Magnetic-metal organic framework (magnetic-MOF): A novel platform for enzyme immobilization and nanozyme applications

Fast Immobilization of Human Carbonic Anhydrase II on Ni-Based Metal-Organic Framework Nanorods with High Catalytic Performance

Carbonic anhydrase (CA) has received considerable attention for its ability to capture carbon dioxide efficiently. This study reports a simple strategy for immobilizing recombinant carbonic anhydrase II from human (hCA II) on Ni-based MOFs (Ni-BTC) nanorods, which was readily achieved in a one-pot immobilization of His-tagged hCA II (His-hCA II). Consequently, His-hCA II from cell lysate could obtain an activity recovery of 99% under optimal conditions. After storing for 10 days, the immobilized His-hCA II maintained 40% activity while the free enzyme lost 91% activity. Furthermore, during the hydrolysis of p-nitrophenyl acetic acid, immobilized His-hCA II exhibited excellent reusability and still retained more than 65% of the original activity after eight cycles. In addition, we also found that Ni-BTC had no fixation effect on proteins without histidine-tag. These results show that the Ni-BTC MOFs have a great potential with high efficiency for and specific binding of immobilized enzymes.

Carbonization and Preparation of Nitrogen-Doped Porous Carbon Materials from Zn-MOF and Its Applications

Nitrogen-doped porous carbon (NPC) materials were successfully synthesized via a Zn-containing metal-organic framework (Zn-MOF). The resulting NPC materials are characterized using various physicochemical techniques which indicated that the NPC materials obtained at different carbonization temperatures exhibited different properties. Pristine MOF morphology and pore size are retained after carbonization at particular temperatures (600 °C-NPC600 and 800 °C-NPC800). NPC800 material shows an excellent surface area 1192 m2/g, total pore volume 0.92 cm3/g and displays a higher CO2 uptake 4.71 mmol/g at 273 k and 1 bar. Furthermore, NPC600 material displays good electrochemical sensing towards H2O2. Under optimized conditions, our sensor exhibited a wide linearity range between 100 µM and 10 mM with a detection limit of 27.5 µM.

Biomimetic mineralization of nitrile hydratase into a mesoporous cobalt-based metal-organic framework for efficient biocatalysis

Nitrile hydratases (NHases) have attracted considerable attention owing to their application in the synthesis of valuable amides under mild conditions. However, the poor stability of NHases is still one of the main drawbacks for their industrial application. Recently, mesoporous metal-organic frameworks (MOFs) have been explored as an attractive support material for immobilizing enzymes. Here, we encapsulated a recombinant cobalt-type NHase from Aurantimonas manganoxydans into the cobalt-based MOF ZIF-67 by a biomimetic mineralization strategy. The nano-catalyst NHase1229@ZIF-67 shows high catalytic activity for the hydration of 3-cyanopyridine to nicotinamide, and its specific activity reached 29.5 U mg-1. The NHase1229@ZIF-67 nanoparticles show a significant improvement in the thermal stability of NHase1229. The optimum reaction temperature of NHase1229@ZIF-67 is at 50-55 °C, and it still retained 40% of the maximum activity at 70 °C. However, the free NHase1229 completely lost its catalytic activity at 70 °C. The half-lives of NHase1229@ZIF-67 at 30 and 40 °C were 102.0 h and 26.5 h, respectively. NHase1229@ZIF-67 nanoparticles exhibit an excellent cycling performance, and their catalytic efficiency did not significantly decrease in the initial 6 cycles using 0.9 M 3-cyanopyridine as the substrate. In a fed-batch reaction, NHase1229@ZIF-67 can efficiently hydrate 3-cyanopyridine to nicotinamide, and the space-time yield was calculated to be 110 g·L-1·h-1. Therefore, the cobalt-type NHase was immobilized in MOF ZIF-67, which is shown as a potential nanocatalyst for the large-scale industrial preparation of nicotinamide.

