Quasielastic Neutron Scattering Study Research Articles

A quasi-elastic neutron-scattering study of the molecular mobility of water associated with a protein both in aqueous solution and adjacent to a charged surfactant interface

The quasi-elastic incoherent neutron-scattering method has been used to investigate the mobility of water molecules associated with the protein, α-chymotrypsin, both in aqueous solution and adjacent to a charged surfactant interface. The latter was studied by solubilising the protein as monomer in the aqueous cores of small water-in-oil microemulsion droplets (radius 3.5 nm). The droplets were stabilised by an interfacial shell of a double-chain surfactant (Aerosol-OT). The spectra of the water in both these protein-containing system contained a component corresponding to a 7-fold reduction in mobility as compared with bulk water. The integrated intensity of this ‘immobilised’ spectra component shows that a maximum of approx. 450 water molecules, corresponding to half complete monolayer coverage, are associated with a single protein molecule. This value of 450 may contain a contribution from exchangeable hydrogens within the protein, but this contribution is estimated to be small. The mobility of the remainder of the water is unaffected. The solvation behaviour of the protein is similar in bulk water and in the microemulsion water droplets.

ChemInform Abstract: QUASIELASTIC NEUTRON‐SCATTERING STUDIES OF INTERCALATED MOLECULES IN CHARGE‐DEFICIENT LAYER SILICATES. PART 2. HIGH‐RESOLUTION MEASUREMENTS OF THE E DIFFUSION OF WATER IN MONTMORILLONITE AND VERMICULITE

Chemischer InformationsdienstVolume 16, Issue 30 Physical Inorganic Chemistry ChemInform Abstract: QUASIELASTIC NEUTRON-SCATTERING STUDIES OF INTERCALATED MOLECULES IN CHARGE-DEFICIENT LAYER SILICATES. PART 2. HIGH-RESOLUTION MEASUREMENTS OF THE E DIFFUSION OF WATER IN MONTMORILLONITE AND VERMICULITE J. J. TUCK, J. J. TUCKSearch for more papers by this authorP. L. HALL, P. L. HALLSearch for more papers by this authorM. H. B. HAYES, M. H. B. HAYESSearch for more papers by this authorD. K. ROSS, D. K. ROSSSearch for more papers by this authorJ. B. HAYTER, J. B. HAYTERSearch for more papers by this author J. J. TUCK, J. J. TUCKSearch for more papers by this authorP. L. HALL, P. L. HALLSearch for more papers by this authorM. H. B. HAYES, M. H. B. HAYESSearch for more papers by this authorD. K. ROSS, D. K. ROSSSearch for more papers by this authorJ. B. HAYTER, J. B. HAYTERSearch for more papers by this author First published: July 30, 1985 https://doi.org/10.1002/chin.198530007AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume16, Issue30July 30, 1985 RelatedInformation

Mobility of two-dimensional ethane adsorbed on graphite. A quasielastic neutron-scattering study

The diffusive mobility of a rod-like molecule, ethane, adsorbed on the (0001) surface of graphite has been studied by incoherent quasielastic neutron scattering as a function of temperature. The measurements have been limited to the submonolayer domain (θ < 0.7 monolayer) and to the 10–122 K temperature range. At 10 K ethane molecules do not display any diffusive motion; at 53.5 K the herringbone solid structure exhibits reorientational motion of the methyl groups about the threefold carbon–carbon axis. Above the two-dimensional melting point (65 K) ethane molecules perform an isotropic rotational motion plus a diffusive translation which can be described, at 87 K, as a jump diffusion between equivalent surface sites (lattice liquid). At 122 K the adsorbed molecules display brownian motion (isotropic liquid).

Quasi-elastic neutron-scattering studies of intercalated molecules in charge-deficient layer silicates. Part 2.—High-resolution measurements of the diffusion of water in montmorillonite and vermiculite

