Photoisomerizable polyme

The physical and chemical properties of photoisomerizable molecular films or photoisomerizable polymers are controlled by light. Photochemical control of the formation of liquid crystal phases, or sol-gel transitions,137 381 of polymers containing photoisomerizable components demonstrates signal regulation of the structure and properties of microscopic and macroscopic phases. Physicochemical properties of photoisomerizable membrane-mimetic assemblies such as liposomes,1241 mono-... 

B) Schematic presentation of the a-helix/random-coil transition of the photoisomerizable polymer 12. 

Scheme 6 Photoswitching of a-chymotrypsin through its immobilization in photoisomerizable polymers.

Photoisomerizable polymers have been well investigated and applied in various systems to allow physical properties to be reversibly controlled by irradiation.24-31 Accordingly, the encapsulation of proteins in photoisomerizable polymers could provide a general strategy for photoregulating enzymes by means of light-induced permeability of the substrate across the polymer membrane. Willner et a/.43 reported the photoregulation of the activity of a-chymotrypsin encapsulated in a photoisomerizable polymer. They chose azobenzene-, leuco-hydroxide-, and spiropyran-attached acrylamides 4-6 as photoisomerizable copo-... 

Several approaches to the photoregulation of proteins have been employed, including photoisomerizable ligands and inhibitors, casting the protein inside a photoisomerizable polymer, and chemical modification of the protein itself [136], Several azobenzene protein effectors have been reported to act as photoregulators of enzymes and receptors. Photoregulation of cysteine and serine proteases was carried out using simple photoswitchable inhibitors which block the active site in their trans form only [137]. Conversely, the cis isomers of a-ketoester-based inhibitors were more potent inhibitors of a-chymotrypsin than the trans forms... 

Several attempts have been made to construct stimuli-responsive polymer solution and gel systems which undergo isothermal phase transitions by external stimulation, such as photons or chemicals. Aqueous solutions of poly(A -isopropylacrylamide) having photoisomerizable chromophores or host molecules in the pendant groups showed reversible phase separations by photoirradiation or by the addition of specific metal or ammonium ions. The gels made of the polymers also underwent photostimulated or chemical-induced volume phase transitions. 

So far, various kinds of polymers which change their conformation reversibly by photoirradiation have been reported [1-6]. The polymers contain pendant or backbone photoisomerizable chromophores, and the molecular property changes, such as geometrical structure or dipole moment changes, control the conformation. The polymers change their conformation in proportion to the number of photoisomerized chromophores. Thus, when the polymers contain more photoisomerizable chromophores and absorb more photons, the conformation changes more. Physical and chemical properties associated with the conformation changes also vary with the number of absorbed photons. 

Monolayers representing two-dimensional arrays of membrane-mimetic assemblies, consisting of azobenzene (poly-L-lysine) with 43 % loading of the photoisomerizable units, were prepared.1441 The compressed trans-azobenzene polymer mono-layer exhibited a surface pressure of 7 mN m 1, whereas photoisomerization of the monolayer to the cis-azobenzene state by UV light decreased the surface pressure to... 

Oge and Zentel [119] have studied a ferroelectric SCLC copolymer, 53, containing a photoisomerizable, chiral 4,4 -bisalkoxyazobenzene mesogen together with a chiral 4-alkoxyphenyl-4 -alkoxybenzoate mesogen that is photo-chemically unreactive at wavelengths where the azobenzene moiety can be photo-excited. This polymer has both a ferroelectric Sc. phase and a SA phase. Films... 

The third mechanism (3) is the simplest one. When trans-cis photoisomerizable chromophores are incorporated into the polymer backbone, the photoinduced configuration change of the chromophores is expected to induce a conformation change of the polymer chain. Azobenzene (4) is the most widely used as the trans-cis photoisomerizable photoreceptor molecule. It undergoes isomerization from the trans to the cis form under ultraviolet irradiation, while the cis form can return to the trans form either thermally or photochemically [11]. 

Poly(iV-isopropylacrylamide) in water has a lower critical temperature at 31 °C. Temperatures at which this system undergoes phase separation are expected to vary when photoisomerizable chromophores are introduced into the polymer. Such an... 

Figure 1 illustrates the proposals to induce the conformational changes of polymer chains by using photochromic reactions. The mechanism (1) utilizes trans-cis geometrical isomerization as a tool to enforce the conformational changes. When the trans-cis photoisomerizable chromophores are incorporated into the polymer backbone, the isomerization from trans to cis form kinks the extended polymer chains, resulting in a compact conformation. 

Voinova MV, Jonson M. 2004. Electronic transduction in model enzyme sensors assisted by a photoisomerizable azo polymer. Biosens Bioelectron 20(6) 1106 1110. 

The use of structural changes of photoisomerizable chromophores to change the size of polymers was first proposed by Merian (1966). He observed that a nylon filament fabric dyed with an azobenzene derivative shrank upon photoirradiation. This effect is ascribed to the photochemical structural change of the azobenzene moiety absorbed on the nylon fibers. However, the observed shrinkage was very small (only 0.1%), and subsequent to this work, much effort was made to find new photomechanical systems with an enhanced efficiency (Irie, 1990 Smets and De Blauwe, 1974). 

In addition to investigating ferroelectric liquid crystalline conjugated polymers with dynamic switching functionahties under an electric field, our group has also developed photoresponsive liquid crystalline conjugated polymers with dynamic switching of linearly and circularly polarized luminescence. This was accomplished through the use of a photoisomerizable moiety in the polymer side chain. 

Tris(styiylbipyildine)zinc(II) complexes functionalized by dialkylamino-azobenzene groups have recently been designed by Le Bozec et al. to prepare photoisomerizable star-shaped nonlinear optical polymers 7 [25]. 

The preparation of the poly(p-phenylene)-based conjugated polymers with photoisomerizable azobenzene units in the main chain can be illustrated as follows ... 

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