor of rhodopsin in the dark state as well as the meta I and meta II photointermediates. Site-specific (2)H NMR labels have been introduced into three regions (methyl groups) of retinal that are crucially important for the photochemical function of rhodopsin. Despite its phenomenal stability (2)H NMR Spectroscopy indicates retinal undergoes rapid fluctuations within the protein binding cavity. The spectral lineshapes reveal the methyl groups spin rapidly about their three-fold (C(3)) axes with an order parameter for the off-axial motion of SC(3) approximately 0.9. For the dark state, the (2)H NMR structure of 11-cis-retinal manifests torsional twisting of both the polyene chain and the beta-ionone ring due to steric interactions of the ligand and the protein. Retinal is accommodated within the rhodopsin binding pocket with a negative pretwist about the C11=C12 double bond. Conformational distortion explains its rapid photochemistry and reveals the trajectory of the 11-cis to trans isomerization. In addition, (2)H NMR has been applied to study the retinylidene dynamics in the dark and light-activated states. Upon isomerization there are drastic changes in the mobility of all three methyl groups. The relaxation data support an activation mechanism whereby the beta-ionone ring of retinal stays in nearly the same environment, without a large displacement of the ligand. Interactions of the beta-ionone ring and the retinylidene Schiff base with the protein transmit the force of the retinal isomerization. Solid-state (2)H NMR thus provides information about the flow of energy that triggers changes in hydrogen-bonding networks and helix movements in the activation mechanism of the photoreceptor.
-
solid state 2H NMR Spectroscopy reveals micromechanics of raft like ternary lipid membranes containing sphingomyelin and cholesterol
Biophysical Journal, 2009Co-Authors: Tim Bartels, Michael F Brown, Ravi S Lankalapalli, Robert Bittmann, Klaus BeyerAbstract:Much interest has been focussed recently on sphingomyelin as an essential component of a variety of biological membranes. Using solid-state 2H NMR Spectroscopy, we investigated the micromechanical effect of varying concentrations of cholesterol in ternary mixtures composed of N-palmitoylsphingomyelin (PSM), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), and cholesterol in unoriented multilamellar bilayers. The hydrocarbon chains of PSM or POPC were 2H labeled which enabled us to investigate the distribution and the order profiles of the individual lipid components in the mixtures [1]. A mean torque potential model [2] was employed to characterize the structural properties and map the existence of lipid domains in these mixtures. By calculating the average hydrocarbon thickness, area per lipid, and structural parameters such as chain extension and thermal expansion coefficients, we were able to further characterize the structural properties of these domains. We then measured R1Z relaxation rates, which in combination with order parameter profiles gave a signature square-law dependence corresponding to the mechanical properties of the respective lipid membranes on a mesoscopic length scale [3]. The slope of the square-law plots of relaxation rates and order parameter were found to decrease progressively with the mole fraction of cholesterol, due to a stiffening of the membrane. Different membrane domains thus gave distinctively different micromechanical signatures which indicated that the modes contributing to R1Z relaxation rates are on a length scale comparable to the lipid domain size.[1] Bartels, T. et al (2008) J. Am. Chem. Soc., in press.[2] Petrache, H.I. et al (2000) Biophys. J. 79, 3172-3192.[3] Brown, M.F. et al (2002) J. Am. Chem. Soc. 124, 8471-8484.
Alexander G Stepanov - One of the best experts on this subject based on the ideXlab platform.
-
exploring propane propylene separation mechanism in zif 8 zn by 2H NMR Spectroscopy
arXiv: Materials Science, 2019Co-Authors: Alexander E Khudozhitkov, Daniil I Kolokolov, Alexander G StepanovAbstract:The molecular mobility of propane and propylene has been studied by 2H NMR method. The activation barriers of diffusion determined from the spin relaxation analysis are in a good agreement with the values obtained by Liu et al. (EC3H8 = 38 kJ/mol, EC3H6 = 13.5 kJ/mol). High activation energy of the rotation inside the cavity for propylene compared to propane (8 kJ/mol vs 3.8 kJ/mol) implies stronger interaction of this adsorbate with the walls of the cavity.
