Search

Metal–organic frameworks (MOFs), with large specific surface area and tunable porosity, have gained lots of attention for immobilizing enzymes. However, the intrinsic open channels of most reported MOFs are generally smaller than 2 nm, which significantly prevents the passage of enzymes, and the diffusion efficiency of substrates and products. Here we report a new hierarchical micro-mesoporous zeolitic imidazolate framework-8 (ZIF-8) with core-shell superstructure (HZIF-8) using colloidal hydrated zinc sulfate (ZnSO4•7H2O) as a soft template for enzyme immobilization. The ZnSO4•7H2O forms an aggregation of colloids due to the self-conglobation effect in methanol, which affords a soft template for the formation of HZIF-8. Cytochrome C (Cyt C) was immobilized in interior of HZIF-8 through entrapment during the formation of HZIF-8. The resultant immobilized Cyt C (Cyt C@HZIF-8) exhibited 4-fold and 3-fold higher activity than free Cyt C and Cyt C encapsulated in conventional microporous ZIF-8 (Cyt C@ZIF-8), respectively. Meanwhile, the Km value of Cyt C@HZIF-8 significantly decreased due to the presence of mesopores compared with Cyt C@ZIF-8, indicating enhanced substrate affinity. After 7 cycles, Cyt C@HZIF-8 still maintained 70% of its initial activity whereas Cyt C@ZIF-8 only retained 10% of its initial activity. Moreover, the obtained HZIF-8 showed outstanding performance in co-immobilization of multi-enzyme for the detection of glucose.

In this study, the surfactant activated lipase from Aspergillus oryzae was used to prepare magnetic hybrid nanoflowers by embedding Fe3O4 magnetic nanoparticles (MNPs) into hybrid nanoflowers (MhNF). Meanwhile, MNPs were integrated into the activated lipase hybrid nanoflowers through covalent cross-linking (cross-linked-MhNF). Activity recovery of the MhNF and cross-linked-MhNF was 190% and 174%, respectively. However, activity recovery of lipase hybrid nanoflowers (hNF) only retained 77%. Furthermore, the MhNF displayed higher Kcat/Km value than free lipase, indicating high catalytic efficiency of MhNF. Compared with free lipase, the MhNF exhibited high tolerance against methanol and storage stability. Furthermore, the MhNF could be easily recycled by magnet without obvious activity loss. After reusing for 10 cycles, the activated hNF only retained 26% activity of its original activity, while the MhNF still maintained 84% activity of its initial activity, indicating excellent reusability. In the reaction of producing biodiesel from soybean oil, the MhNF-catalyzed biodiesel yield reached 88%, while the free enzyme was only 69%. The yield of biodiesel catalyzed by MhNF was maintained at 76% even after 6 consecutive cycles.

In the recent past, numerous new types of nanostructured carriers, as support matrices, have been engineered to advance the traditional enzyme immobilization strategies. The current research aimed to develop a robust enzyme-based biocatalytic platform and its effective deployment in the industrial biotechnology sectors at large and catalysis area, in particular, as low-cost biocatalytic systems. Suitable coordination between the target enzyme molecules and surface pendent multifunctional entities of nanostructured carriers has led an effective and significant contribution in myriad novel industrial, biotechnological, and biomedical applications. As compared to the immobilization on planar two-dimensional (2-D) surface, the unique physicochemical, structural and functional attributes of nano-engineered matrices, such as high surface-to-volume ratio, surface area, robust chemical and mechanical stability, surface pendant functional groups, outstanding optical, thermal, and electrical characteristics, resulted in the concentration of the immobilized entity being substantially higher, which is highly requisite from applied bio-catalysis perspective. Besides inherited features, nanostructured materials-based enzyme immobilization aided additional features, such as (1) ease in the preparation or green synthesis route, (2) no or minimal use of surfactants and harsh reagents, (3) homogeneous and well-defined core-shell nanostructures with thick enzyme shell, and (4) nano-size can be conveniently tailored within utility limits, as compared to the conventional enzyme immobilization. Moreover, the growing catalytic needs can be fulfilled by multi-enzymes co-immobilization on these nanostructured materials-based support matrices. This review spotlights the unique structural and functional attributes of several nanostructured materials, including carbon nanotubes, graphene, and its derivate constructs, nanoparticles, nanoflowers, and metal-organic frameworks as robust matrices for laccase immobilization. The later half of the review focuses on the applied perspective of immobilized laccases for the degradation of emergent contaminants, biosensing cues, and lignin deconstruction and high-value products.

