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Invading target cells: multifunctional polymer conjugates as therapeutic nucleic acid carriers
Ulrich L?CHELT, Ernst WAGNER
Front Chem Sci Eng. 2011, 5 (3): 275-286.
https://doi.org/10.1007/s11705-011-1203-z
Polymer-based conjugates are an interesting option and challenge for the design of nano-sized drug-delivery systems, as they require advanced conjugation chemistry and precise engineering. In the case of nucleic acid therapy, non-viral carriers face several biological barriers during the delivery process, namely 1) protection of the cargo from extracellular degradation, 2) avoidance of non-specific interactions with non-targeted tissues, 3) efficient entry into the target cells, 4) intracellular trafficking to the site of action and 5) cargo release. To take on these obstacles, multifunctional conjugates can act as “smart polymers” with microenvironment-sensing dynamics to facilitate the separate delivery steps. Synthesis of defined polymer architectures with precise functionalization enables structure-activity relationships to be investigated and the integration of key functions for efficient delivery. Thus bioresponsive polymer conjugates, which are equipped with molecular devices responding to the certain microenvironments within the delivery pathway (e.g. pH, redox potential, enzymes) can be assembled. This review focuses on the modular engineering and conjugation of multifunctional polymeric structures for the utilization as “tailor-made” nucleic acid carriers.
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Modeling nanostructured catalyst layer in PEMFC and catalyst utilization
Jiejing ZHANG, Pengzhen CAO, Li XU, Yuxin WANG
Front Chem Sci Eng. 2011, 5 (3): 297-302.
https://doi.org/10.1007/s11705-011-1201-1
A lattice model of the nanoscaled catalyst layer structure in proton exchange membrane fuel cells (PEMFC) was established by Monte Carlo method. The model takes into account all the four components in a typical PEMFC catalyst layer: platinum (Pt), carbon, ionomer and pore. The elemental voxels in the lattice were set fine enough so that each average sized Pt particulate in Pt/C catalyst can be represented. Catalyst utilization in the modeled catalyst layer was calculated by counting up the number of facets of Pt voxels where “three phase contact” are met. The effects of some factors, including porosity, ionomer content, Pt/C particle size and Pt weight percentage in the Pt/C catalyst, on catalyst utilization were investigated and discussed.
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The effect of capping with natural and modified zeolites on the release of phosphorus and organic contaminants from river sediment
Shujuan SUN, Lei WANG, Suiliang HUANG, Teng TU, Hongwen SUN
Front Chem Sci Eng. 2011, 5 (3): 308-313.
https://doi.org/10.1007/s11705-010-0561-2
A microcosm system that included river sediment, water and different zeolite capping materials (natural zeolite, surfactant-modified zeolite (SMZ), or aluminum modified zeolite (AMZ)) was designed to study the effect of capping on the release of phosphorus and three organic pollutants (phenol, pyridine, and pyrene) from the sediment to the overlying water over the course of three month. For the same amount of the three capping materials, the efficiency of phosphorus inactivation was in the order of SMZ>AMZ>natural zeolite. The inactivation of phosphorus was mainly caused by the covering effect, co-precipitation and adsorption by the capping materials. The different zeolites gave different results for the release of phenol, pyridine, and pyrene from the sediment. When natural zeolite was used as the capping material, there was no effect on the release of pyrene and pyridine, whereas capping the sediment with SMZ or AMZ inhibited the release of pyrene and pyridine but to different extents. However, for controlling the release of phenol from the sediment, aluminum modified zeolite was the most efficient material, whereas no effects were observed when natural zeolite or SMZ were used. The different capabilities of the zeolite materials for controlling the release of different organic pollutants are related to the differences in the electrical properties of these pollutants.
