Influence of water on the microscopic dynamics of 1-butyl-3-methylimidazolium tetrafluoroborate studied by means of quasielastic neutron scattering.

We present a systematic study on the effect of water on the microscopic dynamics of 1-butyl-3-methylimidazolium tetrafluoroborate by means of quasielastic neutron scattering. By mixing the ionic liquid with either heavy or light water, the different contributions to the quasielastic broadening could be identified and treated separately. This study was performed at room temperature, which is more than 15 °C above the demixing line. Our results show that even small amounts of water accelerate the diffusion mechanisms considerably. While samples with small water percentage reveal a diffusion process confined within ionic liquid nanodomains, an admixture of more than 15 wt. % water relieves the confinement. Furthermore, the presence of two water species was identified: one behaving as free water, whereas the other was interpreted as a component bound to the ionic liquid motion. Based on the fact that water preferentially binds to the BF4 anion, which itself has a negligible contribution to the scattered intensity, our experiments reveal unprecedented information about the microscopic anion dynamics.

Protein-Polymer Dynamics as Affected by Polymer Coating and Interactions.

We investigate the relaxation dynamics of protein-polymer conjugates by neutron scattering spectroscopy to understand to which extent the coating of a protein by a polymer can replace water in promoting thermal structural fluctuations. For this purpose, we compare the dynamics of protein-polymer mixtures to that of conjugates with a variable number of polymers covalently attached to the protein. Results show that the flexibility of the protein is larger in protein-polymer mixtures than in native protein or in conjugates, even in the dry state. Upon hydration, both the native protein and the conjugate show equivalent dynamics, suggesting that the polymer grafted on the protein surface adsorbs all water molecules.

Changes in dynamics of α-chymotrypsin due to covalent inhibitors investigated by elastic incoherent neutron scattering.

An essential role of enzymes is to catalyze various chemical reactions in the human body and inhibition of the enzymatic activity by small molecules is the mechanism of action of many drugs or tool compounds used to study biological processes. Here, we investigate the effect on the dynamics of the serine protease α-chymotrypsin when in complex with two different covalently bound inhibitors using elastic incoherent neutron scattering. The results show that the inhibited enzyme displays enhanced dynamics compared to the free form. The difference was prominent at higher temperatures (240-310 K) and the type of motions that differ include both small amplitude motions, such as hydrogen atom rotations around a methyl group, and large amplitude motions, such as amino acid side chain movements. The measurements were analyzed with multivariate methods in addition to the standard univariate methods, allowing for a more in-depth analysis of the types of motions that differ between the two forms. The binding strength of an inhibitor is linked to the changes in dynamics occurring during the inhibitor-enzyme binding event and thus these results may aid in the deconvolution of this fundamental event and in the design of new inhibitors.

Dielectric Susceptibility of Liquid Water: Microscopic Insights from Coherent and Incoherent Neutron Scattering.

The analysis of neutron scattering results on H dynamics (H_{2}O) and the dynamic structure factor (D_{2}O) around the intermolecular peak and at intermediate length scales in terms of the susceptibilities reveals three processes (diffusive, local relaxational and vibrational) at frequencies below 3 THz, to which the contributions commonly invoked in dielectric studies can be directly mapped. We achieve a unified description of the results from both techniques, clarifying the nature of the molecular motions involved in the dielectric spectra and their impact on the structural relaxation.

Dynamics of nanoscale polarization fluctuations in a uniaxial relaxor.

We have studied neutron diffuse scattering in a Sr(0.61)Ba(0.39)Nb(2)O(6) single crystal by neutron backscattering at sub-µeV energy resolution. We can identify two response components with transverse polarization: an elastic (resolution limited) central peak, which monotonically increases with decreasing temperature, and a quasielastic central peak, having a maximum intensity around the ferroelectric phase transition close to 350 K. In contrast to previous neutron experiments on this and other relaxor materials, we were able to observe a temperature dependence of the characteristic frequency of these fluctuations, obeying the same Vogel-Fulcher law as the dynamic part of the dielectric permittivity of this material. In this way our findings provide a first direct link between the Vogel-Fulcher-type frequency dependence of dielectric permittivity and dynamic nanoscale lattice modulations with a transverse correlation length of about 5-10 unit cells.

