A Pure Polyproline Type I-like Peptoid Helix by Metal Coordination

Area of Science:

• Supramolecular Chemistry
• Polymer Science
• Biophysical Chemistry

Background:

• Peptoids (N-substituted glycine oligomers) are versatile foldamers capable of adopting specific helical structures.
• Stabilizing pure helical conformations, such as polyproline-I (PP-I), is crucial for their applications.

Purpose of the Study:

• To introduce a novel method for stabilizing a pure PP-I-like peptoid helix via metal coordination.
• To investigate the folding behavior of peptoids with specific ligand placements and metal binding.

Main Methods:

• Synthesis of peptoid heptamers with 8-hydroxyquinoline ligands and varied chiral substituents.
• Spectroscopic analysis including circular dichroism (CD) and electron paramagnetic resonance (EPR) spectroscopy.
• Systematic modifications of peptoid length and derivatization.

Main Results:

• A specific peptoid sequence (7P6) with benzyl groups at positions 3 and 4, upon binding Cu2+, exhibited a CD signal characteristic of a PP-I helix.
• Exciton couplet CD and EPR spectroscopy elucidated the unique folding mechanism.
• Folding is driven by a balance between metal coordination geometry and the peptoid sequence.

Conclusions:

• Metal coordination can effectively stabilize a pure PP-I-like helical structure in peptoids.
• The folding of peptoids is a complex process influenced by both sequence-dependent and coordination-dependent factors.
• This work provides a new strategy for controlling peptoid conformation for potential applications.