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Preparation of P2O5-SiO2 hollow microspheres in the presence of phosphoric acid
Wenjiang LI, Fei XIE, Dongxu HUA, Chunli ZHANG, Chen DAI, Zhenyun YU, Meizhou QI, Shaojun YU
Front Chem Sci Eng. 2011, 5 (3): 314-317.
https://doi.org/10.1007/s11705-010-0573-y
Silica hollow microspheres containing phosphorous have been prepared by a sol-gel/emulsion method which uses tetraethoxysilane (TEOS) as the precursor for the SiO2 and phosphoric acid (H3PO4) as the precursor for P2O5. The hollow structure forms an emulsion system which is composed of an oil phase (kerosene, sorbitan monooleate (Span 80)) and an aqueous phase (a viscous sol solution of ethanol, TEOS and H3PO4). Some of the phosphorous remains in the final silica shell structure even after calcination at 650°C. The hollow structure of the P2O5-SiO2 (silicophosphate) was characterized by X-ray diffraction (XRD), polarized optical microscopy (POM), scanning electron microscopy (SEM), nitrogen adsorption measurement and Fourier transform infrared spectroscopy (FTIR).
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Simultaneous saccharification and fermentation of sweet potato powder for the production of ethanol under conditions of very high gravity
Yinxiu CAO, Hongchi TIAN, Kun YAO, Yingjin YUAN
Front Chem Sci Eng. 2011, 5 (3): 318-324.
https://doi.org/10.1007/s11705-010-1026-3
Due to its merits of drought tolerance and high yield, sweet potatoes are widely considered as a potential alterative feedstock for bioethanol production. Very high gravity (VHG) technology is an effective strategy for improving the efficiency of ethanol fermentation from starch materials. However, this technology has rarely been applied to sweet potatoes because of the high viscosity of their liquid mash. To overcome this problem, cellulase was added to reduce the high viscosity, and the optimal dosage and treatment time were 8 U/g (sweet potato powder) and 1 h, respectively. After pretreatment by cellulase, the viscosity of the VHG sweet potato mash (containing 284.2 g/L of carbohydrates) was reduced by 81%. After liquefaction and simultaneous saccharification and fermentation (SSF), the final ethanol concentration reached 15.5% (v/v), and the total sugar conversion and ethanol yields were 96.5% and 87.8%, respectively.
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Caloric evaporation of the brine in Zangnan Salt Lake
Shiqiang WANG, Yafei GUO, Nan ZHANG, Lingzhong BU, Tianlong DENG, Mianping ZHENG
Front Chem Sci Eng. 2011, 5 (3): 343-348.
https://doi.org/10.1007/s11705-010-1029-0
Zangnan Salt Lake on the south of the Tibet is a type of carbonate lake with high concentrations of lithium, boron, and potassium and obviously it differs from seawater in its chemical composition. An experimental simulation of the caloric evaporation of the lake’s brine was conducted by first freezing the brine and then performing isothermal evaporation at 288.15 K. The freezing path and the physicochemical properties of the brine were determined. The crystallization sequence was natron, hydrohalite, halite, sylvite, zabuyelite, trona, aphthitalite, thermonatrite, and borax. Rubidium and cesium salts did not crystallized out but concentrated in the mother solution. The physicochemical properties (density, refractive index, conductivity, and pH) of the liquid phase changed as the evaporation progressed. In the beginning of the evaporation processes, the concentration of potassium ions in the liquid phase gradually increased but later it decreased. A peak value of 55.21 g/L was obtained when the evaporation was 88% complete. When the mineral aphthitalite began to crystallize; the concentrations of B2O3, Li+, Rb+, and Cs+ gradually increased as the evaporation progressed. When the evaporation was 98% complete, their concentrations in the mother liquor were 40.77 g/L, 4.838 g/L, 400.17 mg/L and 31.95 mg/L, respectively. This essential fundamental study can provide an important reference for the comprehensive utilization of brines in Zangnan Salt Lake.
