查看更多>>摘要：Hirudin, the most potent inhibitor of thrombin found in nature, has a short half-life in serum, which significantly limits its clinical application as an anticoagulant. Recently, PEGylation has been commonly used as an effective method to prolong its half-life in serum. In contrast to the nonspecific PEGylation under basic conditions that targets lysine residues randomly, PEGylation sites under mildly acidic conditions preferably targets histidine residues, and there is only one histidine residue at 51 in r-hirudin; therefore, succinimidyl carbonyl methoxy polyethylene glycol (SC-mPEG, 20000) was attached to r-hirudin at mildly acidic pH to favor the formation of mono-PEGylated r-hirudin. The reaction mixture with high mono-PEGylated ratio was easily separated by a one-step ion-exchange chromatographic (IEC) procedure. Approximately 79.71% of the mono-PEGylated r-hirudin was PEGylated at His51, which showed that the acidic PEGylation operation prevented the PEGylation of active center (Lys47) of r-hirudin in principle. Mono-PEGylated product with purity higher than 95% was obtained as the predominant product, and 34% of the anticoagulant activity was retained in vitro. The staining method for sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) was improved to obtain perfect electrophoretic pattern in less than 5min. More accurate molecular weight was deduced due to the use of PEGs as molecular weight standards.
查看更多>>摘要：Strain EDP3 was isolated from an industrial-activated sludge. It belonged to the gamma group of Pro-teobacteria with an identity of 97.0% to Acinetobacter calcoaceticus according to the 16S rRNA gene sequences. It can tolerate up to 1000mg·L~(-1) phenol at room temperature with a much longer lag phase. This indicates that higher phenol concentration has induced some physiological and genotypic changes in the bacterium. The aim of this study is, therefore, to investigate these responses to phenol concentration variations in strain EDP3. Proteome analysis is conducted by means of a two-dimensional polyacrylamide gel electrophoresis (2D PAGE) and matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS) was conducted to obtain a deeper insight into the adaptive responses inside the bacterium. Comparative analysis of the proteome profiles of strain EDP3 grown in 400mg·L~(-1) and 1000mg·L~(-1) phenol allowed us to identify mat among all the proteins up-regulated under the higher phenol concentration, oxidative stress proteins were dominant. The synthesis of a heat shock protein, 60000 chaperonin GroEL, was also amplified. In addition, the expression of one membrane protein, adenosine 5'-triphosphate (ATP)-binding cassette (ABC) type sugar transporter, was found up-regulated. The inhibition of adenosine 5'-triphosphate (ATP) and RNA/protein synthesis was also observed.
查看更多>>摘要：To improve the covalent immobilization of penicillin acylase (PA), macromolecular crowding theory was applied to its immobilization. Influence of mass ratio of enzyme to the silica, as well as, activation time with glutaraldehyde on the activity of assembled PA, was studied. In the mesopores, the effect of β-cyclodextrin (β-CD) on the immobilization of the enzyme was also investigated. It was remarkable that the coupled yield and relative activity reached 99.5% and 92.3%, respectively, when penicillin acylase assembled covalently in the mesopores. The results here indicate that mimicked macromolecule crowding could significantly ameliorate the performance of covalently immobilized PA.
查看更多>>摘要：A DNA fluorescence probe system based on fluorescence resonance energy transfer (FRET) from CdTe quantum dot (QD) donors to Au nanoparticle (AuNP) acceptors is presented. CdTe QDs, 2.5nm in diameter, as energy donors, were prepared in water. Au nanoparticles, 16nm in diameter, as energy acceptors, were prepared from gold chloride by reduction. CdTe QDs were linked to 5'-NH2-DNA through l-ethyl-3-(dimethylaminopropyl)car-bodiimide hydrochloride (EDC) as a linker, and the 3'-SH-DNA was self-assembled onto the surface of AuNPs. The hybridization of complementary double stranded DNA (dsDNA) bound to the QDs and AuNPs (CdTe-dsDNA-Au) determined the FRET distance of CdTe QDs and Au nanoparticles. Compared to the fluorescence of CdTe-DNA, the fluorescence of CdTe-DNA-Au conjugates decreased extremely, which indicated that the FRET occurred between CdTe QDs and Au nanoparticles. The fluorescence change of this conjugate depended on the ratio of Au-DNA to CdTe-DNA. When the AuNPs-DNA to QD-DNA ratio was 10:1, the FRET efficiency reached a maximum. The probe system would have a certain degree of fluorescence recovery when a complementary single stranded DNA was introduced into this system, which showed that the distance between CdTe QDs and Au nanoparticles was increased.
