Synthesis and conformational studies in solution of sequential copolypeptides: poly(L-prolyl-L-alpha-phenylglycyl-L-proline).
High molecular weight poly(L-porlyl-L-alpha-phenylglycyl-L-proline) was synthesized by condensation of L-prolyl-L-alpha-phenylglycyl-L-proline pentachlorophenyl ester in N,N-dimethylformamide. The solution properties of this material have been investigated by circular dichroism and 220-MHz nuclear magnetic resonance spectroscopy in solvents such as trifluoroethanol (F3EtOH), chloroform, trifluoroacetic acid (F3CCOOH), chloroform-F3CCOOH and F3EtOH-F3CCOOH mixtures. Ordered structures can be formed in F3EtOH and chloroform, which we believe to be similar to the poly-L-proline II form. The ordered form easily undergoes a conformational transition to an unordered form upon addition of small amounts of F3CCOOH to the chloroform solution. The ordered structure is not disrupted upon addition of 12 per cent F3CCOOH to a F3EtOH solution of the polypeptide.