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A recent screening study highlighted a molecular compound, apilimod, for its efficacy against the SARS-CoV-2 virus, while another compound, tetrandrine, demonstrated a remarkable synergy with the benchmark antiviral drug, remdesivir. Here, we find that because of significantly reduced potential energy barriers, which also give rise to pronounced quantum effects, the rotational dynamics of the most dynamically active methyl groups in apilimod and tetrandrine are much faster than those in remdesivir. Because dynamics of methyl groups are essential for biochemical activity, screening studies based on the computed potential energy profiles may help identify promising candidates within a given class of drugs.

Using quasielastic neutron scattering, we compare dynamics in single-element liquids, glass-forming selenium and non glass-forming gallium. There is a single jump-diffusion process in gallium, whereas in selenium there is also a faster, spatially localized process. The fast and slow processes describe β- and α-relaxation, respectively. We then analyze an archetypical glass-former, glycerol, to show that the two-component fit, with β- and α-relaxations explicitly separated, yields the correct value for the translational diffusion coefficient and provides information on the spatial localization of the β-relaxation that is not experimentally accessible otherwise.

Diffusion of water sorbed in a nanofiltration (NF) polyamide membrane as studied by quasielastic neutron scattering (QENS) is reported here. The trimesoyl chloride–piperazine based NF membrane was synthesized by interfacial polymerization technique and was characterized by positron annihilation lifetime spectroscopy (PALS) and SEM techniques. PALS data shows that the membrane has an average pore size ∼4.6 A. QENS data from water sorbed NF membrane show that the diffusion in the sorbed water occurs through jump diffusion with the jump lengths distributed randomly. Translational diffusion coefficient obtained for water sorbed in the NF membrane is found to be smaller than that of bulk water.

Neutrons scattering techniques are ideally suited to directly probe H in materials due to the large incoherent scattering cross-section of hydrogen atom, and have been invaluable in providing direct insight into the local fluctuations and large amplitude motions in AB. Dihydrogen bonding may have a significant affect on materials to be used to store hydrogen for fuel-cell powered applications. We have noticed a trend of low temperature release of H2 in materials composed of hydridic and protonic hydrogen. This phenomenon has caught our attention and motivated our interest to gain more insight into dihydrogen bonding interactions in AB. We present results from a thorough Quasielastic Neutron Scattering (QENS) investigation of diffusive hydrogen motion in NH311BH3 and ND311BH3 to obtain (1) a direct measure of the rotational energy barriers the protonated species and (2) a confirmation of the 3-site jump model for rotational motion. The amplitude of the energy barrier of rotation of BH3 and NH3 determined by QENS are compared to those determined for BD3 and ND3 determined by 2H NMR studies.

Quasielastic neutron scattering (QENS) studies on the reorientational dynamics in the ordered phases (crystalline and the smectic H) of p - n -hexyloxybenzylidine- p′ - n -butylaniline (6O.4) are reported here. Analysis of the QENS data showed that in the crystalline phase (room temperature ∼25 °C) the reorientational motion involves only the core of the molecule, whereas in the S H phase (at 45 °C) the whole molecule is involved. This motion is found to persist even when the sample was cooled back to 25 °C (below the crystalline–S H transition temperature of 33.7 °C) suggesting existence of the liquid crystalline phase as a supercooled state. DSC measurements and X-ray diffraction studies corroborate the QENS results.

An expression for an epithermal neutron scattering cross section from a water cluster is derived by using a time-dependent wavepacket approach. Both the translational motion of the center of mass of the cluster and the vibrational modes of a proton in the cluster are taken into account. Incident energy dependence on the neutron–proton scattering cross sections calculated for a simplified cluster model agrees with experimental results of neutron scattering from water. Time correlation functions of momentum transfer clearly show that both the translational and vibrational motions significantly contribute to the scattering cross section in the low energy regime.

This report concerns measurement of water dynamics associated within the interlamellar region of native saponite and its tridecameric ‘Al 13 ’ intercalated polycation, as investigated using the quasielastic neutron scattering technique. The diffusion constant corresponding to the translational motion is found to be much lower as compared to that of bulk water that indicates the water adsorbed in between layers of saponite clays is dynamically hindered. The dynamics is described by a model in which the molecules undergo random jump diffusion. Diffusivity is found to be larger in case of the Al 13 intercalated saponite than native saponite because of the larger interlayer spacings in the former.

