Mesoporous silicas groups

Recently very reacdve solid bases have been devised, which are prepared by derivadzadon of amorphous silica and hexagonal mesoporous silica fHMSi v/ith the dimethylaminopropyl group fEq 4 113 ... 

Nucleic acids, DNA and RNA, are attractive biopolymers that can be used for biomedical applications [175,176], nanostructure fabrication [177,178], computing [179,180], and materials for electron-conduction [181,182]. Immobilization of DNA and RNA in well-defined nanostructures would be one of the most unique subjects in current nanotechnology. Unfortunately, a silica surface cannot usually adsorb duplex DNA in aqueous solution due to the electrostatic repulsion between the silica surface and polyanionic DNA. However, Fujiwara et al. recently found that duplex DNA in protonated phosphoric acid form can adsorb on mesoporous silicates, even in low-salt aqueous solution [183]. The DNA adsorption behavior depended much on the pore size of the mesoporous silica. Plausible models of DNA accommodation in mesopore silica channels are depicted in Figure 4.20. Inclusion of duplex DNA in mesoporous silicates with larger pores, around 3.8 nm diameter, would be accompanied by the formation of four water monolayers on the silica surface of the mesoporous inner channel (Figure 4.20A), where sufficient quantities of Si—OH groups remained after solvent extraction of the template (not by calcination). 

Similarly, Hg(n) binding to thiol-functionalized mesoporous silica for which effective access to all the binding sites (100% of SH groups com-plexed with Hg(n) was achieved in micelle-templated mesostructures with pore diameters larger than 2.0 nm, whereas incomplete filling was always observed with corresponding amorphous silica-based adsorbents.37... 

The silica networks of mesoporous sihcas are terminated at the surfaces of the amorphous pore walls, thus resulting in terminal silanol groups on the walls. The density of the silanol groups of all mesoporous sihcas (1 to 3 nm 2) is somewhat lower than usually found for other typical silica materials (4 to 6 nm 2) [27], The specific surface areas of the different mesoporous silicas vary depending on their pore sizes, the thicknesses of their pore walls, and the density of their sihca networks. For some MCM-41- and MCM-48-type materials, surface areas of about 1000 to 1400 m2 g 1 have been reported. The surface areas of SBA-15-type materials can be > 600 m2 g 1 [27],... 

Figure 2. Scheme illustrating (A) amine-silanol and (B) amine-amine interactions and (C) single site or site-isolated 3-aminopropyl groups grafted onto mesoporous silica [20]. 

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