低浓度下的仿生矿化及其在对映体拆分中的应用

以L-苯丙氨酸衍生物(L-18Phe6PyBr)的自组装体为模板, 在0.30 mmol/L的浓度下, 研究了pH值、 老化时间和四乙氧基硅烷(TEOS)浓度对二氧化硅形貌的影响. 通过扫描电子显微镜和透射电子显微镜对样品进行表征. 结果表明, 在pH=10.01的条件下可以得到左手扭转的纳米带, 而pH=7.15和12.34时, 得到直线的纳米带. 遵循动态模板的方法, 老化时间的延长有利于直线纳米带的形成. 随着TEOS和L-18Phe6PyBr的质量比由2:1增加到15:1, 扭转纳米带的宽度增加, 螺距变长. 通过煅烧除去有机模板后, 得到带状二氧化硅纳米管. 将TEOS与L-18Phe6PyBr质量比为2:1制备得到的二氧化硅作为气相色谱固定相, 涂渍到毛细管色谱柱中进行对映体拆分. 结果表明, 该气相色谱柱可以拆分1-苯基-1-丙醇、 1-(4-氯苯基)乙醇和2-甲基戊酸3种外消旋化合物, 手性超分子印迹是拆分对映体的主要作用力. 对二氧化硅低聚物与小分子凝胶的协同组装行为以及将无机材料作为手性固定相有了一个更好的认识.     

气-液界面有序介孔SiO2无机膜的仿生合成

早在几百万年以前,自然界就通过生物矿化过程形成了结构高度有序的有机/无机复合材料,如哺乳动物的牙床、骨骼以及贝壳珍珠层等[1]。随着对天然生物材料生物矿化过程研究的逐渐深入,材料研究者从中得到极为重要的启示:先形成有机物自组装体,无机先驱物在自组装聚集体与溶液相的界面处发生化学反应,在有机自组装体的模板作用下,形成有机/无机复合体,再将有机模板去除即可得到具有一定形状与组织结构的无机材料。这种模仿生物矿化中无机物在有机物调制下形成过程的材料合成,称为仿生合成(biomimetic synthesis)[2]。仿生合成过程中,通过选择有…     

Handedness inversion of chiral amphiphilic molecular assemblies evidenced by supramolecular chiral imprinting in mesoporous silica assemblies

Antipodal twisted helical ribbons with lamellar bilayer structure were obtained by self-assembly of chiral amphiphilic molecules in water and water/ethanol. The handedness inversion of the molecular arrangement in these antipodal helical ribbons was investigated by using chiroptical spectroscopy and molecular probes in their antipodal mesoporous silica assemblies synthesized through pairing interaction between the head group of the chiral amphiphilic molecules and a co-structure-directing agent. The supramolecular chirality is imprinted in the pore surface through the organic group of the co-structure-directing agent. The mirror-image diffuse-reflectance circular dichroism spectra of the conjugated discotic probing molecule introduced into their supramolecular chiral imprinted mesoporous silica demonstrated the origin of inverse chirality from the antipodal helical stacking of the molecules.     

Mesoporous silicas by self-assembly of lipid molecules: ribbon, hollow sphere, and chiral materials

Using lipids (N-acyl amino acids) and 3-aminopropyltriethoxysilane as structure- and co-structure-directing agents, mesoporous silicas with four different morphologies, that is, helical ribbon (HR), hollow sphere, circular disk, and helical hexagonal rod, were synthesized just by changing the synthesis temperature from 0 degrees C to 10, 15, or 20 degrees C. The structures were studied by electron microscopy. It was found that 1) the structures have double-layer disordered mesopores in the HR, radially oriented mesopores in the hollow sphere, and highly ordered straight and chiral 2D-hexagonal mesopores in the disklike structure and helical rod, respectively; 2) these four types of mesoporous silica were transformed from the flat bilayered lipid ribbon with a chain-interdigitated layer phase through a solid-solid transformation for HR formation and a dissolving procedure transformation for the synthesis of the hollow sphere, circular disk, and twisted morphologies; 3) the mesoporous silica helical ribbon was exclusively right-handed and the 2D-hexagonal chiral mesoporous silica was excessively left-handed when the L-form N-acyl amino acid was used as the lipid template; 4) the HR was formed only by the chiral lipid molecules, whereas the 2D-hexagonal chiral mesoporous silicas were formed by chiral, achiral, and racemic lipids. Our findings give important information for the understanding of the formation of chiral materials at the molecular level and will facilitate a more efficient and systematic approach to the generation of rationalized chiral libraries.     

