Incoherent Neutron Scattering Research Articles

Proton Diffusion in Liquid 1,2,3-Triazole Studied by Incoherent Quasi-Elastic Neutron Scattering.

Improving the proton transport in polymer electrolytes impacts the performance of next-generation solid-state batteries. However, little is known about proton conductivity in nonaqueous systems due to the lack of an appropriate level of fundamental understanding. Here, we studied the proton transport in small molecules with dynamic hydrogen bonding, 1,2,3-triazole, as a model system of proton hopping in a nonaqueous environment using incoherent quasi-elastic neutron scattering. By using the jump-diffusion model, we identified the elementary jump-diffusion motion of protons at a much shorter length scale than those by nuclear magnetic resonance and impedance spectroscopy for the estimated long-range diffusion. In addition, a spatially restricted diffusive motion was observed, indicating that proton motion in 1,2,3-triazole is complex with various local correlated dynamics. These correlated dynamics will be important in elucidating the nature of the proton dynamics in nonaqueous systems.

Sub-Nanosecond Dynamics of Pathologically Relevant Bio-Macromolecules Observed by Incoherent Neutron Scattering.

Incoherent neutron scattering (iNS) is one of the most powerful techniques to study the dynamical behavior of bio-macromolecules such as proteins and lipid molecules or whole cells. This technique has widely been used to elucidate the fundamental aspects of molecular motions that manifest in the bio-macromolecules in relation to their intrinsic molecular properties and biological functions. Furthermore, in the last decade, iNS studies focusing on a possible relationship between molecular dynamics and biological malfunctions, i.e., human diseases and disorders, have gained importance. In this review, we summarize recent iNS studies on pathologically relevant proteins and lipids and discuss how the findings are of importance to elucidate the molecular mechanisms of human diseases and disorders that each study targets. Since some diseases such as amyloidosis have become more relevant in the aging society, research in this field will continue to develop further and be more important in the current increasing trend for longevity worldwide.

Molecular Dynamics of Lysozyme Amyloid Polymorphs Studied by Incoherent Neutron Scattering.

Lysozyme amyloidosis is a hereditary disease, which is characterized by the deposition of lysozyme amyloid fibrils in various internal organs. It is known that lysozyme fibrils show polymorphism and that polymorphs formed at near-neutral pH have the ability to promote more monomer binding than those formed at acidic pH, indicating that only specific polymorphs become dominant species in a given environment. This is likely due to the polymorph-specific configurational diffusion. Understanding the possible differences in dynamical behavior between the polymorphs is thus crucial to deepen our knowledge of amyloid polymorphism and eventually elucidate the molecular mechanism of lysozyme amyloidosis. In this study, molecular dynamics at sub-nanosecond timescale of two kinds of polymorphic fibrils of hen egg white lysozyme, which has long been used as a model of human lysozyme, formed at pH 2.7 (LP27) and pH 6.0 (LP60) was investigated using elastic incoherent neutron scattering (EINS) and quasi-elastic neutron scattering (QENS). Analysis of the EINS data showed that whereas the mean square displacement of atomic motions is similar for both LP27 and LP60, LP60 contains a larger fraction of atoms moving with larger amplitudes than LP27, indicating that the dynamical difference between the two polymorphs lies not in the averaged amplitude, but in the distribution of the amplitudes. Furthermore, analysis of the QENS data showed that the jump diffusion coefficient of atoms is larger for LP60, suggesting that the atoms of LP60 undergo faster diffusive motions than those of LP27. This study thus characterizes the dynamics of the two lysozyme polymorphs and reveals that the molecular dynamics of LP60 is enhanced compared with that of LP27. The higher molecular flexibility of the polymorph would permit to adjust its conformation more quickly than its counterpart, facilitating monomer binding.

Dynamics of Apolipoprotein B-100 in Interaction with Detergent Probed by Incoherent Neutron Scattering.

