Silica surface grafting

The express method of phenolic compounds determination was designed. It is based on heterogeneous azo-coupling reaction of phenols, which different extracts of fresh raw material contain, with aryldiazonium salts grafted on the silica surface. We can carry out phenols analysis on-site, as formation of immobilized azocompounds leads to a drastic change in the sorbent s color. Thus, we pui pose a new method, that allows to indicate herb phenols in aqueous and non-aqueous medias and to compare it with a well-known Folin-Ciocalteau method. 

For chromatographic sorbents it is necessary that the polymeric cover be uniformly distributed over the silica surface and chemically coupled to it. The appropriate introduction of the initiator is one of the decisive steps of this task. The first method (binding to the surface) increases the yield of grafted polymer. However in this case a large amount of homopolymer is formed. This disadvantage could be prevented by the application of hydroperoxide initiators in combination with the proper redox-agents [78-81],... 

Although open tubular columns have been used for RPLC,42 most applications use packed columns. The most widely used column packings are formed by chemically bonding butyl (C4), octyl (C8), or octadecyl (C18) chains to a silica surface. Phenyl (Ph), cyano (CN), and amino (NH2) functionalities are also used. Polymeric packings which are finding broad acceptance include alkyl-grafted poly(methylmethacrylate) and alkyl-grafted or unmodified... 

Triflic acid has also been supported on a porous silica carrier (220). The authors emphasized the importance of a strong interaction between the acid and the support to prevent leaching of the acid. In pulsed liquid-phase isobutane/ 1-butene alkylation experiments at 298 K, the catalysts produced a very high-quality alkylate, made up almost exclusively of isooctanes. With silanol groups on the silica surface or with added water, triflic acid was found to form a monohydrate that was firmly grafted to the silica surface. 

Only few studies addressed the effect of the silica surface concentration of glycopeptides antibiotics on the chiral performances. The first was performed by Armstrong on a TE CSP toward five racemic test solutes [30]. The study evidenced a modest increase of a and Rs values with increasing the initial selector concentration in the grafting reaction mixture, but no data were reported regarding the effective... 

Ansarian, H.R., Derakhshan, M., Rahman, M.M., Saknrai, T., Takafnji, M., Tanigu-chi, I., and Ihara, H., Evalnation of microstructuralfeatnres of a new polymeric organic stationary-phase grafted on silica surface a paradigm of characterization of HPLC-stationary phases by a combination of suspension-state H-1 NMR and solid-state C-13-CP/MAS-NMR, Anal. Chim. Acta, 547,179, 2005. 

Scheme 8.2 Surface-grafting of N,N-dipyrid-2-ylnorborn-2-en-5-ylcarbamide on silica.

Scheme S.3 Surface grafting of 4 -(norborn-2-en-5-ylmethylenoxy)terpyridine on silica.

Park s group has explored hyperbranched graft chemistry of aziridine on amine functionalized silica surfaces (Eqs. 18 and 19) [74]. Using silicon and silica substrates that have been functionalized with (3-aminopropyl)dieth-oxymethylsilane as initiator substrates, hyperbranched polyethyleneimine grafts were synthesized using aziridine monomers. 

The fact that silsesquioxane molecules like 2-7 contain covalently bonded reactive functionalities make them promising monomers for polymerization reactions or for grafting these monomers to polymer chains. In recent years this has been the basis for the development of novel hybrid materials, which offer a variety of useful properties. This area of applied silsesquioxane chemistry has been largely developed by Lichtenhan et al With respect to catalysis research, the chemistry of metallasilsesquioxanes also receives considerable current interest. As mentioned above, incompletely condensed silsesquioxanes of the type R7Si70g(0H)3 (2-7, Scheme 4) share astonishing structural similarities with p-tridymite and p-cristobalite and are thus quite realistic models for the silanol sites on silica surfaces. Metal... 

The functionalization of silica with PPM and the subsequent immobilization of [Rh(COD)2]BF4 has been achieved by Pugin and Blaser [49]. The PPM ligand was immobilized by grafting the linker, 3-trimethoxysilylpropyl isocyanate, to the silica surface (the silicas used include Grace 332, Merck 100, Merck 60, Merck 40). The isocyanate moiety then reacts with the amine functionality of the PPM ligand to afford an amide linkage (35, Figure 5.17). Introduction of a solution of [Rh(COD)2]... 

---