查看更多>>摘要：The aim of this study was to prepare arsenic trioxide (ATO)-loaded stealth PEGylated PLGA nanoparticles (PEG-PLGA-NPs) and to assess the merits of PEG-PLGA-NPs as drug carriers for ATO delivery. PEG-PLGA copolymer was synthesized with methoxypolyethyleneglycol (M_W=5000), D, L-lactide, and glycolide by the ring-opening polymerization method. Amorphous ATO was transformed into cubic crystal form to increase its solubility in the organic solvent. ATO-loaded PEG-PLGA-NPs were prepared by the modified spontaneous emulsifica-tion solvent diffusion (SESD) method, and the main experimental factors influencing the characteristics of nanoparticles were investigated, to optimize the preparation. To confirm the escape of PEG-PLGA-NPs from phagocytosis by phagocytes, PEG-PLGA-NPs labeled rhodamine B uptake by murine peritoneal macrophages (MPM) were analyzed by flow cytometry. The results showed that the physicochemical characteristics of PEG-PLGA-NPs were affected by the type and concentration of the emulsifiers, polymer concentration, and drug concentration. ATO-loaded PEG-PLGA-NPs, with particle size of 120.8nm, zeta potential of — 10.73mV, encapsulation efficiency of 73.6%, and drug loading of 1.36%, were prepared under optimal conditions. The images of transmission electron microscopy (TEM) indicated that the optimized nanoparticles were near spherical and without aggregation or adhesion. The release experiments in vitro showed the ATO release from PEG-PLGA-NPs exhibited consequently sustained release for more than 26d, which was in accordance with Higuchi equation. The uptake of PEG-PLGA-NPs by MPM was found to decrease markedly compared to PLGA-NPs. The experimental results showed that PEG-PLGA-NPs were potential nano drug delivery carriers for ATO.
查看更多>>摘要：N-doped TiO_2 nanoparticle photocatalysts were prepared through a sol-gel procedure using NH_4Cl as the nitrogen source and followed by calcination at certain temperature. Systematic studies for the preparation parameters and their impact on the structure and photocatalytic activity under ultraviolet (UV) and visible light irradiation were carried out. Multiple techniques (XRD, TEM, DRIF, DSC, and XPS) were commanded to characterize the crystal structures and chemical binding of N-doped TiO_2. Its photocatalytic activity was examined by the degradation of organic compounds. The catalytic activity of the prepared N-doped TiO_2 nanoparticles under visible light (λ > 400nm) irradiation is evidenced by the decomposition of 4-chlorophenol, showing that nitrogen atoms in the N-doped TiO_2 nanoparticle catalyst are responsible for the visible light catalytic activity. The N-doped TiO_2 nanoparticle catalyst prepared with this modified route exhibits higher catalytic activity under UV irradiation in contrast to TiO_2 without N-doping. It is suggested that the doped nitrogen here is located at the interstitial site of TiO_2 lattice.
查看更多>>摘要：The discrete particle method was used to simulate the distribution of gas holdup in a gas-liquid standard Rushton stirred tank. The gas phase was treated as a large number of bubbles and their trajectories were tracked with the results of motion equations. The two-way approach was performed to couple the interphase momentum exchange. The turbulent dispersion of bubbles with a size distribution was modeled using a stochastic tracking model, and the added mass force was involved to account for the effect of bubble acceleration on the surrounding fluid. The predicted gas holdup distribution showed that this method could give reasonable prediction comparable to the reported experimental data when the effect of turbulence was took into account in modification for drag coefficient.
查看更多>>摘要：Pressure drop and compound heat transfer characteristics of a converging-diverging tube with evenly spaced twisted-tapes (CD-T tube) have been investigated experimentally. Swirl was generated by evenly spaced twisted-tape elements which vary in twist ratio and rotation angle. Space ratio also has an important effect on the characteristics. For comparison, experiments in a smooth circular tube and a converging-diverging (CD) tube without twisted-tapes were carried out. The results show that the twisted-tape with twist ratio y=4.72 and rotation angle 0= 180° has the best performance among the four types of twisted-tapes presented in this paper. At Reynolds number ranging from 3400 to 20000, when space ratio 5=48.6, the heat transfer efficiency index, which increases as the Reynolds number increases, is 0.85—1.21 and 1.07—1.15 compared to that of a smooth circular tube and a CD tube without twisted-tape inserts, respectively.
查看更多>>摘要：To date, many models have been developed to calculate the flow field in the structured packing by the computational fluid dynamics (CFD) technique, but little experimental work has been carried out to serve the validation of flow simulation. In this work, the velocity profiles of single-phase flow in structured packing are measured at the Reynolds numbers of 20.0, 55.7 and 520.1, using the laser Doppler velocimetry (LDV). The time-averaged and instantaneous velocities of three components are obtained simultaneously. The CFD simulation is also carried out to numerically predict the velocity distribution within the structured packing. Comparison shows that the flow pattern, velocity distribution and turbulent kinetic energy (for turbulent flow) on the horizontal plane predicted by CFD simulation are in good agreement with the LDV measured data. The values of the x-and z-velocity components are quantitatively well predicted over the plane in the center of the packing, but the predicted y-component is significantly smaller than the experimental data. It can be concluded that experimental measurement is important for further improvement of CFD model.
查看更多>>摘要：A computational model combining large eddy simulation with quadrature moment method was employed to study nanoparticle evolution in a confined impinging jet. The investigated particle size is limited in the transient regime, and the particle collision kernel was obtained by using the theory of flux matching. The simulation was validated by comparing it with the experimental results. The numerical results show coherent structure acts to dominate particle number intensity, size and polydispersity distributions, and it also induce particle-laden jet to be diluted by the ambient. The evolution of particle dynamics in the impinging jet flow are strongly related to the Reynolds number and nozzle-to-plate distance, and their relationships were analyzed.
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