Inorganic–organic hybrid copper phosphate nanoflower coated with an upper rim tetra-imidazolyl-phenanthroline derivatized calix[4]arene: synthesis, characterization and its application as a peroxidase mimic catalyst

Abstract

An upper rim tetra-imidazolyl-phenanthroline derivatized calix[4]arene conjugate (L) was synthesized and characterized using different analytical, spectral, microscopic and diffraction techniques. The incubation of L with CuSO₄·5H₂O in PBS buffer (20 mM) for 1 h resulted in the formation of a nanoflower material. The L-coated copper phosphate nanoflowers (L@CuPNFs) were characterized through Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, powder X-ray diffraction, and microscopy techniques. The peroxidase mimetic activity of L@CuPNFs was assessed, and the results were compared with those of unmodified CuPNFs as a control. The peroxidase activity was demonstrated using three different substrates, viz., tetramethylbenzidine (TMB), ortho-phenylenediamine (OPD) and guaiacol. The progress of the oxidation reaction of the model substrates in the presence of L@CuPNFs and H₂O₂ was demonstrated through absorption spectra measured as a function of time. The changes could be qualitatively gauged from the observed visual colour variation. The oxidized species were identified by measuring the ESI-MS spectrum of the reaction mixture. The rate of oxidation of these substrates in the presence of H₂O₂ was higher when L@CuPNFs were used as a catalyst, and this was much greater than the reaction rate observed with the unmodified CuPNF, which was not coated with L. All these results confirmed that the coating of L enhanced the peroxidase mimetic activity of the nanoflowers.