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Aerosol droplets are fully involved in forming clouds and play a critical role in global climate change. The investigation of the properties, speciation, and structure of aerosol droplets at a molecular level is highly needed for understanding the physicochemical behaviors and processes of aerosol droplets. We investigate the composition, speciation, and structure of a single aqueous MgSO4 droplet of 1 mm size ultrasonically levitated in the air and bulk solutions under ambient conditions by in situ Raman and synchrotron X-ray scattering. The composition and speciation are determined by measuring Raman spectra of the sulfate ion's S–O band and water's O–H bands. The X-ray data are subjected to empirical potential structure refinement modeling to extract the site–site pair correlation function, coordination number distribution, and 3-D structure for the ion solvation, association, and solvent water. In situ X-ray scattering measurements observe the crystallization of MgSO4 hydrates from a droplet. [ABSTRACT FROM AUTHOR]

The structure of electrolyte solutions under pressure at a molecular level is a crucial issue in the fundamental science of understanding the nature of ion solvation and association and application fields, such as geological processes on the Earth, pressure-induced protein denaturation, and supercritical water technology. We report the structure of an aqueous 2 m (=mol kg−1) MgCl2 solution at pressures from 0.1 MPa to 4 GPa and temperatures from 300 to 500 K revealed by X-ray- and neutron-scattering measurements. The scattering data are analyzed by empirical potential structure refinement (EPSR) modeling to derive the pair distribution functions, coordination number distributions, angle distributions, and spatial density functions (3D structure) as a function of pressure and temperature. Mg2+ forms rigid solvation shells extended to the third shell; the first solvation shell of six-fold octahedral coordination with about six water molecules at 0 GPa transforms into about five water molecules and one Cl− due to the formation of the contact ion pairs in the GPa pressure range. The Cl− solvation shows a substantial pressure dependence; the coordination number of a water oxygen atom around Cl− increases from 8 at 0.1 MPa/300 K to 10 at 4 GPa/500 K. The solvent water transforms the tetrahedral network structure at 0.1 MPa/300 K to a densely packed structure in the GPa pressure range; the number of water oxygen atoms around a central water molecule gradually increases from 4.6 at 0.1 MPa/298 K to 8.4 at 4 GPa/500 K. [ABSTRACT FROM AUTHOR]

Inelastic x-ray scattering measurements of hydrated β-lactoglobulin (β-lg) were performed to investigate the collective dynamics of hydration water and hydrated protein on a picosecond time scale. Samples with different hydration levels h [=mass of water (g)/mass of protein (g)] of 0 (dry), 0.5, and 1.0 were measured at ambient temperature. The observed dynamical structure factor S(Q,ω)/S(Q) was analyzed by a model composed of a Lorentzian for the central peak and a damped harmonic oscillator (DHO) for the side peak. The dispersion relation between the excitation energy in the DHO model and the momentum transfer Q was obtained for the hydrated β-lg at both hydration levels, but no DHO excitation was found for the dry β-lg. The high-frequency sound velocity was similar to that previously observed in pure water. The ratio of the high-frequency sound velocity of hydrated β-lg to the adiabatic one of hydrated lysozyme (h=0.41) was estimated as ∼1.6 for h=0.5. The value is significantly smaller than that (∼2) of pure water that has the tetrahedral network structure. The present finding thus suggests that the tetrahedral network structure of water around the β-lg is partially disrupted by the perturbation from protein surface. These results are consistent with those reported from Brillouin neutron spectroscopy and molecular dynamics simulation studies of hydrated ribonuclease A. [ABSTRACT FROM AUTHOR]