The effects of NaOH on tricalcium silicate hydration kinetics were investigated using in situ time-resolved quasielastic neutron scattering. NaOH was confirmed to reduce the induction period. After the induction period the rate of products formation is nearly independent of NaOH concentration. However, NaOH suppresses the quantity of hydration products formed, mainly by decreasing the length of the nucleation and growth period, but also because it may cause morphological changes in the hydration products. These effects are commensurate with NaOH concentration, and explain the previously observed reduction in the early strength of tricalcium silicate pastes hydrated in the presence of NaOH.

Dynamical motions in 4- n -octyloxy-4′-cyanobiphenyl (8OCB) as studied by quasielastic neutron scattering technique in its smectic and nematic phases are reported. Analysis of elastic incoherent structure factor indicated the presence of motions of the side chain around the chain axis and the core group around the molecular axis in both the smectic and nematic phases. It is found that while chain group undergoes 2-fold jump rotation in smectic phase and uniaxial rotational diffusion in nematic phase, the core group follows uniaxial rotational diffusion in both the phases. Dynamical parameters correspond to the side group as well as the core group in both nematic and smectic phases are determined.

The melting behavior of methane adsorbed in a porous silica xerogel has been examined by quasielastic neutron scattering (QENS) from 20 to 115 K. The methane dynamics indicate a heterogeneous xerogel surface with a distribution of rotational and translational diffusion barrier heights from 0.17 to 2.1 kJ/mole. The QENS elastic intensity structure factor indicates that rotational diffusion occurs about a C 2 molecular axis for methane adsorbed in the xerogel. Porous silica and aluminosilica xerogels have also been characterized by small-angle neutron scattering (SANS) and gas adsorption isotherm measurements to determine the porosity, pore size, and tortuosity of the pore network.

Rietveld refinement of neutron diffraction from a powder sample of K1C60 in the orthorhombic phase using a model having polymeric linking by [2+2] cycloaddition of the C60 molecules yields physically reasonable bond lengths from 1.44 to 1.54 A between C atoms in the vicinity of the link. Neutron time-of-flight inelastic scattering measurements display a band of vibrations consistent with linking between 10 and 25 meV not present in pure C60 or in the fcc phase of K1C60. Diffuse scattering is accounted for in terms of rotationally disordered C60 in minority phases and in unlinked boundary regions between polymer grains.

A high-resolution inelastic neutron scattering (INS) spectrum has been observed for trans-polyacetylene films in the range 8–4000 cm−1 at 6 K, and compared with the calculated INS spectrum based on the force field obtained in our previous study. The peak positions as well as the overall intensity profile of the observed INS spectrum are well reproduced by the present calculation, in which the effects of the Debye-Waller factors and the phonon wings are taken into account.

The tunnel frequency of protonated methyl groups in aspirin has been measured, by inelastic neutron scattering, at 2 K, to be 1.22 μeV. This result and the temperature dependence up to 42 K are in poor agreement with NMR measurements of deuterated methyl groups which conclude that the rotational potential is purely three-fold symmetric. The discrepancy is attributed to a six-fold contribution in the rotational potential for which justification is provided by a calculation of the rotational potential based on the room temperature crystal structure.

The capillary melting of methane adsorbed into the uniform parallel mesopores of the new silicate MCM-41 has been studied by neutron inelastic scattering and neutron quasielastic scattering at an energy resolution of about 80 microelectron volts. Differences from bulk methane in both the rotational melting and the solid to liquid transition have been identified. Rotational melting occurs at about 35 K, nearly ten degrees above the onset for the bulk; translational melting starts at around 60 K, nearly 30 degrees below the melting point of bulk methane.

Neutron Compton scattering measurements for the partially deuterated N-methylacetamide molecule (CD3CONHCD3) at 4.5 K give the powder averaged mean frequency of the photon modes: 1457 ± 38 cm−1. This value is lower than that anticipated from the assignment scheme based on infrared and Raman spectra ( ⋍1790 cm −1 ). Anharmonicity and vibrational coupling are such that that assignment scheme must be rejected. The mean frequency obtained with the assignment based on inelastic neutron scattering (INS) ( ⋍1230 cm −1 ) appears realistic. These conclusions are in accord with force-field calculations in the impulse approximation.

The inelastic neutron scattering spectrum of linear PdH2 has been obtained. The spectrum is assigned in agreement with this geometry. The antisymmetric Pd-H stretching mode is observed at 248 meV; there is no trans influence. This agrees with the proposed donation of electrons to a conduction band.

The structure of the quasielastic incoherent neutron scattering from polydimethyl siloxane has been determined at low momentum transfer under conditions of high resolution. Within the limits of experimental error the quasielastic peak is a single component; a two component peak was not found. The findings are consistent with a previous tentative interpretation of the quasielastic peak being due to a Doppler broadening phenomenon attributed to the long range conformational changes of the polymer backbone.