Apolipoprotein B-100 (apo B-100) is the protein moiety of both low- and very-low-density lipoproteins, whose role is crucial to cholesterol and triglyceride transport. Aiming at the molecular dynamics' details of apo B-100, scarcely studied, we performed elastic and quasi-elastic incoherent neutron scattering (EINS, QENS) experiments combining different instruments and time scales. Similar to classical membrane proteins, the solubilization results in remaining detergent, here Nonidet P-40 (NP40). Therefore, we propose a framework for QENS studies of protein-detergent complexes, with the introduction of a combined model, including the experimental apo B-100/NP40 ratio. Relying on the simultaneous analysis of all QENS amplitudes, this approach is sensitive enough to separate both contributions. Its application identified two points: (i) apo B-100 slow dynamics and (ii) the acceleration of NP40 dynamics in the presence of apo B-100. Direct translation of the exposed methodology now makes the investigation of more membrane proteins by neutron spectroscopy achievable.

Polymorphism and Conformational Equilibrium of Nitro-Acetophenone in Solid State and under Matrix Conditions.

Conformational and polymorphic states in the nitro-derivative of o-hydroxy acetophenone have been studied by experimental and theoretical methods. The potential energy curves for the rotation of the nitro group and isomerization of the hydroxyl group have been calculated by density functional theory (DFT) to estimate the barriers of the conformational changes. Two polymorphic forms of the studied compound were obtained by the slow and fast evaporation of polar and non-polar solutions, respectively. Both of the polymorphs were investigated by Infrared-Red (IR) and Raman spectroscopy, Incoherent Inelastic Neutron Scattering (IINS), X-ray diffraction, nuclear quadrupole resonance spectroscopy (NQR), differential scanning calorimetry (DSC) and density functional theory (DFT) methods. In one of the polymorphs, the existence of a phase transition was shown. The position of the nitro group and its impact on the crystal cell of the studied compound were analyzed. The conformational equilibrium determined by the reorientation of the hydroxyl group was observed under argon matrix isolation. An analysis of vibrational spectra was achieved for the interpretation of conformational equilibrium. The infrared spectra were measured in a wide temperature range to reveal the spectral bands that were the most sensitive to the phase transition and conformational equilibrium. The results showed the interrelations between intramolecular processes and macroscopic phenomena in the studied compound.

Experimental Implications of Negative Quantum Conditional Entropy—H2 Mobility in Nanoporous Materials

During the last few decades, considerable advances in quantum information theory have shown deep existing connections between quantum correlation effects (like entanglement and quantum discord) and thermodynamics. Here the concept of conditional entropy plays a considerable role. In contrast to the classical case, quantum conditional entropy can take negative values. This counter-intuitive feature, already well understood in the context of information theory, was recently shown theoretically to also have a physical meaning in quantum thermodynamics [del Rio et al. Nature 2011, 474, 61]. Extending this existing work, here we provide evidence of the significance of negative conditional entropy in a concrete experimental context: Incoherent Neutron Scattering (INS) from protons of H2 in nano-scale environments; e.g., in INS from H2 in C-nanotubes, the data of the H2 translational motion along the nanotube axis seems to show that the neutron apparently scatters from a fictitious particle with mass of 0.64 atomic mass units (a.m.u.)—instead of the value of 2 a.m.u. as conventionally expected. An independent second experiment confirms this finding. However, taking into account the possible negativity of conditional entropy, we explain that this effect has a natural interpretation in terms of quantum thermodynamics. Moreover, it is intrinsically related to the number of qubits capturing the interaction of the two quantum systems H2 and C-nanotube. The considered effect may have technological applications (e.g., in H-storage materials and fuel cells).

