Silica functionalized with biomolecules

We showed that these mesoporous silica materials, with variable pore sizes and susceptible surface areas for functionalization, can be utilized as good separation devices and immobilization for biomolecules, where the ones are sequestered and released depending on their size and charge, within the channels. Mesoporous silica with large-pore-size stmctures, are best suited for this purpose, since more molecules can be immobilized and the large porosity of the materials provide better access for the substrates to the immobilized molecules. The mechanism of bimolecular adsorption in the mesopore channels was suggested to be ionic interaction. On the first stage on the way of creation of chemical sensors on the basis of functionalized mesoporous silica materials for selective determination of herbicide in an environment was conducted research of sorption activity number of such materials in relation to 2,4-D. 

The ion-exchangers used in LC consist either of an organic polymer with ionic functional groups, or silica coated with an organic polymer with ionic functional groups. The types of functional groups used are the same as described in Chapter 18. Since IEC can be carried out with an aqueous mobile phase near physiological conditions, it is an important technique in the purification of sensitive biomolecules such as proteins. 

IUPAC classification, mesoporous materials are defined as porous materials with diameters in the range 2-50 nm, which is rather dose to the dimensions of functional biomolecules such as proteins. Therefore, unexplored phenomena and functions could be observed for biomolecules confined in mesopore channels due to their restricted motion and orientation. In this chapter, we briefly introduce recent developments on the immobilization of biomolecules in mesoporous media, where the use of mesoporous silica and mesoporous carbon are mainly discussed. 

Template synthesized silica nanotubes (SNTs) provide unique features such as end functionalization to control drug release, inner voids for loading biomolecules, and distinctive inner and outer surfaces that can be differentially functionalized for targeting and biocompatibility.50 A general path to synthesize nanotubes utilizes anisotropic materials as template. They are coated with silica using Si(OR)4 precursors and nanotubes of Si02 are obtained after removal of the template (Figure 1.24). 

In many cases, silicon organic compounds are used as connecting links between a silica surface and a biomolecule. The most popular technique utilizes the modification of a hydroxy-functionalized surface with 3-aminopropyltriethoxysilane (APTES) [2] followed by crosslinking with glutaraldehyde (GA) (Fig. 1 A). 

We have synthesized aldehyde-functionalized silanes as a new class of spacer molecules for silica surfaces. The aldehyde group can be used to attach biomolecules directly to the surface, with no bifunctional crosslinking species required (Fig. IB) [3]. As many immobilization problems are closely related to the use of the crosslinking agent (e.g., glutaraldehyde tends to form undesirable polymers) [4], the development of a one-step immobilization method is a significant improvement. 

Silica gel may also be modified with hydrophilic groups that are attached using short-chain nonpolar spacers. Hydrophilic modifications with polar groups include amino, cyano, and diol functionalities. Amino-SG offers weakly basic ion-exchange properties diol-SG considerably less affinity for water when compared with unmodified SG-60. These HPTLC materials offer increased selectivity for complex separations of biomolecules and drugs. 

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