Smart materials from living polypeptides

Attempts to synthesize well-defined polypeptides by the ring-opening polymerization (ROP) of α-amino acid N-carboxyanhydrides (NCAs) with primary amines have been plagued, for more than 50 years, by unwanted side reactions. Recently, we have employed high vacuum techniques (HVT) to create living conditions for the amino-initiated ROP of NCAs (γ-benzyl L-glutamate, ε-Z L-lysine, proline, etc.). With this approach, a wide variety of novel block copolypeptides, having controlled molecular and architectural characteristics have been synthesized in ∼100% yields. The same holds for hybrid-polypeptides (chimeras), only that the initiating amino group is attached to a conventional macromolecule rather than to a small molecule. Along these synthetic lines, a series of novel amphiphilic triblock copoly-peptides, poly(L-lysine)-b-poly(γ-benzyl-L-glutamate)-b-poly(L- lysine), were synthesized. Due to the macromolecular architecture of the tribock copolypeptides and the rigid nature of the poly(γ-benzyl-L-glutamate) middle block, the formation of bilayers was favored, and vesicles formed in water at neutral pH over the entire compositional range. Compared to other vesicular structures derived from conventional polymers, these polypeptidic vesicles possess the unique feature of being stimuli-responsive to pH and temperature (smart materials). In the presence of deoxyguanosine monophosphate, a multilevel self-assembly of the triblock copolypeptides in water was observed.