Quasielastic Spectra Research Articles

High-resolution Neutron Spectroscopy to Study Picosecond-nanosecond Dynamics of Proteins and Hydration Water.

Neutron scattering offers the possibility to probe the dynamics within samples for a wide range of energies in a nondestructive manner and without labeling other than deuterium. In particular, neutron backscattering spectroscopy records the scattering signals at multiple scattering angles simultaneously and is well suited to study the dynamics of biological systems on the ps-ns timescale. By employing D2O-and possibly deuterated buffer components-the method allows monitoring of both center-of-mass diffusion and backbone and side-chain motions (internal dynamics) of proteins in liquid state. Additionally, hydration water dynamics can be studied by employing powders of perdeuterated proteins hydrated with H2O. This paper presents the workflow employed on the instrument IN16B at the Institut Laue-Langevin (ILL) to investigate protein and hydration water dynamics. The preparation of solution samples and hydrated protein powder samples using vapor exchange is explained. The data analysis procedure for both protein and hydration water dynamics is described for different types of datasets (quasielastic spectra or fixed-window scans) that can be obtained on a neutron backscattering spectrometer. The method is illustrated with two studies involving amyloid proteins. The aggregation of lysozyme into µm sized spherical aggregates-denoted particulates-is shown to occur in a one-step process on the space and time range probed on IN16B, while the internal dynamics remains unchanged. Further, the dynamics of hydration water of tau was studied on hydrated powders of perdeuterated protein. It is shown that translational motions of water are activated upon the formation of amyloid fibers. Finally, critical steps in the protocol are discussed as to how neutron scattering is positioned regarding the study of dynamics with respect to other experimental biophysical methods.

Analysis and Comparison of Quasi-Elastic Neutron Scattering (QENS) Spectra Model

The Quasi-Elastic Neutron Scattering (QENS) experiment is a novel method to study confined water dynamics by measuring the neutron energy transfer ( E )and scattering vector (Q) after the neutron interacts with the sample target. By adopting a suitable theoretical model and performing nonlinear least-squares fitting analysis on the Quasi- Elastic Neutron scattering spectra, the relevant physical parameters describing the water dynamics can be obtained, and then the constrained water dynamics in the sample can be detected. There are many types of Quasi-Elastic Neutron Scattering spectra fitting analysis models, and the fitting effects of different models and the relevant physical parameters obtained to characterize water dynamic information are not the same. This paper uses the Jump-diffusion and Rotating-diffusion Model (JRM) and the revised Jump-diffusion and Rotating-diffusion Model (rJRM) to fit the QENS spectra of pure magnesium silicate (M-S-H) and pure calcium silicate (C-S-H) samples, respectively. The measurement temperatures of QENS spectra from M-S-H and C-S-H samples are 210K up to 280K and 230K up to 280K, respectively, the E ranges from -120 to 120μev and the Q value 0.3 A^(-1)~1.9 A^(-1). Different physical parameters describing the dynamic information of confined water can be obtained by using the two models for QENS spectra fitting analysis. Compared with the JRM model, the physical parameters obtained by using the rJRM model are more comprehensive, and it is suitable for all neutron energy transfer and scattering vector measurements. From the qualitative point of view, the QENS spectra fitting curve of rJRM model is more consistent with the original data points. From the quantitative point of view, the chi-square value fitted by the rJRM model is more consistent with the mathematical statistics law than the JRM model, and the time required for nonlinear fitting is shorter.

Dynamics in hydrated inorganic nanotubes studied by neutron scattering: towards nanoreactors in water.

