Cyclohexane-based low molecular weight hydrogelators: a chirality investigation

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Organic Chemistry

Background:

• Small molecules can self-assemble into hydrogels.
• Amino acid chirality is crucial in molecular recognition and self-assembly.

Purpose of the Study:

• To synthesize novel 1,3,5-cyclohexyltricarboxamide-phenylalanine derivatives.
• To investigate the influence of amino acid chirality on hydrogelation properties in water.

Main Methods:

• Synthesis of chiral derivatives.
• Gelation tests in water.
• Concentration-dependent gel-to-sol transition temperature (Tgs) measurements.
• Transmission electron microscopy (TEM) for structural analysis.
• Circular dichroism (CD) spectroscopy.

Main Results:

• Homochiral derivatives (LLL or DDD) are non-hydrogelators, crystallizing from water.
• Heterochiral derivatives (LLD or DDL) are effective hydrogelators.
• Sigmoidal Tgs curves observed for LLD/DDL gels, differing from typical logarithmic curves of low molecular weight gelators (LMWGs).
• TEM revealed networks of 20 nm diameter fiber bundles with distinct helical handedness (right-handed for LLD, left-handed for DDL).
• Incorporation of non-gelators into gel fibers increased Tgs and altered helicity.
• Peripheral functionalization of non-gelators yielded hydrogelators, overcoming chirality's effect.

Conclusions:

• Amino acid chirality is a key determinant in the hydrogelation capability of these cyclohexyltricarboxamide derivatives.
• Heterochiral arrangements promote hydrogel formation through specific fiber bundle interactions.
• Structural modifications can override chirality-induced non-gelation behavior.