A method for preparation of nanoparticles of poorly water-soluble organic materials is presented. By this method, an oil-in-water microemulsion containing a volatile solvent with dissolved model material, propylparaben, undergoes solvent evaporation and conversion into nanoparticles by spray drying. The resulting powder can be easily dispersed in water to give a clear, stable dispersion of nanoparticles with a high loading of propylparaben. By filtration of this dispersion it was found that more than 95wt.% of the dispersed propylparaben is in particles of less than 450nm. X-ray diffraction revealed that propylparaben is present as nanocrystals of 40–70nm. After dispersion of the powder in water, formation of large crystals rapidly occurs. Addition of polyvinylpyrrolidone (PVP) prevented crystal growth during dispersion of the powder in water. The inhibition of propylparaben crystal growth by PVP was studied by molecular dynamic simulations that addressed the binding of PVP to the propylparaben crystal. A comparison was made between PVP and polyvinylalcohol, which did not display crystal inhibition properties.
The formulation of water dispersible nanopermethrin was investigated for its larvicidal property. Nanopermethrin was prepared using solvent evaporation of oil in water microemulsion, which was obtained by mixing an organic and aqueous phase. The mean particle size of nanodispersion in water was 151±27nm. X-ray diffraction (XRD) of nanopermethrin showed it was amorphous. Larvicidal studies were carried out against Culex quinquefasciatus and the results were compared with bulk permethrin. The LC50 of nanopermethrin to Cx. quinquefasciatus was 0.117mg/L. The LC50 of bulk permethrin to Cx. quinquefasciatus was 0.715mg/L. Nanopermethrin may be a good choice as a potent and selective larvicide for Cx. quinquefasciatus.
Nanoparticles of novaluron, a water-insoluble insecticide, were prepared by a novel method, based on a direct conversion of O/W microemulsions containing pesticide and volatile solvents, into powders. The conversion of nanoparticles into powder was achieved by rapid evaporation of all the liquids in the microemulsion by spray drying. The microemulsions were evaluated by SAXS, self diffusion NMR, conductivity, and viscosity. The droplet size was approximately 6nm, and the novaluron particle size, after redispersion and evaluation by DLS, was 200±50nm. These particles consisted of aggregates of nanoparticles (30–100nm), as viewed by Cryo-TEM. Electron diffraction and XRD showed that the nanoparticles were amorphous indicating a possible improved bioactivity. The stability of the dispersed nanoparticles was evaluated by following particle size by DLS for a period of time, revealing a slight increase in particle size despite the high value of zeta potential. In vivo experiments carried out with Egyptian cotton leafworm Spodoptera littoralis larvae indicated that the toxicity of nanoparticles of novaluron resembled that of the commercial formulation.
A new composition of a fully water-dilutable microemulsion system stabilized by natural surfactants is presented as a template for preparation of celecoxib nanoparticles. Nanoparticles are obtained as a dry powder upon rapid conversion of microemulsion droplets with dissolved celecoxib into nanoparticles, followed by evaporation of all the liquid in a spray dryer. The resultant powder is easily re-dispersible in water to form a clear, transparent dispersion. The celecoxib nanoparticles are amorphous and their average size in the dispersion is 17nm, in agreement with cryo-TEM results and concentration measurements after filtration. As a result of the nanometric size and amorphous state, about 10-fold increase in dissolution of the powder was obtained, compared to that for particulate celecoxib in the presence of surfactants.
The electrochemical deposition of organic nanoparticles on conducting surface, such as a coronary stents, in the absence of a polymeric matrix is demonstrated. A novel approach, whereby pH-responsive organic nanoparticles coagulate on a conducting surface as a result of applying positive potential, has been studied. Specifically, latex nanoparticles stabilized by sodium oleate in aqueous solutions were deposited by applying a positive potential that oxidized the water and caused the decrease of pH on various conducting surfaces. It was found that the applied potential, its duration and the concentration of the dispersed nanoparticles govern the deposition characteristics of the coating. This generic approach allows coating objects with complex geometries with thickness ranging from nanometers to microns and therefore can be utilized for coating medical and other devices as well as for controlling drug release.
