Enzyme Catalysis in Non-Native Environment with Unnatural Selectivity Using Polymeric Nanoreactors

Electrostatically Mediated In Situ Polymerization for Enzyme Immobilization and Activation

Enzyme immobilization in nanoparticles is of interest for boosting their catalytic applications, yet rational approaches to designs achieving both high enzyme loading and activation remain a challenge. Herein, we report an electrostatically mediated in situ polymerization strategy that simultaneously realizes enzyme immobilization and activation. This was achieved by copolymerizing cationic monomers with a cross-linker in the presence of the enzyme lipase (anionic) as the template, which produces enzyme-loaded nanogels. The effects of different control factors such as pH, lipase dosage, and cross-linker fraction on nanogel formation are investigated systematically, and optimal conditions for enzyme loading and activation have been determined. A central finding is that the cationic polymer network of the nanogel creates a favorable environment that not only protects the enzyme but also boosts enzymatic activity nearly 2-fold as compared to free lipase. The nanogels improve the stability of the lipase to tolerate a broader working range of pH (5.5-8.5) and temperature (25-70 °C) and allow recycling such that after six cycles of reaction, 70% of the initial activity is conserved. The established fabrication strategy can be applied generally to different cationic monomers, and most of these nanogels exhibit adequate immobilization and activation of lipase. Our study confirms that in situ polymerization based on electrostatic interaction provides a facile and robust strategy for enzyme immobilization and activation. The wide variety of ionic monomers, therefore, features great potential for developing functional platforms toward satisfying enzyme immobilization and demanding applications.

Targeting and Microenvironment-Activated Nanoreactor for Diabetic Chronic Wound Healing via Multienzyme Cascade Reactions

The development of cell-like nanoreactors with the ability to initiate biocatalytic cascades under special conditions holds tremendous potential for therapeutic applications. Herein, conformationally gated nanoreactors that respond to the acidic microenvironment of infected diabetic wounds were developed by cucur[8]bituril (CB[8])-based supramolecular assembly. The bioinspired nanoreactors exhibit not only self-regulated permeability and selectivity to control internal enzyme activities by substance exchange but also distinct binding specificities toward Gram-positive and Gram-negative bacteria via noncovalent modification with different ligands. The encapsulation of glucose oxidase (GOx), Fe3O4 nanozyme, and l-arginine (l-Arg) into the nanocarriers enables intelligent activation of multienzyme cascade reactions upon glucose (Glu) uptake to produce gluconic acid (GA) and hydrogen peroxide (H2O2), which is further converted into highly toxic hydroxyl radicals (·OH) for selective antibacterial activity. Moreover, acidic H2O2 promotes the oxidization of l-Arg, leading to the release of nitric oxide (NO). Consequently, this nanoreactor provides a multifunctional and synergistic platform for diabetic chronic wound healing by combining enzyme dynamic therapy with NO gas therapy to combat bacterial infections and inflammation under high blood Glu levels.

Encapsulation of multiple enzymes within a microgel via water-in-water emulsions for enzymatic cascade reactions

Enzyme-loaded spherical microgels with diameters of several micrometers have been explored for use in therapeutic microreactors and biosensors. Conventional preparation strategies for enzyme-loaded microgels utilized water-in-oil emulsions or flow chemistry techniques. The former damage enzyme activity using organic solvents and the latter are expensive and difficult to expand because of the complex system. In this study, we present a simple strategy for creating multiple enzyme-loaded gelatin-based microgels with tunable diameters in a single flask. This strategy was based on our finding that enzymes spontaneously partitioned in a dispersed methacryloyl gelatin aqueous solution in a poly(vinylpyrrolidone) (WGelMA/WPVP) aqueous solution. The method achieved an encapsulation efficiency of over 70% even with four types of enzymes and retained their activity owing to the full aqueous system. Additionally, the encapsulated β-galactosidase activity was maintained for 24 hours at pH 6, although naked β-galactosidase lost approximately 60% of its activity, which was superior to that of previous enzyme-loaded gelatin gels. Moreover, this simple method enabled the production of 10 g-scale or more microgels in one batch. We also demonstrated that multiple enzyme-loaded gelatin microgels functioned as cascade microreactors for lactose and glucose sensing. This versatile strategy enables the production of enzyme-loaded microgels while maintaining the enzyme activity using very low technologies. This result contributes to the easy preparation of enzyme-loaded microgels and their applications in the biomedical and green catalytic fields.

