Photoinduced Helix-sense Reversal in Azobenzene-containing Poly L-aspartate s

5 Photoinduced Helix-sense Reversal in Azobenzene-containing Poly(L-aspartate)s 

Large photoresponse effects could be observed in solvent mixtures, provided that the irradiation was carried out at appropriate solvent compositions. A copolypeptide composed of 33 mol% P-benzyl-L-aspartate and 67 mol% para-phenylazo-L-aspartate (X) was found to give different kinds of photoresponse, depending on the composition of the solvent in which irradiation was carried out. In dichloroethane (DCE)/ hexafluoropropanol (HFP) = 95/5, irradiation at 320-390 nm produced an increase in right-handed helix content in DCE/HFP = 54/26, a light-induced conformational change from left-handed helix to random coil was observed while, finally, reversal of the helix sense occurred in DCE/HFP = 65/35.150,511 

Two polymers respectively containing 8 and 10 mol% of meta-phenylazo-L-aspartyl residues (XI) were found to be left-handed helices in pure DCE, while existing as right-handed helices in pure trimethylphosphate (TMP). The inversion of the helix occurred at solvent compositions corresponding to 20-50% TMP concentration  

Investigation of light-induced conformational changes has also been extended to solid films of azobenzene-containing poly(L-aspartate)s, but no conformational change was induced by photoisomerization of the azobenzene units. This was probably due to the limited mobility of the polypeptide chains in the films. 57  

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