反胶束中脂肪酶催化合成异丁酸异戊酯

【作者】 王元鸿；

【导师】 褚莹；

【作者基本信息】 东北师范大学 ， 物理化学， 2003， 硕士

【摘要】 有机合成中的酶催化酯化反应已成为立体选择有机化学的一个成型的工具，且有一些专著和大量的综述。然而大部分这方面的文献报道均是基于长链底物的反应，短链酸和醇的酯化反应很少受到人们的注意。低分子量的酯对很多种水果的气味感觉有关键作用。它们主要是由短链脂肪酸的衍生物如：乙酸酯、丙酸酯、丁酸酯或异丁酸酯组成。异戊酯价值较高，有很大的商业需求，被广泛应用于食品、饮料、化妆品和制药行业中。天然的气味酯来源于植物，量少价格高，况且气味的质与量因地域不同而差别很大。大多数此类酯可以由酸与醇在较高的温度下化学催化反应制得。然而近来消费趋势倾向于天然食品，生物催化要比化学催化有优势，因为生物催化的产品会带有一种天然的招牌。与以传统方法制得的类似的酯相比，由象脂肪酶这样的酶催化合成的酯的气味要好得多。 目前已经有人利用固定化脂肪酶Rhizomucor meihei,Lipozyme IM-20在有机溶剂正己烷中催化异丁酸与异戊醇酯合成反应来制备异丁酸异戊酯，取得了较好的效果。但此种脂肪酶成本太高，不利于应用在工业生产中。而应用反胶束作为未反应器以脂肪酶催化此反应未见报道。我们选择了一种价格与之相比低得多、来源广泛的脂肪酶(其在有机溶剂中催化此反应的活性远不如Rhizomucor meihei,Lipozyme IM-20)，采用反胶束为固定化方法，系统研究了两种具有代表性表面活性剂AOT和CTAB与正己烷构成的反胶束体系中，影响反应转化率和酶活性诸因素：含水量、缓冲溶液pH值、反应温度、底物／酶的比例等因素的作用规律，优化出两种反胶束体系中制备异丁酸异戊酯的最适宜反应条件。实验表明，两种反胶束体系均为所选定的脂肪酶(CCL)提供了适宜的环境。与有机溶剂中相比，表现出超活力，分别为有机溶剂中的4倍和6倍，其中AOT体系中脂肪酶CCL的活性接近文献报道值，CTAB反胶束体系中脂肪酶CCL的活性已超过文献报道值，充分体现了反胶束体系的微观结构能模拟酶发挥作用的天然生物环境的明显优势，为反胶束体系中应用脂肪酶催化合成短链脂肪酸酯奠定了工作基础。更多还原

【Abstract】 Lipase-catalyzed esterifications reaction of organic synthesis has become a fashioned tool of stereo-specific organic chemistry , which has been reported in many literatures . However, most of the work on lipase-catalyzed esterifications reported in the literatures have been based on reactions using longer-chain length substrates, the esterifications of short-chain fatty acids and alcohols have received little attention .Low molecular weight esters are responsible for the aroma of many fruits and constitute mainly short-chain fatty acid derivatives like acetate, propionate, butyrate and isobutyrate. For example, ethyl, butyrate and isoamyl isobutyrate are presented in the aroma of strawberry and banana, respectively. Isoamyl esters are valuable and high-demand flavour compounds of commercial importance, and are widely used in the food, beverage, cosmetic and pharmaceutical industries etc. Natural flavour esters extracted from plant sources are often in short supply or expensive. Moreover, flavour quality and quantity varies from region to region, Most of these esters can also be produced chemically by acid -catalyzed condensation of an alcohol and an acid at elevated temperatures . However, recent trends in consumer preference toward ’natural’ products indicate that biocatalysis may have an advantage over chemical synthesis as products of biocatalysis may have a ’natural’ label. It was also observed that fatty acid esters, synthesized by enzymes such as lipase, often have better odour and flavour characteristics compared to similar esters produced by conventional means.Presently, immobilized Rhizomucor miehei lipozyme IM-20 has been used to catalyze the esterification reaction between isobutyric acid and isoamyl alcohol to synthesize isoamyl isobutyrate in n-hexane, which has been proved to be an effective method. But it is not fit for industrialproduction because of the high price of the lipase . However, this esterification catalyzed by lipase in reversed micelles has not been reported . We use another easily obtained lipase (which has much lower activity than Rhizomucor meihie lipozyme IM-20 lipase has in n-hexane) with much lower price compared with the Rhizomucor miehei, and by investigating systematically the regularities of the effects of water content, pH of buffer, temperature and the ratio of substrate/enzyme optimize the suitable condition for the esterification reaction between isobutyric acid and isoamyl isobutyrate in two kinds of typical reversed micelles of AOT and CTAB. Experimental results show that the two kinds of reversed micelles both provide suitable environment for the lipase (CCL), which show superactivity-four and six times as that in n-hexane respectively. The activity of lipase(CCL) in AOT reversed micelles is close to that of Rhizonucor meihei lipozyme IM-20 in n-hexane, while the activity in CTAB reversed micelle is higher than that of Rhizonucor meihei in n-hexane reported in literature, which has certified sufficiently that the microstructure of reversed micelle has obvious superiority which can simulate the natural biological environment for lipase to perform its function, and can lay a foundation for the future work on esterification synthesis between short-chain fatty acids and alcohols.更多还原