Translational Diffusion Of Water Molecules Research Articles

Dynamical properties of solid and hydrated collagen: Insight from nuclear magnetic resonance relaxometry.

1H spin-lattice Nuclear Magnetic Resonance relaxometry experiments have been performed for collagen and collagen-based artificial tissues in the frequency range of 10 kHz-20MHz. The studies were performed for non-hydrated and hydrated materials. The relaxation data have been interpreted as including relaxation contributions originating from 1H-1H and 1H-14N dipole-dipole interactions, the latter leading to Quadrupole Relaxation Enhancement effects. The 1H-1H relaxation contributions have been decomposed into terms associated with dynamical processes on different time scales. A comparison of the parameters for the non-hydrated and hydrated systems has shown that hydration leads to a decrease in the dipolar relaxation constants without significantly affecting the dynamical processes. In the next step, the relaxation data for the hydrated systems were interpreted in terms of a model assuming two-dimensional translational diffusion of water molecules in the vicinity of the macromolecular surfaces and a sub-diffusive motion leading to a power law of the frequency dependencies of the relaxation rates. It was found that the water diffusion process is slowed down by at least two orders of magnitude compared to bulk water diffusion. The frequency dependencies of the relaxation rates in hydrated tissues and hydrated collagen are characterized by different power laws (ωH-β, where ωH denotes the 1H resonance frequency): the first of about 0.4 and the second close to unity.

Unusual dynamics of hydration water around motor proteins with long-ranged hydrodynamic fluctuations

A fluctuation-driven dynamic model is formulated to study the translational diffusion of water molecules around the surface of motor proteins under the combined influence of the thermal fluctuations and the external active forces. The dynamics of such a system, explored within the tenets of generalized Langevin equation is captured by two different models that characterizes the interplay between the active and thermal fluctuations. The results establish that hydration water dynamics is primarily super-diffusive when the active conformational fluctuations of motor proteins outweigh the random thermal fluctuations in the environment. The conformational fluctuations of protein disrupts the hydrogen bonded network of water and enhances its dynamics in a homogeneous environment. First passage time distribution and the survival probability are evaluated from the effective Fokker–Planck equation for both models under two different boundary conditions. The results depict an asymmetric unimodal distribution of FPTD with curves of varying amplitudes obtained at definite intervals of time for two different models. The FPT distribution of water molecules displays broad peaks with a lower amplitude for the hydration layers of increasing thickness. The survival probability of hydration water molecules exhibits a stretched exponential decay for both models with a faster decay rate for the super-diffusive dynamics as compared to the sub-diffusive motion. The water molecule displays a longer residence time within the hydration layer bounded by an absorbing–reflecting boundary as compared to an absorbing–absorbing one.

Coarse-grained molecular dynamics simulation of water diffusion in the presence of carbon nanotubes

Computational modeling of the translational diffusion of water molecules in anisotropic environments entails vital relevance to understand correctly the information contained in the magnetic resonance images weighted in diffusion (DWI) and of the diffusion tensor images (DTI). In the present work we investigated the validity, strengths and weaknesses of a coarse-grained (CG) model based on the MARTINI force field to simulate water diffusion in a medium containing carbon nanotubes (CNTs) as models of anisotropic water diffusion behavior. We show that water diffusion outside the nanotubes follows Ficḱs law, while water diffusion inside the nanotubes is not described by a Ficḱs behavior. We report on the influence on water diffusion of various parameters such as length and concentration of CNTs, comparing the CG results with those obtained from the more accurate classic force field calculation, like the all-atom approach. Calculated water diffusion coefficients decreased in the presence of nanotubes in a concentration dependent manner. We also observed smaller water diffusion coefficients for longer CNTs. Using the CG methodology we were able to demonstrate anisotropic diffusion of water inside the nanotube scaffold, but we could not prove anisotropy in the surrounding medium, suggesting that grouping several water molecules in a single diffusing unit may affect the diffusional anisotropy calculated. The methodologies investigated in this work represent a first step towards the study of more complex models, including anisotropic cohorts of CNTs or even neuronal axons, with reasonable savings in computation time.

