Dramatic specific-ion effect in supramolecular hydrogels.

Area of Science:

• Supramolecular chemistry
• Materials science
• Biomaterials engineering

Background:

• Peptide-based hydrogelators self-assemble into complex structures.
• Molecular self-assembly is driven by non-covalent interactions like hydrogen bonding and pi-stacking.
• Controlling self-assembly is crucial for designing advanced materials.

Purpose of the Study:

• To investigate the specific-ion effect of inorganic salts on peptide-based hydrogelators.
• To understand how anions influence the self-assembly, structure, and properties of fluorenylmethoxycarbonyl (Fmoc)-based peptide amphiphiles.
• To explore the potential for tunable nanofabrication via molecular self-assembly.

Main Methods:

• Synthesis of Fmoc-based peptide amphiphiles.
• Hydrogel formation and characterization.
• Atomic Force Microscopy (AFM) for morphological analysis.
• Rheometry for mechanical property assessment (G' values).
• Spectroscopic analysis to elucidate self-assembly mechanisms.

Main Results:

• Anions significantly altered the morphology of Fmoc-YL peptide hydrogels, from fibrous networks to spherical aggregates.
• Mechanical properties (G') varied between 0.8 kPa and 2.4 kPa depending on the anion.
• Self-assembly was primarily dictated by hydrophobic interactions, influenced by the fluorenyl group, consistent with the Hofmeister anion sequence.
• Less hydrophobic peptides showed a less pronounced effect.

Conclusions:

• Specific anions can precisely control the supramolecular structure and material properties of peptide hydrogelators.
• The observed effects are attributed to specific-ion interactions with the peptide structure, not sol-gel equilibrium.
• This provides a powerful strategy for designing and fabricating structurally diverse nanomaterials through simple adjustments to the ionic environment.