Experimental Implications of Negative Quantum Conditional Entropy—H2 Mobility in Nanoporous Materials

During the last few decades, considerable advances in quantum information theory have shown deep existing connections between quantum correlation effects (like entanglement and quantum discord) and thermodynamics. Here the concept of conditional entropy plays a considerable role. In contrast to the classical case, quantum conditional entropy can take negative values. This counter-intuitive feature, already well understood in the context of information theory, was recently shown theoretically to also have a physical meaning in quantum thermodynamics [del Rio et al. Nature 2011, 474, 61]. Extending this existing work, here we provide evidence of the significance of negative conditional entropy in a concrete experimental context: Incoherent Neutron Scattering (INS) from protons of H2 in nano-scale environments; e.g., in INS from H2 in C-nanotubes, the data of the H2 translational motion along the nanotube axis seems to show that the neutron apparently scatters from a fictitious particle with mass of 0.64 atomic mass units (a.m.u.)—instead of the value of 2 a.m.u. as conventionally expected. An independent second experiment confirms this finding. However, taking into account the possible negativity of conditional entropy, we explain that this effect has a natural interpretation in terms of quantum thermodynamics. Moreover, it is intrinsically related to the number of qubits capturing the interaction of the two quantum systems H2 and C-nanotube. The considered effect may have technological applications (e.g., in H-storage materials and fuel cells).

Protein Backbone and Average Particle Dynamics in Reconstituted Discoidal and Spherical HDL Probed by Hydrogen Deuterium Exchange and Elastic Incoherent Neutron Scattering

Lipoproteins are supramolecular assemblies of proteins and lipids with dynamic characteristics critically linked to their biological functions as plasma lipid transporters and lipid exchangers. Among them, spherical high-density lipoproteins are the most abundant forms of high-density lipoprotein (HDL) in human plasma, active participants in reverse cholesterol transport, and associated with reduced development of atherosclerosis. Here, we employed elastic incoherent neutron scattering (EINS) and hydrogen-deuterium exchange mass spectrometry (HDX-MS) to determine the average particle dynamics and protein backbone local mobility of physiologically competent discoidal and spherical HDL particles reconstituted with human apolipoprotein A-I (apoA-I). Our EINS measurements indicated that discoidal HDL was more dynamic than spherical HDL at ambient temperatures, in agreement with their lipid-protein composition. Combining small-angle neutron scattering (SANS) with contrast variation and MS cross-linking, we showed earlier that the most likely organization of the three apolipoprotein A-I (apoA-I) chains in spherical HDL is a combination of a hairpin monomer and a helical antiparallel dimer. Here, we corroborated those findings with kinetic studies, employing hydrogen-deuterium exchange mass spectrometry (HDX-MS). Many overlapping apoA-I digested peptides exhibited bimodal HDX kinetics behavior, suggesting that apoA-I regions with the same amino acid composition located on different apoA-I chains had different conformations and/or interaction environments.

Dynamics Properties of Photosynthetic Microorganisms Probed by Incoherent Neutron Scattering

Studies on the dynamical properties of photosynthetic membranes of land plants and purple bacteria have been previously performed by neutron spectroscopy, revealing a tight coupling between specific photochemical reactions and macromolecular dynamics. Here, we probed the intrinsic dynamics of biotechnologically useful mutants of the green alga Chlamydomonas reinhardtii by incoherent neutron scattering coupled with prompt chlorophyll fluorescence experiments. We brought to light that single amino acid replacements in the plastoquinone (PQ)-binding niche of the photosystem II D1 protein impair electron transport (ET) efficiency between quinones and confer increased flexibility to the host membranes, expanding to the entire cells. Hence, a more flexible environment in the PQ-binding niche has been associated to a less efficient ET. A similar function/dynamics relationship was also demonstrated in Rhodobacter sphaeroides reaction centers having inhibited ET, indicating that flexibility at the quinones region plays a crucial role in evolutionarily distant organisms. Instead, a different functional/dynamical correlation was observed in algal mutants hosting a single amino acid replacement residing in a D1 domain far from the PQ-binding niche. Noteworthy, this mutant displayed the highest degree of flexibility, and besides having a nativelike ET efficiency in physiological conditions, it acquired novel, to our knowledge, phenotypic traits enabling it to preserve a high maximal quantum yield of photosystem II photochemistry in extreme habitats. Overall, in the nanosecond timescale, the degree of the observed flexibility is related to the mutation site; in the picosecond timescale, we highlighted the presence of a more pronounced dynamic heterogeneity in all mutants compared to the native cells, which could be related to a marked chemically heterogeneous environment.

