Nanoparticles amorphous

In the range of concentrations observed (from 0.06 to 2.5 pg/ml), the amount of GFP adsorbed on SBA-15 silica material increases linearly increasing the concentration of the GFP solution (Fig. 2), while the amount of GFP adsorbed on Aerosil flattens towards a plateau around 2.5 pg/ml (Fig. 2, inset). All silanol groups accessible on the surface of Aerosil interact with the protein that occupies all the available space, and no more protein can be loaded on the amorphous nanoparticles. 

In Figure 5, the normalized emission spectra of the two solid hybrid materials, GFP/SBA-15 and GFP/Aerosil , are reported. The shape of the emission profile for GFP/SBA-15 follows closely that of the GFP in buffer solution, whereas the photoemission intensity of GFP/Aerosil is one order of magnitude lower and slightly different in its tale shape (spectra at the actual intensities not reported). This reduction in intensity could be explained by a multilayer arrangement of the protein molecules on the amorphous nanoparticles, which would explain both the difference in emission spectra ("self-quenching effect") and the difference in adsorption amount shown above. 

Surfactants are employed in nanoparticle suspensions. Chen et al. (2002) evaluated the pre paration of amorphous nanoparticle suspensions containing cyclosporine A using the evaporative precipitation into aqueous solution (ERAS) system. The effect of particle size was studied varying the drug surfactant ratios, type of surfactants, temperature, drug load, and solvent. Acceptable particle sizes suitable for both oral and parenteral administration were also studied. Additional articles in the nanoparticle delivery of poorly water-soluble drugs include Kipp (2004), Perkins et al. (2000), Young et al. (2000), and Tyner et al. (2004). 

Finally, Mirkin and co-workers (137, 138) used a group of salen-Uke Schiff base ligands [bis(metallotridentate) Schiff base or BMSB] for the synthesis of metaHohgand-based CPs. Initial studies on these CPs were on colloidal nanoparticles of these materials, representing one of the earliest studies on CP or MOF nanoparticles (137, 138). Subsequent investigations showed that these amorphous nanoparticles could be transformed to a crystalline form by modifying the solvent conditions (132). 

In a variation of this theme, the stabilizer used is albumin. This technology results in an amorphous nanoparticle form of the drug coated by albumin, and having a size of about 100-200 nm. Drugs prepared by this technology have been tested by intravenous, intra-arterial, inhalational, oral, and topical administration. In the case of i.v. paclitaxel, the albumin is said to result in an increased and prolonged intracellular availability of the drug. ... 

Gedanken and his group were searching to replace the Ni(CO)4, which was the source for the preparation of nickel, and is known to be a hazardous material. They found [67] a new precursor for the sonochemical preparation of amorphous nickel, Ni(cyclooctadiene)2, which yielded relatively large (200 nm) amorphous nanoparticles composed of nickel and carbon atoms. Small nickel particles were dispersed all over the particle. When these particles were heated slightly above their crystallization temperature, much smaller particles (5 nm) of encapsulated crystalline nickel in amorphous carbon were obtained. The XPS spectrum reveals that the crystallization process is also accompanied by the reduction of the surface Ni+ ions by the amorphous carbon atoms. The DSC measurements substantiate this assumption. 

Another research project leading to the formation of amorphous nanoparticles was undertaken by Zhu s group [185]. The product was synthesized by microwave irradiation heating of an aqueous solution containing ferric chloride, polyethylene... 

In a reactional medium (such as water, for several materials), the competition between dissolution and reprecipitation renders this interpretation more complex. Even though the main ideas remain valid, the first stages of the formation of a crystal may be the coalescence of two fairly large clusters, eliminating water, protons, and OH groups from the surface [2,94]. This step - often referred to as poly condensation [43,100] - has no clear activation energy and may differ significantly from classical nucleation. Hence, a conclusion dictated by conunon sense may hold true in some cases the metastable structure of the nanoparticle comes from a memory of the precursor or, in the case of amorphous nanoparticles, the precursor nanostructure constrains the atoms in positions such that crystallization is impossible. 

Such a reaction of Fe(CO)5 (at 293-363 K, PVP) without ultrasonic radiation proceeds very slowly and only after few days there, a material is formed with very low Fe content (2%, the isolated particles 2-5 nm in size). It is of interest that the sonochemical decomposition of Fe(CO)5 does not proceed in the presence of PVP if THF is used as the solvent, but the reaction is very effective when anisole is used as the solvent and PFO is used as the polymer matrix [93]. A black product formed contains up to 10% (in mass) of the spheric particles of nonoxidized Fe (mainly y-Fe, with little content of a-Fe) with 1-12 nm in size (the mean diameter is 3nm, as shown in Figure 3.7). It is likely that the big particles present the flocks of little ones ( 2-2.5nm). The sonochemical synthesis allows us to produce the functionalized amorphous nanoparticles of ferric oxide with 5-16 nm in diameter [94]. The ultrasonic irradiation in the PFO presence allows us to also produce the stabilized nanoparticles of copper, gold, and so on. In the literature the findings are not about the bimetallic particle formation in the ultrasonic fields by carbonyl metal reduction in the polymer matrices presence (as, for example, in the case of the carbon-supported Pt-Ru from PtRu5C(CO)i6 reduced clusters [95]). 

