Superdispersible PVP-coated Fe3O4 nanocrystals prepared by a "one-pot" reaction

Poly( N-vinyl-2-pyrrolidone) (PVP)-coated Fe3O4 nanocrystals were prepared by a "one-pot" synthesis through the pyrolysis of ferric triacetylacetonate (Fe(acac)3) in N-vinyl-2-pyrrolidone (NVP). The polymerization of NVP was followed by measuring the shear viscosity of the reaction mixture. The PVP molecules formed in the reaction mixture was investigated by gel permeation chromatography. As the resultant Fe3O4 nanocrystals presented superdispersibility in 10 different types of organic solvents and aqueous solutions with different pH, including 0.01 M phosphate-buffered saline buffer, their hydrodynamic properties in both organic and aqueous systems were investigated by dynamic light-scattering. The results indicated that the PVP-coated Fe3O4 nanocrystals can completely be dispersed forming stable colloidal solutions in both organic solvents and water. Fourier transform infrared spectroscopy results suggested that PVP interacted with Fe3O4 via its carbonyl groups. Further surface analysis by X-ray photoelectron spectroscopy revealed that there were both coordinating and noncoordinating segments of PVP on the particle surface; the molar ratio between them was of 1:2.6.     

Fluorescent magnetic nanocrystals by sequential addition of reagents in a one-pot reaction: a simple preparation for multifunctional nanostructures

Core-shell nanostructures consisting of FePt magnetic nanoparticles as the core and semiconducting chalcogenides as the shell were synthesized by a series of reactions in a one-pot procedure. Adding Cd(acac)2 as the cadmium precursor to a reaction mixture containing FePt nanoparticles afforded FePt@CdO core-shell intermediates. The subsequent addition of chalcogens yielded FePt@CdX core-shell nanocrystals (where X was S or Se). The reverse sequence of addition, i.e., adding X before Cd, resulted in spongelike nanostructures because the chalcogens readily formed nanowires in the solution. Transmission electron microscopy, energy-dispersive X-ray spectrometry, selected area electron diffraction, fluorescence spectroscopy, and SQUID were used to characterize the nanostructures. These core-shell nanostructures displayed superparamagnetism at room temperature and exhibited fluorescence with quantum yields of 2.3-9.7%. The flexibility in the sequence of addition of reagents, combined with the compatibility of the lattices of the different materials, provides a powerful yet convenient strategy for generating sophisticated, multifunctional nanostructures.     

One-step synthesis of highly water-soluble magnetite colloidal nanocrystals

A high-temperature solution-phase hydrolysis approach has been developed for the synthesis of colloidal magnetite nanocrystals with well-controlled size and size distribution, high crystallinity, and high water solubility. The synthesis was accomplished by the hydrolysis and reduction of iron(III) cations in diethylene glycol with a rapidly injected solution of sodium hydroxide at an elevated temperature. The high reaction temperature allows for control over size and size distribution and yields highly crystalline products. The superior water solubility is achieved by using a polyelectrolyte, that is, poly(acrylic acid) as the capping agent, the carboxylate groups of which partially bind to the nanocrystal surface and partially extend into the surrounding water. The direct synthesis of water-soluble nanocrystals eliminates the need for additional surface modification steps which are usually required for treating hydrophobic nanocrystals produced in nonpolar solvents through the widely recognized pyrolysis route. The abundant carboxylate groups on the nanocrystal surface allow further modifications, such as bioconjugation, as demonstrated by linking cysteamine to the particle surface. The monodisperse, highly water-soluble, superparamagnetic, and biocompatible magnetite nanocrystals should find immediate important biomedical applications.     

Preparation of novel symmetrical bistetrazole-carbazole derivatives through a one-pot Ugi-azide reaction

A series of new symmetrical tetrazole-based carbazole derivatives starting from the initially generated 3,6-diformyl-N-alkylcarbazoles were successfully synthesized through a one-pot Ugi-azide reaction in moderate to high yields. Simplicity, easily accessible chemicals, mild reaction conditions, and fast separation of the products with the formation of bistetrazole-based carbazole derivatives in one step are some advantages of this method. The structure of the products was characterized and confirmed by using spectroscopic techniques such as ¹H NMR, ¹³C NMR, FT-IR, and MS spectroscopy.     

Efficient one-pot synthesis of highly photoluminescent alkyl-functionalised silicon nanocrystals

The chemical reduction of micelles formed by mixing silicon tetrachloride and hexyltrichlorosilane in apolar solvent, where hexyltrichlorosilane serves as both reactant and surfactant, yields brightly luminescent silicon nanocrystals, and enables efficient synthesis of alkyl-functionalised silicon quantum dots (SiQDs) in a single step.     

