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[Display omitted] • Multicomponent polymer materials offer superior and adaptable properties. • Single chain nanoparticles represent an intermediate state between polymers and colloids. • Internal cross-linking impacts the structure and dynamics of SCNPs. • QENS studies show different atomic motions based on the SCNP chemical composition. The industrial sector has made significant strides in the development of multicomponent and multiphasic polymer materials, including polymer blends, composites (such as nanocomposites), and various copolymers. Random copolymers, characterized by their statistical arrangement of repeating units, are particularly noteworthy due to their tunability from amorphous to semicrystalline states. In this study, we focus on poly(tetrahydrofuran- ran -epichlorohydrin) (P(THF- ran -ECH)) copolymers, which serve as precursors for single-chain nanoparticles (SCNPs). These SCNP-based materials are of particular interest as they bridge the gap between traditional polymers and colloids. This research comprehensively investigates how the type and degree of internal cross-linking influence the structure and dynamics of P(THF- ran -ECH) copolymers and their SCNPs. Techniques such as quasielastic neutron scattering (QENS), differential scanning calorimetry (DSC), and broadband dielectric spectroscopy (BDS) were employed to study copolymers with varying compositions and levels of cross-linking. By analyzing two samples with different epichlorohydrin (ECH) contents (13 mol% and 27 mol%), we aim to control crystallization and explore its effects on dynamic behavior. Our results show that both the composition and the degree of cross-linking significantly impact the dynamics of the SCNPs, with SCNPs exhibiting slower dynamics compared to their precursor copolymers. Furthermore, semicrystalline samples display faster dynamics in SCNPs than amorphous samples. These findings provide valuable insights for the design and optimization of advanced multicomponent polymer systems. [ABSTRACT FROM AUTHOR]

The dynamics of methanol within prototype methanol synthesis catalysts were studied using quasi-elastic neutron scattering. Three Cu-exchanged zeolites (mordenite, SSZ-13 and ZSM-5) were studied after methanol loading and showed jump diffusion coefficients between 1.04 × 10−10 and 2.59 × 10−10 m2·s−1. Non-Arrhenius behavior was observed with varying temperature due to methoxy formation at Brønsted acid sites and methanol clustering around copper cations. [ABSTRACT FROM AUTHOR]

We report a neutron spin echo (NSE) study of the nanoscale dynamics of the cell-cell adhesion cadherin-catenin complex bound to vinculin. Our measurements and theoretical physics analyses of the NSE data reveal that the dynamics of full-length a-catenin, ß-catenin, and vinculin residing in the cadherin-catenin-vinculin complex become activated, involving nanoscale motions in this complex. The cadherin-catenin complex is the central component of the cell-cell adherens junction (AJ) and is fundamental to embryogenesis, tissue wound healing, neuronal plasticity, cancer metastasis, and cardiovascular health and disease. A highly dynamic cadherin-catenin-vinculin complex provides the molecular dynamics basis for the flexibility and elasticity that are necessary for the AJs to function as force transducers. Our theoretical physics analysis provides a way to elucidate these driving nanoscale motions within the complex without requiring large-scale numerical simulations, providing insights not accessible by other techniques. We propose a three-way "motorman" entropic spring model for the dynamic cadherin-catenin-vinculin complex, which allows the complex to function as a flexible and elastic force transducer. [ABSTRACT FROM AUTHOR]

In addition to investigations of the three-dimensional protein structure, information on the dynamical properties of proteins is indispensable for an understanding of protein function in general. Correlations between protein dynamics and function are typically anticipated when both molecular mobility and function are concurrently affected under specific temperatures or hydration conditions. In contrast, excitation energy transfer within the major photosynthetic light-harvesting complex II (LHC II) presents an atypical case, as it remains fully operational even at cryogenic temperatures, primarily depending on the interactions between electronic states and involving harmonic protein vibrations only. This review summarizes recent work on vibrational and conformational protein dynamics of LHC II and directly relates these findings to its light-harvesting function. In addition, we give a comprehensive introduction into the use of neutron spectroscopy and molecular dynamics simulations to investigate the protein dynamics of photosynthetic protein complexes in solution, which is information complementary to that obtained by protein crystallography. [ABSTRACT FROM AUTHOR]

