Photoisomerizable enzyme electrodes

Amperometric Transduction of Optical Signals Recorded by Photoisomerizable Enzyme Electrodes... 

Scheme 8 Assembly of a photoisomerizable glucose oxidase monolayer electrode and the reversible photoswitchable activa-tion/deactivation of the bioelectrocatalytic functions of the enzyme electrode.

The photoisomerizable enzyme monolayer electrode also revealed photoswitchable bioelectrocatalytic activity (Figure 7.10). In the presence of ferrocene carboxylic acid (5) as a diffusional electron transfer mediator, the nitrospiropyran-tethered GOx (4a) revealed a high bioelectrocatalytic activity, reflected by a high electrocatalytic anodic current. The protonated nitromerocyanine-GOx (4b) exhibited a two-fold lower activity, as reflected by the decreased bioelectrocatalytic current. By the reversible photoisomerization of the enzyme electrode between the 4a- and 4b-states, the current responses are cycled between high and low values (Figure 7.10, inset). 

Figure 3-30. Organization of a photoswitchable glucose oxidase electrode for the bioelectrocatalyzed oxidation of glucose (A) The synthesis of the photoisomerizable nitrospiropyran-FAD cofactor. (B) The reconstitution of apo-glucose oxidase, apo-GOx, with the photoisomerizable FAD-cofactor (20a). (C) The assembly of the reconstituted photoisomerizable GOx on an electrode surface and the photoswitching of the bioelectrocatalytic function of the enzyme electrode in the presence of ferrocene carboxylic acid (21) as mediator.

A further approach to controlling electrical communication between redox proteins and their electrode support through a photo-command interface includes photo stimulated electrostatic control over the electrical contact between the redox enzyme and the electrode in the presence of a diffusional electron mediator (Scheme 12).[58] A mixed monolayer, consisting of the photoisomerizable thiolated nitrospiropyran units 30 and the semi-synthetic FAD cofactor 25, was assembled on an Au electrode. Apo-glucose oxidase was reconstituted onto the surface FAD sites to yield an aligned enzyme-layered electrode. The surface-reconstituted enzyme (2 x 10-12 mole cm-2) by itself lacked electrical communication with the electrode. In the presence of the positively charged, protonated diffusional electron mediator l-[l-(dimethylamino)ethyl]ferrocene 29, however, the bioelectrocatalytic functions of the enzyme-layered electrode could be activated and controlled by the photoisomerizable component co-immobilized in the monolayer assembly (Figure 12). In the... 

Photoswitchable electrical communication between enzymes and electrodes has also been achieved by the application of photoisomerizable electron-transfer mediators [195, 199]. DilTusional electron mediators (viologen or ferrocene derivatives) were functionalized with photoisomerizable spiropyran/merocyanine units. These mediators can be reversibly photoisomerized from the spiropyran state to the merocyanine state (360 < A < 380 nm) and back (A > 475 nm). An enzyme multilayer array composed of glutathione reductase or glucose oxidase was electrically contacted only when the photoactive group linked to the redox relay (viologen or ferrocene derivative, respectively) was in the spiropyran state. 

FIG. 7.8 Electronk transduction of photoswitchable bioeiectrocatal)rtic functions of redax enzymes by the tethering of photoisomerizable units to the protein. (R is a dtffusional electron mediator that electrically contacts the redox site of the protein with the electrode support.)... 

FIG. 7.19 Electronic transduction of phocoswitchable bioelectrocacalytic functions of enzymesf proteins by the application of a photoisomerizable command Interfece that controis the electrical contact between die redox enzyme/protain and the electrode. 

Fig. 31a). The native FAD cofactor was extracted from GOx and the semisynthetic FAD cofactor was reconstituted into the apo-GOx (apo-GOx) (Fig. 31b). This reconstituted enzyme includes a photoisomerizable unit directly attached to the redox center of the enzyme, and hence, the enzyme is predisposed for optimized photoswitchable bioelectrocatalytic properties. The photoisomerizable enzyme was assembled on an Au-electrode as described in Fig. 31(c). The bioelectrocatalytic oxidation of glucose was stimulated in the presence of ferrocene carboxylic acid as a diffusional electron-transfer mediator. The (28a)-state of the reconstituted GOx was inactive for the bioelectrocatalytic transformation, whereas photoisomerization of the enzyme to the (28b)-state activated the system (Fig. 32). By the cyclic photoisomerization of the enzyme mono-layer between (28a) and (28b) states, the bioelectrocatalyzed oxidation of glucose was cycled between the off and on states, respectively (Fig. 32, inset). It was also found that the direction of the photo-bioelectrocatalytic switch of the (28a/28b)-FAD-reconstituted GOx is controlled by the electrical properties of the diffusional electron-transfer mediator [385]. With ferrocene dicarboxylic acid as a diffusional electron-transfer mediator, the enzyme in the (28a)-state was found to correspond to the switched off biocatalyst, while the (28b)-state exhibits switched on behavior. In the presence of the protonated 1-[1-(dimethylamino)ethyl]ferrocene, the direction of the photobioelectrocatalytic switch is reversed. This control of the photoswitch direction of the photoisomerizable GOx was attributed to electrostatic interactions between the diffusional electron-transfer mediator and the photoisomerizable unit linked to the FAD. The (28b)-state attracts the oxidized negatively charged... 

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