Chirally directed formation of nanometer-scale proline clusters

Area of Science:

• Biophysical Chemistry
• Supramolecular Chemistry
• Chemical Physics

Background:

• Amino acid clusters are crucial for understanding biological processes.
• Chirality plays a significant role in molecular self-assembly and function.
• Previous studies have explored small amino acid aggregates, but large, ordered chiral structures remain less understood.

Purpose of the Study:

• To investigate the formation and structure of enantiopure and racemic proline clusters.
• To explore the influence of chirality on cluster size, shape, and organization.
• To provide insights into the intermolecular forces driving chiral self-assembly in amino acids.

Main Methods:

• Ion mobility measurements to analyze cluster size, shape, and charge state distributions.
• Molecular mechanics simulations to model cluster structures and energetics.
• Electrospray ionization to generate proline clusters.

Main Results:

• Observed broad distributions of cluster sizes (1 to >100 proline units) and charge states (n=1-7).
• Provided direct evidence of nanometer-scale, chirally induced organization in larger clusters.
• Enantiopure proline clusters (n=4, 5) assembled into more elongated structures than racemic clusters.
• Cis-4-hydroxy-proline showed different behavior, highlighting the importance of side chain rigidity and intermolecular interactions.

Conclusions:

• This is the first observation of chirally selective, elongated structures in amino acid clusters of this size range.
• Chirality significantly influences the self-assembly of proline clusters, leading to distinct structural outcomes.
• Intermolecular interactions and side chain rigidity are key factors in forming directed chiral clusters.