Facile synthesis of monodisperse microspheres and gigantic hollow shells of mesoporous silica in mixed water-ethanol solvents

Mesoporous silica materials with a variety of morphologies, such as monodisperse microspheres, gigantic hollow structures comprising a thin shell with a hole, and gigantic hollow structures consisting of an outer thin shell and an inner layer composed of many small spheres, have been readily synthesized in mixed water-ethanol solvents at room temperature using cetyltrimethylammonium bromide (CTAB) as the template. The obtained mesoporous silica generally shows a disordered mesostructure with typical average pore sizes ranging from 3.1 to 3.8 nm. The effects of the water-to-ethanol volume ratio (r), the volume content of tetraethyl orthosilicate TEOS (x), and the CTAB concentration in the solution on the final morphology of the mesoporous silica products have been investigated. The growth process of gigantic hollow shells of mesoporous silica through templating emulsion droplets of TEOS in mixed water-ethanol solution has been monitored directly with optical microscopy. Generally, the morphology of mesoporous silica can be regulated from microspheres through gigantic hollow structures composed of small spheres to gigantic hollow structures with a thin shell by increasing the water-to-ethanol volume ratio, increasing the TEOS volume content, or decreasing the CTAB concentration. A plausible mechanism for the morphological regulation of mesoporous silica by adjusting various experimental parameters has been put forward by considering the existing state of the unhydrolyzed and partially hydrolyzed TEOS in the synthesis system.     

Chiral Carbonaceous Nanotubes Containing Twisted Carbonaceous Nanoribbons,Prepared by the Carbonization of Chiral Organic Self‐Assemblies

Single‐handed helical silica nanotubes containing chiral organic self‐assemblies were prepared by using a supramolecular templating approach. After carbonization and the removal of the silica, single‐handed helical carbonaceous nanotubes that contained twisted carbonaceous nanoribbons were obtained. It is believed that the nanotubes formed as a result of the adsorption of low‐molecular‐weight gelators. The twisted nanoribbons were formed because of the carbonization of the organic self‐assemblies. The samples were characterized by using field‐emission scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, Raman spectroscopy, and circular dichroism. For the samples carbonized at 900 °C for 3.0 h, a partially graphitized structure was identified. The circular dichroism (CD) spectra indicated that the twisted nanoribbons exhibited optical activity. The CD spectrum was simulated by using time‐dependent density functional theory. The results suggested that the CD signals originated from the chiral stacking of aromatic rings.     

Study on the morphological regulation mechanism of hollow silica microsphere prepared via emulsion droplet template

