The facile synthesis of an aldehyde-containing graft copolymer membrane for covalent protein capture with retention of protein functionality

The immobilization of biomolecules onto an insoluble carrier surface has always been a subject of great interest to enhance their resistance to pH and temperature, which aids in an increased activity lifespan as well as easy reuse of the said biomolecules. However, traditional methods are only able to provide single-layer biomolecular binding and require multiple chemical reactions to prepare the final substrate before the immobilization can be carried out properly. Here we report a facile one-step chemical synthesis of a new aldehyde-bearing graft copolymer via atom transfer radical polymerization (ATRP) for covalent protein capture in a multilayered approach to covalently capture bovine serum albumin (BSA) onto a polymeric membrane. The resultant protein-bound membrane illustrated the retention of BSA's stereoselective discrimination ability by binding to an excess of 2 mol of tryptophan/mol of BSA and demonstrated an enantioresolution of a 0.184 mM racemic tryptophan mixture with a time-averaged-separation factor of 2.9.     

Membrane chromatography: Protein purification from E. coli lysate using newly designed and commercial anion-exchange stationary phases

This contribution describes the purification of anthrax protective antigen (PA) protein from Escherichia coli lysate using bind-and-elute chromatography with newly designed weak anion-exchange membranes. Protein separation performance of the new AEX membrane adsorber was compared with the commercial Sartobind^® D membrane adsorber and HiTrap™ DEAE FF resin column under preparative scale conditions. Dynamic protein binding capacities of all three stationary phases were determined using breakthrough curve analysis. The AEX membrane showed higher binding capacities than the Sartobind^® D membrane at equivalent volumetric throughput and higher capacities than the HiTrap™ DEAE FF resin column at 15 times higher volumetric throughput. Anion-exchange chromatography was performed using all three stationary phases to purify PA protein. Quantitative SDS-PAGE analysis of effluent fractions showed that the purity of PA protein was higher for membrane adsorbers than the HiTrap™ DEAE FF resin column and was the same for the new AEX membrane and Sartobind^® D membrane adsorbers. The effects of E. coli lysate load volume and volumetric flow rate on PA protein separation resolution using the membrane adsorbers were minor, and the peak elution profile remained un-changed even under conditions where >75% of the total protein dynamic binding capacity of the membranes had been utilized. PA protein peak resolution was higher using pH-gradient elution than with ionic strength gradient elution. Overall, the results clearly demonstrate that membrane chromatography is a high-capacity, high-throughput, high-resolution separation technique, and that resolution in membrane chromatography can be higher than resin column chromatography under preparative conditions and at much higher volumetric throughput.     

Structure and performance of polyamide-6 membranes prepared by thermally induced phase separation

<正>The asymmetric polyamide-6(PA6) membranes were prepared by thermally induced phase separation.From the scanning electron microscopy(SEM) images,it is observed that with the increase of silicon dioxide(SiO_2) content the structure of obtained membranes gradually varied from cellular structure to large ball-shaped cluster aggregates. Subsequently,with the addition of SiO_2,pure water flux increased first and then decreased,while rejection showed the opposite trend.Besides,raising the coagulation bath temperature was favorable to increase pure water flux.Consequently, different membrane morphologies and performance were obtained by changing SiO_2 content and coagulation bath temperature.     

Spin-label oximetry at Q- and W-band

Spin-lattice relaxation times (T?s) of small water-soluble spin-labels in the aqueous phase as well as lipid-type spin-labels in membranes increase when the microwave frequency increases from 2 to 35 GHz (Hyde, et al., J. Phys. Chem. B 108 (2004) 9524-9529). The T?s measured at W-band (94 GHz) for the water-soluble spin-labels CTPO and TEMPONE (Froncisz, et al., J. Magn. Reson. 193 (2008) 297-304) are, however, shorter than when measured at Q-band (35 GHz). In this paper, the decreasing trends at W-band have been confirmed for commonly used lipid-type spin-labels in model membranes. It is concluded that the longest values of T? will generally be found at Q-band, noting that long values are advantageous for measurement of bimolecular collisions with oxygen. The contribution of dissolved molecular oxygen to the relaxation rate was found to be independent of microwave frequency up to 94 GHz for lipid-type spin-labels in membranes. This contribution is expressed in terms of the oxygen transport parameter W=T??1(Air)-T??1(N?), which is a function of both concentration and translational diffusion of oxygen in the local environment of a spin-label. The new capabilities in measurement of the oxygen transport parameter using saturation-recovery (SR) EPR at Q- and W-band have been demonstrated in saturated (DMPC) and unsaturated (POPC) lipid bilayer membranes with the use of stearic acid (n-SASL) and phosphatidylcholine (n-PC) spin-labels, and compared with results obtained earlier at X-band. SR EPR spin-label oximetry at Q- and W-band has the potential to be a powerful tool for studying samples of small volume, ~30 nL. These benefits, together with other factors such as a higher resonator efficiency parameter and a new technique for canceling free induction decay signals, are discussed.     

