Tomographic Study of Mesopore Formation in Ceria Nanorods.

Porosity in functional oxide nanorods is a recently discovered new type of microstructure, which is not yet fully understood and still under evaluation for its impact on applications in catalysis and gas/ion storage. Here we explore the shape and distribution of pores in ceria in three dimensions using a modified algorithm of geometric tomography as a reliable tool for reconstructing defective and strained nanoobjects. The pores are confirmed as "negative-particle" or "inverse-particle" cuboctahedral shapes located exclusively beneath the flat surface of the rods separated via a sub-5 nm thin ceria wall from the outside. New findings also comprise elongated "negative-rod" defects, seen as embryonic nanotubes, and pores in cube-shaped ceria. Furthermore, we report near-sintering secondary heat treatment of nanorods and cubes, confirming persistence of pores beyond external surface rounding. We support our experiments with molecular modeling and predict that the growth history of voids is via diffusion and aggregation of atomic point defects. In addition, we use density functional theory to show that the relative stability of pore (shape) increases in the order "cuboidal" < "hexagonal-prismatic" < "octahedral". The results indicate that by engineering voids into nanorods, via a high-temperature postsynthetic heat treatment, a potential future alternative route of tuning catalytic activities might become possible.

Transparent ferromagnetic and semiconducting behavior in Fe-Dy-Tb based amorphous oxide films.

We report a class of amorphous thin film material comprising of transition (Fe) and Lanthanide metals (Dy and Tb) that show unique combination of functional properties. Films were deposited with different atomic weight ratio (R) of Fe to Lanthanide (Dy + Tb) using electron beam co-evaporation at room temperature. The films were found to be amorphous, with grazing incidence x-ray diffraction and x-ray photoelectron spectroscopy studies indicating that the films were largely oxidized with a majority of the metal being in higher oxidation states. Films with R = 0.6 were semiconducting with visible light transmission due to a direct optical band-gap (2.49 eV), had low resistivity and sheet resistance (7.15 × 10(-4) Ω-cm and ~200 Ω/sq respectively), and showed room temperature ferromagnetism. A metal to semiconductor transition with composition (for R < 11.9) also correlated well with the absence of any metallic Fe(0) oxidation state in the R = 0.6 case as well as a significantly higher fraction of oxidized Dy. The combination of amorphous microstructure and room temperature electronic and magnetic properties could lead to the use of the material in multiple applications, including as a transparent conductor, active material in thin film transistors for display devices, and in spin-dependent electronics.

Effect of Surfactants on Electrochemical Properties of Vanadium-Pentoxide Nanoparticles Synthesized via Hydrothermal Method.

Vanadium pentoxide (V2O5) nanoparticles were synthesized via an anionic, cationic and non-ionic surfactant assisted hydrothermal method in which Ammonium metavanadate (NH4VO3) was used as precursor. The synthesized nanoparticles were characterized by using powder X-Ray Diffractometer, Scanning Electron Microscopy and UV-Vis spectroscopy. Crystalline nanoparticles were formed using different surfactants like Sodium Dodecyl Sulphate (SDS), Cetyltrimethylammonium Bromide (CTAB), Polyvenylpyrollidone (PVP) and Sodium Dodecyl Benzene Sulfonate (SDBS). The specific capacitance of V2O5 was calculated in 0.5 M KCl and 0.5 M Na2SO4 aqueous electrolyte by using cyclic voltammetry (CV). Electrochemical impedance, and Chronocoulommetry studies revealed a good capacitive and charge-discharge behavior of the prepared V2O5, which is very promising for the application for next-generation high-performance electro-chemical supercapacitors.

Enhanced photocatalytic efficacy of hetropolyacid pillared TiO2 nanocomposites.

The removal of dye from industrial effluents is prime important, photo-catalysis is a finest method to combat dye from effluents. This study concerns about the investigation of photocatalytic activity of TiO2-HPAs (Hetropolyacids) nanocomposite namely TiO2-Phosphomolybdic nanocomposite [TiO2-HMA] and TiO2-Phosphotungstic nanocomposite [TiO2-HWA] which were prepared by Sol-gel method and the same were characterized by using XRD, SEM-EDAX. The photocatalytic activity of prepared photo-catalysts were evaluated and compared by the degradation of Methylene Blue dye in water solution under UV irradiation. In that TiO2-HMA nanocomposite showed superior photocatalytic activity than TiO2-HWA.

