Amine-terminated dendrimers as biomimetic templates for silica nanosphere formation

In diatoms, silica synthesis occurs by use of complex posttranslationally modified peptides, termed silaffins, and highly complex biological polyamine structures. Silaffin peptides have lysine residues that are modified to long-chain polyamine moieties of N-methyl derivatives of polypropylenimine to drive silica synthesis at slightly acidic pH conditions. Using polypropylenimine (PPI) and PAMAM amine-terminated dendrimers as a biomimetic analogue of the polyamine modifications of silaffins, we have demonstrated the condensation of silica nanospheres. We have shown that the dendrimers react in an amine concentration-dependent fashion yielding silica nanospheres with a distinct size distribution reminiscent of the structures produced from both the modified and nonmodified peptides extracted from diatoms. Additionally, the templates were encapsulated by the growing nanospheres and precipitated from solution in a manner similar to that previously described for the bioactive peptides and polyamines.     

Development of various PS-b-P4VP micellar morphologies: fabrication of inorganic nanostructures from micellar templates

A liquid-phase method for preparing uniform-sized silica nanospheres (SNSs) 12 nm in size and their three-dimensionally ordered arrangement upon solvent evaporation have recently been pioneered by us. Here we report the successful control of the sphere sizes in the wide range from 14 to 550 nm by the seed regrowth method. In this method, the dispersion of SNSs 14 nm in size as seeds was prepared in the emulsion system containing Si(OEt)(4) (TEOS), water and arginine under weakly basic conditions (pH 9-10). An appropriate portion of this dispersion is added to the solution containing water, ethanol and arginine, and then TEOS is added. The additional TEOS introduced into the regrowth system contributed only to the resumed growth of the seeds, not to the formation of new silica particles. The size of interparticle pores was finely tuned by changing the size of the spheres. The preparation of three-dimensionally ordered porous carbons by using the colloidal array of silica nanospheres as a template is also reported.     

Enzyme-modified nanoparticles using biomimetically synthesized silica

The entrapment of enzymes within biomimetic silica nanoparticles offers unique and simple immobilization protocols that merge the stability of proteins confined in solid phases with the high loading and reduced diffusion limitations inherent to nano-sized structures. Herein, we report on the biomimetic silica entrapment of chemically derivatized horseradish peroxidase for amperometric sensing applications. Scanning electron microscopy shows evidence of the formation of enzyme-modified nanospheres using poly(ethylenimine) as a template for silicic acid condensation. When these nanospheres are directly deposited on graphite electrodes, chemically modified anionic peroxidase shows direct electron transfer at 0 mV vs Ag|AgCl. Microgravimetric measurements as well as SEM images demonstrate that negatively charged peroxidase is also entrapped when silica precipitates at gold electrodes are modified with a self-assembled monolayer of poly(ethylenimine). Electrostatic interactions may play a crucial role for efficient enzyme entrapment and silica condensation at the PEI template monolayer. The in-situ biomimetically synthesized peroxidase nanospheres are catalytically active, enabling direct bioelectrocatalysis at 0 mV vs Ag|AgCl with long-term stability.     

Synthesis and Catalytic Applications of Sulfonic Acid Group–Functionalized Nano- and Microsilica Structures

Sulfonic acid group–functionalized nano- and microsilica with different sizes and shapes were synthesized. Silica nanospheres with an average size of 225 nm, silica microtubes, and fine silica gel were prepared and functionalized by sulfonic acid. Their catalytic activity was investigated in the three-component Biginelli reaction for the synthesis of dihydropyrimidinones.     

Magnetic-sensitive silica nanospheres for controlled drug release

Recently, magnetic silica-based nanospheres have received great attention and displayed magnificent potential for bioimaging and therapeutic purposes. This study provided a way to accelerate drug release from magnetic-sensitive silica nanospheres by controlled bursting to a therapeutically effective concentration by a high-frequency magnetic field (HFMF). The magnetic-sensitive silica nanospheres were synthesized by an in situ process, with particle sizes about 50 nm and able to release specific amounts of drug in a burst manner via short exposure to a HFMF. The HFMF accelerates the rotation of magnetic nanoparticles deposited in the silica matrix with generated heat energy and subsequently enlarges the nanostructure of the silica matrix to produce porous channels that cause the drug to be released easily. By taking these magnetic-responsive controllable drug release behaviors, the magnetic silica nanospheres can be designed for controlled burst release of therapeutic agents for especially urgent physiological needs.     