Characterization, immobilization, and mutagenesis of a novel cold-active acetylesterase (EaAcE) from Exiguobacterium antarcticum B7

Cold-active enzymes with distinctive properties from a psychrophilic Exiguobacterium antarcticum B7 could be excellent biocatalysts in industrial and biotechnological processes. Here, the characterization, immobilization, and site-directed mutagenesis of a novel cold-active acetylesterase (EaAcE) from E. antarcticum B7 is reported. EaAcE does not belong to any currently known lipase/esterase family, although there are some sequence similarities with family III and V members. Biochemical characterization of EaAcE was carried out using activity staining, mass spectrometry analysis, circular dichroism spectra, freeze-thaw experiments, kinetic analysis, acetic acid release assays, and enantioselectivity determination. Furthermore, immobilization of EaAcE using four different approaches was explored to enhance its thermal stability and recyclability. Based on a homology model of EaAcE, four mutations (F45A, S118A, S141A, and T216A) within the substrate-binding pocket were investigated to elucidate their roles in EaAcE catalysis and substrate specificity. This work has provided invaluable information on the properties of EaAcE, which can now be used to understand the acetylesterase enzyme family.

One pot synthesis of α-amylase metal organic framework (MOF)-sponge via dip-coating technique

Enzyme embedded metal-organic frameworks (MOFs) are blooming in the field of enzyme immobilization on account of their superior catalytic efficiency, thermal and chemical stability as compared to native enzyme. However, the separation and recovery of enzyme embedded MOF composite is quite challenging due to its nanometer size, high dispersity and low density which limits the reusability. In this work, α-amylase embedded zeolite imidazole framework (ZIF)-67 was fabricated onto melamine sponge using surfactant assisted dip coating technique. This was achieved in single pot making the method facile and rapid. α-Amylase MOF-sponge was analysed and characterized by FT-IR, XRD, SEM and TGA. We demonstrated that the encapsulation could maintain the active conformational structure of α-amylase after immobilization procedure with excellent bioactivity. Further, apart from merits of framework shielding, it offers mass transfer limitation for macromolecular substrate (like starch) which was determined and expressed as effectiveness factor (η) by using Michaelis-Menten enzyme kinetics. At the end, recycling studies were carried out for α-amylase MOF-sponge which showed 32% residual activity after six consecutive cycles. It is believed that this strategy has great potential in the field of continuous biotransformation (catalysis), biosensing and biomedicine application.

Recent applications of immobilized biomaterials in herbal analysis

Immobilization of biomaterials developed rapidly due to the great promise in improving their stability, activity and even selectivity. In this review, the immobilization strategies of biomaterials, including physical adsorption, encapsulation, covalent attachment, cross-linking and affinity linkage, were briefly introduced. Then, the major emphasis was focused on the reported various types of immobilized biomaterials, including proteins, enzymes, cell membrane and artificial membrane, living cells, carbohydrates and bacteria, used in the herbal analysis for bioactive compound screening, drug-target interaction evaluation and chiral separation. In addition, a series of carrier materials applied in biomaterials immobilization, such as magnetic nanoparticles, metal-organic frameworks, silica capillary column, cellulose filter paper, cell membrane chromatography, immobilized artificial membrane chromatography and hollow fiber, were also discussed. Perspectives on further applications of immobilized biomaterials in herbal analysis were finally presented.

Metal-Organic Frameworks Based Nano/Micro/Millimeter-Sized Self-Propelled Autonomous Machines

Synthetic nano/micro/millimeter-sized machines that harvest energy from the surrounding environment and then convert it to motion have had a significant impact on many research areas such as biology (sensing, imaging, and therapy) and environmental applications. Autonomous motion is a key element of these devices. A high surface area is preferable as it leads to increased propellant or cargo-loading capability. Integrating highly ordered and porous metal-organic frameworks (MOFs) with self-propelled machines is demonstrated to have a significant impact on the field of nano/micro/millimeter-sized devices for a wide range of applications. MOFs have shown great potential in many research fields due to their tailorable pore size. These fields include energy storage and conversion; catalysis, biomedical application (e.g., drug delivery, imaging, and cancer therapy), and environmental remediation. The marriage of motors and MOFs may provide opportunities for many new applications for synthetic nano/micro/millimeter-sized machines. Herein, MOF-based micro- and nanomachines are reviewed with a focus on the specific properties of MOFs.

