Synthesis, structure and stimulus-responsive properties of a metallogel of a designer ferrocene appended peptide mimetic†

This study reports a simple protocol for the synthesis of ferrocene substituted benzoic acid and an efficient synthetic approach towards a ferrocene appended peptide mimetic with a high reaction rate, yield and purity. From X-ray single crystal analysis, the ferrocene appended peptide mimetic adopts an extended conformation and self-aggregates to form a dimer structure by intermolecular hydrogen bonds. The dimer formation is also supported by mass spectrometry. In higher order packing, the dimeric subunits further self-assembled to form a complex sheet-like structure stabilized by multiple π–π stacking interactions between the phenyl and cyclopentandienyl rings of ferrocene. Moreover, the ferrocene appended peptide mimetic forms a stimulus-responsive metallogel in DMF–water. The rheology experiments support the formation of a strong gel. The metallogel burst on addition of other salts such as Cu(OAc)₂·4H₂O, Pb(OAc)₂, Zn(OAc)₂·2H₂O, Cd(OAc)₂·4H₂O, and Mn(OAc)₂·4H₂O. The metallogel is responsive to pH. On addition of triethylamine the metallogel turned into a golden yellow solution. However, on further addition of trifluoroacetic acid the metallogel reappeared.