Theoretical results are presented for the incoherent neutron quasi-elastic scattering law for a simple model of a liquid crystal. Experimental results are given for magnetically aligned specimens of two nematogens at low momentum transfer using a back scattering spectrometer of high energy resolution (≈ 1μeV fwhm). It is shown that information about both rotational and translational motions are contained in the data and values are obtained for the components of the self-diffusion tensor perpendicular and parallel to the nematic director for 5CB (C 5 H 11 ⦾—⦾ CN), D-5CB (C 5 D 11 -) and D-MBCA (CD 3 O ⦾ CH=N ⦾ CN) and the diffusion constant for the isotropic liquid phase of D-5CB.

The incoherent inelastic neutron scattering spectrum of hydrogen adsorbed on palladium black contains two bands centred at 916 and 823 cm −1 . These are assigned to the vibrations parallel and perpendicular to the surface respectively, of hydrogen bound at a bridging site. This assignment differs from that previously given from an infrared study of hydrogen adsorbed on palladium hydride.

Inelastic neutron scattering spectra of KHCO3 and CsH(NO3)2 have been obtained in the region 400 → 2400 and 400 → 2800 cm−1 respectively. The in- and out-of-phase bending vibrations of the hydrogen bonds have been observed and assigned. For CsH(NO3)2 the two bending modes are closer in frequency than in KHCO3 and they are not resolved from the antisymmetric stretch.

The hydrogen bond stretching and bending vibrations in solid trimethylammonium chloride are distinguished from the lattice vibrations by comparing the inelastic neutron scattering spectra of the fully hydrogenated salt (CH 3 ) 3 NH + Cl − with the partially deuterated derivatives (CH 3 ) 3 ND + Cl − and (CD 3 3 NH + Cl − . The information brought by the neutron technique allow the more precise but complicated infrared and Raman spectra to be more thoroughly analysed.

A multicomponent oil-in-water microemulsion containing CTAB (C 16 H 33 NMe 3 Br), n -octane, 1-butanol, NaBr, and D 2 O has been studied by small-angle neutron scattering at several temperatures. The size of the microemulsion droplets was found to be independent of temperature. Correlation lengths for the critical concentration fluctuations agree with those determined earlier by light scattering.

We have measured the neutron inelastic scattering from hexamethylenetetramine at 5 K on a beryllium and graphite filter spectrometer. Comparison with previous work shows that the spectral resolution has been much improved. Most of the intramolecular modes are resolved and their assignment is discussed. Overtones and combination peaks are also clearly identified.

Neutron inelastic incoherent scattering spectra of 9,10-anthraquinone crystal were measured at 20 and −144°C, and the spectra obtained were compared with the calculated frequency distribution of the lattice vibrations. Mean square amplitude tensors of the molecule in the crystal were also calculated at various temperatures. The calculated tensors agree well with the ones obtained from an X-ray diffraction study.

The scattering of NO molecules from a clean graphite surface is studied by means of laser techniques. Molecules with two different scattering histories, namely direct quasielastic collisions and multiple collisions, are characterized by their angular, velocity, and rotational distributions for both in-plane and out-of-plane scattering. It is found that the rotational state distributions are affected by the scattering history, but no variation can be observed when the out-of-plane angle is varied.

The scattering density distribution in β-N 2 at 1.2 kbar has been determined by neutron scattering methods. Diffuse scattering has been observed as a function of pressure. Calculations of the diffuse scattering on the assumption of randomly oriented N 2 molecules are in poor agreement with the experimental observation.

Phonon dispersion curves of single crystal iodine at 77 K have been measured by one-phonon coherent inelastic neutron scattering techniques. The data are analysed in terms of two Buckingham-six intermolecular potentials; one to represent the shortest intermolecular interaction (3.5 A) and the other to represent the more distant interactions. Moderate agreement is obtained between the observed and calculated frequencies, but it also oappears necessary to treat the second-nearest-neighbor interaction (3.97 A) separately from the van der Waals interactions (distances ⩾ 4.2 A).

Neutron inelastic scattering spectra of crystalline ethylene have been measured at two temperatures, 4 and 80 K, between 80 and 250 meV. The spectra are found to consist of weak and shifted peaks superimposed on a very broad background. This is accounted for by multi-phonon effects and Doppler broadening due to the small molecular mass of ethylene. A generalization to neutron scattering from adsorbed molecules is made.

