Zigzag Sheets Research Articles

Polymers of tripeptides as collagen models: VI. Synthesis and structural investigation of poly( l-alanyl- l-prolyl-glycine)

The polytripeptide (Ala-Pro-Gly) n has been synthesized and a study made of its structure in solution and in the solid state. The lyophilized polymer is not readily soluble in water, but can be dissolved in organic acids and on dilution with water will remain in solution, apparently in an unaggregated structureless state. In the solid state, the polymer can exist in several forms obtained by different solvent treatments and characterized by different X-ray patterns. The structure of one of these forms, which is stabilized by water, has been determined. In this form, the molecules form left-handed helices in the polyproline II conformation, with each tripeptide corresponding to an axial translation of 9.4 Å and a rotation of 360 °, approximately equally divided between the three amino acid residues. The polypeptide chains are aggregated to form zigzag sheets, with neighbouring chains antiparallel to each other and joined by one NH … O hydrogen bond per tripeptide.