Rippled Sheets: The Early Polyglycine Days and Recent Developments in Nylons.

Area of Science:

• Biochemistry
• Polymer Science
• Materials Science

Background:

• The pleated sheet structure, proposed in 1951, is widely accepted for homochiral proteins.
• The rippled sheet structure, also proposed by Pauling and Corey, applies to blends of poly(L-peptides) and poly(D-peptides) and has seen limited adoption.
• The rippled sheet structure has a complex history, with limited recognition until recent decades.

Purpose of the Study:

• To provide a historical account of the rippled sheet structure.
• To highlight the significance of the rippled sheet structure in understanding protein and polymer conformations.
• To connect the rippled sheet structure to recent findings in polymer crystallography and material properties.

Main Methods:

• Review of historical proposals and scientific literature.
• Analysis of structural models for proteins and polymers.
• Application of structural models to explain experimental observations in materials science.

Main Results:

• The rippled sheet structure was validated as a model for achiral polyglycine (polyglycine I) in the 1970s.
• This validation improved the structural model of Bombyx mori silk fibroin.
• Recent studies show that both pleated and rippled sheet structures explain unsolved crystal structures of various nylons.
• These structures elucidate the high-temperature Brill transition in nylon 6-6.

Conclusions:

• The rippled sheet structure is crucial for understanding the conformations of specific polymers, including polyglycine and nylons.
• The structural insights provided by rippled sheets explain long-standing material science phenomena like the Brill transition.
• Further research into these secondary structures can advance polymer science and materials engineering.