Ionic Liquid Stabilized Niobium Oxoclusters Catalyzing Oxidation of Sulfides with Exceptional Activity

We present here a new class of niobium oxoclusters that are stabilized effectively by carboxylate ionic liquids. These functionalized ILs are designated as [TBA][LA], [TBA][PA], and [TBA][HPA] in this work, in which TBA represents tetrabutylammonium and LA, PA, and HPA refer to lactate, propionate, 3-hydroxypropionate anions, respectively. The as-synthesized Nb oxoclusters have been characterized by use of elemental analysis, NMR, IR, XRD, TGA, HRTEM. It was found that [TBA][LA]-stabilized Nb oxoclusters (Nb−OC@[TBA][LA]) are uniformly dispersed with an average particle size of 2–3 nm and afforded exceptionally high catalytic activity for the selective oxidation of various thioethers. The turnover number with Nb−OC@[TBA][LA] catalyst was over 56 000 at catalyst loading as low as 0.0033 mol % (1 ppm). Meantime, the catalyst also showed the high activity for the epoxidation of olefins and allylic alcohols by using only 0.065 mol % of catalyst (50 ppm). The characterization of ⁹³Nb NMR spectra revealed that the Nb oxoclusters underwent structural transformation in the presence of H₂O₂ but regenerated to their initial state at the end of the reaction. In particular, the highly dispersed Nb oxoclusters can absorb a large amount of polar organic solvents and thus were swollen greatly, which exhibited “pseudo” liquid phase behavior, and enabled the substrate molecules to be highly accessible to the catalytic center of Nb oxocluster units.     

陶瓷材料三点及四点弯曲断裂强度关系之讨论

利用Katayama在一种Si断裂强度; 弯曲试验; 加载因子; Weibull模量fracture strength, bending test, load factor, Weibull modulus2002年6月25日2003-12-10 利用Katayama在一种Si断裂强度; 弯曲试验; 加载因子; Weibull模量fracture strength, bending test, load factor, Weibull modulus2002年6月25日2003-12-10利用Katayama在一种Si3N4陶瓷得到的实验数据,考察了一条关联陶瓷材料三点及四点弯曲断裂强度的式子,其准确度较好,简要地导出了一般教材上较少提及其推导的四点弯曲加载因子。     

A new neolignan glycoside from Dolomiaea souliei

Abstract

One new neolignan glycoside, dolomiside A (1), together with 11 known phenylpropanoid glycosides were isolated from Dolomiaea souliei (Franch.) Shih. The structures of these isolates were determined by UV, CD, HR-ESI-TOFMS, 1D and 2D NMR analysis.     

A strategy for qualitative and quantitative profiling of Angelicae Pubescentis Radix and detection of its analgesic and anti-inflammatory components by spectrum–effect relationship and multivariate statistical analysis

This study established a spectrum–effect relationship method for screening and quantifying the analgesic and anti-inflammatory active ingredients in Angelicae Pubescentis Radix (AP) by ultra-high-performance liquid chromatography–quadrupole mass spectrometry detector analysis (UPLC–QDA). First, the fingerprint of AP was established to determine the common peaks. Next, six batches of AP samples, with significant differences, were selected for evaluation of pharmacological activity. Subsequently, the spectrum–effect relationship was used to screen the active ingredients. Finally, the screened ingredients were quantified using UPLC–QDA. In total, 21 common peaks were identified and four effective compounds (bergapten, columbianetin acetate, osthole and isoimperatorin) were selected using the gray relational analysis and partial least squares regression analysis. Quantitative analysis showed that the content of the four effective compounds was the highest in a randomly selected batch, S7 (Hubei). To our knowledge, this is the first attempt that evaluated the quality and spectrum–effect relationship of AP by quantitative analysis and chemometrics. This study identified the key pharmacologically active components of AP and thereby improved the quality evaluation system of AP. This method has broad application prospects for screening effective components and will be helpful in establishing more reliable, scientific and reasonable quality standards for AP and other traditional Chinese medicines.     