How can we derive hydration water dynamics with incoherent neutron scattering and molecular dynamics simulation?

Incoherent neutron scattering (INS) is one of the useful experimental methods for studying protein dynamics at the pico-nanosecond timescale. At this timescale, protein dynamics is highly coupled with hydration, which is observed as protein dynamical transition (PDT). INS is very sensitive to hydrogen atomic dynamics because of the large incoherent scattering cross section of hydrogen atom, and thus, the INS of a hydrated protein provides overall dynamic information about the protein, including hydration water. Separation of hydration water dynamics is essential for understanding hydration-related protein dynamics. H2O/D2O exchange is an effective method in the context of INS experiments for observing the dynamics of protein and hydration water separately. Neutron scattering is directly related to the van Hove space-time correlation function, which can be calculated quantitatively by performing molecular dynamics (MD) simulations. Diffusion and hydrogen bond dynamics of hydration water can be analyzed by performing MD simulation. MD simulation is useful for analyzing the dynamic coupling mechanism in hydration-related protein dynamics from the viewpoint of interpreting INS data because PDT is induced by hydration. In the present work, we demonstrate the methodological advantages of the H2O/D2O exchange technique in INS and the compatibility of INS and MD simulation as tools for studying protein dynamics and hydration water.

Influence of Enantiomeric Inhibitors on the Dynamics of Acetylcholinesterase Measured by Elastic Incoherent Neutron Scattering.

The enzyme acetylcholinesterase (AChE) is essential in humans and animals because it catalyzes the breakdown of the nerve-signaling substance acetylcholine. Small molecules that inhibit the function of AChE are important for their use as drugs in the, for example, symptomatic treatment of Alzheimer's disease. New and improved inhibitors are warranted, mainly because of severe side effects of current drugs. In the present study, we have investigated if and how two enantiomeric inhibitors of AChE influence the overall dynamics of noncovalent complexes, using elastic incoherent neutron scattering. A fruitful combination of univariate models, including a newly developed non-Gaussian model for atomic fluctuations, and multivariate methods (principal component analysis and discriminant analysis) was crucial to analyze the fine details of the data. The study revealed a small but clear increase in the dynamics of the inhibited enzyme compared to that of the noninhibited enzyme and contributed to the fundamental knowledge of the mechanisms of AChE-inhibitor binding valuable for the future development of inhibitors.

Molecular Dynamics of POPC Phospholipid Bilayers through the Gel to Fluid Phase Transition: An Incoherent Quasi-Elastic Neutron Scattering Study

The microscopic dynamics for the gel and liquid-crystalline phase of highly aligned D2O-hydrated bilayers of 1-palmitoyl-oleoyl-sn-glycero-phosphocholine (POPC) were investigated in the temperature range from 248 to 273 K by using incoherent quasi-elastic neutrons scattering (QENS). We develop a model for describing the molecular motions of the liquid phase occurring in the 0.3 to 350 ps time range. Accordingly, the complex dynamics of hydrogen are described in terms of simple dynamical processes involving different parts of the phospholipid chain. The analysis of the data evidences the existence of three different motions: the fast motion of hydrogen vibrating around the carbon atoms, the intermediate motion of carbon atoms in the acyl chains, and the slower translational motion of the entire phospholipid molecule. The influence of the temperature on these dynamical processes is investigated. In particular, by going from gel to liquid-crystalline phase, we reveal an increase of the segmental motion mainly affecting the terminal part of the acyl chains and a change of the diffusional dynamics from a localized rattling-like motion to a confined diffusion.

