无搅拌条件下的Pickering乳液用于脂肪酶催化合成酯的反应

Enzymatic synthesis of esters in stirring-free Pickering emulsions

为了解决目前酶催化领域中所存在的酶催化效率低和搅拌会对酶结构造成破坏的问题,采用了一种新的体系来进行无搅拌下两相酶催化反应。该体系是通过加入一定量的界面活性固体颗粒作为乳化剂将传统两相酶催化反应转变为W/O的Pickering乳液体系。该体系中,催化剂洋葱伯克霍尔德菌脂肪(BCL)酶包裹在微米尺度的液滴中,而有机反应底物溶解在油相(乳滴外部)中。实验证明,无搅拌条件下的Pickering乳液反应体系中酶的催化效率明显高于搅拌的两相体系,这是由于Pickering乳液乳滴具有大的反应界面积和短的分子扩散距离。实验进一步发现,酶的比活度取决于乳滴的大小,更加体现出了反应体系中乳滴的重要性。此外,仅通过简单地离心破乳即可实现BCL酶循环利用,且经过6次循环后,转化率依旧可达86%,这可能是因为无搅拌反应体系不会破坏酶的立体结构。这一研究证明,Pickering乳液体系提供了一种不需要搅拌和固载就可高效进行的酶催化酯交换反应的新平台。

To solve the problems currently in enzymatic reactions（ such as low efficiency and the destruction of enzyme structure induced by stirring）,a novel strategy of stirring-free two-phase enzymatic reaction was developed. In this strategy,the conventional two-phase enzymatic reaction was altered by a system of water-in-oil（ W/O） Pickering emulsion in which a small amount of interfacial-active solid particles were used as emulsifier. In this system,a Burkholderia Cepacia lipase（ BCL） enzyme was packaged within micron-sized water droplets,while organic substrates were dissolved in oil phase（ outside the droplets）. The experimental results show that,the reaction efficiency of BCL-catalyzed transesterification is obviously higher in the stirring-free Pickering emulsion than in the conventional two-phase system under stirring. The reasons may be that the droplets of Pickering emulsion have a large area of reaction interface and a short distance for molecular diffusion. In addition,it is found that the specific activity of enzyme depends on the size of water droplets,indicative of the importance of droplets in the reaction system. Moreover,effective recycling of BCL enzyme can be simply realized through demulsification by centrifugation. After 6 reaction cycles,the conversion is still as high as 86%,probably due to the avoidance of stirring that may cause damage to the three-dimensional structure of enzyme. This study demonstrates that the Pickering emulsion is an innovative platform for efficient enzyme-catalyzed transesterification without stirring or immobilization.