孔结构梯度分布SiO2膜的仿生合成

以正硅酸乙酯为硅源,十六烷基三甲基溴化铵大分子的组装体为有机模板,研究在气-液界面仿生合成SiO2膜的过程。考察了影响成膜的订因素并优化了操作条件,进而仿生合成了孔结构梯度分布的无机膜。SEM与孔径分布表征,表明所制备的SiO2膜顶层孔径为1.9nm,底部的则为25nm,膜的比表面积为313.5m^2·g^-1。     

Double function of tris(hydroxymethyl)aminomethane (THAM) for the preparation of colloidal silica nanospheres and the conversion to ordered mesoporous carbon

Tris(hydroxymethyl)aminomethane (THAM) has been found to be an excellent catalyst for the preparation of colloidal silica nanospheres around 10 to 20 nm in size, and THAM on the surfaces of nanospheres is an efficient carbon source for the synthesis of highly ordered mesoporous carbon with controlled pore size by using closely packed nanospheres as a porogen.     

Polypeptide-templated synthesis of hexagonal silica platelets

Several studies have demonstrated the use of biomimetic approaches in the synthesis of a variety of inorganic materials. Poly-L-lysine (PLL) promotes the precipitation of silica from a silicic acid solution within minutes. The molecular weight of PLL was found to affect the morphology of the resulting silica precipitate. Larger-molecular weight PLL produced hexagonal silica platelets, whereas spherical silica particles were obtained using low-molecular weight PLL. Here we report on the polypeptide secondary-structure transition that occurs during the silicification reaction. The formation of the hexagonal silica platelets is attributed to the PLL helical chains that are formed in the presence of monosilicic acid and phosphate ions. Hexagonal PLL crystals can also serve as templates in directing the growth of the silica in a manner that generates a largely mesoporous silica phase that is oriented with respect to the protein crystal template.     

Surface oxidation states in Si/SiO2 nanostructures prepared from Si/SiO2 mixtures

Silica nanospheres have been produced by a novel technique where surface Si oxidation states can be adjusted using the ratio of metalloid ions/metalloid atoms in the starting mixture. When the proportions of Si4+/Si0 are equal in the synthesis, the resulting solid is considerably more reactive than Cab-O-Sil toward the phenol hydroxylation reaction and the surface shows an average Si oxidation state of +3. On the other hand, those silica nanospheres, produced from a mixture of Si4+/Si0 = 0.25, showed a lower reactivity comparable to that of Cab-O-Sil which XPS demonstrates has a surprisingly low average Si oxidation state close to +1. We speculate that the silicon surface oxidation state and the number of surface silanol groups play important roles in determining the activity of the solid toward the phenol hydroxylation reaction. In expanding our earlier report4 on the copper-silica system, we establish that the surface chemistry of the silica nanospheres is apparently different from that of fumed, amorphous silica. These results suggest that we are developing a technique that can be generalized to create supported, mixed metal oxides having tunable average surface oxidation states.     

Tailored core-shell-shell nanostructures: sandwiching gold nanoparticles between silica cores and tunable silica shells

Size tunable and structure tailored core-shell-shell nanospheres containing silica cores, gold nanoparticle shells, and controlled thicknesses of smooth, corrugated, or porous silica shells over the gold nanoparticles have been synthesized. The synthesis involved the deposition of gold nanoparticles on silica cores, followed by sol-gel processing of tetraethoxysilane (TEOS) or sodium silicate to form dense or porous silica shells, respectively, over the gold nanoparticles. The structures and sizes of the resulting core-shell-shell nanospheres were found to heavily depend on the sizes of the core nanoparticles, the relative population of the gold nanoparticles on each core, and the concentration of TEOS. While a higher TEOS concentration resulted in thicker and more uniform silica shells around individual larger silica cores (approximately > or =250 nm in diameter), the same TEOS concentration resulted in aggregated and twin core-shell-shell nanostructures for smaller silica cores (approximately < or =110 nm in diameter). The thinner silica shells were synthesized by using a lower TEOS concentration. By using sodium silicate (Ung et al. J. Phys. Chem. B 1999, 103, 6770), the porous silica shells were synthesized. Controlled chemical etching of the core-shell-shell nanoparticles with an aqueous KCN solution resulted in corrugated silica shells around the gold nanoparticles or corrugated silica nanospheres with few or no gold nanoparticles. This has allowed synthesis of new types of core-shell-shell nanoparticles with tailored corrugated shells. The nanoporous silica shells provided accessible structures to the embedded metal nanoparticles as observed from the electrochemical response of the gold nanoparticles.     