Besides a well-adapted structure, proteins often require a specific dynamical flexibility to undergo conformational changes in order to carry out their function. The latter dynamics can be directly measured by quasielastic neutron scattering as demonstrated here for three variants of the orange carotenoid protein (OCP), which plays a pivotal role in the protection of the cyanobacterial photosynthetic apparatus against photodamage. We investigate the dynamics of the structurally compact, dark-adapted wild type of OCP (OCPwt) in comparison with that of two mutant forms. The latter two mutants differ preferentially in their structures. The orange mutant OCP-W288A is assumed to have a compact structure and to preferentially bind the pigment echinenone, while the pink mutant OCP-W288A appears to represent the more elongated structure of the red active state of OCP binding the carotenoid canthaxanthin, respectively. The study reveals three major findings: (a) the dynamics of the red active state of OCP is significantly enhanced due to a larger number of protein residues being exposed to the solvent at the surface of the protein; (b) the dynamics of all OCP forms appear to be suppressed upon the freezing of the solvent, which is most likely due to an ice-induced aggregation of the proteins; and (c) the wild type and the compact mutant exhibit different dynamics attributed to a missing H-bond between the pigment and protein, resulting a destabilization of the surrounding protein. [ABSTRACT FROM AUTHOR]

Molecular Dynamics simulations study material structure and dynamics at the atomic level. X-ray and neutron scattering experiments probe exactly the same time- and length scales as the simulations. In order to benchmark simulations against measured scattering data, a program is required that computes scattering patterns from simulations with good single-core performance and support for parallelization. In this work, the existing program Sassena is used as a potent solution to this requirement for a range of scattering methods, covering pico- to nanosecond dynamics, as well as the structure from some Ångströms to hundreds of nanometers. In the case of nanometer-level structures, the finite size of the simulation box, which is referred to as the finite size effect, has to be factored into the computations for which a method is described and implemented into Sassena. Additionally, the single-core and parallelization performance of Sassena is investigated, and several improvements are introduced. [ABSTRACT FROM AUTHOR]

In addition to investigations of the three-dimensional protein structure, information on the dynamical properties of proteins is indispensable for an understanding of protein function in general. Correlations between protein dynamics and function are typically anticipated when both molecular mobility and function are concurrently affected under specific temperatures or hydration conditions. In contrast, excitation energy transfer within the major photosynthetic light-harvesting complex II (LHC II) presents an atypical case, as it remains fully operational even at cryogenic temperatures, primarily depending on the interactions between electronic states and involving harmonic protein vibrations only. This review summarizes recent work on vibrational and conformational protein dynamics of LHC II and directly relates these findings to its light-harvesting function. In addition, we give a comprehensive introduction into the use of neutron spectroscopy and molecular dynamics simulations to investigate the protein dynamics of photosynthetic protein complexes in solution, which is information complementary to that obtained by protein crystallography.

The dynamics of water and agarose molecules in an agarose aqueous solution has been studied by means of quasielastic neutron scattering (QENS). The dynamic structure factor S (Q,E) of the agarose aqueous solution was fitted well to the sum of the Lorentz and delta function. The former is attributed to the diffusive motion of water molecules and the latter to the local vibrational motion of agarose molecules. The self-diffusion coefficient D of water molecules was obtained from the Q-dependence of the width of the Lorentz function, while the mean square displacement 2> of agarose molecules was obtained from the Q-dependence of the intensity of the delta term. In the cooling direction, both D and 2> decreased with decreasing temperature and showed discontinuous changes around the thermal gelation temperature (around 314 K). In the heating direction, however, D and 2> did not show the obvious change below 343 K, indicating a large hysteresis effect. The present results of 2> and D revealed that the thermal gelation suppresses the motion of the polymer and accelerates the diffusion of water molecules. The activation energy Ea of the diffusion of water in the sol state is the same as that of bulk water, but the Ea in the gel state is clearly smaller than that of bulk water. [ABSTRACT FROM AUTHOR]

A detailed comprehension of protein function requires information on the spatial structure of the protein, which is often gathered from X-ray crystallography. However, conformational dynamics often also plays an important functional role in proteins and can be directly investigated by complementary quasielastic neutron scattering. A classic example for dynamics–function correlations is Photosystem II, which is a multimeric pigment–protein complex responsible for catalyzing the light-induced photosynthetic water splitting into protons and oxygen. Several functional subprocesses of photosynthetic electron transfer and water splitting are strongly dependent on temperature and hydration, two factors also known to affect protein dynamics. Photosystem II is often investigated in the form of membrane fragments, where the protein complex remains embedded into its native lipid environment. However, experiments on protein function are often carried out in solution state, while direct investigations of molecular dynamics by quasielastic neutron scattering are mainly performed using specifically hydrated membrane fragments only. The present study provides the first quasielastic neutron scattering investigation of the molecular dynamics of Photosystem II membrane fragments (PSIImf) in solution over a wide temperature range from 50 to 300 K. At physiological temperatures above the melting point of water, we observed that the dynamics of PSIImf are significantly activated, leading to larger atomic mean square displacement values compared to those of specifically hydrated membrane stacks. The QENS data can be described by two dynamical components: a fast one, most probably corresponding to methyl group rotation; and a slower one, representing localized conformational dynamics. The latter component could be fitted by a jump-diffusion model at 300 K. The dynamics observed characterize the level of flexibility necessary for the proper PS II functionality under physiological conditions. In contrast, we observe a severe restriction of molecular dynamics upon freezing of the solvent below ~276 K. We associate this unexpected suppression of dynamics with a substantial aggregation of PSIImf caused by ice formation. [ABSTRACT FROM AUTHOR]

