Redox-enzymes, tethered with

Redox-Enzymes Tethered with Photoisomerizable Groups... 

Figure 17.6 Redox hydrogel approach to immobilizing multiple layers of a redox enzyme on an electrode, (a) Structure of the polymer, (b) Voltammograms for electrocatalytic O2 reduction by a carbon fiber electrode modified with laccase in the redox hydrogel shown in (a) (long tether) or a version with no spacer atoms in the tether between the backbone and the Os center (short tether). Reprinted with permission fi om Soukharev et al., 2004. Copyright (2004) American Chemical Society.

A further approach to electrically wire redox enzymes by means of supramolecular structures that include CNTs as conductive elements involved the wrapping of CNTs with water-soluble polymers, for example, polyethylene imine or polyacrylic acid.54 The polymer coating enhanced the solubility of the CNTs in aqueous media, and facilitated the covalent linkage of the enzymes to the functionalized CNTs (Fig. 12.9c). The polyethylene imine-coated CNTs were covalently modified with electroactive ferrocene units, and the enzyme glucose oxidase (GOx) was covalently linked to the polymer coating. The ferrocene relay units were electrically contacted with the electrode by means of the CNTs, and the oxidized relay mediated the electron transfer from the enzyme-active center to the electrode, a process that activated the bioelectrocatalytic functions of GOx. Similar results were observed upon tethering the ferrocene units to polyacrylic acid-coated CNTs, and the covalent attachment of GOx to the modifying polymer. 

Diffusional electrochemistry of enzymes functionalized with tethered redox relays... 

FIG. 7.8 Electronic transduction of photoswitchable bioelectrocatalytic functions of redox>enzymes by the tethering of photolsomerizable units to the protein. (R is a diifuslonal electron mediator that electrically contacts the redox site of the protein with the electrode support.)... 

Most work related to the covalent labeling of proteins with organometallic is related to the development of enzyme or antibody amperometric biosensors. For the majority of redox enzymes, the active center (or redox-aetive cofactors) are buried inside the protein and are therefore electrically inaccessible for direct electron transfer to the electrode surface of an amperometric biosensor. This problem has been resolved by (i) addition of a diffusional redox-active mediator, (ii) covalent tethering of the mediator to the protein, or (iii) immobilization of the protein in a redox-active polymer. Ferrocenyl derivatives have frequently been used in all three formats as mediators because of their almost ideal electrochemical properties. 

Immobilization of a redox enzyme in a conductive polymer network is another means of enabling electrical communication between the enzyme and the electrode (see Fig. 6.1, configuration C). A non-organized multilayer of ferrocene-tethered GOx was constructed on the surface of a gold electrode by cross-linking of GOx and 2-aminoethyl ferrocene 13 with glutaraldehyde (Fig. 6.4). The molar ratio between ferrocene and GOx in the film was found around 10 and the sensitivity of glucose response was proportional to the amount of GOx [23]. 

Figure 39. Electrical communication between an enzyme redox center and a photoexcited species attaining light-induced biocatalyzed transformations (A) direct electrical wiring of the protein by its chemical modification with tethered electron-relay units (B) electrical communication by the immobilization of the protein into a redox-functionalized polymer matrix.

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