Nanostructured materials constitute an interesting and novel class of support matrices for the immobilization of peroxidase enzymes. Owing to the high surface area, robust mechanical stability, outstanding optical, thermal, and electrical properties, nanomaterials have been rightly perceived as immobilization matrices for enzyme immobilization with applications in diverse areas such as nano-biocatalysis, biosensing, drug delivery, antimicrobial activities, solar cells, and environmental protection. Many nano-scale materials have been employed as support matrices for the immobilization of different classes of enzymes. Nanobiocatalysts, enzymes immobilized on nano-size materials, are more stable, catalytically robust, and could be reused and recycled in multiple reaction cycles. In this review, we illustrate the unique structural/functional features and potentialities of nanomaterials-immobilized peroxidase enzymes in different biotechnological applications. After a comprehensive introduction to the immobilized enzymes and nanocarriers, the first section reviewed carbonaceous nanomaterials (carbon nanotube, graphene, and its derivatives) as a host matrix to constitute robust peroxidases-based nanobiocatalytic systems. The second half covers metallic nanomaterials (metals, and metal oxides) and some other novel materials as host carriers for peroxidases immobilization. The next section vetted the potential biotechnological applications of the resulted nanomaterials-immobilized robust peroxidases-based nanobiocatalytic systems. Concluding remarks, trends, and future recommendations for nanomaterial immobilized enzymes are also given.

Multienzymatic conversion of carbon dioxide (CO2) into chemicals has been extensively studied. However, regeneration and reuse of co-factor are still the main problems for the efficient conversion of CO2. In this study, a nanoscale multienzyme reactor was constructed by encapsulating simultaneously carbonic anhydrase (CA), formate dehydrogenase (FateDH), co-factor (NADH), and glutamate dehydrogenases (GDH) into ZIF-8. In the multienzyme reactors, cationic polyelectrolyte (polyethyleneimine, PEI) was doped in the ZIF-8 by dissolving it in the precursors of ZIF-8. Co-factor (NADH) was anchored in ZIF-8 by ion exchange between PEI (positive charge) and co-factor (negative charge), and regenerated through GDH embedded in the ZIF-8, thus keeping high activity of FateDH. Activity recovery of FateDH in the multienzyme reactors reached 50%. Furthermore, the dissolution of CO2 in the reaction solution was increased significantly by the combination of CA and ZIF-8. As a result, the nanoscale multienzyme reactor exhibited superior capacity for conversion of CO2 to formate. Compared with free multienzyme system, formate yield was increased 4.6-fold by using the nanoscale multienzyme reactor. Furthermore, the nanoscale multienzyme reactor still retained 50% of its original productivity after 8 cycles, indicating excellent reusability.

Baker's yeast industries generate highly polluted effluents, especially the cell free broth (i.e., vinasse) characterized by high chemical oxygen demand, nitrogen, and salts. In this work, it was found that the residual by-products (i.e., ethanol and acetic acid) and salts in the vinasse severely inhibited the cell growth, which hindered the reuse of the vinasse for the production of Saccharomyces cerevisiae. Through optimizing a suitable control strategy, the productions of ethanol and acetic acid were eliminated. Then, a nanofiltration membrane (i.e., NF5) was preferred for preliminarily and simultaneously separating and concentrating valuable molecules (i.e., invertase, food grade proteins and pigments) in the vinasse, and the main fouling mechanism was cake layer formation. Subsequently, a reverse osmosis membrane (RO) was suitable to separate and concentrate salts in the NF5 permeate, where the membrane fouling was negligible. Finally, the RO permeate was successfully reused for the production of S. cerevisiae. In addition, without calculating the benefit from the recovery of the valuable molecules, the cost of the integrated process can be decreased by 59.8% compared with the sole triple effect evaporation. Meanwhile, the volume of the fresh water used in the fermentation process can be decreased by 68.8%. Thus, it is a sustainable process for the cleaner production of baker's yeast using the integrated fermentation and membrane separation process.