Previously reported inelastic x-ray scattering spectra of a typical van der Waals molecular liquid CCl 4 were reanalyzed using a generalized Langevin formalism with a memory function including a thermal and two viscoelastic relaxation processes and simple sparse modeling. The obtained excitations of longitudinal acoustic phonons show a largely positive deviation from the hydrodynamic value by about 57%, much larger than about 37% by the previously reported damped harmonic oscillator result. Such large values of fast sounds in molecular liquids larger than 15-20% of typical liquid metals are interpreted as extra energy losses for terahertz phonons by molecules' vibrational and rotational motions. The rates of the fast and slow viscoelastic relaxations in the memory function at low Q indicate large values, about 0.5 and 2 ps, which correspond to the vibrational and rotational motions of CCl 4 molecules, respectively. These values are larger than those of the typical polar molecular liquid acetone, which may reflect the heavier atomic mass of CCl 4. The Q dependences of the viscoelastic relaxation rates are discussed in terms of the lifetime and propagating length of the terahertz phonon oscillations. The microscopic kinematic longitudinal viscosity was obtained from the viscoelastic relaxation magnitudes and times, rapidly decreasing with Q from a macroscopic value at Q → 0. • Generalized Langevin formalism was applied to inelastic x-ray scattering spectra of liquid CCl 4. • A large deviation from hydrodynamic prediction was found in the phonon dispersion relation. • Fast sound in terahertz oscillations originates from viscoelastic damping by vibrational and rotational molecular motions. [ABSTRACT FROM AUTHOR]

[Display omitted] • In-situ observation of QPAF-4 was performed under various humidity conditions by synchrotron X-ray scattering measurements. • Hysteresis of the adsorption and desorption processes of water vapor to the membrane is observed. • The information of hydrogen bonding interaction in the membrane at various humidity conditions is obtained. • In-situ observation in the present study clarified the humidity dependence of the bonding state of water in the membrane. In-situ observation of an anion exchange membrane (AEM), QPAF-4, synthesized by the group of University of Yamanashi, was performed under various humidity conditions by synchrotron X-ray scattering measurements. The absorption process of water vapor into the AEM was slow, taking even a few hours. When the environmental humidity decreased, the amount of water contained in the membrane decreased also very slowly. Hysteresis was clearly observed during the absorption and desorption processes. Although the amount of absorbed water was very small, a meaningful difference in the X-ray scattering intensity was found between water-absorbed and dry membrane. The radial distribution functions (RDFs) of the membrane under various humidity conditions were obtained by subtracting the scattering of the chamber, where the humidity and the temperature were contorted from the scattering intensity from the membrane in the chamber. The peak at 2.8 Å was assigned to the hydrogen bonding interaction of O(water)-O(water) and non-hydrogen bonded interaction of water molecules. These peaks increased under a high humidity condition. In-situ observation in the present study clarified the humidity dependence of the bonding state of water in the AEM. [ABSTRACT FROM AUTHOR]

Previously reported inelastic X-ray scattering spectra of molecular liquid benzene were reanalyzed by a generalized Langevin formalism (GLF) with a memory function including a thermal and two viscoelastic relaxation processes. A new algorithm was containing a simple sparse modeling to smooth Q dependences of dynamical parameters used in the present GLF analysis. The obtained excitation energies of longitudinal acoustic phonons show a largely positive deviation from the hydrodynamic value by about 50%, the same as that by previous analysis and similar to existing results of several molecular liquids. Such a large deviation of dynamical sound velocity in liquid benzene is interpreted as extra energy-losses for terahertz phonons by vibrational and rotational motions of benzene molecules. The rates of the fast and slow viscoelastic relaxations in the memory function at low Q are undetectable and 0.4-0.8 ps, respectively. These can be explained by the vibrational and anisotropic rotational motions of benzene molecules. The microscopic kinematic longitudinal viscosity rapidly decreases with Q from a reasonable macroscopic value. • Generalized Langevin formalism was applied to inelastic x-ray scattering spectra of liquid benzene. • A large deviation from hydrodynamic prediction was found in phonon dispersion relation by about 50%. • Fast sound in terahertz oscillations originates from viscoelastic damping by vibrational and rotational molecular motions. [ABSTRACT FROM AUTHOR]

Inelastic x-ray scattering is conducted to investigate the reason why the thermal conductivity of nanofluids increases beyond a theoretical value by the addition of a small amount of nanoparticles (NPs). High-frequency sound velocity is obtained by analyzing inelastic x-ray scattering data of nanofluids. Since the high-frequency sound velocity reflects thermal conductivity and structural relaxation of solvent molecules, the effect of nanoparticles on heat transport and molecular dynamics of the medium of nanofluids could be clarified. Cu nanoparticles (Cu NPs) are found to be extremely effective to largely increase the high-frequency sound velocity of medium ethylene glycol, while the effect of alumina NPs on water is limited. The increase in high-frequency sound velocity agrees well with that in thermal conductivity. It is concluded that solvent molecules are highly restrained by Cu NPs in nanofluid, leading to high thermal conductivity. [ABSTRACT FROM AUTHOR]

