Immobilization of Acetobacter sp. CCTCC M209061 for efficient asymmetric reduction of ketones and biocatalyst recycling.
Immobilization of Acetobacter sp. CCTCC M209061 for efficient asymmetric reduction of ketones and biocatalyst recycling.
复制标题
醋杆菌属的固定化。
DOI：
10.1186/1475-2859-11-119
复制
发表时间：
2012-09-04
影响因子：
6.4
通讯作者：
Chen XD
中科院分区：
文献类型：
--
作者：
Chen XH;Wang XT;Lou WY;Li Y;Wu H;Zong MH;Smith TJ;Chen XD
背景
醋酸杆菌属（Acetobacter sp.）CCTCC M209061是一种有前途的全细胞生物催化剂，具有独特的反Prelog立体选择性，用于还原前手性酮，可用于制备有价值的手性醇，如（R）-4-（三甲基硅烷基）-3-丁炔-2-醇。虽然它具有很好的催化性能，但与其他生物催化剂相比，其稳定性和可重复使用性相对较差。因此，我们探索各种固定化活性细胞的材料，以提高生物催化剂的操作稳定性。
结果
结果表明，海藻酸钙的固定化效果最好，壳聚糖对固定化生物催化剂进行包覆，可进一步提高其机械强度和抗溶胀性能。优化了制备可重复使用的固定化微球的条件，该微球可用于4′-氯苯乙酮的重复批量不对称还原。优化后的固定化生物催化剂对4′-氯苯乙酮的不对称还原比活性为游离细胞的85%（固定化催化剂为34.66 μ mol/min/g干重，游离细胞为40.54 μ mol/min/g干重）。与游离细胞相比，固定化细胞具有更好的热稳定性、pH稳定性、耐溶剂性和贮存性。经过25个循环的反应，固定化微球仍保持50%的催化活性，这是以类似方式重复使用的游离细胞的活性保留程度的3.5倍。细胞可以在珠粒中再培养以恢复完全活性并进行另外25个循环的还原反应。由Damkohler模量Da 1推断，外部传质阻力可以忽略不计;由有效因子η 1和Thiele模量0.3 <$1推断，内部传质限制影响还原作用，但不是主要的速率控制步骤。
结论
壳聚糖包被海藻酸钙是一种高效的固定化醋酸杆菌CCTCC M209061细胞的材料，可重复用于酮的不对称还原。与游离细胞相比，就催化活性而言，只有很小的成本可以得到高度实用的固定化生物催化剂。
Background
The bacterium Acetobacter sp. CCTCC M209061 is a promising whole-cell biocatalyst with exclusive anti-Prelog stereoselectivity for the reduction of prochiral ketones that can be used to make valuable chiral alcohols such as (R)-4-(trimethylsilyl)-3-butyn-2-ol. Although it has promising catalytic properties, its stability and reusability are relatively poor compared to other biocatalysts. Hence, we explored various materials for immobilizing the active cells, in order to improve the operational stability of biocatalyst.
Results
It was found that Ca-alginate give the best immobilized biocatalyst, which was then coated with chitosan to further improve its mechanical strength and swelling-resistance properties. Conditions were optimized for formation of reusable immobilized beads which can be used for repeated batch asymmetric reduction of 4′-chloroacetophenone. The optimized immobilized biocatalyst was very promising, with a specific activity of 85% that of the free-cell biocatalyst (34.66 μ mol/min/g dw of cells for immobilized catalyst vs 40.54 μ mol/min/g for free cells in the asymmetric reduction of 4′-chloroacetophenone). The immobilized cells showed better thermal stability, pH stability, solvent tolerance and storability compared with free cells. After 25 cycles reaction, the immobilized beads still retained 50% catalytic activity, which was 3.5 times higher than degree of retention of activity by free cells reused in a similar way. The cells could be recultured in the beads to regain full activity and perform a further 25 cycles of the reduction reaction. The external mass transfer resistances were negligible as deduced from Damkohler modulus Da 1, and internal mass transfer restriction affected the reduction action but was not the principal rate-controlling step according to effectiveness factors η 1 and Thiele modulus 0.3∅ 1.
Conclusions
Ca-alginate coated with chitosan is a highly effective material for immobilization of Acetobacter sp. CCTCC M209061 cells for repeated use in the asymmetric reduction of ketones. Only a small cost in terms of the slightly lower catalytic activity compared to free cells could give highly practicable immobilized biocatalyst.