Zeolitic imidazole frameworks (ZIFs) with tunable pore sizes and high surface areas have recently used as an effective support for immobilizing enzymes. However, the instability in the aqueous acidic environment has limited their practical applications in some cases. In this work, we develop a novel catalase/ZIFs composite with mesoporous silica shell (mSiO2@CAT/ZIFs) via co-precipitation, and controlled self-assembly of silanes. During preparation, the cetyltrimethylammonium bromide induced the formation of the mesostructured silica layer on the outer surface of CAT/ZIFs. The resultant mSiO2@CAT/ZIFs exhibited high activity recovery (92%). Compared with the conventional CAT/ZIFs and free CAT, mSiO2@CAT/ZIFs exhibited excellent acid resistance. For example, after 30 min in acetate buffer solution (pH 3.0), the CAT/ZIFs and free CAT almost lost activity whereas the mSiO2@CAT/ZIFs still retained 35% of original activity. Meanwhile, the thermostability of the mSiO2@CAT/ZIFs was enhanced significantly compared with conventional CAT/ZIFs. In addition, the mSiO2@CAT/ZIFs displayed excellent storage stability, and retained 60% of its initial activity after 15 days storage period. Furthermore, the mSiO2@CAT/ZIFs could maintain 70% of its initial activity after 8 continuous uses, demonstrating superior reusability than the free CAT and CAT/ZIFs. These results demonstrated that the mSiO2@CAT/ZIFs are potential for practical applications even in the acidic environment.

Enzyme catalysis has been attracting increasing interest in the past twenty years. Nevertheless, most reports concerning enzyme catalysis have been carried out using single enzymes. Recent years, multiple enzyme cascade reactions have a significant role for the production of many compounds at an industrial level because they permit to perform very complex reactions. Especially, the development of coimmobilized multienzymatic systems is increasingly driven by economic and environmental constraints that provide an impetus to develop alternatives to conventional multistep synthetic methods. Up to now, process optimization and novel strategies of coimmobilized multienzymatic systems hardly have been reviewed. In this review, we focus on some recent novel techniques in preparing co-immobilized multienzymatic systems and the up-to-date advances in the application of multienzymatic systems. Moreover, we also discuss the improvements that co-immobilization multienzymatic systems offer enzymes such as reusability, catalytic activity, and stability.

Bacterial cellulose (BC) has numerous excellent properties but the absence of antibacterial activity restricts its applications in biomedical field. Therefore, in order to introduce the antibacterial characteristics into BC; herein, a facile method for incorporation of ZnO nanoparticles (ZnO-NPs) is presented. BC films were first immersed in zinc nitrate solution, followed by treating with NaOH solution, the BC loaded ZnO nanocomposite films were dried by a sheet former instrument at 80 °C for 20 min. The obtained BC/ZnO nanocomposites were characterized by different techniques. XRD results showed the hexagonal wurtzite structure of ZnO-NPs while FE-SEM results displayed the particle size of ZnO-NPs was ranging from 70 to 100 nm. Thermogravimetric study revealed the thermal stability of nanocomposite films. The nanocomposite exhibited photocatalytic activity and revealed 91% degradation of methyl orange (MO) under UV-irradiation within 2 h. Moreover, the nanocomposites demonstrated significant UV-blocking properties and showed antibacterial activities against tested Gram-positive and Gram-negative bacterial strains. This work provides a simple and novel method for the synthesis of BC/ZnO nanocomposite as a functional biomaterial.

