Department of Chemistry and Biochemistry, North Dakota State University, Fargo, North Dakota 58102, United States.
Department of Plant Sciences, North Dakota State University, Fargo, North Dakota 58102, United States.
ACS Appl Mater Interfaces. 2020 Sep 16;12(37):41794-41801. doi: 10.1021/acsami.0c13148. Epub 2020 Sep 3.
Immobilizing enzymes on nanoparticles (NPs) enhances the cost-efficiency of biocatalysis; however, when the substrates are large, it becomes difficult to separate the enzyme@NP from the products while avoiding leaching or damage of enzymes in the reaction medium. Metal-organic framework (MOF)-coated magnetic NPs (MNPs) offer efficient magnetic separation and enhanced enzyme protection; however, the involved enzymes/substrates have to be smaller than the MOF apertures. A potential solution to these challenges is coprecipitating metal/ligand with enzymes on the MNP surface, which can partially bury (protect) the enzyme below the composite surface while exposing the rest of the enzyme to the reaction medium for catalysis of larger substrates. Here, to prove this concept, we show that using Ca and terephthalic acid (BDC), large-substrate enzymes can be encapsulated in CaBDC-MOF layers coated on MNPs via an enzyme-friendly, aqueous-phase one-pot synthesis. Interestingly, we found that using MNPs as the nuclei of crystallization, the composite size can be tuned so that nanoscale composites were formed under low Ca/BDC concentrations, while microscale composites were formed under high Ca/BDC concentrations. While the microscale composites showed significantly enhanced reusability against a non-structured large substrate, the nanoscale composites displayed enhanced catalytic efficiency against a rigid, crystalline-like large substrate, starch, likely due to the improved diffusivity of the nanoscale composites. To our best knowledge, this is the first report on aqueous-phase one-pot synthesis of size-tunable enzyme@MOF/MNP composites for large-substrate biocatalysis. Our platform can be applied to immobilize other large-substrate enzymes with enhanced reusability and tunable sizes.
将酶固定在纳米颗粒 (NPs) 上可以提高生物催化的成本效益；然而，当底物较大时，在避免酶在反应介质中浸出或损坏的同时，从产物中分离出酶@NP 变得困难。金属-有机骨架 (MOF) 涂层的磁性 NPs (MNPs) 提供了有效的磁分离和增强的酶保护；然而，所涉及的酶/底物必须小于 MOF 孔径。解决这些挑战的一种潜在方法是在 MNP 表面上将金属/配体与酶共沉淀，这可以部分掩埋（保护）酶低于复合表面，同时将其余的酶暴露于反应介质中，以催化较大的底物。在这里，为了证明这一概念，我们表明，使用 Ca 和对苯二甲酸（BDC），可以通过酶友好的水相一锅合成，将大底物酶封装在涂覆在 MNPs 上的 CaBDC-MOF 层中。有趣的是，我们发现使用 MNPs 作为结晶的核，复合材料的尺寸可以被调节，使得在低 Ca/BDC 浓度下形成纳米级复合材料，而在高 Ca/BDC 浓度下形成微尺度复合材料。虽然微尺度复合材料对非结构化大底物表现出显著增强的可重复使用性，但纳米尺度复合材料对刚性、类似结晶的大底物淀粉显示出增强的催化效率，这可能是由于纳米尺度复合材料的扩散性得到了提高。据我们所知，这是关于水相一锅法合成可调节尺寸的酶@MOF/MNP 复合材料用于大底物生物催化的首次报道。我们的平台可用于固定其他具有增强的可重复使用性和可调尺寸的大底物酶。
