Controlled Synthesis of Au@AgAu Yolk-Shell Cuboctahedra with Well-Defined Facets.

The synthesis of Au@AgAu yolk-shell cuboctahedra nanoparticles formed by galvanic replacement in a seed-mediated method is described. Initially, single-crystal Au seeds are used for the formation of Au@Ag core-shell nanocubes, which serve as the template material for the deposition of an external Au layer. The well-controlled synthesis yields the formation of cuboctahedra nanoparticles with smooth inner and outer Au/Ag surfaces. The deposition/oxidation process is described to understand the formation of cuboctahedra and octahedra nanoparticles. The Au core maintains the initial morphology of the seed and remains static at the center of the yolk-shell because of residual Ag. Structural analysis of the shell indicates intrinsic stacking faults (SFs) near the surface. Energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) compositional analysis show an Au-Ag nonordered alloy forming the shell. The three-dimensional structure of the nanoparticles presented open facets on the [111] as observed by electron tomography SIRT reconstruction over a stack of high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images. The geometrical model was validated by analyzing the direction of streaks in coherent nanobeam diffraction (NBD). The catalytic activity was evaluated using a model reaction based on the reduction of 4-nitrophenol (4-NTP) by NaBH4 in the presence of Au@AgAu yolk-shell nanoparticles.

Ligand-modulated interactions between charged monolayer-protected Au144(SR)60 gold nanoparticles in physiological saline.

In order to determine how functionalized gold nanoparticles (AuNPs) interact in a near-physiological environment, we performed all-atom molecular dynamics simulations on the icosahedral Au144 nanoparticles each coated with a homogeneous set of 60 thiolates selected from one of these five (5) types: 11-mercapto-1-undecanesulfonate -SC11H22(SO3(-)), 5-mercapto-1-pentanesulfonate -SC5H10(SO3(-)), 5-mercapto-1-pentaneamine -SC5H10(NH3(+)), 4-mercapto-benzoate -SPh(COO(-)), or 4-mercapto-benzamide -SPh(CONH3(+)). These thiolates were selected to elucidate how the aggregation behavior of AuNPs depends on ligand parameters, including the charge of the terminal group (anionic vs. cationic), and its length and conformational flexibility. For this purpose, each functionalized AuNP was paired with a copy of itself, placed in an aqueous cell, neutralized by 120 Na(+)/Cl(-) counter-ions and salinated with a 150 mM concentration of NaCl, to form five (5) systems of like-charged AuNPs pairs in a saline. We computed the potential of mean force (the reversible work of separation) as a function of the intra-pair distance and, based on which, the aggregation affinities. We found that the AuNPs coated with negatively charged, short ligands have very high affinities. Structurally, a significant number of Na(+) counter-ions reside on a plane between the AuNPs, mediating the interaction. Each such ion forms a "salt bridge" (or "ionic bonds") to both of the AuNPs when they are separated by its diameter plus 0.2-0.3 nm. The positively charged AuNPs have much weaker affinities, as Cl(-) counter-ions form fewer and weaker salt bridges between the AuNPs. In the case of Au144(SC11H22(SO3(-)))60 pair, the flexible ligands fluctuate much more than the other four cases. The large fluctuations disfavor the forming of salt bridges between two AuNPs, but enable hydrophobic contact between the exposed hydrocarbon chains of the two AuNPs, which are subject to an effective attraction at a separation much greater than the AuNP diameter and involve a higher concentration of counter ions in the inter-pair space.

Supramolecular complexes of quantum dots and a polyamidoamine (PAMAM)-folate derivative for molecular imaging of cancer cells.

Polyamidoamine (PAMAM) dendrimers and water-soluble 3-mercaptopropionic acid (MPA)-capped CdSe quantum dots (QDs) were combined to produce a new gel containing supramolecular complexes of QDs/PAMAM dendrimers. The formation of the QDs/PAMAM supramolecular complexes was confirmed by high resolution electron microscopy and Fourier transform infrared (FTIR) analyses. Molecular dynamics simulations corroborated the structure of the new QDs/PAMAM-based supramolecular compound. Finally, on the basis of the prominent fluorescent properties of the supramolecular complexes, PAMAM dendrimer was functionalized with folic acid to produce a new QDs/PAMAM-folate derivative that showed an efficient and selective performance as a marker for gastric cancer cells.

State of the art of the bi- and trimetallic nanoparticles on the basis of gold and iron.