The relative influence of water–surface and water–cation interactions in hydrates of the charge-deficient expanding-lattice layer silicates montmorillonite and vermiculite have been studied using high-resolution quasi-elastic neutron-scattering (QENS) measurements made with the back-scattering spectrometer at ILL, Grenoble. Detailed measurements have been made Ca2+–montmorillonite equilibrated at seven different water-vapour partial-pressure (p/p0) values and for Ca2+, Mg2+ and Na+ vermiculite samples at fixed p/p0.The QENS data are fitted to a model consisting of an elastic and a single Lorentzian quasi-elastic component plus a flat background. The quasi-elastic linewidth and the relative intensities of the three components are adjustable parameters. The resultant quasi-elastic broadenings were approximately five times smaller than the values derived previously from measurements at lower energy resolution. Also, the quasi-elastic scattering intensity increased with p/p0 and decreased with increasing scattering angle, the latter being the reverse of the behaviour observed at the broader energy resolution.The low- and high-resolution measurements taken together indicate the occurrence of two different phases of translational motion of water molecules not directly coordinated to the exchangeable (Ca2+) cations. These are attributed (i) to rapid localized motions in ‘cages’ bounded by the silicate sheets and the hydrated cations and (ii) to slower, longer-range inter-cage diffusion. In addition, the relative intensities of the quasi-elastic scattering at high and low wavevector transfer suggest that the high-resolution measurements also observe rotations of the complete six-fold coordinated hydration shells of the cations about one of the C3 axes of the octahedron. To explain the observed width, this rotation must have a correlation time of ca. 10–10 at ambient temperature.The present QENS data yielded effective diffusion coefficients for water in Ca2+–montmorillonite which increased rapidly from < 1.0 × 10–10 m2 s–1 at p/p0= 0.15 to ca. 4.5 × 10–10 m2 s–1 at p/p0= 0.33. At higher values of p/p0 the effective diffusion coefficients remained approximately constant within the limits of experimental error. For water adsorbed by vermiculite having Na+, Ca2+ or Mg2+ as the exchangeable cation the diffusion coefficient measured at p/p0= 0.76 was found to be significantly smaller than the corresponding value for Ca2+–montmorillonite. This may be attributed to the hindering effect of the more densely packed network of hydrated cations in the more highly charged vermiculite.

Dynamics of non-rigid molecules. - II. — Quasi-Elastic Neutron Scattering study of liquid cyclopentene

Quasi-Elastic Neutron Scattering (Q.E.N.S.) measurements have been performed on liquid cyclopentene in order to detect an eventual contribution of the ring-puckering dynamics to the observed profiles. For small momentum transfer values Q and at high resolution, the self-diffusion coefficient has been extracted between 298 and 128 K. Its values are in good agreement with those measured using the NMR spin-echo technique D (cm2. s-1) = 1.3 x 10-3 exp( - 8 653/RT), with R = 8.314 J. degree-1. mole-1. Furthermore, it has been possible to describe reorientations of the whole molecule in terms of spherical rotational diffusion with a Dr value of 6.2 x 1010 s -1 at 180 K. Finally, a precise analysis of the wings of the Q.E.N.S. spectra at higher Q values allows a further component of the motion to be detected. It is due to the internal dynamics and corresponds to a mean jump rate of 1.1 x 1012 s-1 at 180 K. However, the Q . dependence of the width of this component indicates that the ring-puckering process does not occur by instantaneous jumps between two puckered conformations but certainly involves a more complicated diffusive model.

A Quasi-Elastic Neutron Scattering Study of NH4+-Ion Rotation in NH4ReO4 and an explanation of its anomalous NQR Frequency

A Quasi-Elastic Neutron Scattering Study of NH4+-Ion Rotation in NH4ReO4 and an explanation of its anomalous NQR Frequency

Quasi-elastic neutron-scattering studies of the dynamics of intercalated molecules in charge-deficient layer silicates. Part. 1.—Temperature dependence of the scattering from water in Ca2+-exchanged montmorillonite

Quasi-elastic neutron scattering (QENS) measurements on a Ca2+-exchanged montmorillonite containing two layers of adsorbed interlayer water have been made at three different temperatures. The data were analysed using a multi-dimensional non-linear least-squares minimisation method which separated the intensity into an elastic and a quasi-elastic part and fitted a broadening to the quasi-elastic part. The resulting broadenings were then fitted to two alternative jump-diffusion models which differed in the shape of the jump-length distributions assumed. The resulting jump correlation times (the mean time between jumps) were found to be model dependent, but for both models the temperature dependence of the correlation times gave a straight line on an Arrhenius plot, with the same activation energy, namely 11.0 ± 1 kJ mol–1. However, because of the variation in the mean jump length with temperature, the effective diffusion coefficients did not show Arrhenius behaviour.A detailed analysis of the correctly internormalised elastic and quasi-elastic intensities is presented. This suggests that both the water in the first hydration shell of the exchangeable interlayer cations and the protons of the hydroxyl groups within the aluminosilicate lattice have a small Debye–Waller factor. For the non-hydration shell water the Debye–Waller factor was found to be comparable with that for bulk water and to increase markedly with temperature in the range of the experiment. Water directly coordinated to the exchangeable cation was shown to be immobile on the time scale of the neutron measurements, but the apparent intensity of this ‘bound’ water fraction was found to decrease with increasing temperature. The elastic incoherent structure factors (EISF) were derived from the quasi-elastic intensities to avoid the complications due to coherent effects in the elastic intensities. The form of these functions suggested that the volume of the restricted diffusion (ca. 300 A at 300 K) increased with increasing temperature. To complete the explanation of the observed peaks the coherent components in the total intensity were attributed to small-angle scattering caused by inhomogeneities in the clay layer and to the (001) reflection. The above description shows that water in the two-layer hydrate of Ca2+-exchanged montmorillonite can be separated into relatively ‘free’ and ‘bound’ components, the former exhibiting relatively rapid, spatially restricted motions.