-
porous metal organic polyhedral frameworks with optimal molecular dynamics and pore geometry for methane storage
Journal of the American Chemical Society, 2017Co-Authors: Yong Yan, Daniil I Kolokolov, Alexander G Stepanov, Ivan Da Silva, Alexander J Blake, Anne M Dailly, Pascal Manuel, Chiu C Tang, Sihai Yang, Martin SchroderAbstract:Natural gas (methane, CH4) is widely considered as a promising energy carrier for mobile applications. Maximizing the storage capacity is the primary goal for the design of future storage media. Here we report the CH4 storage properties in a family of isostructural (3,24)-connected porous materials, MFM-112a, MFM-115a, and MFM-132a, with different linker backbone functionalization. Both MFM-112a and MFM-115a show excellent CH4 uptakes of 236 and 256 cm3 (STP) cm–3 (v/v) at 80 bar and room temperature, respectively. Significantly, MFM-115a displays an exceptionally high deliverable CH4 capacity of 208 v/v between 5 and 80 bar at room temperature, making it among the best performing metal–organic frameworks for CH4 storage. We also synthesized the partially deuterated versions of the above materials and applied solid-state 2H NMR Spectroscopy to show that these three frameworks contain molecular rotors that exhibit motion in fast, medium, and slow regimes, respectively. In situ neutron powder diffraction st...
-
probing the guest mediated structural mobility in the uio 66 zr framework by 2H NMR Spectroscopy
Journal of Physical Chemistry C, 2017Co-Authors: Daniil I Kolokolov, Alexander G Stepanov, Alexander E Khudozhitkov, Hervé Jobic, Dieter Freude, Jurgen HaaseAbstract:The solid-state 2H NMR technique (analysis of both the spectrum line shape and the spin–lattice relaxation) was used to probe both slow and fast dynamical modes of the phenylene fragments of terephthalate linkers of the UiO-66(Zr) framework affected by the presence of benzene guest in the pores of the material. Such approach allowed us to probe different motions within a broad range of time scale, 10–3–10–11 s. The internal dynamics in the UiO-66(Zr) framework is represented by torsional motions of the phenylene fragment of the linker including 2-site 180° flips (π-flips) of the plane of the phenylene ring and its restricted librations. In the presence of benzene loaded in the MOF pores the rate of π-flips decreases essentially and the activation barrier for this motion increases. The activation barrier has been found to increase almost in a linear fashion on benzene loading. Such observation is surprisingly unique among other MOFs with mobile linkers, like MIL-53(Al) or MOF-5. The fast librational motion...
-
Probing the Guest-Mediated Structural Mobility in the UiO-66(Zr) Framework by 2H NMR Spectroscopy
2017Co-Authors: Alexander E. Khudozhitkov, Daniil I Kolokolov, Hervé Jobic, Dieter Freude, Jürgen Haase, Alexander G StepanovAbstract:The solid-state 2H NMR technique (analysis of both the spectrum line shape and the spin–lattice relaxation) was used to probe both slow and fast dynamical modes of the phenylene fragments of terephthalate linkers of the UiO-66(Zr) framework affected by the presence of benzene guest in the pores of the material. Such approach allowed us to probe different motions within a broad range of time scale, 10–3–10–11 s. The internal dynamics in the UiO-66(Zr) framework is represented by torsional motions of the phenylene fragment of the linker including 2-site 180° flips (π-flips) of the plane of the phenylene ring and its restricted librations. In the presence of benzene loaded in the MOF pores the rate of π-flips decreases essentially and the activation barrier for this motion increases. The activation barrier has been found to increase almost in a linear fashion on benzene loading. Such observation is surprisingly unique among other MOFs with mobile linkers, like MIL-53(Al) or MOF-5. The fast librational motion occurs on a scale of ∼1010 Hz and shows no notable dependence on the guest loading. It has been established that anisotropy of T1 relaxation of the 2H NMR powder pattern of the phenylene fragments is especially sensitive to the librational motion when this motion is in a range of 107–1011 Hz. Within this range of libration frequencies, analysis of the anisotropic spin–lattice (T1) relaxation allows quantitative estimation of the rate of librational motion
-
mobility of tert butyl alcohol in mfi framework type studied by deuterium NMR
Journal of Physical Chemistry C, 2012Co-Authors: Alena M Nishchenko, Daniil I Kolokolov, Anton A Gabrienko, Alexander G StepanovAbstract:The molecular mobility of deuterated tert-butyl alcohol (TBA) adsorbed in MFI framework type (silicalite-1 and ZSM-5 zeolite) has been studied by use of 2H NMR Spectroscopy in the range of 106–453 K. In H-ZSM-5, the reorientation of the molecule as a whole is strongly restricted (τC ≪ Q0–1 ≈ 10–6 s) by hydrogen bonding to Bronsted acid sites (BAS). Being adsorbed to BAS, the motion of TBA molecules is described by intramolecular rotations around two successive C3 and C3′ axes (CD3–C and C–O bonds). The activation energy for the methyl groups rotation around the C–O bond (Ea = 8.0 ± 1.6 kJ mol–1) is two times lower compared to that in solid TBA (J. Phys. Chem. A2011, 115, 7428). This shows that the motion of the butyl fragment of TBA in MFI framework is less restricted compared to the case of solid TBA. In silicalite-1, the TBA molecule is additionally involved into reorientational motions as a whole: one of the motions represents an exchange among orientations provided by the directions of four framework ...
