Tailoring the interfacial microenvironment of magnetic metal-organic frameworks using amino-acid-based ionic liquids for lipase immobilization.

Modifying the carrier interface is a promising method to improve the microenvironment of immobilized enzymes and enhance their activity and stability. In this work, using proline as amino acid, magnetic metal-organic frameworks (MOFs) were modified with an amino-acid-based ionic liquid (AAIL) with two hydroxyl groups followed by adsorption of porcine pancreatic lipase (PPL). The activity recovery of the prepared immobilized lipase (MMOF-AAIL/PPL) was up to 162 % higher than that of MMOF-PPL (70.8 %). The Michaelis constant of MMOF-AAIL/PPL was 0.0742 mM lower than that of MMOF-PPL, but the catalytic efficiency was 0.0223 min-1 which was higher than MMOF-PPL. Furthermore, MMOF-AAIL/PPL maintained 85.6 % residual activity after stored for 40 days and its residual activity was 71.9 % while that for MMOF-PPL was 58.8 % after incubated in 6 M urea for 2 h. Particularly, after ten consecutive cycles, the residual activity of MMOF-AAIL/PPL still reached 84.4 %. In addition, the magnetic properties of the support facilitate the separation process which improves the utilization efficiency of immobilized enzymes.

Lipase in-situ immobilized in covalent organic framework: Enzymatic properties and application in the preparation of 1, 3-dioleoyl-2-palmitoylglycerol.

In this study, the critical importance of designing an appropriate immobilized carrier and method for free lipase to ensure exceptional biological catalytic activity and stability was emphasized. Covalent organic frameworks (COF-1) were synthesized as a novel porous carrier with an azine structure (-CN-NC-) through the condensation of hydrazine hydrate and benzene-1,3,5-tricarbaldehyde at room temperature. Simultaneously, Rhizomucor miehei lipase (RML) was immobilized within the COF-1 carrier using an in-situ aqueous phase method. Characterization of the carrier and RML@COF-1 and evaluation of the lipase properties of RML and RML@COF-1 through p-Nitrophenyl palmitate hydrolysis were conducted. Additionally, application in the synthesis of 1, 3-dioleoyl-2-palmitoylglycerol (OPO) was explored. The results showed that RML@COF-1 exhibited a high enzymatic loading of 285.4 mg/g. Under 60℃ conditions, the activity of RML@COF-1 was 2.31 times higher than that of free RML, and RML@COF-1 retained 77.25% of its original activity after 10 cycles of repeated use, indicating its excellent thermal stability and repeatability. Under the optimal conditions (10%, 1:8 PPP/OA, 45℃, 5 h), the yield of OPO reached 47.35%, showcasing the promising application prospects of the novel immobilized enzyme synthesized via in-situ aqueous phase synthesis for OPO preparation.

Calcium-based MOFs as scaffolds for shielding immobilized lipase and enhancing its stability.

The enzyme immobilization technology has become a key tool in the field of enzyme applications; however, improving the activity recovery and stability of the immobilized enzymes is still challenging. Herein, we employed a magnetic carboxymethyl cellulose (MCMC) nanocomposite modified with ionic liquids (ILs) for covalent immobilization of lipase, and used Ca-based metal-organic frameworks (MOFs) as the support skeleton and protective layer for immobilized enzymes. The ILs contained long side chains (eight CH2 units), which not only enhanced the hydrophobicity of the carrier and its hydrophobic interaction with the enzymes, but also provided a certain buffering effect when the enzyme molecules were subjected to compression. Compared to free lipase, the obtained CaBPDC@PPL-IL-MCMC exhibited higher specific activity and enhanced stability. In addition, the biocatalyst could be easily separated using a magnetic field, which is beneficial for its reusability. After 10 cycles, the residual activity of CaBPDC@PPL-IL-MCMC could reach up to 86.9%. These features highlight the good application prospects of the present immobilization method.

Covalent immobilization of lipase on an ionic liquid-functionalized magnetic Cu-based metal-organic framework with boosted catalytic performance in flavor ester synthesis.

