Photoswitchable activation

Scheme 10 Reversible photoswitchable activation/deactivation of the electrical contact between cytochrome c and the electrode and the secondary activation/deactivation of the COx-biocata-lyzed reduction of oxygen using a thiolated nitrospiropyran and thiolated pyridine mixed monolayer as a command interface.

Photoswitchable activation of enzymes provides a means to trigger a biocata-lytic transformation ON and OFF . This feature shows two important functions ... 

FIG. 7.9 Ass mbix of a photoisomerizabie glucose ackfase monofayer eleciro[Pg.229]

FIG. 7.21 (A) Reversible photoswitchable activation/deactivation of e electrical contact between... 

Willner et al. introduced a system that enables the photoswitchable activation and deactivation of Cytochrome c using a mixed monolayer consisting... 

Fig. 39 Photoswitchable activation and deactivation of the electrical contact of Cyt. c and an electrode, and secondary Cyt. c-mediated biocatalysed reduction of O2 by COx, using a pyridine-nitrospiropyrane photoisomerisable mixed monolayer electrode [17]...

Photoswitching of the coordination number of the silicon atom is also the key to control the reactivity of the allyl group in 2-(phenylazo)phenylallyldifluorosilane 839 and 840. Only the (if)-form 839 reacts with KF/H20/18-crown-6 to the corresponding allyhydrazine tetrafluorosilicate derivative 841 (Scheme 117). Apparently, the involvement of the azo group in the coordination of the silicon atom leads to an activation of the N-N double bond.831... 

It is at present still difficult to correlate the absolute intensity of the SHG with the number of cationic complexes at the membrane surface. Therefore, a quantitative discussion, showing how the permselective uptake of primary cations forming SHG active complexes into the membrane side of the phase boundary corresponds to the increase in the membrane potential, is not possible yet. Lipophilic derivatives of photoswitchable azobis(benzo-15-crown-5) were recently shown as a molecular probe to determine photoinduced changes in the amount of the primary cation uptake into the membrane phase boundary in relation to the photoinduced EMF changes under otherwise identical conditions. 

Fig. 4 Photoswitchable hydrolytic activities of 4-carboxyazobenzene-tethered papain (10) ...

To optimize the photoswitchable bioelectrocatalytic features of the protein, site-specific functionalization or mutation of the active site microenvironment is essential. This was accomplished by a semisynthetic approach involving the reconstitution of the flavoenzyme-glucose oxidase with a semisynthetic photoisomerizable FAD cofactor (Scheme 9).1511 The photoisomerizable nitrospiropyran carboxylic acid (24) was covalently coupled to N6-(2-aminoethyl)-FAD (25), to yield the synthetic photoisomerizable nitrospiropyran-FAD cofactor 26a (Scheme 9(A)). The native FAD cofactor was removed from glucose oxidase, and the synthetic photoisomeriz-able-FAD cofactor 26a was reconstituted into the apo-glucose oxidase (apo-GOx), to yield the photoisomerizable enzyme 27a (Scheme 9(B)). This reconstituted protein... 

Table 2 summarizes different possible applications of photoswitchable biomaterials, while detailing the nature of the biomaterial, the area of application, and, when possible, specific examples. Reversible light-induced activation and deactivation of redox proteins (enzymes) corresponds to write - read - erase functions. The photonic activation of the biomaterial corresponds to the write function, whereas the amperometric transduction of the recorded optical information represents the read function of the systems. Switching off of the redox functions of the proteins erases the stored photonic information and regenerates the photosensory biomaterial. These integrated, photoswitchable redox enzyme electrode assemblies mimic logic functions of computers, and may be considered as first step into the era of biocomputers. 

Photonic activation of redox enzymes results in the light-induced bioelectrocataly-tic activation of an enzyme cascade. This permits application of photoswitchable enzymes as amplifiers of weak photonic signals. Alternatively, sensitive actino-meters, measuring low irradiation doses, might be envisaged. 

Redox enzymes are the active component in many electrochemical enzyme electrode biosensor devices.1821 The integration of two different redox enzymes with an electrode support, in which one of the biocatalysts is photoswitchable between ON and OFF states, can establish a composite multisensor array. The biomaterial interface that includes the photoswitchable enzyme in the OFF state electrochemi-cally transduces the sensing event of the substrate corresponding to the nonphoto-switchable enzyme. Photochemical activation of the light-active enzyme leads to the full electrochemical response, corresponding to the analysis of the substrates of the two enzymes. As a result, the processing of the signals transduced by the composite biomaterial interface in the presence of the two substrates permits the assay of the... 

Photoswitchable enzymes could have an important role in controlling biochemical transformations in bioreactors. Various biotechnological processes generate an inhibitor, or alter the environmental conditions (pH, for example) of the reaction medium. Photochemical activation of enzymes that adjust environmental conditions or deplete the inhibitor to a low concentration may maintain the bioreactor at optimal performance. More specifically, integration of the photoswitchable biocataly-tic matrix with a sensory electrode might yield a feedback mechanism in which the sensor element triggers the light-induced activation/deactivation of the photosensitive biocatalyst. 

Science is entering into the nanoscale world, and the organization of microscale or nanoscale biomaterial structures on surfaces has been demonstrated and is a subject of extensive research effort.184,851 Single biomaterial molecules have been imaged on surfaces,186 871 and the individual affinity interactions of biomaterials probed at the molecular level.188,891 While the different scanning microscopy techniques provide useful means to image and manipulate biomaterials on surfaces, the use of the near-field scanning optical microscope (NSOM) 9<) in the activation of photoswitchable biomaterials on surfaces should be emphasized specifically. One... 

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