Versatile peptide dendrimers for nucleic acid delivery.

Dendrimers are nonviral vectors that have attracted interest on account of a number of features. They are structurally versatile because their size, shape, and surface charge can be selectively altered. Here we examine the functions of a new family of composite dendrimers that were synthesized with lipidic amino acid cores. These dendrimers are bifunctional because they are characterized by positively charged (lysine) modules for interaction with nucleic acids and neutral lipidic moieties for membrane lipid-bilayer transit. We assessed their structure-function correlations by a combination of molecular and biophysical techniques. Our assessment revealed an unexpected pleitropy of functions subserved by these vectors that included plasmid and oligonucleotide delivery. We also generated a firefly luciferase cell line in which we could modulate luciferase activity by RNA interference. We found that these vectors could also mediate RNA suppression of luciferase expression by delivering double-stranded luciferase transcripts generated in vitro. The structural uniqueness of these lipidic peptide dendrimers coupled with their ease and specificity of assembly and the versatility in their choice of cargo, puts them in a new category of macromolecule carriers. These vectors, therefore, have potential applications as epigenetic modifiers of gene function.

Adsorption of amphipathic dendrons on polystyrene nanoparticles.

Adsorption of dendrons onto nanoparticles may provide new model structures which may be useful in drug and gene delivery. Tritiated amphipathic dendrons having three lipidic (C(14)) chains coupled to branched (dendritic) lysine head groups with 8, 16 or 32 free terminal amino groups have been synthesised by solid phase peptide techniques. The interaction between these tritiated dendrons and 200 nm polystyrene latex nanoparticles was investigated in phosphate buffered saline. The amount of dendron adsorbed increased with increasing concentration of dendrons and then decreased. Maximum adsorption of dendrons per gram of nanoparticles was found to be between 8.2 and 84 x 10(-6)M, the amounts adsorbed being inversely proportional to the number of amino groups present in the molecule. The number of dendron molecules adsorbed per nanoparticle was found to be between 430 and 4421. The degree of adsorption was found to be slightly altered by the temperature.

Non-aqueous emulsions: hydrocarbon-formamide systems.

There are few reports in the literature on formulation of non-aqueous emulsions. This study was designed to evaluate some design criteria for such systems. Formamide is the closest polar solvent that has the ability to replace water in emulsification when employing established non-ionic surfactants as stabilisers. For the majority of studies, linear alkanes (C6-C16) were dispersed in formamide as the continuous phase were stabilised with polysorbate 20. Initial studies involved gentle emulsification and observing mean globule size. The mean globule size varied in a non-linear fashion with alkyl chain length, the minimum being between C10 and C12. Sonication for 30 s led to smaller differences in the mean globule size. The effect of various parameters such as surfactant concentration and solvophilicity of the surfactant was observed. The surface activities of polysorbate 20, 40, 60 and 80 in formamide and critical micellar concentrations were determined. The latter were several orders of magnitude higher in formamide than in water, and the areas per molecule larger. The addition of water to the dodecane formamide systems did not destabilise the emulsion. Release of the model drug dehydroepiandrosterone from dodecane in formamide emulsions was studied in distilled water, the rate of release being dependent on the volume fraction of dodecane.

Interfacial behaviour and micelle formation of novel amphiphilic sequential lipid-lysine oligomers.

