Organically modified silica

Furthermore, the same sol-gel matrices have been used in a system where acid and base catalysis occur in the same pot without quenching either catalyst [29]. In this case, the acids were either entrapped Nafion (perfluorinated resin sulfonic super acid, a3) or entrapped molybdic acid (M03-Si02, a2), while the bases were two ORMOSILs (organically modified silica sol-gel materials), one with H2N (CH2)2NH(CH2)3 groups (bi) and the other guanidine base residues (b2) (Scheme 5.12). 

An example of the appropriate application of organically-modified silica precursors is alkoxides with an alkyl group. When methyltrimethoxy- or methyl-triethoxysilane (Figure 3.2) was added in formulations to increase the hydro-phobicity of ORMOSILs, it resulted in a better enzymatic activity of lipases immobilized in the alkyl-modified silica than in a hydrophilic matrix fabricated by means ofTEOS alone [51,80,129-133]. Similarly, an increased stability of lipase from Candida antarctica B was observed after its immobilization in a silica matrix... 

Organically-modified silica precursors have three alkoxy groups. As a result, alcohol is separated after the hydrolysis. Its appearance causes a detrimental effect on biopolymers typical to that ofalkoxides. The next disadvantage of these precursors is the absence of universality. They are appropriate only in particular cases. 

Ferrer, M.L., Yuste, L., Rojo, F. and Del Monte, F. (2003) Biocompatible sol-gel route for encapsulation of living bacteria in organically modified silica matrixes. Chemistry of Materials 15, 3614-3618. 

Roy, I., Ohulchanskyy, T.Y., Bharali, D.J., Pudavar, H.E., Mistretta, R.A., Kaur, N. and Prasad, P.N. (2005) Organically modified silica nanoparticles A non-viral vector for in-vivo gene delivery and expression. Proceedings of the National Academy of Sciences of the United States of America, 102, 11539-11544. 

On the basis of the sol-gel process, much more attention has been paid to silicate-containing Class II hybrids, also referred to as organically modified silicas, ormosils. In this section, the synthesis of some of the most characteristic ormosils for bone and dental applications are described. 

Fu, L., Ferreira, R.A.S., Nobre, S.S., Carlos, L.D., and Rocha, J. (2006) Organically modified silica-based xerogels derived from 3-aminopropyltrimethoxysilane and 3-isocyanatepropyltriethoxysilane through carboxylic acid solvolysis. Mater. Sci. Forum 514-516, 108-112. 

Counter to intuition that would exclude non-conductive glassy materials from the field of electrochemistry, organically modified silica-based materials have a rich and varied electrochemistry39 made possible by the accessible inner porosity. This allows oxidant and reducing reactant molecules to diffuse through the material and eventually to the surface either of a conducting electrode or of a conductive material (Figure 1.18). 

Organically modified silica nanoparticles a nonviral vector for in vivo gene delivery and expression in the brain, Proc. Natl. Acad. Sci. USA, 2005, 102, 11539. 

I. Roy, T. Y. Ohulchanskyy, D. J. Bharali, H. E. Pudavar, R. A. Mistretta, N. Kaur and P. N. Prasad, Optical tracking of organically modified silica nanoparticles as DNA carriers a nonviral, nanomedicine approach for gene delivery, Proc. Natl. Acad. Sci. USA, 2005, 102, 279. 

Kim S, Pudavar FIE, Prasad PN (2006) Dye-concentrated organically modified silica nanoparticles as a ratiometric fluorescent pH probe by one- and two-photon excitation. Chem Commun (Camb) 19 2071-2073... 

Finally, some hybrid inorganic-organic materials such as Ormosil (=Organically modified silica) are also very popular. The structure and properties of Ormosils resemble those of silica and organic polymers. 

Fig. 1 Chemical structures of the polymers commonly used for preparation of beads poly (styrene-co-maleic acid) (=PS-MA) poly(methyl methacrylate-co-methacrylic acid) (=PMMA-MA) poly(acrylonitrile-co-acrylic acid) (=PAN-AA) polyvinylchloride (=PVC) polysulfone (=PSulf) ethylcellulose (=EC) cellulose acetate (=CAc) polyacrylamide (=PAAm) poly(sty-rene-Wocfc-vinylpyrrolidone) (=PS-PVP) and Organically modified silica (=Ormosil). PS-MA is commercially available as an anhydride and negative charges on the bead surface are generated during preparation of the beads...

Note 1 Organically modified silicas can be obtained by sol-gel processing. 

Note 3 Though it is a commonly used acronym for organically modified silica, OrmosiF is a trademark and as such its terminological use is discouraged. 

Figure 8 Preparation of organically modified silicas via sol-gel methodology...

There are four major functions of amino groups attached to organically modified silica gels ... 

FIGURE 4. Schematic pathway of the elaboration of mesoporous organically modified silica by surfactant templating and micelle formation... 

Chemistry and Properties of Porous, Organically Modified Silica... 

Sol-gel techniques were used to prepare porous, organically modified silica materials. The introduction of organic groupings was carried out with alkoxysilanes as precursors methyl and propyl amino groups were used. The results show that high-porosity materials can be synthesized the microstructure strongly depends on reaction conditions such as composition, solvent, catalyst type, and concentration. Microstructure tailoring affects mechanical as well as adsorption properties, and custom-made materials such as abrasives and adsorbents with special properties were synthesized. 

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