Quasielastic neutron scattering study of hydrogen motions in an aqueous poly(vinyl methyl ether) solution.

We present a quasielastic neutron scattering (QENS) investigation of the component dynamics in an aqueous Poly(vinyl methyl ether) (PVME) solution (30% water content in weight). In the glassy state, an important shift in the Boson peak of PVME is found upon hydration. At higher temperatures, the diffusive-like motions of the components take place with very different characteristic times, revealing a strong dynamic asymmetry that increases with decreasing T. For both components, we observe stretching of the scattering functions with respect to those in the bulk and non-Gaussian behavior in the whole momentum transfer range investigated. To explain these observations we invoke a distribution of mobilities for both components, probably originated from structural heterogeneities. The diffusive-like motion of PVME in solution takes place faster and apparently in a more continuous way than in bulk. We find that the T-dependence of the characteristic relaxation time of water changes at T ≲ 225 K, near the temperature where a crossover from a low temperature Arrhenius to a high temperature cooperative behavior has been observed by broadband dielectric spectroscopy (BDS) [S. Cerveny, J. Colmenero and A. Alegría, Macromolecules, 38, 7056 (2005)]. This observation might be a signature of the onset of confined dynamics of water due to the freezing of the PVME dynamics, that has been selectively followed by these QENS experiments. On the other hand, revisiting the BDS results on this system we could identify an additional "fast" process that can be attributed to water motions coupled with PVME local relaxations that could strongly affect the QENS results. Both kinds of interpretations, confinement effects due to the increasing dynamic asymmetry and influence of localized motions, could provide alternative scenarios to the invoked "strong-to-fragile" transition.

Investigation of the relationship between hydrogen bonds and macroscopic properties in hybrid core-shell gamma-Fe2O3-P(NIPAM-AAS) microgels.

We investigate in a hybrid material the interactions existing between magnetic nanoparticles of gamma-Fe(2)O(3) and the polymer matrix constituted by core-shell poly(N-isopropylacrylamide-sodium acrylate) microgels. These interactions provoke the shifting of the microgel volume phase transition to higher temperatures when the amount of gamma-Fe(2)O(3) increases. The study was performed using different techniques such as incoherent quasi-elastic neutron scattering (IQNS), infrared spectroscopy (FTIR-ATR), and dynamic light scattering (DLS). Below the low critical solution temperature (LCST) of the polymer, the IQNS data confirm that the presence of inorganic nanoparticles affects the PNIPAM chain motions. Thus, in the swollen state both the mean-square displacement of the polymer segments and the diffusive motion of the polymer chains decrease as the iron oxide content increases. The FTIR-ATR study indicates that the reduction of vibrational and diffusional motions of the polymer chains is due to the formation of hydrogen bonds between the amide groups of the polymer matrix and the OH groups of the magnetic nanoparticles. The creation of this hybrid complex would explain the reduction of the swelling capacity with increasing the iron content in the microgels. Furthermore, this interaction could also explain the shift of the polymer LCST to higher temperatures as due to the extra energy required by the system to break the hydrogen bonds prior to the PNIPAM collapse.

Consequence of excess configurational entropy on fragility: the case of a polymer-oligomer blend.

By taking advantage of the molecular weight dependence of the glass transition of polymers and their ability to form perfectly miscible blends, we propose a way to modify the fragility of a system, from fragile to strong, keeping the same glass properties, i.e., vibrational density of states, mean-square displacement, and local structure. Both slow and fast dynamics are investigated by calorimetry and neutron scattering in an athermal polystyrene-oligomer blend, and compared to those of a pure 17-mer polystyrene considered to be a reference, of the same Tg. Whereas the blend and the pure 17-mer have the same heat capacity in the glass and in the liquid, their fragilities differ strongly. Thus, the difference in fragility is related to an extra configurational entropy created by the mixing process and acting at a scale much larger than the interchain distance, without affecting the fast dynamics and the structure of the glass.

