State Key Laboratory of Pulp and Paper Engineering, South China University of Technology, Guangzhou 510640, People's Republic of China.
Microb Cell Fact. 2012 Sep 4;11:119. doi: 10.1186/1475-2859-11-119.
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.
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 μmol/min/g dw of cells for immobilized catalyst vs 40.54 μmol/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.
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.
醋酸杆菌 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，可用于还原前手性酮，从而制备有价值的手性醇，如（R）-4-（三甲基甲硅烷基）-3-丁炔-2-醇。尽管它具有有前途的催化性能，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，我们探索了各种材料来固定活性细胞，以提高生物催化剂的操作稳定性。
发现海藻酸钙可以得到最好的固定化生物催化剂，然后用壳聚糖进一步改善其机械强度和抗溶胀性能。优化了形成可重复使用的固定化珠粒的条件，这些珠粒可用于重复分批不对称还原 4'-氯苯乙酮。优化的固定化生物催化剂非常有前途，其比游离细胞生物催化剂的比活性高 85%（固定化催化剂不对称还原 4'-氯苯乙酮的比活性为 34.66 μmol/min/g dw 的细胞，游离细胞为 40.54 μmol/min/g）。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、溶剂耐受性和储存稳定性。在 25 次循环反应后，固定化珠粒仍保留 >50%的催化活性，是类似方式重复使用的游离细胞保留活性的 3.5 倍。细胞可以在珠粒中重新培养以恢复全部活性，并进一步进行 25 次还原反应。根据效能因子 η < 1 和 Thiele 模数 0.3<∅ <1，推断出外部传质阻力可以忽略不计，而内部传质限制影响还原作用，但不是主要的速率控制步骤。
壳聚糖包被的海藻酸钙是固定醋酸杆菌 CCTCC M209061 细胞用于酮类不对称还原的重复使用的高效材料。与游离细胞相比，只是催化活性略有降低，但可以获得非常实用的固定化生物催化剂。
