Silica with organic molecules

Low temperature sol-gel technology is promising approach for preparation of modified with organic molecules silica (SG) thin films. Such films are perspective as sensitive elements of optical sensors. Incorporation of polyelectrolytes into SG sol gives the possibility to obtain composite films with ion-exchange properties. The addition of non-ionic surfactants as template agents into SG sol results formation of ordered mechanically stable materials with tunable pore size. 

Silica nanoparticles are commonly prepared by polymerization of appropriate precursors such as silicates, silicon alkoxides, or chlorides (Fig. 11.2).2 Besides the industrial methods, which rely mainly on condensation of sodium silicate in water induced by sodium removal through ion exchange, three different synthetic methods are currently used in research labs to prepare silica nanoparticles loaded with organic molecules. In the first method, proposed by Kolbe in 1956s and developed by Stober and coworkers in the late 1960s,6 the particles are formed via hydrolysis and... 

Table 23.2 Comparison of POSS densities with those of inorganic silica and organic molecules.

The preparation of silica spheres (Scheme 8.1) is straightforward [16], self-assembly of the spheres is well developed [17], and the pore size in the crystals can be readily controlled by selecting the sphere size (the distance from the center of the nanopore projection to the nearest silica sphere surface is 15% of the sphere radius). Surface silanol groups can be directly modified by nucleophilic silylation to introduce a variety of functional groups [18]. Alternatively, silica surface can be first modified with 3-aminopropyltriethoxysilane (Scheme 8.1), followed by treatment with organic molecules carrying electrophilic moieties such as acyl chloride, isocyanate, isothiocyanate, carboxylic acid, sulfonyl chloride [19], or succinimidyl ester [20]. 

The X-band measurements cannot identify which one of the iron sites can react with the carotenoid. Only the 95 GHz measurements (Figure 9.14) were able to demonstrate that adsorption of carotenoid results in a significant decrease of the =2.07 signal and moderate decrease of the =2.45 signal, while the intensity of the narrow line with ,= ->,=2.003, gz= 1.999 is almost unaffected. The results show that the extra-framework Fe3+ ions located on the surface of the pore are primarily responsible for carotenoid oxidation. Probably, these sites are more accessible for bulky organic molecules than the framework iron within silica walls. 

Nanoparticles such as those of the heavy metals, like cadmium selenide, cadmium sulfide, lead sulfide, and cadmium telluride are potentially toxic [14,15]. The possible mechanisms by which nanoparticles cause toxicity inside cells are schematically shown in Fig. 2. They need to be coated or capped with low toxicity or nontoxic organic molecules or polymers (e.g., PEG) or with inorganic layers (e.g., ZnS and silica) for most of the biomedical applications. In fact, many biomedical imaging and detection applications of QDs encapsulated by complex molecules do not exhibit noticeable toxic effects [16]. One report shows that the tumor cells labeled with QDs survived in circulation and extravasated into tissues... 

Figure 1.1 A silica sol precursor doped with a coloured organic molecule.

In 1985, Aronovitch and Mazur [28] reported that irradiation of several organic molecules absorbed on a heterogeneous reaction matrix (silica gel, neutral, acidic, or basic alumina, and Florisil) with 350 nm light in the presence of oxygen re-... 

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