两亲分子聚集相的扫描隧道显微镜研究

用最近发展起来的局域探测手段－扫描隧道显微镜（ＳＴＭ）及其相伴的方法如局域功函数等，对具有十分丰富局域结构的两亲分子和水的两系统的聚集相作了初步研究，以期为两亲分子研究及局域化学的发展添砖加瓦，结果表明由ＳＴＭ可以真实对反映出各种聚集相的不同形貌，而且加上局域功函数像还可以揭示两亲分子的头尾取向，这对有机分子系统的局域结构的研究有普遍意义。     

5.6 Cellulose acetate in separation technology

Cellulose acetate has been utilized in a variety of separation and purification processes. In membrane separation, cellulosics, in particular cellulose acetate, have played important roles. Hemodialysis and desalination are the established fields where acetate membranes have been applied. Recently, a new application, that is the purification of drinking water, is growing. The history of cellulosic membranes, preparation of acetate membranes, and applications will be reviewed. Cellulose acetate is also useful in chromatography and related separation technologies. These application will also be reviewed and the relationship between the superstructure of cellulose triacetate and its adsorptive behavior is briefly mentioned.     

Design and Functionalization of a µPAD for the Enzymatic Determination of Nitrate in Urine

In this work, the design of a microfluidic paper-based analytical device (μPAD) for the quantification of nitrate in urine samples was described. Nitrate monitoring is highly relevant due to its association to some diseases and health conditions. The nitrate determination was achieved by combining the selectivity of the nitrate reductase enzymatic reaction with the colorimetric detection of nitrite by the well-known Griess reagent. For the optimization of the nitrate determination μPAD, several variables associated with the design and construction of the device were studied. Furthermore, the interference of the urine matrix was evaluated, and stability studies were performed, under different conditions. The developed μPAD enabled us to obtain a limit of detection of 0.04 mM, a limit of quantification of 0.14 mM and a dynamic concentration range of 0.14–1.0 mM. The designed μPAD proved to be stable for 24 h when stored at room temperature in air or vacuum atmosphere, and 60 days when stored in vacuum at −20 °C. The accuracy of the nitrate μPAD measurements was confirmed by analyzing four certified samples (prepared in synthetic urine) and performing recovery studies using urine samples.     

水分子通道蛋白的结构与功能

水分子穿越双磷脂生物膜的输运机理是生理学和细胞生物学中一个长期未能解决的重要问题.AQP1水通道蛋白的发现和鉴定使得人们确认出一个新的蛋白质家族--水通道蛋白家族.正是这一蛋白家族的存在,使得水分子可以进行快速的跨膜传输.由晶体学方法解出的哺乳动物AQP1水通道蛋白的原子结构,最终揭示了水通道蛋白只允许水分子快速传输而阻挡其他的小分子和离子(包括质子H+)的筛选输运机理.本文概述了水通道蛋白的发现和其对水分子的筛选传输机理.     

支撑液膜研究及应用进展

支撑液膜技术是高选择性膜分离技术,本文对支撑液膜分离技术的研究进展进行了回顾,详述了用于金属离子分离的支撑液膜所采用的载体、影响支撑液膜稳定性的原因以及改善途径,并对支撑液膜的发展前景进行了展望。     

两种医用胶原膜 60Co辐照改性的比较

胶原作为一种新型生物材料,具有无毒,良好的生物相容性,生物可降解性及可吸收性,广泛用于皮肤创伤的治疗、骨缺损的修复、药物缓释的载体、止血敷料、组织工程支架材料等。但胶原在体内降解太快,不能与组织再生速度相匹配。有必要探讨胶原生物材料的改性方法,便于其更好     

