Processes of Ordered Structure Formation in Polypeptide Thin Film Solutions

Abstract

An experimental study is presented on hierarchical assembly of α-helical block copolymers [polystyrene-poly(γ-benzyl-L-glutamate)] into anisotropic ordered structures. Using thin solid films transformed into solutions via the exposure to solvent vapor, allowed studying in such solutions the processes of nucleation and growth of ordered three-dimensional structures, depending on supersaturation with respect to the solubility limit. Interestingly, polymer solubility could be significantly influenced via variation of humidity in the surrounding gas-phase. It is concluded that the interfacial tension between the ordered structures and the solution increased with humidity. The same effect was observed for other protic non-solvents in the surrounding gas-phase and is attributed to a complexation (via hydrogen bonding interactions) of poly(γ-benzyl-L-glutamate) by protic non-solvent molecules. This change of polymer solubility was demonstrated to be reversible by adding/removing small amounts of protic non-solvent in the surrounding gas-phase. At a constant polymer concentration, ordered ellipsoidal structures could be dissolved by removing water or methanol present in the solution. Such structures formed once again when water or methanol was reintroduced via the vapor phase.