Polypeptides at the air‐water interface and in solution

Monomolecular films of various polypeptides spread at the air‐water interface have been investigated. The conformation in the solid state (e.g., a‐helical or β‐structure) was known for all the polymers studied. In the surface pressure‐area isotherms the a‐helical polymers gave a distinct flat plateau, whereas the β‐form polymers showed only an inflexion. A correlation between the collapse pressure and the stability in solution for β‐form polymers was found, while no similar relationship was observed for the a‐helical polymers. Surface entropy and enthalpy were determined for each polymer and these results indicated that the polypeptides retained the same conformation in the monolayer as in the solid state, i.e., a‐helical or β‐structure. For a‐form polymers a correlation exists between the intermolecular forces in solution and the cohesive forces at the interface. The lack of such a correlation for a‐helical polypeptides thus provides a means of determining the conformation of polypeptides and proteins at the interface.