多约束膜结构截面优化及在MSC/Nastran上的程序实现

将准则法和数学规划法相结合,借助满应力准则将应力约束转化为动态尺寸约束,利用单位虚载荷法将位移约束转化为设计变量的显式表达式建立优化模型,然后用数学规划法求解;采用无量纲设计变量实现设计变量连接,对膜结构的厚度进行优化设计;根据对偶理论,应用对偶规划精确映射原问题,再按泰勒展式建立对偶问题的二阶近似。为了提高优化效率,采用射线步调整结构性态,运用粗选有效约束技术筛选约束,并采用主、被动变量循环确保收敛稳定。以MSC／Nastran软件作为结构分析的求解器,以MSC／Patran软件作为开发平台,完成了膜结构截面优化程序。对膜结构的单变位、多变位的结构优化问题进行了优化计算,并与MSC／Nastran优化模块的计算结果进行比较。算例结果表明程序的可靠性、高效性和稳定性以及理论算法的优越性。     

The physical aging phenomenon of 6FDA‐durene polyimide hollow fiber membranes

The aging phenomenon of asymmetric 6FDA‐durene polyimide hollow fibers spun with different shear rates for gas separation has been investigated. The permeances and selectivities of different gases, such as H₂, O₂, N₂, CH_4, and CO₂, were experimentally determined as a function of time for around five months at room temperature. It was found that the gas permeation fluxes of the uncoated and silicone rubber‐coated hollow fibers decreased significantly during the first 30 days following fabrication and then slightly deteriorated thereafter. In the early stage of aging, because of different molecular orientations and skin morphologies induced by shear rates, the percentage of permeance drop for uncoated fibers increased with increasing shear rates, then decreased with increasing shear rates. The permeance of 6FDA‐durene hollow fibers coated with silicone rubber dropped more significantly than the uncoated fibers, implying that silicone rubber coating did affect the aging behavior. This might be due to the fact that silicone rubber layer hindered the molecular relaxation and tightened interface molecules between the dense selective layer and silicone rubber, thus the selectivity increased with aging. Thermal analysis data suggest two processes occurring simultaneously during the aging: one is the relaxation of shear oriented chains, and the other is the densification of chain packing through the reduction of interstitial space among chains. The former has been confirmed by an increase in CTE, while the latter was confirmed by an increase in the peak of β‐relaxation temperature. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 765–775, 2000     

An Introduction to Monolithic Disks as Stationary Phases for High Performance Biochromatography

Monolithic stationary phases have revolutionized protein chromatography because they combine speed, capacity, and resolution in a unique manner. Since such stationary phases contain no particles but only flow‐through pores, the usual mass transfer restrictions to the chromatography of large molecules are not observed and extremely fast separations become possible. Recently the area of application of monolith chromatography has been extended to the separation and analysis of small molecules and plasmid DNA. This review summarizes the state of art in high performance monolith and especially high performance monolithic disk chromatography (HPMDC). The current understanding of the theory of protein HPMDC is summarized, while an introduction to the evolving field of small molecule HPMDC is attempted. The basic differences between the monolithic disks and columns packed with conventional stationary phases (including perfusion and micropellicular particles) but also monolithic columns (porous rods) are outlined. Finally, the potential of HPMDC to analytical and preparative biochromatography is demonstrated by a discussion of recent applications of chromatographic disks for protein isolation and bioprocess analysis.     

Permeability and morphology of poly(cis‐butadiene)/ester‐ether liquid crystal composite membranes

Various amounts of diethylene glycol bis[4‐(4′‐ethoxybenzoyloxy)benzoate] (DEBEB) were added into a poly(cis‐butadiene) (PB) membrane to improve its gas permeation ability. This type of rubber/liquid crystal (LC) composite membranes showed two obvious characteristics that are different from the gas permeation behavior reported in previous literature: (1) The permeabilities to O₂, N₂, and CO₂ were enhanced at room temperature, for example, the permeabilities for the PB/DEBEB (90/10) membrane were higher above six times than those of PB membrane under the same conditions. It is suggested that the interface microvoids probably existed on pontes between polar crystal domains and nonpolar PB matrix. (2) All relationships between the permeability coefficient (P) and temperature (T) were characterized by N‐shape, that is, there were the peaks and valleys on the P‐T curves. Furthermore, morphology studies demonstrated that when DEBEB content in the membranes was above 10 wt %, it was spherically dispersed and embedded in the PB matrix in a crystal domain state. Gas permeation characteristics of the composite membranes were appropriately interpreted as together influence results of DEBEB phase transition behavior and the membrane morphology. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1833–1840, 2000