Intermediate States Enable Keratin-like α-To-β Transformations in Strain-Responsive Synthetic Polypeptides.

Area of Science:

• Materials Science
• Polymer Chemistry
• Biomimetic Materials

Background:

• Nature's fibrous proteins, like alpha-keratin, exhibit superior mechanical strength through strain-induced alpha-to-beta conformational transitions.
• These natural materials have operational temperature limitations.
• Developing synthetic analogs with enhanced thermal stability is crucial for broader applications.

Purpose of the Study:

• To design synthetic polypeptides capable of alpha-to-beta conformational transitions at elevated temperatures, exceeding natural protein limits.
• To create materials with tunable mechanical resilience and responsiveness.
• To explore biomimetic strategies for advanced polymer design.

Main Methods:

• Helix-confined ring-opening polymerization (ROP) of N-carboxyanhydrides (NCAs) using a poly(gamma-benzyl-l-glutamate) (PBLG) precursor.
• Synthesis of poly(O-benzyl-l-serine) (PBLS) and related polypeptides.
• Compression molding to induce intermediate alpha-beta states.
• In situ synchrotron X-ray analysis to characterize structural transformations under strain.

Main Results:

• PBLS chains adopt an alpha-helical structure and transition to beta-sheets upon heating.
• Compression molding creates intermediate states that convert to beta-sheets under mechanical strain, inducing strain-hardening.
• The approach is effective for various side chains (e.g., poly(S-benzyl-l-cysteine)) up to ~200 °C.
• Stepwise chain alignment, beta-sheet formation, and domain growth were observed during deformation.

Conclusions:

• A novel strategy for designing synthetic polypeptides with tunable, temperature-resilient mechanical properties was developed.
• The method surpasses the thermal limitations of natural fibrous proteins.
• This offers a versatile platform for next-generation materials with broad-temperature mechanical adaptability.