Nanometal water-soluble

Using long-chain alkylsulfobetaines as the stabilizer, a number of highly water soluble nanometal colloids have been isolated in excellent yields (see Figure 8). The core particle size can be tailored between 1 and 10 nm. TEM examinations have shown that the resulting materials are generally mono-disperse. Further, a combination of spectroscopic methods confirmed the zerovalent nature of the metal cores [200]. 

As alternatives to amphiphilic betaines, a wide range of cationic, anionic, and non-ionic surfactants including environmentally benign sugar soaps have been successfully used as colloidal stabilizers [201]. Electrochemical reduction of the metal salts provides a very clean access to water soluble nanometal colloids [192]. 

PVP, a water soluble amine-based pol5mer, was found to be an optimum protective agent because the reduction of noble metal salts by polyols in the presence of other surfactants often resulted in non-homogenous colloidal dispersions. PVP was the first material to be used for generating silver and silver-palladium stabilized particles by the polyol method [231-233]. By reducing the precur-sor/PVP ratio, it is even possible to reduce the size of the metal particles to few nanometers. These colloidal particles are isolable but surface contaminations are easily recognized because samples washed with the solvent and dried in the air are subsquently not any more pyrophoric [231,234 236]. 

Generally the smaller the molecule the more easily it will be taken up. Molecular weights below 500 are favorable for absorption molecular weights in the 1000s do not favor absorption. Generally solids have to dissolve before they can be absorbed. It is possible for small amounts of particles in the nanometer size range to be taken up by pinocytosis. The absorption of very large particles, several hundreds of micrometers in diameter, that are administered dry (e.g., in the diet) or in a suspension may be reduced because of the time taken for the particle to dissolve. This would be particularly relevant for poorly water-soluble substances. 

This concept has found expression in a proprietary nanoparticle technology in which a drug is reduced to nanometer-size particles in the presence of stabilizers. Originally developed for IV computer imaging, this technology shows considerable promise to increase absorption of poorly water soluble compounds. As the nanoparticle system is purely formulation in nature, it is unlikely to affect GI mucosal integrity. Nanoparticles are sufficiently small that they can be used parenterally, apparently without ill effects. More is... 

Shapes of vesicular aggregates range from tubular to spherical, from more exotic large compound (LCV) and starfish vesicles to simpler extended lamellae. Both unilamellar [75] and multilamellar ( onions ) [47,76] vesicles have been observed. One of the possible morphologies formed in solution are tubular vesicles, also known as tubes (rods) [77,78], Soft, water-filled polymer tubes of nanometer-range diameters and several tens of millimeters in length have been prepared via self-assembly of amphiphilic ABA triblock copolymer in aqueous media (Fig. 4). The tubes were mechanically and chemically stable and could be loaded with water-soluble substances [23],... 

Reversed micelles are defined as small aggregates formed by surfactant molecules surrounding a water core of a well-defined nanometer size. Potentially, the water droplets in the microemulsion may be considered as reaction media, microreactors, for the synthesis of particles. Reactants are confined within such dispersed droplets, provided that water-soluble precursors are used. ... 

Figure 4. Solubility Sa of amorphous silica in water V5. particle size. Key d, particle diameter in nanometers Si, solubility of particle of infinite diameter, assumed to be 70 ppm E, ergs/cm 298 K and logiofsa/SJ = 5.7 E/Td.

A broad variety of hydrophilic surfactants may also be used as alternatives to amphiphilic sulfobetaines. Isolable nanometal colloids soluble in water with at least 100 mg of metal 1 have been obtained with a wide range of cationic, anionic, and nonionic surfactants. Even, environmentally benign sugar soaps have been successfully applied [see Table 2 in Ref. [11]]. 

In a variation of the above process, a water soluble monomer A is adsorbed on water-immiscible solvent droplets dispersed in the aqueous solution of A and then polymerized to form closed shell structure. For example, cross-linked polysaccharide capsules with diameters ranging from 200 nm to several microns and wall thicknesses of several tens of nanometers have been fabricated by interfacial polymerization of methacrylated N,N-diethylaminoethyl dextran (DdexMA) [212]. In a typical method of preparation of DdexMA (see Figure 5.85), a mixture of N,N-diethylaminoethyl dextran (Ddex),... 

FIGURE 54.23 A schematic representation of inverse miniemulsion or microemulsion polymerization for the preparation of nanometer-sized particles of water-soluble and water-swellable polymers as well as cross-linked particles in the presence of cross-linkers. (Reprinted from Polymer, 50(19), Oh, J.K., Bencherif, S.A., and Matyjaszewski, K., Atom transfer radical polymerization in inverse miniemulsion A versatile route toward preparation and functionalization of microgels/nanogels for targeted drug delivery applications, 4407-4423. Copyright 2009, with permission from Elsevier.)... 

Micelles are composed of amphiphilic block copolymers that self-assemble into spherical shapes of nanometer diameter due to energy minimization with the surrounding solvent. When exposed to a hydrophilic solvent the hydrophilic domains orient toward the solvent, while the hydrophobic domains orient toward the core and form a clump away from the solvent. In a similar manner, when amphiphilic molecules are exposed to a hydrophobic solvent they form micelles with a hydrophobic block on the surface and a hydrophilic block in the core. Micelles thus have a unique core-shell architecture composed of either hydrophobic or hydrophilic blocks depending on the chemical structures and the medium. The hydrophobic or hydrophilic core provides a reservoir for water-soluble or insoluble drugs and protects them from decomposition in order to maintain activity and stability. Stearic acid (SA)-grafted chitosan oligosaccharide (CSO-SA) formed... 

The emulsion process allows the production of particles with a diameter in the nanometer range (10-10 nm). The monomer is dispersed in water with a water-soluble initiator and a surfactant which forms uniform micelles. Polymerization occurs inside micelles, in which the monomer is able to diffuse, because the initiator is not miscible in the dispersed monomer phase. 

Polymers can be effective stabilisers of NPs through electronic and steric effects. Dendrimers are highly branched polymers only a few nanometers in diameter. Dendrimers are defined by a central core, interior polymeric branches and an exterior functionalized surface. Their uniform size, dispersity and water solubility (due to outer hydrophilic and metal encapsulating functional groups) make them ideal candidates as polymeric stabilizers for NP catalysed cross-coupling reactions. The encapsulated NPs are primarily eonfined sterically... 

While not strictly considered emulsions, two other systems may be classified in this category, both of which comprise very small particles of silicone fluids in aqueous dispersions. The first method of preparing these microdroplets involves in situ polymerization of a water-soluble vinyl monomer or mixtures of said monomer and acryl comonomers. The silicone fluids are first dispersed into microdroplets in the water phase by means of high-speed agitation and then the vinyl monomers or cationic polymers are added at elevated temperatures in the presence of free-radical catalysts. The resulting aqueous polymer matrix contains stable, discreet microdroplets of the silicone fluids. The second method utilized to prepare such a fine dispersion is very-high-pressure injection of silicone into the aqueous phase. These microdroplets have been referred to as nanoparticles, but they are actually nanometer-sized fluid droplets as opposed to nanometer-sized sihcone resin particles, which are referred to by the same term (86). Both of the systems described above have been claimed to readily deposit onto hair and skin, and to increase ease of formulation (87,88). 

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