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931.
Zheng Y  Li Y  Lu N  Deng Z 《The Analyst》2011,136(3):459-462
Surface-initiated DNA polymerization has been employed in this work as an appealing signal amplification strategy for electrochemical DNA sensors. This strategy is especially superior in that enzymes, colloidal particles and other bulky structures are not involved in order to achieve amplified signals, and thus is highly promising in circumventing problems due to uncontrolled nucleation, adsorption, aggregation or disassembly of nanoparticles, liposomes and proteins, as well as enzyme deactivations. Our preliminary results have shown that a decrease (as compared to an amplification-free system) in detection limit by a factor greater than 300 can be easily achieved by cyclic voltammetry under still not optimized conditions, with an ability of differentiating a single base mutation.  相似文献   
932.
An efficient and convenient method for synthesis of 3,5‐bis‐carbamoyl‐2,6‐dimethylpyridine derivatives was achieved in good to excellent yields by reaction of anilines with 3,5‐bis(3′,5′‐dimethyl‐1′‐pyrazolyl‐carbonyl)‐2,6‐dimethylpyridine, in which pyrazoles served as leaving groups. The structures of products were confirmed by spectra data and microanalysis.  相似文献   
933.
采用高温熔融方法制备了玻璃成分分析标准物质.对标准物质的制备技术、均匀性检验、稳定性考察及定值不确定度进行了分析.研制的耐辐照成分分析标准物质具有良好的均匀性和稳定性,各组分不确定度均小于5%.  相似文献   
934.
A novel ion‐imprinted strategy is developed for synthesizing responsive hydrogels with rapid response to potassium ions. With potassium ions as templates, ion‐imprinted poly(N‐isopropylacrylamide‐co‐benzo‐15‐crown‐5‐acrylamide) (P(NIPAM‐co‐B15C5Am)) hydrogels are synthesized with 15‐crown‐5 crown ethers mounted on the polymer networks in pairs; therefore, it is very easy and fast for the crown ethers to capture potassium ions again by their Venus flytrap action and form stable 2:1 “host–guest” complexes with potassium ions in the ion‐recognition process. As a result, the response rate of the ion‐imprinted hydrogels to potassium ions is significantly faster than that of normal P(NIPAM‐co‐B15C5Am) hydrogels in which 15‐crown‐5 crown ethers are randomly pendent on the polymeric networks. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   
935.
Coelectrospun polylactide(PLA)/gelatin (GE) composite fibrous matrixes have been identified to exhibit much improved performances compared to the respective components; however, the reasons for their water contact angles decreasing to zero at proper PLA/GE ratios remain unclear. To get a deep understanding of the phenomenon, PLA and GE were coelectrospun with different PLA/GE ratios in this study. Although the resulting composite fibers were homogeneous in appearance, they were detected different microscopic structures by transmission electron mircroscope (TEM) and via morphological observations after selective removal of either PLA or GE component. Together with the results of degradation study in phosphate buffered solution, a kind of cocontinuous phase separation microstructure could be identified for the PLA(50 wt%)/GE(50 wt%) composite fibers, which also showed the water contact angle of 0°. This value was far lower than those of electrospun PLA (~123°) and GE (~42°) fibrous matrixes. The X‐ray photoelectron spectrometry (XPS) data revealed that the polar side groups of protein macromolecules have moved toward composite fiber surface with solvent evaporation during electrospinning, due to the hydrophobic interaction between PLA and GE. Then the excellent hydrophilicity of PLA(50 wt%)/GE(50 wt%) composite fibers could be suggested as the consequence of: (1) the cocontinuous phase separation structure could provide more interface and void for water molecules penetrating; and (2) the accumulation of polar groups on composite fiber surface significantly increased the surface wettability. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   
936.
