Structural investigations on poly(4-hydroxy-L-proline). 1. Theoretical studies

Model building studies on poly(hydroxypro1ine) indicate that in addition to the well-known helical structure of form A, a left-handed helical structure with trans peptide units and with h=2.86 Å and n=2.67 (i.e., 8 residues in 3 turns) is also possible. In this structure which is shown to be in agreement with X-ray data of the form B in the next paper, the y-hydroxyl group of an (i+1)th Hyp residue is hydrogen bonded to the carbonyl oxygen of an (i−1)th residue. The possibility of a structure with cis peptide units is ruled out. It is shown that both forms A and B are equally favorable from considerations of intramolecular energies. Since form B is further stabilized by intrachain hydrogen bonds, we believe that this is likely to be the ordered conformation for poly(hydroxypro1ine) in water