Cellulase could not be selectively collected from fermentation broth by simple foam fractionation, because of the presence
of other more surface-active compounds. A new approach of affinity foam fractionation was investigated for improvement. A
hardwood hydrolysate (containing cellulose oligomers, substrates to cellulase) and two substrate analogs, i.e., carboxymethyl
cellulose (CMC) and xylan hydrolysate, were added before the foaming process. The substrates and substrate analogs were indeed
found to bind the cellulase selectively and form more hydrophobic complexes that partition more readily onto bubble surfaces.
In this study, the effects of the type and concentration of substrate/analog as well as the presence of cells at different
growth stages were examined. The foam fractionation properties evaluated included foaming speed, foam stability, foamate volume,
and enrichment of filter paper unit (FPU) and individual cellulase components (i.e., endoglucanases, exoglucanases, and β-glucosidases).
Depending on the broth and substrate/analog employed, the foamate FPU could be more than fourfold higher than the starting
broth FPU. Addition of substrate/analog also deterred the enrichment of other extracellular proteins, resulting in the desired
cellulase purification in the foamate. The value of E/P (enzyme activity-FPU/g/L of proteins) in the foamate reached as high
as 18, from a lactose-based fermentation broth with original E/P of 5.6. Among cellulase components, exoglucanases were enriched
the most and β-glucosidases the least. The study with CMC of different molecular weights (MW) and degrees of substitution
(DS) indicated that the CMC with low DS and high MW performed better in cellulase foam fractionation. 相似文献
Pretty porous POMs: Ionothermal synthesis was applied to prepare porous POM-based open frameworks. The structural integrity remains unchanged until 300?°C; most importantly, the bulky tetrabutylammonium cations within their nanosized channels can be replaced by transition-metal ions through a cation-exchange process, and subsequent gas adsorption measurements confirm their permanent porosity. 相似文献
An ethylene glycol solution was used as the electrophoretic running buffer in unmodified cyclic olefin copolymer (COC) microchips to minimize the interactions between the analytes and the hydrophobic walls of the plastic microchannels, enhance the resolution of the analytes and eliminate the uncontrollable dispersion caused by uneven liquid levels and non-uniform surfaces of the separation channels. Five amino acids that were labeled with fluorescein isothiocyanate (FITC) were used as model analytes to examine the separation efficiency. The effects of ethylene glycol concentration, pH and sodium tetraborate concentration were systematically investigated. The five FITC-labeled amino acids were effectively resolved using a COC microchip with an effective length of 2.5 cm under optimum conditions, which included using a running buffer of 20 mmol/L sodium tetraborate in ethylene glycol:water (80:20, v/v), pH 6.7. A theoretical plate number of 4.8 × 10(5)/m was obtained for aspartic acid. The system exhibited good repeatability, and the relative standard deviations (n=5) of the peak areas and migration times were no more than 3.4% and 0.7%, respectively. Furthermore, the system was successfully applied to elucidate these five amino acids in human saliva. 相似文献
MnO has a high theoretical capacity, moderate discharge plateau, and low polarization when it is used as the anode material in lithium battery. However, the issues that limit its application are its poor conductivity and large volume changes, which can easily result in the collapse of electrode structure during long-term cycling. In the present work, a carbon-coated MnO/graphene 3D-network anode material is synthesized by an electrostatic adsorption of dispersed precipitates precipitation method. The MnO nanoparticles coated by carbon are uniformly distributed on the surface of graphene nanosheets and form a 3D sandwich-like nanostructure. A carbon layer is coated on the surface of MnO nanoparticles, which slows down the volume expansion in the process of lithium intercalation. The graphene nanosheets are cross-linked through carbons in this 3D nanostructure, which provides mechanical support and effective electron conduction pathways during the charge-discharge. The electrochemical tests indicate that the prepared 3D carbon-coated MnO/graphene electrode exhibits an excellent rate capacity of 1247.3 and 713.2 mAh g?1 at 100 and 1000 mA g?1, respectively. The capacity is 792.2 mAh g?1 after long cycle at a current density of 1000 mA g?1. The specific capacity is higher than that of MnO-based composite lithium anode materials currently reported. The superior rate and cycling performances are attributed to the unique 3D-network structure, which provides an effectively conductive network, buffers volume expansion, and prevents falling and aggregation of MnO in the charge and discharge process of the electrode materials. The 3D-structured carbon-coated MnO/graphene anode material will have an excellent application prospect.