Li Y  Zhao P  Kang Q  Ma J  Bai L  Deng Z 《Chemistry & biology》2011,18(12):1571-1580
Carbamoylation is one of the post-PKS modifications in ansamitocin biosynthesis. A novel ansamitocinoside with carbamoyl substitution at the C-4 hydroxyl group of the N-β-D-glucosyl moiety was identified from the ansamitocin producer, Actinosynnema pretiosum. Through biotransformation, the carbamoyltransferase gene asm21 was suggested to be responsible for the carbamoylation of the glucosyl moiety. Three new derivatives without the backbone carbamoyl group were isolated from an asm21 mutant and characterized by NMR spectroscopy. Among them, 18-O-methyl-19-chloroproansamitocin was the major product and the preferred substrate for macrolactam C-7 carbamoylation by Asm21. However, Asm21 exhibited higher catalytic efficiency toward the glucosyl moiety. Furthermore, the dual carbamoylations and N-glycosylation were precisely demonstrated in vivo. This work represents the first biochemical characterization of an O-carbamoyltransferase performing dual actions on both a polyketide backbone and a glycosyl moiety during ansamitocin biosynthesis.  相似文献   
937.
In this work, graphene or graphene oxide was utilized, for the first time, to identify small molecular components from traditional Chinese medicine (TCM) herbs, by acting as matrix of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Due to the large surface area of graphene or graphene oxide, the analytes were trapped tightly to the matrix, which avoids the contamination of the ion source and vacuum system. Besides, their excellent electronic, thermal and mechanical properties make them desired matrices for MALDI-TOF-MS. Stable analysis was achieved with no background inference even at the concentration of 100 nM. Moreover, the limit of detection (LOD) could be greatly lowered by utilizing graphene or graphene oxide as a pre-enrichment adsorbent. In summary, the promoted MALDI-TOF-MS methodology was demonstrated to be simple, sensitive, fast, cost effective and, most importantly, high throughput.  相似文献   
938.
The screening of several Chinese medicinal herbs for insecticidal principles showed that Euphorbia fischeriana roots possessed significant feeding deterrent activity against two stored-product insects (Tribolium castaneum and Sitophilus zeamais). From ethanol extract, four feeding deterrents were isolated by bioassay-guided fractionation. The compounds were identified as jolkinolide B, 12-deoxyphorbol 13-(9Z)-octadecenoate 20-acetate, 17-hydroxyjolkinolide A and B on the basis of their phytochemical and spectral data. Jolkinolide B and 17-hydroxyjolkinolide B possessed strong feeding deterrent activities against S. zeamais (EC?? = 342.1 and 543.9 ppm, respectively) and T. castaneum adults (E?? = 361.4 and 551.5 ppm, respectively). 17-Hydroxyjolkinolide A and 12-deoxyphorbol 13-(9Z)-octadecenoate 20-acetate A also exhibited feeding deterrent activity against the two grain storage insects with EC?? values of 631.9 and 884.3 ppm for S. zeamais and 656.5 and 1058.4 ppm for T. castaneum adults.  相似文献   
939.
The immunomodulatory function of longan pulp polysaccharide-protein complex (LP3) was investigated in immunosuppressed mice models. Compared with the model control, peroral administration of 100 mgkg?1d?1 LP3 could significantly increase/enhance antibody production against chicken red blood cell (CRBC), concanavalin A (ConA)-induced splenocyte proliferation, macrophage phagocytosis, NK cell cytotoxicity against YAC-1 lymphoma cell, and interferon-gamma (INF-γ) and interleukin-2 (IL-2) secretion in serum (P < 0.05). The immunomodulatory effects, except for those on splenocytes and macrophages (P > 0.05), were also observed in mice administered with 50 or 200 mgkg?1d?1 LP3 (P < 0.05). The beneficial effects of 50-200 mgkg?1d?1 LP3 were comparable to those of 50 mgkg?1d?1 ganoderan. The strong immunomodulatory activity of LP3 confirmed its good potential as an immunotherapeutic adjuvant.  相似文献   
940.
Natural killer T (NKT) cells recognize glycolipids produced by Sphingomonas bacteria, and these glycolipids contain C6-oxidized sugars, either glucuronic acid or galacturonic acid, linked to ceramides. Glycolipids with gluco stereochemistry are the most prevalent. Multiple studies have demonstrated that galactosylceramides are more potent stimulators of NKT cells than their glucose isomers. To determine if this stereoselectivity is retained in the context of the C6-oxidized sugars found in bacterial glycolipids, we prepared two sets of gluco and galacto-glycolipids oxidized at their C6 positions and compared their NKT stimulatory properties. In the context of carboxylic acid groups at C6, gluco stereochemistry gave the more potent responses. We also prepared bacterial glycolipids containing more complex ceramide groups to determine if these chains impact NKT cell responses.  相似文献   
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