The effect of UV irradiation on the reduction of Au(III) ions adsorbed on manganese dioxide.

The effect of UV (ultraviolet) irradiation on the adsorption of Au(III) ions on manganese dioxide and their reduction to Au(0) (gold with 0 valence state) was investigated using XPS (X-ray photoelectron spectroscopy) and 197Au M?ssbauer spectroscopy. The UV irradiation accelerated the adsorption and the reduction. From the fact that the proportion of Au(0) estimated from Au 4f XPS spectra for surface analysis was significantly smaller than that from 197Au M?ssbauer spectra for bulk analysis, we deduced that Au(0) was interpenetrated to the inside of manganese dioxide (into deeper places than about 30 A) where XPS is impossible to detect. The content of surface hydroxyl groups on manganese dioxide also increased due to the UV irradiation. The relationship between the charge in the content of hydroxyl groups and the interpenetration of Au(0) is discussed.     

Studies on orally active cephalosporin esters. IV. Effect of the C-3 substituent of cephalosporin on the gastrointestinal absorption in mice

The effect of the C-3 substituent on the oral absorbability of pivaloyloxymethyl (POM) ester of cephalosporin in mice is described. The C-3 substituent affects the physicochemical and biochemical properties of POM ester, such as lipophilicity, water solubility, chemical stability and enzymatic stability. Quantitative analyses of the relationships between these properties and the oral bioavailability have been attempted. Lipophilicity made a parabolic contribution to the absorption. The optimum log P octanol/water value was estimated to be around 2.22. The chemical isomerization of the cephem double bond from delta 3 to delta 2 in the intestinal lumen prior to absorption contributed linearly to decrease of absorption. In the case of POM ester having a larger isomerization rate, more delta 2 isomer was detected in feces and urine. Enzymatic hydrolysis of POM ester to the parent acid in intestinal tissue was faster for a more lipophilic ester. Hydrolytic activity, which was detected in the content of the intestinal lumen, would lower the absorption. The effect of the C-3 substituent on water solubility was not important for the absorption of cephalosporin employed in the present study. Isomerization of the double bond, which was found to be characteristic for cephalosporin ester, presented a problem in the prodrug approach for oral use.     

Diffuse mode bifurcation of soil causing convection-like shear investigated by group-theoretic image analysis

Diffuse mode bifurcation of soil under plane-strain compression test is shown, by means of an image analysis based on group-theoretic bifurcation theory, to trigger convection-like shear and to precede shear band formation. First digital photos of Toyoura sand specimens are processed by PIV (particle image velocimetry) to gather digitized images of deformation. Next bifurcation from a uniform state is detected by expanding these images into the double Fourier series and finding a predominant harmonic diffuse bifurcation mode based on that theory. This harmonic bifurcation mode, which is the mixture of a few harmonic functions, expresses complex convection-like shear. Last bifurcation from a non-uniform state is detected by decomposing each image into a few images with different symmetries to extract non-harmonic diffuse bifurcation modes. Diffuse modes of bifurcation, which hitherto were hidden behind predominant uniform compressive deformation, have thus been made transparent by virtue of the group-theoretic image analysis proposed. A possible course of deformation suggested herein is the evolution of diffuse mode bifurcation with a convection-like bifurcation mode breaking uniformity and symmetry, followed by the formation of shear bands through localization.     

Coherent fine scale eddies in turbulence transition of spatially-developing mixing layer

To investigate the relationship between characteristics of the coherent fine scale eddy and a laminar–turbulent transition, a direct numerical simulation (DNS) of a spatially-developing turbulent mixing layer with Re_ω,0 = 700 was conducted. On the onset of the transition, strong coherent fine scale eddies appears in the mixing layer. The most expected value of maximum azimuthal velocity of the eddy is 2.0 times Kolmogorov velocity (u_k), and decreases to 1.2u_k, which is an asymptotic value in the fully-developed state, through the transition. The energy dissipation rate around the eddy is twice as high compared with that in the fully-developed state. However, the most expected diameter and eigenvalues ratio of strain rate acting on the coherent fine scale eddy are maintained to be 8 times Kolmogorov length (η) and :β:γ = −5:1:4 in the transition process. In addition to Kelvin–Helmholtz rollers, rib structures do not disappear in the transition process and are composed of lots of coherent fine scale eddies in the fully-developed state instead of a single eddy observed in early stage of the transition or in laminar flow.     