Collective dynamics of liquid deuterated methanol was studied at room temperature using neutron scattering. The inelastic excitation energy of coherent scattering from liquid deuterated methanol was proportional to the momentum transfer Q in the range of 0.2 to 0.9 Å − 1 ; the high-frequency sound velocity of liquid deuterated methanol obtained from the dispersion relation was 1770 ± 30 m s − 1 . The positive dispersion for liquid deuterated methanol was ~ 60%, about half that of liquid heavy water (~ 100%) previously reported. This could be reflective of the different number of hydrogen bonds. At Q positions below the first peak in S ( Q ), the dispersion relation of liquid deuterated methanol derived from neutron scattering was almost identical to that obtained from X-ray scattering. However, the excitation energy obtained from neutron scattering at Q positions above the first peak in S ( Q ) is larger than that from X-ray scattering, which could be ascribed to intramolecular methanol vibrations. [ABSTRACT FROM AUTHOR]

Abstract: Inelastic X-ray scattering experiments have been performed on methanol as a function of density from ambient to the supercritical state. Positive dispersion of the sound velocity, as compared to the hydrodynamic values, is ∼50% in the ambient condition and decreases to zero at 0.50gcm−3 over the momentum transfer Q =1–10nm−1 with lowering density; however, it increases again with a further decrease in density down to 0.20gcm−3 in the supercritical state only in the Q-range above ∼5nm−1. These results have been interpreted as the formation of small oligomers in the low-density supercritical methanol. [Copyright &y& Elsevier]

High-resolution inelastic X-ray scattering (IXS) measurements were performed for room-temperature ionic liquids (ILs) of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide and bis(fluorosulfonyl)amide, [C2mIm+][TFSA-] and [C2mIm+][FSA-], respectively, at ambient temperature. The observed spectra as a function of Q of 1.4-6 nm-1 can be ascribed to quasi-elastic and inelastic scatterings, so that they are well represented with the fitting by using the Lorentz and the damped harmonic oscillator model functions to yield the dynamic structure factors. It was found in the intermediate scattering function, F(Q, t) that both ILs show the relaxation at t < 10 ps. The IXS measurements were also made on [C2mIm+][TFSA-] and [C2mIm+][FSA-] solutions dissolving Li salt. It is suggested that the adding of Li salt to IL significantly prolongs the relaxation time. [ABSTRACT FROM AUTHOR]

Structure and dynamical properties of hydrated actin filament (F-actin) are revealed by X-ray diffraction and inelastic X-ray scattering (IXS) in a temperature range of 180–298 K, respectively. We assigned the peaks in the radial distribution functions of the hydrated F-actin by molecular dynamics (MD) simulation for F-actin in water. Although the hydration water of F-actin does not freeze in the temperature range measured, the hydrogen-bonded network where hydration water molecules mediate the hydrophilic groups of F-action becomes enhanced with decreasing temperature, as previously seen for many hydrated proteins. By applying a damped harmonic oscillator model to the dynamical structure factor obtained from the IXS spectra of hydrated F-actin, we investigated the intensity and energy of the phonon excitation as a function of temperature. The phonon excitation energy decreased and the phonon population which is proportional to the intensity of the phonon excitation increased with increasing temperature as previously reported for hydrated lysozyme and could be related to the conformational flexibility of the protein regarding the intraprotein short-time collective vibrational motions. In contrast to hydrated lysozyme, these phenomena for hydrated F-actin were observed at ~11 nm−1 of momentum transfer, Q , indicating that they arise from water dimer mediating the hydrophilic parts of F-actin. Unlabelled Image • Structure and dynamical properties of the hydrated F-actin were revealed by X-ray diffraction and inelastic X-ray scattering • The phonon excitation energy decreased and the phonon population increased with increasing temperature • The intraprotein short-time collective vibrational motions could be related to the conformational flexibility of the protein [ABSTRACT FROM AUTHOR]