Enzymatic esterification plays an important role in the fields of chemistry and biotechnology. In this study, lipase was immobilized on an ionic liquid (IL)-modified magnetic metal-organic framework (MOF) and used to synthesize isoamyl acetate. The immobilized lipase (PPL-ILs/Fe3O4@MOF) showed 2.1-fold and 1.8-fold higher activity compared to the free and immobilized lipase without ILs (PPL-Fe3O4@MOF), respectively. In addition, the anti-denaturant ability and reusability of the PPL-ILs/Fe3O4@MOF were also higher than those of other samples. The ester yield reached 75.1% when the biocatalyst was used to synthesize isoamyl acetate in hexane. The synthesized supports supplied a good microenvironment for the immobilized lipase through multiple interactions. Results of the structural analysis showed that the conformation state of lipase molecules changed after immobilization. The magnetism of the prepared biocatalyst makes it easy to recycle so that PPL-ILs/Fe3O4@MOF maintained 70.2% of the initial activity after eight cycles. The prepared composite materials exhibited good potential in lipase immobilization with enhanced catalytic ability and stability.

Surface Modification of Magnetic ZIF-90 Nanoparticles Improves the Microenvironment of Immobilized Lipase and Its Application in Esterification.

Interactions of enzymes with supports significantly affect the activity and stability of immobilized enzymes. Herein, amino-functionalized ionic liquid (IL)-grafted magnetic zeolitic imidazolate framework-90 (MZIF-90) was prepared and used to immobilize porcine pancreatic lipase (PPL). The nanocomposites were fully characterized; meanwhile, the interactions between ILs and ZIF-90 were calculated based on density functional theory. The prepared biocatalyst (PPL-ILs/MZIF-90) had a lipase loading of 178.3 mg/g and hydrolysis activity up to 287.5 U/g. When the biocatalyst was used to synthesize isoamyl acetate, the reaction media, molar ratio of alcohol/acid, temperature, and reaction time were optimized. Under the optimized reaction conditions (in hexane, alcohol/acid = 3:1, under 45 °C, reacted for 9 h), the ester yield reached 85.5%. The results of the stability test showed that PPL-ILs/MZIF-90 retained 88.7% of the initial activity after storing for 35 days and 92.5% of the initial activity after reusing for seven cycles for synthesizing isoamyl acetate. Moreover, the secondary structure analysis showed that the synthesized supports protected the active conformation of immobilized lipase, which lead to the enhanced catalytic performance. Additionally, the biocatalyst can be easily separated with a magnet, which facilitated the reusability. This study provides insights regarding the application of metal organic framework composites in the field of enzyme catalysis.

Preparation and Characterization of Magnetic Metal-Organic Frameworks Functionalized by Ionic Liquid as Supports for Immobilization of Pancreatic Lipase.

Enzymes are difficult to recycle, which limits their large-scale industrial applications. In this work, an ionic liquid-modified magnetic metal-organic framework composite, IL-Fe3O4@UiO-66-NH2, was prepared and used as a support for enzyme immobilization. The properties of the support were characterized with X-ray powder diffraction (XRD), Fourier-transform infrared (FTIR) spectra, transmission electron microscopy (TEM), scanning electronic microscopy (SEM), and so on. The catalytic performance of the immobilized enzyme was also investigated in the hydrolysis reaction of glyceryl triacetate. Compared with soluble porcine pancreatic lipase (PPL), immobilized lipase (PPL-IL-Fe3O4@UiO-66-NH2) had greater catalytic activity under reaction conditions. It also showed better thermal stability and anti-denaturant properties. The specific activity of PPL-IL-Fe3O4@UiO-66-NH2 was 2.3 times higher than that of soluble PPL. After 10 repeated catalytic cycles, the residual activity of PPL-IL-Fe3O4@UiO-66-NH2 reached 74.4%, which was higher than that of PPL-Fe3O4@UiO-66-NH2 (62.3%). In addition, kinetic parameter tests revealed that PPL-IL-Fe3O4@UiO-66-NH2 had a stronger affinity to the substrate and, thus, exhibited higher catalytic efficiency. The results demonstrated that Fe3O4@UiO-66-NH2 modified by ionic liquids has great potential for immobilized enzymes.

Correction: Naphthalimide-containing coordination polymer with mechanoresponsive luminescence and excellent metal ion sensing properties.

