Pressure effects on collective density fluctuations in water and protein solutions

Neutron Brillouin scattering and molecular dynamics simulations have been used to investigate protein hydration water density fluctuations as a function of pressure. Our results show significant differences between the pressure and density dependence of collective dynamics in bulk water and in concentrated protein solutions. Pressure-induced changes in the tetrahedral order of the water HB network have direct consequences for the high-frequency sound velocity and damping coefficients, which we find to be a sensitive probe for changes in the HB network structure as well as the wetting of biomolecular surfaces

Texture and structure studies on marbles from Villa Adriana via neutron diffraction technique

The primary objective of this work is the characterisation of ancient roman marble fragments through neutron diffraction, a non-destructive experimental method. The neutron diffractometer ROTAX, operating at the pulsed neutron source ISIS, in the UK has been used to determine composition down to a 0.5 wt% level and to obtain information on preferred orientations of grains in the marble tiles

The puzzling problem of cardiolipin membrane-cytochrome c interactions: A combined infrared and fluorescence study

The interaction of cytochrome c (cyt c) with natural and synthetic membranes is known to be a complex phenomenon, involving both protein and lipid conformational changes. In this paper, we combined infrared and fluorescence spectroscopy to study the structural transformation occurring to the lipid network of cardiolipin-containing large unilamellar vesicles (LUVs). The data, collected at increasing protein/lipid ratio, demonstrate the existence of a multi-phase process, which is characterized by: (i) the interaction of cyt c with the lipid polar heads; (ii) the lipid anchorage of the protein on the membrane surface; and (iii) a long-distance order/disorder transition of the cardiolipin acyl chains. Such effects have been quantitatively interpreted introducing specific order parameters and discussed in the frame of the models on cyt c activity reported in literature

The New Sorgentina Fusion Source-NSFS: 14 MeV neutrons for fusion and beyond

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On the nitrogen-induced far-infrared absorption spectra

The rototranslational absorption spectrum of gaseous N2 is analyzed, considering quadrupolar and hexadecapolar induction mechanisms. The available experimental data are accounted for by using a line-shape analysis in which empirical profiles describe the single-line translational profiles. We thus derive the simple procedure that allows one to predict the N2 spectrum at any temperature. On the basis of the results obtained for the pure gas, we also propose a procedure to compute the far-infrared spectrum of the N2–Ar gaseous mixture. The good agreement between computed and experimental N2–Ar data indicates that it is possible to predict the far-infrared absorption induced by N2 on the isotropic polarizability of any interacting partner

New determination of the He-Xe gas-gas demixing surface in the high Xe concentration region

By analysing the results of a previous experimental work it has been found that the transition changes from a liquid-gas type at low pressure to a liquid-liquid one at high pressure. However, not much experimental data are available in the literature at high Xe concentrations, and some criticism can be applied to them. Therefore, new measurements of the isobaric coexistence curves for He-Xe mixtures at three pressures (80, 132, 200 atm) have been performed, with the use of a more precise technique, based on energy resolved neutron transmission measurements. A qualitative agreement with the previous data has been found, while a disagreement is present in the behaviour of T c versus p c, thus confirming our picture of a change in the nature of the transition as the pressure increase

Inelastic and quasi-elastic dynamics in superoxide dismutase

Inelastic and quasi-elastic neutron scattering were used to determine the dynamics at a molecular level of the enzyme Cu, Zn superoxide dismutase, in the frequency and momentum range 0-15 meV and 0.3-8.5 Angstrom(-1), at various temperatures between 4-320 K. The results are compared with that of myoglobin

Far infrared absorption of the gaseous CH4–Ar mixture

We present the first measurements of the rototranslational absorption spectrum of the CH4cm –Ar gaseous system in the far infrared region 40–600−1K at densities as low as possible; the binary absorption spectrum of the CH . Measurements were made at 296, 243, and 1954–Ar pair was then obtained. We performed a line-shape analysis of these spectra following the procedure previously introduced for pure methane. We find that the experimental data can be described at high frequencies by using ab initio values of the octopole and hexadecapole multipole moments and anisotropic overlap intensities very close to those used for pure methane. At low frequencies, the computed spectrum is significantly lower than the experimental data at any temperature. We thus include in our analysis a low-frequency spectral contribution associated with the isotropic overlap induction mechanism. Good fits of the experimental data are then obtain at each temperature over all the spectral range

Enhancing the performances of a resonance detector spectrometer for deep inelastic neutron scattering measurements

The possibility is explored to sum up neutron Compton profiles at different scattering angles in deep inelastic neutron scattering measurements within the Resonance Detector (RD) configuration to enhance the statistics for a more reliable extraction of the momentum distribution of the constituents in the target. The RD configuration allows to select the energy of the scattered neutrons up to several tens of electron Volt, thus accessing energy and wave vector transfers well above 1 eV and 30 ˚A 1, respectively. In the high-q/o regime, the final state effects could be considered as negligible, as shown in a series of simulations using a Monte Carlo method with different inverse geometry instrument setups. The simulations show that it could be possible to conceive an instrument set up where the RD configuration allows the proper summation of several spectra at different scattering angles, providing a good separation of the proton recoil signal from that of the heavier atoms, thus avoiding the cell subtraction by fitting procedure