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1.
甲醇营养型毕赤酵母表达外源蛋白是在醇氧化酶(alcohol oxidase,AOX)启动子(PAOXI)严格调控下进行的,然而这种启动子在转录水平受到葡萄糖的阻遏。本文研究了毕赤酵母在葡萄糖替代甘油为生长相碳源时表达重组植酸酶蛋白的发酵特征。结果表明:初始葡萄糖浓度为20dL的细胞得率高,为0.39g[DCW]/g。通过基于实时参数(溶氧和呼吸商)调控的葡萄糖补料策略,生长相40h后细胞密度达到100g[DCW]/L,甲醇诱导100h后植酸酶产量达到2200FTUphytase/mL,甲醇得率系数为0.25FTU phytase/gmethnol。因此,在毕赤酵母高表达重组蛋白培养中葡萄糖能够用作生长相基质,并能实现重组蛋白的高效表达。  相似文献   

2.
Ferritin in the field of nanodevices   总被引:2,自引:0,他引:2  
Biomineralization of ferritin core has been extended to the artificial synthesis of homogeneous metal complex nanoparticles (NPs) and semiconductor NPs. The inner cavity of apoferritin is an ideal spatially restricted chemical reaction chamber for NP synthesis. The obtained ferritin (biocomplexes, NP and the surrounding protein shell) has attracted great interest among researchers in the field of nanodevices. Ferritins were delivered onto specific substrate locations in a one-by-one manner or a hexagonally close-packed array through ferritin outer surface interactions. After selective elimination of protein shells from the ferritin, bare NPs were left at the positions where they were delivered. The obtained NPs were used as catalysts for carbon nanotube (CNT) growth and metal induced lateral crystallization (MILC), charge storage nodes of floating gate memory, and nanometer-scale etching masks, which could not be performed by other methods.  相似文献   

3.
A novel strategy for the fabrication of sensitive immunosensor to detect alpha-fetoprotein (AFP) in human serum has been proposed. The immunosensor was prepared by immobilizing AFP antigen onto the glassy carbon electrode (GC) modified by gold nanoparticles and carbon nanotubes doped chitosan (GNP/CNT/Ch) film. GNP/CNT hybrids were produced by one-step synthesis based on the direct redox reaction. The electrochemical properties of GNP/CNT/Ch films were characterized by impedance spectroscopy and cyclic voltammetry. It was indicated that GNP/CNT nanohybrid acted as an electron promoter and accelerated the electron transfer. Sample AFP, immobilized AFP, and alkaline phosphatase (ALP)-labeled antibody were incubated together for the determination based on a competitive immunoassay format. After the immunoassay reaction, the bound ALP label on the modified GC led to an amperometric response of 1-naphthyl phosphate (1-NP), which was changed with the different antigen concentrations in solution. Under the optimized experimental conditions, the resulting immunosensor could detect AFP in a linear range from 1 to 55 ng ml(-1) with a detection limit of 0.6 ng ml(-1). The proposed immunosensor, by using GNP/CNT/Ch as the immobilization matrix of AFP, offers an excellent amperometric response of ALP-anti-AFP to 1-NP. The immunosensor provided a new alternative to the application of other antigens or other bioactive molecules.  相似文献   

4.
AimsCarbon nanotube (CNT) membranes offer an exciting opportunity to mimic natural protein channels due to 1) a mechanism of dramatically enhanced fluid flow 2) ability to place ‘gatekeeper’ chemistry at the entrance to pores 3) the ability for biochemical reactions to occur on gatekeeper molecules and 4) an ability to chemically functionalize each side of the membrane independently.Main methodsAligned CNT membranes were fabricated and CNT pore entrances modified with gatekeeper chemistry. Pressure driven fluid flow and diffusion experiments were performed to study the mechanisms of transport through CNTs.Key findingsThe transport mechanism through CNT membranes is primarily 1) ionic diffusion near bulk expectation 2) gas flow enhanced 1–2 orders of magnitude primarily due to specular reflection 3) fluid flow 4–5 orders of magnitude faster than conventional materials due to a nearly ideal slip-boundary interface. The transport can be modulated by ‘gatekeeper’ chemistry at the pore entrance using steric hindrance, electrostatic attraction/repulsion, or biochemical state. The conformation of charged tethered molecules can be modulated by applied bias setting the stage for programmable drug release devices.SignificanceThe membrane structure is mechanically far more robust than lipid bilayer films, allowing for large-scale chemical separations, delivery or sensing based on the principles of protein channels. The performance of protein channels is several orders of magnitude faster than conventional membrane materials. The fundamental requirements of mimicking protein channels are present in the CNT membrane system.  相似文献   