Besides a well-adapted structure, proteins often require a specific dynamical flexibility to undergo conformational changes in order to carry out their function. The latter dynamics can be directly measured by quasielastic neutron scattering as demonstrated here for three variants of the orange carotenoid protein (OCP), which plays a pivotal role in the protection of the cyanobacterial photosynthetic apparatus against photodamage. We investigate the dynamics of the structurally compact, dark-adapted wild type of OCP (OCPwt) in comparison with that of two mutant forms. The latter two mutants differ preferentially in their structures. The orange mutant OCP-W288A is assumed to have a compact structure and to preferentially bind the pigment echinenone, while the pink mutant OCP-W288A appears to represent the more elongated structure of the red active state of OCP binding the carotenoid canthaxanthin, respectively. The study reveals three major findings: (a) the dynamics of the red active state of OCP is significantly enhanced due to a larger number of protein residues being exposed to the solvent at the surface of the protein; (b) the dynamics of all OCP forms appear to be suppressed upon the freezing of the solvent, which is most likely due to an ice-induced aggregation of the proteins; and (c) the wild type and the compact mutant exhibit different dynamics attributed to a missing H-bond between the pigment and protein, resulting a destabilization of the surrounding protein.

The dynamics of pure ionic liquids and solutions with acetonitrile have been investigated through quasielastic neutron scattering (QENS). The translational diffusive motion of the 1-butyl-3-methyl-imidazolium cation was revealed as a function of concentration and temperature. The diffusion coefficients obtained are in reasonably good agreement with molecular dynamics (MD) computer simulations based on a classical potential. The diffusive mobility of the cation dramatically increases when adding acetonitrile. This increase in diffusivity is directly related to a maximum in conductivity of these ionic liquid solutions and might pave the way for new design of electrolytes. The translational motions in pure ionic liquids are too slow to be resolved by our experiment. However, localized motion resembling rotation on a sphere of the measured proton signal could be identified in the pure ionic liquids. [ABSTRACT FROM AUTHOR]

Hydrogen (H) conductivity on oxide‐based materials is crucially important in fuel cells and related catalysis. Here, this work measures the diffusion rate of H generated from Ru nanoparticles loaded on polar MgO(111) facet particles under H2 at elevated temperatures without moisture and compares it to conventional nonpolar MgO(110) for the first time by in situ quasielastic neutron scattering (QENS). The QENS reveals an exceptional diffusion rate on the polar facet via a proton (H+) hopping mechanism, which is an order of magnitude superior to that of typical H+‐conducting oxides. This work attributes this to the unique atomic arrangement of alternate layers of Mg cations and O anions of the polar MgO(111) where the strong electrostatic field of terminal oxygen anions facilitates protonic migration with a lower degree of local covalency. [ABSTRACT FROM AUTHOR]

[Display omitted] • The tetrahedral hydrogen bond structure of H 2 O is distorted in OMC pores. • The confined water diffuses with smaller energy as the hydrophobicity of pores increases. • H 2 O confined in hydrophobic pores tend to aggregate in the central part of the pores. • EISF analysis proved evidence for immobile and mobile fractions of confined water. The structure and dynamic properties of capillary-condensed water confined in ordered microporous carbon (OMC) of pores diameter 18.7 Å are investigated over a temperature range of 200–300 K by adsorption/desorption isotherms, X-ray diffraction (XRD), and quasielastic neutron scattering (QENS). The nitrogen adsorption/desorption isotherm of OMC pores at 77 K exhibits an I-type pattern. The water adsorption/desorption isotherm of OMC pores at 298 K is of type V. The XRD data on water confined in OMC reveal that the tetrahedral network structure of water is perturbed from the bulk water structure, but not to such an extent as found for water confined in MCM-41 and Ph-PMO previously reported. With decreasing the temperature, the ∼2.8 Å peak shifts to shorter distances, while the second-neighbor H 2 O– H 2 O interaction distances gradually increase from 3.95 Å and 4.49 Å to 4.43 Å and 4.84 Å, indicating a tendency to form a more tetrahedral-like hydrogen-bonded water structure at subzero temperatures. Below 230 K, the hexagonal ice I h was partially formed in OMC pores. The QENS spectra were analyzed using a jump-diffusion model to translate water molecules. The translational diffusion of water molecules in OMC pores is comparable to that of bulk water at 300 K and higher than that in MCM-41, and the mobility slows as the temperature decreases. The elastic incoherent structure factor (EISF) analysis found evidence for immobile and mobile fractions of confined water. The mobile fraction exhibited jump diffusion, with a jump length consistent with a sphere of confinement radius of 4–8 Å. The results obtained in the present work are compared with those reported for MCM-41 with a hydrophilic interface and Ph-PMO with an amphiphilic interface, and the influence of interface effect on local structure and dynamic properties of confined water is discussed. [ABSTRACT FROM AUTHOR]

