STRUCTURAL INVESTIGATIONS ON POLY(4-HYDROXY-L-PROLINE) .1. THEORETICAL STUDIES

Model building studies on poly(hydroxyproline) 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 γ-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(hydroxyproline) in water. © 1979, American Chemical Society. All rights reserved.