Catalytic hydrogenation of carboxamides and esters by well-defined Cp*Ru complexes bearing a protic amine ligand

A novel catalytic method for the straightforward hydrogenation of carboxamides and esters to primary alcohols has been developed. Chiral modification in the ligand sphere of the well-defined Cp*Ru catalyst molecule opens up a new possibility for the development of an enantioselective hydrogenation of racemic substrates via dynamic kinetic resolution.     

Chiral ruthenabicyclic complexes: precatalysts for rapid, enantioselective, and wide-scope hydrogenation of ketones

A novel ruthenabicyclic complex with base shows excellent catalytic activity in the asymmetric hydrogenation of ketones. The turnover frequency of the hydrogenation of acetophenone reaches about 35,000 min(-1) in the best case, affording 1-phenylethanol in >99% ee. Several aliphatic and base-labile ketones are smoothly converted to the corresponding alcohols in high enantioselectivity. The catalytic cycle for this hydrogenation, in which the ruthenabicyclic structure of the catalyst is maintained, is proposed on the basis of the deuteration experiment and spectroscopic analysis data.     

Partial-filling affinity capillary electrophoresis of glycoprotein oligosaccharides derivatized with 8-aminopyrene-1,3,6-trisulfonic acid

Partial-filling affinity capillary electrophoresis has been applied to the simultaneous analysis of interactions between glycoprotein oligosaccharides and certain plant lectins. A lectin solution and a mixture of glycoprotein-derived oligosaccharides labeled with 8-aminopyrene-1,3,6-trisulfonic acid were introduced to a neutrally coated capillary in this order, and separated by application of a negative voltage. Interaction of a lectin with each oligosaccharide in the mixture was observed as the specific retardation or dissipation of peaks, in addition to the size/charge separation of oligosaccharides by zone electrophoresis in the remainder (≈90%) of the capillary. The strength of the interaction with lectin was controlled by introducing an appropriate volume of lectin solution. Application of various specificities of lectins indicated characteristic migration profiles of the oligosaccharides. Moreover, sequential injection of four lectins (Maachia amurensis mitogen, Sambucus sieboldiana agglutinin, Erythrina cristagalli agglutinin, Aleuria aurantia lectin) induced complete dissipation of complex-type oligosaccharides and enabled specific determination of the presence of high-mannose oligosaccharides without the interference or alteration of the electropherogram in porcine thyroglobulin. This method was also applied to determine the binding constants of ovalbumin-derived oligosaccharides to wheat germ agglutinin.     

Rapid determination of glyphosate, glufosinate, bialaphos, and their major metabolites in serum by liquid chromatography-tandem mass spectrometry using hydrophilic interaction chromatography

We developed a simple and rapid method for the simultaneous determination of phosphorus-containing amino acid herbicides (glyphosate, glufosinate, bialaphos) and their major metabolites, aminomethylphosphonic acid (AMPA) and 3-methylphosphinicopropionic acid (MPPA), in human serum. Serum samples were filtrated through an ultrafiltration membrane to remove proteins. The filtrate was then washed with chloroform, and injected into a liquid chromatography-tandem mass spectrometry (LC-MS/MS) system. Chromatographic separation was achieved on a hydrophilic interaction chromatography (HILIC) column. Determination of the target herbicides and metabolites was successfully carried out without derivatization or solid phase extraction (SPE) cartridge clean-up. The recoveries of these compounds, added to human serum at 0.2μg/mL, ranged from 94% to 108%, and the relative standard deviations (RSDs) were within 5.9%. The limits of detection (LODs) were 0.01μg/mL for MPPA, 0.02μg/mL for AMPA, 0.03μg/mL for both glyphosate and glufosinate, and 0.07μg/mL for bialaphos, respectively.     

Electron channeling X-ray microanalysis for partially filled skutterudite structure

Occupancy of Ce atoms on voids and coordinates of Sb atoms in a partially filled skutterudite CeFe6Ni2Sb24 were determined by the method for atomic location by channeling enhanced microanalysis (ALCHEMI), where characteristic X-ray intensities were measured and calculated at various electron incidence directions in a transmission electron microscope. The calculation was based on dynamical electron diffraction and inelastic scattering theories. The calculated intensities were significantly dependent on the occupation probability of Ce atoms on voids, the coordinates of Sb atoms and the sample thickness. Using the Levenberg-Marquardt least squares method, the occupation probability of Ce atoms and the coordinates of Sb atoms were 0.33 and 0 0.336 0.147, respectively.     

Structures of two new phenolic glycosides, kaempferiaosides A and B, and hepatoprotective constituents from the rhizomes of Kaempferia parviflora

Two new phenolic glycosides, kaempferiaosides A and B were isolated from the rhizomes of Kaempferia parviflora (Zingiberaceae) together with 24 known compounds. Their structures including absolute stereochemistry were elucidated on the basis of chemical and spectroscopic evidence. Among the isolates, 5,3'-dihydroxy-3,7,4'-trimethoxyflavone showed higher activity than silybin, a commercial hepatoprotective agent.     

