The State of Aggregation of α-Helical Poly(L-glutamic acid) in Aqueous Salt Solutions

摘要

Highly protonated poly(L-glutamic acid) is predominantly α-helical in aqueous salt solutions, whereas the fully charged poly(L-glutamate) polyion is randomly coiled. Potentiometric titration of poly(L-glutamic acid) with base therefore allows one to sweep through the entire helix—coil transition at a given temperature. Such titration curves reveal four distinguishable regions as the solution is brought from highly acidic to more basic pH. These have been interpreted as a region of aggregation (A), a region of helical, but dispersed, polymer (H), a transition region (HC), and a region of random coil (C).