Polarisation analysis for neutron scattering experiments is a powerful tool suitable for a wide variety of studies, including soft-matter samples which have no bulk magnetic behaviour and/or a significant hydrogen content. Here, we describe a method to leverage the versatility and spin-polarisation capabilities of a cold triple-axis spectrometer to perform a measurement to separate coherent and incoherent neutron scattering for a non-magnetic sample in the quasielastic neutron scattering (QENS) regime. Such measurements are complementary to unpolarised QENS measurements, which may typically be performed on a backscattering or time-of-flight spectrometer instrument where polarisation analysis can be significantly more difficult to achieve, and utilise the strengths of each type of instrument.

The dynamics of water and agarose molecules in an agarose aqueous solution has been studied by means of quasielastic neutron scattering (QENS). The dynamic structure factor S (Q,E) of the agarose aqueous solution was fitted well to the sum of the Lorentz and delta function. The former is attributed to the diffusive motion of water molecules and the latter to the local vibrational motion of agarose molecules. The self-diffusion coefficient D of water molecules was obtained from the Q-dependence of the width of the Lorentz function, while the mean square displacement of agarose molecules was obtained from the Q-dependence of the intensity of the delta term. In the cooling direction, both D and decreased with decreasing temperature and showed discontinuous changes around the thermal gelation temperature (around 314 K). In the heating direction, however, D and did not show the obvious change below 343 K, indicating a large hysteresis effect. The present results of and D revealed that the thermal gelation suppresses the motion of the polymer and accelerates the diffusion of water molecules. The activation energy Ea of the diffusion of water in the sol state is the same as that of bulk water, but the Ea in the gel state is clearly smaller than that of bulk water.

A detailed comprehension of protein function requires information on the spatial structure of the protein, which is often gathered from X-ray crystallography. However, conformational dynamics often also plays an important functional role in proteins and can be directly investigated by complementary quasielastic neutron scattering. A classic example for dynamics–function correlations is Photosystem II, which is a multimeric pigment–protein complex responsible for catalyzing the light-induced photosynthetic water splitting into protons and oxygen. Several functional subprocesses of photosynthetic electron transfer and water splitting are strongly dependent on temperature and hydration, two factors also known to affect protein dynamics. Photosystem II is often investigated in the form of membrane fragments, where the protein complex remains embedded into its native lipid environment. However, experiments on protein function are often carried out in solution state, while direct investigations of molecular dynamics by quasielastic neutron scattering are mainly performed using specifically hydrated membrane fragments only. The present study provides the first quasielastic neutron scattering investigation of the molecular dynamics of Photosystem II membrane fragments (PSIImf) in solution over a wide temperature range from 50 to 300 K. At physiological temperatures above the melting point of water, we observed that the dynamics of PSIImf are significantly activated, leading to larger atomic mean square displacement values compared to those of specifically hydrated membrane stacks. The QENS data can be described by two dynamical components: a fast one, most probably corresponding to methyl group rotation; and a slower one, representing localized conformational dynamics. The latter component could be fitted by a jump-diffusion model at 300 K. The dynamics observed characterize the level of flexibility necessary for the proper PS II functionality under physiological conditions. In contrast, we observe a severe restriction of molecular dynamics upon freezing of the solvent below ~276 K. We associate this unexpected suppression of dynamics with a substantial aggregation of PSIImf caused by ice formation.

The article presents a study describing the observed nanoscopic dynamics of cetyltrimethylammonium bromide (CTAB) molecules in hybrid synthetic hydroxyapatite (HAp)-CTAB composite. The quasielastic neutron scattering (QENS) technique was used. The microstructure of CTAB micelles was assessed using small angle x-ray scattering (SAXS) experiments.

