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1.
吴继龙 《芜湖职业技术学院学报》2002,4(4):16-17
小型建筑施工企业建立科学合理的机械设备维修保养制度,是保证工程质量和提高企业经济效益的重要环节。 相似文献
2.
Vandana Singh Ashutosh TiwariDevendra Narayan Tripathi Tulika Malviya 《Tetrahedron letters》2003,44(39):7295-7297
O-Methylation is of outstanding importance in structural polysaccharide chemistry. A novel method for the methylation of polysaccharides using microwave (MW) irradiation is described. Seed gum from Cyamopsis tetragonolobus (Guar) was fully methylated with dimethyl sulphate and sodium hydroxide using 100% microwave power for 4 min in 68% yield. The completely methylated seed gum thus obtained was hydrolyzed by 70% formic acid followed by 0.5N H2SO4 under full microwave power for 1.16 and 1.66 min, respectively. The partially methylated monosaccharides were separated and identified. 相似文献
3.
Cerium(IV) mediated grafting of polyacrylonitrile on to guar gum was studied. Grafting parameters were studied gravimetrically, as a function of temperature, initiator concentration and Guar to acrylonitrile ratio. Higher temperatures resulted in higher monomer conversion and homopolymer formation. Both monomer conversion and extent of grafting increased with increase in cerium ion concentration in the range studied (0.91–9.12 mmol/l). Similar results were obtained with increase in monomer to guar gum ratio from 1 to 5. Grafting with this initiator was found to be generally good with high grafting efficiencies and low homopolymer formation for most experiments. The copolymers obtained were subjected to alkaline hydrolysis to convert nitrile groups in to carboxylic acid groups and the water absorbency of the resulting anionic guar gum was studied. Materials with water absorption up to 300 g/g could be obtained from this study. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
4.
本文研究结果表明,水溶性大分子化合物阿拉伯胶和非离子表面活性剂TritonX-100共同存在下,锑碘配阴离子和罗丹明B的显色反应具有很高的灵敏度。缔合物的最大吸收在5g0nm,摩尔吸光系数ε=6.1×10 ̄5L·mol-1·cm-1。用巯基棉富集锑,分离干扰离子。本法可应用于有色金属中痕量锑的测定。 相似文献
5.
Wang xiu jun 《科技信息》2008,(25)
阐述了生产玻璃钢地下输水管道的工艺流程及管壁各层的设计内容及其作用,分析了各工艺中的工艺要点,并给出了生产工艺数据。 相似文献
6.
7.
Photocleavable protecting groups are important in synthesis and caging. Among many such groups, 2-nitrobenzyl and related groups have been found useful in many applications. However, most of the known 2-nitrobenzyl-based caging chromophores show either low quantum yield or the photolysis wavelength is not suitable for various applications. In this paper, we report 2-nitro-3-naphthalenemethanol (NNM) as an efficient photocleavable protecting group for molecules containing a carboxylic function. NNM possesses photochemical properties better than the 2-nitrobenzyl chromophores as it is photoactivatable at 380 nm in aqueous medium (CH3CN/H2O, 3:2 v/v) showing the desired photochemistry. The carboxylic acids are efficiently photoreleased from NNM-based esters in almost quantitative yield. 相似文献
8.
Olivier Busnel 《Tetrahedron letters》2007,48(33):5767-5770
The preparation of new Nβ-Fmoc-protected aza-β3-amino acids (aza-β3-aa) with proteinogenic side chains as well as their Nβ-Fmoc, Nβ-Cbz or Nβ-Boc aza-β3-amino esters (from Pro, Asn, Asp, Glu, Gln) by successive nucleophilic substitutions will be described. 相似文献
9.
Hammed H. A. M. Hassan 《Central European Journal of Chemistry》2005,3(4):803-829
A concise method for a stereocontrolled synthesis of a set of selectively protected disaccharides is reported. Coupling of
the donor 11 onto acceptors 23 and 24, promoted by trimethylsilyl triflate-N-iodosuccinimide (TMSOTf-NIS), generated the disaccharides 25 and 26. Under typical conditions, condensation of the fully protected donor 12 onto acceptors 23 and 24 produced the disaccharides 27 and 28. The building blocks 25–28 were prepared in moderate yields having exclusive β-stereoselectivity. A unique pattern of protecting groups distinguished
clearly between positions to be sulfated and functional groups remaining as free hydroxyl groups. Acetyl and/or levulinoyl
esters temporarily protected the positions to be sulfated, while benzyl ethers were used for permanent protection. The anomeric
positions were protected as allyl ethers, whereas the 4′-positions were masked as p-methoxybenzyl (PMB) ethers. The orthogonality of the PMB and allyl groups can then be used for further elongation of the
chain by recurrent deprotection and activation steps. The hydroxyl group, OH-6, of glucosamine moieties was protected as a
TBDPS ether to avoid oxidation. A five-step deprotection/sulfonation sequence was applied to the disaccharide 27 to generate the corresponding sulfated [β-D-GlcUA-2-OSO3Na-(1→4)-β-D-Glc pNAc]-(1→O-Pro) 34. 相似文献
10.
I Sebastián-Francisco 《Analytica chimica acta》2004,508(2):135-140
A quantitative assay for guar gum in carob gum, based on the extraction of proteins in acetonitrile-water (7:3), separation by capillary electrophoresis and multiple linear regression (MLR) using the areas of nine selected peaks as predictors, was improved by performing the extraction in the presence of gamanase. In the absence of the enzyme, peak migration times and areas depended on the guar content, which complicated peak identification and evaluation. Manual correction of the migration times by comparison with standard electropherograms obtained with pure carob and carob-guar mixtures was required; however, when the proteins were extracted under sonication at 60 °C for 30 min in the presence of gamanase, the migration times and peak areas did not vary with the composition of the carob-guar mixtures, and its reproducibility improved largely. These effects were attributed to the reduction of the viscosity of the extracts and the removal of the galactomannose interactions with the proteins and the capillary walls. Peak identification and evaluation were easily and directly performed on these electropherograms without further processing. An MLR model constructed with 36 carob-guar mixtures containing up to 20% guar, and by measuring the areas of 12 selected peaks and using eight of them as predictors, yielded a detection limit of 2.8% guar (α=β=0.05 criterion). A model of similar quality was obtained by partial least-squares (PLS) regression. 相似文献