5.
The electrochemical behavior of L-cysteine (CySH) on platinum (Pt)/carbon nanotube (CNT) electrode was investigated by cyclic voltammetry. CNTs used in this study were grown directly on graphite disk by chemical vapor deposition. Pt was electrochemically deposited on the activated CNT/graphite electrode by electroreduction of Pt(IV) complex ion on the surface of CNTs. Among graphite, CNT/graphite, and Pt/CNT electrodes, improved electrochemical behavior of CySH oxidation was found with Pt/CNT electrode. On the other hand, a sensitive CySH sensor was developed based on Pt/CNT/graphite electrode. A linear calibration curve can be observed in the range of 0.5 microM-0.1 mM. The detection limit of the Pt/CNT electrode is 0.3 microM (signal/nose=3). Effects of pH, scan rate, and interference of other oxidizable amino acids were also investigated and discussed. Additionally, the reproducibility, stability, and applicability of the Pt/CNT electrode were evaluated.  相似文献   

6.
A novel strategy for the fabrication of sensitive immunosensor to detect α-fetoprotein (AFP) in human serum has been proposed. The immunosensor was prepared by immobilizing AFP antigen onto the glassy carbon electrode (GC) modified by gold nanoparticles and carbon nanotubes doped chitosan (GNP/CNT/Ch) film. GNP/CNT hybrids were produced by one-step synthesis based on the direct redox reaction. The electrochemical properties of GNP/CNT/Ch films were characterized by impedance spectroscopy and cyclic voltammetry. It was indicated that GNP/CNT nanohybrid acted as an electron promoter and accelerated the electron transfer. Sample AFP, immobilized AFP, and alkaline phosphatase (ALP)-labeled antibody were incubated together for the determination based on a competitive immunoassay format. After the immunoassay reaction, the bound ALP label on the modified GC led to an amperometric response of 1-naphthyl phosphate (1-NP), which was changed with the different antigen concentrations in solution. Under the optimized experimental conditions, the resulting immunosensor could detect AFP in a linear range from 1 to 55 ng ml−1 with a detection limit of 0.6 ng ml−1. The proposed immunosensor, by using GNP/CNT/Ch as the immobilization matrix of AFP, offers an excellent amperometric response of ALP-anti-AFP to 1-NP. The immunosensor provided a new alternative to the application of other antigens or other bioactive molecules.  相似文献   

7.
A novel nanocomposite cathode consisting of sulfur and hollow‐mesoporous titania (HMT) embedded within carbon nanotubes (CNT), which is designated as S‐HMT@CNT, has been obtained by encapsulating elemental sulfur into the pores of hollow‐mesoporous, spherical TiO2 particles that are connected via CNT. A carbon‐paper interlayer, referred to as dual functional porous carbon wall (DF‐PCW), has been obtained by filling the voids in TiO2 spheres with carbon and then etching the TiO2 template with a chemical process. The DF‐PCW interlayer provides a medium for scavenging the lithium polysulfides and suppressing them from diffusing to the anode side when it is inserted between the sulfur cathode and the separator. Lithium–sulfur cells fabricated with the thus prepared S‐HMT@CNT cathode and the DF‐PCW interlayer exhibit superior performance due to the containment of sulfur in TiO2 and improved lithium–ion and electron transports. The Li–S cells display high capacity with excellent capacity retention at rates as high as 1C, 2C, and 5C rates.  相似文献   