The microscopic basis of the glass transition in polymers from neutron scattering studies.

Recent neutron scattering experiments on the microscopic dynamics of polymers below and above the glass transition temperature T(g) are reviewed. The results presented cover different dynamic processes appearing in glasses: local motions, vibrations, and different relaxation processes such as alpha- and beta-relaxation. For the alpha-relaxation, which occurs above T(g), it is possible to extend the time-temperature superposition principle, which is valid for polymers on a macroscopic scale, to the microscopic time scale. However, this principle is not applicable for temperatures approaching T(g). Below T(g), an inelastic excitation at a frequency of some hundred gigahertz (on the order of several wave numbers), the "boson peak," survives from a quasi-elastic overdamped scattering law at high temperatures. The connection between this boson peak and the fast dynamic process appearing near T(g) is discussed.

Molecular dynamics of glycerol and glycerol-trehalose bioprotectant solutions nanoconfined in porous silicon.

Glycerol and trehalose-glycerol binary solutions are glass-forming liquids with remarkable bioprotectant properties. Incoherent quasielastic neutron scattering is used to reveal the different effects of nanoconfinement and addition of trehalose on the molecular dynamics in the normal liquid and supercooled liquid phases, on a nanosecond time scale. Confinement has been realized in straight channels of diameter D=8 nm formed by porous silicon. It leads to a faster and more inhomogeneous relaxation dynamics deep in the liquid phase. This confinement effect remains at lower temperature where it affects the glassy dynamics. The glass transitions of the confined systems are shifted to low temperature with respect to the bulk ones. Adding trehalose tends to slow down the overall glassy dynamics and increases the nonexponential character of the structural relaxation. Unprecedented results are obtained for the binary bioprotectant solution, which exhibits an extremely non-Debye relaxation dynamics as a result of the combination of the effects of confinement and mixing of two constituents.

Atomic motions in poly(vinyl methyl ether): A combined study by quasielastic neutron scattering and molecular dynamics simulations in the light of the mode coupling theory.

Quasielastic neutron scattering experiments (time-of-flight, neutron spin echo, and backscattering) on protonated poly(vinyl methyl ether) (PVME) have revealed the hydrogen dynamics above the glass-transition temperature. Fully atomistic molecular dynamics simulations properly validated with the neutron scattering results have allowed further characterization of the atomic motions accessing the correlation functions directly in real space. Deviations from Gaussian behavior are found in the high-momentum transfer range, which are compatible with the predictions of mode coupling theory (MCT). We have applied the MCT phenomenological version to the self-correlation functions of PVME atoms calculated from our simulation data, obtaining consistent results. The unusually large value found for the lambda-exponent parameter is close to that recently reported for polybutadiene and simple polymer models with intramolecular barriers.

Iron dynamics in Al-Cu-Fe quasicrystals and approximants: Mössbauer and neutron experiments.

We present new results on the iron dynamics in the icosahedral quasicrystal i-AlCuFe and two cubic approximants as well as the non-approximant Al-Cu-Fe cubic B2 phase. Conventional Mössbauer spectroscopy is used as well as, for the i-AlCuFe phase, high Doppler velocity Mössbauer spectroscopy and quasielastic neutron scattering for samples with different Fe isotope contents. We show that in the i-phase the Fe Lamb-Mössbauer recoilless fraction decreases below that predicted for lattice vibrations alone for temperatures above about 550 K. This decrease is correlated with the onset of a quasielastic signal seen in both Mössbauer and neutron backscattering spectroscopy, which indicates the presence above 550 K of Fe jump processes confined in a local cage. The timescale of the Fe jumps (660 ps at 1000 K) and their temperature dependence differ widely from those of Cu jumps in the same i-AlCuFe quasicrystal. From the temperature dependence of the quadrupole splitting of the (57)Fe Mössbauer spectrum, one can distinguish two kinds of Fe jumps, one starting at 550 K and the second above 800 K. In the two cubic approximants, a loss in the Fe recoilless fraction also occurs above 550 K, revealing the same kind of Fe dynamics as in the i-phase but the effect is smaller. On the other hand, no anomalous Fe dynamics (other than lattice vibrations) is detected in the B2-AlCuFe phase. Since the cubic approximants possess similar local configurations as the quasicrystal, we conclude that locally a Penrose tile description is appropriate. This shows that the detected Fe jumps can be interpreted in terms of phason-like local tiling flips.