Translational diffusion of hydration water correlates with functional motions in folded and intrinsically disordered proteins.

Hydration water is the natural matrix of biological macromolecules and is essential for their activity in cells. The coupling between water and protein dynamics has been intensively studied, yet it remains controversial. Here we combine protein perdeuteration, neutron scattering and molecular dynamics simulations to explore the nature of hydration water motions at temperatures between 200 and 300 K, across the so-called protein dynamical transition, in the intrinsically disordered human protein tau and the globular maltose binding protein. Quasi-elastic broadening is fitted with a model of translating, rotating and immobile water molecules. In both experiment and simulation, the translational component markedly increases at the protein dynamical transition (around 240 K), regardless of whether the protein is intrinsically disordered or folded. Thus, we generalize the notion that the translational diffusion of water molecules on a protein surface promotes the large-amplitude motions of proteins that are required for their biological activity.

Water confinement in faujasite cages: a deuteron NMR investigation in a wide temperature range. 2. Spectra and relaxation at high temperature.

Deuteron NMR spectra and spin-lattice relaxation were measured for D2O confined in NaX, NaY, and DY faujasites with various loadings at temperatures ranging from 200 to 310 K with the aim to study molecular mobility of confined water. Hysteresis of spin-lattice relaxation was observed for both DY and NaY(2.4) samples at 500% loading (280 water molecules per unit cell) in a heating-cooling cycle between 264.5 and 277.7 K. The hysteresis is most likely reflecting formation and decomposition of water clusters at different temperature. Spin-lattice relaxation rates obtained from the experiment are consistent with a picture of the fast magnetization exchange between two dynamically different deuteron populations. The observed relaxation behavior as a function of temperature and loading is most likely an effect of interplay between translational and rotational diffusion. Translational diffusion of water molecules is found to be related to the strength of the electrostatic interaction of water oxygen atoms to faujasite sodium cations, whereas water molecule reorientations seem to depend on the strength of hydrogen bonding to faujasite oxygen atoms and the strength of hydrogen bonds between water molecules, at outer and inner positions in water clusters, respectively.

Enhanced translational diffusion of confined water under electric field

High resolution quasielastic neutron scattering measurements have been used to study the effects of applied electric field on the dynamics of water molecules confined in the pores of folded silica sheet material FSM-12 with an average pore diameter (apd) of 16 Å. In the absence of field, there is a significant slowing down of the water molecule diffusion as the temperature is lowered, in agreement with previous observations. The application of a moderate electric field of 2.5 kV/mm remarkably enhances the translational diffusion of water molecules. We interpret this as being due to a disruption of the hydrogen bonding by the electric field. This new observation suggests that existing theories valid at large electric field strengths may have to be corrected at moderate fields.

Comment on “Structure and dynamics of liquid water on rutile TiO2(110)”

Liu and co-workers [Phys. Rev. B 82, 161415 (2010)] discussed the long-standing debate regarding whether H${}_{2}$O molecules on the defect-free (110) surface of rutile (\ensuremath{\alpha}-TiO${}_{2}$) sorb associatively, or there is dissociation of some or all first-layer water to produce hydroxyl surface sites. They conducted static density functional theory (DFT) and DFT molecular dynamics (DFT-MD) investigations using a range of cell configurations and functionals. We have reproduced their static DFT calculations of the influence of crystal slab thickness on water sorption energies. However, we disagree with several assertions made by these authors: (a) that second-layer water structuring and hydrogen bonding to surface oxygens and adsorbed water molecules are ``weak''; (b) that translational diffusion of water molecules in direct contact with the surface approaches that of bulk liquid water; and (c) that there is no dissociation of adsorbed water at this surface in contact with liquid water. These assertions directly contradict our published work, which compared synchrotron x-ray crystal truncation rod, second harmonic generation, quasielastic neutron scattering, surface charge titration, and classical MD simulations of rutile (110) single-crystal surfaces and (110)-dominated powders in contact with bulk water, and (110)-dominated rutile nanoparticles with several monolayers of adsorbed water.

