Photoisomerization transduction

The azo-modified, elastin-like polypeptide XIV illustrated in Scheme 9 exhibits a so-called inverse temperature transition" that is, the compound gives cross-linked gels that remain swollen in water at temperature below 25 °C but deswell and contract upon a rise of temperature. The trans-cis photoisomerization of the azo units, obtained through alternating irradiation at 350 and 450 nm, permits photomodulation of the inverse temperature transition.[S9] The result indicates that attachment of a small proportion of azobenzene chromophores is sufficient to render inverse temperature transition of elastin-like polypeptides photoresponsive, and provides a route to protein-based polymeric materials capable of photomechanical transduction. 

Cyclic photoisomerization of the electron-acceptor between the trans- and cis-states permitted reversible piezoelectric transduction of the formation of the complexes with trans-A,A -bNA, and trans-3,3 -bN A at the monolayer interface, and their dissociation upon photoisomerization to czs-4,4 -bNA and c/s-3,3 -bNA. 

ELECTRONIC AND OPTICAL TRANSDUCTION OF PHOTOISOMERIZATION PROCESSES AT MOLECULAR-AND BIOMOLECULAR-FUNCTIONALIZED SURFACES... 

Photo-responsive Synthetic Membranes. Although the visual Information transduction Is too complexed to be realized in vitro, the photoeffects of retinal-containing synthetic membranes have been investigated. Alzawa et al. (74) prepared a photo-responsive membrane from a solution of 11-cis retinal, phosphatidyl choline and trlacetyl cellulose. The retinal was assumed to be incorporated into the molecular assemblies of phosphatidyl choline, which were dispersed In the trlacetyl cellulose membrane matrix. The membrane responded to visible light by showing a transmembrane potential in association with the photoisomerization of membrane-bound 11-cis retinal. On the other hand, a membrane Incorporating 11-cls retinal without phosphatidyl choline exhibited little light-induced transmembrane potential (75). 

Figure 5. Combination of energy transfer and a reversible photoisomerization for signal transduction in a bistable system.

The kinetics of the photoisomerization of bilirubin has been studied because of the relevance to phototherapy. The fluorescence of bilirubin increases on binding to human serum albumin. This and other primary photoprocesses have been investigated by picosecond spectroscopy. Karvaly has put forward a new photochemical mechanism for energy conversion in bacteriorhodopsin. An extensive review of the photophysics of light transduction in rhodopsin and bacteriorhodopsin has been made by Birge. The dynamics of cis-trans isomerization in rhodopsin has been analysed by INDO-CISD molecular orbital theory. Similar calculations on polyenes and cyanine dyes have also been reported. A new picosecond resonance Raman technique shows that a distorted... 

Molecular opto-electronic assemblies, which consist of a functionalized gold electrode with a photo-isomerizable redox-activated monolayer, enables amperometric transduction of the photonic information recorded by the interface. On-off operation of superstructure formation of hermaphroditic cyclodextrin derivatives is brought about by disturbing the monomer/dimer equilibrium of -azobenzene structures by photoisomerization. When the structures have the Z-form, the dimer dissociates. The thermal Z— isomerization can be enhanced by heating in favor of the dimer formation (Figure 89.8). ... 

---