Silica chemically modified

The silanol group can be esterified with an alcohol, ROH, where R may be an alkyl or any other functional group. For steric reasons, reaction is confined to the silica 

Esterified silica is prone to hydrolysis and so cannot be used with mobile phases containing water or alcohol, products with Si- O—Si C bonds generally being preferred. 

Reaction with thionyl chloride SOCE produces chlorides which combine with 

Silicas in which the functional group is bonded by an Si—O—Si—C bond (reaction with mono- or dichlorosilane) are the most stable of all. 

Octadecylsilane ODS, in which R = —(CH2)i7CH3, is the most widely used of these chemically modified products. It is extremely nonpolar and is the preferred choice for use in reversed-phase chromatography. 

Reaction with thionyl chloride SOCI2 produces chlorides which combine with amines to give an Si-N bond. R can be chosen at random. These products have better hydrolytic stability. 

---

It was shown that X-Ray-fluorescence method do possible to separate metals in the multycomponents samples by different methods of synthesis chemical modified silica and different ways of coordination of ion metals on the surface. 

The most widely used columns contain a chemically modified silica stationary phase, with the chemical modification determining the polarity of the column. A... 

Nonmodified silica gel is used most commonly for the separation of substances of medical interest. The separation is based on the interactions (hydrogen bonding, van der Waals forces, and ionic bonding) between the molecules of drugs, lipids, bile acids, etc., and the silica gel. Alumina has similar properties but is rarely used. Successful separation of endogenous substances, drugs, or their metabolites can also be achieved using physically or chemically modified silica gel. 

Stahlberg, J. and Almgren, M., Polarity of chemically modified silica surfaces and its dependence on mobile-phase composition by fluorescence spectrometry, Anal. Chem., 57, 817, 1985. 

Stahlberg, J., Almgren, M., and Alsins, J., Mobility of pyrene on chemically modified silica surfaces, AnaZ. Chem., 60, 2487, 1988. 

From the data presented in Table 4 it may be concluded that the porous nature of the chemically modified silica remains more or less the same after immobilization of the cobalt(lll) complexes. In addition, there is a decrease in the surface area of the support following the incorporation of the metal complexes. The AAS data on Co(III)-CMS2 and Co(lll)-CMS3 appear to suggest that the extent of cobalt loading is dependent upon the initial amount of cobalt used. The cobalt loadings obtained for the catalysts prepared by H2O2 oxidation of CMS suspensions in 1 and 2 mmol cobalt(ll) solutions (in presence of 1 and 2... 

Cadogan, D. F., Sawyer, D. F. Gas-solid chromatographic using various thermally activated and chemically modified silicas. Anal. Chem. 42, 190 (1970). 

The procedures used for the chemical modification of silica, will be discussed using these criteria. This survey is restricted to the preparation of chemically modified silicas, used as a base material in the above-cited applications. Procedures are ordered according to the possibility to control the ultimately formed layer. 

Silica gel 60, the most versatile and most frequently used TLC sorbent, was taken as a basis. The mean particle size of this sorbent was optimized simultaneously, the particle size distribution was brought to within as narrow limits as possible (L- ) The sorbent material thus obtained was used t prepare HPTLC pre-coated plates silica gel 60, being followed subsequently by the development of other sorbents for processing into HPTLC pre-coated layers. The materials chosen were largely "reversed phase" sorbents, that is to say, chemically modified silica gels with a non-polar surface (, 8), as well as microcrystalline cellulose ( )""... 

Keywords porous copolymers, divinylbenzene, styrene, methacrylic monomers, chemically modified silicas, fillers... 

Chemically modified silica fillers with grafted methyl groups or methyl and silicon hydride groups, influenced the micro- and macrostructures of various copolymers. Changes in cross-linking, orderliness, crystallinity, microtacticity and conformation of macromolecules have been detected in the presence of fillers. Surface functionality of the silica filler determines the disposition of macromolecular chains at the interface. 

By interaction of calculated amounts of pretreated at 600 °C (10 torr) silica with (EtO)2Si(CH2)2N[PR2]2 in boiling benzene there was obtained chemically modified silica containing N[PR2]2 group, characterized by significant electron-donor capability. 

The suggested method of preparation of chemically modified silica helps us to obtain support, which contains the similar compounds and avoids the influence of the steric factors, because the preliminarily prepared modifier immobilizes on the surface of support. The obtained data have most important theoretical and practical significance, and as suggested in the literature [7], the phosphining of amino groups contained in chemically... 

Sol-gel matrices can also provide a chemical surrounding that favors enzymatic reactions. Lipases act on ester bonds and are able to hydrolyze fats and oils into fatty acids and glycerol. These are interphase-active enzymes with lipophilic domains and the catalytic times reaction occurs at the water-lipid interface. Entrapped lipases can be almost 100 times more active when a chemically modified silica matrix is used. The cohydrolysis of Si(OMe)4 and RSi(OMe)3 precursors provides alkyl groups that offer a lipophihc environment that can interact with the active site of Upases and increase their catalytic activity. Such entrapped lipases are now commercially available and offer new possibilities for organic syntheses, food industry, and oil processing. ... 

As we mentioned above, chemically modified silica always retains a significant amount of residual silanols. In fact, at least half of the original silanols on the silica surface remain unreacted after chemical modification. Silanols have acidic nature, but their ionization constants are highly dependent on the surface environment and on sihca purity. SUanol pK is estimated to be between 5 and 7 [7]. 

---