Immobilization water insoluble matrices

In recent years a large number of techniques have been suggested in the literature for immobilizing enzymes on insoluble carriers in particular, immobilization on polymeric solid supports or glass beads. A stable attachment can result from ionic binding, cross-linking and covalent linking to a water-insoluble matrix. A full description of chemical and/or physical procedures required to make enzymes insoluble is beyond the scope of this chapter and is extensively dealt with elsewhere.112 113... 

However, irrespective of all these impressing practical achievements, the affinity chromatography concept - i.e. the highly specific binding of the target molecule to a ligand covalently immobilized onto a solid support, followed by washing of the contaminants prior to elution with an appropriate buffer-theoretically has limitations inherent to the use of a water-insoluble matrix ... 

The polymer has the function to retain the indicator in place so that no leaching into e.g. aqueous sample solution occurs. This can be achieved by covalently immobilizing the dye to the matrix but also by simply dissolving a hydrophobic and water-insoluble dye in a hydrophobic polymer. 

An unusual type of derivative is the complex that forms between urease and bentonite in acid medium (61). The adsorbed form was found catalytically active. Similarly, urease immobilized in a polyacrylamide gel matrix has been used to prepare a urea-specific enzyme electrode (62). Yet another active water-insoluble derivative has been prepared (63) by allowing p-chloromercuribenzoate-treated urease to react with a diazotized copolymer of p-amino-D,L-Phe and L-Leu. Urease has been found to retain about 20% of its original activity when encapsulated in 100 n microcapsules of benzalkonium-heparin in collodion (64). 

Since most enzymes are globular protein, they are soluble in water. Therefore, it is very difficult or impractical to separate the enzyme for reuse in a batch process. Enzymes can be immobilized on the surface of or inside of an insoluble matrix either by chemical or physical methods. They can be also immobilized in their soluble forms by retaining them ivith a semipermeable membrane. 

Shamby et al. described a surface finish that consists of a water-insoluble composite of silver bromide nanoparticles and poly(4-vinylpyridinium) salts. Again, silver is released and the quarternary ammonium groups kill on contact [139], Gyomard et al. incorporated the natural antimicrobial peptide gramicidin A into a LbL matrix and were able to show, that the peptide kills Enterococcus faecalis in the surroundings when released and on the surface in immobilized form [140], It is also possible that the antimicrobial a-poly-L-lysine in the LbL layer helped a little. 

The reuse of an enzyme can be economically favorable when a high-cost enzyme is used. It can be difficult to separate and reuse an enzyme because enzymes are typically globular proteins that are highly soluble in water. A common technique to facilitate the reuse of a high-value enzyme is to immobilize the enzyme onto a surface, inside of an insoluble matrix or within a semipermeable membrane. Both chemical and physical means can be employed to immobilize enzymes. The former method involves the covalent attachment of enzymes to water-insoluble supports and is the most widely used method for enzyme immobilization. ... 

The ASTM procedure determines an ability of microbes to stick to the surface of polymeric materials (containing incorporated biocides) and continue to inhabit it. The same procedure can be applicable to composite materials. Clearly, if the composite contains biocide, which diffuses to the surface, it would diminish microbial colonies on the surface. If, on the contrary, biocide is firmly immobilized within the matrix (e.g., if it is practically water-insoluble and does not move to the surface), it would not prevent microbial staining. Obviously, a biocide should not be too water-soluble and promptly leached out of the material, and it should not be practically irreversibly bound within the matrix. Actually, if the biocide quickly leaves the matrix, such as wet deck boards, the ASTM procedure would also be helpful in determining this fact. 

In this article, we describe the preparation and use of amperometric electrodes for sensing the analytically significant substrate glucose based on a PEG-modified glucose oxidase (GOD) (4,5) and on a lipid-modified GOD (6). The PEG-modified GOD has been incorporated into a carbon paste (CP) electrode the modified enzyme exhibits higher activity in a hydrophobic CP matrix than hydrophilic, native GOD (7-10). The lipid-modified GOD has been immobilized on a glassy carbon (GC) electrode with a thin Nafion overcoat. The water-insoluble modified enzyme is far more stable between the electrode surface and the polymer layer than native GOD (77). 

Modification of GOD with PEG was effective for enhancing the affinity of the enzyme for a hydrophobic CP matrix. A water-insoluble, lipid-modified GOD could be immobilized on the GC electrode surface far more ti tly than the native enzyme. These modifiers produced high performance characteristics for GOD-based electrc s. 