Metal-organic frameworks (MOFs) have recently emerged as a promising candidate for the immobilization of enzymes due to their diversified structures and porosity. However, it is difficult to handle and fully recover the enzyme-MOF composites from the reaction medium due to their nanometer size and good dispersity in solvents, which limits their practical applications. Here, a novel enzyme-MOF composite with both highly stable and easily reusable features was prepared via encapsulating catalase/ZIF-8 nanocrystals into large mesoporous silica layer (silica@CAT/ZIF-8). This immobilized system exhibited high activity recovery (81%). The silica layer around the catalase/ZIF-8 particles provided a “shield” to protect from biological and chemical degradation for enzyme. As a result, the silica@CAT/ZIF-8 composites exhibited higher stability against proteolytic agent and extreme conditions (such as low pH) than that of conventional catalase/ZIF-8 composites. More importantly, the micrometer-sized silica@CAT/ZIF-8 can be easily repeatedly used without obvious activity loss. The silica@CAT/ZIF-8 composites still remained 50% of their original activity after 10 cycles, whereas the conventional catalase/ZIF-8 composites only retained 7% of their original activity after 5 cycles. These results demonstrated that this approach could be an efficient strategy to prepare enzyme-ZIF-8 composite with both high stability and excellent recyclability.

CO2 capture by immobilized carbonic anhydrase (CA) has become an alternative and environmental friendly approach in CO2 sequestration technology. However, the immobilized CA usually exhibits low CO2 sequestration efficiency due to no gas adsorption function for the conventional CA supports. Metal organic frameworks (MOFs) are an excellent material for gas adsorption and enzyme immobilization. Herein, a combined immobilization system of CA and ZIF-8 with cruciate flower-like morphology for CO2 adsorption was prepared for the first time by adsorbing CA onto ZIF-8. The immobilization efficiency was greater than 95%, and the maximum activity recovery reached 75%, indicating the highly efficient immobilization process. The resultant CA@ZIF-8 composites exhibited outstanding thermostability, the tolerance against denaturants, and reusability compared with free CA. Furthermore, we demonstrated for the first time that the shape of ZIF-8 could be controlled by adjusting concentrations of Zn2+ ions at the high concentration of 2-methylimidazole (1 M). More importantly, we also demonstrated the applicability of the CA@ZIF-8 composites to the sequestration of CO2 in carbonate minerals. The yields of the CaCO3 obtained by using CA@ZIF-8 composites were 22-folds compared to free CA. Thus, this CA@ZIF-8 composite can be successfully used as a robust biocatalyst for sequestration of CO2.

Enzyme immobilization on the external surface of solid supports is a commonly adopted method to improve stability and reuse for continuous operations, which, however, is prone to cause the enzyme denaturation due to no carriers protection. Herein, we describe enzyme-shielding strategy to prepare hybrid organic/inorganic nanobiocatalysts; it exploits the self-assembly of silane building blocks at the surface of immobilized enzymes on Fe3O4/silica core-shell nanospheres to grow a protective silica layer. The silica shell around the immobilized enzyme particles provides a “shield” to protect from biological, thermal and chemical degradation for enzyme. As a result, the recycling of the immobilized catalase with a protective silica layer was improved remarkably compared with immobilized catalase without a protective silica layer. The immobilized catalase with a protective silica layer still remained 70% of their original activity after 9 cycles, whereas the immobilized catalase without a protective silica layer only retained 20% of their original activity. Moreover, the immobilized catalase with a protective silica layer exhibited significantly enhanced resistance to denaturing stresses (such as proteolytic agent, denaturants, and heat). Therefore, the enzyme-shielding strategy showed promising applications for preparing obtain stable and recycled nanobiocatalyst.

Non-small cell lung cancer (NSCLC) is one of the most prevailing malignancies worldwide. It has been previously shown that wogonoside exerts anti-tumor activities in various kinds of human cancers. But its role in NSCLC remains elusive. In the present study, we determined the anti-tumor effect of wogonoside in human NSCLC A549 cells. We found that wogonoside effectively inhibits A549 cell viability through inducing cell cycle arrest and apoptosis. Moreover, administration of wogonoside by intraperitoneal injection inhibits the growth of A549 cell xenografts in athymic nude mice. Additionally, mitochondrial membrane potential was disrupted and cytochrome c was released to cytosol in the wogonoside-treated A549 cells. Finally, we found that AMPK/mTOR signaling might be implicated in the anti-NSCLC efficacy of wogonoside. Therefore, we may assume that wogonoside may be considered as a potential therapeutic agent for the treatment of NSCLC.

