Immobilization of lipase in hierarchically ordered macroporous/mesoporous silica with improved catalytic performance

Macroporous honeycomb-like magnesium oxide fabricated as long-life and outstanding Pb(II) adsorbents combined with mechanism insight

The macroporous honeycomb-like MgO (MHM) had been successfully prepared by hard template method using polystyrene (PS) spheres with different particle sizes of about 400, 600, and 800 nm, respectively. The adsorption performance (3700, 3470, and 3087 mg/g) and specific surface areas (64.0, 51.4, and 34.4 m2/g) of MHM materials were inversely proportional to their pore diameters. Among the prepared MHM materials, MHM-400 exhibited the most excellent adsorption performance of 3700 mg/g towards Pb(II) at 25 °C. In this study, the macropore size in MHM played a major role in the adsorption process; Dubinin-Radushkevich (D-R) model further indicated that Pb(II) removal by MHM-400 was dominated by chemical adsorption. The thermodynamic analysis (ΔG0 < 0, ΔH0 > 0, and ΔS0 > 0) revealed that the Pb(II) adsorption was spontaneous and endothermic. After storing for 360 days, the Pb(II) removal efficiency of MHM-400 was still higher than 98.2%, exhibiting ultra-long life for Pb(II) capture. MHM-400 also exhibited high anti-interference ability towards typically coexisting ions (Na+ and K+). According to the density functional theory (DFT) calculation, the Pb could be adsorbed on the top site of the oxygen atom at the surface of the cubic MgO (200) plane; the adsorption energy (Ead) was 0.159 eV. The XRD and FTIR analyses revealed the further formation of Pb3(CO3)2(OH)2 and PbO after Pb(II) adsorption. Furthermore, MHM-400 could effectively remove both Cd(II) and Pb(II) ions from wastewater within 20 min, and the adsorption efficiency achieved > 99%, suggesting that MHM-400 was a potential material for effective Pb(II) removal.

Lipase Immobilization in Mesoporous Silica Nanoparticles for Biofuel Production

Lipases are ubiquitous enzymes whose physiological role is the hydrolysis of triacylglycerol into fatty acids. They are the most studied and industrially interesting enzymes, thanks to their versatility to promote a plethora of reactions on a wide range of substrates. In fact, depending on the reaction conditions, they can also catalyze synthesis reactions, such as esterification, acidolysis and transesterification. The latter is particularly important for biodiesel production. Biodiesel can be produced from animal fats or vegetable oils and is considered as a biodegradable, non-toxic and renewable energy source. The use of lipases as industrial catalysts is subordinated to their immobilization on insoluble supports, to allow multiple uses and use in continuous processes, but also to stabilize the enzyme, intrinsically prone to denaturation with consequent loss of activity. Among the materials that can be used for lipase immobilization, mesoporous silica nanoparticles represent a good choice due to the combination of thermal and mechanical stability with controlled textural characteristics. Moreover, the presence of abundant surface hydroxyl groups allows for easy chemical surface functionalization. This latter aspect has the main importance since lipases have a high affinity with hydrophobic supports. The objective of this work is to provide an overview of the recent progress of lipase immobilization in mesoporous silica nanoparticles with a focus on biodiesel production.

Effect of eggshell membrane as porogen on the physicochemical structure and protease immobilization of chitosan-based macroparticles

Chitosan-based macroparticle is a common carrier for enzyme immobilization applied in food industry. Driven by the requirement of large carrier pores for the biomacromolecular substrates such as protein, the eggshell membrane powder (ESMP) was employed as multifunctional porogen to improve the physicochemical structure of chitosan-based macroparticles. The prepared macroparticles were characterized by SEM, XRD, FTIR, Raman spectroscopy, nitrogen adsorption-desorption isotherms, and thermogravimetric analysis. The results showed that an increase of ESMP percentage could improve the porosity of macro holes in macroparticles, and it also enlarged the size of mesopores. Moreover, the ESMP significantly increased (P < 0.05) the amount of papain immobilization, whereas the specific activity of immobilized papain achieved a maximum value of 871.95 U/mg at CSESM2 and then declined with the increase of ESMP. Therefore, the inclusion of 20 % ESMP in chitosan-based macroparticles gave the highest activity of its immobilized protease.