The morphology regulation of hollow silica microspheres is significant for their properties and applications. In this paper, hollow silica microspheres were formed through the hydrolysis and condensation reaction of tetraethyl orthosilicate (TEOS) at the interface of the emulsion droplet templates composed of liquid paraffin and TEOS, followed by dissolving paraffin with ethanol. The effects of various factors including the emulsifier structure and content, TEOS content, catalyst type, and the ethanol content in the continuous water phase on the particle size, shell thickness and morphology of the prepared hollow silica microspheres were studied in detail. The results show that the diffusion and contact of TEOS and water molecules as well as the hydrolysis condensation reaction of TEOS at the oil-water interface are two critical processes for the synthesis and morphological regulation of hollow silica microspheres. Cationic emulsifier with a hydrophobic chain of appropriate length is the prerequisite for the successful synthesis of hollow silica microspheres. The ethanol content in water phase is the dominant factor to determine the average diameter of hollow microspheres, which can vary from 96 nm to 660 nm with the increase of the volume ratio of alcohol-water from 0 to 0.7. The silica wall thickness varies with the content and the hydrophobic chain length of the emulsifier, TEOS content, and the activity of the catalyst. The component of the soft template will affect the morphology of the silica wall. When the liquid paraffin is replaced by cyclohexane, hollow microspheres with fibrous mesoporous silica wall are fabricated. This work not only enriches the basic theory of interfacial polymerization in the emulsion system, but also provides ideas and methods for expanding the morphology and application of hollow silica microspheres.     

Preparation and characterizations of helical mesoporous silica nanorods using CTAB and alcohols

Helical mesoporous silica nanorods were prepared using cetyltrimethylamrnonium bromide and achiral alcohols as the co-structure-directing agents.They were characterized using field-emission scanning electron microscopy,transmission electron microscopy,nitrogen sorptions,and small angle X-ray diffraction.The length of the silica nanorods increases with increasing the length of the alcohols.When n-heptanol and n-octanol were used,helical mesoporous silica nanorods with lamellar mesopores on the surfaces were obtained.     

Ultrafast enzyme immobilization over large-pore nanoscale mesoporous silica particles

By finely tuning the TEOS/P123 molar ratio of the octane/water/P123/TEOS quadruple emulsion system and by controlling the synthesis conditions, an ultrafine emulsion system was isolated, under the confinement of which, nanoscale silica particles with ordered large mesopores (approximately 13 nm) have been successfully constructed; the obtained mesoporous silica particles have an unusual ultrafast enzyme adsorption speed and the amount of enzyme that can be immobilized is larger than that of conventional mesoporous silica, which has potential applications in the fast separation of biomolecules.     

Synthesis of mesoporous silica helical fibers using a catanionic-neutral ternary surfactant in a highly dilute silica solution: biomimetic silicification

Mesoporous silica helical fibers in many different shapes have been synthesized in a highly dilute silicate solution at pH approximately 2.0 by using CnTMAB-SDS-P123 (n = 14-18) ternary surfactant as a template. The mesoporous silica helical fibers possess a well-ordered hexagonal mesostructure, high surface area, and large pore volume. Thus, the microtome sections of the helical fibers demonstrate a concentric mesotructure or two hemiconcentric mesostructures. In addition to triblock copolymer, adding the proper amount of 1-butanol or pentanol can promote the yield of the helical fibers as well. The yield of the surfactant-templated helical fibers is also dependent on the water content, reaction temperature, and pH value of the solution. The mesoporous silica helical fiber can be used as a solid template to prepare mesoporous carbon helical fibers via impregnation of phenol-formaldehyde, pyrolysis, and silica removal.     

Critical micelle concentrations of cetyltrimethylammonium chloride and their influence on the periodic structure of mesoporous silica

The influence of micelle morphology transformation on the structure of mesoporous materials is fundamental in designing optimal, well-ordered, mesoporous materials. Firstly, the steady-state fluorescence technique was adopted to determine the first and second critical micelle concentrations of cetyltrimethylammonium chloride (CTAC) as 125 and 210 mmol L⁻¹ in an equimolar mixture of water and ethanol at 25°C. Using tetraethylorthosilicate (TEOS) as the precursor, mesoporous silicas (with a surface area of 545.7–1210.5 m 545.7 ∼ 1210.5 m² g⁻¹ and a pore volume of 0.26 ∼ 0.80 cm³ g⁻¹) were synthesized with the CTAC templates in the equimolar mixture of water and ethanol. Characterization by small-angle X-ray diffraction and N 2 adsorption/desorption techniques revealed that the surface area and pore volume of silica increased with the content of CTAC, whereas there existed a transition point at the CTAC/TEOS ratio of 0.15 corresponding to the fade-away of well-ordered mesoporous structure. The negative effect of the much higher content CTAC on the periodic structure of mesoporous silica is attributed to micelle transformation from spheres to cylinders related to the second critical micelle concentration of CTAC. The text was submitted by the authors in English.     