A theoretical investigation on photocatalytic oxidation on the TiO2 surface

The TiO(2) photocatalytic oxidation mechanism was theoretically investigated by using long-range corrected time-dependent density functional theory (LC-TDDFT) with a cluster model of the anatase TiO(2)(001) surface. We found that LC-TDDFT with the cluster model quantitatively reproduces the photoexcitations of the TiO(2) surface by calculating the electronic spectra of a clean TiO(2) surface and one with oxygen defects. We calculated the electronic spectra of a molecularly adsorbed TiO(2) surface for the adsorptions of phenol, methanol, and methane molecules as typical organic molecules. We obtained the surprising result that the main peak of the phenol-adsorbed TiO(2) surface, which overlaps with the main peak of the clean TiO(2) surface, corresponds to charge transfers from the phenol molecule to the TiO(2) surface. This indicates that the TiO(2) photocatalytic oxidation proceeds through direct charge transfer excitation from the substrate molecules to the TiO(2) surface. In contrast, we found slight and no charge transfer for methanol and methane adsorption, respectively, in agreement with the experimental findings for their reactivities. In light of these results, we propose a new mechanism for heterogeneous TiO(2) photocatalytic oxidations.     

Evaluation of electrodeposited gold nanostructures for applications in QCM sensing

The electrodeposition of gold nanostructures increases the surface area of a biosensor, which brings an enhancement of the sensitivity by increasing the amount of analyte binding to the surface. To evaluate the relationship among the surface structure, the area and the analyte binding, we quantitatively analyzed them for quartz crystal microbalance (QCM) sensing by scanning electron microscopy and cyclic voltammetry measurements. The results indicate a several-times increase of analyte bindings, and also the limitation of the sensing performance.     

Quantitative determination of phosphatidylcholine hydroperoxides during copper oxidation of LDL and HDL by liquid chromatography/mass spectrometry

1-Palmitoyl-2-linoleoylphosphatidylcholine monohydroperoxide (PC 16:0/18:2-OOH) and 1-stearoyl-2-linoleoylphosphatidylcholine monohydroperoxide (PC 18:0/18:2-OOH) were measured by liquid chromatography/mass spectrometry (LC/MS) using nonendogenous 1-palmitoyl-2-heptadecenoylphosphatidylcholine monohydroperoxide as an internal standard. The calibration curves for synthetic PC 16:0/18:2-OOH and PC 18:0/18:2-OOH, which were obtained by direct injection of the internal standard into the LC/MS system, were linear throughout the calibration range (0.8-12.8 pmol). Within-day and between-day coefficients of variation were less than 10%, and the recoveries were between 86% and 105%. The limit of detection (LOD) and the limit of quantification (LOQ) were determined using synthetic standards. The LOD (signal-to-noise ratio 3:1) was 0.01 pmol, and the LOQ (signal-to-noise ratio 6:1) was 0.08 pmol for both PC 16:0/18:2-OOH and PC 18:0/18:2-OOH. With use of this method, the concentrations of PC 16:0/18:2-OOH and PC 18:0/18:2-OOH in the lipoprotein fractions during copper-mediated oxidation were determined. We prepared oxLDL and oxHDL by incubating native LDL and native HDL from human plasma (n = 10) with CuSO(4) for up to 4 h. The time course of the PC 16:0/18:2-OOH and PC 18:0/18:2-OOH levels during oxidation consisted of three phases. For oxidized LDL, both compounds exhibited a slow lag phase and a subsequent rapidly increasing propagation phase, followed by a gradually decreasing degradation phase. In contrast, for oxidized HDL, both compounds initially exhibited a prompt propagation phase with a subsequent plateau phase, followed by a rapid degradation phase. The analytical LC/MS method for phosphatidylcholine hydroperoxides might be useful for the analysis of biological samples.     

The effect of mass transfer on the temperature gradient of a crystal growing from melt

The change in the temperature gradient on the crystal side while the rate of crystal growth from melt is varied has long been debated. Abe and Takahashi have recently reported an unambiguous experimental demonstration that the temperature gradient is a decreasing function of the growth rate, which is different from previous theories, experimental results, and widely held notion of other researchers. The present paper provides a theoretical basis for this seemingly peculiar effect of the growth rate on the temperature gradient. The essential matter is the effect of mass transfer, the role of which had been commonly disregarded in old studies. Although the rate of mass transfer is not large compared to that of heat conduction, it is proven that the temperature gradient is subjected to the mass transfer in a definite manner. Our analysis shows that the effect becomes significant when the crystal diameter is large, which is consistent with the experimental observation. Another effect of the mass transfer is the change in the shape of melt/crystal interface. In old studies, the temperature gradient was determined by Stefan's equation; however, this treatment confuses the cause and effect. The temperature gradient should be determined by the fundamental equation of heat conduction. When the gradient is determined in this way, the shape of the melt/crystal interface spontaneously adjusts to satisfy Stefan's equation.