Shape-selective synthesis and oxygen storage behavior of ceria nanopolyhedra, nanorods, and nanocubes

Single-crystalline and uniform nanopolyhedra, nanorods, and nanocubes of cubic CeO2 were selectively prepared by a hydrothermal method at temperatures in the range of 100-180 degrees C under different NaOH concentrations, using Ce(NO3)3 as the cerium source. According to high-resolution transmission electron microscopy, they have different exposed crystal planes: {111} and {100} for polyhedra, {110} and {100} for rods, and {100} for cubes. During the synthesis, the formation of hexagonal Ce(OH)3 intermediate species and their transformation into CeO2 at elevated temperature, together with the base concentration, have been demonstrated as the key factors responsible for the shape evolution. Oxygen storage capacity (OSC) measurements at 400 degrees C revealed that the oxygen storage takes place both at the surface and in the bulk for the as-obtained CeO2 nanorods and nanocubes, but is restricted at the surface for the nanopolyhedra just like the bulk one, because the {100}/{110}-dominated surface structures are more reactive for CO oxidation than the {111}-dominated one. This result suggests that high OSC materials might be designed and obtained by shape-selective synthetic strategy.     

Separation of PAHs in aerosol by thin layer chromatography for compound-specific stable carbon isotope analysis

A method using a thin layer chromatography (TLC) for compound-specific stable carbon isotope analysis of polycyclic aromatic hydrocarbons (PAHs) with four to seven rings was developed in this study. Five aerosol samples were used as test samples. Two stationary phases and eight developing systems were tested. The results indicated: (1) silica gel is superior to aluminum oxide and the silica gel precoated plate developed with hexane:chloroform (45:5, v/v) can give the best separation effect; (2) individual PAHs associated with aerosols can be effectively separated from unresolved complex mixture (UCM) by this procedure. The carbon isotope composition of PAHs can be measured with a standard deviation (S.D.) < 0.5‰, n = 4. No significant isotopic fractionation was observed during the TLC procedure. And this technique can be used as a potential tool for source identification of PAHs in the aerosols.     

Xanthine oxidase inhibitors from the heartwood of Vietnamese Caesalpinia sappan

From the MeOH extract of Vietnamese Caesalpinia sappan, a novel biogenetically exclusive benzindenopyran, with a new carbon framework, neoprotosappanin (1), and a new compound, protosappanin A dimethyl acetal (3), were isolated together with protosappanin E-2 (2), neosappanone A (4), and 13 previously reported phenolic compounds (5-17). Their structures were elucidated on the basis of spectroscopic data. Compounds 1-4, 7, 13, and 15-17 showed significant xanthine oxidase inhibitory activity in a concentration-dependent manner, and sappanchalcone (17) showed the most potent activity with an IC50 value of 3.9 microM, comparable to that of positive control allopurinol (IC50, 2.5 microM). The kinetic study of these inhibitors indicated that they are competitive inhibitors, the same as allopurinol, except for 1 and 16 which are noncompetitive inhibitors.     

Relation between surface preconditioning and metal deposition in direct galvanic metallization of insulating surfaces

The relation between surface preconditioning and metal deposition in the direct galvanic metallization of different insulating polymer surfaces by the so-called PLATO technique was studied using electrochemical and surface analytical methods. AFM, XPS and contact angle measurements show that the chromic acid etching of original polymer surfaces leads to an increase of the surface energy and hydrophilicity of polymer substrates due to both surface roughening and the formation of -COOH and/or -COH surface groups. However, decisive for the subsequent surface activation with cobalt sulfide is the increase in surface roughness. The influence of the degree of activation and the electrode potential on the kinetics of Ni metallization was studied by current transient measurements on activated line-shaped structures. The results suggest that the electrochemical reduction of cobalt sulfide to cobalt is a necessary step to induce the process of Ni electrodeposition. Successful Ni metallization could be obtained on ABS (acrylonitrile-butadiene-styrene) and PEEK (poly-ether-ether-ketone) surfaces. The lateral propagation rate, V _x , of the depositing Ni layer depends exponentially on the applied potential and was found to be several orders of magnitude higher than the Ni deposition rate, V _z , in the normal z-direction (V _x /V _z =10²–10⁴). It was demonstrated that the approach involving cobalt sulfide pre-activation can also be applied successfully for metallization of oxidized porous silicon surfaces.Presented at the 3rd International Symposium on Electrochemical Processing of Tailored Materials held at the 53rd Annual Meeting of the International Society of Electrochemistry, 15–20 September 2002, Düsseldorf, Germany     

Perinadine A, a novel tetracyclic alkaloid from marine-derived fungus Penicillium citrinum

[structure: see text] A novel tetracyclic alkaloid, perinadine A (1), was isolated from the cultured broth of the fungus Penicillium citrinum, which was separated from the gastrointestine of a marine fish, and the structure was elucidated on the basis of spectroscopic data including 2D NMR spectra. Biogenetically, perinadine A (1) may be derived from citrinin (4), a well-known mycotoxin, and a scalusamide A-type pyrrolidine alkaloid.     