Construction and evaluation of nagR-nagAa::lux fusion strains in biosensing for salicylic acid derivatives

The NagR protein is a response regulatory protein found in the bacterium Ralstonia sp. U2 that is involved in sensing for salicylic acid and the subsequent induction of the operon just upstream of its gene. The genes encoded for in this operon are involved in the degradation of salicylic acid. Escherichia coli strain RFM443 carrying a fusion of the Photorhabdus luminescens luxCDABE operon with the nagR gene and upstream region of the nagAa gene was constructed and characterized with respect to its optimum temperature, its response time and kinetics, and its ability to detect numerous benzoic acid derivatives. Although capable of detecting 0.5 mM salicylic acid at any temperature between 28 and 40 degrees C, this E. coli strain, labeled DNT5, showed its greatest relative activity at 30 degrees C, i.e., the temperature at which the largest induction was seen. Furthermore, experiments done with numerous benzoic acid derivatives found the NagR protein to be responsive to only a few of the compounds tested, including salicylic acid and 3-methyl salicylic acid, and acetyl salicylic acid was the strongest inducer. The lower limits of detection for these compounds with E. coli strain DNT5 were also established, with the native inducer, salicylic acid, giving the most sensitive response and detectable down to a concentration of about 2 microM. A second lux fusion plasmid was also constructed and transformed into an NahR background, Pseudomonas putida KCTC1768. Within this strain, NAGK-1768, the supplemental activity of the NahR protein on the nagAa promoter, was shown to extend both the range of chemicals detected and the sensitivity.     

Sample-specific and ensemble-averaged magnetoconductance of individual single-wall carbon nanotubes

We discuss magnetotransport measurements on individual single-wall carbon nanotubes (SWNTs) with low contact resistance, performed as a function of temperature and gate voltage. We find that the application of a magnetic field perpendicular to the tube axis results in a large magnetoconductance of the order of e2/h at low temperature. We demonstrate that this magnetoconductance consists of a sample-specific and of an ensemble-averaged contribution, both of which decrease with increasing temperature. The observed behavior resembles very closely the behavior of more conventional multichannel mesoscopic wires, exhibiting universal conductance fluctuations and weak localization. A theoretical analysis of our experiments will enable us to reach a deeper understanding of phase-coherent one-dimensional electronic motion in SWNTs.     

Ordering the relative power of electrophilic fluorinating,trifluoromethylating, and trifluoromethylthiolating reagents: A summary of recent efforts

Electrophilic fluorination and fluoroalkylation are one of the most promising and efficient strategies in the synthesis of organofluorine compounds. The rapid progress of this field has been made possible by the emergence of a wide variety of power-variable, readily prepared, and easy-to-handle electrophilic fluorinating and fluoroalkylating reagents. Understanding the relative power of these reagents is thus vital for their use in synthetic transformations. This digest will outline some recent efforts to quantitatively ordering the relative power of electrophilic fluorinating, trifluoromethylating, and trifluoromethylthiolating reagents.     

Synthesis of a unique dimethyl thiazoline containing intermediate of novel peroxisome proliferator-activated receptors(PPAR)δ agonists

Peroxisome proliferator-activated receptor delta (PPARδ) is considered as a promising biological target for the development of new drugs to treat metabolic syndrome including hyperlipidemia. In this study, a simple and efficient method for the preparation of a unique dimethyl thiazoline containing intermediate (13) of new PPARδ agonists as GW501516 analogue is described. The intermediate 13 was readily obtained by coupling reaction of 4-(chloromethyl)-5,5-dimethyl-2-(4-(trifluoromethyl)phenyl)-4,5-dihydrothiazole (11) with 4-mercapto-2-methylphenol (12) in the presence of tetrabutylammonium hydrogensulfate (TBAHS) and Cs₂CO₃ in DMF at 80?°C for 1?h. This unique intermediate could be useful for the synthesis of various novel PPARδ agonists to understand the structural and biological significance of PPARδ.