Measuring velocity of sound with nuclear resonant inelastic x-ray scattering

Nuclear resonant inelastic x-ray scattering is used to measure the projected partial phonon density of states of materials. A relationship is derived between the low-energy part of this frequency distribution function and the sound velocity of materials. Our derivation is valid for harmonic solids with Debye-like low-frequency dynamics. This method of sound velocity determination is applied to elemental, composite, and impurity samples which are representative of a wide variety of both crystalline and noncrystalline materials. Advantages and limitations of this method are elucidated

Dynamics of Metal Centers Monitored by Nuclear Inelastic Scattering

Nuclear inelastic scattering of synchrotron radiation has been used now since 10 years as a tool for vibrational spectroscopy. This method has turned out especially useful in case of large molecules that contain a M\"ossbauer active metal center. Recent applications to iron-sulfur proteins, to iron(II) spin crossover complexes and to tin-DNA complexes are discussed. Special emphasis is given to the combination of nuclear inelastic scattering and density functional calculations

Dissipative electro-elastic network model of protein electrostatics

We propose a dissipative electro-elastic network model (DENM) to describe the dynamics and statistics of electrostatic fluctuations at active sites of proteins. The model combines the harmonic network of residue beads with overdamped dynamics of the normal modes of the network characterized by two friction coefficients. The electrostatic component is introduced to the model through atomic charges of the protein force field. The overall effect of the electrostatic fluctuations of the network is recorded through the frequency-dependent response functions of the electrostatic potential and electric field at the active site. We also consider the dynamics of displacements of individual residues in the network and the dynamics of distances between pairs of residues. The model is tested against loss spectra of residue displacements and the electrostatic potential and electric field at the heme's iron from all-atom molecular dynamics simulations of three hydrated globular proteins

In-vivo X-ray Dark-Field Chest Radiography of a Pig

X-ray chest radiography is an inexpensive and broadly available tool for initial assessment of the lung in clinical routine, but typically lacks diagnostic sensitivity for detection of pulmonary diseases in their early stages. Recent X-ray dark-field (XDF) imaging studies on mice have shown significant improvements in imaging-based lung diagnostics. Especially in the case of early diagnosis of chronic obstructive pulmonary disease (COPD), XDF imaging clearly outperforms conventional radiography. However, a translation of this technique towards the investigation of larger mammals and finally humans has not yet been achieved. In this letter, we present the first in-vivo XDF full-field chest radiographs (32 × 35 cm²) of a living pig, acquired with clinically compatible parameters (40s scan time, approx. 80 μSv dose). For imaging, we developed a novel high-energy XDF system that overcomes the limitations of currently established setups. Our XDF radiographs yield sufficiently high image quality to enable radiographic evaluation of the lungs. We consider this a milestone in the bench-to-bedside translation of XDF imaging and expect XDF imaging to become an invaluable tool in clinical practice, both as a general chest X-ray modality and as a dedicated tool for high-risk patients affected by smoking, industrial work and indoor cooking

Protein dynamics on different timescales

Structure and dynamics determine the function of proteins. This contribution discusses two aspects of protein dynamics, the structural fluctuation and the structural relaxation connected with conformational changes. Myoglobin and haemoglobin were investigated. To cover a wide time range different experimental techniques had to be used. Moreover, measurements in a large temperature regime were used to separate contributions from different modes of motions. Phonon assisted Mo ̈ssbauer effect using synchrotron radiation allowed the study of the harmonic vibrations which have characteristic times of 1 fs to 0.6 ps. They are present in the whole temperature range from cryogenic to room temperature. With a combination of neutron structure analysis and incoherent neutron scattering it was possible to distinguish three types of hydrogen mean square displacements which are present only above a characteristic temperature Tc: These are the backbone-like (slower than about 100 ps), methyl-like (partly slower partly faster than about 100 ps) and lysine-like (faster than about 100 ps) displacements. The exceptional high energy resolution of Mo ̈ssbauer absorption on 57Fe allowed the measurement of quasi diffusive modes of molecular segments which have characteristic times slower than 1 ns and are present only above Tc. Conformational changes from the ligated to the unligated structure of myoglobin and haemoglobin were investigated by creating a metastable interme- diate and observing the relaxation into the equilibrium conformation. A metastable state was obtained by X-ray irradiation. Structural relaxation was investigated as a function of time and temperature using the Mo ̈ssbauer hyperfine interactions as indicator. Furthermore it was possible to measure intermediates created by photolysis of a ligand with temperature dependent X-ray structure analysis or time dependent X-ray structure analysis with the Laue technique. It was shown that the quasi diffusive structural fluctuations above Tc strongly facilitate structural relaxations

Vibrational properties of the polymeric spin crossover (SCO) Fe(ii) complexes [{Fe(4-amino-1,2,4-triazole) 3}X 2] n: A nuclear inelastic scattering (NIS), Raman and DFT study

The vibrational properties of the cationic spin crossover (SCO) coordination polymers [{Fe(4-amino-1,2,4-triazole) 3} +2] n containing the anions chlorine, methanosulfonate and 1-naphthalenesulfonate have been studied via nuclear inelastic scattering of synchrotron radiation (NIS) as well as by Raman spectroscopy. Although the different anions have a strong influence on the spin crossover temperature, they have little effect on the positions of the spin marker bands in the NIS and Raman spectra. By comparing the line positions of the NIS spin marker bands with those observed by Raman spectroscopy, it has been possible to distinguish vibrations symmetry (A u or A g) because modes of A u and A g symmetries are NIS active, but only the A g modes are Raman active. The normal mode analysis of charge compensated cationic pentameric and hexameric model structures which have been obtained by density functional calculations reproduces the experimentally observed mode frequencies and the geometry optimization reproduces iron-ligand distances reported for these and related SCO coordination complexes. The effect of charge compensation appears to be independent of the choice of the functional and the basis set which shows that DFT calculations using B3LYP in conjunction with the basis set CEP-31G are a time effective approach in order to study vibrational properties of Fe(ii) SCO compounds. This journal is © 2012 the Owner Societies