The aim of this paper is to decide which of the two possible thermodynamic expressions for the cooperativity length in glass forming liquids is the correct one. In the derivation of these two expressions, the occurrence of temperature fluctuations in the considered nanoscale subsystems is either included or neglected. Consequently, our analysis gives also an answer to the widely discussed problem whether temperature fluctuations have to be generally accounted for in thermodynamics or not. To this end, the characteristic length-scales at equal times and temperatures for propylene glycol were determined independently from AC calorimetry in both the above specified ways and from quasielastic neutron scattering (QENS), and compared. The result shows that the cooperative length determined from QENS coincides most consistently with the cooperativity length determined from AC calorimetry measurements for the case that the effect of temperature fluctuations is incorporated in the description. This conclusion indicates that--accounting for temperature fluctuations--the characteristic length can be derived by thermodynamic considerations from the specific parameters of the liquid at glass transition and that temperature does fluctuate in small systems. [ABSTRACT FROM AUTHOR]

We have developed a hybrid piston cylinder cell for quasielastic neutron scattering (QENS) experiments up to about 1 GPa. It consists of a fretted cylinder made of the high tensile steel (SNCM439) liner and the Al alloy (NA700) jacket. Performance tests revealed that the cell can withstand a pressure of 0.8 GPa without irreversible damage and has 4.4 times larger neutron transmission at 3.14 meV (5.10 Å in wavelength) than that of a conventional CuBe monobloc cylinder. Combined with the sample assembly devised for suppressing multiple scattering, high quality QENS spectra of water were obtained up to 0.8 GPa. This study illustrates the efficacy of the hybrid cylinders not only for increasing maximum available pressure but also manipulating the available pressure and the signal intensity, depending on the purpose of the experiments. [ABSTRACT FROM AUTHOR]

Background and Objectives: Intrinsically disordered proteins (IDPs) and proteins containing intrinsically disordered regions (IDRs) are known to be involved in various human diseases. Since the IDPs/IDRs are fluctuating between many structural substrates, the dynamical behavior of the disease-related IDPs/IDRs needs to be characterized to elucidate the mechanisms of the pathogenesis of the diseases. As protein motions have a hierarchy ranging from local side-chain motions, through segmental motions of loops or disordered regions, to diffusive motions of entire molecules, segmental motions, as well as local motions, need to be characterized. Materials and Methods: Combined analysis of quasielastic neutron scattering (QENS) spectra with the structural data provides information on both the segmental motions and the local motions of the IDPs/IDRs. Here, this method is applied to re-analyze the QENS spectra of the troponin core domain (Tn-CD), various mutants of which cause the pathogenesis of familial cardiomyopathy (FCM), and α-synuclein (αSyn), amyloid fibril formation of which is closely related to the pathogenesis of Parkinson's disease, collected in the previous studies. The dynamical behavior of wild-type Tn-CD, FCM-related mutant Tn-CD, and αSyn in the different propensity states for fibril formation is characterized. Results: In the Tn-CD, the behavior of the segmental motions is shown to be different between the wild type and the mutant. This difference is likely to arise from changes in the intramolecular interactions, which are suggested to be related to the functional aberration of the mutant Tn-CD. In αSyn, concerted enhancement of the segmental motions and the local motions is observed with an increased propensity for fibril formation, suggesting the importance of these motions in fibril formation. Conclusions: Characterization of the segmental motions as well as the local motions is thus useful for discussing how the changes in dynamical behavior caused by the disease-related mutations and/or environmental changes could be related to the functional and/or behavioral aberrations of these proteins. [ABSTRACT FROM AUTHOR]

The severity of the cancer statistics around the globe and the complexity involving the behavior of cancer cells inevitably calls for contributions from multidisciplinary areas of research. As such, materials science became a powerful asset to support biological research in comprehending the macro and microscopic behavior of cancer cells and untangling factors that may contribute to their progression or remission. The contributions of cellular water dynamics in this process have always been debated and, in recent years, experimental works performed with Quasielastic neutron scattering (QENS) brought new perspectives to these discussions. In this review, we address these works and highlight the value of QENS in comprehending the role played by water molecules in tumor cells and their response to external agents, particularly chemotherapy drugs. In addition, this paper provides an overview of QENS intended for scientists with different backgrounds and comments on the possibilities to be explored with the next-generation spectrometers under construction. [ABSTRACT FROM AUTHOR]

Quasielastic Neutron Scattering (QENS) was employed in order to probe the dynamics of water confined within copper-loaded MOR, MFI and CHA zeolite frameworks in the temperature range 100–300 K. At 100 K, motion was outside the experimental time window and the adsorbate appeared static. Rotational quasielastic line broadenings were observed across all three Cu-zeolites at 200 K; and both rotation and translation were pronounced at 300 K. The findings indicate Cu content and the cavity size affect water mobility, which appears to represent diffusion within localised clusters.

