Cu(II)-Based Nanofibrous Metallogel for Phenoxazinone Synthase-like Activity

Sougata Sarkar, Pradip K. Maji, Yuichi Negishi, Soumen Dutta, Tarak N. Das, Rahul Pan, Saikat Sarkar

Research output: Contribution to journalArticlepeer-review


Metallogel formation by an individual ligand is well known, but simultaneous need of two ligands in selective metallogelation is relatively less common. In our present study, we have shown that disodium succinate and hexamethylenetetramine, when allowed to react simultaneously with CuCl2 in an aqueous medium, instantaneously form a greenish metallogel. The gelation is not attainable in the absence of any of the two ligands, which ascertains the cooperativity of the ligands to successfully achieve the metallogelation. Different microanalytical studies [Fourier transform infrared (FTIR), powder X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, rheology, and so on] have been performed for complete characterizations of the gel sample. The gel shows a nanodimensional entangled network morphology. Metal-ligand coordination in association with solvent-mediated hydrogen bonding interactions becomes a part-and-parcel in making the nanoscale fibrillar network of the metallogel. Different related ligands and metal ions were also reviewed in lieu of the above two ligands and the Cu(II) ion, but none of the alternatives was able to result in the gel formation. Thus, both the ligands were highly specific for the said metallogelation with Cu(II) only. The effect of counter anions of the Cu(II) salt was also studied. The gel also exhibits its stimuli-responsive nature toward different interfering chemical parameters such as pH, selective anions, selective complexing agents, and so forth. Finally, the robust Cu(II) metallogel was deliberately exploited as a heterogeneous catalyst for successful oxidative conversion of 2-aminophenol (OAPH) to phenoxazinone hiring atmospheric oxygen and thereby conferring its role as a biomimetic nanozyme catalyst. The catalytic conversion has been followed spectrophotometrically. The detailed kinetics for the reaction was performed with varied reaction parameters. The Michaelis-Menten model was applied to analyze the results. Based on the experimental results (e.g., FTIR, XRD, thermogravimetric analysis, and electrospray ionization-mass spectrometry), a mechanistic approach has also been anticipated to establish the catalytic process. Finally, recyclability of the catalyst was also verified. This nanozymatic phenoxazinone synthase-like activity of a nanodimensional metallogel is hitherto unknown and thus suggests its enzyme mimicking feature.

Original languageEnglish
JournalACS Applied Nano Materials
Publication statusAccepted/In press - 2021


  • catalyst
  • copper
  • heterogeneous
  • metallogel
  • nanozyme
  • phenoxazinone synthase

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