Steroidal glycosides from the underground parts of Solanum sodomaeum

A new steroidal glycoside has been isolated from the underground parts of Solanum sodomaeum L., along with seven known steroidal glycosides. Their chemical structures were determined on the basis of spectroscopic data and chemical evidence, and the structure of one known pregnane type glycoside was corrected. In addition, their antiproliferative activity against human promyelocytic leukemia (HL-60) cells was investigated, and five compounds exhibited stronger activity than cisplatin.     

Synthesis and structure of dilacunary decatungstogermanate, [gamma-GeW10O36]8-

The dilacunary decatungstogermanate [gamma-GeW10O36]8- (1) has been synthesized and structurally characterized in solution and in the solid state. Reaction of germanium dioxide with sodium tungstate in aqueous acidic medium results in the formation of [beta2-GeW11O39]8- (2), which is then used as a precursor for the synthesis of 1. The (183)W spectrum of 2 shows the expected 11 peaks of equal intensity, whereas that of 1 exhibits the expected three peaks with relative intensities 2:2:1. Polyanion 1 represents a novel lacunary polyoxometalate, giving rise to a multitude of derivatives by reaction with transition metals, lanthanides, and other electrophiles.     

Enzyme treatment-free and ligation-independent cloning using caged primers in polymerase chain reactions

A new simple scheme for constructing recombinant vectors that does not require any restriction enzyme, ligase, or any other special enzyme treatment has been developed. By using caged primers in PCR, unnatural sticky-ends of any sequence, which are sufficiently long for ligation-independent cloning (LIC), are directly prepared on the product after a brief UVA irradiation. Target genes and vectors amplified by this light-assisted cohesive-ending (LACE) PCR join together in the desired arrangement in a simple mixture of them, tightly enough to be repaired and ligated in competent cells.     

New speckle control technique using high-speed electro-optic modulators with resonant electrode and polarization-reversed structures

We propose a new technique for reducing speckle noise in laser displays utilizing a high-speed optical phase modulator for expanding the laser beam spectrum. By adopting standing-wave resonant electrodes and polarization-reversed structures to LiTaO₃ electro-optic modulators, high-efficiency phase modulation with a large modulation index at high microwave frequency ranges is obtainable for different color laser beams at the same time. This enables us to expand laser spectra to over 100 GHz and reduce speckle noise. The device design, fabrication, and experimental demonstration for speckle control are reported.     

Control over Internal Structure of Liquid Crystal Polymer Nanofibers by Electrospinning

Liquid crystal polymer nanofibers with a diameter ranging from 0.13 to 4.71 µm were prepared by electrospinning from a main‐chain liquid crystalline polyester, BB‐5(3‐Me). WAXD measurements showed that the formation and orientation of the ordered structure in the electrospun fibers were controlled by the fiber diameter formed during electrospinning. For BB‐5(3‐Me), the SmA structure with two layer spacings was formed in the fiber during the electrospinning. Under optimal spinning conditions, the SmA structure is highly oriented in the fiber. In addition, annealing transformed the metastable SmA structure in the BB‐5(3‐Me) fiber into stable SmCA one.

     

Determination of perfluorooctanoic acid and perfluorooctane sulfonate by automated in-tube solid-phase microextraction coupled with liquid chromatography-mass spectrometry

We have developed a simple, rapid, and sensitive method for the determination of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) by on-line in-tube solid-phase microextraction (SPME) coupled with liquid chromatography-mass spectrometry (LC-MS). PFOA and PFOS were separated within 10 min by high-performance liquid chromatography using an Inertsil ODS-3 column and 10 mM ammonium acetate/methanol (35/65, v/v) as a mobile phase at a flow rate of 0.25 mL min⁻¹. Electrospray ionization conditions in the negative ion mode were optimized for MS detection of PFOA and PFOS. The optimum in-tube SPME conditions were 20 draw/eject cycles with a sample size of 40 μL using a CP-Pora PLOT amine capillary column as the extraction device. The extracted compounds could be desorbed easily from the capillary by passage of the mobile phase, and no carryover was observed. Using the in-tube SPME LC-MS method, good linearity of the calibration curve (r = 0.9990 for PFOA, r = 0.9982 for PFOS) was obtained in the range of 0.05-5 ng mL⁻¹ each compound. The detection limits (S/N = 3) for PFOA and PFOS were 1.5 and 3.2 pg mL⁻¹, respectively. The method described here showed about 100-fold higher sensitivity than the direct injection method. The within-day and between-day precisions (relative standard deviations) were below 3.7 and 6.0%, respectively. This method was applied successfully to the analysis of PFOA and PFOS in environmental water samples and to the elution test from a Teflon^®-coated frying pan without interference peaks. The recoveries of PFOA and PFOS spiked into river samples were above 81%, and PFOA was detected at pg mL⁻¹ levels in environmental water samples and eluate from the frying pan.     