We have measured the dynamics of water confined in a porous magnesium carbonate material, Upsalite®, using the high-resolution neutron backscattering spectrometer SPHERES. We found quasielastic scattering that does not flatten out up to 360 K, which means that the dynamics of water are much slower than in other matrix materials. Specifically, a single Lorentzian line could be fitted to the quasielastic part of the acquired spectra between 220 and 360 K. This, accompanied by an elastic line from dynamically frozen water present at all experimental temperatures, even above the melting point, signaled a significant amount of bound or slow water. [ABSTRACT FROM AUTHOR]

The paper deals with a model-free approach to the analysis of quasielastic neutron scattering intensities from anomalously diffusing quantum particles. All quantities are inferred from the asymptotic form of their time-dependent mean square displacements which grow ?ta, with 0 = a < 2. Confined diffusion (a = 0) is here explicitly included. We discuss in particular the intermediate scattering function for long times and the Fourier spectrum of the velocity autocorrelation function for small frequencies. Quantum effects enter in both cases through the general symmetry properties of quantum time correlation functions. It is shown that the fractional diffusion constant can be expressed by a Green-Kubo type relation involving the real part of the velocity autocorrelation function. The theory is exact in the diffusive regime and at moderate momentum transfers. [ABSTRACT FROM AUTHOR]

Quasielastic neutron scattering measurements and molecular dynamics simulations were combined to investigate the collective dynamics of deuterated methanol, CD3OD. In the experimentally determined dynamic structure factor, a slow, non-Fickian mode was observed in addition to the standard density-fluctuation heat mode. The simulation results indicate that the slow dynamical process originates from the hydrogen bonding of methanol molecules. The qualitative behavior of this mode is similar to the previously observed α-relaxation in supercooled water [M. C. Bellissent-Funel et al., Phys. Rev. Lett. 85, 3644 (2000)] which also originates from the formation and dissolution of hydrogen-bonded associates (supramolecular clusters). In methanol, however, this mode is distinguishable well above the freezing transition. This finding indicates that an emergent slow mode is not unique to supercooled water, but may instead be a general feature of hydrogen-bonding liquids and associating molecular liquids. [ABSTRACT FROM AUTHOR]

The ionic stochastic motions in the molten alkali halide NaF are investigated by quasielastic neutron scattering and first principles molecular dynamics simulation. Quasielastic neutron scattering was employed to extract the diffusion behavior of the sodium ions in the melt. An extensive first principles based simulation on a box of up to 512 particles has been performed to complement the experimental data. From that large box, a smaller 64-particle box has then been simulated over a runtime of 60 ps. A good agreement between calculated and neutron data on the level of spectral shape has been obtained. The obtained sodium diffusion coefficients agree very well. The simulation predicts a fluorine diffusion coefficient similar to the sodium one. Applying the Nernst-Einstein equation, a remarkable large cross correlation between both ions can be deduced. The velocity cross correlations demonstrate a positive correlation between the ions over a period of 0.1 ps. That strong correlation is evidence that the unlike ions do not move completely statistically independent and have a strong association over a short period of time. [ABSTRACT FROM AUTHOR]

The hydrogen storage performance of reactive hydride composite Mg(NH2)2+2LiH can be significantly improved by the addition of LiBH4 and the subsequent formation of an amide–borohydride compound Li4(BH4)(NH2)3 during hydrogen release. Herein, an investigation into the structure and anion motions of Li4(BH4)(NH2)3 using synchrotron radiation powder X‐ray diffraction (SR‐PXD; 295–573 K) and quasielastic neutron scattering (QENS; 297–514 K) is described. The highest temperature studied with QENS (514 K) is above the melting point of Li4(BH4)(NH2)3. The neutron measurements confirm a long‐range diffusive motion of hydrogen‐containing species with the diffusion coefficient D≈10−6 cm2 s−1. Interestingly, this value is comparable to that of Li+ diffusion inferred from conductivity measurements. SR‐PXD confirms the recrystallization of Li4(BH4)(NH2)3 from the melt into the α‐phase upon cooling. At temperatures below 514 K, localized rotational motions are observed that are attributed to (BH4)− tetrahedra units mainly undergoing rotations around the C3 axes. The activation energy for this thermally activated process is found to be Ea=15.5±0.9 and 17.4±0.9 kJ mol−1 respectively for the two instrumental resolutions utilized in the QENS measurements, corresponding to observation times of 55 and 14 ps. [ABSTRACT FROM AUTHOR]

