CONFORMATIONAL STUDIES ON POLY-L-PHENYLALANINE . CIRCULAR DICHROISM PROPERTIES OF COPOLYMERS OF L-PHENYLALANINE AND NEPSILON-CARBOBENZOXY-L-LYSINE

Circular dichroism (CD) measurements have been carried out on pure poly-ε-carbobenzoxy-l-lysine (PCBL) and on copolymers of l-phenylalanine and Nε-carbobenzoxy-l-lysine in tetrahydrofuran as the solvent. The CD spectrum of pure PCBL does correspond to that of a polypeptide having the right-handed α-helical conformation. When increasing amounts of l-phenylalanine residues were introduced into the peptide chain, a gradual change in the CD spectra was observed. From these data it was concluded that an increasing proportion of L-phenylalanine residues does not change the a-helical conformation of PCBL. Furthermore, by optical titration experiments it was found that the a-helical structure of copolymers containing increasing amounts of the aromatic residues is less stable than that of pure PCBL. © 1969, American Chemical Society. All rights reserved.