Alfred Delville - One of the best experts on this subject based on the ideXlab platform.
-
influence of strong confinement on the structure and dynamics of liquids a study of the clay water interface exploiting 2H NMR Spectroscopy and spin locking relaxometry
Journal of Physical Chemistry C, 2018Co-Authors: Patrice Porion, Virginie Marry, Anne-laure Rollet, Anne Marie Faugere, Laurent J. Michot, E Dubois, Alfred DelvilleAbstract:2H NMR Spectroscopy, multiquanta relaxation, and spin-locking relaxometry are used to investigate the structural and dynamical properties of water molecules confined within dense sediments of synthetic fluorohectorite. As shown by the large residual splitting of the 2H NMR resonance line, water molecules confined in the interlamellar space of the clay are strongly oriented to contact with the fluorinated basal surface of the clay. Multiquanta relaxation measurements are used to identify and quantify the contributions of the quadrupolar and heteronuclear dipolar couplings by monitoring the NMR relaxation of the confined water molecules. Finally, the average residence time of the water molecules confined within the interlamellar space of the clay platelets is quantified by detailed analysis of 2H spin-locking relaxometry measurements. Thanks to the significant contributions of both quadripolar and heteronuclear dipolar relaxation mechanisms, 2H spin-locking relaxation measurements probe a broad dynamical ra...
-
multiscale water dynamics within dense clay sediments probed by 2H multiquantum NMR relaxometry and two time stimulated echo NMR Spectroscopy
Journal of Physical Chemistry C, 2013Co-Authors: Patrice Porion, Anne Marie Faugere, Alfred DelvilleAbstract:2H NMR Spectroscopy, relaxometry, and two-time correlation measurements are used to investigate the structural and dynamical properties of water molecules confined within the multiscale porous netw...
-
2H NMR Spectroscopy and multiquantum relaxometry as a probe of the magnetic field induced ordering of clay nanoplatelets within aqueous dispersions
Journal of Physical Chemistry C, 2011Co-Authors: Patrice Porion, Laurent J. Michot, Anne Marie Faugere, Erwan Paineau, Alfred DelvilleAbstract:2H NMR Spectroscopy and relaxometry were used to investigate the orientation of nontronite clay nanoplatelets induced by the static magnetic field within dilute aqueous dispersions by exploiting the residual quadrupolar splitting resulting from the specific orientation of heavy water molecules physisorbed at the clay surface. A careful analysis of the variation of the residual 2H splitting as a function of clay concentration and magnetic field strength was required to extract the intrinsic clay ordering induced by the magnetic field. The variation of clay ordering as a function of clay concentration clearly indicated two concentration regimes, corresponding to free and collective orientations of the clay platelets, respectively. Multiquantum NMR relaxation measurements were further used to identify the main NMR relaxation mechanism whose temperature variation is compatible with a fast exchange, at the NMR time scale, between free and physisorbed water molecules.
-
orientational microdynamics and magnetic field induced ordering of clay platelets detected by 2H NMR Spectroscopy
Langmuir, 2010Co-Authors: Patrice Porion, Laurent J. Michot, Anne Marie Faugere, Erwan Paineau, Alfred DelvilleAbstract:The orientation of montmorillonite clays induced by a static magnetic field is quantified by using 2H NMR Spectroscopy. Indeed, the residual quadrupolar splitting of the 2H resonance line measured for heavy water is a direct consequence of the specific orientation of the clay platelets in the static magnetic field. In the dilute regime, this residual splitting increases linearly with clay concentration, which confirms that the clay/clay electrostatic repulsions remain negligible by comparison with the diamagnetic coupling of these anisotropic platelets. At higher concentration, the electrostatic repulsion between clay particles markedly enhances the detected splitting. Such enhancement is well predicted by numerical simulations. By varying the size of the clay platelets and the strength of the static magnetic field, it is possible to evaluate the order of magnitude of the diamagnetic susceptibility of these anisotropic colloids.
