Balancing the intermolecular forces in peptide amphiphiles for controlling self-assembly transitions

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Biotechnology

Background:

• Controlling self-assembly in stimuli-responsive peptides is challenging, unlike simple surfactants where alkyl chain length and headgroup size effects are understood.
• Rational design of peptide self-assembly based on pH and concentration remains an elusive goal in materials science.

Purpose of the Study:

• To demonstrate that different amphiphilic peptides can achieve similar self-assembly phase diagrams by balancing attractive and repulsive forces.
• To explore strategies for designing self-assembled peptide vehicles with tunable sizes and consistent self-assembly profiles for MRI applications.

Main Methods:

• Synthesized and characterized amphiphilic peptides, including palmitoyl-YYAAEEEEK(DO3A:Gd)-NH2 and palmitoyl-YAAEEEEK(DO3A:Gd)-NH2, with varying hydrophobic and electrostatic components.
• Investigated the self-assembly behavior of these peptides across different pH and concentrations to map their phase diagrams.
• Evaluated the resulting self-assembled structures (micelles, nanofibers) and their magnetic resonance imaging (MRI) properties, specifically spin-lattice T1 relaxivity.

Main Results:

• Reducing hydrophobic attractive forces (fewer methylene groups) or increasing electrostatic repulsive forces (adding glutamic acid) led to similar self-assembly phase diagrams.
• Self-assembled MRI vehicles were created with slightly different micelle and nanofiber diameters.
• Minimal changes in spin-lattice T1 relaxivity were observed despite variations in vehicle size.

Conclusions:

• Balancing attractive and repulsive forces provides a powerful strategy for designing self-assembled peptide vehicles with predictable self-assembly behavior.
• This approach enables the creation of MRI contrast agents with tunable physical characteristics (size) while maintaining consistent performance (relaxivity).
• The findings offer a new paradigm for rationally designing complex self-assembled nanostructures for biomedical applications.