Correction for 'Naphthalimide-containing coordination polymer with mechanoresponsive luminescence and excellent metal ion sensing properties' by Jian-Jun Liu et al., Dalton Trans., 2020, 49, 3174-3180, DOI: 10.1039/C9DT04928B.

Enhancing bio-catalytic performance of lipase immobilized on ionic liquids modified magnetic polydopamine.

In this study, imidazolium-based ionic liquid with [tf2N]- as the anion was successfully grafted to magnetic polydopamine nanoparticles (MPDA). The prepared materials were well characterized and used as supports for lipase immobilization. The immobilized lipase (PPL-ILs-MPDA) exhibited excellent activity and stability. The specific activity of PPL-ILs-MPDA was 2.15 and 1.49 folds higher than that of free PPL and PPL-MPDA. In addition, after 10 rounds of reuse, the residual activity of PPL-ILs-MPDA was 86.2 % higher than that of PPL-MPDA (75.4 %). Furthermore, the kinetic assay indicated that the affinity between PPL-ILs-MPDA and substrate had increased. Analysis of the secondary structure using circular dichroism was used to explain the mechanism underlying the improvement in the performance of PPL-ILs-MPDA. In addition, the immobilized lipase can be easily separated from the reaction system with a magnet. The observations regarding the development of new supports for lipase immobilization may provide new ideas regarding further studies in this field.

Co-immobilization of laccase and ABTS onto amino-functionalized ionic liquid-modified magnetic chitosan nanoparticles for pollutants removal.

This work aims to achieve the co-immobilization of laccase and 2,2-binamine-di-3-ethylbenzothiazolin-6-sulfonic acid (ABTS) to improve removal capability of the biocatalyst for pollutants while avoiding potential pollution caused by ABTS. The laccase was immobilized on magnetic chitosan nanoparticles modified with amino-functionalized ionic liquid containing ABTS (MACS-NIL) based on Cu ion chelation (MACS-NIL-Cu-lac). The carrier was characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, x-ray diffraction and etc., and electron paramagnetic resonance confirmed the mediator molecule ABTS on the carrier could also play the role of electron transmission. MACS-NIL-Cu-lac presented relatively high immobilization capacity, enhanced activity (1.7-fold that of free laccase), improved pH and temperature adaptability, and increased thermal and storage stability. The removal performance assay found that MACS-NIL-Cu-lac had a good removal efficiency with 100.0 % for 2,4-dichlorophenol in water at 25 °C, even when the concentration reached 50 mg/L. Reusability study showed that after six catalytic runs, the removal efficiency of 2,4-dichlorophenol by MACS-NIL-Cu-lac could still reach 93.2 %. Additionally, MACS-NIL-Cu-lac exhibited higher catalytic efficiencies with 100.0 %, 70.5 % and 93.3 % for bisphenol A, indole, and anthracene, respectively. The high catalytic performance in pure water system obtained by the novel biocatalyst co-immobilizing laccase and electron mediator ABTS showed greater practical application value.

Naphthalimide-containing coordination polymer with mechanoresponsive luminescence and excellent metal ion sensing properties.

Mechanoresponsive luminescent materials coupled with other functionalities are of particular interest due to their multiple external stimuli responsive properties. In this paper, a new sensitive mechanoresponsive luminescent coordination polymer, [Cd(INI)(DMF)2·DMF] (1) (H2INI = N-(5-isophthalic acid)-1,8-naphthalimide), has been successfully designed and synthesized. Complex 1 exhibits interesting mechanoresponsive and grinding-enhanced luminescence properties, and its luminescence colour changed from weak blue-green to bright blue upon grinding owing to the external pressure-induced destruction of ππ stacked arrangements in local defective areas. Moreover, the luminescence properties and uncoordinated carbonyl groups of well-ground g-1 endow it with excellent sensing ability for Cr3+ ions. This work will provide a new perspective to rationally design multifunctional coordination polymers that can serve as practical multi-responsive sensors to pressure and chemicals.

Ionic liquids-modified cellulose coated magnetic nanoparticles for enzyme immobilization: Improvement of catalytic performance.