Water dynamics in inorganic nanotubes is studied by neutron scattering technique. Two types of aluminosilicate nanotubes are investigated: one is completely hydrophilic on the external and internal surfaces (IMO-OH) while the second possesses an internal cavity which is hydrophobic due to the replacement of Si–OH bonds by Si–CH3 ones (IMO-CH3), the external surface being still hydrophilic. The samples have internal radii equal to 7.5 and 9.8 Å, respectively. By working under well-defined relative humidity (RH) values, water dynamics in IMO-OH was revealed by quasi-elastic spectra as a function of the filling of the interior of the tubes. When one water monolayer is present on the inner surface of the tube, water molecules can jump between neighboring Si–OH sites on the circumference by 2.7 Å. A self-diffusion is then measured with a value (D = 1.4 × 10−5 cm2 s−1) around half of that in bulk water. When water molecules start filling also the interior of the tubes, a strong confinement effect is observed, with a confinement diameter (6 Å) of the same order of magnitude as the radius of the nanotube (7.5 Å). When IMO-OH is filled with water, the H-bond network is very rigid, and water molecules are immobile on the timescale of the experiment. For IMO-OH and IMO-CH3, motions of the hydroxyl groups are also evidenced. The associated relaxation time is of the order of 0.5 ps and is due to hindered rotations of these groups. In the case of IMO-CH3, quasi-elastic spectra and elastic scans are dominated by the motions of methyl groups, making the effect of the water content on the evolution of the signals negligible. It was however possible to describe torsions of methyl groups, with a corresponding rotational relaxation time of 2.6 ps. The understanding of the peculiar behavior of water inside inorganic nanotubes has implications in research areas such as nanoreactors. In particular, the locking of motions inside IMO-OH when it is filled with water prevents its use under these conditions as a nanoreactor, while the interior of the IMO-CH3 cavity is certainly a favorable place for confined chemical reactions to take place.

Effects of the Serber first step in 3DHZETRN-v2.1

3DHZETRN-v2 includes a detailed three dimensional (3D) treatment of neutron/light-ion transport based on a quasi-elastic/multiple production assumption allowing improved agreement of the neutron/light-ion fluence compared with results of three Monte Carlo (MC) codes in the sense that the variance with respect to the individual MC results is less than the variance among the MC code results. The current numerical methods are no longer the main limitation to HZETRN code development and further changes in the nuclear model are required. In a prior study, an improved quasi-elastic spectrum based on a solution of the transport approximation to nuclear media effects showed promise, but the remaining multiple-production spectrum was based on a database derived from the Ranft model that used Bertini multiplicities. In the present paper, we will implement a more complete Serber first step into the 3DHZETRN-v2 code, but we retain the Bertini–Ranft branching ratios and evaporation multiplicities. It is shown that the new Serber model in the 3HZETRN-v2 code reduces the variance with individual MC codes, which are largely due to nuclear cross section model differences. The code will be available through the software system, OLTARIS, for shield design and validation and provides a basis for personal computer software capable of space shield analysis and optimization.

Dynamics of Hydride Ions in Metal Hydride-Reduced BaTiO3 Samples Investigated with Quasielastic Neutron Scattering

Perovskite-type oxyhydrides, BaTiO3–xHx, have been recently shown to exhibit hydride-ion (H–) conductivity at elevated temperatures, but the underlying mechanism of hydride-ion conduction and how it depends on temperature and oxygen vacancy concentration remains unclear. Here, we investigate, through the use of quasielastic neutron scattering techniques, the nature of the hydride-ion dynamics in three metal hydride-reduced BaTiO3 samples that are characterized by the simultaneous presence of hydride ions and oxygen vacancies. Measurements of elastic fixed window scans upon heating reveal the presence of quasielastic scattering due to hydride-ion dynamics for temperatures above ca. 200 K. Analyses of quasielastic spectra measured at low (225 and 250 K) and high (400–700 K) temperature show that the dynamics can be adequately described by established models of jump diffusion. At low temperature, ≤250 K, all of the models feature a characteristic jump distance of about 2.8 A, thus of the order of the distanc...

Isothermal equation of state and high-pressure phase transitions of synthetic meridianiite (MgSO4·11D2O) determined by neutron powder diffraction and quasielastic neutron spectroscopy

