Zigzag-Helix Transformation of Expanded Polyvaline Induced by Racemization

Area of Science:

• Biochemistry
• Polymer Chemistry
• Structural Biology

Background:

• Biological macromolecules, such as proteins, exhibit homochirality, predominantly using L-amino acids.
• The behavior of chiral molecules interacting with their mirror images is a fundamental question in chemistry.

Purpose of the Study:

• To synthesize and characterize expanded polyvalines with bis(pyridine)silver(I) moieties.
• To investigate the secondary structures formed by chiral and racemic expanded polyvalines.

Main Methods:

• Synthesis of expanded polyvalines containing bis(pyridine)silver(I) moieties.
• Isolation of compounds as single crystals.
• X-ray crystallographic analysis to determine molecular structures.

Main Results:

• Chiral expanded poly(L-valine) and poly(D-valine) adopt zigzag chain conformations.
• Racemic mixtures of these molecules form left- and right-handed 41 helices, preserving their sequences.
• The observed secondary structures are interconvertible via C-terminal amide plane flipping, analogous to alpha-helix and beta-strand relationships.

Conclusions:

• Expanded polyvalines exhibit distinct secondary structures based on chirality.
• These findings suggest the possibility of constructing expanded proteins with tailored three-dimensional structures and novel functions.