The aggregation behavior of O-carboxymethylchitosan in dilute aqueous solution

O-Carboxymethylchitosan (OCMCS) is a kind of biocompatible derivatives of chitosan whose water solubility is strongly dependent on the degree of carboxymethylation. The OCMCS with 100 carboxymethyl groups and 75 amino groups per 100 anhydroglucosamine units of OCMCS was synthesized by the reaction of chitosan and monochloroacetic. When OCMCS was dissolved in water, its solution was neutral and OCMCS behaved like a weak polyanionic polyeclectrolyte because most of carboxylic groups were not dissociated in neutral aqueous solution. The aggregation behavior of OCMCS in aqueous solution was studied by surface tensiometry, steady-state fluorescence spectroscopy and viscometry. The critical aggregation concentration (cac) of OCMCS was determined to be between 0.042 mg/ml and 0.050 mg/ml. The possible aggregation mechanism of OCMCS in water was elucidated.     

Pyrolysis of mesoporous silica-immobilized 1,3-diphenylpropane. Impact of pore confinement and size

Mesoporous silicas such as SBA-15 and MCM-41 are being actively investigated for potential applications in catalysis, separations, and synthesis of nanostructured materials. A new method for functionalizing these mesoporous silicas with aromatic phenols is described. The resulting novel hybrid materials possess silyl aryl ether linkages to the silica surface that are thermally stable to ca. 550 degrees C, but can be easily cleaved at room temperature with aqueous base for quantitative recovery of the organic moieties. The materials have been characterized by nitrogen physisorption, FTIR, NMR, and quantitative analysis of surface coverages. The maximum densities of 1,3-diphenylpropane (DPP) molecules that could be grafted to the surface were less than those measured on a nonporous, fumed silica (Cabosil) and were also found to decrease as a function of decreasing pore size (5.6-1.7 nm). This is a consequence of steric congestion in the pores that is magnified at the smaller pore sizes, consistent with parallel studies conducted using a conventional silylating reagent, 1,1,3,3-tetramethyldisilazane. Pyrolysis of the silica-immobilized DPP revealed that pore confinement leads to enhanced rates and altered product selectivity for this free-radical reaction compared with the nonporous silica, and the rates and selectivities also depended on pore size. The influence of confinement is discussed in terms of enhanced encounter frequencies for bimolecular reaction steps and pore surface curvature that alters the accessibility and resultant selectivity for hydrogen transfer steps.     

The melting behavior of small clusters of atoms

The melting transition of small clusters composed of 13 particles interacting via the Lennard-Jones 6-12 potential has been investigated by means of extensive Metropolis Monte Carlo simulations. The results indicate that whereas the cluster evaporates in vacuum, in a confined pore the cluster undergoes a smooth melting transition from an icosahedral microcrystal to an inhomogeneous liquid phase, with a specific heat peak centered at 39 K. No evidence was found to support the suggestion of a solid-liquid transition in vacuum at 29 K.     

同位素氧-18分子的HeⅠ紫外光电子能谱

气体分子的HeI紫外光电子能谱（UPS）可提供分子不同能级的振动结构、能量以及成健类型上的大量信息．其中在探讨稳态分子的UPS研究中，人们对氧分子的研究已十分详尽门，但尚未计及同位素氧-18分子的UPS报导．涉及同位素分子的UPS研究，迄今为止仅有氛分子及其少数由氛原子组成的个别小分子，如DH，D2O和ND3等[2－4].鉴于同位素氧-18在高能物理、生物、医学以及化学等领域的重要作用，近期我国科学工作者已成功地制得高纯度的氧-18分子．研究它的性质及其与电子结构间的关系是十分紧迫的课题．为儿我们在开展与氧一18分子有关的UP…     

Biocompatible Micelles Based on Comb‐like PEG Derivates: Formation,Characterization, and Photo‐responsiveness

A novel comb‐like derivative CPEG‐g‐DNQ was prepared by incorporating light responsive 2‐diazo‐1,2‐naphthoquinone (DNQ) groups into the structure of comb‐like poly(ethylene glycol) (CPEG). DLS and TEM results showed that CPEG‐g‐DNQ self‐assembled into spherical micelles with an average size of about 135 nm in water. Upon exposure to light, the micelles could be disrupted because of the conversion of hydrophobic DNQ to hydrophilic 3‐indenecarboylic acid. Additionally, hydrophobic coumarin 102 was successfully loaded into the micelles and photo‐induced ON‐OFF release was demonstrated by fluorescence spectroscopy. MTT assay revealed that the micelles are biocompatible. These photo‐responsive micelles might have great potential for controlled release of hydrophobic drugs.

