Development of thermally stable nickel-based catalysts is highly desirable for industrial gas-phase olefin polymerizations. On the basis of the strategy of promoting the thermostability of nickel catalyst by the ligand backbone, we herein reported novel dibenzobarrelene-derived α-diimine nickel precatalysts for ethylene polymerization. Increasing the steric bulk on the ligand backbone was expected to inhibit the N-aryl rotation of the α-diimine ligands by the repulsive interactions, thus enhancing thermal stability (100 °C) and living fashion a temperatures up to 80 °C. Bulk ligand backbone also improved tolerance of nickel catalyst toward polar groups, and the α-diimine nickel catalyst containing a 2,6-t Bu-dibenzobarrelene backbone catalyzed living copolymerization of ethylene and methyl 10-undecenoate.

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Original Paper Ultra-performance LC/TOF MS analysis of medicinal Panax herbs for metabolomic researchIn this study, metabolite profiling of five medicinal Panax herbs including Panax ginseng (Chinese ginseng), Panax notoginseng (Sanchi), Panax japonicus (Rhizoma Panacis Majoris), Panax quinquefolium L. (American ginseng), and P. ginseng (Korean ginseng) were performed using ultra-performance LC-quadrupole TOF MS (UPLC-QTOFMS) and multivariate statistical analysis technique. Principal component analysis (PCA) of the analytical data showed that the five Panax herbs could be separated into five different groups of phytochemicals. The chemical markers such as ginsenoside Rf, 20(S)-pseudoginsenoside F11, malonyl gisenoside Rb1, and gisenoside Rb2 accountable for such variations were identified through the loadings plot of PCA, and were identified tentatively by the accurate mass of TOFMS and partially verified by the available reference standards. Results from this study indicate that the proposed method is reliable for the rapid analysis of a group of metabolites present in herbal medicines and other natural products and applicable in the differentiation of complex samples that share similar chemical ingredients. IntroductionMetabolomics aims to identify and quantify the full complement of low-molecular-weight, soluble metabolites in actively metabolizing tissues [1 -4], which has aroused extensive awareness and interests, especially in the botanical studies such as quality control of plants [5 -9], plant engineering [10, 11] using a number of techniques including NMR or different combinations of LC, GC, and MS. Also, based on the multivariate analysis of complex biological profiles, metabolomics has been successfully applied to plant genotype discrimination and differentiation [1, 12 -14]. Plants are rich in chemically diverse metabolites, which cannot be completely detected by a single analytical method currently available in phytochemical laboratories. Over the past 20 years, HPLC/MS (LC/MS) has become one of the main analytical techniques used in controlling the quality and consistency of both the chemical markers and active substances of traditional Chinese medicines (TCMs). Despite early claims that MS, and particularly MS/MS, is able to remove the need for good chromatographic separation in the analysis of low abundance samples, a poor LC run prior to MS analysis will lead to issues of ion suppression and isobaric interferences that cannot be overcome by a spectrometer alone. More recently, the desire for significantly reduced analysis time with increased sample throughput, resolution, and sensitivity has resulted in the development of ultrafast separation and identification using LC-MS techniques [15,16]. Among the various LC platforms, ultra-performance LC (UPLC) is considered suitable for metabolite profiling and metabolomics [17 -28], especially, for large-scale untargeted metabolic profiling due to its enhanced reproducibility in retention time [24]. The ability to generate high peak capacities in short...

Coordination insertion polymerization is unsurpassed as a straightforward method for synthesis of highvalue polyolefins by the copolymerization of ethylene and polar monomers, but poison effects of polar groups on the metal center result in a lack of fine control over the polymer architecture. Herein we reported a thermally stable dibenzobarrelene-derived α-diimine palladium catalyst for the precision synthesis of functionalized polyolefins by living copolymerization of ethylene and a variety of acrylate comonomers. The introduction of the bulky dibenzobarrelene backbone can improve migratory insertion selectivity of methyl acrylate (MA) in a 2,1-mode, thus preventing polar groups from poisoning palladium centers by stable five-membered palladacycle intermediates formed by 1,2-insertion of MA. In this living chain-walking catalyst system, the composition, molecular weight, and branching topology of the copolymer can be facilely tunable by simple variation of the ethylene pressure.

Thioredoxin system plays an important role in regulation of intracellular redox balance and various signaling pathways. Thioredoxin reductase (TrxR) is overexpressed in many cancer cells and has been identified as a potential target of anticancer drugs. Auranofin (AF) is potent TrxR inhibitor with novel in vitro and in vivo anticancer activities. Selenocystine (SeC) is a nutritionally available selenoamino acid with selective anticancer effects through induction of apoptosis. In the present study, we demonstrated the synergistic effects and the underlying molecular mechanisms of SeC in combination with AF on MCF-7 human breast cancer cells. The results showed that SeC and AF synergistically inhibited the cancer cell growth through induction of ROS-dependent apoptosis with the involvement of mitochondrial dysfunction. DNA damage-mediated p53 phosphorylation and down-regulation of phosphorylated AKT and ERK also contributed to cell apoptosis. Moreover, we demonstrated the important role of TrxR activity in the synergistic action of SeC and AF. Taken together, our results suggest the strategy to use SeC and AF in combination could be a highly efficient way to achieve anticancer synergism by targeting TrxR.