Linking micellar structures to hydrogelation for salt-triggered dipeptide gelators.

Area of Science:

• Supramolecular chemistry
• Materials science

Background:

• Functionalized dipeptides are known to form hydrogels under specific conditions.
• High pH and salt addition are key factors influencing hydrogel formation.

Purpose of the Study:

• To characterize the phase behavior and structural transformations of the naphthalene-dipeptide 2NapFF in solution.
• To investigate the mechanism of hydrogel formation induced by calcium salt addition.

Main Methods:

• Surface tension, conductivity, rheology, optical microscopy (confocal, scanning electron microscopy).
• (1)H NMR, UV-Vis spectroscopy, IR spectroscopy, and SANS (Small-Angle Neutron Scattering).

Main Results:

• 2NapFF undergoes concentration-dependent structural changes: spherical micelles to worm-like micelles, then micelle association.
• Hydrogel formation is facilitated by the presence of worm-like micelles and calcium salt.
• Structural re-organizations occur at lower concentrations, enabling gelation at reduced concentrations.

Conclusions:

• The study elucidates the self-assembly pathway of 2NapFF from disordered structures to ordered hydrogels.
• The presence of worm-like micelles is crucial for calcium-induced hydrogelation.
• Structural insights into solution and hydrogel phases were obtained using complementary spectroscopic and microscopic techniques.