     

Self‐Assembly of Rod–Coil Polyethylenimine–Poly(ethylene glycol)–α‐Cyclodextrin Inclusion Complexes into Hollow Spheres and Rod‐Like Particles

This paper describes the self‐assembly of rod–coil inclusion complexes, polyethylenimine–poly(ethylene glycol)–α‐cyclodextrin (PEI–PEG–α‐CD). It is demonstrated that α‐CDs should exclusively thread on the PEG block in PEI–PEG copolymers and the resulting complexes have both rigid block (PEG–α‐CD) and coil block (protonated PEI). By varying the rigid block fraction, aggregates with hollow spheres or rod‐like particles could be formed simply by self‐assembly in aqueous solution.     

全光学高灵敏度铷原子磁力仪的研究

报道了一种全光学的高灵敏度铷原子磁力仪.其原理是基于激光束与处于微弱磁场中的铷原子的相互作用.这种相互作用与铷原子所处的环境中的磁场有关,因而通过测量透过铷原子气体的激光强度的变化可以获得磁场信息.分析了该磁力仪的工作原理,建立了相应的实验装置,并对其性能进行了测试.结果表明实验结果与理论相符合.进一步研究了影响磁力仪灵敏度的一些因素,提出了优化各参数来提高磁力仪灵敏度的方法.     

飞秒激光制备硅窗口增透保护类金刚石膜

采用飞秒激光(800 nm,120 fs,3 W,1 000 Hz)制备类金刚石膜,研究了不同偏压、生长温度和氧气氛等辅助手段对激光沉积类金刚石膜的影响,实验发现在室温(25℃)、无偏压和低气压氧气氛(2 Pa)条件下沉积的类金刚石膜性能最优。在单面预镀普通增透膜的硅红外窗口材料上镀制出了无氢类金刚石膜,3~5μm波段平均透过率达到90%以上,纳米硬度高达40 GPa,用压力为9.8 N的橡皮磨头,摩擦105次,膜层未见磨损,并且通过了军标规定的高温、低温、湿热、盐雾等环境试验,所制类金刚石膜可对红外窗口起到较好的增透保护作用。     

基于时间相关单光子计数的荧光寿命成像技术

采用时域法中的时间相关单光子计数方法记录荧光寿命,时间相关单光子计数采用多波长通道同时记录荧光光子数,可以提高计数效率和信息量,还可以在稳态图像中分离不同荧光团,形成4维图像。并采用多光子激发技术,利用长波长光源发出的两个或多个光子可以激发出一个短波长的光子。多个光子必须几乎同时到达激发点,才能提供被激发分子足够的能量以产生荧光。多光子激发波长较长,生物组织对其散射减小,因而可以穿透到更深层的组织,从而提高荧光成像深度和空间分辨力,并减少对活体样品的损伤。     

螺旋扁管管外蒸汽冷凝双侧强化传热试验研究

为促进螺旋扁管在冷凝换热装置上的应用,对螺旋椭圆管管外蒸汽冷凝工况下的传热特性进行了试验研究。研究结果表明,螺旋椭圆管在强化管内无相变对流传热的同时也可以强化管外冷凝传热。相同工况下,同圆管相比,所用螺旋椭圆扁管的总传热系数高11%-16%,管内传热系数高约18%,管外冷凝传热系数高约9%。并从二次流减薄传热边界层及冷凝表面利于排除冷凝液的角度,分析了螺旋椭圆扁管的双侧强化传热机理。