Background During lipase-mediated biodiesel production, by-product glycerol adsorbing on immobilized lipase is a common trouble that hinders enzymatic catalytic activity in biodiesel production process. In this work, we built a hydrophobic pore space in macroporous ZIF-8 (named as M-ZIF-8) to accommodate lipase so that the generated glycerol would be hard to be adsorbed in such hydrophobic environment. The performance of the immobilized lipase in biodiesel production as well as its characteristics for glycerol adsorption were systematically studied. The PDMS (polydimethylsiloxane) CVD (chemical vapor deposition) method was utilized to get hydrophobic M-ZIF-8-PDMS with hydrophobic macropore space and then ANL (Aspergillus niger lipase) was immobilized on M-ZIF-8 and M-ZIF-8-PDMS by diffusion into the macropores. Results ANL@M-ZIF-8-PDMS presented higher enzymatic activity recovery and better biodiesel production catalytic performance compared to ANL@M-ZIF-8. Further study revealed that less glycerol adsorption was observed through the hydrophobic modification, which may attribute to the improved immobilized lipase performance during biodiesel production and ANL@M-ZIF-8-PDMS remained more than 96% activity after five cycles' reuse. Through secondary structure and kinetic parameters' analysis, we found that ANL@M-ZIF-8-PDMS had lower extent of protein aggregation and twice catalytic efficiency (V max/K m) than ANL@M-ZIF-8. Conclusions Hydrophobic pore space constituted in macroporous ZIF-8 for lipase immobilization greatly improved lipase catalytic performance in biodiesel preparation. The hydrophobic modification time showed negligible influence on the reusability of the immobilized lipase. This work broadened the prospect of immobilization of enzyme on MOFs with some inspiration.

中文翻译：

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大孔ZIF-8构成的疏水孔空间用于脂肪酶的固定化，大大提高了生物柴油制备中的脂肪酶催化性能。

背景在脂肪酶介导的生物柴油生产过程中，副产物甘油吸附在固定化脂肪酶上是阻碍生物柴油生产过程中酶催化活性的常见问题。在这项工作中，我们在大孔 ZIF-8（命名为 M-ZIF-8）中构建了一个疏水孔空间来容纳脂肪酶，使生成的甘油在这种疏水环境中难以被吸附。系统研究了固定化脂肪酶在生物柴油生产中的性能及其对甘油的吸附特性。利用PDMS（聚二甲基硅氧烷）CVD（化学气相沉积）方法获得具有疏水大孔空间的疏水M-ZIF-8-PDMS，然后将ANL（黑曲霉脂肪酶）固定在M-ZIF-8和M-ZIF-8上-PDMS 通过扩散到大孔中。结果与ANL@M-ZIF-8相比，ANL@M-ZIF-8-PDMS具有更高的酶活性回收率和更好的生物柴油生产催化性能。进一步的研究表明，通过疏水改性观察到较少的甘油吸附，这可能归因于生物柴油生产过程中固定化脂肪酶性能的提高，并且 ANL@M-ZIF-8-PDMS 在重复使用五个循环后仍保持 96% 以上的活性。通过二级结构和动力学参数分析，我们发现ANL@M-ZIF-8-PDMS具有比ANL@M-ZIF-8更低的蛋白质聚集程度和两倍的催化效率（V max/K m）。结论用于脂肪酶固定的大孔ZIF-8构成的疏水孔空间大大提高了生物柴油制备中脂肪酶的催化性能。疏水修饰时间对固定化脂肪酶的可重复使用性的影响可以忽略不计。这项工作拓宽了酶在 MOFs 上的固定化前景，并带来了一些启发。