Electrostatic Control of Shape Selection and Nanoscale Structure in Chiral Molecular Assemblies

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Biophysics

Background:

• Molecular chirality's nanoscale manifestation remains a challenge since Pasteur's discovery of biochirality.
• Chiral molecules self-assemble into diverse meso-structures like helices, ribbons, and scrolls.
• Understanding these self-assembly processes is crucial for developing novel nanomaterials.

Purpose of the Study:

• To analyze the self-assembly of amphiphiles C_n-K (lysine coupled to alkyl tails) to understand chiral assembly formation.
• To investigate the influence of electrostatic and van der Waals interactions on chiral assembly structures.
• To explore methods for controlling nano- to meso-scale structures in chiral assemblies.

Main Methods:

• Synthesis and characterization of C_n-K amphiphiles (n=12, 14, 16).
• Small/wide-angle X-ray scattering (SAXS/WAXS) to determine assembly structures.
• Molecular dynamics (MD) simulations to elucidate molecular interactions and packing.
• Membrane energetics modeling to explain shape selection.

Main Results:

• At low pH, C₁₆-K forms planar crystalline bilayers with interdigitated tails.
• Increasing salt concentration induces cochleate formation in C₁₆-K assemblies.
• Elevated pH leads to helical assemblies for all C_n-K variants.
• Shape selection between helices and scrolls is governed by membrane energetics.

Conclusions:

• Solution ionic conditions continuously control the nano- to meso-scale structure of chiral assemblies.
• The study provides a foundation for an electrostatics-based approach to shape selection in chiral systems.
• This work advances the control over nanoscale structure formation in self-assembling chiral molecules.