ε-Poly-l-lysine (ε-PL) is widely used as an antibacterial agent because of its broad antimicrobial spectrum. However, the antimicrobial mechanism of ε-PL against Saccharomyces cerevisiae (S. cerevisiae) is only vaguely described. Especially, it is widely accepted that membrane disruption is its main antimicrobial mode of action, but its effect on the cell wall remains unclear. In this study, the effects of ε-PL on cell wall of S. cerevisiae were investigated, and the possible action mode of ε-PL on the cell wall was discussed. The results showed that ε-PL affected significantly the cell wall composition such as β-1, 3-glucan, mannosylphosphate and chitin, and caused cell wall more fragile. The cell wall permeability was significantly increased. Furthermore, ε-PL induced the intracellular accumulation of reactive oxygen species (ROS), as well as lead to DNA fragmentation. These results indicate that ε-PL may have a complicated antimicrobial mode of action with multi-target mechanisms against S. cerevisiae cells.

Metal-organic frameworks (MOFs) are a type of porous material that have tunable porosity, desirable functionality, extremely high surface area, and chemical/thermal stability. MOFs consist of metal containing nodes and organic ligands linked through coordination bonds. Owing to the unique properties of MOFs, there is considerable interest in using them as a potential matrix for enzyme immobilization. Recent studies have focused on developing enzyme-MOF composites with potential applications. Many MOF-enzyme composites exhibit excellent catalytic performance, far outperforming free enzymes in many aspects. This review summarizes recent developments in enzyme-MOF composites with special emphasis on novel synthesizing strategies, process optimization, and improvement of catalytic performance of the enzyme-MOF composites over free enzymes.

Enzyme immobilization on solid supports is a valuable approach to address enzyme stability and reuse for continuous operations. However, the enzymes immobilized on the external surface of solid supports may not be protected by carriers and suffer inactivation caused by denaturing stresses and hazard external environment. Herein, we describe for the first time a enzyme-shielding strategy to prepare hybrid organic/inorganic nanobiocatalysts; it exploits the self-assembly of supramolecular metal-organic coordination complex (tannic acid (TA) and Fe3+) at the surface of immobilized catalase on Fe3O4/silica core-shell nanospheres to grow a protective nanocoating (Fe3+-TA nanocoating). The nanocoatings around the immobilized catalase (Fe3+-TA@Fe3O4/SiO2-catalase) provide a “shield effect” to protect from biological, thermal and chemical degradation for enzyme. As a result, the stability of immobilized catalase against proteolytic agent, denaturants and heat were improved remarkably compared to the immobilized catalase without a protective nanocoating and free catalase. More importantly, the recycling of the immobilized catalase was improved remarkably. The Fe3+-TA@Fe3O4/SiO2-catalase still retained 55% of their original activity after 9 cycles, whereas the immobilized catalase without a protective nanocoating only retained 20% of original activity. These results demonstrated that the novel enzyme-shielding strategy is an efficient method to obtain stable and recycled biocatalyst with yolk-shell structure.

In the past few years, organic–inorganic hybrid nanoflowers technology has been emerged as an effective immobilization method. This method has motivated a considerable interest in exploiting them as a potential matrix for biomolecule immobilization due to their simple synthesis, high efficiency, great promise of enhancing biomolecule stability, activity and even selectivity. Recent years, many efforts have focused on this topic to develop biomolecule-inorganic hybrid nanoflowers with potential applications. In this review, recent advances in functional biomolecule-inorganic hybrid nanoflowers are discussed with an emphasis on the novel synthesizing strategies, process optimization, and their potential applications in biosensor, biocatalysis, drug delivery, and chemical analysis. Trends in current developments toward the rational design of these nanoflowers are identified.

