Bonding, immobilization methods

The adsorption of proteins onto surfaces is the oldest and easiest immobilization method. Adsorbing forces can be of different types Van der Waals interactions, ionic, hydrophobic or hydrogen bonding. The main advantages of this procedure are the simplicity of preparation and the little... 

The covalent attachment of enzymes to water-insoluble carriers is usually the preferred immobilization method for sensor manufacturing. Obviously, the selected procedure should avoid the loss of enzymatic activity and keep the accessibility of the binding site to the substrate molecules. Unfortunately, this is usually not the case and due to the severe conditions of many of these procedures, major activity losses and/or changes on the substrate selectivity are produced during immobilization. Some authors have pointed out that the enzyme activity decreases approximately one fifth per formed bond [66]. 

Rogers YH, Jiang-Baucom P, Huang ZJ, Bogdanov V, Anderson S, Boyce-Jacino MT. Immobilization of oligonucleotides onto a glass support via disulfide bonds a method for preparation of DNA microarrays. Anal Biochem 1999 266(1) 23—30. 

A model of a biphasic enzyme membrane reactor for the hydrolysis of triglycerides has been formulated according to the bond graph method of network thermodynamics, and the kinetics, the permeabilities of fatty acids and glycerides, the rates of inhibition of the immobilized enzyme, and the concentration of enzyme in a reaction zone are studied. 

Enzyme immobilization methods are classified as chemical or physical. Chemical methods involve the formation of covalent bonds between functional groups on the... 

Physical immobilization methods do not involve covalent bond formation with the enzyme, so that the native composition of the enzyme remains unaltered. Physical immobilization methods are subclassified as adsorption, entrapment, and encapsulation methods. Adsorption of proteins to the surface of a carrier is, in principle, reversible, but careful selection of the carrier material and the immobilization conditions can render desorption negligible. Entrapment of enzymes in a cross-linked polymer is accomplished by carrying out the polymerization reaction in the presence of enzyme the enzyme becomes trapped in interstitial spaces in the polymer matrix. Encapsulation of enzymes results in regions of high enzyme concentration being separated from the bulk solvent system by a semipermeable membrane, through which substrate, but not enzyme, may diffuse. Physical immobilization methods are represented in Figure 4.1 (c-e). 

Covalent immobilization methods rely on functional groups on both the enzyme and the support material for the formation of stable covalent bonds. For this reason, the choice of a support is crucial in that it determines the immobilization chemistry... 

Chemical immobilization methods may alter the local and net charges of enzymes, through covalent modification of charged residues such as lysine (NH4), aspartate, and glutamate (COO-). Conformational changes in secondary and tertiary protein structure may occur as a result of this covalent modification, or as a result of electrostatic, hydrogen-bonding or hydrophobic interactions with the support material. Finally, activity losses may occur as a result of the chemical transformation of catalytically essential amino acid residues. 

The immobilization methods ate identified either as chemical or physical procedures depending on whether covalent bonds ate established or not. °... 

Immobilization is referred to the CDs that are linked to the macromolecule skeleton by chemical bonds. The basic skeleton could be polystyrene, polysiloxane, polyethylene, cellulose, chitosan and so on. According to the different synthetic routes, the immobilization methods can be divided into the following types, (a) Before immobilization of the CDs to the skeleton, a series of special functional groups are attached to the skeleton. Then, the related CDs react with the group to form the target polymers, (b) First, modify the CDs to monomer CD derivatives by the chemical method, and then immobilize the monomer derivatives to the skeleton, (c) The macromolecular carrier and the CDs would need to be modified before immobilization. 

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