-
structural and dynamical properties of the water molecules confined in dense clay sediments a study combining 2H NMR Spectroscopy and multiscale numerical modeling
Journal of Physical Chemistry C, 2007Co-Authors: Patrice Porion, Laurent J. Michot, And Anne Marie Faugere, Alfred DelvilleAbstract:2 H NMR Spectroscopy was used to detect the influence of confinement on the structural and dynamical properties of water molecules adsorbed in the interlamellar space of a natural clay (Montmorillonite) within partially hydrated self-supporting films. Multiscale numerical modeling (Monte Carlo simulations, molecular dynamics, and Brownian dynamics) was used to quantify the importance of the various relaxation mechanisms likely to be responsible for the NMR relaxation of the water molecules within such complex environment. Because of the significant fraction of iron present in these natural clays, the large value of the transverse relaxation rate measured for the confined water molecules is compatible with a dominant paramagnetic coupling modulated by the long-range diffusion of water molecules. Finally, the angular variation of the apparent relaxation rate can be used to extract the distribution of the directors of the clay lamellae within the self-supporting film.
Kenneth D M Harris - One of the best experts on this subject based on the ideXlab platform.
-
high resolution solid state 2H NMR Spectroscopy of polymorphs of glycine
Journal of Physical Chemistry A, 2011Co-Authors: Abil E Aliev, Samuel Edward Mann, Dinu Iuga, Colan E Hughes, Aisha S Rahman, Paul F Mcmillan, Furio Cora, Kenneth D M HarrisAbstract:High-resolution solid-state 2H MAS NMR studies of the α and γ polymorphs of fully deuterated glycine (glycine-d5) are reported. Analysis of spinning sideband patterns is used to determine the 2H quadrupole interaction parameters, and is shown to yield good agreement with the corresponding parameters determined from single-crystal 2H NMR measurements (the maximum deviation in quadrupole coupling constants determined from these two approaches is only 1%). From analysis of simulated 2H MAS NMR sideband patterns as a function of reorientational jump frequency (κ) for the −N+D3 group in glycine-d5, the experimentally observed differences in the 2H MAS NMR spectrum for the −N+D3 deutrons in the α and γ polymorphs is attributed to differences in the rate of reorientation of the −N+D3 group. These simulations show severe broadening of the 2H MAS NMR signal in the intermediate motion regime, suggesting that deuterons undergoing reorientational motions at rates in the range κ ≈ 104–106 s–1 are likely to be undetectable in 2H MAS NMR measurements for materials with natural isotopic abundances. The 1H NMR chemical shifts for the α and γ polymorphs of glycine have been determined from the 2H MAS NMR results, taking into account the known second-order shift. Further quantum mechanical calculations of 2H quadrupole interaction parameters and 1H chemical shifts reveal the structural dependence of these parameters in the two polymorphs and suggest that the existence of two short intermolecular C–H···O contacts for one of the H atoms of the >CH2 group in the α polymorph have a significant influence on the 2H quadrupole coupling and 1H chemical shift for this site.
-
natural abundance solid state 2H NMR Spectroscopy at high magnetic field
Journal of Physical Chemistry A, 2011Co-Authors: Abil E Aliev, Samuel Edward Mann, Dinu Iuga, Colan E Hughes, Kenneth D M HarrisAbstract:High-resolution solid-state 2H NMR Spectroscopy provides a method for measuring 1H NMR chemical shifts in solids and is advantageous over the direct measurement of high-resolution solid-state 1H NMR spectra, as it requires only the application of routine magic angle sample spinning (MAS) and routine 1H decoupling methods, in contrast to the requirement for complex pulse sequences for homonuclear 1H decoupling and ultrafast MAS in the case of high-resolution solid-state 1H NMR. However, a significant obstacle to the routine application of high-resolution solid-state 2H NMR is the very low natural abundance of 2H, with the consequent problem of inherently low sensitivity. Here, we explore the feasibility of measuring 2H MAS NMR spectra of various solids with natural isotopic abundances at high magnetic field (850 MHz), focusing on samples of amino acids, peptides, collagen, and various organic solids. The results show that high-resolution solid-state 2H NMR can be used successfully to measure isotropic 1H chemical shifts in favorable cases, particularly for mobile functional groups, such as methyl and −N+H3 groups, and in some cases phenyl groups. Furthermore, we demonstrate that routine 2H MAS NMR measurements can be exploited for assessing the relative dynamics of different functional groups in a molecule and for assessing whole-molecule motions in the solid state. The magnitude and field-dependence of second-order shifts due to the 2H quadrupole interaction are also investigated, on the basis of analysis of simulated and experimental 1H and 2H MAS NMR spectra of fully deuterated and selectively deuterated samples of the α polymorph of glycine at two different magnetic field strengths.
