Understanding and optimizing the structure of novel peptide-based ionic liquids: Water as modulating agent

Area of Science:

• Materials Science
• Physical Chemistry
• Chemical Engineering

Background:

• Choline-peptides ([Ch][Pep]) are emerging biocompatible ionic liquids (ILs).
• Understanding the molecular behavior of {[Ch][Pep],H2O} blends is crucial for novel applications.
• Existing knowledge of these systems, especially at the molecular level, is limited.

Purpose of the Study:

• To investigate the nano-structuration of five {[Ch][Pep],H2O} binary systems using molecular dynamics.
• To identify distinct structural regimes and transitions as a function of water content.
• To elucidate the influence of water on both polar and apolar domains within the ILs.

Main Methods:

• Molecular dynamics (MD) simulations were performed on five {[Ch][Pep],H2O} binary systems.
• Analysis focused on the spatial distribution of water and the resulting nanostructure.
• Specific attention was given to the behavior of phenyl rings (Pher) in phenylalaninate-based ILs ([Ch][P] and [Ch][PP]).

Main Results:

• Water disperses unevenly, favoring anionic charge centers in the IL network.
• Five distinct structural regimes were identified, with key transitions around 70% and 95% water.
• Apolar domains (Pher) exhibit different disruption patterns in [Ch][P] versus [Ch][PP] systems with increasing water content.
• At high dilutions (e.g., 99.6% water), [Ch][PP] shows fractured apolar domains.

Conclusions:

• Water significantly reorganizes polar and apolar motifs in {[Ch][Pep],H2O} systems.
• Composition-dependent structural regimes and transitions were delineated.
• These findings provide insights for designing hydrotrope solvents for pharmaceutical formulations.