Dual‐Pore Mesoporous Carbon@Silica Composite Core–Shell Nanospheres for Multidrug Delivery

Monodispersed mesoporous phenolic polymer nanospheres with uniform diameters were prepared and used as the core for the further growth of core–shell mesoporous nanorattles. The hierarchical mesoporous nanospheres have a uniform diameter of 200 nm and dual‐ordered mesopores of 3.1 and 5.8 nm. The hierarchical mesostructure and amphiphilicity of the hydrophobic carbon cores and hydrophilic silica shells lead to distinct benefits in multidrug combination therapy with cisplatin and paclitaxel for the treatment of human ovarian cancer, even drug‐resistant strains.     

线性聚胺介导的SiO2 杂化纳米粒子的仿生合成

我们报道了在环境条件下采用简单的线性聚胺作为仿生结构导向剂快速可控的合成了聚合物杂化的SiO2纳米粒子。采用TEM, EDX, FT IR, TGA等方法对所合成的纳米粒子的形态、结构和组成进行了详细表征。另外,我们也发现纳米粒子的形成强烈依赖于体系中SiO2的矿化反应时间。所合成的杂化纳米粒子预期将在催化和生物医学等领域具有重要的应用价     

以手性两亲小分子为模板剂制备介孔二氧化硅纳米空心球

以L-亮氨酸为手性源合成了手性阳离子两亲性小分子化合物L-18Leu6NEtBr,用其自组装体作为模板,氢氧化钠为催化剂,经溶胶-凝胶过程制备出介孔二氧化硅纳米空心球;分析了介孔二氧化硅纳米空心球的尺寸和孔径.结果表明,所制备的二氧化硅空心球直径约100nm;其介孔孔道平行于壳表面,孔径为3.1nm.     

Synthesis of hollow CaCO3 nanospheres templated by micelles of poly(styrene-b-acrylic acid-b-ethylene glycol) in aqueous solutions

An asymmetric triblock copolymer, poly(styrene-b-acrylic acid-b-ethylene glycol) (PS-b-PAA-b-PEG), was synthesized via reversible addition-fragmentation chain transfer controlled radical polymerization. Micelles of PS-b-PAA-b-PEG with PS core, PAA shell, and PEG corona were then prepared in aqueous solutions, followed by extensive characterization based on dynamic light scattering, zeta-potential, and transmission electron microscopy (TEM) measurements. The well-characterized micelles were used to fabricate hollow nanospheres of CaCO(3) as a template. It was elucidated from TEM measurements that the hollow nanospheres have a uniform size with cavity diameters of ca. 20 nm. The X-ray diffraction analysis revealed a high purity and crystallinity of the hollow nanospheres. The hollow CaCO(3) nanospheres thus obtained have been used for the controlled release of an anti-inflammatory drug, naproxen. The significance of this study is that we have overcome a previous difficulty in the synthesis of hollow CaCO(3) nanospheres. After mixing of Ca(2+) and CO(3)(2-) ions, the growth of CaCO(3) is generally quite rapid to induce large crystal, which prevented us from obtaining hollow CaCO(3) nanospheres with controlled structure. However, we could solve this issue by using micelles of PS-b-PAA-b-PEG as a template. The PS core acts as a template that can be removed to form a cavity of hollow CaCO(3) nanospheres, the PAA shell is beneficial for arresting Ca(2+) ions to produce CaCO(3), and the PEG corona stabilizes the CaCO(3)/micelle nanocomposite to prevent secondary aggregate formation.     

Controlled synthesis of monodisperse sub-100 nm hollow SnO2 nanospheres: a template- and surfactant-free solution-phase route, the growth mechanism, optical properties, and application as a photocatalyst

Controlled synthesis of low‐dimensional materials, such as nanoparticles, nanorods, and hollow nanospheres, is vitally important for achieving desired properties and fabricating functional devices. We report a systematic investigation of the growth of low‐dimensional sub‐100 nm SnO₂ hollow nanostructures by a mild template‐ and surfactant‐free hydrothermal route, aiming to achieve precise control of morphology and size. The starting materials are potassium stannate and urea in an ethylene glycol (EG)/H₂O system. We found the size of the SnO₂ hollow nanospheres can be controlled by simply adjusting the urea concentration. Investigation of the mechanism of formation of the SnO₂ hollow nanospheres revealed that reaction time, urea concentration, and reaction temperature make significant contributions to the growth of hollow nanospheres. On switching the solvent from EG/H₂O to H₂O or ethanol, the SnO₂ nanostructures changed from nanospheres to ultrafine nanorods and nanoparticles. On the basis of reaction parameter dependent experiments, oriented self‐assembly and subsequent evacuation through Ostwald ripening are proposed to explain the formation of hollow nanostructures. Their size‐dependent optical properties, including UV/Vis absorption spectra and room‐temperature fluorescence spectra, were also studied. Moreover, the studies on the photocatalytic property demonstrate that the fabricated hollow structures have slightly enhanced photocatalytic degradation activity for rhodamine B when exposed to mercury light irradiation compared to solid SnO₂ nanospheres under the same conditions. The synthesized tin oxide nanoparticles display high photocatalytic efficiency and have potential applications for cleaning polluted water in the textile industry.     

