Critical chain length for the formation of the α-helix in the solid state: synthesis and conformation of sequential oligopeptides and polypeptide having l-leucyl- l-leucylglycine sequence

Abstract

Synthesis and conformation in the solid state of a novel series of sequential oligopeptides and polypeptides having the sequence of l-leucyl- l-leucylglycine have been studied to demonstrate critical chain length for the formation of the α-helix of the peptide. The far infra-red spectra and X-ray powder diffraction patterns suggest that the dodeca and lower peptides take the β-structure and the pentadeca and higher peptides form the α-helix in the solid state. This result leads to the conclusion that the formation of the α-helix of this peptide system begins at the pentadecapeptide. This is consistent with the result of our earlier study on the sequential oligopeptide Nps-( l-Ala- l-Leu-Gly) n -OEt.