Facile shape and size-controlled growth of uniform magnetite and hematite nanocrystals with tunable properties

Monodispersed magnetite Fe3O4 and hematite α-Fe2O3 nanocrystals have been grown in co-solvents of alcohol and water. Either the shape or the size of the nanocrystals could be easily controlled. Both the phases and nanostructures have been characterized by powder X-ray diffraction patterns and electron microscopy. The magnetic and catalytic properties of these products were investigated and compared with each other. The obtained results clearly demonstrate that these iron oxide nanocrystals are soft ferromag...     

Starch nanocrystals with large chain surface modifications

Nanoscale monocrystalline starch particles were successfully modified using stearic acid chloride and poly(ethylene glycol) methyl ether. Surface modification was confirmed using FTIR, XPS spectroscopy, and contact angle measurements. X-ray diffraction and DSC analysis confirmed that there was no alteration of the starch crystalline structure due to the surface modification. The grafts at the starch surface were also found to crystallize on the surface. TEM showed the individualization of nanoparticles as a result of the reduction of polar and hydrogen bonding forces. These results show our ability to modify the starch nanocrystal surface with plasticizing chains. Modified nanoparticles can find applications as compatibilized polymer additives, surface-active particles, and co-continuous nanocomposite precursors.     

Targeting cell surface receptors with ligand-conjugated nanocrystals

To explore the potential for use of ligand-conjugated nanocrystals to target cell surface receptors, ion channels, and transporters, we explored the ability of serotonin-labeled CdSe nanocrystals (SNACs) to interact with antidepressant-sensitive, human and Drosophila serotonin transporters (hSERT, dSERT) expressed in HeLa and HEK-293 cells. Unlike unconjugated nanocrystals, SNACs were found to dose-dependently inhibit transport of radiolabeled serotonin by hSERT and dSERT, with an estimated half-maximal activity (EC(50)) of 33 (dSERT) and 99 microM (hSERT). When serotonin was conjugated to the nanocrystal through a linker arm (LSNACs), the EC(50) for hSERT was determined to be 115 microM. Electrophysiology measurements indicated that LSNACs did not elicit currents from the serotonin-3 (5HT(3)) receptor but did produce currents when exposed to the transporter, which are similar to those elicited by antagonists. Moreover, fluorescent LSNACs were found to label SERT-transfected cells but did not label either nontransfected cells or transfected cells coincubated with the high-affinity SERT antagonist paroxetine. These findings support further consideration of ligand-conjugated nanocrystals as versatile probes of membrane proteins in living cells.     

Formation of orientation-ordered superlattices of magnetite magnetic nanocrystals from shape-segregated self-assemblies

Magnetic magnetite (Fe3O4) nanocrystals have been synthesized by combining nonhydrolytic reaction with seed-mediated growth. The shape of these magnetite nanocrystals can be controlled either as pure spheres or a mixture of mainly faceted nanocrystals. Faceted magnetite nanocrystals consist of truncated tetrahedral platelets (TTPs), truncated octahedrons (TOs), and octahedrons (OTs). Transmission electron microscopy analysis indicates that the faceted nanocrystal mixture tends to self-segregate based upon the shape in a self-assembly process, and each shape forms its own distinct crystallographic orientation-ordered superlattice assemblies. Self-assemblies of the Fe3O4 nanocrystals in the shapes of TTP, TO, and OT show hexagonal, primitive cubic, and distorted body-centered cubic (bcc) superlattice structures, respectively. The possible mechanism for the formation of different superstructures is attributed to van der Waals interactions. Nanocrystals with different shapes provide diverse building blocks for bottom-up approaches in building nano- and mesosystems. Furthermore, the self-segregation phenomenon of different shaped nanocrystals in self-assembly processes could be very important in envisioning efficient assembly strategies for nanoscience- and nanotechnology-based devices.     

Rigid-Rod benzobisthiazole polymers with reactive fluorene moieties: Synthesis and characterization

High purity 2,7-fluorenedicarboxylic acid chloride was synthesized in a multistep reaction scheme from 2,7-dibromofluorene. Subsequent polycondensation in polyphosphoric acid of 2,5-diamino-1,4-benzenedithiol dihydrochloride with terephthaloyl chloride and 2,7-fluorenedicarboxylic acid chloride led to rigid-rod benzobisthiazole polymers with reactive fluorene moieties. The proportion of fluorene in the resultant polymers was controlled through reaction stoichiometry. Soluble polymers with intrinsic viscosities as high as 33.7 dL/g (methanesulfonic acid, 30°C) were obtained if the polymerization temperature was not allowed to exceed 165°C. Insoluble, presumably crosslinked polymers were obtained at higher temperature (190–200°C). Thermal characterization of the polymers by differential thermal analysis and thermal gravimetric analysis/mass spectroscopy did not disclose any thermal transition to 450°C. Onset of weight loss in air did not occur until over 550°C.     

