Activity, Recyclability, and Stability of Lipases Immobilized on Oil-Filled Spherical Silica Nanoparticles with Different Silica Shell Structures

Spatial Confinement of Enzyme and Nanozyme in Silica-Based Hollow Microreactors

Designing a strategy for encasing enzymes and nanozymes in microreactors with spatial confinement in a way to improve the selectivity and activity of nanozymes is an exciting goal. In the present work, we report a facile route to encapsulate glucose oxidase (GOx) and poly(ethylenimine) (PEI)-conjugated magnetite nanoparticles (Fe₃O₄-PEI) in the hollow interior of hybrid microreactors. The microreactors are prepared by polyallylamine hydrochloride (PAH)-mediated silica (SiO₂) nanoparticle assembly on calcium carbonate (CaCO₃) particles as a removable core. By tuning both shape and phase (vaterite/calcite and pure calcite) of CaCO₃, it allows generation of GOx and Fe₃O₄-PEI-encapsulated silica hollow microspheres (GOx-Fe₃O₄@SHS) and microcubes (GOx-Fe₃O₄@SHC). As observed, in a biomimetic cascade catalysis, the confined GOx in the microreactors is able to catalyze oxidation of glucose to gluconic acid and hydrogen peroxide (H₂O₂), followed by the activation of H₂O₂ by Fe₃O₄-PEI for the oxidation of the chromogenic substrate o-phenylenediamine (oPD) to 2,3-diaminophenazine. Comparison of the peroxidase-like activity of the encapsulated Fe₃O₄-PEI shows that the hollow microspheres (GOx-Fe₃O₄@SHS) result in activity 14 times higher than that of the hollow microcubes (GOx-Fe₃O₄@SHC), which in turn is corroborated to the differential loading capacity of GOx in microspheres and microcubes. The evaluation of kinetic parameters indicates a fivefold increase in the catalytic constant (k_cat) of Fe₃O₄-PEI confined in hollow microspheres (GOx-Fe₃O₄@SHS) compared to the mixture comprising free GOx and Fe₃O₄-PEI in solution. It suggests that the confined space in the microreactors allows the tandem reactions of GOx and Fe₃O₄-PEI to take place in close proximity, leading to an improved overall activity. This indeed is seen in the k_cat obtained for Fe₃O₄@SHS (GOx added externally during the assay), which is 14 times lower than that of GOx-Fe₃O₄@SHS.

PEGylation and macroporous carrier adsorption enabled long-term enzymatic transesterification

A novel enzyme catalyst with excellent stability and catalytic efficiency expected to be used in the ERD industry was prepared.

Enhanced catalytic activity and thermal stability of lipase bound to oxide nanosheets

The present study reports the effects of binding of lipase, which is an inexpensive digestive enzyme (candida antarctica lipase) that catalyzes the hydrolysis reaction and is frequently utilized for artificial synthesis of a variety of organic molecules, to titanate nanosheets (TNSs) on their biocatalytic activities and stabilities under several lipase concentrations. TNSs were prepared through a hydrolysis reaction of titanium tetraisopropoxide (TTIP) with tetrabutylammonium hydroxide (TBAOH), resulting in formation of a colorless and transparent colloidal solution including TNSs with nanometric dimensions (hydrodynamic diameter: ca. 5.6 nm). TNSs were bound to lipase molecules through electrostatic interaction in an aqueous phase at an appropriate pH, forming inorganic-bio nanohybrids (lipase-TNSs). The enzymatic reaction rate for hydrolysis of p-nitrophenyl acetate (pNPA) catalyzed by the lipase-TNSs, especially in diluted lipase concentrations, was significantly improved more than 8 times as compared with free lipase. On the other hand, it was confirmed that heat tolerance of lipase was also improved by binding to TNSs. These results suggest that the novel lipase-TNSs proposed here have combined enhancements of the catalytic activity and the anti-denaturation stability of lipase.

A nitrogen-doped PtSn nanocatalyst supported on hollow silica spheres for acetic acid hydrogenation

The interaction between N and Pt significantly enhanced Pt dispersion and the activity in the hydrogenation of acetic acid.

