Study by circular dichroism and optical rotatory dispersion of polypeptides with aromatic side-chain chromophores

Poly(ortho-, meta-, and para-γ-nitrobenzyl-L-glutamates) were studied by circular dichroism (CD) and optical rotatory dispersion (ORD) in two helicogenic solvents, hexafluoroisopropanol (HFIP) and dichloroethane (EDC), and two non-helicogenic solvents, dichloracetic acid (DCA) and trifluoroacetic acid (TFA). The corresponding glutamates were also studied in DCA and TFA. The symmetric nitrobenzylic chromophore is optically active when the polymers are in solution in DCA and TFA. The corresponding glutamates are also optically active under the same conditions. Thus, it was not possible to explain the origin of the optical activity of the side-chain chromophore when the polymer is in solution in a helicogenic solvent. Nevertheless, from a side-chain dichroic band, a helix–coil transition curve was determined and the stability of each poly(γ-nitrobenzyl-L-glutamate) given; this stability depends on the position of the nitro substituent on the aromatic ring.