1‐MCP does not improve the shelf‐life of Chinese cabbage

Chinese cabbages cv ‘Yuki’ (Brassica campestris L ssp pekinensis (Lour) Olsson) were treated with air containing 1‐methylcyclopropene (1‐MCP) at concentrations ranging from 0 to 1 µl l^?1 for 12 h at 22°C before storage for 9 weeks at 3°C. Quality, weight loss and trimming loss were measured before treatment, and before and after storage, but were not influenced by 1‐MCP. 1‐MCP at 0.1 and 1.0 µl l^?1 elicited increased levels of respiration and ethylene production which subsided when the cabbages were placed in cold storage. Copyright © 2004 Society of Chemical Industry     

气相色谱技术测定棉籽及其饼(粕)中环丙烯脂肪酸含量北大核心CSCD

为了解决棉籽及其饼(粕)中环丙烯脂肪酸分析测定的技术难题,通过比较脂肪酸衍生化方法、优化气相色谱条件建立了气相色谱技术(GC)测定棉籽及其饼(粕)中环丙烯脂肪酸(锦葵酸和苹婆酸)含量的方法。结果表明:碱式甲酯化对环丙烯脂肪酸的衍生化效果最佳;优化的GC条件为DB-1ht毛细管柱,氮气流速0.6 mL/min,升温程序为从100℃以2℃/min的速度上升到220℃。在此基础上,通过建立苹婆酸与锦葵酸回归方程(R^(2 )≥0.997)测得棉籽、棉籽饼和棉籽粕中的锦葵酸含量分别为2.62、0.68 mg/g和0.09 mg/g,苹婆酸含量分别为1.02、0.27 mg/g和0.04 mg/g。方法的重复性和回收率良好,为棉籽及其饼(粕)中环丙烯脂肪酸的分析检测提供了技术依据和指导。     

Preparation of malvalic and sterculic acid methyl esters from Bombax munguba and Sterculia foetida seed oils

A method has been developed for the preparation of highly pure malvalic (cis-8,9-methyleneheptadec-8-enoic) and sterculic (cis-9,10-methyleneoctadec-9-enoic) acid methyl esters starting from Bombax munguba and Sterculia foetida seed oils. The methyl esters of these oils were prepared by sodium methylate-catalyzed transmethylation followed by cooling (6°C) the hexane solution of crude methyl esters and separation of insoluble fatty acid methyl esters by centrifugation in the case of B. munguba and by column chromatography in the case of S. foetida. Subsequently, the saturated straight-chain fatty acid methyl esters were almost quantitatively removed by urea adduct formation. Finally, methyl malvalate and methyl sterculate were separated from the remaining unsaturated fatty acid methyl esters, in particular methyl oleate and methyl linoleate, by preparative high-performance liquid chromatography on C₁₈ reversed-phase using acetonitrile isocratically. Methyl malvalate and methyl sterculate were obtained with purities of 95–97 and 95–98%, respectively.     

Modular Enzyme- and Light-Based Activation of Cyclopropene–Tetrazine Ligation

We describe a modular activation strategy for cyclopropene–tetrazine ligation. This activation strategy uses chemically diverse enzyme- or photolabile protecting groups as cyclopropene reactivity cages. The linkages between the caging groups and cyclopropene are through carbamates, thus permitting the application of diverse cages to allow bioorthogonal reactivity by administering enzymes or light.