Recently reported patents and experimental articles on the synthesis, properties, and main applications of core-shell nanoparticles, containing iron or its oxides and gold, as well as trimetallic systems on their basis, are reviewed. These nanostructures were obtained by a series of methods, including reduction in reverse micelles, decomposition of organometallic compounds, electron-beam, laser and gamma-irradiation, sonolysis and electrochemical methods. (Fe or Fe(X)O(y))/Au nanoparticles are subject to be functionalized with organic moieties, may expand their main applications, which consist of catalysis, biological and biomedical uses.

Stabilizer choice for rapid dissolving high potency itraconazole particles formed by evaporative precipitation into aqueous solution.

The objective of this study was to investigate the influence of stabilizer type on the physicochemical properties, including dissolution, of ultra-high potency powders containing itraconazole (ITZ) formed by evaporative precipitation into aqueous solution (EPAS). ITZ was dissolved in dichloromethane, which was then atomized through a heated coil at 80 degrees C into an aqueous solution over precise periods of time. Stabilizers were present in either the aqueous, organic or both phases. The dispersions were centrifuged and the supernatant was removed. Three hydrophilic stabilizers were investigated, including polysorbate 80, polyvinyl pyrrolidone and poloxamer 407. Rapid dissolving ultra-high potency of ITZ powders was successfully produced. Greater than 80% of ITZ was dissolved in 5 min compared to only 13% of ITZ bulk powders. The resulting stabilizer-coated drug particles had high drug-to-stabilizer ratios greater than 12, corresponding to potencies (wt drug/wt drug+wt surfactant) as high as 93%. An increase in dissolution rate was correlated with the amount of stabilizer adsorbed and the wettability. The combination of polysorbate 80 and poloxamer 407 present in the aqueous and organic phases, respectively, was superior in achieving high wetting and rapid dissolving ITZ powders. The ability to control the adsorption behavior of stabilizers by using synergistic combinations affords the opportunity to achieve high dissolution rates with higher potencies compared to previously reported values.

Rapid dissolution of high-potency danazol particles produced by evaporative precipitation into aqueous solution.

High-potency danazol particles with high dissolution rates were produced by evaporative precipitation into aqueous solution (EPAS). Aqueous suspensions formed by EPAS were centrifuged to remove the nonadsorbed surfactant. The resulting surfactant-coated drug particles had extremely high drug-to-surfactant ratios greater than 5, corresponding to potencies (wt drug/wt drug + wt surfactant) as high as 93%. The mechanism of the high dissolution rates was characterized as a function of surfactant adsorption, particle size and surface area, drug crystallinity, and the contact angle for water on the drug surface. For danazol stabilized by polyvinyl pyrrolidone (PVP) alone or with sodium lauryl sulfate (SLS), small particle diameter and high surface area led to high dissolution rates with approximately 90% drug dissolved in 2 min. The crystallinity of the danazol was typically 80%. The properties of the particles and the dissolution rates were mostly unchanged under a 2-week thermal cycling stress test.

Micronized powders of a poorly water soluble drug produced by a spray-freezing into liquid-emulsion process.

The purpose of this paper is to investigate the influence of the emulsion composition of the feed liquid on physicochemical characteristics of drug-loaded powders produced by spray-freezing into liquid (SFL) micronization, and to compare the SFL emulsion process to the SFL solution process. Danazol was formulated with polyvinyl alcohol (MW 22,000), poloxamer 407, and polyvinylpyrrolidone K-15 in a 2:1:1:1 weight ratio (40% active pharmaceutical ingredient (API) potency based on dry weight). Emulsions were formulated in ratios up to 20:1:1:1 (87% API potency based on dry weight). Ethyl acetate/water or dichloromethane/water mixtures were used to produce o/w emulsions for SFL micronization, and a tetrahydrofuran/water mixture was used to formulate the feed solutions. Micronized SFL powders were characterized by X-ray diffraction, surface area, scanning and transmission electron microscopy, contact angle and dissolution. Emulsions containing danazol in the internal oil phase and processed by SFL produced micronized powders containing amorphous drug. The surface area increased as drug and excipient concentrations were increased. Surface areas ranged from 8.9 m(2)/g (SFL powder from solution) to 83.1 m(2)/g (SFL powder from emulsion). Danazol contained in micronized SFL powders from emulsion and solution was 100% dissolved in the dissolution media within 2 min, which was significantly faster than the dissolution of non-SFL processed controls investigated (<50% in 2 min). Micronized SFL powders produced from emulsion had similar dissolution enhancement compared to those produced from solution, but higher quantities could be SFL processed from emulsions. Potencies of up to 87% yielded powders with rapid wetting and dissolution when utilizing feed emulsions instead of solutions. Large-scale SFL product batches were manufactured using lower solvent quantities and higher drug concentrations via emulsion formulations, thus demonstrating the usefulness of the SFL micronization technology in pharmaceutical development.