8.
Lithium insertion into sulfur confined within 200 nm cylindrical inner pores of individual carbon nanotubes (CNTs) was monitored in situ in a transmission electron microscope (TEM). This electrochemical reaction was initiated at one end of the S‐filled CNTs. The material expansion during lithiation was accommodated by the expansion into the remaining empty pore volume and no fracture of the CNT walls was detected. A sharp interface between the initial and lithiated S was observed. The reaction front was flat, oriented perpendicular to the confined S cylinder, and propagated along the cylinder length. Lithiation of S in the proximity of conductive carbon proceeded at the same rate as the one in the center of the pore, suggesting the presence of electron pathways at the Li2S/S interface. Density of states calculations further confirmed this hypothesis. In situ electron diffraction showed a direct phase transformation of S into nanocrystalline Li2S without detectable formation of any intermediates, such as polysulfides and LiS. These important insights may elucidate some of the reaction mechanisms and guide the improvements in the design of C–S nanocomposites for high specific energy Li–S batteries. The proposed use of conductive CNTs with tunable pore diameter as cylindrical reaction vessels for in situ TEM studies of electrochemical reactions proved to be highly advantageous and may help to resolve the ongoing problems in battery technology.  相似文献   

9.
Developing advanced supercapacitors with both high areal and volumetric energy densities remains challenging. In this work, self‐supported, compact carbon composite electrodes are designed with tunable thickness using 3D printing technology for high‐energy‐density supercapacitors. The 3D carbon composite electrodes are composed of the closely stacked and aligned active carbon/carbon nanotube/reduced graphene oxide (AC/CNT/rGO) composite filaments. The AC microparticles are uniformly embedded in the wrinkled CNT/rGO conductive networks without using polymer binders, which contributes to the formation of abundant open and hierarchical pores. The 3D‐printed ultrathick AC/CNT/rGO composite electrode (ten layers) features high areal and volumetric mass loadings of 56.9 mg cm?2 and 256.3 mg cm?3, respectively. The symmetric cell assembled with the 3D‐printed thin GO separator and ultrathick AC/CNT/rGO electrodes can possess both high areal and volumetric capacitances of 4.56 F cm?2 and 10.28 F cm?3, respectively. Correspondingly, the assembled ultrathick and compact symmetric cell achieves high areal and volumetric energy densities of 0.63 mWh cm?2 and 1.43 mWh cm?3, respectively. The all‐component extrusion‐based 3D printing offers a promising strategy for the fabrication of multiscale and multidimensional structures of various high‐energy‐density electrochemical energy storage devices.  相似文献   

10.
ABSTRACT

Exo– and endo–adsorption of ethylene oxide (EO) on pristine (9,0) (zigzag) carbon nanotube (CNT) and its doped forms with silicon (Si–CNT), aluminum (Al–CNT) and boron (B–CNT) were investigated using density functional theory (DFT) at M06–2X/6–311++G** level. The natural bond orbital (NBO) and the quantum theory of atoms in molecules (QTAIM) analyses were also performed by using the same level of theory. The effect of the doping on sensing behaviour of the CNT toward EO molecule was investigated through intermolecular interactions studies by calculation of total and partial density of states (DOS, PDOS). The enhanced sensitivity of doped–CNTs towards EO molecule associated with adsorption energies (Eads) and the changes in geometric and electronic structures was examined and the global chemical reactivity parameters were calculated and comprehensively analysed. The thermodynamic property changes were calculated and compared. The results indicated that the EO adsorption on the pristine and doped CNTs was an exothermic spontaneous process. Moreover, based on the calculated Eg change (ΔEg) and Eads values, Al–CNT with superior sensitivity for sensing of EO molecule, indicates promising perspectives for its use in fabrication of new EO gas–sensing devices.  相似文献   

