Nano/Bio-Combined Catalytic Hybrids for Selective Chemical Synthesis

Abstract

As nanotechnology and biocatalysis have enormously developed, nanobiohybrids, which combine synthetic nanomaterials with living systems, have emerged, enabling the creation of the distinct properties for various applications. Nanobiohybrids have drawn significant interests from the perspective of functional extension through controllable integration of synthetic and biological components due to their synergistic and new functions resulting in enhanced stability, programmed metabolism and proliferation, artificial photosynthesis, or conductivity. However, although the catalytic efficiency and the synthetic capability of various chemicals has been expanded by hybrid systems via internal or external integration with synthetic materials, it is still challenging to control the interface between biological system and synthetic materials due to the lack of understanding of nano-bio interface interaction and proper design strategies. Thus, a new system capable of systematically control of nano-bio interface is required, in this sense, we developed a silica nanoreactor system based on nanospace-confined approach” developed in our research group. The nanoreactor system can provide a variety of catalysts with different configurations and compositions through the confined chemical reactions within the range of tens of nanometers. This confined system isolated from exterior environment not only stabilize various catalysts by the biocompatible silica shell, but can also help understanding of the phenomena in the nanoscale medium, thus enabling novel synthetic protocol for efficient hybrid catalysts and widening the synthetic capability than before strategies. In this thesis, we provide novel synthetic protocol for customizable nanobiohybrid catalysts with enhanced synthetic capability using silica nanoreactor system based on nanospace-confined approach. The content of chapter 1 describe the background and stature of the nanobiohybrid catalysts with their limitations, and silica-based nanoreactors with nanospace-confined approach as new synthetic strategies for novel nanobiohybrid catalysts. In chapter 2, we demonstrated the construction of open-mouth structure of chemoenzymatic silica nanocompartments as an intercellular-level system. As closed shells restrict the large size biomolecules, designing the intended open-mouthed shell-morphology is important. Here, we utilize yolk-shell structure to modify the composition of the selected part in shell. Yolk-shell structure of MnO@h-SiO2 was transformed to asymmetric hollow structure (SiJAR), consisting of segregated Mn-silicate patch in the silica shell, by controlled solid-state conversion at the arc-section of silica shell. Due to unique composition and hollow jar-like structure of SiJAR, intermediate isolated from solid-state conversion, Mn-silicate region was decorated with tiny Pd grains, resulting a negatively curved Pd-modified-lid on SiJAR through the galvanic replacement reactions. Furthermore, incubation of Pd-lid@SiJAR in phosphate buffer solution resulted in a lid dissociation from the surface, creating an open-mouth structure accommodating ligand-free Pd NCs inside. After further enzyme encapsulation by the large mouth-opening and negatively curved hollow interior, a chemoenzymatic catalytic nanoreactor (Cal-Pd@SiJAR) was generated. The final Cal-Pd@SiJAR exhibited high asymmetric catalytic efficiency through direct aldol reaction and also functioned as the artificial catalytic organelles in inside living cells. This effort can provide the possibility of customizable hybrid nanodevices and advanced platforms for new-to-nature catalysis. As an extended research on nanoreactor-based hybrid catalysts, described in chapter 3, a cellular-level nanobiohybrid system with active shells composed of 2D nanoreactors for the advanced microbial production was demonstrated. Due to chemical versatility for widen applicability as well as cytoprotection, the development of active shells capable of performing chemical reactions has been actively pursued. However, there are just a few examples of active shells and even those have limited versatility of functionality. Thus, we can customize the functionality of active shells on yeast cells through assembly process based on layer-by-layer (LBL) approach by utilizing biocompatible 2D silica nanoreactor system with nanospace-confined metal growth and further functionalization of silica surface. This strategy does not affect the cell viability and metabolism under various hostile environments. The very thin thickness of the shell can specifically regulate the nano-bio interface and catalysis. This strategy can be applied not only bacteria and fungi, but also mammalian cells, thus, the nanoreactor-assembled shells will be a versatile tool for various applications.