Immobilized Enzymes in Covalent Organic Frameworks as Active Heterogeneous Catalyst

Paul, Satyadip (2024) Immobilized Enzymes in Covalent Organic Frameworks as Active Heterogeneous Catalyst. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Satyadip Paul (18RS105)) 18RS105.pdf - Submitted Version Restricted to Repository staff only Download (16MB)

Abstract

Biocatalysis serves as a complementary approach to traditional chemical synthesis, offering higher selectivity and efficiency under mild conditions. In this process, enzymes function as catalysts, with their catalytic pockets facilitating the appropriate orientation of substrates to enable specific chemical reactions. However, enzymes are susceptible to denaturation and typically can not be reused. To address this, the strategy of enzyme engineering and enzyme immobilization onto carrier supports has emerged as a promising solution. Enzyme engineering has been used to make stable enzymes with high activity and selectivity. It could not solve the issue of reusability. To address both challenges, immobilization has emerged as a potential way out. In this context, covalent organic framework becomes a promising material as a solid carrier for the immobilization of enzymes. Covalent organic framework is a crystalline porous material composed of light elements. High thermal chemical stability and robust framework make it a suitable material for heterogeneous biocatalysis. Chapter I depicts the division of catalysis and the importance of biocatalysis over the state of the other catalytic pathways. However, the fragile nature of the biocatalyst is the major problem in this field. Enzyme engineering has evolved as a successful technique to make a stable enzyme with higher activity and selectivity. In another way, the immobilization of enzymes in solid support also becomes a strategy to introduce stability and enhanced performance. Initially, silica, cellulose, and PVA have been used for this, but the lack of proper interactions with enzymes made them unsuitable for enzyme immobilization. In this context, porous materials have been serving as potential carriers. Metal-organic framework, the hydrogenbonded organic framework, offers enzymes for immobilization. However, due to lower stability and leaching of toxic metals led to bring another porous material covalent organic framework. Covalent organic framework serves as a robust platform for enzyme immobilization and further implication in biocatalysis. Chapter II describes the fabrication of hierarchical nanostructure possessing micro, meso, and macroporosity. This nanostructure is called COF-foam, and it has been synthesized mechanochemically. This COF foam is an ideal platform for immobilizing multiple enzymes and is also active toward multienzyme tandem catalysis. Apart from that, this chapter discusses the ability of foam to provide stability to the enzymes in the presence of organic solvents and elevated temperatures. The recyclability of the enzymeimmobilized foam also plays a crucial role in the catalysis. Chapter III depicts the potential ability of a metal-anchored covalent organic framework as a column matrix for the purification of recombinant enzymes. Recognizing the significance of enzyme purification from cell lysates in biotechnology, we have also created a metal anchored covalent organic framework tailored for this purpose. This chapter shows that a metal-anchored covalent organic framework can be used to build a technique where immobilization and purification can happen simultaneously. This enzyme-immobilized metal-anchored COF is active toward biocatalysis and shows extensive stability at room temperature, unlike free enzymes. Chapter IV describes a one-pot methodology to produce enzyme-immobilized COF. It is an encapsulation method that secures enzymes within matrix rather than on its surface using a co-precipitation technique, thus enhancing stability against proteolytic agents. Chapter V summarizes the fabrication of different covalent organic frameworks and the development of a new strategy for enzyme immobilization. It also directs how these can be applied to artificial enzymes where high-cost enzymes can be recovered after immobilizing them in the nano framework.

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