氧化钨介孔材料的制备与表征

以介孔二氧化硅(KIT-6)为硬模板, 硅钨酸为钨源, 用硬模板法制备WO3-SiO2复合材料, 再利用HF除去二氧化硅, 得到了介孔三氧化钨材料. 用X射线衍射(XRD)、能量扩散X射线(EDX)、高分辨透射电镜(HRTEM)、N2吸附-脱附等表征手段, 对制备复合材料的物料比、煅烧温度以及不同分散剂等条件进行了考察. 结果表明, 硅钨酸与硅介孔的物料比(m(WO3)/m(SiO2))在3:1到4:1之间, 在600-750 ℃下煅烧, 能制备结构较好的介孔氧化钨. 乙醇和蒸馏水为分散剂时, 用乙醇为分散剂所得的介孔WO3材料具有更高的比表面积和孔体积.     

Characterization of single-handed,coiled, carbonaceous,tubular nanoribbons

Left-handed, coiled, 4,4＇-biphenylene bridged polybissilsesquioxane, tubular nanoribbons were prepared according to the published literature. After carbonization and removal of silica using HF aqueous solution, left-handed, coiled, carbonaceous, tubular nanoribbons were obtained. The left- handed, coiled, carbonaceous, tubular nanoribbons were characterized using field-emission scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, Raman spectropho- tometer, diffuse reflectance circular dichroism （DRCD）, and N2 adsorptions. Micropores were formed due to the removal of silica. The nitrogen BET surface area is 1727 m2/g. A broad, positive DRCD signal, identified at 400-800 rim, indicates the carbonaceous, tubular nanoribbons exhibit optical activity. The helical pitch is proposed to play an important role in the position of the DRCD signal.     

疏水介孔二氧化硅膜的制备与表征

用甲基三乙氧基硅烷(MTES)代替部分正硅酸乙酯(TEOS)作为前驱体，以聚乙烯醚-聚丙烯醚-聚乙烯醚三嵌段共聚物(P123)作有机模板剂，通过共水解缩聚反应制备了甲基修饰的介孔SiO₂膜。利用N₂吸附、FTIR、²⁹Si MAS NMR以及接触角测量仪对膜的孔结构和疏水性进行了表征。结果表明，修饰后的膜材料具有良好的介孔结构，最可几孔径为4.65 nm，孔体积为0.69 cm³·g^-1，比表面积为938.4 m²·g^-1；同时疏水性明显提高，当n_MTES/n_TEOS达到1.0时，其对水的接触角达到109°± 1.1°。气体渗透实验表明气体通过膜孔的扩散由努森机制所控制。     

Preparation and characterization of twisted periodic mesoporous ethenylene-silica nanorods

Twisted periodic mesoporous ethenylene-silica nanorods were prepared using cetyltrimethylammonium bromide in concentrated aqueous ammonia solutions at the stirring rate of 600 rpm. The pore channels run along the long axis of the nanorod. The helical pitches are about 1.2 micrometers. Small-angle X-ray diffraction pattern was indexed to the p6 mm hexagonal symmetry. The morphologies of the ethenylene-silicas are sensitive to stirring conditions. For example, twisted nanorods and spiral nanofibers combined with nanospheres were obtained under static condition. With increasing stirring speed, both the length and helical pitch of the nanorod increased slightly. With decreasing the concentration of ammonia, the particle lengths decreased, while the particle diameters increased. Chiral mesostructures were obtained when the ammonia concentration was ≥ 20 wt%. The formation of the twisted mesoporous ethenylene-silica nanorods was studied by taking TEM images after different reaction time.     

