Conformational Heterogeneity and Self-Assembly of α,β,γ-Hybrid Peptides Containing Fenamic Acid: Multistimuli-Responsive Phase-Selective Gelation

The effect of fenamic acid−α-aminoisobutyric acid
corner motif in α,β,γ-hybrid peptides has been reported.
From X-ray single-crystal diffraction studies, it is observed that
Phe-containing peptide 1 has an “S”-shaped
conformation that is stabilized by two consecutive intramolecular
N–H···N hydrogen bonds. However, the tyrosine
analogue peptide 2 has an “S”-shaped conformation,
which is stabilized by consecutive intramolecular six-member N–H···N
and seven-member N–H···O hydrogen bonds. The
asymmetric unit of peptide 3 containing m-aminobenzoic acid has two molecules which are stabilized by multiple
intermolecular hydrogen-bonding interactions. There are also π–π
stacking interactions between the aromatic rings of fenamic acid.
The peptides 1 and 2 have a polydisperse
microsphere morphology, but peptide 3 has an entangled
fiber-like morphology. Peptides 1–3 do not form
organogels. However, in the presence of water, the peptide 3 forms a phase-selective instant gel in xylene. The gel exhibits
high stability and thermal reversibility. The phase-selective gel
of peptide 3 is highly responsive to H2SO4.