Abstract Structure of alkaline aqueous NaBH 4 solutions at NaBH 4 concentrations of 1.0 to 9.1 mol·dm−3 (almost saturated) as well as a 1.3 mol·dm−3 NaOH solution was studied by X-ray diffraction and Empirical Potential Structure Refinement (EPSR) modelling. In the 1.0 mol dm−3 alkaline NaBH 4 solution, Na+ is surrounded by around six water molecules with octahedral geometry. With an increase in NaBH 4 concentration, the hydration number of Na+ decreases from 4.8 ± 1.1 at 2.25 mol·dm−3 solution to 2.9 ± 1.3 at 9.1 mol·dm−3 with an almost constant Na+-O (W: H 2 O) distance of 2.34 Å. The decrease in hydration number for Na+ is compensated by the formation of ion pairs between Na+ and BH 4 − to ensure an octahedral hydrated geometry for Na+. About 6.0 ± 1.6 water molecules are likely to bond to BH 4 − via tetrahedral edges or tetrahedral corners without a very specific hydration geometry, giving rise to each hydrogen atom of BH 4 − bound to 2.3 ± 1.0 water molecules through dihydrogen bonds. The hydration number around BH 4 − decreases with increasing concentration. BH 4 − tends to form contact ion pairs with Na+ at the Na-B distances of 3.24 Å and 2.82 Å in tetrahedral-corner-shared and tetrahedral-edge-shared fashions, respectively; the number of Na-B interactions increases from 0.3 ± 0.5 in 1.0 mol·dm−3 (almost negligible) to 2.1 ± 0.9 in 9.0 mol·dm−3. Tetrahedral-edge-shared bidentate ion pair is likely to be the preferred and dominant ion cluster over the wide concentration range. Ion association between the Na+ and BH 4 − was crosschecked by density function theory (DFT) calculations on [NaBH 4 (H 2 O) 6 ] clusters. Graphical abstract Unlabelled Image Highlights • Hydridic-to-protonic dihydrogen bonds in aqueous NaBH 4 solutions are observed. • 6.0 ± 1.6 H 2 O molecules bond to BH 4 − in tetrahedral-edge or tetrahedral-corner forms. • 2.3 ± 1.0 H 2 O molecules hydrate each hydrogen of BH 4 − through dihydrogen bonding. • Tetrahedral-edge-shared ion association between Na+ and BH 4 − is likely to be preferred and dominant. [ABSTRACT FROM AUTHOR]

The dynamic structure factors S (Q , ω) of liquid acetone were measured in a wide Q range 1.9–41.2 nm−1 with a high-resolution inelastic X-ray scattering (IXS) spectrometer installed at BL35XU of the SPring-8. Highly damped collective excitations of the longitudinal acoustic (LA) phonons are observed. The IXS spectra were analyzed by using a generalized Langevin formalism with the help of a sparse modeling to deduce reasonable Q dependences of the fitting parameters. The dispersion relation of the LA phonon excitations shows a highly positive deviation by about 65% from the adiabatic velocity of sound, which is larger than that in non-polar liquids such as CCl 4 and benzene with van der Waals interactions, due probably that the acetone is a polar liquid. Microscopic dynamic parameters, such as viscoelastic relaxation rates and viscosity, are discussed by comparing with existing macroscopic dynamic properties. The fast and slow viscoelastic relaxations correspond to the vibration dynamics and reorientation correlations, respectively. Dynamical velocity of sound of longitudinal acoustic phonons in liquid acetone obtained from inelastic X-ray scattering, which exceeds about 65% in the low Q region from hydrodynamic value of 1161 m/s. [Display omitted] • Phonon dynamics of acetone as a polar liquid is investigated by inelastic X-ray scattering. • Obtained data are analyzed by using generalized Langevin formalism. • Dispersion of longitudinal phonon shows highly positive deviation from hydrodynamics. • Viscoelastic relaxations in memory function are related to macroscopic correlations. [ABSTRACT FROM AUTHOR]

