PHOTORESPONSIVE POLYMERS .4. CONFORMATIONAL-CHANGES OF POLYPEPTIDES UPON IRRADIATION

Poly(5-(4-phenylazobenzyl)-L-glutamate) was synthesized to study the photoinduced helix coil transition of a unipolymer. The crucial point in the synthesis is the selective esterification of the L-glutamic acid, which was carried out as an alcoholysis of the N-protected cyclic anhydride. The 5-ester was treated with phosgene to obtain the N-carboxyanhydride, which was polymerized by base catalysis. The polymer was investigated in dilute dioxane solutions. The photoinduced transition was followed by means of UV spectroscopy for the chromophore and viscosimetric experiments for the configuration of the polymer chain. The changes in viscosity are more complex than expected for a helix coil transition, so aggregates have to be taken into account.