Neutron Scattering Study on Dynamics of Water Molecules in MCM-41. 2. Determination of Translational Diffusion Coefficient

Quasielastic neutron scattering (QENS) spectra of water-filled MCM-41 samples (pore diameters: 21.4 and 28.4 Angstrom) were measured over the temperature range 238-298 K and the momentum transfer range 0.31-0.99 A(-1) to investigate the dynamics of confined water molecules. The spectra, which consist mainly of contributions from the translational diffusion of water molecules, were analyzed by using the Lorentzian and the stretched exponential functions. Comparison of the fits indicated that the latter analysis is more reliable than the former one. The fraction of immobile water molecules located in the vicinity of the pore walls, which give an elastic component, was found to be 0.044-0.061 in both pores. The stretch exponent beta was determined as 0.66-0.80. It was shown that the translational diffusion of water molecules in the pores is decelerated by confinement and that the deceleration becomes marked with a decrease in pore size. The ratios of the translational diffusion coefficient D(T) of confined water to that of bulk water at room temperature were within a range of 0.47-0.63.

TOF-SIMS analysis of ion–water interactions

The behavior of protons formed in liquid and solid water is elusive in spite of its importance. Here we demonstrate that the proton-water interactions, leading to the proton jump and acid–base reactions, as well as the thermodynamic properties of amorphous solid water, such as glass–liquid transition and crystallization, can be analyzed by using temperature-programmed TOF-SIMS. Since the primary He + ion creates anion–cation pairs in water via the proton-transfer reaction, the sputtered secondary ions provide us information about the hydrogen-bond reorganization, H/D exchange, and acid–base reactions between the hydrogen-bonded molecules. The holes created electronically in the waters’ valence orbitals are delocalized, and the hydrated protons are ejected from physisorbed water nanoclusters via the Coulombic fission. The H/D exchange in water is basically induced by the translational diffusion of water molecules above the glass transition temperature (136 K), whereas an additional mechanism due to the proton jump and rotation of hydronium ions may contribute to the H/D exchange in acidic water ice at lower temperatures ( T > 110 K). The HCl molecules adsorbed on the water ice film create ionic hydrates above 70 K and the hydronium-chloride ion pair is hardly separable, as confirmed from the ineffective ammonium-chloride formation by the co-adsorbed NH 3 molecules below the glass transition temperature.

Translational dynamics of water in a nanoporous layered silicate

Neutron time-of-flight and backscattering spectroscopy have been used to study the translational diffusion of water molecules in the unusual layered material AMH-3, which consists of (zeolitelike) three-dimensionally nanoporous silicate layers spaced by (claylike) interlayer regions. The synthesis of AMH-3 and its characterization by $^{29}\mathrm{Si}$ NMR, Raman, and infrared spectroscopy, are described. An analysis of quasielastic neutron scattering (QENS) spectra using the random jump diffusion model reveals two translational diffusive motions clearly separated in time scales: a fast process ($D\ensuremath{\sim}{10}^{\ensuremath{-}9}\phantom{\rule{0.3em}{0ex}}{\mathrm{m}}^{2}∕\mathrm{s}$ at 300 K), and a much slower process ($D\ensuremath{\sim}{10}^{\ensuremath{-}11}\phantom{\rule{0.3em}{0ex}}{\mathrm{m}}^{2}∕\mathrm{s}$ at 300 K). Considering the structural model of AMH-3 and the transport properties extracted from the QENS data, it is suggested that the slower motion corresponds to diffusion by water molecules in the interlayer spaces whereas the fast process involves diffusion in the silicate layer. This first investigation of transport phenomena in nanoporous layered silicates like AMH-3 indicates that they have the potential to offer mass transport properties different from zeolite materials and layered clays.