We have collected neutron powder diffraction data from MgSO4·11D2O (the deuterated analogue of meridianiite), a highly hydrated sulfate salt that is thought to be a candidate rock-forming mineral in some icy satellites of the outer solar system. Our measurements, made using the PEARL/HiPr and OSIRIS instruments at the ISIS neutron spallation source, covered the range 0.1 < P < 800 MPa and 150 < T < 280 K. The refined unit-cell volumes as a function of P and T are parameterized in the form of a Murnaghan integrated linear equation of state having a zero-pressure volume V 0 = 706.23 (8) Å3, zero-pressure bulk modulus K 0 = 19.9 (4) GPa and its first pressure derivative, K′ = 9 (1). The structure's compressibility is highly anisotropic, as expected, with the three principal directions of the unit-strain tensor having compressibilities of 9.6 × 10−3, 3.4 × 10−2 and 3.4 × 10−3 GPa−1, the most compressible direction being perpendicular to the long axis of a discrete hexadecameric water cluster, (D2O)16. At high pressure we observed two different phase transitions. First, warming of MgSO4·11D2O at 545 MPa resulted in a change in the diffraction pattern at 275 K consistent with partial (peritectic) melting; quasielastic neutron spectra collected simultaneously evince the onset of the reorientational motion of D2O molecules with characteristic time-scales of 20–30 ps, longer than those found in bulk liquid water at the same temperature and commensurate with the lifetime of solvent-separated ion pairs in aqueous MgSO4. Second, at ∼ 0.9 GPa, 240 K, MgSO4·11D2O decomposed into high-pressure water ice phase VI and MgSO4·9D2O, a recently discovered phase that has hitherto only been formed at ambient pressure by quenching small droplets of MgSO4(aq) in liquid nitrogen. The fate of the high-pressure enneahydrate on further compression and warming is not clear from the neutron diffraction data, but its occurrence indicates that it may also be a rock-forming mineral in the deep mantles of large icy satellites.

Crossover from localized to diffusive water dynamics in carbon nanohorns: A comprehensive quasielastic neutron-scattering analysis.

Incoherent neutron scattering by water confined in carbon nanohorns was measured with the backscattering spectrometer SPHERES and analyzed in exemplary breadth and depth. Quasielastic spectra admit δ-plus-Kohlrausch fits over a wide q and T range. From the q and T dependence of fitted amplitudes and relaxation times, however, it becomes clear that the fits do not represent a uniform physical process, but that there is a crossover from localized motion at low T to diffusive α relaxation at high T. The crossover temperature of about 210 to 230 K increases with decreasing wave number, which is incompatible with a thermodynamic strong-fragile transition. Extrapolated diffusion coefficients D(T) indicate that water motion is at room temperature about 2.5 times slower than in the bulk; in the supercooled state this factor becomes smaller. At even higher temperatures, where the α spectrum is essentially flat, a few percentages of the total scattering go into a Lorentzian with a width of about 1.6μeV, probably due to functional groups on the surface of the nanohorns.

Neutron scattering study of spin ordering and stripe pinning in superconductingLa1.93Sr0.07CuO4

The relationships among charge order, spin fluctuations, and superconductivity in underdoped cuprates remain controversial. We use neutron scattering techniques to study these phenomena in La$_{1.93}$Sr$_{0.07}$CuO$_4$, a superconductor with a transition temperature of $T_c = 20$~K. At $T\ll T_c$, we find incommensurate spin fluctuations with a quasielastic energy spectrum and no sign of a gap within the energy range from 0.2 to 15 meV. A weak elastic magnetic component grows below $\sim10$~K, consistent with results from local probes. Regarding the atomic lattice, we have discovered unexpectedly strong fluctuations of the CuO$_6$ octahedra about Cu-O bonds, which are associated with inequivalent O sites within the CuO$_2$ planes. Furthermore, we observed a weak elastic $(3\bar{3}0)$ superlattice peak that implies a reduced lattice symmetry. The presence of inequivalent O sites rationalizes various pieces of evidence for charge stripe order in underdoped \lsco. The coexistence of superconductivity with quasi-static spin-stripe order suggests the presence of intertwined orders; however, the rotation of the stripe orientation away from the Cu-O bonds might be connected with evidence for a finite gap at the nodal points of the superconducting gap function.

Dynamic neutron scattering from conformational dynamics. II. Application using molecular dynamics simulation and Markov modeling

Neutron scattering experiments directly probe the dynamics of complex molecules on the sub pico- to microsecond time scales. However, the assignment of the relaxations seen experimentally to specific structural rearrangements is difficult, since many of the underlying dynamical processes may exist on similar timescales. In an accompanying article, we present a theoretical approach to the analysis of molecular dynamics simulations with a Markov State Model (MSM) that permits the direct identification of structural transitions leading to each contributing relaxation process. Here, we demonstrate the use of the method by applying it to the configurational dynamics of the well-characterized alanine dipeptide. A practical procedure for deriving the MSM from an MD is introduced. The result is a 9-state MSM in the space of the backbone dihedral angles and the side-chain methyl group. The agreement between the quasielastic spectrum calculated directly from the atomic trajectories and that derived from the Markov state model is excellent. The dependence on the wavevector of the individual Markov processes is described. The procedure means that it is now practicable to interpret quasielastic scattering spectra in terms of well-defined intramolecular transitions with minimal a priori assumptions as to the nature of the dynamics taking place.