-
hydrogen bond dynamics in solid triphenylsilanol
Journal of Physical Chemistry B, 2002Co-Authors: Abil E Aliev, Catherine E Atkinson, Kenneth D M HarrisAbstract:Dynamic properties of the hydroxyl groups in a selectively deuterated polycrystalline sample of triphenylsilanol (Ph3SiOD) have been studied using variable-temperature solid-state 2H NMR Spectroscopy. The crystal structure of triphenylsilanol contains eight crystallographically independent molecules, which are arranged in two tetrameric building units. Within each of these tetrameric units, the four silicon atoms are arranged in the form of a slightly distorted square, with the O atoms of the four hydroxyl groups involved in O−H···O hydrogen bonding. The temperature dependence of the quadrupole echo 2H NMR line shape in the temperature range 213−358 K and 2H NMR spin−lattice relaxation time measurements at 368 K demonstrate that the hydrogen-bonding arrangement is dynamic. From the 2H NMR line-shape analysis, the dynamic process is interpreted as interconversion between “clockwise” and “anticlockwise” hydrogen-bonding arrangements within each tetrameric unit, via a two-site jump motion of each hydroxyl de...
-
dynamic properties of the tetrahydrofuran clathrate hydrate investigated by solid state 2H NMR Spectroscopy
Journal of Physical Chemistry B, 2001Co-Authors: Marta Bachverges, Kenneth D M Harris, And Simon J Kitchin, Minjas Zugic And, Carolyn A KohAbstract:Clathrate hydrates are solid inclusion compounds in which cages formed by a water host structure accommodate guest molecules of appropriate size and shape. Dynamic properties of the clathrate hydra...
-
dynamics of the hydrogen bonding arrangement in solid triphenylmethanol an investigation by solid state 2H NMR Spectroscopy
Journal of Physical Chemistry B, 1998Co-Authors: Abil E Aliev, Kenneth D M Harris, Elizabeth J Maclean, Benson M Kariuki, Christopher GlidewellAbstract:Dynamic properties of the hydrogen-bonding arrangement in a selectively deuterated sample of solid triphenylmethanol (Ph3COD) have been studied by wide-line 2H NMR Spectroscopy. In the crystal structure of Ph3COD, the molecules form hydrogen-bonded tetramers, with the oxygen atoms positioned approximately at the corners of a tetrahedron. The tetramer has point symmetry C3 (rather than Td); three of the Ph3COD molecules (denoted as “basal”) are related to each other by a 3-fold rotation axis, and the fourth molecule (denoted as “apical”) lies on this axis. Thus, the oxygen atoms from the four molecules in the tetramer form a pyramidal arrangement with an equilateral triangular base, and the O···O distances are consistent with the tetramer being held together by O−H···O hydrogen bonds. The 2H NMR line shape for Ph3COD varies with temperature (in the range 97− 373 K), demonstrating clearly that the hydrogen-bonding arrangement is dynamic. Several plausible dynamic models are proposed, and it is found that on...
Patrice Porion - One of the best experts on this subject based on the ideXlab platform.
