Gel-to-Gel Transformation in an Fe(III) Metallohydrogel: Kinetic Modulation, Mechanistic Insights, and Dual-Responsive Intrinsic Nanozyme Activity

Nanodimensional metallohydrogels with fascinating supramolecular architectures showing potential enzyme-mimicking behavior are a key concern in current research. Here, we have addressed a wet chemistry approach for the synthesis of an Fe(III) metallohydrogel employing the sodium salt of 5-sulfoisophthalic acid. At the outset, the metallogelation results in an opaque gel. Both metal-ligand coordination and solvent-assisted hydrogen bonding interactions are responsible for gel formation. Here, the most intriguing feature was the spontaneous transformation of the as-synthesized opaque gel to a completely transparent gel under ambient conditions over time. The kinetic modulation of this transformation was clearly reflected in differences in the microanalytical results between the opaque and transparent gel materials. Herein, the opaque gel is assigned as a kinetically controlled product (KCP), while the transparent gel is identified as a thermodynamically controlled product (TCP). A mechanism encompassing a delicate balance between KCP and TCP is proposed to elucidate the complex pathway. The nanoscale metallohydrogel was then successfully employed as a heterogeneous catalyst in enzyme mimetic reactions and oxidase and peroxidase mimicking. A simple method for low-level detection of glutathione (GSH) was also reported. Thus, this nanoscale Fe(III) metallohydrogel is illustrated as an efficient dual-purpose artificial enzyme mimic, i.e., nanozyme, showing its application potential in biomimetic research.