Metalloporphyrin-based porous polymers prepared via click chemistry for size-selective adsorption of protein

Zinc porphyrin-based porous polymers (PPs-Zn) with different pore sizes were prepared by controlling the reaction condition of click chemistry, and the protein adsorption in PPs-Zn and the catalytic activity of immobilized enzyme were investigated. PPs-Zn-1 with 18 nm and PPS-Zn-2 with 90 nm of pore size were characterized by FTIR, NMR and nitrogen absorption experiments. The amount of adsorbed protein in PPs-Zn-1 was more than that in PPs-Zn-2 for small size proteins, such as lysozyme, lipase and bovine serum albumin (BSA). And for large size proteins including myosin and human fibrinogen (HFg), the amount of adsorbed protein in PPs-Zn-1 was less than that in PPs-Zn-2. The result indicates that the protein adsorption is size-selective in PPs-Zn. Both the protein size and the pore size have a significant effect on the amount of adsorbed protein in the PPs-Zn. Lipase and lysozyme immobilized in PPs-Zn exhibited excellent reuse stability.

Conversion of levulinic acid into alkyl levulinates: Using lipase immobilized on meso-molding three-dimensional macroporous organosilica as catalyst

For conversion of biomass-derived levulinic acid into alkyl levulinates, a novel kind of lipase-based biocatalyst was prepared through immobilized lipase B from C. antarctica (CALB) on organosilica material with highly ordered 3D macroporous organosilica frameworks and a 2D hexagonal meso-structure (named 3DOM/m-OS) for the first time. The catalytic performance of the immobilized lipase (NER@3DOM/m-OS) was investigated. NER@3DOM/m-OS was used as biocatalyst to catalyze the esterification reaction between levulinic acid (LA) and n-butanol. Under optimized reaction conditions, 74.59% of ester yield was achieved after 12h of reaction. NER@3DOM/m-OS was also used to production of other alkyl levulinates, the ester yields increased to 84.51% (octyl levulinate) and 91.14% (dodecyl levulinate), respectively. When NER@3DOM/m-OS was used repeatedly in batch reactions, the ester yields of n-butyl, octyl, and dodecyl levulinate could retain 46.18%, 82.33% and 81.25% after 9 reaction cycles, respectively, which was better than commercial lipase Novozym 435 under the same condition.

Strep-tag II fusion technology for the modification and immobilization of lipase B from Candida antarctica (CALB)

Fusion tags - amino acid sequences that are genetically coded to be expressed as attached moieties to a protein - have the potential to enhance the activity of native enzyme, enable specific purification of the enzyme, and promote simple and efficient immobilization of enzymes onto material supports. In this work, we demonstrate the effect of a Strep-tag II fusion tag on the properties of free and immobilized lipase B from Candida antarctica (CALB). The gene encoding the mature portion of CALB was codon-optimized and cloned in pASG-IBA2 plasmid for expression in E. coli. Purified recombinant Strep-tag II CALB was immobilized to Strep-Tactin based support through affinity binding, and the immobilized and free Strep-tag II CALB were compared to a commercial CALB. Following modification, the enzyme could be selectively purified from culture media with no observable non-specific binding. The catalytic efficiency of the purified fusion-tagged enzyme was significantly greater than that of the commercial CALB in its free form. Immobilization of the fusion-tagged enzyme to Strep-Tactin modified crosslinked agarose support yielded a catalytically active enzyme; however, the k_cat of the immobilized enzyme was significantly reduced compared to the free tagged enzyme. This work indicates that a C-terminus Strep-tag II fusion tag may be employed to improve the catalytic efficiency of free CALB, but may not be suitable for immobilized applications that employ binding of the enzyme to a Strep-Tactin-modified support.