The structure of synthetic polypeptides III. The molecular configurations and physical properties of some regenerated synthetic polypeptides

Abstract

An examination of some physical properties of the α ll and β forms of three synthetic polypeptides (the 1:1 copolymer of DL- β -phenylalanine and DL-leucine, the 1:1 copolymer of DL- β -phenylalanine and L-leucine, and the 1:1:1 copolymer of DL- β -phenylalanine, DL-leucine, and γ -benzyl-DL-glutamate) has been carried out. The two modifications were found to exhibit strikingly different solubilities in non-polar liquids. This result is in agreement with the structures suggested in part I for the α ll and β forms, in which the peptide hydrogen bonds are intra- and inter-chain respectively. The results of a study of the regeneration of the polypeptides from carboxylic acid solutions under various conditions have enabled us to elaborate the mechanism of the action of formic acid given in part I. Further, it has been found possible to effect an α ll → β change solely in the amorphous region of the polymer. The β forms of the two polypeptides have been found to be unstable at high temperatures and to revert to the α ll . The α ll is stable at temperatures up to 280°C, and may readily be obtained in a highly crystalline and oriented form by a suitable heat treatment. X-ray photographs of such specimens show resolution of the polar arcs at 5·2 to 5·3 Å, indicating that the unit cells may have mono- or triclinic symmetry.