Four cyclo(l-Lys-l-Glu) derivatives (<b>3</b>–<b>6</b>) were synthesized from the coupling reaction
of protecting l-lysine with l-glutamic acid followed
by the cyclization, deprotection, and protection reactions. They can
efficiently gelate a wide variety of organic solvents or water. Interestingly,
a spontaneous chemical reaction proceeded in the organogel obtained
from <b>3</b> in acetone exhibiting not only visual color alteration
but also increasing mechanical strength with the progress of time
due to the formation of Schiff base. Moreover, <b>6</b> bearing
a carboxylic acid and Fmoc group displayed a robust hydrogelation
capability in PBS solution. Transmission electron microscopy (TEM)
and scanning electron microscopy (SEM) revealed the characteristic
gelation morphologies of 3D fibrous network structures in the resulting
organo- and hydrogels. FT-IR and fluorescence analyses indicated that
the hydrogen bonding and π–π stacking play as major
driving forces for the self-assembly of these cyclic dipeptides as
low-molecular-weight gelators. X-ray diffraction (XRD) measurements
and computer modeling provided information on the molecular packing
model in the hydrogelation state of <b>6</b>. A spontaneous
chemical reaction proceeded in the organogel obtained from <b>3</b> in acetone exhibiting visual color alteration and increasing mechanical
strength. <b>6</b> bearing an optimized balance of hydrophilicity
to lipophilicity gave rise to a hydrogel in PBS with MGC at 1 mg/mL