Efficient calculation of two‐electron integrals for high angular basis functions

The computation of electron repulsion integrals (ERIs) is the most time‐consuming process in the density functional calculation using Gaussian basis set. Many temporal ERIs are calculated, and most are stored on slower storage, such as cache or memory, because of the shortage of registers, which are the fastest storage in a central processing unit (CPU). Moreover, the heavy register usage makes it difficult to launch many concurrent threads on a graphics processing unit (GPU) to hide latency. Hence, we propose to optimize the calculation order of one‐center ERIs to minimize the number of registers used, and to calculate each ERI with three or six co‐operating threads. The performance of this method is measured on a recent CPU and a GPU. The proposed approach is found to be efficient for high angular basis functions with a GPU. When combined with a recent GPU, it accelerates the computation almost 4‐fold. © 2014 Wiley Periodicals, Inc.     

Engineering the promiscuous racemase activity of an arylmalonate decarboxylase

Variant G74C of arylmalonate decarboxylase (AMDase) from Bordatella bronchoseptica has a unique racemising activity towards profens. By protein engineering, variant G74C/V43A with a 20-fold shift towards promiscuous racemisation was obtained, based on a reduced activity in the decarboxylation reaction and a two-fold increase in the racemisation activity. The mutant showed an extended substrate range, with a 30-fold increase in the reaction rate towards ketoprofen. Molecular dynamics simulations and the substrate profile of the racemase indicate that the steric and polar effects of the substrate structure play a more dominant role on catalysis than mere kinetic α-proton acidity. The observation that the conversion of β,γ-unsaturated carboxylic acids does not lead to a rearrangement to form their α,β isomers indicates a concerted rather than a stepwise mechanism. Interestingly, a substrate bearing a nitro group instead of the carboxylic acid group on the α-carbon atom was also converted by the racemase.     

Deciphering the molecular details for the binding of the prion protein to main ganglioside GM1 of neuronal membranes

The prion protein (PrP) resides in lipid rafts in?vivo, and lipids modulate misfolding of the protein to infectious isoforms. Here we demonstrate that binding of recombinant PrP to model raft membranes requires the presence of ganglioside GM1. A combination of liquid- and solid-state NMR revealed the binding sites of PrP to the saccharide head group of GM1. The binding epitope for GM1 was mapped to the folded C-terminal domain of PrP, and docking simulations identified key residues in the C-terminal region of helix C and the loop between strand S2 and helix B. Crucially, this region of PrP is linked to prion resistance in?vivo, and structural changes caused by lipid binding in this region may explain the requirement for lipids in the generation of infectious prions in?vitro.     

Organogold clusters protected by phenylacetylene

A new class of monolayer-protected Au clusters with Au-C covalent bonds (organogold clusters) was synthesized by ligating phenylacetylene (PhC≡CH) to PVP-stabilized Au clusters. Matrix-assisted laser desorption ionization mass spectrometry revealed for the first time a series of stable compositions of the organogold (Au:C(2)Ph) clusters.     

Electroless galvanic inks on inorganic WO3/Al boards

A tungsten trioxide (WO(3)) coated aluminium (Al) substrate exhibits a reversible color change without light irradiation or an electric power supply. The sample turns blue upon exposure to an aqueous acid solution, but exposure to oxygen restores the original light yellow color. This color change is due to the galvanic redox reaction between WO(3) and Al.