As part of work on the design and synthesis of new supramolecular carrier systems for drugs, a series of novel linear oligomers of alternating alpha-amino tetradecanoic acid and lysine having positively charged groups and lipid chains was synthesised. The smallest member of the series (n=2) is insoluble in water and diluted acid solutions, but the larger members are soluble in acid conditions and poorly soluble in alkaline conditions. Hence, in one series, one can conduct experiments both on the determination of micelle formation and spread monolayer behaviour. The surface pressure-area isotherms revealed limiting surface areas at the air/water interface ranged from 0.04 to 0.9 nm(2) according to the oligomer size, and a linear correlation between the observed area per molecule and that projected by computer-generated molecular models was demonstrated. The surface tension of the soluble members in dilute acid solution fell as the concentration of the oligomers was increased, indicating that all of these polymers were surface active with quite clearly defined critical micelle concentrations. The fluorescence intensity ratio of third to first band in the emission spectra of pyrene as a function of the polymer concentrations demonstrated that, even after normalising the data for the amount of lipid chains in the system, the (n=3) oligomer had fewer accessible hydrophobic sites for pyrene, and the forces of the repulsion between the charged head groups was crucial on the formation of micelles, especially in the case of the n=3 oligomer. Supramolecular fibre-like structures were observed in aqueous solution only when n=3 by transmission electron microscopy (TEM). Cryogenic TEM observation of the (n=3) solution also revealed that the micelles might elongate to form long cylindrical or fibrous structures. The diameter of these structures was estimated to be 6.0-13 nm, although their length varied.

Interaction of cationic partial dendrimers with charged and neutral liposomes.

Amphipathic partial dendrimers having three lipidic (C(14)) chains coupled to dendritic lysine head groups with eight, 16 or 32 free terminal amino groups have been synthesised by solid-phase peptide synthesis. Liposomes were prepared with positive, negative and neutral charge using the dehydration-rehydration method and their interaction with the partial dendrimers studied. The interaction efficiency of the partial cationic dendrimers studied was greater than 88%. Interaction of the cationic partial dendrimer converted liposomes with very low or negative charge into positively charged species. Apparent vesicle size increased with the head size of the partial dendrimer but, in the case of negatively charged liposomes, large changes in properties were observed after ultracentrifugation due to the formation of myelin figures. To investigate the mode of interaction with the liposomes, adsorption studies were performed by adding the partial dendrimer after the preparation of dehydration-rehydration vesicles. The results indicated that adsorption is inversely proportional to the head size of the partial dendrimer molecules and the extent of adsorption was similar on both positively and negatively charged liposomes. Adsorption produced liposomes with greater or similar zeta potentials to liposomes that incorporated partial dendrimer through the dehydration-rehydration method. Taking account of the different interaction efficiencies, this suggests there is a degree of partial dendrimer entrappment inside the liposomes.

DNA transfection and transfected cell viability using amphipathic asymmetric dendrimers.

Amphipathic asymmetric dendrimers have been investigated for use in delivery of genes into cells, with the objective of optimising transfection efficiency and maintaining cell viability. We have synthesised amphipathic asymmetric dendrimers by solid phase methods. The ability of two of these to transfect BHK cells in culture with beta-galactosidase gene was determined by X-gal staining. Cell viability was measured by the MTT assay for BHK cells, and by spectroscopy for lysis of erythrocytes. Interactions between dendrimer and DNA were investigated by agarose gel electrophoresis. BHK cells were optimally transfected at 5:1 +/- charge ratio yielding 20% cells receiving at least one copy of the plasmid. Cell viability decreased when the dendrimer to DNA ratio exceeded 5:1. Raising the pH significantly affected the electrophoretic mobility of complexes of dendrimer and DNA. We conclude that amphipathic asymmetric dendrimers enable efficient plasmid DNA uptake into BHK cells. Cell viability is maintained at high concentrations of dendrimer when complexed with DNA at a 5:1 +/- charge ratio. Efficiency of transfection and cell viability suggest the system may be suitable for gene delivery in vivo.

Oral uptake and translocation of a polylysine dendrimer with a lipid surface.