Neutron Spin-Echo and TOF Reveals Protein Dynamics in Solution

The ps to ns dynamics of the protein alcohol dehydrogenase (ADH) has been measured in dilute solution by time-of-flight (TOF) neutron spectroscopy. The investigation extends previous experiments on ADH solutions with neutron-spin-echo spectroscopy. The interpretation of TOF experiments used the diffusion data from NSE as input to decribe the observed slow component of the quasielastic spectra, in addition a fast component to be associated to mobile groups in the protein could be observed. The description within a simple model for translational and rotational diffusion and a fraction of protons with confined local mobility is given together with a novel method to accurately and efficiently account for the instrumental resolution.

Hydration water and peptide dynamics – two sides of a coin. A neutron scattering and adiabatic calorimetry study at low hydration and cryogenic temperatures

In the present work we bridge neutron scattering and calorimetry in the study of a low-hydration sample of a 15-residue hybrid peptide from cecropin and mellitin CA(1-7)M(2-9) of proven antimicrobial activity. Quasielastic and low-frequency inelastic neutron spectra were measured at defined hydration levels - a nominally 'dry' sample (specific residual hydration h = 0.060 g/g), a H2O-hydrated (h = 0.49) and a D2O-hydrated one (h = 0.51). Averaged mean square proton mobilities were derived over a large temperature range (50-300 K) and the vibrational density of states (VDOS) were evaluated for the hydrated samples. The heat capacity of the H2O-hydrated CA(1-7)M(2-9) peptide was measured by adiabatic calorimetry in the temperature range 5-300 K, for different hydration levels. The glass transition and water crystallization temperatures were derived in each case. The existence of different types of water was inferred and their amounts calculated. The heat capacities as obtained from direct calorimetric measurements were compared to the values derived from the neutron spectroscopy by way of integrating appropriately normalized VDOS functions. While there is remarkable agreement with respect to both temperature dependence and glass transition temperatures, the results also show that the VDOS derived part represents only a fraction of the total heat capacity obtained from calorimetry. Finally our results indicate that both hydration water and the peptide are involved in the experimentally observed transitions.

Neutron Scattering Studies of Green Fluorescent Protein, Nanosecond-Picosecond Dynamics

We present a detailed analysis of the picosecond-to-nanosecond motions of green fluorescent protein (GFP) and its hydration water using incoherent and coherent neutron scattering and hydrogen/deuterium contrast. Our results reveal that while much of the dynamics in the hydrated protein are connected to motions of hydration water, there are significant differences in the dynamics of protein and its hydration water. On the picosecond-to-nanosecond timescale, the hydration water exhibits diffusive dynamics, while the protein motions are localized to less than ∼3A. The beta-barrel structure of GFP differs from previously studied globular proteins; which may explain the differences observed in the direct comparison of the atomic displacements (on a timescale of ∼1ns) between GFP and lysozyme. We expand upon this and the recent Biophysical Journal article on this system with a more in depth analysis of the quasielastic spectra and a comparison of the data for GFP to current models for dry and hydrated protein motions. Finally, coherent scattering measurements allow us to comment on the cooperativity of protein and hydration water dynamics.View Large Image | View Hi-Res Image | Download PowerPoint Slide

High-temperature high pressure cell for neutron-scattering studies

In this study, a simple high-temperature high pressure cell concept has been developed to enable neutron diffraction and quasi-elastic and inelastic neutron-scattering studies to be conducted on large-volume powder samples of ceramic proton conductors at pressures of up to 1 GPa and at temperatures of up to 770 K. Details of the cell are provided, along with the first experimental neutron diffractograms (at 0.62 GPa and 300 K), quasi-elastic neutron-scattering spectra (at 0.58 GPa and 770 K) and inelastic neutron spectra (at 0.75 GPa and 530 K) determined for samples of BaCe0.8Y0.2O3.