In this work, ionic liquids-modified magnetic carboxymethyl cellulose nanoparticles (IL-MCMC) were prepared and used as supports for enzyme immobilization. The specific activity of immobilized lipase PPL-IL-MCMC was 1.43 and 2.81 folds higher than that of free PPL and PPL-MCMC, respectively. Water contact angle analysis indicated that the introduction of ionic liquids increased the hydrophobicity of supports, which in tune induced the lid-opening of lipase, allowing its active sites to become more accessible. In addition, the affinity between lipase and substrate immobilized on the prepared supports was enhanced. The same method was also applied to analyze immobilize penicillin G acylase (PGA) to further investigate the general applicability of the method. The results showed that the immobilized PGA exhibited higher stability than many other reported PGAs. The developed composites may be utilized as excellent supports for enzyme immobilization in industrial application.

Enhanced catalytic performance of lipase covalently bonded on ionic liquids modified magnetic alginate composites.

We prepared ionic liquids (ILs) modified magnetic alginate nanoparticles and used these as supports for lipase immobilization. The novel supports were characterized using Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (1HNMR), vibrating sample magnetometry (VSM), thermogravimetry (TG), transmission electron microscopy (TEM) and water contact angle (WCA) measurements. The immobilized lipase (PPL-IL-MSA) exhibited high activity, 2.1-fold higher than that compared to free lipase and 1.59-fold higher compared to immobilized lipase without IL (PPL-MSA). In addition, the pH and temperature application range of PPL-IL-MSA were both found to be broader than that of free lipase and PPL-MSA. The thermal stability, denaturation stability, and reusing stability of PPL-IL-MSA were also higher than those of other samples. After 10 times of reuse, the residual activity of PPL-IL-MSA was 89.7% higher than that of PPL-MSA (84.4%). Furthermore, the kinetic constant Km of PPL-IL-MSA was 13.7 mg/mL lower than that of free lipase (21.2 mg/mL) and PPL-MSA (18.4 mg/mL). Circular dichroism (CD) was used to study the secondary structure of enzymes in order to explain the mechanism of the performance improvement of PPL-IL-MSA. This work involving the development of a new supports for enzyme immobilization may serve as a reference for further studies in this field.

Synthesis of functional ionic liquid modified magnetic chitosan nanoparticles for porcine pancreatic lipase immobilization.

We developed magnetic chitosan nanoparticles (CS­Fe3O4) with mean diameter of 15-20 nm. Subsequently, these inorganic-organic composite nanoparticles were modified using an imidazole-based functional ionic liquid (IL). The prepared support (IL­CS­Fe3O4), which was used to immobilize porcine pancreatic lipase (PPL), was characterized using Fourier transform infrared (FTIR) spectroscopy, vibrating sample magnetometry (VSM), thermogravimetry (TG), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Circular dichroism (CD) was used to analyze the secondary structure of immobilized PPL. The immobilized PPL (PPL­IL­CS­Fe3O4) exhibited 1.93-fold higher specific activity than PPL­CS-Fe3O4 when triacetin was used as the substrate, and showed 95 mg/g of lipase immobilization capacity and 382% of activity recovery. The residual activity of PPL­IL­CS­Fe3O4 was above 60% of the initial activity after incubation at 50 °C for 6 h, as was higher than that of PPL­CS­Fe3O4 which showed 40% of the initial activity. In addition, PPL­IL­CS­Fe3O4 retained 84.6% of the initial activity after 10 cycles, whereas PPL­CS­Fe3O4 retained only 75.5% activity. Furthermore, the kinetic parameters, apparent Km and Vmax of PPL­IL­CS­Fe3O4 were 2.51 mg/mL and 1.395 U/mg respectively, these results indicated that the immobilized PPL had better affinity towards the substrate, especially when the nanoparticles were modified by functional IL. Besides, the magnetic chitosan nanoparticles loaded with PPL were easily recovered. A novel, efficient, and practical method for enzyme immobilization was developed.

Design of GO-Ag-functionalized Fe3O4@CS composite for magnetic adsorption of rhodamine B.