A series of lipidic peptide dendrimers based on lysine with 16 surface alkyl (C(12)) chains has been synthesised in our laboratories. One of the series, a fourth generation dendrimer with a diameter of 2.5 nm was chosen to study its absorption after oral administration to female Sprague-Dawley rats (180 g, 9 weeks old). It was synthesised as the tritiated derivative (all acetyl portions) and had a molecular weight of 6300 and log P (octanol/water) of 1.24. First a single oral dose 14 mg/kg was administered by gavage. Maximum levels of dendrimer observed were 15% in the small intestine, 5% in the large intestine and 3% in the blood at 6 h after administration, while 1.5% reached the liver, 0.1% the spleen and 0. 5% the kidneys. In a parallel study with a higher dose of 28 mg/kg, approximately 1% was absorbed via Peyer's patches of the small intestine at 3 h. The maximum uptake by small intestine enterocytes was 4% of the dose after 3 h. After 12 h, 0.3 and 4% dendrimer was measured respectively in Peyer's patches and enterocytes of the large intestine. When calculated on the basis of target tissue weight, the total percentage of the dose absorbed through Peyer's patches was greater than through normal enterocytes in the small intestine after 3 and 24 h, but the opposite was true in the large intestine. These levels of uptake and translocation are lower than those exhibited by polystyrene particles in the range from 50 to 3000 nm. This might suggest that there is an optimum size for nanoparticulate uptake by the gut.

Distribution of a lipidic 2.5 nm diameter dendrimer carrier after oral administration.

The biodistribution of a lipidic peptide dendrimer has been studied after oral administration to female Sprague-Dawley rats (180 g, 9 weeks old). Uptake by gut epithelial tissue of the radiolabelled dendrimer molecule (mol. wt. 6300; diameter 2.5 nm; log P=1.24) was studied in rats after a single oral dose by gavage (14 mg/kg). The maximum levels of dendrimer observed were 3% (blood), 1.5% (liver), 0.1% (spleen), 0.5% (kidneys), 15% (small intestine) and 5% (large intestine). Approximately 6% of a single administered dose (28 mg/kg) was recovered from the entire gastrointestinal tract while 1% was absorbed via the small intestine lymphoid tissue after 3 h; after 12 h, 0.1% was detected. The maximum uptake by the non-lymphoid small intestine was 4% of the dose after 3 h. After 12 h, 0.3 and 4% dendrimer was measured in the lymphoid large intestine and the non-lymphoid large intestine, respectively. The total percentage of the administered dose absorbed through the lymphoid tissue was comparatively greater than through the non-lymphoid tissue of the small intestine with respect to organ weight after 3 and 24 h.

Synthesis and physicochemical properties of lipophilic polyamide dendrimers.

PURPOSE: To synthesise symmetrical dendritic macromolecules with external lipid surfaces, to investigate their behaviour at the air-water interface and their ability to form supramolecular aggregates, and to gain an understanding of their potential as drug carriers. METHODS: Dendrimeric compounds were synthesised with molecular weights ranging from 737 (1st generation dendrimer) to 25,246 (6th generation dendrimer) with carbon numbers ranging from 40 to 1404. The surface behaviour of these compounds was determined using spread films at the air/water interface on a Langmuir trough, and transmission electron microscopy was used to study the supramolecular aggregates formed by the more hydrophobic members of the series. RESULTS: Dendrimers up to a maximum of 6 generations were synthesised. Surface saturation did not allow the completion of the synthesis of the 7th generation. The limiting surface areas at the air/water interface ranged from 0.4 nm2 to 16.1 nm2 values in good agreement with the areas derived from computer generated molecular models (0.5 nm2 to 14 nm2). CONCLUSIONS: The synthesised dendrimers exhibited a linear relationship between area per molecule and the molecular weight of the compounds. A dendrimer with 16 lipoamino acid branches formed tubular supramolecular aggregates with a helical structure and dimensions in the long axis of 140-200 nm.

Pressurized pack-based liposomes for pulmonary targeting of isoprenaline--development and characterization.

Pressurized packs containing a phospholipid and drug that permits in situ formation of liposomes following deposition of the aerosolized cloud in the respiratory tract have been investigated. Prepared pressure packs and preformed liposomes of different lipoidal contents were characterized for shape, size, lamellarity and percentage drug entrapment. Pressure packs were studied for airway penetration efficiency. The study revealed that pressure packs-derived liposomes containing isoprenaline were fairly comparable with preformed liposomes by the ether injection method. The liposomal charge was found to effect drug disposition. However, drug sustained action was recorded in the case of liposomal inhalation(s) as compared to plain drug inhalation. The pressure packs thus demonstrated therapeutic potentiality in lung targeting of isoprenaline, as well as avoiding the liposome stability problem.