posted on 2019-06-11, 00:00authored byPooja Sharma, Harsimran Kaur, Sangita Roy
Controlling
the self-assembly pathways can be an effective means
to create complex multifunctional structures based on a single gelator
design. To this direction, an ion mediated approach to control and
direct supramolecular structure of the low molecular weight peptide
hydrogelator would be an excellent methodology for bottom-up nanofabrication
of these advanced functional materials. Our work primarily aims to
understand the role of different metal ions as well as anions in modulating
the self-assembly of the peptide amphiphiles. Our approach relies
on rational incorporation of histidine in the peptide amphiphile,
which can impart an ion responsive behavior to the hydrogels. Interestingly,
the self-assembly pathway of histidine based dipeptide amphiphile
was found to be largely influenced by various metal salts. A gel to
sol transition occurred at physiological pH in the presence of Cu2+, Ni2+ and Co2+ ions, owing to their
strong interactions with the histidine, thus shifting the gelation
to pH 3.0. However, in the case of Fe2+ and Mn2+, the weak interactions of histidine–metal ion can still hold
the gel at physiological pH but gel strength was significantly decreased.
Our studies provide a clear insight into this ion-responsive behavior
across a wide pH range, which is mainly governed by the stability
of a peptide–metal ion complex as per Irving–Williams
series. Moreover, anions also influenced the mechanical strength as
well as morphology of the nanostructures owing to their differential
interaction with water as depicted in the Hofmeister series of anions.
This bioinspired approach will provide an elegant strategy for accessing
diverse structures, which are “out of equilibrium” and
otherwise only accessible through differential molecular design. We
envisage that our systematic studies on histidine–metal ion
interaction can be an extremely useful methodology, which will pave
a way to design and develop the stimuli responsive biomaterials.