Effect of CuO addition on the optical and electrical properties of sodium zinc borophosphate glasses

Sodium borophosphate glasses doped with copper ions having general composition 20Na₂O-20ZnO-25B₂O₃-(35-x) P₂O₅-x CuO (x=1-8 mol %) were prepared using conventional melt-quench method and characterized by density, UV-visible optical absorption, photoluminescence and conductivity measurements. E_optical values for different glass samples are found to decrease systematically from 3.5 to 2.5 eV with increase in CuO content in the glass. Network modifying action of CuO with the glass network has been confirmed from the UV-visible optical absorption studies. Presence of Copper in the form of Cu⁺ species has been confirmed from photoluminescence measurements. The electrical conductivity (σ) increases with increase in copper oxide content in the glass and temperature dependence of electrical conductivity confirmed the semiconducting nature of the samples.     

C20分子的一个电子输运模型研究

本文构建了Li链为电极的富勒烯C20分子的电子输运模型, 使用非平衡格林函数方法(Non-equilibrium Green's function, NEGF)对构建的Li电极和C20分子构成的分子器件进行了电子输运性质的计算. 计算得出了电子透射谱和电流电压曲线, 分析了产生这个分子器件电子输运性质的原因. 研究计算结果发现,大部分能量的电子是不会穿过器件的, 即使考虑不同偏压,能穿过器件的电子都集中在几个固定的能量上, 且在这几个固定能量上透过率比较高. 计算得出的伏安曲线说明在偏压为1.925V时电流达到最大, 只有在这个偏压周围才有相对明显的电流.     

Catalytic activity of carbon-supported iridium oxide for oxygen reduction reaction as a Pt-free catalyst in polymer electrolyte fuel cell

Iridium oxide supported on Vulcan XC-72 carbon black (IrO₂/C) as a cathode catalyst for polymer electrolyte fuel cell (PEFC) has been characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD) measurement. The IrO₂ particles were 8-160 nm in diameter. The oxygen electroreduction activity was studied by cyclic voltammetry (CV). It was found that IrO₂/C had high oxygen reduction reaction (ORR) activity. The performance of the membrane electrode assemble (MEA) was also tested in a single PEFC and showed that IrO₂/C catalyst would be potential candidates for use as cathode catalyst in PEFC.     

Improving separation capability of regenerated cellulose ultrafiltration membrane by surface modification

In this study we introduced dialdehyde groups to a commercial regenerated cellulose (RC) ultrafiltration membrane by periodate oxidation. They were further converted to nitrogen-containing derivatives by Schiff base reaction with diethylenetriamine (DETA). The modified membrane was challenged with aqueous solution containing Pb(II) metal ions. The different variables affecting the rejection of lead ion by membrane including oxidization time, concentration of DETA, initial metal ion concentration and pH of the solution were elucidated. The membranes were characterized by FTIR-ATR, SEM, EDAX and elemental analyses. The process efficiency was enhanced by improving the oxidization time up to a certain period. In our case this was diminished after 9 h due to deterioration in the membrane integrity. The Pb²⁺ removal was facilitated by increasing feed pH and DETA concentration. This was diminished for more concentrated metal ion in the feed. Membrane regeneration was successfully utilized using 0.1 M HNO₃ solution. The removal capability of the regenerated membranes was maintained even after four cycles.     

Single-molecule conductance measurement of self-assembled organic monolayers using scanning tunneling spectroscopy in combination with statistics analysis

Based on ambient atmosphere scanning tunneling microscope (STM) technique, scanning tunneling spectroscopy (STS) combined with statistics analysis was developed to investigate the single-molecule conductance of various kinds of molecules which were self-assembled on the Au (1 1 1). Conductance histograms obtained from current-voltage curves revealed well-defined peaks at integer multiples of a fundamental conductance and were used to identify the conductance of a single molecule. The conductances of saturated molecules like 1,8-octanedithol and hexanethiocyanate were found to be 0.072 × 10⁻⁴G₀ and 0.06 × 10⁻⁴G₀ respectively and 0.23 × 10⁻⁴G₀ and 0.13 × 10⁻⁴G₀ for unsaturated molecules like 5,5′-dithiol- 2,2′,5′,2″-terthiophene and 4,4′-dithio-tert(phenylene ethylene).     

电导法研究树脂与游离酸的相互作用

利用电导实验技术跟踪树脂吸附游离酸的行为 ,讨论了外加盐和乙醇等因素对吸附的影响 ,利用固 -液相互作用方程求取吸附剂 -吸附质相互作用能。实验结果表明 ,树脂吸附游离酸 ,其表观吸附速率常数随着外加盐离子浓度的增大而减少 ;表观吸附速率常数与吸附剂 -吸附质相互作用能存在线性关系。