Direct evidence for the Nd magnetic ordering in NdMnO(3) from the hyperfine field splitting of Nd nuclear levels.

We investigated the low energy excitations in NdMnO(3) in the µeV range by a backscattering neutron spectrometer. The energy spectra on polycrystalline NdMnO(3) samples revealed inelastic peaks at E = 2.15 ± 0.01 µeV at T = 2 K on both energy gain and energy loss sides. The inelastic peaks move gradually towards lower energy with increasing temperature and tend to merge with the elastic peak at the electronic magnetic ordering temperature of Nd, T(Nd)≈20 K. However, at temperatures higher than T(Nd)≈20 K the energy of the inelastic peak decreases at a much slower rate and remains finite up to T = 55 K, the highest temperature investigated. We interpret the inelastic peaks to be due to the transition between the hyperfine-split nuclear level of the (143)Nd and (145)Nd isotopes with spin I = 7/2 caused by the magnetic ordering of Nd electronic moment below T(Nd)≈20 K. We ascribe the finite energy of the inelastic peak and its much smaller temperature dependence at T>20 K to be due to the polarization of the Nd magnetic moment by the field of Mn moments that order below T(N)≈78 K.

New sources and instrumentation for neutrons in biology.

Neutron radiation offers significant advantages for the study of biological molecular structure and dynamics. A broad and significant effort towards instrumental and methodological development to facilitate biology experiments at neutron sources worldwide is reviewed.

Evidence of a one-dimensional thermodynamic phase diagram for simple glass-formers.

Glass formers show motional processes over an extremely broad range of timescales, covering more than ten orders of magnitude, meaning that a full understanding of the glass transition needs to comprise this tremendous range in timescales. Here we report simultaneous dielectric and neutron spectroscopy investigations of three glass-forming liquids, probing in a single experiment the full range of dynamics. For two van der Waals liquids, we locate in the pressure-temperature phase diagram lines of identical dynamics of the molecules on both second and picosecond timescales. This confirms predictions of the isomorph theory and effectively reduces the phase diagram from two to one dimension. The implication is that dynamics on widely different timescales are governed by the same underlying mechanisms.

Influence of pressure on the boson peak: stronger than elastic medium transformation.

We study the changes in the low-frequency vibrational dynamics of poly(isobutylene) under pressure up to 1.4 GPa, corresponding to a density change of 20%. Combining inelastic neutron, x-ray, and Brillouin light scattering, we analyze the variations in the boson peak, transverse and longitudinal sound velocities, and the Debye level under pressure. We find that the boson peak variation under pressure cannot be explained by the elastic continuum transformation only. Surprisingly, the shape of the boson peak remains unchanged even at such high compression.

ESPEN Guidelines on Enteral Nutrition: Non-surgical oncology.

Enteral nutrition (EN) by means of oral nutritional supplements (ONS) and tube feeding (TF) offers the possibility of increasing or ensuring nutrient intake in cases where normal food intake is inadequate. These guidelines are intended to give evidence-based recommendations for the use of ONS and TF in cancer patients. They were developed by an interdisciplinary expert group in accordance with officially accepted standards, are based on all relevant publications since 1985 and were discussed and accepted in a consensus conference. Undernutrition and cachexia occur frequently in cancer patients and are indicators of poor prognosis. EN should be started if undernutrition already exists or if food intake is markedly reduced for more than 7-10 days. Standard formulae are recommended for EN. Nutritional needs generally are comparable to non-cancer subjects. In cachectic patients metabolic modulators such as progestins, steroids and possibly eicosapentaenoic acid may help to improve nutritional status. EN is indicated preoperatively for 5-7 days in cancer patients undergoing major abdominal surgery. During radiotherapy of head/neck and gastrointestinal regions dietary counselling and ONS prevent weight loss and interruption of radiotherapy. Routine EN is not indicated during (high-dose) chemotherapy.