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 3THz, 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.

Probing the Thermal Stability of Lysozyme in Crowded Environments: Tracking Lindemann Criterion

Our work focuses on determining the effect of crowded environment and different solvents on the thermal stability of the protein Lysozyme [1] placed in a dilute water solution, dehydrated protein powder, and in a protein powder glycerol solution, the latter two representing crowded environments.The ultimate goal of our work is to probe the validity of the Lindemann criterion for protein melting [2, 3]. We employ an enhanced sampling Molecular Dynamics technique, REST2 [4, 5], where mutually exchangeable protein replicas are simulated at different effective temperatures, achieved by rescaling the force-field potential energy terms. The simulations are paralleled with Elastic Incoherent Neutron Scattering experiments.We first estimate the in silico melting temperature of our systems and reconstruct the stability curves. Instructed by this information, we calculate the scaling of atomic fluctuation approaching melting. Our results show that the atomic fluctuations of different Lysozyme systems converge to similar values approaching the melting temperature, which agrees both with the experimental results [unpublished] and the Lindemann criterion [2, 3]. Furthermore, we show that the thermal stability of the hydrated Lysozyme is increased in the presence of crowders (powder) and even more so if glycerol is present in addition to the crowders. The molecular factors, excluded volume versus specific interactions, will be discussed as source of the stability shifts.[1] H.-X. Zhou, G. Rivas, A.P. Minton, Annu. Rev. Biophys. (2008) 37, 375-397.[2] C. Chakravarty, P.G. Debenedetti, F.H. Stillinger, J. Chem. Phys. (2007) 126, 204508.[3] Y. Zhou, D. Vitkup, M. Karplus, J. Mol. Biol. (1999) 285, 1371-1375[4] L. Wang, R.A. Friesner, B.J. Berne, J. Phys. Chem. B (2011) 115, 9431-9438.[5] G. Stirnemann and F. Sterpone, submitted to J. Chem. Theory Comput. (2015).

(Invited) Water and Proton Dynamics in Perfluorinated Surfactants and Membranes by QENS

The proton transport in fuel cell ionomer membranes is intimately related to the dynamical properties of water molecules confined in the interconnected network of ionic domains. The confinement of a fluid at the nanoscale profoundly affects the molecular dynamics and results in important deviations with respect to the bulk. The rotational and translational motions can be uniquely investigated by means of Quasi Elastic Neutron Scattering experiments, especially in the case of protonated systems due to the high incoherent cross section of hydrogen. Insights into the nature of the motions, i.e. diffusive or confined, can be gained by analysing the scattering function S(Q,w) measured on the ps-ns time-scale, Q being the momentum transfer and w the energy transfer of the neutrons. We will present here a comprehensive QENS study of water/proton dynamics in PFSA membranes [1,2] and perfluorinated surfactants used as a model soft confining system [3.4]. The Gaussian model for localized translational diffusion [5] was used to obtain quantitative parameters as the relaxation times, confinement sizes and local/nanometric diffusion coefficients of protons and water molecules. The comparison between state-of-the art fuel cell membranes and self-assembled well-defined surfactant phases as host confining matrices will be used to highlight the subtle interplay between spatial confinement and local interactions, resulting in the presence of slow hydronium motions and faster water motions localized in nanometric droplets. Additionally, we will show that the QENS technique can be invaluably combined with PFG-NMR to obtain a multi-scale comprehensive description of the ionic diffusion and water behaviour [1,2]. These experimental results are also cross-fertilized by Molecular Dynamics simulations performed on the same materials using a coarse-grained backbone and explicit solvent molecules [6]. [1] J-C. Perrin, S. Lyonnard and F. Volino; Quasielastic neutron scattering study of water dynamics in hydrated nafion membranes, Journal of Physical Chemistry C, 111 (2007), 3393-3404.[2] S. Lyonnard and G. Gebel, Neutrons for Fuel Cells Membranes: structure, sorption and transport properties, European Physical Journal 213 (1) (2012), 195-211;S. Lyonnard, Structure and Transport Properties in Polymer Electrolyte Membranes Probed at Microscopic Scales, Springer-Verlag, New Energies, Ed. German Antonio Ferreira, 2013. [3] S. Lyonnard, Q. Berrod, B-A. Bruning, G. Gebel, A. Guillermo, H. Ftouni, J. Ollivier and B. Frick, Perfluorinated surfactants as model charged systems for understanding the effect of confinement on proton transport and water mobility in fuel cell membranes. A study by QENS., Eur. Phys. Journal Special Topics, 189 (1), 205-216 (2010). [4] Q. Berrod; S. Lyonnard ; A. Guillermo.;J.Ollivier.; B. Frick; G.Gebel, QENS investigation of proton confined motions in hydrated perfluorinated sulfonic membranes and self-assembled surfactants, The European Physical Journal 2014, in press. [5] F. Volino, J-C. Perrin and S. Lyonnard; Gaussian Model for Localized Translational Motion: Application to Incoherent Neutron Scattering, Journal of Physical Chemistry B, 110 (2006), 11217-11223. [6] S. Hanot, S. Lyonnard and S. Mossa, Water confined in self-assembled ionic surfactants nanostructures, under review (2014).

