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Conformation of poly(γ‐glutamic acid) in aqueous solution

Local conformation and overall conformation of poly(γ‐DL‐glutamic acid) (PγDLGA) and poly(γ‐L‐glutamic acid) (PγLGA) in aqueous solution was studied as a function of degree of ionization ε by 1H‐NMR, circular dichroism, and potentiometric titration. It was clarified that their local conformation is represented by random coil over an entire ε range and their overall conformation is represented by expanded random‐coil in a range of ε > ε*, where ε* is about 0.3, 0.35, 0.45, and 0.5 for added‐salt concentration of 0.02M, 0.05M, 0.1M, and 0.2M, respectively. In a range of ε < ε*, however, ε dependence of their overall conformation is significantly differentiated from each other. PγDLGA tends to aggregate intramolecularly and/or intermolecularly with decreasing ε, but PγLGA still behaves as expanded random‐coil. It is speculated that spatial arrangement of adjacent carboxyl groups along the backbone chain essentially affects the overall conformation of PγGA in acidic media. © 2015 Wiley Periodicals, Inc. Biopolymers 105: 191–198, 2016.