Inelastic X-ray scattering (IXS) experiments were carried out at room temperature at BL35XU of the SPring-8 on a single crystal Mg 85 Zn 6 Y 9 alloy with a synchronized long-period stacking ordered (LPSO) phase of purely 18R type. The IXS measurements were carried out in both the longitudinal and transverse directions along the Γ -K and Γ -M (momentum vector q ⊥ lattice axis c ), and Γ -A ( q ∥ c ) directions for the energy transfers ω below 40 meV. Peaks arising from longitudinal and transverse acoustic (LA and TA) modes were clearly observed in the IXS spectra. The dispersion relations of the LA and TA modes in the Mg 85 Zn 6 Y 9 LPSO alloy are mostly similar to those of previous INS data on single crystal pure Mg. New impurity-derived dispersion-less excitation modes are observed along all of the crystal directions at about 5, 10, and 17 meV. Partial vibrational density of states (vDOS) was obtained using an a b i n i t i o molecular dynamics simulation, and it was found that the ∼ 10 meV peak mainly originates from the phonon excitations inside the L1 2 -type Zn 6 Y 8 clusters and the ∼ 17 meV peak from those between the cluster and the host Mg atoms, and a small shoulder at 5 meV consists of motions of all the elements. These findings clarify that the dispersion-less modes mainly correspond to localized stretching and twisting modes around the impurity clusters in the LPSO alloys. [ABSTRACT FROM AUTHOR]

[Display omitted] • The oxygen atoms of 18-crown-6 and the hydrogen atoms of water molecule form strong hydrogen bonds in aqueous solution. • Cs+ is located directly above the 18-crown-6 ring plane, about 1.15 Å from the centroid of 18-crown-6. • The higher the concentration of CsCl, the lower the complexation percentage of 18-crown-6 to Cs+. • Cs+ complexing with 18-crown-6 mainly hydrates with four water molecules. Wide angle X-ray scattering (WAXS) and density functional theory (DFT) were employed to study the structures of aqueous 18-crown-6/CsCl solutions with CsCl concentrations of 0.25, 0.50 and 1.00 mol·L-1. The empirical potential structure refinement (EPSR) modelling was adopted to get the pair distribution functions (PDFs), coordination numbers (CN), coordination number distributions (CND), angle distribution functions (ADFs), independent gradient model (IGM) and spatial density functions (SDFs) for the 18-crown-6 hydration, the complexation of 18-crown-6 and Cs+, the hydration of 18-crown-6/Cs+ complex, and the association of Cl- and 18-crown-6/Cs+ complex. Judging from the distance and orientation of water molecules, and the IGM between 18-crown-6 and water molecules, the oxygen atoms of 18-crown-6 (Oc) and the hydrogen atoms of water molecules (Hw) form strong hydrogen bonds, and these water molecules were distributed on both sides of the 18-crown-6 ring plane. However, the hydrogen atoms of 18-crown-6 (Hc) hardly form hydrogen bonds with the oxygen atoms of water molecules (Ow). Cs+ is located directly above the 18-crown-6 ring plane of 0.35 to 2.05 Å away from the centroid of 18-crown-6, and forms 18-crown-6/Cs+ complex with six Oc at r Cs + - O c = 3.06 Å. When the concentrations of CsCl are 0.25, 0.50 and 1.00 mol·L-1, the complexation percentage of 18-crown-6 to Cs+ are about 100%, 58% and 54%, respectively. No classic 2:1 "sandwich" 18-crown-6/Cs+ complex structure was found in the solutions we surveyed. Both interaction energies and solvation stability energies reveal that the hydrates of 18-crown-6/Cs+ complexes were formed in aqueous solutions. Cs+ uncomplexed with 18-crown-6 hydrates with eight water molecules in aqueous solution, while Cs+ can also hydrate with about four water molecules when it complexes with 18-crown-6. The results of atomic pair distances, the dipole distance of water molecules, the SDF and the IGM indicate that although water molecules can be located on both sides of the 18-crown-6 ring plane when the hydrates are formed, they hydrate with Cs+ on the side where Cs+ only existed. Cs+ of 18-crown-6/Cs+ complex associates with Cl- with the r Cs + - Cl - = 3.79 Å by electrostatic attraction. [ABSTRACT FROM AUTHOR]