Noncovalent immobilization

A nanohybrid, synthesized by immobilizing noncovalently 5,10,15,20-tetrakis(4-hydroxyphenyl) porphyrin, H2THPP, on RGO nanosheets, loaded with Pt nanoparticles, showed enhanced photocatalytic activity under UV-vis light irradiation to promote hydrogen evolution [109]. 

The most commonly used hydrolase for biocatalysis is lipase B from C. antarctica (CAL-B). The commercial material is usually Novozym 435, which is protein immobilized noncovalently on an acrylic resin. This immobilization is suitable for use in organic solvents, but in water, the lipase desorbs from the support. CAL-B is a recombinant protein from the yeast C. antarctica produced in a strain of the fungus Aspergillus oryzae [5]. CAL-B shows little or no interfacial activation and hydrolyzes long chain triglycerides only slowly. For this reason, it may be better classified as an esterase It shows high activity and enantioselertivity toward a... 

Liu Y, Wu DC, Zhang WD, Jiang X, He CB, Chung TS, Goh SH, Leong KW (2005) Polyethylenimine-grafted multiwalled carbon nanotubes for secure noncovalent immobilization and efficient delivery of DNA. Angew. Chem. Int. Ed. 44 4782 4785. 

Chen RJ, Zhang Y, Wang D, Dai H (2001). Noncovalent sidewall functionalization of single-walled carbon nanotubes for protein immobilization. J. Am. Chem. Soc. 123 3838-3839. 

Noncovalent attachment is a popular method of immobilization, and numerous different support materials have been employed, ranging from organic supports, like cellulose. 

In summary, enzyme immobilization is extremely important in the scale-up of many biocatalytic processes. The preferred method for pharmaceutical production involves covalent binding through cross-linking or attachment to a support. Noncovalent attachment is less attractive, but it is heavily utihzed owing to the commercial availabihty of industrial quantities of some enzymes immobilized using this technique. 

Call et al. (2001) of the Pacific Northwest National Laboratory in Richland, WA, also studied the immobilization of unmodified oligonucleotides. Amine-modified and unmodified oligonucleotides could be attached to epoxysilane slides (covalent attachment) or acid-washed slides (noncovalent attachment) under the same conditions by printing in an alkaline-sodium... 

The same authors compared catalysts prepared from these precursors and [Ru(BINAP)Cl2]2 adsorbed on MCM-41 (with 26 and 37 A pores) and an amorphous mesoporous silica (with 68 A pores) all treated with combinations of SiPh2Cl2 and Si(CH2)3X (X = NH2, CO2H). Catalysts were also prepared in which the organometallic precursors were immobilized by entrapment into silica (using sol-gel techniques). This is one of the few studies in which the performance of chiral phosphine catalysts immobilized by covalent and noncovalent procedures are compared directly. The materials were examined as catalysts for the hydrogenation of sodium a-acetamidocinnamate and of a-acetamidocinnamic acid under similar conditions to those used for the catalysts on unmodified MCM-41. The catalysts... 

A third item to consider in using affinity chromatography is the way in which the ligand is attached to the solid support, or the immobilization method. Several techniques are available for this, including both covalent and noncovalent coupling methods [25,36]. For a protein or peptide, this generally... 

In protein microarrays, capture molecules need to be immobilized in a functional state on a solid support. In principle, the format of the assay system does not limit the choice of appropriate surface chemistry. The same immobilization procedure can be applied for both planar and bead-based systems. Proteins can be immobilized on various surfaces (Fig. 1) (12). Two-dimensional polystyrene, polylysine, aminosilane, or aldehyde, epoxy- or thiol group-coated surfaces can be used to immobilize proteins via noncovalent or covalent attachment (13,14). Three-dimensional supports like nitrocellulose or hydrogel-coated surfaces enable the immobilization of the proteins in a network structure. Larger quantities of proteins can be immobilized and kept in a functional state. Affinity binding reagents such as protein A, G, and L can be used to immobilize antibodies (15), streptavidin is used for biotinylated proteins (16), chelate for His-tagged proteins (17, 18), anti-GST antibodies for GST fusion proteins (19), and oligonucleotides for cDNA or mRNA-protein hybrids (20). 

Other Immobilization Techniques Along with noncovalent and covalent immobilization methods, other techniques have been developed for the preperation of affinity supports. Such methods include entrapment, molecular imprinting, and the use of the ligands as both the support and stationary phase. Although these methods are not as common as the approaches already examined, they have important advantages in some applications [8]. 

These noncovalently anchored catalysts in general exhibit a behavior similar to their covalently bound analogues, but can now be separated from the support after the reactions by a simple filtration step. So far, these immobilized systems have not been used in continuous flow reactors. 

Immobilization techniques can be classified by basically two methods, the chemical and the physical method. The former is covalent bond formation dependent and the latter is noncovalent bond formation dependent.1... 

DNA oligonucleotide arrays to profile mRNA expression patterns. In these spotted arrays, purified cDNA clones or PCR products are micropipetted as an array on a substrate surface and immobilized by one of a variety of covalent or noncovalent methods.(72 74)... 

---