排序方式: 共有11条查询结果,搜索用时 31 毫秒
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Dahlberg CJ Harris G Urban J Tripp ML Bland JS Carroll BJ 《Journal of separation science》2012,35(9):1183-1189
Commercially available hops (Humulus lupulus L.) bitter acid extracts contain a mixture of three major congeners (co-, n-, and ad-) in addition to cis/trans diastereomers for each congener. Individual isomerized α-acids were obtained by the consecutive application of two separate countercurrent chromatography methods. First, individual isomerized α-acid congeners as a mixture of cis/trans diastereomers were obtained using a solvent system consisting of hexane and aqueous buffer. The second purification, capable of separating cis/trans diastereomers, was accomplished using a quaternary solvent system; an alternative procedure using β-cyclodextrin followed by countercurrent chromatography was also investigated. The NaBH(4) reduction of the purified isomerized α-acid compounds followed by countercurrent chromatography purification resulted in individual ρ iso α-acids (>95%). Similarly, catalytic hydrogenation of the purified isomerized α-acid compounds followed by countercurrent chromatography purification produced individual tetrahydro isomerized α-acids (>95%). Reported herein is a widely applicable approach that focuses on three critical variables--solvent system composition, pH, and buffer-to-sample ratio--that enable the efficient purification of individual bitter acids (≥95%) from commercially available hops extracts. 相似文献
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十六烷基三甲基溴化铵对脱水四环素和异四环素荧光增强作用研究 总被引:3,自引:0,他引:3
在不同pH值的标准缓冲溶液及不同表面活性剂十六烷基三甲基溴化铵(CTMAB)浓度的胶束溶液环境中,研究了CTMAB对盐酸四环素的降解产物脱水四环素和异四环素的荧光强度的影响。结果表明,CTMAB对脱水四环素和异四环素具有荧光增强作用,荧光增强幅度与介质的pH值和CTMAB浓度有关,在中性和碱性条件下对脱水四环素荧光增强作用较大,在pH=9.2的条件下可使异四环素的荧光强度达到最大值,CTMAB对脱水四环素和异四环素的这种荧光增强作用,为建立较灵敏的盐酸四环素及其降解产物的荧光定量方法提供了依据。 相似文献
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Christian Lherbet David Soupaya Cécile Baudoin-Dehoux Chantal André Casimir Blonski Pascal Hoffmann 《Tetrahedron letters》2008,49(38):5449-5451
A new route to functionalized iso(thio)chromans is described. The compounds are accessible easily in a one pot-reaction by using different benzaldehydes and phenylethanethiol or phenylethanol in presence of bismuth triflate. 相似文献
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在弱酸性介质中,有溴化十六烷基三甲铵(CTMAB)存在条件下,CN-与异烟酸-硫代巴比妥酸形成一蓝色化合物,其最大吸收波长(λmax)位于646 nm,表观摩尔吸光系数6ε46=4.67×104L.mol-1.cm-1,且其吸光度A与氰化物含量在一定的范围内呈良好的线性关系。据此,建立了测定生活饮用水中微量氰化物的CTMAB-异烟酸-硫代巴比妥酸显色光度法。本法氰化物含量在0~4.0μg/10.0 mL范围内符合比耳定律,用于生活饮用水中微量氰化物的测定,结果令人满意。 相似文献
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Lilly Capuano Marott Bronder Wolfgang Hell Peter Mörsdorf Reinhold Hoge 《Monatshefte für Chemie / Chemical Monthly》1980,111(4):899-907
The reaction of diethyl bromomalonate (1) or diethyl diazomalonate (6) with benzoyl isothiocyanate (2) proceeds via the carbene intermediates4, 7 or12 to afford the 1,3-dithiole5, the 2-oxazoline8 or the 1,3-oxathioles9 depending upon the catalyst employed. In contrast, the bis(ethoxycarbonyl)methylpyridinium bromides14 upon treatment with benzoyl isocyanates15 in pyridine give rise to vinylene dipyridinium dibromides18. 相似文献
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VMgO催化剂上丙烷和异丁烷临氧催化转化机理 总被引:1,自引:0,他引:1
用程序升温反应 -红外光谱技术研究 2 0VMgO和 6 0VMgO催化剂上丙烷和异丁烷临氧催化转化的机理 .结果表明 ,临氧条件下的反应性是异丁烷 >丙烷 ,与其分子中最弱C -H键键能从弱到强顺序相同 ,这意味着临氧活化的第一步可能是断裂分子中强度最弱的C -H键、且为速率控制步骤 ;丙烷临氧反应的深度氧化产物COx 与氧化脱氢产物丙烯的生成是平行和 (或 )连续反应关系 ,而裂解产物乙烯和甲烷的生成则是平行反应 ;异丁烷氧化脱氢反应中C -C键的断裂比丙烷的容易 . 相似文献
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