Nitrospiropyran

Experimental Preparation of 6-nitrospiropyran 2 (R = Bu). Triethyl-amine (2.65 g, 26 mmol) was added to a suspension of 2,3,3-trimethyl-7V-butylindolinium iodide (9.0 g, 26 mmol) and 5-nitro-salicylaldehyde (4.38 g, 26 mmol) in EtOH (100 ml) under stirring. The mixture was refluxed for 2 h, and filtered off. Recrystallization from hexane gave 6-nitrospiropyran 2 (R = Bu). Also, spiropyran 2 was isolated from the filtrate, which was evaporated under reduced pressure and then was chromatographed on silica gel with dichloromethane-methanol (60 1 v/v). Total yield of 2 (8.3 g) is 88%. 

Huang T, Hu Z, Zhao A, Wang H, Wang B, Yang J, Hou JG (2007) Quasi chiral phase separation in a two-dimensional orientationally disordered system 6-nitrospiropyran on Au (111). J Am Chem Soc 129 3857-3862... 

Scheme 3 Synthesis of photoisomerizable Concanavalin A by the chemical linkage of photoisomerizable thiophene fulgide or nitrospiropyran residues to the protein.

Similar results are observed with the nitrospiropyran-acrylamide copolymer 18 (Figure 8(B)). The enzyme activity is almost entirely blocked in the presence of the copolymer 18a incorporating 0.12 mol% of nitrospiropyran unitsJ47bI Photoisomeri-... 

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... 

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.

Scheme 11 Photochemical control of electrical contact between a ferrocene-tethered glucose oxidase and the electrode using a thiolated nitrospiropyran as a command interface.

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... 

Scheme 12 Surface reconstitution of apo-glucose oxidase on a mixed monolayer associated with an electrode consisting of an FAD cofactor and photoisomerizable nitrospiropyran units, and reversible photoswitching of the bioelectrocatalytic functions of the enzyme electrode.

Fig. 12 Photoswitchable bioelectrocatalyzed oxidation of glucose (8 x 10-2 M) by a composite monolayer consisting of COx reconstituted onto FAD units and nitrospiropyran photoi-somerizable units in the presence of 29 as a diffusional electron mediator, (a) In the presence...

Figure 5.39 Schematic of a photoswitchable monolayer based on pyridine thiol/mercapto butyl-nitrospiropyran, reported by Doron and co-workers [72]...

Figure 5.40 Cyclic voltammetry of (a) 3,4-hyd roxyphenylacetic acid, and (b) dopamine at pho-toswitchable nitrospiropyran electrodes the insets show the corresponding photoswitched reversible induced currents monitored at 470 mV. Reprinted with permission from A. N. Shipway and I. Willner, Acc. Chem. Res., 34,6 (2001). Copyright (2001) American Chemical Society...

Figure 12.4 Photoinduced bioelectrocatalyzed oxidation of glucose to gluconic acid by glucose oxidase (COD) reconstituted with a nitrospiropyran-modified FAD cofactor (Sp-FAD) assembled as a monolayer on the Au electrode. Fhe Sp-FAD reveals reversible photoisomeriz-able properties yielding nitromerocyanine-FAD isomer (MRH+-FAD) [34]...

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). 

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