Anisotropic Features of Water and Ion Dynamics in Synthetic Na- and Ca-Smectites with Tetrahedral Layer Charge. A Combined Quasi-elastic Neutron-Scattering and Molecular Dynamics Simulations Study

The temperature- and orientation-dependent dynamics of water molecules and sodium or calcium cations confined in the interlayer space of synthetic saponite with contrasting layer charge were analyzed through the combination of three-axis neutron spectroscopy and molecular dynamics (MD) simulation. We first show that it is possible to generate MD simulated quasi-elastic spectra that are equivalent to the experimental ones. As a consequence, the analysis of spectra in terms of Lorentzian decomposition can be advantageously replaced by a direct exploitation of MD results. We show that such strategy provides classical information on the influence of clay crystal chemistry on water and ion dynamical features as well as reliable additional information on (i) dynamics associated to different types of water molecules (bonded or not to interlayer cations) and (ii) interlayer cation dynamics. The same strategy applied to data obtained at higher temperature provided further confirmation of the validity of the atomic potentials used in simulations while allowing the extraction of activation energies for water and cations translational motions.

Fluxionality of Hydrogen Ligands in Fe(H)2(H2)(PEtPh2)3

Extensive computational investigations along with additional quasielastic neutron scattering data were used to obtain a consistent picture of the extensive fluxionality of hydride and dihydrogen ligands in Fe(H)(2)(H(2))(PEtPh(2))(3) over a wide range of temperatures from 1.5 to 320 K. We were able to identify three different regimes in the dynamical processes based on activation energies obtained from line spectral broadening. The rotational tunneling lines (coherent exchange of the two hydrogens of the H(2) ligand) are broadened with increasing temperature by incoherent exchange up to about 80 K at which point they merge into a quasielastic spectrum from 100 K to about 225 K. The effective activation energies for the two regions are 0.14 and 0.1 kcal mol(-1), respectively. A third dynamical process with a higher activation energy of 0.44 kcal mol(-1) dominates above 225 K, which we attribute to a quantum dynamical exchange of dihydrogen and hydride ligands. Our detailed density functional theory (DFT) structural calculations involving the three functionals (B3LYP, TPSS, and wB97XD) provide a good account of the experimental structure and rotational barriers when only the hydrogen ligands are relaxed. Full relaxation of the "gas-phase" molecule, however, appears to occur to a greater degree than what is possible in the crystal structure. The classical dihydrogen-hydride exchange path involves a cis-dihydrogen and tetrahydride structure with energies of 6.49 and 7.38 kcal mol(-1), respectively. Experimental observation of this process with much lower energies would seem to suggest involvement of translational tunneling in addition to the rotational tunneling. Dynamics of this type may be presumed to be important in hydrogen spillover from metal particles, and therefore need to be elucidated in an effort to utilize this phenomenon.

Light scattering in a phonon gas

Light-scattering spectrum in dielectric crystals is studied with extended thermodynamics (ET) for a phonon gas, covering from hydrodynamic to ballistic (collisionless) regimes. The ET equation is solved to obtain the power spectrum of the energy density in a phonon-gas mixture, which consists of interacting phonon gases of longitudinal and transverse acoustic (LA and TA) phonon modes. In the hydrodynamic regime, where phonon collisions take place frequently, it is found that the light-scattering spectrum consists of two components, which can be interpreted as the two normal modes formed by the two second-sound modes defined in each of the LA and TA phonon gases. Out of the two normal-mode spectra, the low-frequency component arises from thermal fluctuations and gives rise to a narrow quasielastic spectrum, which corresponds to the well-known thermal Rayleigh scattering due to thermal diffusion, i.e., due to overdamped second sound. With sufficient momentum-conserving phonon collisions (normal phonon scattering), the narrow quasielastic component is demonstrated to develop, from the diffusive central peak, into a pair of shifted inelastic peaks due to propagation of underdamped second sound. The other spectrum component gives rise to a much broader quasielastic scattering, whose wing extends out to the Brillouin-scattering lines of the LA and TA phonons (first sounds). The broader quasielastic spectrum has a linewidth equal to the phonon-collision rate, which suggests that this component originates from a nonequilibrium process in the phonon gas. As the ballistic regime is approached, the line shapes and linewidths of the two normal-mode spectra approach each other, and the two components finally coincide in the limit of the ballistic regime, which is in good agreement with the reported behavior for these spectra that were experimentally observed in many crystals. In the ballistic limit, the light-scattering mechanism in the present model is found to become formally equivalent to the previously proposed microscopic framework, i.e., the second-order difference Raman scattering (two-phonon difference light scattering) on a same phonon dispersion. The derived spectral formula is fitted to the spectra previously observed in the experiments for rutile $({\text{TiO}}_{2})$ and strontium titanate $({\text{SrTiO}}_{3})$. The fits are quite successful in wide ranges of frequency and temperature, i.e., regardless of degree of nonequilibrium, owing to the ET analysis. The relaxation times for the normal and resistive phonon collisions (${\ensuremath{\tau}}_{\text{N}}$ and ${\ensuremath{\tau}}_{\text{R}}$) are determined through the analysis. The temperature dependences of ${\ensuremath{\tau}}_{\text{N}}$ and ${\ensuremath{\tau}}_{\text{R}}$ indicate that the origin of the broad shifted peaks (the ``broad doublet''), which were observed in ${\text{SrTiO}}_{3}$ at around 30 K, is likely due to underdamped second sound at least in a narrow temperature range around 30 K.