Cross-linked enzyme aggregates (CLEAs) have recently emerged as a promising method for enzyme immobilization due to its simplicity and low cost. However, a lack of good size and morphological control over the as-prepared CLEAs has limited their practical applications in some cases. Here, monodisperse spherical CLEAs of phenylalanine ammonia lyase (PAL microspheres) were prepared based on CaCO3 microtemplates. The preparation procedure involves filling porous CaCO3 microtemplates with the protein by salt precipitation, glutaraldehyde crosslinking, and dissolution of the microtemplates. The formulation of CaCO3 templates with controlled size was studied in detail. Characterization of the prepared PAL microspheres was investigated. The results showed that the PAL microspheres with high immobilization efficiency (79%) exhibited excellent stability, including increased tolerance to proteolysis, low pH, and denaturants, and excellent mechanical properties. For example, free PAL almost lost all activity after they were incubated in the presence of trypsin for 2min, whereas PAL microspheres still retained 95% of their initial activity. Moreover, scanning electron microscope, transmission electron microscope, and N2 adsorption-desorption isotherms revealed that the resultant PAL microspheres possessed good monodispersity and mesoporous structure instead of the amorphous clusters of conventional CLEAs with few pores. Compared with conventional CLEAs, the monodisperse PAL microspheres with mesoporous make them more potentially useful for biomedical and biotechnological applications.

Ultrahigh-vacuum conditions for microelectromechanical systems (MEMS) packaging can be achieved and sustained using a nonevaporable getter (NEG) film technology. Better understanding of the processes involved in film deposition, activation, and poisoning could help optimization and engineering of the film properties. In the present work, highly porous ZrCoCe films were deposited on (100) silicon substrates by direct current magnetron sputtering. Film morphology and performance dependence on deposition pressure, substrate temperature and substrate outgassing were investigated. The studies reveal that the pressure of the Ar sputtering gas affects significantly the film structure. High working pressures produce open columnar structures, whereas low pressures produce dense layers. It is demonstrated that the variation of the substrate temperature results in a significant modification of the film morphology. The highest sorption speed obtained for substrate temperature of 150 °C, is clearly correlated with the high specific surface area and porosity of the ZrCoCe film. It has also been confirmed that sorption properties can be improved by substrate outgassing prior to deposition.

In recent years, lignocellulosic wastes have gathered much attention due to increasing economic, social, environmental apprehensions, global climate change and depleted fossil fuel reserves. The unsuitable management of lignocellulosic materials and related organic wastes poses serious environmental burden and causes pollution. On the other hand, lignocellulosic wastes hold significant economic potential and can be employed as promising catalytic supports because of impressing traits such as surface area, porous structure, and occurrence of many chemical moieties (i.e., carboxyl, amino, thiol, hydroxyl, and phosphate groups). In the current literature, scarce information is available on this important and highly valuable aspect of lignocellulosic wastes as smart carriers for immobilization. Thus, to fulfill this literature gap, herein, an effort has been made to signify the value generation aspects of lignocellulosic wastes. Literature assessment spotlighted that all these waste materials display high potential for immobilizing enzyme because of their low cost, bio-renewable, and sustainable nature. Enzyme immobilization has gained recognition as a highly useful technology to improve enzyme properties such as catalytic stability, performance, and repeatability. The application of carrier-supported biocatalysts has been a theme of considerable research, for the past three decades, in the bio-catalysis field. Nonetheless, the type of support matrix plays a key role in the immobilization process due to its influential impact on the physicochemical characteristics of the as-synthesized biocatalytic system. In the past, an array of various organic, inorganic, and composite materials has been used as carriers to formulate efficient and stable biocatalysts. This review is envisioned to provide recent progress and development on the use of different agricultural wastes (such as coconut fiber, sugarcane bagasse, corn and rice wastes, and Brewers' spent grain) as support materials for enzyme immobilization. In summary, the effective utilization of lignocellulosic wastes to develop multi-functional biocatalysts is not only economical but also reduce environmental problems of unsuitable management of organic wastes and drive up the application of biocatalytic technology in the industry.