Structural Determinants of Stimuli-Responsiveness in Amphiphilic Macromolecular Nano-assemblies

Stimuli-responsive nano-assemblies from amphiphilic macromolecules could undergo controlled structural transformations and generate diverse macroscopic phenomenon under stimuli. Due to the controllable responsiveness, they have been applied for broad material and biomedical applications, such as biologics delivery, sensing, imaging, and catalysis. Understanding the mechanisms of the assembly-disassembly processes and structural determinants behind the responsive properties is fundamentally important for designing the next generation of nano-assemblies with programmable responsiveness. In this review, we focus on structural determinants of assemblies from amphiphilic macromolecules and their macromolecular level alterations under stimuli, such as the disruption of hydrophilic-lipophilic balance (HLB), depolymerization, decrosslinking, and changes of molecular packing in assemblies, which eventually lead to a series of macroscopic phenomenon for practical purposes. Applications of stimuli-responsive nano-assemblies in delivery, sensing and imaging were also summarized based on their structural features. We expect this review could provide readers an overview of the structural considerations in the design and applications of nanoassemblies and incentivize more explorations in stimuli-responsive soft matters.

Supramolecular Ionic Liquid Gels for Enzyme Entrapment

Reported herein is an entrapment method for enzyme immobilization that does not require the formation of new covalent bonds. Ionic liquid supramolecular gels are formed containing enzymes that can be shaped into gel beads and act as recyclable immobilized biocatalysts. The gel was formed from two components, a hydrophobic phosphonium ionic liquid and a low molecular weight gelator derived from the amino acid phenylalanine. Gel-entrapped lipase from Aneurinibacillus thermoaerophilus was recycled for 10 runs over 3 days without loss of activity and retained activity for at least 150 days. The procedure does not form covalent bonds upon gel formation, which is supramolecular, and no bonds are formed between the enzyme and the solid support.

Lipase-Entrapped Colloidosomes with Tunable Positioning at the Oil-Water Interface for Pickering Emulsion-Enhanced Biocatalysis

Pickering interfacial biocatalysis (PIB) paves the way for efficient enzymatic catalysis in the biphasic system. However, the Pickering interfacial biocatalysts located on the oil-water interface still face the inevitable deactivation when one of the phases contains the reactant that inactivates the enzyme. Herein, the positioning of lipase-entrapped colloidosomes (LECs) at the emulsion interface is rationally designed by physically tuning the wettability, which allows LECs to protrude into the selected phase to protect the lipase away from the damage of the reactant. As a proof of concept, LECs with different positioning at the interface are used as Pickering interfacial biocatalysts to produce biodiesel by esterification of lauric acid and methanol. Impressively, the LECs that protrude into the oil phase possess an optimal catalytic performance to protect more lipases away from the damage of the reactant of short-chain alcohol, which shows an 8.18-fold enhancement in specific activity relative to the free lipase, reach a biodiesel yield of 80.37% after 8 h, and retain the 96.44% of relative activity after 10 cycles. This study provides a novel and robust platform for Pickering emulsion-enhanced biocatalysis.

Facile Fabrication of 1-Methylimidazole/Cu Nanozyme with Enhanced Laccase Activity for Fast Degradation and Sensitive Detection of Phenol Compounds

Facile construction of functional nanomaterials with laccase-like activity is important in sustainable chemistry since laccase is featured as an efficient and promising catalyst especially for phenolic degradation but still has the challenges of high cost, low activity, poor stability and unsatisfied recyclability. In this paper, we report a simple method to synthesize nanozymes with enhanced laccase-like activity by the self-assembly of copper ions with various imidazole derivatives. In the case of 1-methylimidazole as the ligand, the as-synthesized nanozyme (denoted as Cu-MIM) has the highest yield and best activity among the nanozymes prepared. Compared to laccase, the K_m of Cu-MIM nanozyme to phenol is much lower, and the v_max is 6.8 times higher. In addition, Cu-MIM maintains excellent stability in a variety of harsh environments, such as high pH, high temperature, high salt concentration, organic solvents and long-term storage. Based on the Cu-MIM nanozyme, we established a method for quantitatively detecting phenol concentration through a smartphone, which is believed to have important applications in environmental protection, pollutant detection and other fields.