Organogelators from self-assembling peptide based dendrimers: structural and morphological features

Two peptide based dendrimers containing l-aspartic acid as the branching unit and succinic acid/terephthalic acid as the core unit were synthesized, characterized, and studied. These dendritic peptides form gels in various organic solvents including n-hexanol, benzene, toluene, chlorobenzene, 1,2-dichlorobenzene, o-xylene, tetralin, and nitrobenzene. Gels were characterized by freeze fracture transmission electron microscopic (FF-TEM), field emission scanning electron microscopic (SEM), transmission electron microscopic (TEM), wide angle X-ray powder diffraction (WAXPD), and variable temperature FTIR (VT-FTIR) studies. The VT-FTIR study indicates that amides and ester groups are involved in intermolecular hydrogen bonding in the gel state. Two transitions have been observed for both the dendrimer gels upon heating: the first one corresponds to the gel to sol transition and corresponds to the breaking of hydrogen bonds between esters and amides; the second one corresponds to the breaking of hydrogen bonds between amides. In the case of dendrimer 1 structural reorganization occurs in the sol state after the first transition, which is absent in the dendrimer 2 in the sol state. FF-TEM observations showed that both dendritic peptides form a platelet structure in gel state. SEM images of these dried gels indicate different geometry in different solvents in their self-assembled gel state.