Dynamics of Water Trapped between Hydrophobic Solutes

We describe the model dynamical behavior of the solvent between two nanoscopic hydrophobic solutes. The dynamics of the vicinal water in various sized traps is found to be significantly different from bulk behavior. We consider the dynamics at normal temperature and pressure at three intersolute distances corresponding to the three solvent separated minima in the free energy profile between the solutes with attractions. These three states correspond to one, two, and three intervening layers of water molecules. Results are obtained from a molecular dynamics simulation at constant temperature and pressure (NPT) ensemble. Translational diffusion of water molecules trapped between the two solutes has been analyzed from the velocity correlation function as well as from the mean square displacement of the water molecules. The rotational behavior has been analyzed through the reorientational dynamics of the dipole moment vector of the water molecule by calculating both first and second rank dipole-dipole correlation functions. Both the translational and reorientational mobilities of water are found to be much slower at the smaller separation and increases as the separation between solutes becomes larger. The occupation time distribution functions calculated from the trajectories also show that the relaxation is much slower for the smallest intersolute separation as compared to other wider separations. The sublinear trend in mean square displacement and the stretched exponential decay of the relaxation of dipolar correlation and occupation distribution function indicate that the dynamical behavior of water in the confined region between two large hydrophobic solutes departs from usual Brownian behavior. This behavior is reminiscent of the behavior of water in the vicinity of protein surface clefts or trapped between two domains of a protein.

Molecular-Dynamics Study of Aqueous Solution of Trehalose and Maltose: Implication for the Biological Function of Trehalose

Abstract Molecular-dynamics simulation of aqueous solution of trehalose and maltose were performed to reveal any difference in the hydration ability between them, and to obtain information about how trehalose protects biological materials from water stress. Here, in order to examine the spatial distribution of water molecules around the hydroxy oxygen of sugar, a two-dimensional pair distribution function was introduced in addition to the conventional radial-distribution function. Both sugars were found to be extensively hydrogen bonded to solvent molecules. However, in a solution of maltose, defective hydrogen bonding was found at the exocyclic hydroxymethyl group of the reducing residue. Thus, maltose has a smaller value in hydration number than does trehalose. The translational diffusion of water molecules around trehalose has been found to be slightly more restrained than that around maltose. These findings are consistent with available experimental data concerning the solution properties of both sugars. On the basis of these results, the functional mechanism of tolerance is briefly discussed.

Fluctuations, exchange processes, and water diffusion in aqueous protein systems: A study of bovine serum albumin by diverse NMR techniques

Experimental frequency, concentration, and temperature dependences of the deuteron relaxation times T(1) and T(2) of D(2)O solutions of bovine serum albumin are reported and theoretically described in a closed form without formal parameters. Crucial processes of the theoretical concept are material exchange, translational diffusion of water molecules on the rugged surfaces of proteins, and tumbling of the macromolecules. It is also concluded that, apart from averaging of the relaxation rates in the diverse deuteron phases, material exchange contributes to transverse relaxation by exchange modulation of the Larmor frequency. The rate limiting factor of macromolecular tumbling is determined by the free water content. In a certain analogy to the classical free-volume theory, a "free-water-volume theory" is presented. There are two characteristic water mass fractions indicating the saturation of the hydration shells (C(s) approximately 0.3) and the onset of protein tumbling (C(0) approximately 0.6). The existence of the translational degrees of freedom of water molecules in the hydration shells has been verified by direct measurement of the diffusion coefficient using an NMR field-gradient technique. The concentration and temperature dependences show phenomena indicating a percolation transition of clusters of free water. The threshold water content was found to be C(c) (w) approximately 0.43.

Dynamic processes in aqueous protein systems. Molecular theory and NMR relaxation

AbstractA model theory is presented explaining a series of striking phenomena observed with nuclear magnetic relaxation in protein systems such as solutions or tissue. The frequency and concentration dependences of the nuclear magnetic relaxation times are discussed. It is concluded that the translational diffusion of water molecules along the rugged surfaces of proteins and ‐ to a minor degree ‐ protein backbone fluctuations are crucial processes. The rate limiting factor of macromolecular tumbling is assumed to be given by the free‐water content in a certain analogy to the free‐volume model of Cohen and Turnbull. The two characteristic water mass fractions indicating the saturation of the hydration shells and the onset of protein tumbling can be related to each other on this basis. A closed and relatively simple set of relaxation formulas is presented. The potentially fractal nature of the diffusion of water molecules on the protein surface is discussed.