In Section 9.3.2 it was shown that amorphous nanoparticles of cellulose (ANP) have spherical to elliptical shapes with average diameters of 100 nm, high degree of amorphicity and increased content of sulfonic groups (Table 9.16). 

Table 9.16 Main Features of Amorphous Nanoparticles of Cellulose...

Crystallization of the Si NPs is also affected by the rate of reduction. High reduction rates would produce a fast disordered growth of Si NPs and a poor crystaUiza-tion with abundance of amorphous nanoparticles, while a low rate of reduction would give better crystalline Si NPs. 

However, we have also some other colouristic needs - from a completely different area. Worldwide, 2,400,000 tonnes of salmon are grown annually in wire cages (Fig. 1.5). In order to ensure that fillets from this farmed salmon have the same colour as those from wild salmon, the farmed fish are fed the naturally occurring carotenoid dyestuff astaxanthin, in the form of amorphous nanoparticles, as part of their regular diet. 

A more general and important point is made by Wu et al [223] regarding the calcination step for amorphous nanoparticles. Such heatings generally lead to increase in particle size and the advantage of synthesis in size-controlled water pools of reverse microemulsions is generally lost. These authors therefore justified hydrothermal crystallization under mild conditions. In this process, which is currently in use by other workers as well [224], the (mixed or single) microemulsions are... 

The overview provided above covers the classical perspective on crystallization and particularly nucleation. A rapidly growing body of work shows that this view is not complete. The alternative model for nucleation is often termed the two-step nucleation theory. In brief, this model sng-gests that nucleation is a multistep process where the first step involves phase separation via the formation of liquid or amorphous nanoparticles. This is then followed by crystallization within this particle. The activation energy for each of these steps is relatively small, and it is expected that the overall process would be faster when compared with a single-step (classical) process with the same overall activation energy. Experimental and theoretical evidence supports this mechanism, and it has been suggested that the nucleation process is likely to proceed in this way in most, if not all, cases. ... 

Amorphous Nanoparticles of Amoxicillin Using SAS technology, Kalogiannis et al. produced amorphous nanoparticles of amoxicillin. The crystalline drug was dissolved in dimethysulfoxide (DMSO), or mixtures of DMSO with ethanol or methanol. Partially replacing the DMSO with ethanol or methanol further helped to reduce the particle size (Kalogiannis et al. 2005). 

A1 and PTFE are typically less impact ignition sensitive than A1 combined with other oxidizers. The ductility and malleability of PTFE tend to cushion impact enough to require A1 -H PTFE impact ignition energies almost twice that of intermetallic or metal-metal oxide formulations. Toward this end, studies have examined the influence of carbon additives to sensitize A1 -i- PTFE to impact ignition. Specifically, three forms of carbon additives were investigated and selected based on different physical and structural properties spherically shaped amorphous nanoparticles of carbon. 

An example was reported for hollow spheres composed of calcite rombo-hedra, which where grown on a sacrificial spherical vaterite template particle grown in the presence of PEO-fo-PMAA at an acidic starting pH [61]. Initially, amorphous nanoparticles were formed and stabilized by the DHBC. Subse-... 

Fig. 27 Top SEM images of CaCOs particles grown on a glass slip in the early reaction stage, PEO-6-PMAA, [CaCb] = 10 mM, lgL , 5h. a CaCOs particles with either spherical or hollow structures, b Zoom showing the calcite rhombohedral subunits grown on the surface of the hollow structure and the inner part consisting of tiny primary nanocrystals with a grain size of about 320 nm as indicated by the arrow (sacrificial vaterite template). Bottom Proposed formation mechanism of the calcite hollow spheres a polymer-stabilized amorphous nanoparticles b Formation of spherical vaterite precursors c aggregation of the vaterite nanoparticles d vaterite-calcite transformation starting on the outer sphere of the particles e formation of calcite hollow spheres under consumption of the sacrificial vaterite precursors. Reproduced in part from [61] with permission of the American Chemical Society...

Doped amorphous Fe203 nanoparticles were prepared by irradiating the mixture of amorphous Fe20s nanoparticles [360] and Mn2(CO)io in 40 mL of decahydronaphthalene with a high-intensity ultrasonic horn under ambient conditions for 2 h. The resulting product was separated by centrifuge, washed thoroughly with dry pentane, and dried under vacuum. The as-prepared amorphous nanoparticles were then crystallized in a tube furnace under air. 

The IR spectra of the as-prepared nanoparticles and nanocubes are shown in Fig. 9.22. The peaks at 2856, 2928, and 2962 cm" were assigned to the antisymmetric stretches, symmetric methylene stretches (Vas(CH2), Vs(CH2)), and antisymmetric methyl stretches (Vas (CH3)) of l-methyl-3-octylimidazolium cations. The peak at 1465 cm" was assigned to ring in-plane asymmetry stretches and CH3 (N) stretches. These results identified the presence of alkylimidazolium cations on the surfaces of the amorphous nanoparticles and the nanocubes. 

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