The condensed phases of the carbon-based nanobowl corannulene are herein investigated in the temperature range 200–573 K, combining differential scanning calorimetry, synchrotron X-ray diffraction, and quasielastic neutron-scattering. For the first time, we identify the presence of a well-defined thermal event at 382 K, a figure well below a melting point of 540 K. Contrary to naïve expectation, detailed analysis of the neutron-scattering data below and above this pre-melting transition signals the emergence of correlated stochastic dynamics within both thermodynamically stable solid phases of the material. We find that these are progressively responsible for the suppression of molecular and supramolecular order over mesoscopic length scales, and are associated with the formation of high-symmetry rotor-like states exhibiting localized stochastic motions. Upon cooling from the melt, we have also discovered a robust hysteresis associated with the existence of hitherto-unknown metastable liquid (deep-supercooled) and disordered-solid phases. This behaviour is markedly different from that observed in the quintessential Buckminsterfullerene C 60 or other chemically substituted fullerene adducts studied to date at this level of detail. These results evince new and yet-to-tapped opportunities for the use of the stable and metastable phases of carbon-based nanobowls in novel applications exploiting the emergence of dynamical disorder at the nanoscale. [Display omitted] [ABSTRACT FROM AUTHOR]

In quasieleastic neutron scattering spectrometers one usually faces a trade-off between energy resolution and counting statistics. If the resolution is improved the intensity at the detectors reduces and vice versa. It is not immediately clear how to weigh both factors against each other. In this paper it is proposed to use the maximum time obtainable by Fourier transform of the spectra as the quantity to be optimised. It is shown that this leads to a well-defined criterion for the choice of the resolution. [ABSTRACT FROM AUTHOR]

Relaxation processes for imidazolium-based ionic liquids (ILs) were investigated by means of an incoherent quasielastic neutron scattering technique. In order to clarify the cation and anion effects on the relaxation processes, ten samples were measured. For all of the samples, we found three relaxations at around 1 ps, 10 ps, and 100 ps-10 ns, each corresponding to the alkyl reorientation, the relaxation related to the imidazolium ring, and the ionic diffusion. The activation energy (Ea) for the alkyl relaxation is insensitive to both anion and alkyl chain lengths. On the other hand, for the imidazolium relaxation and the ionic diffusion processes, Ea increases as the anion size decreases but is almost independent of the alkyl chain length. This indicates that the ionic diffusion and imidazolium relaxation are governed by the Coulombic interaction between the core parts of the cations (imidazolium ring) and the anions. This is consistent with the fact that the imidazolium-based ILs have nanometer scale structures consisting of ionic and neutral (alkyl chain) domains. It is also found that there is a clear correlation between the ionic diffusion and viscosity, indicating that the ionic diffusion is mainly associated with the glass transition which is one of the characteristics of imidazolium-based ILs. [ABSTRACT FROM AUTHOR]

We have investigated a mixture of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and tetrahydrofuran (THF) (70 wt.% PDMAEMA/30 wt.% THF) by combining dielectric spectroscopy and quasielastic neutron scattering (QENS) on a labelled sample, focusing on the dynamics of the THF molecules. Two independent processes have been identified. The "fast" one has been qualified as due to an internal motion of the THF ring leading to hydrogen displacements of about 3 Å with rather broadly distributed activation energies. The "slow" process is characterized by an Arrhenius-like temperature dependence of the characteristic time which persists over more than 9 orders of magnitude in time. The QENS results evidence the confined nature of this process, determining a size of about 8 Å for the volume within which THF hydrogens' motions are restricted. In a complementary way, we have also investigated the structural features of the sample. This study suggests that THF molecules are well dispersed among side-groups nano-domains in the polymer matrix, ruling out a significant presence of clusters of solvent. Such a good dispersion, together with a rich mobility of the local environment, would prevent cooperativity effects to develop for the structural relaxation of solvent molecules, frustrating thereby the emergence of Vogel-Fulcher-like behavior, at least in the whole temperature interval investigated. [ABSTRACT FROM AUTHOR]

We report on quasielastic neutron spectroscopy experiments on ferrocene (bis(5-cyclopentadienyl)iron) in its three different crystalline phases: the disordered monoclinic crystalline phase (T > 164 K), the metastable triclinic phase (T < 164 K), and the stable orthorhombic phase (T < 250 K). The cyclopentadienyl rings in ferrocene are known to undergo rotational reorientations for which the analysis of our large data set suggests partially a revision of the known picture of the dynamics and allows for an extension and completion of previous studies. In the monoclinic phase, guided by structural information, we propose a model for rotational jumps among non-equivalent sites in contrast to the established 5-fold jump rotation model. The new model takes the dynamical disorder into account and allows the cyclopentadienyl rings to reside in two different configurations which are found to be twisted by an angle of approximately 30°. In the triclinic phase, our analysis demands the use of a 2-ring model accounting for crystallographically independent sites with different barriers to rotation. For the orthorhombic phase of ferrocene, we confirm a significantly increased barrier of rotation using neutron backscattering spectroscopy. Our data analysis includes multiple scattering corrections and presents a novel approach of simultaneous analysis of different neutron scattering data by combining elastic and inelastic fixed window temperature scans with energy spectra, providing a very robust and reliable mean of extracting the individual activation energies of overlapping processes. [ABSTRACT FROM AUTHOR]

