Molecular conformations ofd,l-alternating polypeptides

D,L-Alternating poly(γ-benzyl glutamate) (PBDLG) and poly(γ-phenethyl glutamate) (PPDLG) were prepared by the racemization-free method proposed by Caille et al. (1) for the synthesis of PBDLG. Both polymers were fractionated into two components, (A) and (B), using solubility differences in DMF, methanol, and ethanol. Infrared and X-ray data support the α-helical molecular conformation for the (A) films obtained from chloroform solutions, as was reported by Heitz et al. (2) for PBDLG. The molecular conformation of PPDLG-(B) is essentially the same as that of PBDLG-(B), which was assigned to the antiparallel-chain polar pleated-sheet structure by Lotz et al. (3). The ω-helical conformation was found for PBDLG by exposing the (A) film to the vapor from DMF with a small amount of water, but not for PPDLG.