Quasielastic Neutron Scattering Study of Dynamics at the Crossover from Dilute to Semidilute Behavior in Polymer Solutions

Quasielastic Neutron Scattering Study of Dynamics at the Crossover from Dilute to Semidilute Behavior in Polymer Solutions

Critical behavior of pure and site-random two-dimensional antiferromagnets

Quasielastic neutron scattering studies of the static critical behavior in the two-dimensional antiferromagnets ${\mathrm{K}}_{2}$Ni${\mathrm{F}}_{4}$, ${\mathrm{K}}_{2}$Mn${\mathrm{F}}_{4}$, and ${\mathrm{Rb}}_{2}$${\mathrm{Mn}}_{0.5}$${\mathrm{Ni}}_{0.5}$${\mathrm{F}}_{4}$ are reported. For $T&lt;0.95{T}_{N}$ the diffuse scattering arises principally from the noncritical transverse susceptibility ${\ensuremath{\chi}}^{\ensuremath{\perp}}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{Q}})$. In all three materials ${\ensuremath{\chi}}^{\ensuremath{\perp}}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{Q}})$ is found to be only weakly temperature dependent for $T&lt;{T}_{N}$ with a half width, ${\ensuremath{\kappa}}^{\ensuremath{\perp}}$, consistent with spin-wave theory. For $|1\ensuremath{-}\frac{T}{{T}_{N}}|&lt;0.05$. the overall scattering is dominated by the critical Ising component ${\ensuremath{\chi}}^{\ensuremath{\parallel}}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{Q}})$. The total scattering is proportional to ${\ensuremath{\chi}}^{\ensuremath{\parallel}}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{Q}})+{\ensuremath{\chi}}^{\ensuremath{\perp}}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{Q}})$ so that, with an appropriate correction for ${\ensuremath{\chi}}^{\ensuremath{\perp}}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{Q}})$, the detailed critical behavior for ${\ensuremath{\chi}}^{\ensuremath{\parallel}}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{Q}})$ may be determined. For the reduced temperature range $0.008&lt;\frac{T}{{T}_{N}}\ensuremath{-}1&lt;0.15$ one finds in all three materials $v=0.9\ifmmode\pm\else\textpm\fi{}0.1$, $\ensuremath{\gamma}=1.6\ifmmode\pm\else\textpm\fi{}0.15$, and from the scaling relation $\ensuremath{\gamma}=\ensuremath{\nu}(2\ensuremath{-}\ensuremath{\eta})$, $\ensuremath{\eta}=0.2\ifmmode\pm\else\textpm\fi{}0.05$. For $T&lt;{T}_{N}$ one finds $\ensuremath{\beta}=0.15\ifmmode\pm\else\textpm\fi{}0.015$ in the three systems: Finally, in ${\mathrm{K}}_{2}$Ni${\mathrm{F}}_{4}$ for $T&lt;{T}_{N}$, ${\ensuremath{\chi}}^{\ensuremath{\parallel}}(0)$ and ${\ensuremath{\kappa}}^{\ensuremath{\parallel}}$ are consistent with two-dimensional Ising behavior with exponents ${\ensuremath{\gamma}}^{\ensuremath{'}}=1.75$, ${\ensuremath{\nu}}^{\ensuremath{'}}=1$; further ${\ensuremath{\chi}}^{\ensuremath{\parallel}}(+|\ensuremath{\epsilon}|\ensuremath{\simeq}(50\ifmmode\pm\else\textpm\fi{}10){\ensuremath{\chi}}^{\ensuremath{\parallel}}(\ensuremath{-}|\ensuremath{\epsilon}|)$ compared with the Ising asymmetry factor of 37. These results thence demonstrate that the site-random and pure systems have identical critical behavior in agreement with current theory. Further, the critical behavior is close to that of the two-dimensional Ising model, although there are small differences assumedly due to the fact that the experiments do not probe the true asymptotic region. Finally a number of inconsistencies in earlier experiments are resolved.

Intermediate scattering functions of high-density gaseous argon obtained by quasielastic neutron-scattering studies

In this paper coherent and incoherent neutron quasielastic scattering experiments on high-density gaseous argon at various thermodynamic states are described. The results in the form of intermediate scattering functions have been tabulated. Diffusion coefficients obtained from the measurements are in good agreement with molecular-dynamics results and with macroscopic data.