11.
Meldola's blue (MB) functionalized carbon nanotubes (CNT) nanocomposite film (MB/CNT) electrode was prepared by non-covalent adsorbing MB on the surface of a carbon nanotubes modified glassy carbon electrode (CNT/GCE). Electrochemical behaviors of the resulting electrode were investigated thoroughly with cyclic voltammetry in the potential range of -0.6 to 0.2V, and two well-defined redox couples were clearly visualized. We also studied the electron transfer kinetics of MB loaded on CNT (MB/CNT) in comparison with that of MB on conventional graphite powder (MB/GP). The heterogeneous electron transfer rate constant (k(s)) of MB/CNT was calculated to be about three times larger than that of MB/GP. The accelerated electron transfer kinetics was attributed to the unique electrical and nanostructural properties of CNT supports as well as the interaction between MB and CNT. In connection with the oxidation of nicotinamide adenine dinucleotide (NADH), excellent electrocatalytic activities were observed at MB/CNT/GCE compared with MB/GP modified glassy carbon electrode (MB/GP/GCE). Based on the results, a new NADH sensor was successfully established using the MB/CNT/GCE. Under a lower operation potential of -0.1V, NADH could be detected linearly up to a concentration of 500 microM with an extremely lower detection limit of 0.048+/-0.02 microM estimated at a signal-to-noise ratio of 3. Sensitivity, selectivity, reproducibility and stability of the NADH sensor were also investigated and the main analytical data were also compared with those obtained with the MB/GP/GCE.  相似文献   

12.
Multiwalled carbon nanotubes (CNT) of diameters of 10-40 nm are synthesized on Fe and Co coated nm-scale catalyst support in a xylene chemical vapor deposition (CVD) process without the need for ferrocene iron source. Silica (∼40 nm diameter) and nanocrystalline Au (∼10 nm) are coated with a monolayer of amine, sulfonate, or thiol termination to ensure monolayer Fe loading, reduce Fe surface migration and reduce agglomeration of catalyst support particles during dispersion. Coordination with surface functionalization did not noticeably hinder Fe surface diffusion nor hinder catalytic activity of CNT formation. CNT diameters of ∼40 nm were seen for most chemical treatments. Functionalization of substrate (SiO2/Si) surface with carboxylic termination aided in the dispersion of amine functionalized silica nanoparticles. Another approach to limit catalytic support to nm-scale dimensions was to deposit a thin film of Co (5-25 nm thick) in a multilayer structure that after etching left a nm-scale Co line at the edge of the pattern. In the ferrocene CVD process, CNT diameters down to 10 nm are controlled directly by the catalytic metal film thickness.  相似文献   

13.
Carbon materials have attracted extensive attention as the host materials of sulfur for lithium–sulfur battery, especially those with 3D architectural structure. Here, a novel 3D graphene nanosheet–carbon nanotube (GN–CNT) matrix is obtained through a simple one‐pot pyrolysis process. The length and density of CNTs can be readily tuned by altering the additive amount of carbon source (urea). Specifically, CNTs are in situ introduced onto the surface of the graphene nanosheets (GN) and show a stable covalent interaction with GN. Besides, in the GN–CNT matrix, cobalt nanoparticles with different diameters exist as being wrapped in the top of CNTs or scattering on the GN surface, and abundant heteroatoms (N, O) are detected, both of which can help in immobilizing sulfur species. Such a rationally designed 3D GN–CNT matrix makes much more sense in enhancing the electrochemical performance of the sulfur cathode for rapid charge transfer and favorable electrolyte infiltration. Moreover, the presence of dispersed cobalt nanoparticles is beneficial for trapping lithium polysulfides by strong chemical interaction, and facilitating the mutual transformation between the high‐order polysulfides and low‐order ones. As a result, the S/GN–CNT composite presents a high sulfur utilization and large capacity on the basis of the S/GN–CNT composite as active material.  相似文献   

