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Conclusions
In summary, we have demonstrated that N-[4-n-alkyloxy-
benzoyl]-L-carnosine amphiphiles form thermo-reversible
hydrogels in buffered water over a wide pH range. The gelation
of water by the amphiphile occurs at concentrations less than 1%
(w/v). The gelation was found to be very sensitive to pH. No
gelation could be observed between pH 3 and pH 6 and at pH >
11. Among the hydrogelators, C16OBC has the highest gel
melting temperature at all pHs. Unlike other amphiphilic gela-
tors reported in the literature, the gelation ability and gel melting
temperature were found to be highest with C16OBC due to
maximum hydrophobic effect and van der Waals interactions.
For any of the gelators, the gel melting temperature is highest in
pH 2 and it decreases with an increase in pH. The supramolecular
aggregates of the amphiphiles have ribbon-like bilayer struc-
tures, which are formed through a p–p stacking interaction of
the phenyl group and van der Waals interactions of the hydro-
carbon chain of adjacent molecules. The gel formed by C16OBC
has the highest mechanical strength at all pHs as indicated by the
yield stress values which are much higher than the corresponding
values of other gelators. For all the gelators, the yield stress at pH
7 is highest due to its zwitterionic character which reduces ionic
repulsion between headgroups. At a pH higher or lower than 7.0
the gelation ability, thermal stability and mechanical strength are
reduced due to the increased headgroup repulsion. Due to ther-
moreversibility and pH- and rheology-modulated hydrogelation,
the amphiphiles could have potential applications in drug
delivery.
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The authors acknowledge the Indian Institute of Technology,
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