Oriented Enzyme Immobilization at the Oil/Water Interface Enhances Catalytic Activity and Recyclability in a Pickering Emulsion

Enzyme-loaded water-in-oil Pickering emulsion is a promising system for biphasic catalytic reactions. In this paper, we report on oriented enzyme immobilization at the oil/water interface in a Pickering emulsion, in which CHO-Janus silica nanoparticles (CHO-JNPs) are utilized as a stabilizer of the emulsion and support for the enzyme to enhance both catalytic activity and recyclability. The catalytic performance of this immobilized enzyme (lipase from Candida sp.) was evaluated by esterification of hexanoic acid and 1-hexanol in a water/heptane biphasic medium. The results show that the specific catalytic activity of the immobilized enzyme (33.2 U mL^-1) was 6.5 and 1.4 times higher than that of free enzyme (5.1 U mL^-1) and encapsulated enzyme in the liquid core (23.3 U mL^-1), respectively. Moreover, the immobilized enzyme demonstrated good stability and recyclability, retaining 75% of its activity after 9 cycles. We expect that oriented enzyme immobilization at the oil/water interface will be an important strategy for enhancing catalytic performance in Pickering emulsions.

Controlling Photocatalytic Activity and Size Selectivity of TiO2 Encapsulated in Hollow Silica Spheres by Tuning Silica Shell Structures Using Sacrificial Biomolecules

Yolk-shell nanostructured photocatalyst which consists of inner core photocatalytic particles and outer silica shell exhibits high photocatalytic efficiency and molecular size selectivity due to the molecular sieving property of the outer shell. Creation of extended porosity in the shell endows it with improved adsorption properties and size selectivity toward targeted reactants. In this study, yolk-shell nanostructured photocatalyst consisting of TiO₂ NPs core and porous silica shell with controllable pore size was fabricated through a facile single-step dual-templating approach utilizing oil-in-water (O/W) microemulsions and amphiphilic protein molecules. Addition of optimum amount of protein (ovalbumin) as a sacrificial template together with O/W microemulsion during the synthesis led to the expansion of average pore size from 2.0 to 3.6 nm, while retaining TiO₂-encapsulated yolk-shell nanostructures. Photocatalytic degradation tests using gaseous 2-propanol and huge proteins as model substrates clearly revealed that the obtained material (TiO₂@HSS_pro) showed superior photocatalytic performances with both improved photocatalytic efficiency and molecular size selectivity due to the increased surface area and expanded pore diameter.

Fabrication of Photocatalytic Paper Using TiO2 Nanoparticles Confined in Hollow Silica Capsules

TiO₂ nanoparticles (NPs) encapsulated in hollow silica spheres (TiO₂@HSSs) show a shielding-effect that can insulate photocatalytically active TiO₂ NPs from the surrounding environment and thus prohibit the self-degradation of organic support materials under ultraviolet (UV)-light irradiation. In this study, photocatalytically active papers were fabricated by combining TiO₂@HSS and cellulose fibers, and their photocatalytic activities and durability under UV-light irradiation were examined. The yolk-shell nanostructured TiO₂@HSS, which has an ample void space between inner TiO₂ NPs and an outer silica shell, was synthesized using a facile single-step method utilizing an oil-in-water microemulsion as an organic template. The thus-prepared TiO₂@HSS particles were deposited onto a cellulose paper either by the chemical adhesion process via ionic bonding or by the physical adhesion process using a dual polymer system. The obtained paper containing TiO₂@HSS particles with high air permeability exhibited a higher photocatalytic activity in the photocatalytic decomposition of volatile organic compounds than unsupported powdery TiO₂@HSS particles because of the uniform dispersion on the paper with a reticular fiber network. In addition, the paper was hardly damaged under UV-light irradiation, whereas the paper containing naked TiO₂ NPs showed a marked deterioration with a considerably decreased strength, owing to the ability of the silica shell to prevent direct contact between TiO₂ and organic fibers. This study can offer a promising method to fabricate photocatalytically active papers with a photoresistance property available for real air cleaning.

Improved performance of immobilized lipase by interfacial activation on Fe3O4@PVBC nanoparticles

An effective strategy for enhancement of catalytic activity and stability of immobilized lipase by interfacial activation on Fe₃O₄@polyvinylbenzyl chloride nanoparticles is proposed.

Evaluation of different commercial hydrophobic supports for the immobilization of lipases: tuning their stability, activity and specificity

Immobilization of different lipases on diffferent hydrophobic supportsviainterfacial activation has permitted to tunning enzyme performance.

Nanomaterials for biocatalyst immobilization – state of the art and future trends

Advantages, drawbacks and trends in nanomaterials for enzyme immobilization.