Curdlan is a microbial polysaccharide that occurs naturally as a linear (triple-helix) polysaccharide composed of 1,3-P-hnked D-glucose units, produced by a strain of Mcaligenes faecalis (Figure 2.38). It is a neutral, bacterial polysaccharide without branched chains. It is insoluble in water and alcohol but soluble in alkaline solution and dimethyl sulfoxide (DMSO) [274-276]. It occurs as a tasteless powder, stable in dry state. It was reported as a support matrix for enzyme immobilization, through activation with epichlorohydrin that can be covalently linked to the available amino, hydroxyl, and suHhydryl enzyme groups [277]. It has the specific character to form an irreversible gel by heating of a water suspension [278]. Its water-insoluble nature helps to improve a material s water barrier capabihty, and its solubility in... 

HPAs, however, is their solubility in polar solvents or reactants, such as water or ethanol, which severely limits their application as recyclable solid acid catalysts in the liquid phase. Nonetheless, they exhibit high thermal stability and have been applied in a variety of vapor phase processes for the production of petrochemicals, e.g. olefin hydration and reaction of acetic acid with ethylene [100, 101]. In order to overcome the problem of solubility in polar media, HPAs have been immobilized by occlusion in a silica matrix using the sol-gel technique [101]. For example, silica-occluded H3PW1204o was used as an insoluble solid acid catalyst in several liquid phase reactions such as ester hydrolysis, esterification, hydration and Friedel-Crafts alkylations [101]. HPAs have also been widely applied as catalysts in organic synthesis [102]. 

As mentioned in Section 17.3.1, retention of quadrivalent actinide oxides within the phosphate matrix is not a major issue because these oxides are insoluble in water, and all that is needed is their microencapsulation by the phosphate components of the matrix. This was demonstrated in a number of studies on UO2 and PUO2 and their surrogate Ce02. If the actinides are found in a trace amount in the waste, their chemical form is not so important because the phosphate matrix immobilizes them very efiectively. For example, the wastewater in the case study given in Section 16.3.2.2 contained 32 pCi/ml of and 0.6 pCi/ml of The ANS 16.1 tests conducted on the waste forms with 18.6pCi/g loading of combined U in the waste form showed that the leaching index was 14.52. XCLP tests also showed that levels in the leachate were below the detection limit of 0.2 pCi/ml. This implies that microencapsulation of trace-level U is very efiective in the Ceramicrete matrix. 

Despite their high chemiluminescence efficiency, aromatic oxalic acid esters do have some disadvantages. At high levels of ester, there is some background emission (C9). They are also relatively insoluble in water, which means they are applicable only in situations in which organic solvents or water/solvent mixtures can be tolerated. A novel way of overcoming this problem is to have solid ester (e.g., TCPO) incorporated into the matrix of the immobile phase and allow it to slowly dissolve and leach out in the solvent stream, i.e., aqueous acetonitrile or aqueous methanol (P13, V8). 

In particular, for the synthesis of optically pure chemicals, several immobilization techniques have been shown to give stable and active chiral heterogeneous catalysts. A step further has been carried out by Choi et al. [342] who immobilized chiral Co(III) complexes on ZSM-5/Anodisc membranes for the hydrolytic kinetic resolution of terminal epoxides. The salen catalyst, loaded into the macroporous matrix of Anodise by impregnation under vacuum, must exit near the interface of ZSM-5 film to contact with both biphasic reactants such as epoxides and water. Furthermore, the loading of chiral catalyst remains constant during reaction because it cannot diffuse into the pore channel of ZSM-5 crystals and is insoluble in water. The catalytic zeolite composite membrane obtained acts as liquid-liquid contactor, which combines the chemical reaction with the continuous extraction of products simultaneously (see Figure 11.28) the... 

The d.s. of macroporous cellulose /m/i5-2,3-carbonate obtained when cellulose reacts with ethyl chloroformate can be controlled by the addition of small quantities of water,225 This procedure produced a matrix that is suitable for the covalent binding of chymotrypsin the insolubilized enzyme is appreciably active towards high-molecular-weight substrates. The amount of chymotrypsin covalently bound to macroporous cellulose /mn5-2,3-carbonate and the caseinolytic activity of the immobilized enzyme are substantially improved by swelling the matrix in DMSO before the enzyme is coupled.22 The porosity of the insoluble support is increased by swelling, so that macromolecules can diffuse into it. The physical properties of cellulose /ra 5-2,3-carbonate are irreversibly destroyed unless it is properly stored. 

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