The myelin sheath is a tightly packed, multilayered membrane structure wrapped around selected nerve axons in the central and the peripheral nervous system. Because of its electrical insulation of the axons, which allows fast, saltatory nerve impulse conduction, myelin is crucial for the proper functioning of the vertebrate nervous system. A subset of myelin-specific proteins is well-defined, but their influence on membrane dynamics, i.e. myelin stability, has not yet been explored in detail. We investigated the structure and the dynamics of reconstituted myelin membranes on a pico- to nanosecond timescale, influenced by myelin basic protein (MBP) and myelin protein 2 (P2), using neutron diffraction and quasi-elastic neutron scattering. A model for the scattering function describing molecular lipid motions is suggested. Although dynamical properties are not affected significantly by MBP and P2 proteins, they act in a highly synergistic manner influencing the membrane structure.

Clathrates hydrates are nanoporous crystalline materials made of water cages encapsulating guest molecules. By inserting H2 molecules with the help of a promoter (tetrahydrofuran, noted THF), systems relevant for hydrogen storage application are formed by using relatively soft pressure (of the order of 100 bar) near room temperature. Dynamic properties of hydrogen molecules confined in the small cages of the deuterated THF clathrate hydrate have been investigated at equilibrium by means of incoherent quasi-elastic neutron scattering (QENS). These QENS investigations provide direct experimental evidence about the fundamental aspect of translational diffusive motions of the hydrogen molecules. A comprehensive study of the hydrogen molecules dynamics above 100 K has been achieved through a quantitative analysis of the structure factors (i.e., the spatial extend of the H2 diffusive motion) as well as of the QENS broadening (i.e., the characteristic time of the diffusive motion). On the probed time scale, the H2 molecular translations occur within localized spherical area in the cage with low activation energy of 1.59 ± 0.06 kJ mol–1. The dynamical diameter of H2 molecules varies from 2.08 Å at 250 K to 1.64 Å at 100 K, and the diffusion constant ranges from 0.16 ± 0.03 rad ps–1 at 100 K to 0.49 ± 0.03 rad ps–1 at 250 K. These results indicate that no diffusion between the cages is observed in the picosecond time scale.

Metal-organic frameworks, in addition to being sufficiently robust to support substantial micropore volume and therefore display reversible host-guest chemistries, [1] are increasingly being appreciated for their rich structural flexibilities. [2][3][4] The under-constrained connectivities and low deformation energies of these materials manifest themselves both in their often marked static deformations with guest exchange [3] and in their dynamic deformations with the thermal population of low energy transverse vibrations. [4] Interest in the latter has seen the discovery of two broad new classes of negative thermal expansion (NTE) material, namely, metal cyanides [5] and metal-organic frameworks, [6,7] noteworthy due to their novel NTE mechanisms and pronounced NTE behaviors.Among the metal-organic framework systems yet shown to display NTE, [Cu 3 (btc) 2 ] (also "HKUST-1"; [8] btc = 1,3,5benzenetricarboxylate), consisting of a cubic 3D framework of dinuclear {Cu 2 (carboxylate) 4 } "paddlewheel" units bridged by btc, is of particular interest in providing two new vibrational mechanisms for NTE: transverse displacement of the pseudo-planar btc units (the first instance where 3-rather than 2-connecting bridges contribute to NTE) and twisting within the paddlewheel units (the first instance where local deformations are thought to contribute to NTE); [6] see insets to Figure 1. For the former, variable-temperature single crystal X-ray diffraction (SCXRD) analysis suggested two important low-energy btc modes: translation perpendicular to the plane and libration about axes within the plane, with these modes thought to be coupled through the concerted rotation of the dinuclear paddlewheels to give a broad spectrum of rigid unit modes; notably, some libration of the btc units is necessary to relieve frustration arising from the strained octahedral supramolecular subunits within the structure. [6] Here we explore the nature and relative importance of these mechanisms through a detailed investigation of the lattice dynamics, which shows that the low-energy paddlewheel motions are essentially localized.To probe the low-temperature thermal expansion behavior we collected high-resolution neutron powder diffraction (NPD) data on a deuterated sample of [Cu 3 (btc) 2 ] over 20 to 300 K (see Figure 1). The data in the range 100 to 300 K gave an NTE coefficient a a = (@lna/@T) p = À4.9(1) 10 À6 K À1 , consistent with that found for the protonated phase by X-ray diffraction (XRD). [6] Unusually, we find an increase in NTE at lower temperatures, with a a = À7.5(3) 10 À6 K À1 in the range 20 to 100 K. The temperature dependent structural models refined from these data are consistent with those determined by SCXRD at higher temperatures: [6] from 20 to 100 K the most rapid increase in isotropic atomic displacement parameters (ADPs) occurs for the carboxylate oxygen atom, and the largest negative rate of apparent bond-length change occurs for the Cu À O bond; both behaviors are consistent with that expected for thermal population of ...

We calculate the spectrum of internal vibrations of a single ferrocene Fe͑C 5 H 5 ) 2 molecule using ab initio density functional theory ͑without free parameters͒ and compare this with inelastic neutron scattering data on ferrocene in the solid state at 28 K. Due to the good agreement, we can assign each vibrational mode to each observed peak in the neutron spectrum and so remove ambiguities existing in the literature. There is also consistency between the calculated potential energy of a single ferrocene molecule for different orientations, , of the two cyclopentadienyl C 5 H 5 rings with respect to each other, which shows a potential barrier of 0.9 kcal/mol, and electron diffraction, and between the calculated shallow minimum at ϭ9 deg and x-ray diffraction.

Quasielastic neutron scattering experiments were performed with Na-hectorite, Ni-hectorite, and Sm-hectorite samples in order to find out whether Sm 3+ is present in the clay interlayer as a fully hydrated cation (outer-sphere complex), or, as it follows from neutron diffraction data analysis, it is dehydrated and bound to the clay surface (inner-sphere complex). The results obtained for the Sm-hectorite were compared with other interlayer cations: strongly hydrated Ni 2+ and relatively weakly hydrated Na+. It was found that water mobility in the Sm-hectorite sample is very close to the water mobility in Ni-hectorite. This is only possible if the Sm 3+ ion is fully hydrated. It was shown that water molecules hydrating Ni 2+ and Sm 3+ exhibit diffusion 2 mobility measurable with backscattering spectrometers. The diffusion coefficients of the exchangeable cations were found using the slow exchange approximations D Ni = (0.05 -0.14)x 10 -9 m 2 /s and D Sm = (0.04 -0.18) x 10 -9 m 2 /s.