A solid state synthesis for obtaining nanocrystalline silicon was performed by high temperature reduction of commercial amorphous nanosilica with magnesium powder. The obtained silicon powder contains crystalline silicon phase with lattice spacings characteristic of diamond cubic structure (according to high resolution TEM), and an amorphous phase. In 29Si CP MAS NMR a broad multicomponent peak corresponding to silicon is located at −61.28 to −69.45ppm, i.e. between the peaks characteristic of amorphous and crystalline Si. The powder has displayed red luminescence while excited under UV illumination, due to quantum confinement within the nanocrystals. The silicon nanopowder was successfully dispersed in water containing poly(vinyl alcohol) as a stabilizing agent. The obtained dispersion was also characterized by red photoluminescence with a band maximum at 710nm, thus enabling future functional coating applications.
Sodium reduction of a mixture of tetrabromosilane with imidazole ionic liquids in organic solvents gives dispersions of silicon nanoparticles stabilized by carbene ligands. It was shown that the size of silicon nanoclusters depends on the size of substituents at nitrogen atoms of 1,3-dialkylimidazol-2-ylidenes.
In the past few years, the synthesis of Cu nanoparticles has attracted much attention because of its huge potential for replacing expensive nano silver inks utilized in conductive printing. A major problem in utilizing these copper nanoparticles is their inherent tendency to oxidize in ambient conditions. Recently, there have been several reports presenting various approaches which demonstrate that copper nanoparticles can resist oxidation under ambient conditions, if they are coated by a proper protective layer. This layer may consist of an organic polymer, alkene chains, amorphous carbon or graphenes, or inorganic materials such as silica, or an inert metal. Such coated copper nanoparticles enable achieving high conductivities by direct printing of conductive patterns. These approaches open new possibilities in printed electronics, for example by using copper based inkjet inks to form various devices such as solar cells, Radio Frequency Identification (RFID) tags, and electroluminescence devices. This paper provides a review on the synthesis of copper nanoparticles, mainly by wet chemistry routes, and their utilization in printed electronics.
A new composition of a fully water-dilutable microemulsion system stabilized by natural surfactants is presented as a template for preparation of celecoxib nanoparticles. Nanoparticles are obtained as a dry powder upon rapid conversion of microemulsion droplets with dissolved celecoxib into nanoparticles, followed by evaporation of all the liquid in a spray dryer. The resultant powder is easily re-dispersible in water to form a clear, transparent dispersion. The celecoxib nanoparticles are amorphous and their average size in the dispersion is 17 nm, in agreement with cryo-TEM results and concentration measurements after filtration. As a result of the nanometric size and amorphous state, about 10-fold increase in dissolution of the powder was obtained, compared to that for particulate celecoxib in the presence of surfactants. (C) 2010 Elsevier B.V. All rights reserved.
A method for preparation of silica nanocapsules is described, by interfacial polymerisation of nanoemulsions which are prepared by the phase inversion temperature (PIT) method. This is a low-energy emulsification technique which does not require any special equipment, such as high-pressure homogenisers. The nanoemulsions were prepared with decane as the oil phase, in which tetraethoxysilane (TEOS) was dissolved with an ethoxylated alcohol as the surfactant. The hydrolysis and polymerisation of the TEOS was performed under acidic and basic conditions using HCl and ammonia, respectively. The obtained nanocapsules with an average size between 100 and 300 nm, which were comprised of an oil core (decane) and silica shell, were characterised using dynamic light scattering, fourier transform infrared spectroscopy (FTIR), high-resolution scanning electron microscopy (HR-SEM) and by fluorescence of an encapsulated solvatochromic dye. The capsules could be positively or negatively charged by adsorption of ionic surfactants after they were formed.