Exonuclease I-assisted fluorescent method for ochratoxin A detection using iron-doped porous carbon, nitrogen-doped graphene quantum dots, and double magnetic separation

In this paper, a fluorescent method was developed for ochratoxin A (OTA) detection that uses iron-doped porous carbon (MPC) and aptamer-functionalized nitrogen-doped graphene quantum dots (NGQDs-Apt) as probes. In this method, the adsorbance of the NGQDs-Apt on the MPC due to a π-π interaction between the aptamer and the MPC results in the quenching of the fluorescence of the NGQDs-Apt. However, since OTA interacts strongly with the aptamer, the presence of OTA leads to the detachment of the NGQDs-Apt from the MPC, resulting in the resumption of fluorescence from the NGQDs-Apt. When exonuclease I (Exo I) is also added to the solution, this exonuclease specifically digests the aptamer, leading to the release of the OTA back into the solution. This free OTA then interacts with another MPC-NGQDs-Apt system, inducing the release of more NGQDs into the solution, which enhances the fluorescent intensity compared to that of the system with no Exo I. Utilizing this behavior of OTA in the presence of NGQDs-Apt, it was possible to detect concentrations of OTA ranging from 10 to 5000 nM, with a limit of detection of 2.28 nM. Our method was tested by applying it to the detection of OTA in wheat and corn samples. This method has four advantages: (1) the magnetic porous carbon is easy to prepare, its porosity enhances its loading capacity for NGQDs, it highly efficiently quenches the fluorescence of the NGQDs, and its magnetic properties facilitate the separation of the MPC from other species in solution; (2) applying double magnetic separation decreases the background signal; (3) Exo I digests the free aptamer effectively, which allows the resulting free OTA to induce the release of more NGQDs-Apt, ultimately enhancing the fluorescent signal; and (4) the proposed method presented high sensitivity and a wide linear detection range. This method may prove helpful in food safety analysis and new biosensor development (achieved by using different aptamer sequences to that used in the present work). Graphical abstract Exonuclease I (Exo I)-assisted fluorescent method for ochratoxin A (OTA) detection using magnetic porous carbon (MPC), nitrogen-doped graphene quantum dots (NGQDs), and double magnetic separation.

Alkaline Modification of a Metal–Enzyme–Surfactant Nanocomposite to Enhance the Production of L-α-glycerylphosphorylcholine

Microenvironment modification within nanoconfinement can maximize the catalytic activity of enzymes. Phospholipase A1 (PLA1) has been used as the biocatalyst to produce high value L-α-glycerylphosphorylcholine (L-α-GPC) through hydrolysis of phosphatidylcholine (PC). We successfully developed a simple co-precipitation method to encapsulate PLA1 in a metal–surfactant nanocomposite (MSNC), then modified it using alkalescent 2-Methylimidazole (2-Melm) to promote catalytic efficiency in biphasic systems. The generated 2-Melm@PLA1/MSNC showed higher catalytic activity than PLA1/MSNC and free PLA1. Scanning electron microscopy and transmission electron microscopy showed a typical spherical structure of 2-Melm@PLA1/MSNC at about 50 nm, which was smaller than that of 2-Melm@MSNC. Energy disperse spectroscopy, N2 adsorption isotherms, Fourier transform infrared spectrum, and high-resolution X-ray photoelectron spectroscopy proved that 2-Melm successfully modified PLA1/MSNC. The generated 2-Melm@PLA1/MSNC showed a high catalytic rate per unit enzyme mass of 1.58 μmol mg-1 min-1 for the formation of L-α-GPC. The 2-Melm@PLA1/MSNC also showed high thermal stability, pH stability, and reusability in a water–hexane biphasic system. The integration of alkaline and amphiphilic properties of a nanocomposite encapsulating PLA1 resulted in highly efficient sequenced reactions of acyl migration and enzymatic hydrolysis at the interface of a biphasic system, which cannot be achieved by free enzyme.