-
influence of strong confinement on the structure and dynamics of liquids a study of the clay water interface exploiting 2H NMR Spectroscopy and spin locking relaxometry
Journal of Physical Chemistry C, 2018Co-Authors: Patrice Porion, Virginie Marry, Anne-laure Rollet, Anne Marie Faugere, Laurent J. Michot, E Dubois, Alfred DelvilleAbstract:2H NMR Spectroscopy, multiquanta relaxation, and spin-locking relaxometry are used to investigate the structural and dynamical properties of water molecules confined within dense sediments of synthetic fluorohectorite. As shown by the large residual splitting of the 2H NMR resonance line, water molecules confined in the interlamellar space of the clay are strongly oriented to contact with the fluorinated basal surface of the clay. Multiquanta relaxation measurements are used to identify and quantify the contributions of the quadrupolar and heteronuclear dipolar couplings by monitoring the NMR relaxation of the confined water molecules. Finally, the average residence time of the water molecules confined within the interlamellar space of the clay platelets is quantified by detailed analysis of 2H spin-locking relaxometry measurements. Thanks to the significant contributions of both quadripolar and heteronuclear dipolar relaxation mechanisms, 2H spin-locking relaxation measurements probe a broad dynamical ra...
-
multiscale water dynamics within dense clay sediments probed by 2H multiquantum NMR relaxometry and two time stimulated echo NMR Spectroscopy
Journal of Physical Chemistry C, 2013Co-Authors: Patrice Porion, Anne Marie Faugere, Alfred DelvilleAbstract:2H NMR Spectroscopy, relaxometry, and two-time correlation measurements are used to investigate the structural and dynamical properties of water molecules confined within the multiscale porous netw...
-
2H NMR Spectroscopy and multiquantum relaxometry as a probe of the magnetic field induced ordering of clay nanoplatelets within aqueous dispersions
Journal of Physical Chemistry C, 2011Co-Authors: Patrice Porion, Laurent J. Michot, Anne Marie Faugere, Erwan Paineau, Alfred DelvilleAbstract:2H NMR Spectroscopy and relaxometry were used to investigate the orientation of nontronite clay nanoplatelets induced by the static magnetic field within dilute aqueous dispersions by exploiting the residual quadrupolar splitting resulting from the specific orientation of heavy water molecules physisorbed at the clay surface. A careful analysis of the variation of the residual 2H splitting as a function of clay concentration and magnetic field strength was required to extract the intrinsic clay ordering induced by the magnetic field. The variation of clay ordering as a function of clay concentration clearly indicated two concentration regimes, corresponding to free and collective orientations of the clay platelets, respectively. Multiquantum NMR relaxation measurements were further used to identify the main NMR relaxation mechanism whose temperature variation is compatible with a fast exchange, at the NMR time scale, between free and physisorbed water molecules.
-
orientational microdynamics and magnetic field induced ordering of clay platelets detected by 2H NMR Spectroscopy
Langmuir, 2010Co-Authors: Patrice Porion, Laurent J. Michot, Anne Marie Faugere, Erwan Paineau, Alfred DelvilleAbstract:The orientation of montmorillonite clays induced by a static magnetic field is quantified by using 2H NMR Spectroscopy. Indeed, the residual quadrupolar splitting of the 2H resonance line measured for heavy water is a direct consequence of the specific orientation of the clay platelets in the static magnetic field. In the dilute regime, this residual splitting increases linearly with clay concentration, which confirms that the clay/clay electrostatic repulsions remain negligible by comparison with the diamagnetic coupling of these anisotropic platelets. At higher concentration, the electrostatic repulsion between clay particles markedly enhances the detected splitting. Such enhancement is well predicted by numerical simulations. By varying the size of the clay platelets and the strength of the static magnetic field, it is possible to evaluate the order of magnitude of the diamagnetic susceptibility of these anisotropic colloids.
-
structural and dynamical properties of the water molecules confined in dense clay sediments a study combining 2H NMR Spectroscopy and multiscale numerical modeling
Journal of Physical Chemistry C, 2007Co-Authors: Patrice Porion, Laurent J. Michot, And Anne Marie Faugere, Alfred DelvilleAbstract:2 H NMR Spectroscopy was used to detect the influence of confinement on the structural and dynamical properties of water molecules adsorbed in the interlamellar space of a natural clay (Montmorillonite) within partially hydrated self-supporting films. Multiscale numerical modeling (Monte Carlo simulations, molecular dynamics, and Brownian dynamics) was used to quantify the importance of the various relaxation mechanisms likely to be responsible for the NMR relaxation of the water molecules within such complex environment. Because of the significant fraction of iron present in these natural clays, the large value of the transverse relaxation rate measured for the confined water molecules is compatible with a dominant paramagnetic coupling modulated by the long-range diffusion of water molecules. Finally, the angular variation of the apparent relaxation rate can be used to extract the distribution of the directors of the clay lamellae within the self-supporting film.