脂质体为模板仿生硅化固定葡萄糖氧化酶

将脂质体囊泡与仿生硅化技术相结合,模拟细胞纳微环境,实现以脂质体为模板仿生制备氧化硅固定葡萄糖氧化酶(GOx),建立性能稳定的固定化酶.扫描电镜分析显示,固定化GOx为球形纳米粒子,粒径分布在200nm左右,在优化反应条件下GOx回收率达到71.8%.由于载体的空间限制作用及其提供的较稳定微环境,固定化GOx表现出良好的热稳定性和pH稳定性,其对变性剂耐受性和操作稳定性等也得到明显提高.     

Efficient eco-friendly approach towards bimetallic nanoparticles synthesis and characterization using Exiguobacterium aestuarii by statistical optimization

ABSTRACT

Biogenic synthesis of bimetallic nanoparticles (gold – AuNp and selenium – SeNp) using inexpensive Tryptophan Enriched Banana Peel Media for the growth of marine isolate (Exiguobacterium aestuarii SBG4 MH185868). The response surface methodology is employed for optimizing production conditions. The surface plasmon resonance band showed λ_max at 540?nm (AuNp) and 284?nm (SeNp). FTIR and zeta potential analysis confirmed the stability, whereas XRD spectra revealed the nature of nanoparticles obtained at optimum conditions. SEM micrographs showed nanospheres of the following size: AuN, 30?±?5 nm and SeNp, 50?±?5 nm. Biocompatibility of Np evaluated by the hemolytic activity showed <20% hemolysis even at highest concentrations (100?µg/ml). AuNp showed the least cytotoxicity, whereas SeNp showed considerable cytotoxicity against the breast cancer cell lines MCF – 7 and MDA-MB-231. Hence, we utilized the environment-friendly growth media for the controlled synthesis of dual Np using single bacterial strain involving feasible steps in downstream processing.     

Influence of poly-L-lysine on the biomimetic growth of silica tubes in confined media

Pore channels of polycarbonate membranes were recently used as biomimetic models to study the effect of confinement on silicate condensation, leading to the formation of silica tubes exhibiting a core-shell structure. In this work, we preimmobilized poly-L-lysine on the membrane pores, leading to modification of the tube shell formation process and variation in core particle size. These data strengthen previous assumptions on the role of confinement on silica growth, i.e., interfacial interactions and perturbation of the diffusion coefficient. They also suggest that this approach is suitable to investigate in more detail the contribution of confinement effects on silica biomineralization.     

Seed‐Mediated Synthesis of Single‐Crystal Gold Nanospheres with Controlled Diameters in the Range 5–30 nm and their Self‐Assembly upon Dilution

Single‐crystal gold nanospheres with controlled diameters in the range 5–30 nm were synthesized by using a facile approach that was based on successive seed‐mediated growth. The key to the success of this synthesis was the use of hexadecyltrimethylammonium chloride (CTAC) as a capping agent and a large excess of ascorbic acid as a reductant to ensure fast reduction and, thus, single crystallinity and a spherical shape of the resultant nanoparticles. The diameters of the gold nanospheres could be readily controlled by varying the amount of seeds that were introduced into the reaction system. The gold nanospheres could be produced with uniform diameters of up to 30 nm; thus, their localized surface plasmon resonance properties could be directly compared with the results that were obtained from theoretical calculations. Interestingly, we also found that these gold nanospheres self‐assembled into dimers, larger aggregates, and wavy nanowires when they were collected by centrifugation, dispersed in deionized water, and then diluted to different volumes with deionized water.     

聚合物在仿生合成中的应用研究进展

仿生合成技术通过模拟生物矿化机理,以有机物为模板控制无机物的生成,制备具有特殊结构及性能的无机材料.聚合物是仿生合成中较多采用的有机模板之一,用来控制无机粒子的成核、生长及排列,能够在温和条件下合成具有多级结构、特殊形貌和优异性能的有机,无机复合材料.本文综述了聚合物在仿生合成中的应用研究进展,并指出了存在的问题及发展方向.