The cross section for inelastic neutron scattering by a diatomic molecule is calculated. Scattering accompanied by electronic excitation of the molecule is shown to be more probable, under certain conditions, than that accompanied by purely vibrational excitation. The possibility of a neutron-stimulated tunneling transition of the molecule is considered.

From incoherent inelastic neutron scattering studies of solid C 2 Cl 6 the in- and out-of-phase torsions about the C-C axis are assigned at 56 and 95 cm −1 , respectively. Using a model for the potential barriers in the solid the torsional frequency in the gas has been calculated to be 76.7 cm −1 and the internal barrier to be 67.8 kJ mol −1 .

Samples of H2O suspended in Ar were prepared which permitted us to record inelastic incoherent neutron scattering spectra of matrix-isolated water. In the energy loss spectrum, five peaks were found below 45 cm−1, including a strong ortho-para transition. Earlier assignments of free monomer rotations observed by far-IR spectroscopy could be confirmed. In the range 45 to 90 cm−1, only very weak intensity is found. The respective band positions do not agree with earlier far-IR data.

Variable temperature quasielastic neutron scattering studies have been used to investigate motions in 12-tungstophosphoric acid hexahydrate (H 3 PW 12 O 40 ·6H 2 O). A twofold reorientation (180° flip) of “terminal waters” within centrosymmetric H 5 O 2 + ions has been identified and the results of a previous NMR study reinterpreted. The activation energy and Arrhenius prefactor for the reorientation are 14 kJ mol −1 and 6×10 −13 s, respectively.

Results of cold neutron scattering by plastic neopentane at several temperatures are presented. The measured quasielastic peak widths are compared with calculations for two simple models of molecular reorientation. An activation energy for reorientation of 0.88 ± 0.11 kcal/mole is derived.

We present experimental evidence that at relative energies above 10 eV the non-reactive inelastic scattering of O + by H 2 , D 2 , and HD arises from impulsive elastic scattering of 0 + by individual H or D atoms. The relation of this impulsive non-reactive scattering to the reactive scattering from these systems is briefly discussed.

Neutron inelastic scattering from the intramolecular vibration of hydrogen at ≈516 meV (4162 cm−1) has been observed for the first time using the system C28Cs(H2)1.52 at 4 K. The data are consistent with an effective mass of the scattering particle of ≈1.33 amu which confirms the presence of H2 species. The extrapolated excitation energy at zero momentum transfer is, within experimental error, the same as the gas-phase value for H2, indicating little effect of the electronegative environment on the adsorbed hydrogen molecular force constant.

Neutron inelastic scattering measurements are reported for hexamethylenetetramine-d12 and for adamantane-d16 in the energy range 200–800 cm−1. The observed intensities are strongest for those modes of vibration with the largest deuterium displacements. These displacements were computed from a normal-coordinate analysis based on both neutron and optical data. In spite of the much smaller incoherent scattering cross section of deuterium as compared with hydrogen, the results show that the NIS technique can be used successfully on deuterated samples.

A neutron quasi-elastic investigation of the plastic phase of a randomly orientated sample of n -nonadecane shows good agreement with a simple continuous rotational diffusion model of the molecule about its long axis. No quasi-elastic broadening is observed in the lower temperature phase.

Methyl tunnel frequencies of 150 ± 20 MHz and 1.54 ± 0.1 GHz have been measured from inelastic peaks in the high-resolution inelastic neutron scattering spectrum of pentamethylbenzene. The Spectrum, with spin-lattice relaxation data, indicates that the five methyl groups reorient independently. The smaller frequency confirms the value obtained by nuclear magnetic relaxation resonance by Gabryś and van Gerven.

Coherent inelastic neutron scattering results have been obtained from a single crystal of hydrogenous (hydrogen content 44 at.%) 1-methylthymine. The results have been directly interpreted as acoustic phonons and effective elastic constants determined at 150 and 296 K.

Neutron inelastic scattering spectra of 1,2-dichloroethane crystal have been measured at three temperatures above and below 177°K where the crystal undergoes a broad phase transition. Two and three peaks have been observed in the high and low temperature phases, respectively. The frequency distribution g ( v ) has been calculated in the first Brillouin zone for the low temperature phase and is compared with the observed spectra. The results show that the phase transition at 177°K is associated with rotational motion of the molecule around the axis passing through two chlorine atoms.

The rational time correlation function obtained from the infrared vibrational band shape has been used to calculate the intensity of neutrons inelastically scattered by liquid HCI at 183°K. The agreement between theory and experiment is satisfactory.