Manipulation of the magnetic properties of magnetite-silica nanocomposite materials by controlled Stober synthesis

The paper describes the synthesis and characterization of the magnetic properties of magnetite/silica nanocomposites using a modified Stober method. Magnetite nanoparticles averaging 8-10 nm in diameter and stabilized with oleic acid in toluene were used as the magnetic component of the nanocomposites. SQUID magnetic measurements and ferromagnetic resonance spectroscopy measurements were performed at each stage of the synthesis to understand the properties of the formed composites. Changes of blocking temperature in ZFC/FC SQUID curves correlated with corresponding changes of the resonance field in the ferromagnetic spectra of the sample at each stage of formation. The paper concludes that it is possible to manipulate the magnetic properties of silica/magnetite composite materials by controlling their surface properties and silica coating thickness.     

Layer-by-layer nanotube template synthesis

Electroless deposition of gold on the pore walls of polycarbonate templates is currently the best known method for controlling inside diameters of template-synthesized nanotubes. It would be very useful to have alternative template-based synthetic chemistries that yield nanotubes composed of other materials, but which still allow for precise control over the nanotube wall thickness and i.d. A film-formation process that is based on layer-by-layer deposition of the film-forming material along the pore walls of the template membrane provides this desired alternative synthetic chemistry. We describe here the use of Mallouk's alpha,omega-diorganophosphonate/Zr layer-by-layer film-forming method for preparing nanotubes within the pores of alumina template membranes. We have found that this method allows accurate, quantitative, and predictable control over the wall thickness, and thus i.d., of the layered nanotubes obtained.     

Characterization of nanoscale metal structures obtained by template synthesis

Generating submicron objects made of nanostructured materials is one of the challenges of nanotechnology. A method for producing micron-sized structures without the use of lithographic techniques has been developed. Electrochemical deposition of metals into nanometer-wide parallel pores of porous anodic oxide films on aluminium is used to produce micro- to nano-wires or -tip arrays. The nanoscale structures and the structuring procedure have been investigated by the examination of lateral and cross-sectional specimens by SEM, EDS and XPS. The investigations show the feasibility of generating films with a variety of different compositions, a high density of tips, and tip diameters in the range of 30–150 nm. Furthermore, impedance spectroscopy was used to characterize the properties of the nanostructured surface. The results show a structure and composition dependent behavior due to the large (electrochemically) active surface area.     

Preparation of ZnS nanorods by a liquid crystal template

ZnS nanorods were synthesized in lamellar liquid crystals of C(12)E(4) by mixing zinc ions and thioacetamide (TAA) solution. The effects of the reactant concentration and the surfactant/water molar ratio in the liquid crystal system on the morphology and size of the ZnS particles were investigated. The prepared ZnS particles are regular nanorods having a width of about 60 nm and a length of about 80-380 nm, with a largest aspect ratio of about 6.3. A lamellar liquid crystal templating mechanism has been proposed to interpret the experimental results.     

Microstructure of zirconium oxide ceramic fibers obtained by template synthesis

Ceramic fibers of zirconium oxide partially stabilized by ceric oxide were obtained by the template synthesis using sols of initial metals oxides. The formation of the microstructure of ceramic fibers has been studied by the methods of thermal analysis, differential scanning calorimetry, X-ray analysis, scanning electron microscopy, and X-ray spectral analysis. Features of formation of a microstructure of fibers depending on conditions of their preparation were revealed.     

Preparation of single-hole hollow polymer nanospheres by raspberry-like template method

Single-hole hollow polymer nanospheres were fabricated by raspberry-like template method using "graft-from" strategy through atom transfer radical polymerization (ATRP). Nanometer-sized silica spheres were covalently attached onto the surfaces of micrometer-sized silica spheres. Crosslinked polymer shells on the nano-sized spheres outside the attached area were formed by "graft-from" strategy through ATRP. After removal of the silica cores, single-hole hollow crosslinked polymer nanospheres were obtained. In this strategy, most of ATRP monomers may be used and thus many functional groups can be easily incorporated into the single-hole hollow crosslinked polymer nanospheres.     

Interaction of porphyrins with a dendrimer template: self-aggregation controlled by pH

The interaction between self-aggregated porphyrins such as 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and 5,10,15,20-tetrakis(4-phosphonatophenyl)porphyrin (TPPP), and a generation 5 (G5) PAMAM dendrimer template is governed by minute differences of porphyrin acido-basic properties. While at neutral pH both monomeric TPPS and TPPP form complexes with G5, decreasing pH did not lead to porphyrin ring protonation (pK(a) approximately 5) but rather to the preferential formation of H-aggregates (probably H-dimers), most likely due to protonation of the G5. Upon further acidification of the solution, this face-to-face orientation of the porphyrin units is being converted to edge-to-edge aligned J-aggregates with a tightly defined structure. This process starts by protonation of the porphyrin ring at pH below 2.3 and 2.8 for TPPS and TPPP, respectively. The AFM imaging of porphyrin/G5 nanostructures obtained at pH 0.7 shows the formation of long nanorods of TPPS with partially aggregated G5 and small aggregates of TPPP connected to individual G5 molecules.     

A porous carbon material prepared by template synthesis using Aerosil

Synthesis of a porous carbon material using Aerosil as template is suggested. The material obtained has high specific surface area (2800 m² g^?1) and high limiting sorption volume (6.2 cm³ g^?1). The porous carbon material prepared by this procedure can be used in solid-phase extraction of organic toxicants from aqueous solutions.     