Density fractionated hollow silica microspheres with high-yield by non-polymeric sol–gel/emulsion route

Hollow silica microspheres were synthesized by non-polymeric sol–gel/emulsion technique using tetra ethyl orthosilicate (TEOS) as a source of silica. A sol mixture of TEOS, water, ethanol and acid was emulsified in a solution of light paraffin oil and surfactant (Span-80). Calcined spheres were density fractionated between density ranges: <1.0, 1.0–1.594, 1.594–1.74 and >1.74 g cm⁻³. The samples were characterized by optical and scanning electron microscopy with energy dispersive X-ray analysis, Fourier transform infrared spectroscopy and laser diffraction size analyzer. Spheres of densities lower than 1.74 g cm⁻³ were found to be hollow as observed from scanning electron microscopy (SEM) images and their yield was maximized to 100% by using a specific TEOS volume ratio with respect to volumes of surfactant and oil. Decreasing the calcination temperature from 700 to 500 °C enhances the yield of hollow spheres emphasizing importance of slower diffusion kinetics at lower calcination temperature. Outer diameters of spheres were between 5 and 60 μm with mean diameter expectedly increasing with increase in TEOS sol volume and with decrease in sphere density. It is proposed that silica shells form via hydrolysis and polycondensation at oil–water/ethanol interface in the water-in-oil emulsion, which subsequently form hollow spheres on removal of water–ethanol during calcination.     

Helix parameters in bi- and multicomponent mixtures composed of orthoconic antiferroelectric liquid crystals with three ring molecular core

Eight types of bicomponent systems composed of antiferroelectric compounds with different polarity of achiral chain and different temperature dependence of helical pitch as well as three multicomponent mixtures composed of antiferroelectric compounds with opposite helical twist sense were studied. The phase miscibility was tested by polarising optical microscopy. The results of the helical pitch and helical twist sense measurements obtained by a spectrophotometric method of selectively reflected light and by polarimetric method, respectively, are presented. It was found that it is possible to control helical pitch length and temperature of helix twist inversion in antiferroelectric mixtures by controlling the ratio of compounds with left- and right-handed helix in such mixtures, although all of them have the same chiral terminal chain.     

Metal phthalocyanine nanoribbons and nanowires

Nanoribbons and nanowires of different metal phthalocyanines (copper, nickel, iron, cobalt, and zinc), as well as copper hexadecafluorophthalocyanine (F(16)CuPc), have been grown by organic vapor-phase deposition. Their properties, as a function of substrate type, source-to-substrate distance, and substrate temperature, were studied by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and absorption measurements. The size and morphology of the nanostructures were found to be mainly determined by the substrate temperature. The crystal structure was dependent on the substrate temperature as well. At substrate temperatures below 200 degrees C, in addition to straight nanoribbons, twisted nanoribbons were found for all investigated materials except F(16)CuPc, which formed helical nanoribbons upon exposure to an electron beam. The formation of different nanostructures (nanoribbons, twisted nanoribbons, and helical nanoribbons) is discussed.     

A Systematic Study of the Use of DL-Tartaric Acid in the Synthesis of Silica Materials Obtained by the Sol-Gel Method

DL-tartaric acid was used as a template for the formation of silica nanotubes and spheres by the sol-gel method from tetraethylorthosilicate (TEOS) as silica source. The reactions were carried out in ethanol/water mixtures in the presence of aqueous ammonia, between 0°C and 75°C, using both stirred and non-stirred conditions. TEM and SEM images show that the yield and microstructure of the silica is influenced by the synthetic conditions (temperature, ammonia (aq) concentration, gelation time, solvent mixture). It was observed that the chiral form of the tartaric acid used and the diffusion of TEOS to the template determines the eventual silica structure.