Synchrotron x-ray-diffraction study of α-cristobalite at high pressure and high temperature

Abstract

Energy-dispersive x-ray diffraction using synchrotron radiation was carried out on α-cristobalite to 3 GPa and 350°C in a cubic anvil press. A cascading structural phase transition occurred beyond 0.61 GPa at room temperature. The transition was accompanied by a splitting of most of the a-cristobalite reflections: the (111) reflection at 0.61 GPa through the (211) reflections at 2.13 GPa, with many other lines between. The pressure of this transition decreased with increasing temperature.     

Mordell–Tornheim multiple zeta values at non-positive integers

We study the Mordell–Tornheim multiple zeta function with all the same parameters. Its values at non-positive integers are evaluated explicitly.     

A Remark on the Global Existence of a Third Order Dispersive Flow into Locally Hermitian Symmetric Spaces

We prove time-global existence of solutions to the initial value problem for a third order dispersive flow into compact locally Hermitian symmetric spaces. The equation under consideration generalizes two-sphere-valued completely integrable systems modeling the motion of vortex filament. Unlike one-dimensional Schrödinger maps, our third order equation is not completely integrable under the curvature condition on the target manifold in general. The idea of our proof is to exploit two conservation laws and an “almost conserved quantity” which prevents the formation of a singularity in finite time.     

Evaluations of molecular docking programs for virtual screening

Structure-based virtual screening is carried out using molecular docking programs. A number of such docking programs are currently available, and the selection of docking program is difficult without knowing the characteristics or performance of each program. In this study, the screening performances of three molecular docking programs, DOCK, AutoDock, and GOLD, were evaluated with 116 target proteins. The screening performances were validated using two novel standards, along with a traditional enrichment rate measurement. For the evaluations, each docking run was repeated 1000 times with three initial conformations of a ligand. While each docking program has some merit over the other docking programs in some aspects, DOCK showed an unexpectedly better screening performance in the enrichment rates. Finally, we made several recommendations based on the evaluation results to enhance the screening performances of the docking programs.     

Label-free detection of protein-protein interactions at the GaAs/water interface through surface infrared spectroscopy: discrimination between specific and nonspecific interactions by using secondary structure analysis

Here, we propose a label-free detection of protein-protein interactions that enables simultaneous qualitative analysis of target proteins by using Fourier transform infrared (FTIR) absorption spectroscopy in multiple internal reflection geometry (MIR-FTIR). Using this method, the target proteins were detected based on the peak height of the amide I and amide II bands, while discrimination of specific and nonspecific signals is made based on the secondary structure of the analytes, which is determined through second-derivative analysis of the amide I band. As a model system, an antigen peptide was immobilized on the surface of GaAs, which was transparent to mid-infrared light, and the interaction with its antibody was examined in aqueous media. We demonstrated that the binding of the antibody to the antigen immobilized on a GaAs surface selectively gave rise to beta-sheet amide I vibrations (1639 and 1690 cm-1), while no structurally related signals were induced by nonspecifically adsorbed proteins. The peak height of the beta-peak (1639 cm-1) in the amide I band linearly increased with the antiserum concentration as well as that of the amide II band. The detection limit (S/N = 3) was a 1:36 000 dilution for the amide I signal. In addition, through the use of surface-sensitive MIR-FTIR, the present sensor selectively detected the antigen-antibody interactions at the surfaces without being affected by the presence of bulk species, enabling rapid and wash-free detection. Our method provides not only rapid label-free detection of protein-protein interactions but a more accurate discrimination between specific and nonspecific interactions through the use of the secondary structure of the target proteins as a measure for the specific signals.     

Time-Resolved Measurements of in vivo Optical Properties of Piglet Brain

The in vivo optical properties of a piglet brain were measured using a time-resolved system at three different wavelengths (759, 794, 824 nm). To separate the contribution of different head layers to the detected signals, the measurements were acquired from the surfaces of skin, skull, dura mater and brain. The source detector distance was chosen to assure a mean penetration depth within each layer. Measurements were analyzed and compared with the results of other in vivo measurements reported in literature.     

Direct conversion to 2-phenyl-4-quinolones via a 4-alkoxyflavylium salt from a naturally occurring flavanone

A flavanone, in which a hydroxyl group at the 5-position was protected with a methyl group, converted to the corresponding 5-methoxy-2-phenyl-4-quinolone via flavylium salt under mild conditions. Flavanone-O-rhamnoglucoside, naringin, was also converted to 5-methoxy-2-phenyl-4-quinolon-7-O-rhamnoglucoside in the same way in an overall 25% yield.     

Influence of nanometer scale film structure of ZDDP tribofilm on Its mechanical properties: A computational chemistry study

We investigated the influence of a nanometer scale film structure of a tribofilm generated from zinc dialkyldithiophosphate (ZDDP) anti-wear additive on its mechanical properties using a combined molecular dynamics (MD) and finite element (FE) method. The frictional behavior of an interface between a native iron oxide layer on steel surface and zinc metaphosphate - regarded as a model material of ZDDP tribofilm - was firstly studied using the MD method. The results showed that the iron atoms in the oxide layer diffused into the phosphate layer during the friction process. The zinc atoms in the phosphate layer also diffused into the oxide layer. Significant interdiffusion of iron and zinc atoms was observed with increasing simulation time. Thus, metallic phosphate with a gradient composition of iron and zinc atoms was formed on the phosphate/oxide interface. We then constructed an axisymmetric nanoindentation simulation model from the MD-derived structures at a certain simulation time and carried out a FE calculation. As a result, we found that the rubbed ZDDP tribofilm, including the phosphate with the gradient composition of metallic atoms, showed larger contact stiffness and hardness. The combined MD/FE simulation indicates that the tribofilm becomes stiffer and harder due to the interdiffusion of iron and zinc atoms on the tribofilm/oxide interface. We have found that the gradient composition formation in ZDDP tribofilm during friction process influences on its mechanical properties.     

Effect of Hydrated Ionic Liquid on Photocycle and Dynamics of Photoactive Yellow Protein

The mechanism by which proteins are solvated in hydrated ionic liquids remains an open question. Herein, the photoexcitation dynamics of photoactive yellow protein dissolved in hydrated choline dihydrogen phosphate (Hy[ch][dhp]) were studied by transient absorption and transient grating spectroscopy. The photocyclic reaction of the protein in Hy[ch][dhp] was similar to that observed in the buffer solution, as confirmed by transient absorption spectroscopy. However, the structural change of the protein during the photocycle in Hy[ch][dhp] was found to be different from that observed in the buffer solution. The known change in the diffusion coefficient of the protein was apparently suppressed in high concentrations of [ch][dhp], plausibly due to stabilization of the secondary structure.