The aim of this study was to develop an environmentally safe and efficient method for phenyllactic acid (PLA) production using whole-cell cascade catalysis with l -amino acid deaminase ( l -AAD), lactate dehydrogenase (LDH), and formate dehydrogenase (FDH). The PPA titer was low due to relatively low expression of LDH, intermediate accumulation, and lack of cofactors. To address this issue, ribosome binding site regulation, gene duplication, and induction optimization were performed to increased the PLA titer to 43.8 g/L. Then co-substrates (glucose, yeast extract, and glycerol) were used to increase NADH concentration and cell stability, resulting that the PLA titer was increased to 54.0 g/L, which is the highest reported production by biocatalyst. Finally, glucose was replaced with wheat straw hydrolysate as co-substrate to decrease the cost. Notably, the strategies reported herein may be generally applicable to other whole-cell cascade biocatalysts.

Ba0.6Sr0.4Ti1−xMnxO3 [BST(Mn), x = 0.0000, 0.0025, 0.0050, 0.0075, 0.0100 and 0.0125] powders were synthesized by solid-state reaction process, and then BST(Mn)/MgO ceramic composites (60 wt% MgO) were fabricated by conventional ceramic process. Mn was found distributed in the BST grains homogeneously after sintering at 1420 °C for 4 h, neither grain-boundary segregation nor diffusion into the MgO grains could be found obviously. The dielectric nonlinearity of the materials was enhanced with the addition of Mn-dopant, and relatively high tunability, more than 27% (8 kV/mm DC field, 500 Hz), was obtained in BST(Mn)/MgO samples with x ≤ 0.0100. The dielectric loss at microwave frequency of the samples with Mn-dopant was significantly reduced, and a tremendously low dielectric loss was acquired for the sample with x = 0.0050, which is only 4.5 × 10−3 (at 3.64 GHz). Both the low dielectric loss and enhanced tunable properties of the BST(Mn)/MgO composites are useful for tunable microwave applications.

ZnO additions to Ba 0.3 Sr 0.7 TiO 3 ceramics have been studied in order to determine the role of this dopant on dielectric property and energy storage density development. The temperature and frequency dependences of dielectric constant, the breakdown strength, and the dielectric dissipation were measured. The dependence of dielectric constant to applied DC field was used to evaluate the energy storage densities. The crystalline structure and morphology were also investigated by XRD and SEM, respectively. Experimental results show that the stored energy density for the sample with 1.6 wt% ZnO addition is the highest among all the compositions. At 40 kV mm −1 electric fieled, its stored energy density can reach 3.9 J cm −3 . Moreover, the ceramic with this composition has higher dielectric constant and breakdown strength, lower loss and dependency characteristic of dielectric constant to applied electric field.

A combined promoter expression vector pBV–PAL for high-level expression of phenylalanine ammonia lyase gene of Rhodosporidium toruloides was constructed. Pal gene was cloned and inserted into the region between SalI and PstI restriction sites of expression vector pBV220 (containing PLPR promoter) to obtain recombinant expression vector pBV220–PAL. The tac promoter obtained from the plasmid pKtac was inserted into the expression vector pBV220–PAL to construct expression vector pBV–PAL. The recombinant plasmid pBV220–PAL and pBV–PAL were introduced into Escherichia coli JM109 by transformation. The result showed that the transformant E. coli JM109 (pBV–PAL) gave a much higher PAL activity than that transformant E. coli JM109 (pBV220–PAL). Recombinant PAL expression level of the transformant JM109 (pBV–PAL) was about 9.6% of total cellular protein, specific enzyme activity was 2.3-fold higher than that of the transformant JM109 (pBV220–PAL), reached 35 U/g (dry cells weight, DCW). PAL specific activity of 123 U/g (DCW) could be achieved in a 5-l fermentor. 80.5% conversion rate of trans-cinnamic acid to l -phenylalanine and 5.12 g/l l -phenylalanine were obtained after 3 h bioconversion using the transformant JM109 (pBV–PAL). The recombinant strain JM109 containing the combined promoter expression vector pBV–PAL was shown to be effective and practical to product l -phenylalanine.