气相色谱/高分辨质谱联用测定环境样品中的二噁英和类二噁英多氯联苯

样品采用索氏抽提,抽提液依次经酸性硅胶床、多段混合硅胶柱和凝胶渗透色谱柱(GPC)净化后,用Florisil硅藻土柱分离出样品中的二噁英(PCDD/Fs)和类二噁英多氯联苯(dioxin-like PCBs),采用同位素稀释法和气相色谱/高分辨质谱联用仪(GC/HRMS)测定了其中的17个2,3,7,8-氯取代二噁英类化合物和12个类二噁英多氯联苯。结果表明,用该法分析二噁英和多氯联苯标准溶液,平行4次的分析结果为:RSD(PCDD/Fs)<8.9%,RSD(PCBs)<11.4%;回收率可达60%-105%。PCDD/Fs和PCBs的检出限分别为0.1-0.8 pg/g和0.05-0.6 pg/g。应用本方法成功测定了沉积物、淤泥、土壤和飞灰中的二噁英和类二噁英多氯联苯,并计算出它们的毒性当量。     

Species specific isotope dilution for the accurate and SI traceable determination of arsenobetaine and methylmercury in cuttlefish and prawn

Methods based on species specific isotope dilution were developed for the accurate and SI traceable determination of arsenobetaine (AsBet) and methylmercury (MeHg) in prawn and cuttlefish tissues by LC-MS/MS and SPME GC-ICPMS. Quantitation of AsBet and MeHg were achieved by using a ¹³C-enriched AsBet spike (NRC CRM CBET-1) and an enriched spike of Me¹⁹⁸Hg (NRC CRM EMMS-1), respectively, wherein analyte mass fractions in enriched spikes were determined by reverse isotope dilution using natural abundance AsBet and MeHg primary standards. Purity of these primary standards were characterized by quantitative ¹H-NMR with the use of NIST SRM 350b benzoic acid as a primary calibrator, ensuring the final measurement results traceable to SI. Validation of employed methods of ID LC-MS/MS and ID SPME GC-ICPMS was demonstrated by analysis of several biological CRMs (DORM-4, TORT-3, DOLT-5, BCR-627 and BCR-463) with satisfying results.     

Expression and Characterization of a Novel 1,3-Propanediol Dehydrogenase from <Emphasis Type="Italic">Lactobacillus brevis</Emphasis>

1,3-Propanediol dehydrogenase (PDOR) is important in the biosynthesis of 1,3-propanediol. In the present study, the dhaT gene encoding PDOR was cloned from Lactobacillus brevis 6239 and expressed in Escherichia coli for the first time. Sequence analysis revealed that PDOR containing two Fe²⁺-binding motifs and a cofactor motif belongs to the type III alcohol dehydrogenase. The purified recombinant PDOR exhibited a single band of 42 kDa according to SDS-PAGE. Optimal temperatures and pH values of this dehydrogenase are 37 °C, 7.5 for reduction and 25 °C, 9.5 for oxidation, respectively. We found that PDOR was more stable in acid buffer than in alkaline condition, and 60 % of its relative activity still remained after a 2-h incubation at 37 °C. The activity of PDOR can be enhanced in the presence of Mn²⁺ or Fe²⁺ iron and inhibited by EDTA or PMSF by different degrees. The K _m and V _max of this dehydrogenase are 1.25 mM, 64.02 μM min^?1 mg^?1 for propionaldehyde and 2.26 mM, 35.05 μM min^?1 mg^?1 for 1,3-PD, respectively. Substrate specificity analysis showed that PDOR has a broad range of substrate specificities. The modeling superposition indicated that the structural differences may account for the diversity of PDORs’ properties. Thus, our PDOR is a potential candidate for facilitating the 1,3-PD biosynthesis.     

Optimization of spectral sensitivities of mosaic five-band camera for estimating chromophore densities from skin images including shading and surface reflections

Optical Review - In this paper, the spectral sensitivities of a mosaic five-band camera were optimized using a numerical skin phantom to perform the separation of chromophore densities, shading and...     

Structural characterization and identification of flavonoid aglycones in three Glycyrrhiza species by liquid chromatography with photodiode array detection and quadrupole time‐of‐flight mass spectrometry

Flavonoids, including flavones, isoflavones, flavanones, chalcones, and isoflavans, have long been recognized as the main active ingredients in licorice. A method combining liquid chromatography with photodiode array detection and quadrupole time‐of‐flight mass spectrometry was developed to characterize components in three Glycyrrhiza species, and to expound the characteristic fragmentation behaviors in the positive ion mode. Based on the fragmentation patterns of reference compounds, a total of 39 compounds, including 37 flavonoid aglycones and two coumestans, were identified or tentatively identified. Besides, some common features, such as H₂O, CO, and CH₂O₂ losses, together with retro‐Diels–Alder fragmentation, were observed in these compounds. Furthermore, diagnostic fragmentations of C‐ring cleavages and UV absorption on the skeleton groups were observed to structurally characterize flavonoid aglycones. In addition, typical losses of different substituent groups were detected: Neutral losses of 56 (C₄H₈) and 68 Da (C₅H₈) were yielded from a prenyl chain; neutral losses of 42 (C₃H₆), 54 (C₄H₆), and 70 Da (C₄H₆O) were generated by a pyran ring. Particularly, neutral losses of 18 (H₂O), 16 (CH₄), 112 (C₈H₁₆), and 98 Da (C₇H₁₄) predicted a hydroxyl, a methoxyl, double prenyl chains, and a prenyl chain with a pyran ring, respectively.