The structure of diaminodurene and the dynamics of the methyl groups

Diaminodurene crystallizes in the orthorhombic space group Pbca, with eight molecules in the unit cell. Four inequivalent methyl groups with different environments exist in a molecule. The amino groups are also different, which is well reflected in infrared spectra. Two tunneling modes are resolved at 23.7 and 7.0 microeV at 4.5 K. Their intensities are consistent with the presence of two further unresolved tunneling modes. Quasielastic spectra are composed of three Lorentzians of equal intensities. The two low activation energies and tunnel modes are modeled into consistent rotational potentials. The third activation energy and a librational band are used to guess the strength of the two stronger rotational potentials. The internal modes related to the torsional/librational vibrations mix with ring torsions in the range of 70-220 cm(-1). This way the tunnel modes couple to ring torsions whose energy determines the broadening of both tunnel bands. The calculations for free molecules yield mode frequencies a little bit lower than the experimental inelastic neutron scattering (INS) values. Application of theoretical methods elaborated for the crystalline state leads to a satisfactory consistency. It is also valid for bending modes of NH(2) groups, which in the solid state show much higher frequencies than in the gas phase, as expected.

Systematic study of the nuclear potential diffuseness through high precision back-angle quasi-elastic scattering

High precision measurements for back-angle quasi-elastic scattering of $^{16}\mathrm{O}$ from various target nuclei have been made, and are compared with coupled channels calculations to determine the diffuseness of the real part of the Woods-Saxon nuclear potential. The extracted diffuseness parameters are in the range of $0.60$ to $0.69$ fm, and agree well with previous results using a $^{32}\mathrm{S}$ projectile. The measured quasi-elastic energy spectra close to the barrier show both discrete peaks and a broad continuous structure with $Q$-values down to $\ensuremath{-}25$ MeV. These suggest the inadequacy of coupled channels calculations that include couplings only to low energy, discrete states of the colliding nuclei.

Dynamics and adsorption sites for guest molecules in methyl chloride hydrate

Methyl rotational tunneling, quasielastic spectra and phonondensities of states measured with neutrons at energy transfers from35 µeV to 40 meV are used to characterize the adsorption sites and potentials ofCH3Cl guest molecules in the two kinds of cages of cubic I methyl chloride hydrate.The model of adsorption to hydrogen bonds of the ice cage explains the broadtunnel spectrum as a superposition of four bands. Up to a temperatureT∼80 K the quasielastic scattering is influenced by quantum motion. Only aboveT∼80 K does the effective linewidth follow an Arrhenius behavior with an average activationenergy. Rotational potentials contain a significant sixfold component supporting theproposed adsorption to hydrogen bonds with their mirror symmetry. Positional disorder ofprotons in the hydrogen bonds of the host ice lattice leads to potential distributions oflarge relative widths .

Observation of a dynamic crossover in RNA hydration water which triggers a dynamic transition in the biopolymer

High-resolution quasielastic neutron scattering spectroscopy was used to measure H2O and D2O hydrated RNA samples. The contribution of scattering from RNA was subtracted out by taking the difference of the signals between the two samples. The measurements were made at a series of temperatures from 270 K down to 180 K. The relaxing-cage model was used to analyze the difference quasielastic spectra. We observed clear evidence of a fragile-to-strong dynamic crossover (FSC) at TL=220 K in RNA hydration water. We further show that the mean-square displacements of the hydrogen atoms in both RNA and its hydration water exhibit a sharp change in slope at approximately the same temperature 220 K. This latter fact suggests that the dynamic transition in RNA is triggered by the abrupt change of mobility of the hydration water at its FSC temperature.