Cooperativity of copper and molybdenum centers in polyoxometalate-based electrocatalysts: cyclic voltammetry, EQCM, and AFM characterization

Electrochemical behaviors of selected Dawson-type polytungstates including 2-K10[P2W15Mo2O61box] where the symbol [box] designates a vacant site, alpha2-K7[Fe(OH2)P2W15Mo2O61], alpha2-K8[Cu(OH2)P2W15Mo2O61], alpha1- and alpha2-K8[Cu(OH2)P2W17O61], alpha2-K8[Cu(OH2)P2W13Mo4O61], and alpha2-K8[Cu(OH2)P2W12Mo5O61] were investigated by cyclic voltammetry (CV) coupled with the electrochemical quartz microbalance (EQCM), and the results were completed by atomic force microscopy (AFM) observations of the electrodeposited films. The electrocatalytic abilities of these polyoxometalates (POMs) in the reduction of dioxygen, hydrogen peroxide, and NOx were also assessed by CV and EQCM. It turns out that the remarkable electrocatalysis obtained at the reduction potential of Mo centers within alpha2-K8[Cu(OH2)P2W15Mo2O61], but in a domain where Cu2+ is not deposited, benefits from the assistance of the copper center because such catalysis could not be observed in the absence of Cu2+. EQCM confirms that no copper deposition occurs under the experimental conditions used. Analogous behaviors are encountered in the electrocatalytic reduction of nitrite where assistance by the presence of the Cu2+ center induced the observation of catalysis at the potential location of Mo centers. Finally, the reduction of nitrate is triggered by electrodeposited copper but was remarkably favored by the presence of molybdenum atoms within these polyoxometalates (POMs). All of the results converge to indicate a cooperative effect between the Mo and Cu centers within these POMs. The various results suggest that copper deposition from these POMs should give morphologically different surfaces. AFM studies confirm this expectation, and the observed morphologies and sizes of particles were rationalized by taking into account the role of the POM skeleton and its atomic composition in the electrodeposition process.     

Polyoxoanion with Octahedral Germanium(IV) Hetero Atom: Synthesis, Structure, Magnetism, EPR, Electrochemistry and XPS Studies on the Mixed-Valence 14-Vanadogermanate [GeVV 12VIV 2O40]8−

The mixed-valence 14-vanadogermanate [GeV^V ₁₂V^IV ₂O₄₀]^8? (1) has been synthesized and characterized in solution by ⁵¹V-NMR, UV–vis and electrochemistry and in the solid state by IR, magnetism, EPR, XPS and elemental analysis. Single-crystal X-ray analysis was carried out on K₂Na₆[GeV^V ₁₂V^IV ₂O₄₀]·10H₂O (KNa-1), which crystallizes in the orthorhombic system, space group Immm, with a=10.9623(3) Å, b=11.6205(3) Å, c=20.2658(5) Å, and Z=2. Polyanion 1 is composed of a central Ge^IVO₆ octahedron which is surrounded by a total of 14 VO₆ octahedra. Vanadium-51 NMR in solution results in three peaks with intensity ratio of 8:4:2 which is in complete agreement with the solid state structure. The presence of two V^IV centers was established by UV–vis, electrochemistry, magnetism, EPR, XPS and elemental analysis. Electrochemistry revealed that the two V^IV-centers in 1 are oxidized through a single well-defined step, which does not split with changes in scan rate or pH. Polyanion 1 is also an active two-electron oxidation catalyst for the coenzyme NADH at pH 8, unprecedented in polyoxometalate chemistry. Magnetic susceptibility, magnetization and EPR data on KNa-1 complement the X-ray and electrochemistry results by confirming the presence of two unpaired electrons per molecule of 1. The two V^IV ions possessing the spin are very weakly coupled, essentially acting as two well-isolated S=1/2 ions. The observed g-value of 1.977 from EPR and magnetic susceptibility measurements is consistent with literature reported value for a V^IV ion, suggesting a possible ground state of $3d_{x^{2}-y^{2}}.The mixed-valence 14-vanadogermanate [GeV^V ₁₂V^IV ₂O₄₀]⁸⁻ (1) has been synthesized and characterized in solution by ⁵¹V-NMR, UV–vis and electrochemistry and in the solid state by IR, magnetism, EPR, XPS and elemental analysis. Single-crystal X-ray analysis was carried out on K₂Na₆[GeV^V ₁₂V^IV ₂O₄₀]·10H₂O (KNa-1), which crystallizes in the orthorhombic system, space group Immm, with a=10.9623(3) ?, b=11.6205(3) ?, c=20.2658(5) ?, and Z=2. Polyanion 1 is composed of a central Ge^IVO₆ octahedron which is surrounded by a total of 14 VO₆ octahedra. Vanadium-51 NMR in solution results in three peaks with intensity ratio of 8:4:2 which is in complete agreement with the solid state structure. The presence of two V^IV centers was established by UV–vis, electrochemistry, magnetism, EPR, XPS and elemental analysis. Electrochemistry revealed that the two V^IV-centers in 1 are oxidized through a single well-defined step, which does not split with changes in scan rate or pH. Polyanion 1 is also an active two-electron oxidation catalyst for the coenzyme NADH at pH 8, unprecedented in polyoxometalate chemistry. Magnetic susceptibility, magnetization and EPR data on KNa-1 complement the X-ray and electrochemistry results by confirming the presence of two unpaired electrons per molecule of 1. The two V^IV ions possessing the spin are very weakly coupled, essentially acting as two well-isolated S=1/2 ions. The observed g-value of 1.977 from EPR and magnetic susceptibility measurements is consistent with literature reported value for a V^IV ion, suggesting a possible ground state of XPS measurements on KNa-1 also confirmed the coexistence of V^V and V^IV in 1.Dedicated to Professor Michael T. Pope on the occasion of his retirement.     

Electrocatalytic nitrate hydrogenation over an H+ -conducting solid polymer electrolyte membrane-modified cathode assembly

Selective electrocatalytic hydrogenation of NO3- to N2 in water has successfully been achieved at room temperature using a membrane-electrode assembly (MEA) consisting of an H+ -conducting solid polymer electrolyte (Nafion-117) and a surface-modified Pt cathode.