Molecular theory for nuclear magnetic relaxation in protein solutions and tissue: Surface diffusion and free-volume analogy

A model theory is presented explaining a series of striking phenomena observed with nuclear magnetic relaxation in protein systems such as solutions or tissue. The frequency, concentration and temperature dependences of proton or deuteron relaxation times of protein solutions and tissue are explained. It is concluded that the translational diffusion of water molecules along the rugged surfaces of proteins and, to a minor degree, protein backbone fluctuations are crucial processes. The rate limiting factor of macromolecular tumbling is assumed to be given by the free water content in a certain analogy to the free-volume model of Cohen and Turnbull. There are two characteristic water mass fractions indicating the saturation of the hydration shells and the onset of protein tumbling. A closed and relatively simple set of relaxation formulas is presented. The potentially fractal nature of the diffusion of water molecules on the protein surface is discussed.

The temperature dependence of 35Cl NQR spectrum and study of spin—lattice relaxation times in chloral hydrate

The temperature investigation of nuclear quadrupole spin—lattice relaxation times in chloral hydrate above 290 K revealed the presence of an additional mechanism of relaxation. Its activation energy is 14.5 kcal mol −1 which is almost 6 kcal mol −1 greater than the energy corresponding to the hindered rotation of the CCl 3 group. We propose this additional mechanism to be the breaking of hydrogen bonds and translational diffusion of water molecules.

Chemically relayed nuclear overhauser effects. Connectivities between resonances of nonexchangeable protons and water

In NOESY spectra recorded in H 2O, cross peaks between nonexchangeable protons and water can be observed. From theoretical and experimental studies of this phenomenon we conclude that it is brought about by a “relay” mechanism which involves dipolar cross relaxation between a nonexchangeable proton and an exchangeable one followed by chemical exchange of the latter with water. This process dominates strongly over the “direct” mechanism which is caused by translational diffusion of water molecules to and from the solute. It was found that the “chemically relayed nuclear Overhauser effect” does not stand in the way of proper determination of exchange rates of exchangeable protons or of interproton distance, if one uses measured relaxation rates for the diagonal terms of the relaxation matrix.

ChemInform Abstract: NUCLEAR MAGNETIC RESONANCE IN HEMIHYDRATE GYPSUM

The proton spin-lattice relaxation times T1 and T1D along the static and dipolar magnetic fields have been measured at 18 MHz for the water molecule in powdered hemihydrate gypsum CaSO4·(1/2)H2O. The minima of T1 and T1D were observed at 103⁄T=4.3(233 K) and 7.0(143 K) respectively. These are ascribed to the 180° flip motion of water molecules, with an activation energy of 15.1 kJ/mol. At higher temperatures, the translational diffusion of water molecules becomes dominant; this is not observed in gypsum CaSO4·2H2O. The activation energy of this motion is estimated to be 32.2 kJ/mol. In hemihydrate gypsum, though the diffusion is supposed to be anisotropic, the jumping distance of the water molecule is tentatively examined by Torrey’s lattice diffusion theory.

Nuclear Magnetic Resonance in Hemihydrate Gypsum

Abstract The proton spin-lattice relaxation times T1 and T1D along the static and dipolar magnetic fields have been measured at 18 MHz for the water molecule in powdered hemihydrate gypsum CaSO4·(1/2)H2O. The minima of T1 and T1D were observed at 103⁄T=4.3(233 K) and 7.0(143 K) respectively. These are ascribed to the 180° flip motion of water molecules, with an activation energy of 15.1 kJ/mol. At higher temperatures, the translational diffusion of water molecules becomes dominant; this is not observed in gypsum CaSO4·2H2O. The activation energy of this motion is estimated to be 32.2 kJ/mol. In hemihydrate gypsum, though the diffusion is supposed to be anisotropic, the jumping distance of the water molecule is tentatively examined by Torrey’s lattice diffusion theory.

Reorientation and diffusion of water molecules in xenon hydrate and other structure.

In contrast to ice Ih, in which the translational diffusion of water molecules is faster than their reorientation, the good correlation between proton magnetic resonance line narrowing and dielectric relaxation rates of the water molecules which form the structure I clathrate hydrate lattice suggests that reorientation is the faster process. This is certainly so for the hydrate of ethylene oxide-d4, for which two separate line-narrowing regions are observed. Both processes depend on the nature of the guest molecule.