Understanding the Decreased Segmental Dynamics of Supported Thin Polymer Films Reported by Incoherent Neutron Scattering

Incoherent neutron scattering (INS) has commonly reported a suppression of segmental dynamics for supported thin polymer films as thickness is decreased, which is counter to expectations based on other measurement techniques such as ellipsometry and fluorescence. Here INS is utilized to measure the dynamics of thin films of comb polystyrene (PS) from 50 to 525 K. There is a significant suppression in dynamics as determined from the ∼5 ns Debye–Waller factor, ⟨u2⟩, as measured via INS for films as thick as 213 nm, while there is no change in the glass transition temperature (Tg) as determined by ellipsometry for films as thin as 20 nm. This poor correlation between Tg from ellipsometry and dynamics as measured by ⟨u2⟩ is attributed to contamination of nanosecond ⟨u2⟩ by incipient relaxation processes, differences in sensitivity to the postulated dynamically dead layer near the substrate due to the relative weighting of the distribution of dynamics between the two techniques, differences in the time scales probed, and possible decoupling between fast and slow dynamics under nanoconfinement. These results suggest that branching of PS significantly increases the interactions with the substrate to suppress the dynamics. Both technique-specific sensitivity to time scales and its weighing of the average over the gradient in dynamic properties present at the interfaces are important to consider when qualitatively different phenomena are inferred from different measurements.

Hydration and Dynamics of Bio-molecule Studied by Incoherent Neutron Scattering and Molecular Simulation

Bio-molecular dynamics should be characterized with wide time-space ranges. Incoherent neutron scattering is the powerful method to observe the dynamics in THz region, which is essential for the solvent-coupled dynamics. Furthermore, this method is sensitive to the hydration water dynamics. The incoherent scattering gives auto-correlation function of a single atom, therefore, information of the molecular structure is lost in this kind of neutron experiment. The molecular dynamics simulation is effective for analysis and interpretation of the experimental data. We have shown that the protein dynamical transition is coupled with the fluctuation of the hydration water network on protein surface, and that DNA dynamics is sequence dependent, by incoherent neutron scattering and molecular simulation.