14.
Direct electron transfer of glucose oxidase promoted by carbon nanotubes   总被引:11,自引:0,他引:11  
A stable suspension of carbon nanotubes (CNT) was obtained by dispersing the CNT in a solution of surfactant, such as cetyltrimethylammonium bromide (CTAB, a cationic surfactant). CNT (dispersed in the solution of 0.1% CTAB) has promotion effects on the direct electron transfer of glucose oxidase (GOx), which was immobilized onto the surface of CNT. The direct electron transfer rate of GOx was greatly enhanced after it was immobilized onto the surface of CNT. Cyclic voltammetric results showed a pair of well-defined redox peaks, which corresponded to the direct electron transfer of GOx, with a midpoint potential of about -0.466 V (vs SCE (saturated calomel electrode)) in the phosphate buffer solution (PBS, pH 6.9). The electrochemical parameters such as apparent heterogeneous electron transfer rate constant (ks) and the value of midpoint potential (E1/2) were estimated. The dependence of E1/2 on solution pH indicated that the direct electron transfer reaction of GOx is a two-electron-transfer coupled with a two-proton-transfer reaction process. The experimental results also demonstrated that the immobilized GOx retained its bioelectrocatalytic activity for the oxidation of glucose, suggesting that the electrode may find use in biosensors (for example, it may be used as a bioanode in biofuel cells). The method presented here can be easily extended to immobilize and obtain the direct electrochemistry of other redox enzymes or proteins.  相似文献   

15.
The practice of carbon capture and storage (CCS) requires efficient capture and separation of carbon dioxide from its gaseous mixtures such as flue gas, followed by releasing it as a pure gas which can be subsequently compressed and injected into underground storage sites. This has been mostly achieved via reversible thermochemical reactions which are generally energy-intensive. The current work examines a biocatalytic approach for carbon capture using an NADP(H)-dependent isocitrate dehydrogenase (ICDH) which catalyzes reversibly carboxylation and decarboxylation reactions. Different from chemical carbon capture processes that rely on thermal energy to realize purification of carbon dioxide, the biocatalytic strategy utilizes pH to leverage the reaction equilibrium, thereby realizing energy-efficient carbon capture under ambient conditions. Results showed that over 25 mol of carbon dioxide could be captured and purified from its gas mixture for each gram of ICDH applied for each carboxylation/decarboxylation reaction cycle by varying pH between 6 and 9. This work demonstrates the promising potentials of pH-sensitive biocatalysis as a green-chemistry route for carbon capture.  相似文献   

16.
Wang L  Yi C  Zou H  Gan H  Xu J  Xu W 《Journal of molecular modeling》2011,17(11):2751-2758
The dissociation and isomerization reactions of methyl-nitramine(MNA) confined inside armchair CNT(5,5) single-walled carbon nanotube were investigated by using the ONIOM (B3LYP/6-311++G**:UFF) method. The results showed that some geometries of the confined MNA were modified by the CNT(5,5) in comparison with the structure of the isolated MNA. By analyzing the relevant structures and energies involved in the dissociation and isomerization reactions, we found that the transition state structures of the isomerization reactions to form CH3NHONO (R1) and CH3NNOOH (R2) were modified by the confinement of CNT(5,5). However, this confinement does not evidently affect the transition state structure of the HONO elimination reaction (R3). In addition, no transition state was found for the N-N bond dissociation (R4) of the isolated MNA, but this dissociation process occurred via a transition state for the confined MNA. When MNA was confined inside CNT(5,5), the activation energies of R1, R2, and R4 were decreased obviously but the energy barrier of R3 was increased slightly. The order of activation energy for these four initial reactions was also changed by the confinement of CNT(5,5). Furthermore, it was found that the relative energies of the intermediates formed by the isomerization and dissociation of MNA were also modified by the confinement of CNT(5,5). These intermediates become more stable in the confined case than in the isolated case. It was concluded that the initial reactions of MNA could be modified evdiently by confinement within a carbon nanotube.  相似文献   

17.
High-quality, free-standing, and vertically interconnected three-dimensional (3-D) graphitic nanosheets (GNSs) were synthesized over the surface of hemispherical carbon particles/GaN at 700 °C by microwave plasma chemical vapor deposition (CVD) in presence of methane gas, whereas the hemispherical carbon particles have been directly deposited on GaN/sapphire template. The GNSs are ∼1–5 nm in thickness and have a graphitic flake structure on hemispherical carbon particles. The vertically interconnected 3-D GNSs on hemispherical carbon particles have been characterized by scanning electron microscopy, transmission electron microscopy, selective area electron diffraction pattern, X-ray diffraction, atomic force microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and nitrogen gas adsorption-Brunauer-Emmet-Teller. The present CVD approach is capable of producing large quantities of GNSs with high purity. Moreover, a high-purity free-standing and vertically interconnected 3-D GNSs on hemispherical carbon particles have an enormous potential for applications in electronic devices, biological sensors, gas uptake and storage, fuel cells, lithium ion batteries, and more.  相似文献   