Polyelectrolyte protected beta-carotene nanoparticles (nanosuspensions) with average diameter of <100 nm were achieved by turbulent mixing and flash nanoprecipitation (FNP). Three types of multi-amine functional polyelectrolytes, epsilon-polylysine (epsilon-PL), poly(ethylene imine) (PEI), and chitosan, were investigated to electrosterically protect the nanoparticles. Particle size and distribution were measured by dynamic light scattering (DLS); particles were imaged via scanning electron microscopy (SEM) and cryogenic transmission electron microscopy (cryo-TEM). Low pH and high polyelectrolyte molecular weight gave the smallest and most stable particles. High drug loading capacity, >80 wt%, was achieved by using either PEI or chitosan. X-ray diffraction (XRD) patterns showed that beta-carotene nanoparticles were amorphous. These findings open the way for utilization of FNP for preparation of nanoparticles with enhanced bioavailability for highly water insoluble drugs. (C) 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:4295-4306, 2010
A new approach to achieve coalescence and sintering of metallic nanoparticles at room temperature is presented. It was discovered that silver nanoparticles behave as soft particles when they come into contact with oppositely charged polyelectrolytes and undergo a spontaneous coalescence process, even without heating. Utilizing this finding in printing conductive patterns, which are composed of silver nanoparticles, enables achieving high conductivities even at room temperature. Due to the sintering of nanoparticles at room temperature, the formation of conductive patterns on plastic substrates and even on paper is made possible. The resulting high conductivity, 20% of that for bulk silver, enabled fabrication of various devices as demonstrated by inkjet printing of a plastic electroluminescent device.
It was found that during the evapn. of water from a droplet of a silver nanoparticles dispersion a self-assembly process leads to the coalescence of the nanoparticles at room temp. and eventually results in a 3D, micrometer-sized dendrite. Direct in situ HR-TEM observation of coalescence events of individual nanoparticles revealed that during this process a transformation of the nanoparticles' crystal structure takes place, from the common fcc silver structure to the unusual hcp structure. It was found that even-though a majority of the nanoparticles in the dispersion have the fcc structure the obtained dendrites are characterized by the hcp structure, reflecting the crystal structure transformation due to the coalescence process. [on SciFinder(R)]
How do intricate multi-residue features such as protein-protein interfaces evolve. To address this question, we evolved a new colicin-immunity binding interaction. We started with Im9, which inhibits its cognate DNase ColE9 at 10-14 M affinity, and evolved it toward ColE7, which it inhibits promiscuously (Kd > 10-8 M). Iterative rounds of random mutagenesis and selection toward higher affinity for ColE7, and selectivity (against ColE9 inhibition), led to an ∼105-fold increase in affinity and a 108-fold increase in selectivity. Anal. of intermediates along the evolved variants revealed that changes in the binding configuration of the Im protein uncovered a latent set of interactions, thus providing the key to the rapid divergence of new Im7 variants. Overall, protein-protein interfaces seem to share the evolvability features of enzymes, i.e., the exploitation of promiscuous interactions and alternative binding configurations via 'generalist' intermediates, and the key role of compensatory stabilizing mutations in facilitating the divergence of new functions. [on SciFinder(R)]
Copper nanoparticles can be utilized as a low-cost replacement for silver and gold nanoparticles which are currently used in ink-jet printing of conductive patterns. However, the main obstacle for using copper nanoparticles is their spontaneous oxidn. at ambient conditions. Here the authors describe the synthesis of nonoxidizable copper nanoparticles by coating them with a silver shell, and ink-jet printing of these particles. The formation of these core-shell nanoparticles is driven by a transmetalation reaction on the surface of copper nanoparticles, where the copper atoms present on the particles' surface are used as the reducing agent for the silver. This process results in formation of solely copper-silver core-shell nanoparticles, with no individual silver particles. It was found that coating 40 nm copper nanoparticles with a 2 nm layer of silver prevents oxidn. of the copper core and preserves its metallic characteristic. Characterization of these nanoparticles by HR-TEM, SEM, EDS, XRD, spectrophotometry and XPS confirm the core-shell structure and their stability to oxidn. Ink-jet printing of concd. aq. dispersions of these copper-silver nanoparticles was done on various substrates, and it was found that conductive and decorative patterns with metallic appearance, stable to oxidn. (up to 150°) are formed. [on SciFinder(R)]
Highly luminescent org. nanoparticles were formed by embedding hydrophobic and hydrophilic (CdSe)ZnS quantum dots with core/shell structure into Et cellulose nanoparticles. The nanoparticles were prepd. from oil-in-water nanoemulsions by a phase inversion process at const. temp., followed by a solvent evapn. The obtained fluorescent Et cellulose nanoparticles were functionalized by immobilization of a specific antibody, and applied in rapid agglutination test for detection of Yersinia pestis F1-antigen. [on SciFinder(R)]