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Mass and heat balance calculations and economic evaluation of an innovative biomass pyrolysis project
Quanyuan WEI, Yongshui QU, Tianwei TAN
Front Chem Sci Eng. 2011, 5 (3): 355-361.
https://doi.org/10.1007/s11705-010-0567-9
Biomass can be converted into flammable gas, charcoal, wood vinegar, wood tar oil and noncombustible materials with thermo-chemical pyrolysis reactions. Many factors influence these processes, such as the properties of the raw materials, and temperature control and these will affect the products that are produced. Based on the data from a straw pyrolysis demonstration project, the mass and heat balance of the biomass pyrolysis process were analyzed. The statistical product and service solutions (SPSS) statistical method was used to analyze the data which were monitored on-site. A cost-benefit analysis was then used to study the viability of commercializing the project. The analysis included net present value, internal rate of return and investment payback period. These results showed that the straw pyrolysis project has little risk, and will produce remarkable economic benefits.
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An investigation of reaction furnace temperatures and sulfur recovery
S. ASADI, M. PAKIZEH, M. POURAFSHARI CHENAR
Front Chem Sci Eng. 2011, 5 (3): 362-371.
https://doi.org/10.1007/s11705-011-1106-z
In a modern day sulfur recovery unit (SRU), hydrogen sulfide (H2S) is converted to elemental sulfur using a modified Claus unit. A process simulator called TSWEET has been used to consider the Claus process. The effect of the H2S concentration, the H2S/CO2 ratio, the input air flow rate, the acid gas flow of the acid gas (AG) splitter and the temperature of the acid gas feed at three different oxygen concentrations (in the air input) on the main burner temperature have been studied. Also the effects of the tail gas ratio and the catalytic bed type on the sulfur recovery were studied. The bed temperatures were optimized in order to enhance the sulfur recovery for a given acid gas feed and air input. Initially when the fraction of AG splitter flow to the main burner was increased, the temperature of the main burner increased to a maximum but then decreased sharply when the flow fraction was further increased; this was true for all three concentrations of oxygen. However, if three other parameters (the concentration of H2S, the ratio H2S/CO2 and the flow rate of air) were increased, the temperature of the main burner increased monotonically. This increase had different slopes depending on the oxygen concentration in the input air. But, by increasing the temperature of the acid gas feed, the temperature of the main burner decreased. In general, the concentration of oxygen in the input air into the Claus unit had little effect on the temperature of the main burner (This is true for all parameters). The optimal catalytic bed temperature, tail gas ratio and type of catalytic bed were also determined and these conditions are a minimum temperature of 300°C, a ratio of 2.0 and a hydrolysing Claus bed.
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Hemocompatible polyurethane/gelatin-heparin nanofibrous scaffolds formed by a bi-layer electrospinning technique as potential artificial blood vessels
Heyun WANG, Yakai FENG, Marc BEHL, Andreas LENDLEIN, Haiyang ZHAO, Ruofang XIAO, Jian LU, Li ZHANG, Jintang GUO
Front Chem Sci Eng. 2011, 5 (3): 392-400.
https://doi.org/10.1007/s11705-011-1202-0
In this paper, a scaffold, which mimics the morphology and mechanical properties of a native blood vessel is reported. The scaffold was prepared by sequential bi-layer electrospinning on a rotating mandrel-type collector. The tubular scaffolds (inner diameter 4 mm, length 3 cm) are composed of a polyurethane (PU) fibrous outer-layer and a gelatin-heparin fibrous inner-layer. They were fabricated by electrospinning technology, which enables control of the composition, structure, and mechanical properties of the scaffolds. The microstructure, fiber morphology and mechanical properties of the scaffolds were examined by means of scanning electron microscopy (SEM) and tensile tests. The PU/gelatin-heparin tubular scaffolds have a porous structure. The scaffolds achieved a breaking strength (3.7±0.13 MPa) and an elongation at break (110±8%) that are appropriate for artificial blood vessels. When the scaffolds were immersed in water for 1 h, the breaking strength decreased slightly to 2.2±0.3 MPa, but the elongation at break increased to 145±21%. In platelet adhesion tests the gelatin-heparin fibrous scaffolds showed a significant suppression of platelet adhesion. Heparin was released from the scaffolds at a fairly uniform rate during the period of 2nd day to 9th day. The scaffolds are expected to mimic the complex matrix structure of native arteries, and to have good biocompatibility as an artificial blood vessel owing to the heparin release.
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