Diastereoselective synthesis of gamma-lactams by a one-pot, four-component reaction

A new one-pot, four-component reaction (4CR) between amines, maleic anhydrides, aldehydes, and thiols has been discovered to form tetra- and pentasubstituted gamma-lactams with high diastereoselectivity. Each component is independently variable and employed in equivalent stoichiometry, producing only water as a byproduct.     

Preparation of reactive surfaces by electrografting

The electrografting process has been applied to a new monomer in order to induce reactivity to the surface of various conducting substrates which are then appropriate for the anchoring of a large variety of molecules (catalysts, proteins, amino-polymers etc.).     

Synthesis of stilbene analogues by one-pot oxidation-Wittig and oxidation-Wittig-Heck reaction

Synthesis of symmetrical (and unsymmetrical) stilbene derivatives is achieved by a combination of one-pot steps of Kornblum type oxidation of benzyl halide, its simultaneous in situ formation of phosphonium salt, and subsequently their Wittig reaction. In other variant it is oxidized to aldehyde, treated with ylide generated from phosphonium salt (CH₃PPh₃X) to give styrene, and subjected to Pd catalyzed Heck reaction with arylhalide to give stilbenes as the three-step one-pot sequence.     

Preparation of surface organometallic catalysts by gas-phase ligand stripping and reactive landing of mass-selected ions

Organometallic complexes immobilized on surfaces combine the high selectivity of homogeneous catalysts with the ease of separation of catalyst from products attainable with heterogeneous catalysts. Here we report a novel approach for the highly controlled preparation of surface organometallic catalysts by gas-phase ligand stripping combined with reactive landing of mass-selected ions onto self-assembled monolayer surfaces. Collision-induced dissociation is used to generate highly reactive undercoordinated metal complexes in the gas-phase for subsequent surface immobilization. Complexes with an open coordination shell around the metal center are demonstrated to show enhanced activity towards reactive landing in comparison to fully ligated species. In situ TOF-SIMS analysis indicates that the immobilized complexes exhibit behavior consistent with catalytic activity when exposed to gaseous reagents.     

In situ one-pot synthesis of 1-dimensional transition metal oxide nanocrystals

One-dimensional colloidal metal oxide nanocrystals are of great importance in materials chemistry, but reports on these materials are rare due to lack of well-defined synthetic protocols. In this paper, we present a general and highly effective one-pot synthetic protocol to produce 1-dimensional nanostructures of transition metal oxide (e.g., W(18)O(49), TiO(2), Mn(3)O(4), and V(2)O(5)) through thermally induced crystal growth processes from a mixture of metal chloride and surfactants.     

Surfactant-assisted one-pot synthesis of superparamagnetic magnetite nanoparticle clusters with tunable cluster size and magnetic field sensitivity

Magnetic nanoparticles (MNPs) have many potential biomedical applications. Improvements in their magnetic properties and solubility are necessary for these applications to realize their full potential. In this study, MNPs in the form of raspberry-like magnetite (Fe(3)O(4)) nanoparticle clusters, consisting of tiny Fe(3)O(4) particles with a diameter of approximately 20 nm, were prepared under hydrothermal conditions at 200 °C in the presence of 3,4-dihydroxyhydroxysinnamic acid (DHCA). The primary particles were connected by DHCA molecules to form the clusters, which were well dispersed in water media because a COOH group from DHCA appeared on their surfaces. The cluster size could be tuned from 50 to 400 nm without changing the primary particle size by controlling the reaction time. Therefore, all prepared clusters displayed superparamagnetic properties at room temperature. In addition, the sensitivity of Fe(3)O(4) to an external magnetic field could also be controlled by the cluster size.     

Flux stabilization of silicon nitride microsieves by backpulsing and surface modification with PEG moieties

The influence of the surface properties of chemically modified silicon nitride microsieves on the filtration of protein solutions and defatted milk is described in this research. Prior to membrane filtrations, an antifouling polymer based on poly(ethylene glycol), poly(TMSMA-r-PEGMA) was synthesized and applied on silicon-based surfaces like silicon, silicon nitride, and glass. The ability of such coating to repel proteins like bovine serum albumin (BSA) was confirmed by ellipsometry and confocal fluorescence microscopy. In BSA and skimmed milk filtrations no differences could be seen between unmodified and PEG-coated membranes (decreasing permeability in time). On the other hand, reduced fouling was observed with PEG-modified microsieves in combination with backpulsing and air sparging.