Preparation and characterisation of laterally monofluorinated mesogenic benzimidazole-based compounds

Series of laterally monofluorinated compounds, 2-(4?-alkoxy-3-fluorobiphenyl-4-yl)-1H-benzimidazole derivatives (nPPF(3)Mx) bearing different substituents (H, CH₃, NO₂, coded as nPPF(3)MH, nPPF(3)MM and nPPF(3)MN, respectively) at 5-position, were prepared and their structures were characterised. According to the results from differential scanning calorimetry and polarising optical microscopy, the present compounds nPPF(3)Mx exhibit enantiotropic smectic mesophases, for which the mesophase ranges are 13–67 and 47–111°C on heating and cooling for nPPF(3)MH, 84–112 and 126–154°C for nPPF(3)MM, and 23–102 and 49–117°C for nPPF(3)MN, respectively. Compared to non-fluorinated analogues, monofluorinated nPPF(3)Mx have low melting/clearing points and display enhanced mesophase range both in heating and cooling, which are attributed to the disruption of the side-to-side intermolecular packing caused by the ortho lateral fluoro substituents and the increased dipole–dipole interaction between the polar fluoro-substituted molecules, respectively. It is noted that nPPF(3)MM and nPPF(3)MN show a much wider mesophase range than nPPF(3)MH, which suggest that the substituent at benzimidazole moiety can improve the mesophase stability.     

Preparation and properties of laterally multifluorinated benzoxazole-based nematic mesogens

Series of laterally multifluorinated heterocyclic compounds, 2-(2?,3-difluoro-4?-alkoxy-1,1?-biphenyl-4-yl)-benzoxazole derivatives (nPF(2)PF(3)Bx), are prepared and characterised. They mainly display enantiotropic nematic mesophases with wider mesophase ranges of 12–107°C (heating process) and 22–134°C (cooling process) than the corresponding analogues. The enhanced nematic mesophase stability is achieved via slightly increasing inter-ring twist angle with inter-ring lateral fluorine substitute in biphenyl unit, as well as through improving the molecular polarity with multifluorine substitutes. Meanwhile, two inter-ring lateral fluorine atoms lead to a decrease in melting/clearing points and a wide nematic mesophase range, which makes it possible for heterocyclic mesogens nPF(2)PF(3)Bx to use in nematic liquid crystal display mixtures.     

Polyaniline composites: improving the electrochemical properties by template synthesis

We have been exploring the idea of using the heterogeneous porosity of inorganic (sol-gel silica) and organic (poly(vinylidene fluoride)) films as a template for the preparation of polyaniline composites. The large size pore distribution (~2.5–800 nm) in both template matrices results in a part of the polyaniline growing more ordered than in films synthesized without spatial restriction. Small-angle X-ray scattering and scanning electron microscopy experiments were done to determine the extreme values of the pore diameters. Using other experimental techniques, including cyclic voltammetry, UV-Vis-NIR spectroscopy, electrochemical impedance and chronopotentiometry, we concluded that the electrochemical properties of polyaniline, such as oxidation and reduction charges, diffusion coefficient and charge-discharge capacity, are improved in these composites. Electronic Publication     

Indole synthesis by controlled carbolithiation of o-aminostyrenes

An effective synthesis of the functionalized indole ring system has been developed from substituted o-aminostyrene starting material. Our methodology involves a novel cascade reaction sequence of alkyllithium addition to the styrene double bond and subsequent trapping of the intermediate organolithium with a suitable electrophile, followed by an in situ ring closure and dehydration to generate the indole ring. This new reaction sequence allows for the introduction of molecular diversity at all positions on the indole scaffold. The procedure was shown to be successful with a range of both C and N substituents on the o-aminostyrenes. The reaction sequence was tolerant to the reactivity range of alkyllithiums such as tert-, sec-, and n-butyllithium. The electrophiles used were DMF, which generated indole products with C-2 unsubstituted, and nitriles, which incorporated the nitrile substituent at C-2. The o-aminostyrene starting materials were generated by a Pd-catalyzed cross-coupling reaction of a vinyl boronic acid equivalent with the readily available substituted o-bromoanilines.     

Microwave assisted template removal of siliceous porous materials

Organic templates of meso- and macro-porous siliceous materials can be completely removed within minutes by microwave digestion, resulting in highly ordered inorganic frameworks with higher surface areas, larger pore volumes, lower structural shrinkage and richer silanol groups compared with those from conventional template removal methods.     

Photoinduced template synthesis of cyclobutane-containing crown ether

The photoinitiated [2+2]-cycloaddition of 1,5-bis[2-(3-phenyl-3-oxoprop-1-en-1-yl)phenoxy]-3-oxapentane in solution was studied. In the presence of potassium cations, the reaction is intramolecular and gives crown ether containing the γ-truxin-type cyclobutane fragment (anti, head-to-head) as the major product. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 204–206, January, 2008.     

Direct synthesis of uniform hollow carbon spheres by a self-assembly template approach

Hollow carbon spheres (50-100 nm) have been synthesized by a self-assembly approach using hexachlorobenzene and Na. NaCl which generated during the reaction has been successfully exploited as a template for the direct synthesis of porous carbon materials, which can be subsequently removed from carbon product by annealing above 1400 degrees C.