The complexation of NiCl2 with 2,2′-Bipyridine was followed using quasielastic neutron scattering to observe reaction progress. Water adsorption in chabazite with time resolution was observed using strain induced in the aluminosilicate framework with a high-resolution engineering diffractometer. These reactions illustrate the recent progress and possibilities in using neutron probes to observe realistic catalytic reactions as they progress. [ABSTRACT FROM AUTHOR]

We present a study on the single ion dynamics in the molten alkali halide NaBr. Quasielastic neutron scattering was employed to extract the self-diffusion coefficient of the sodium ions at three temperatures. Molecular dynamics simulations using rigid and polarizable ion models have been performed in parallel to extract the sodium and bromide single dynamics and ionic conductivities. Two methods have been employed to derive the ion diffusion, calculating the mean squared displacements and the velocity autocorrelation functions, as well as analysing the increase of the line widths of the self-dynamic structure factors. The sodium diffusion coefficients show a remarkable good agreement between experiment and simulation utilising the polarisable potential. [ABSTRACT FROM AUTHOR]

The molecular dynamics of solutions of di-propylene glycol methylether (2PGME) and H2O (or D2O) confined in 28 À pores of MCM-41 have been studied by quasielastic neutron scattering and differential scanning calorimetry over the concentration range 0-90 wt.% water. This system is of particular interest due to its pronounced non-monotonic concentration dependent dynamics of 2PGME in the corresponding bulk system, showing the important role of hydrogen bonding for the dynamics. In this study we have elucidated how this non-monotonic concentration dependence is affected by the confined geometry. The results show that this behaviour is maintained in the confinement, but the slowest diffusive dynamics of 2PGME is now observed at a considerably higher water concentration; at 75 wt.% water in MCM-41 compared to 30 wt.% water in the corresponding bulk system. This difference can be explained by an improper mixing of the two confined liquids. The results suggest that water up to a concentration of about 20 wt.% is used to hydrate the hydrophilic hydroxyl surface groups of the silica pores, and that it is only at higher water contents the water becomes partly mixed with 2PGME. Hence, due to this partial micro-phase separation of the two liquids larger, and thereby slower relaxing, structural entities of hydrogen bonded water and 2PGME molecules can only be formed at higher water contents than in the bulk system. However, the Q-dependence is unchanged with confinement, showing that the nature of the molecular motions is preserved. Thus, there is no indication of localization of the dynamics at length scales of less than 20 À. The dynamics of both water and 2PGME is strongly dominated by translational diffusion at a temperature of 280 K. [ABSTRACT FROM AUTHOR]

Dynamics of crystal water in Prussian blue (PB), Fe(III)4[Fe(II)(CN)6]3.14H2O and its analogue Prussian green (PG), ferriferricynaide, Fe(III)4[Fe(III)(CN)6]4.16H2O have been investigated using Quasielastic Neutron Scattering (QENS) technique. PB and its analogue compounds are important materials for their various interesting multifunctional properties. It is known that crystal water plays a crucial role towards the multifunctional properties of Prussian blue analogue compounds. Three structurally distinguishable water molecules: (i) coordinated water molecules at empty nitrogen sites, (ii) non-coordinated water molecules in the spherical cavities, and (iii) at interstitial sites exist in PB. Here spherical cavities are created due to the vacant sites of Fe(CN)6 units. However, PG does not have any such vacant N or Fe(CN)6 units, and only one kind of water molecules, exists only at interstitial sites. QENS experiments have been carried out on both the compounds in the temperature range of 260-360K to elucidate the dynamical behavior of different kinds of water molecules. Dynamics is found to be much more pronounced in case of PB, compared to PG. A detailed data analysis showed that localized translational diffusion model could describe the observed data for both PB and PG systems. The average diffusion coefficient is found to be much larger in the PB than PG. The obtained domain of dynamics is found to be consistent with the geometry of the structure of the two systems. Combining the data of the two systems, a quantitative estimate of the dynamics, corresponding to the water molecules at different locations is made. [ABSTRACT FROM AUTHOR]