Redox centers, communication

Describe various routes for facilitating the electrical communication between the redox center of glucose oxidase and an electrode surface. 

Enzyme biocatalyst assemblies on electrode surfaces usually do not achieve significant electron-transfer communication between the redox center and the conductive support, mostly because of the electrical insulation of the biocatalytic site by the surrounding protein matrixes. During the past four decades, several methods have been proposed and investigated in the field of bioelectrochemical technology in an effort to establish efficient electrical communication between biocatalysts and electrodes. " In general, electron transfer is classified by two different mechanisms (see Figure 2) ... 

Methods to electrically wire redox proteins with electrodes by the reconstitution of apo-proteins on relay-cofactor units were discussed. Similarly, the application of conductive nanoelements, such as metallic nanoparticles or carbon nanotubes, provided an effective means to communicate the redox centers of proteins with electrodes, and to electrically activate their biocatalytic functions. These fundamental paradigms for the electrical contact of redox enzymes with electrodes were used to develop amperometric sensors and biofuel cells as bioelectronic devices. 

Nanoparticles are well suited for construction of third generation enzyme biosensors that rely on the direct electron transfer between redox centers buried within the protein and electrodes. The small size of the particles provides ideal environments for contacting redox centers with little loss of bioactivity, while the conductive nature of the metal particles facilitates communication with the underlying electrode by providing a means of electron shuttling. 

In order to elucidate primarily the electrostatic through-bond mode of electrochemical communication between the ferrocene redox center and the heteroatoms of the crown ionophore, a variety of conjugated... 

Extensive studies of the redox chemistry of [ Co3(CO)9 2 n-C(C=C)mC ] (m = 0, 271 1, 286) have been made independently by the groups of Robinson439 and Osella481,482 and the electrochemical behavior of the C2 and C4 complexes has been compared with that of Co2(CO)6 2(p-r 2-PhC2C2Ph).482,483 Two distinct one-electron reduction processes are found, of which the first shifts to more negative potentials as the carbon chain is lengthened. This is consistent with effective electronic communication between the redox centers. This is attenuated when a Co2(CO)6 group is attached to the carbon chain. All scans contain a wave due to the [Co(CO)4] anion formed by chemical decomposition. 

The third generation of enzyme electrodes uses direct electrical communication between the redox centers of the enzymes and the electrode surface. This con-... 

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.

Electrical communication between redox centers of glucose oxidase and electrodes via electrostatically and covalently bound redox polymers. Journal of the American Chemical Society, 111, 2357-2358. 

Since the electrode and the protein redox center may be considered as a donor-acceptor pair, the distance, or spatial, separation of the enzyme redox center from the electrode by means of the protein shell prohibits the direct electrical communication between the redox site and the electrode. Substantial research efforts were directed during the last two decades to overcome the insulating protein barrier surrounding the redox centers and... 

Since the reconstitution of apo-GOx onto an FAD-monolayer linked to the Au-electrode did not yield an electrically contacted enzyme electrode, and since the electrocatalytic anodic current observed for the integrated electrode was observed at the redox-potential of the PQQ units, the electrical communication between the enzyme redox center and the electrode and its bioelectrocatalytic activation was attributed to the PQQ-mediated electron transfer in the system. Fig. 3-4A. The FAD centers of reconstituted GOx are reduced by glucose, and the reduced cofactors are then oxidized by the PQQ... 

Other oligomers of clusters were reported using the bridging ligand dppf and considering the Co2(C2) core as a cluster.147 Several examples were prepared, including 187-190, and were analyzed by cyclic voltammetry. Elemental analyses and H NMR established the relative stoichiometry of dppf versus cluster. No evidence of communication between the redox centers was observed. 

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