Amino-Acid-Based Metallo-Hydrogel That Acts Like an Esterase.

A histidine-based amphiphile containing a C14 fatty acyl chain, N- histidyl N'-myristry ethyl amine (, 14.7 mM) forms hydrogels in the presence of Fe (within the range 1.47 to 4.41 mM) and Hg (within the range 3.67 to 11.02 mM) ions in aqueous dispersions at pH 6.6 (27 °C). The imidazole ring of the histidine residue plays a vital role to interact with these metal-ions. The thermal and mechanical stability of these metallo-hydrogels can be tuned by changing the proportion of amphiphile to metal ion ratio (1:0.1 to 1:0.3 for Fe-containing gel and 1:0.25 to 1:0.75 for Hg-containing gel). The metallo-hydrogels were characterized by different spectroscopic and microscopic techniques, low- and wide-angle powder X-ray diffraction, and small-angle X-ray scattering studies. FT-IR and NMR spectroscopic studies indicate the participation of the imidazole ring in metal-ion binding. Low- and wide-angle powder X-ray diffraction and small-angle X-ray scattering data are in favor of a layered structure of the supramolecular assembly of the in the presence of metal-ions. Both, the amphiphiles and the metal ion induced hydrogels reveal catalytic activity of -nitrophenyl esters hydrolysis for the acetyl, -butyl and -octyl esters . Ferric ion containing metallo-hydrogel exhibits higher catalytic activity than the corresponding aggregate in the absence of metal ions.