Abstract:The neutron instruments suite, installed at the spallation neutron source of the Materials and Life Science Experimental Facility (MLF) at the Japan Proton Accelerator Research Complex (J-PARC), is reviewed. MLF has 23 neutron beam ports and 21 instruments are in operation for user programs or are under commissioning. A unique and challenging instrumental suite in MLF has been realized via combination of a high-performance neutron source, optimized for neutron scattering, and unique instruments using cutting-edge technologies. All instruments are/will serve in world-leading investigations in a broad range of fields, from fundamental physics to industrial applications. In this review, overviews, characteristic features, and typical applications of the individual instruments are mentioned.
An imaging plate Weissenberg camera was installed in the BL04B2 beamline of SPring-8 aiming at automated crystal structure determinations of small molecules. Since this beamline is designed to provide X-rays with the energies higher than 37 keV (λ < 0.33 Å), this camera is advantageous in crystal structure analyses of heavily X-ray absorbing materials. The title crystal structure analysis led to precise positional parameters and well-behaved displacement parameters not only for heavy atoms but also for light atoms.
The
crystal structure of polydiacetylene giant single crystal has
been analyzed on the basis of the two different methods of wide-angle
neutron diffraction and X-ray diffraction. The X-ray result gives
us the total electron density distribution [ρ(x)] of polymer chain. The neutron result tells the positions
of atomic nuclei, which can allow us to speculate the electron density
distributions [ρ
0(x)] around
the nonbonded isolated atoms. As a result, the so-called bonded (or
deformed) electron density Δρ(x) [≡
ρ(x) – ρ0(x) = ρX(x) – ρN(x)], i.e., the electron density distribution due to
the conjugation among the covalently bonded atoms along the polymer
chain, can be estimated using the two information obtained by the
X-ray and neutron data analyses (the so-called X-ray–neutron
subtraction (X–N) method). The present report
is the first example of the application of X–N method to the
synthetic polymer species. The Δρ(x) derived
for polydiacetylene was found similar to that of the low-molecular-weight
model compound having the similar electronically conjugated chemical
formula. The Δρ(x) was calculated by the
density functional theory, which was in a good agreement with the
experimental result qualitatively.
The planarity of the peptide bond is important for the stability and structure formation of proteins. However, substantial distortion of peptide bonds has been reported in several high-resolution structures and computational analyses. To investigate the peptide bond planarity, including hydrogen atoms, we report a 1.2-Å resolution neutron structure of the oxidized form of high-potential iron-sulfur protein. This high-resolution neutron structure shows that the nucleus positions of the amide protons deviate from the peptide plane and shift toward the acceptors. The planarity of the H─N─C═O plane depends strongly on the pyramidalization of the nitrogen atom. Moreover, the orientation of the amide proton of Cys
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is different in the reduced and oxidized states, possibly because of the electron storage capacity of the iron-sulfur cluster.
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