18.
A Rhizopus oryzae lipase gene has been expressed in Pichia pastoris as a reporter using the formaldehyde dehydrogenase 1 promoter (PFLD1) of this organism, which has been reported to be strongly and independently induced by either methanol as sole carbon source or methylamine as sole nitrogen source. Levels of lipase expressed and secreted under the control of the PFLD1 at different induction conditions have been compared to those obtained with the commonly used alcohol oxidase 1 promoter (PAOX1) in small (shake flask) and 1l bioreactor batch cultures. PFLD1-controlled heterologous gene expression was strongly repressed by excess of either glycerol or glucose-but not sorbitol-during growth using methylamine both as sole nitrogen source and inducing substrate. Co-induction of PFLD1 with methanol and methylamine resulted in a synergistic effect on extracellular lipase expression levels. In all tested conditions, the substitution of ammonium for methylamine as carbon source provoked a clear decrease in the specific growth rate and yield of biomass per gram of carbon source. Overall, this study demonstrates that the PFLD1 promoter is at least as efficient as the PAOX1 for extracellular expression of heterologous proteins in P. pastoris bioreactor cultures and provides a first basis for the further design of methanol-free high cell density fed-batch cultivation strategies for controlled overproduction of foreign proteins in P. pastoris.  相似文献   

19.
In this paper, our recent work concerning theoretical studies on the functionalization of carbon nanotubes (CNTs) is reviewed. In particular, two different aspects of the functionalization process are taken into account. On the one hand, the chemical functionalization of the sidewall is exploited as a way to develop nanostructured gas sensing devices. On the other hand, we investigated the possibility of functionalizing the sidewall with transition metal complexes, thus extending the concepts of organometallic chemistry to CNTs. Calculations were performed by applying statical and dynamical (Car-Parrinello) density functional theory methods, as well as hybrid (quantum mechanics/molecular mechanics) schemes. The structural and electronic peculiarities of the CNT model under study, due, for example to the presence of defects, were found to play a crucial role in the modelization of the functionalization process. In most cases, the use of realistic models was essential to achieve a full agreement with experiments.  相似文献   

20.
Despite the importance of polymer–polymer multiphase systems, very little work has been carried out on the preferred localization of solid inclusions in such multiphase systems. In this work, carbon nanotubes (CNT) are dispersed with polycaprolactone (PCL) and thermoplastic starch (TPS) at several CNT contents via a combined solution/twin-screw extrusion melt mixing method. A PCL/CNT masterbatch was first prepared and then blended with 20 wt% TPS. Transmission and scanning electron microscopy images reveal a CNT localization principally in the TPS phase and partly at the PCL/TPS interface, with no further change by annealing. This indicates a strong driving force for the CNTs toward TPS. Young's model predicts that the nanotubes should be located at the interface. X-ray photoelectron spectroscopy (XPS) of extracted CNTs quantitatively confirms an encapsulation by TPS and reveals a covalent bonding of CNTs with thermoplastic starch. It appears likely that the nanotubes migrate to the interface, react with TPS and then are subsequently drawn into the low viscosity TPS phase. In a low shear rate/low shear stress internal mixer the nanotubes are found both in the PCL phase and at the PCL/TPS interface and have not completed the transit to the TPS phase. This latter result indicates the importance of choosing appropriate processing conditions in order to minimize kinetic effects. The addition of CNTs to PCL results in an increase in the crystallization temperature and a decrease in the percent crystallinity confirming the heterogeneous nucleating effect of the nanotubes. Finally, DMA analysis reveals a dramatic decrease in the starch rich phase transition temperature (∼26 °C), for the system with nanotubes located in the TPS phase.  相似文献   

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