In this study, a novel magnetic composite (Fe3O4@CS/GO/Ag) modified with chitosan (CS), graphene oxide (GO) and Ag nanoparticles (Ag NPs) was successfully prepared as an efficient adsorbent for detection of rhodamine B (RB) combined with a fluorescence technique. The properties of the magnetic composite were confirmed by field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and vibrating sample magnetometry. The components of Fe3O4@CS/GO/Ag endowed it with excellent extraction performance and convenient operation. The main parameters affecting extraction and desorption efficiency were all investigated systematically. Under the optimized experimental conditions, the proposed method showed linear ranges (0.2-6.0 µg L-1) with R 2 = 0.9992. The limits of detection (LODs) and quantification (LOQs) were 0.05 and 0.2 µg L-1 (n = 3), respectively. Fe3O4@CS/GO/Ag exhibited outstanding extraction efficiency for RB, compared with CS-coated Fe3O4 nanoparticles (Fe3O4@CS) and GO-modified Fe3O4@CS (Fe3O4@CS/GO). The applicability of the proposed method was investigated by analyzing four real samples (waste water, soft drink, shampoo, and red pencil) and the spiked recoveries ranged between 94% and 97% with RSD ranging from 3% to 6%, which showed that the proposed method had satisfactory practicability and operability.

Enhancement of catalytic performance of porcine pancreatic lipase immobilized on functional ionic liquid modified Fe3O4-Chitosan nanocomposites.

Magnetic chitosan nanocomposites were designed and fabricated by combining the magnetic nanoparticles Fe3O4 and chitosan covalently modified by imidazole-based ionic liquids with various functional groups, to be utilized as a support matrix for immobilization of porcine pancreatic lipase (PPL). Ionic liquids modified chitosan was characterized with nuclear magnetic resonance (NMR) and the nanocomposites were characterized with Fourier transform infrared spectroscopy (FTIR), vibrating-sample magnetometer (VSM), thermogravimetry analysis (TGA), Transmission electron microscope (TEM) and Scanning electron microscopy (SEM). The enzymatic properties of PPL were significantly improved by immobilization onto all thus prepared nanocomposites, and among the supports, modified with ionic liquids bearing hydroxyl group exhibited relatively enhanced performance. Particularly, the MCS-IL(8C)-OH-PPL exhibited the highest specific activity which was 6.68 times that of free PPL, and the residual activity of MCS-IL(8C)-OH-PPL remarkably maintained 91.5% of its initial activity even after 10 repeated cycles. The residual activity of MCS-IL(8C)-OH-PPL retained 55.8% after incubated in 6 M urea solution for 1 h and maintained the noticeable initial activity of 75.5% after incubated in phosphate buffer at 50 °C with pH 7.5 for 6 h. In conclusion, the study demonstrated that Fe3O4@Chitosan nanocomposites modified with functional ionic liquids could be utilized as a novel nanosupport for enzyme immobilization.

Covalent immobilization of lipase onto chitosan-mesoporous silica hybrid nanomaterials by carboxyl functionalized ionic liquids as the coupling agent.

Chitosan-mesoporous silica SBA-15 hybrid nanomaterials (CTS-SBA-15) were synthesized by means of carboxyl functionalized ionic liquids as the coupling agent. The as-prepared CTS-SBA-15 support was characterized by TEM, FTIR, TG and nitrogen adsorption-desorption techniques. Porcine pancreas lipase (PPL) was then bound to the hybrid nanomaterials by using the cross-linking reagent glutaraldehyde (GA). Further, the parameters like cross-linking concentration, time and ratio of supports to enzyme were optimized. The property of immobilized lipase were tested in detail by enzyme activity assays. The results indicated that the hybrid nanomaterials could form three-dimensional (3D) structure with homogeneous mesoporous structures and immobilized PPL revealed excellent enzymatic performance.

Fabrication of chitosan-mesoporous silica SBA-15 nanocomposites via functional ionic liquid as the bridging agent for PPL immobilization.

A nanocomposite (SBA-CIL-CS) which was combined mesoporous silica SBA-15 material with chitosan via ionic liquid as the bridging agent was successfully fabricated. The morphology and structure of the nanocomposite were characterized in detail with transmission electron microscope, fourier transform infrared spectroscopy, thermogravimetric analysis and nitrogen adsorption-desorption techniques. SBA-CIL-CS was investigated as an efficient support for immobilization of porcine pancreas lipase (PPL) and possessed high immobilization efficiency. The properties of immobilized enzyme (SBA-CIL-CS-PPL) such as activity, stability and reusability have been significantly improved, and a preferable pH and temperature tolerance were obtained as well. Results demonstrated the inorganic-organic nanocomposite could be used as an ideal support for enzyme immobilization.