Interferon-gamma-induced conversion of tryptophan: immunologic and neuropsychiatric aspects.

Tryptophan is an essential amino acid and the least abundant constituent of proteins. In parallel it represents a source for two important biochemical pathways: the generation of neurotransmitter 5-hydroxytryptamine (serotonin) by the tetrahydrobiopterin-dependent tryptophan 5-hydroxylase, and the formation of kynurenine derivatives and nicotinamide adenine dinucleotides initiated by the enzymes tryptophan pyrrolase (tryptophan 2,3-dioxygenase, TDO) and indoleamine 2,3-dioxygenase (IDO). Whereas TDO is located in the liver cells, IDO is expressed in a large variety of cells and is inducible by the cytokine interferon-gamma. Therefore, accelerated tryptophan degradation is observed in diseases and disorders concomitant with cellular immune activation, e. g. infectious, autoimmune, and malignant diseases, as well as during pregnancy. According to the cytostatic and antiproliferative properties of tryptophan-depletion on T lymphocytes, activated T-helper type 1 (Th-1) cells may down-regulate immune response via degradation of tryptophan. Especially in states of persistent immune activation availability of free serum tryptophan is diminished and as a consequence of reduced serotonin production, serotonergic functions may as well be affected. Accumulation of neuroactive kynurenine metabolites such as quinolinic acid may contribute to the development of neurologic/psychiatric disorders. Thus, IDO seems to represent a link between the immunological network and neuroendocrine functions with far reaching consequences in regard to the psychological status of patients. These observations provide a basis for the better understanding of mood disorder and related symptoms in chronic diseases.

Moderate hyperhomocysteinemia and immune activation.

Moderate hyperhomocysteinemia is associated with an increased risk of atherosclerosis, thrombosis and neurodegenerative diseases. Homocysteine accumulation in the blood can be due to many underlying causes, which may interact with each other, e.g. genetic disposition and B-vitamin status. The role of the sulfur-containing amino acid homocysteine in the pathogenesis of diseases remains unclear, even if many studies suggest a causal relationship between homocysteine-mediated processes like oxidative stress, NO-inactivation and endothelial deficiency and atherogenesis. Proposed mechanisms of action of homocysteine are discussed, and the question is addressed, whether effects that are attributed to homocysteine, are not rather the consequence of folate and vitamin B12-deficiency. Deficiency of these B-vitamins in parallel with moderate hyperhomocysteinemia is often found in patients with enhanced activation of the cellular immune system, like Alzheimer's disease, rheumatoid arthritis and also vascular diseases. In patients with these diseases an association between homocysteine metabolism, oxidative stress and immune activation exists. On the one hand proliferation of immunocompetent cells having an enhanced demand for B-vitamins leads to the accumulation of homocysteine. On the other hand macrophages stimulated by TH1-type cytokine interferon-gamma form reactive oxygen species (ROS), which oxidize antioxidants, lipoproteins and oxidation-sensitive B-vitamins. Thereby Th1-type immune response could contribute importantly to the development of hyperhomocysteinemia, and may also be a major determinant of disease progression.

Methyl group dynamics in a confined glass.

We present a neutron scattering investigation on methyl group dynamics in glassy toluene confined in mesoporous silicates of different pore sizes. The experimental results have been analysed in terms of a barrier distribution model, such a distribution following from the structural disorder in the glassy state. Confinement results in a strong decreasing of the average rotational barrier in comparison to the bulk state. We have roughly separated the distribution for the confined state in a bulk-like and a surface-like contribution, corresponding to rotors at a distance from the pore wall respectively larger and smaller than the spatial range of the interactions which contribute to the rotational potential for the methyl groups. We have estimated a distance of 7 A as a lower limit of the interaction range, beyond the typical nearest-neighbour distance between centers-of-mass (4.7 A).