Glucose mediated electron transfer

It is clear from these results that the ability of the redox polymers to mediate electron transfer from reduced choline oxidase is dependent upon the structure of the polymer backbone. The trend in mediating efficiency is qualitatively the same as that found for the glucose sensors siloxane-ethylene oxide branch polymer > poly(ethylene oxide) > poly(siloxane). 

An average of one mediator was boimd per f 2-75 kDa of enzyme. The mediators used have redox potentials 0.07 V to 0.55 V positive of the FAD/FADH enzyme s redox potential (—0.05 V relative to the NHE at pH 7), but those which have a redox potential more negative than glucose oxidase enzyme do not mediate electron transfer. Electrons can be relayed both by tunneling and by motion of the mediator in and out of the protein chains. For distances >8 A, tunneling rates decrease ex-... 

Although enzymes with deeply embedded active centers do not normally allow significant non-mediated electron transfer [44], under carefully chosen conditions direct electron transfer is possible, and has been reported for glucose oxidase (GOx) at a bare Ag electrode [45] and in graphite paste electrodes [46]. These systems are unusual and the nonmediated mechanism of such long-range electron transfer is not fully understood. 

Chitnis, Reilly and Nelson obtained a mutant of Synechocystis sp. PCC 6803 that is devoid of PsaE and, although incapable of autotrophic growth, can grow normally in the presence of glucose. The PS-I RC complex prepared from this mutant could not photoreduce Ed but could mediate electron transfer from plastocyanin to artificial electron acceptors such as methyl viologen. Thus PsaE is demonstrated to promote and enhance the electron transfer between [EeS-A/B] and Ed. 

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... 

Polysiloxane random co-polymers (with molecular weights of 5,000-10,000) with pendant ferrocene groups have recently been synthesized 37 via hydrosilylation of vinylferrocene or 9-ferrocenyl-l-nonene with a poly(methylhy-drosiloxane)-r-poly(dimethylsiloxane) random co-polymer (Equation (12)). These materials were used as ampero-metric biosensors for the detection of glucose. In this case, the polymers effectively mediated electron transfer between reduced glucose oxidase and a conventional carbon paste electrode. The response of the sensor to glucose was dependent upon the nature of the polymeric backbone. The optimal response was achieved by finding a compromise between increased polymer flexibility and decreased spacing between individual relay (i.e., ferrocene) sites. 

Figure 14-7. Cyclic voltammogram demonstrating mediated electron transfer from glucose oxidase to a platinum electrode with ferrocene carboxylic acid, a) 2mM ferrocene carboxylic acid b) +10 mg glucose oxidase c) +30 mg glucose. —100 to +700 mV vs. SCE 5 mV s 0,1 M phosphate buffer (ph 7.4) with 0.5 M NaCl platinum disk electrode, 1 mm diameter.

Pravda, M., Adeyoju, O., Iwuoha, E.I., Vos, J.G., Smyth, M.R., and Vytfas, K. (1995) Amperometric glucose biosensors based on an osmium(2-l-/3-l-) redox polymer-mediated electron transfer at carbon paste electrodes. Electroanalysis, 7, 619-625. 

In a more recent study, the mediating electron transfer reactions of glucose oxidase have been reexamined in great detail using simulation methods. Several outstanding problems were resolved regarding the pH dependence of the... 

The concept of a redox-modified hydrogel has also been successfully expanded to covalently immobilized ferrocene onto linear poly-(ethyl-enimine) (LPEI)." Ferrocene-modified LPEI has been shown to effectively mediate electron transfer for a wide range of enzymes including glucose oxidase, fructose dehydrogenase, and horseradish peroxidase to produce current densities as high as 13... 

Amperometric glucose electrodes based on glucose oxidase, chemical or electrochemical steps, 124-125 Amperometric glucose sensors glucose oxidase and nonphysiological redox mediators, electron-transfer mechanism, 169-170 poly(etheramine-quinone)s as electron transfer relay systems, 124-135 viologen derivative containing polysiloxane as electron-transfer mediator, 169-178... 

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