Critical chain length for the formation of the α-helix in the solid state. Synthesis and conformation of sequential oligopeptides and a polypeptide containing the sequence L-leucyl-L-alanyl-L-leucylglycine

A series of sequential oligopeptides and a polypeptide containing the sequence L-leucyl-L-alanyl-L-leucylglycine have been prepared by the fragment condensation method and the self-polycondensation method, respectively. The conformations of the peptides have been studied by far-i.r. spectroscopy and X-ray powder diffraction. The polypeptide and hexadecapeptide form an α-helix and the dodeca- and lower oligo-peptides a β-structure in the solid state. The results suggest that the critical chain length for the formation of an α-helix in the solid state is 16 residues.