Polymer Diffusion in Microgels with Upper Critical Solution Temperature as Studied by Incoherent Neutron Scattering

Poly(acrylic-acrylamide) interpenetrated microgels present continuous phase transition from collapsed to swollen state around 42 °C. The upper critical solution temperature (UCST) of this polymeric system has prompted scientists to consider them candidates for its use in biological applications such as smart drug delivery devices since the swelling of the polymer matrix would permit the release of the drug previously entrapped within the microgels. In these systems the increment of the temperature can break inter-chain interactions, mainly hydrogen bonds, which reduce the elastic tension that stabilizes the microgel, favoring the polymer swelling. The microgel molecular dynamics at the UCST can be investigated using Incoherent Elastic (IENS) and Quasielastic Neutron Scattering (IQNS). From the analysis of the IQNS data we obtained that the diffusion coefficient of the polymer segments depends on the composition of the interpenetrated matrix. Thus, at room temperature, microgels with a polymer composition of 50% of each component present a diffusion coefficient 1·10−12 m2/s, while for the microgels formed by only one component the diffusion coefficient is 5.10−10 m2/s. This huge difference in the diffusion coefficient is conspicuously reduced when temperature increases, and we attribute this effect to the breaking of the inter-chain interaction. By means of FTIR-ATR analysis we have identified the groups that are involved in this phenomenon and we associate the breaking of the polyacrylic-polyacrylamide interactions with the swelling of the microgels.

Deep Sea Microbes Probed by Incoherent Neutron Scattering Under High Hydrostatic Pressure

Abstract The majority of the biosphere is a high pressure environment. Around 70% of the marine biosphere lies at depths below 1000 m, i.e. at pressures of 100 bars or higher. To survive in these environments, deep-biosphere organisms have adapted to life at high pressure. In vitro studies showed that the activity of certain proteins originating from deep-sea organisms is less affected by high pressure than that of enzymes from surface organisms . However, the genetic and structural bases for this increased pressure resistance are still unknown. Elastic incoherent neutron scattering studies, which provide access to information about molecular dynamics, constitute a very promising approach to decipher the structural adaptation in proteins living under high pressure. This approach has been used in the past to investigate the adaptation of biological systems to temperature and salinity and proved to be essential and complementary to structural studies. Here first investigations of high pressure effects on cell dynamics are presented using Thermococcales as models.

Vibrations and reorientations of H2O molecules in [Sr(H2O)6]Cl2 studied by Raman light scattering, incoherent inelastic neutron scattering and proton magnetic resonance

Vibrational–reorientational dynamics of H2O ligands in the high- and low-temperature phases of [Sr(H2O)6]Cl2 was investigated by Raman Spectroscopy (RS), proton magnetic resonance (1H NMR), quasielastic and inelastic incoherent Neutron Scattering (QENS and IINS) methods. Neutron powder diffraction (NPD) measurements, performed simultaneously with QENS, did not indicated a change of the crystal structure at the phase transition (detected earlier by differential scanning calorimetry (DSC) at TCh=252.9K (on heating) and at TCc=226.5K (on cooling)). Temperature dependence of the full-width at half-maximum (FWHM) of νs(OH) band at ca. 3248cm−1 in the RS spectra indicated small discontinuity in the vicinity of phase transition temperature, what suggests that the observed phase transition may be associated with a change of the H2O reorientational dynamics. However, an activation energy value (Ea) for the reorientational motions of H2O ligands in both phases is nearly the same and equals to ca. 8 kJmol−1. The QENS peaks, registered for low temperature phase do not show any broadening. However, in the high temperature phase a small QENS broadening is clearly visible, what implies that the reorientational dynamics of H2O ligands undergoes a change at the phase transition. 1H NMR line is a superposition of two powder Pake doublets, differentiated by a dipolar broadening, suggesting that there are two types of the water molecules in the crystal lattice of [Sr(H2O)6]Cl2 which are structurally not equivalent average distances between the interacting protons are: 1.39 and 1.18Å. However, their reorientational dynamics is very similar (τc=3.3⋅10−10s). Activation energies for the reorientational motion of these both kinds of H2O ligands have nearly the same values in an experimental error limit: and equal to ca. 40kJmole−1. The phase transition is not seen in the 1H NMR spectra temperature dependencies. Infrared (IR), Raman (RS) and inelastic incoherent neutron scattering (IINS) spectra were calculated by the DFT method and quite a good agreement with the experimental data was obtained.