Bioinspired Approach to Multienzyme Cascade System Construction for Efficient Carbon Dioxide Reduction

An efficient multienzyme cascade system based on ultrathin, hybrid microcapsules was constructed for converting CO₂ to methanol by combining the unique functions of catechol and gelatin. Gelatin was modified with catechol groups (GelC) via well-defined EDC/NHS chemistry, thus endowed with the ability to covalently attach enzyme molecules. Next, the first enzyme (FateDH)-containing CaCO₃ templates were synthesized via coprecipitation and coated with a GelC layer. Afterward, GelC was covalently attached with the second enzyme (FaldDH) via Michael addition and Schiff base reactions. Then, GelC induced the hydrolysis and condensation of silicate, and the third enzyme (YADH) was entrapped accompanying the formation of silica particles. After removal of CaCO₃ templates, the GelCSi-based multienzyme system was obtained, in which the three enzymes were appropriately positioned in different places of the GelCSi microcapsules, and the amount of individual enzyme was regulated according to enzyme activity. The system exhibited high activity and stability for converting CO₂ into methanol. In detail, the system displayed much higher methanol yield and selectivity (71.6%, 86.7%) than that of multienzyme in free form (35.5%, 47.3%). The methanol yield remained 52.6% after nine times of recycling. This study will provide some guidance on constructing diverse scaffolds for applications in catalysis, drug and gene delivery, and biosensors

Enhancing Catalytic Activity and Stability of Yeast Alcohol Dehydrogenase by Encapsulation in Chitosan-Calcium Phosphate Hybrid Beads

A kind of calcium phosphate-mineralized chitosan beads (chitosan–CaP) was prepared via a one-pot method by adding droplets of Ca²⁺-containing chitosan aqueous solution into phosphate-containing sodium tripolyphosphate aqueous solution. The chitosan beads formed immediately coupled with in situ precipitation of calcium phosphate on the surface. The antiswelling properties of hybrid beads were greatly improved with the swelling degree as low as 5%. The morphology of the resultant chitosan–CaP hybrid beads was observed by scanning electron microscopy (SEM). Yeast alcohol dehydrogenase (YADH) was encapsulated in the hybrid beads with an about 40% lower enzyme leakage compared with that in the pure chitosan beads. The optimal temperature and pH value for enzymatic conversion catalyzed by YADH immobilized in the chitosan–CaP beads were 30 °C and 7.0, respectively, which were identical to those for free YADH. The immobilized YADH displayed obviously higher thermal stability, pH stability, recycling stability, and storage stability than the free YADH counterpart

Preparation of Ultrathin, Robust Protein Microcapsules through Template-Mediated Interfacial Reaction between Amine and Catechol Groups

A novel approach to the synthesis of protein microcapsules is developed through template-mediated interfacial reaction. Protein-doped CaCO₃ templates are first synthetized via coprecipitation and then coated with a catechol-containing alginate (AlgDA) layer. Afterward, the templates are exposed to ethylenediamine tetraacetic acid disodium (EDTA) solution to dissolve CaCO₃. During CaCO₃ dissolution, the generated CO₂ gas pushes protein molecules moving to the AlgDA layer, and thereby Michael addition and Schiff base reactions proceed, forming the shell of protein microcapsules. Three kinds of proteins, namely, bovine serum albumin, catalase, and protamine sulfate, are utilized. The shell thickness of microcapsule varies from 25 to 82 nm as the doping amount of protein increased from 2 to 6 mg per 66 mg CaCO₃. The protein microcapsules have a robust but flexible shell and can be reversibly deformed upon exposure to osmotic pressure. The bioactivity of protein microcapsules is demonstrated through enzymatic catalysis experiments. The protein microcapsules remain about 80% enzymatic activity of the equivalent free protein. Hopefully, our approach could be extended to many other applications such as drug/gene delivery, tissue scaffolds, and catalysis due to the universality of Michael reaction and Schiff base reactions

Polydopamine Microcapsules with Different Wall Structures Prepared by a Template-Mediated Method for Enzyme Immobilization

Microcapsules with diverse wall structures may exhibit different performance in specific applications. In the present study, three kinds of mussel-inspired polydopamine (PDA) microcapsules with different wall structures have been prepared by a template-mediated method. More specifically, three types of CaCO₃ microspheres (<i>poly­(allylamine hydrochloride), (PAH)-doped CaCO</i>_<i>3</i>; <i>pure-CaCO</i>_<i>3</i>; <i>and poly­(styrene sulfonate sodium), (PSS)-doped CaCO</i>_<i>3</i>) were synthesized as sacrificial templates, which were then treated by dopamine to obtain the corresponding PDA-CaCO₃ microspheres. Through treating these microspheres with disodium ethylene diamine tetraacetic acid (EDTA-2Na) to remove CaCO₃, three types of PDA microcapsules were acquired: that was (1) PAH-PDA microcapsule with a thick (∼600 nm) and highly porous capsule wall composed of interconnected networks, (2) pure-PDA microcapsule with a thick (∼600 nm) and less porous capsule wall, (3) PSS-PDA microcapsule with a thin (∼70 nm) and dense capsule wall. Several characterizations confirmed that a higher degree in porosity and interconnectivity of the capsule wall would lead to a higher mass transfer coefficient. When serving as the carrier for catalase (CAT) immobilization, these enzyme-encapsulated PDA microcapsules showed distinct structure-related activity and stability. In particular, PAH-PDA microcapsules with a wall of highly interconnected networks displayed several significant advantages, including increases in enzyme encapsulation efficiency and enzyme activity/stability and a decrease in enzyme leaching in comparison with other two types of PDA microcapsules. Besides, this hierarchically structured PAH-PDA microcapsule may find other promising applications in biocatalysis, biosensors, drug delivery, etc

Exploring the Segregating and Mineralization-Inducing Capacities of Cationic Hydrophilic Polymers for Preparation of Robust, Multifunctional Mesoporous Hybrid Microcapsules

A facile approach to preparing mesoporous hybrid microcapsules is developed by exploring the segregating and mineralization-inducing capacities of cationic hydrophilic polymer. The preparation process contains four steps: segregation of cationic hydrophilic polymer during template formation, cross-linking of the segregated polymer, biomimetic mineralization within cross-linked polymer network, and removal of template to simultaneously generate capsule lumen and mesopores on the capsule wall. Poly­(allylamine hydrochloride) (PAH) is chosen as the model polymer, its hydrophilicity renders the segregating capacity and spontaneous enrichment in the near-surface region of CaCO₃ microspheres; its biopolyamine-mimic structure renders the mineralization-inducing capacity to produce titania from the water-soluble titanium­(IV) precursor. Meanwhile, CaCO₃ microspheres serve the dual templating functions in the formation of hollow lumen and mesoporous wall. The thickness of capsule wall can be controlled by changing the polymer segregating and cross-linking conditions, while the pore size on the capsule wall can be tuned by changing the template synthesizing conditions. The robust hybrid microcapsules exhibit desirable efficiency in enzymatic catalysis, wastewater treatment and drug delivery. This approach may open facile, generic, and efficient pathway to designing and preparing a variety of hybrid microcapsules with high and tunable permeability, good stability and multiple functionalities for a broad range of applications