Enzyme mimic of heterobimetallic Cu(II) and Fe(III) tetrapyridylporphine modified nanoparticles

Abstract

The covalent binding of the porphyrin to immobilized gold nanoparticles resulted in a very useful and simple method to evaluate the absorption spectroscopy of a monolayer of porphyrins and the spectral changes produced by additional ligands. The layer by layer deposition showed no distinguishable porphyrin-related absorption bands whereas the direct simultaneous binding of porphyrins (Cu(II) and Fe(III) tetrapyridylporphine) to immobilized gold nanoparticles showed a significantly higher absorption band at 412 nm corresponding to the Soret band of the porphyrin ring. The ATR-FTIR spectra showed typical absorptions bands of porphyrin core at around 1000 cm−1 and 800 cm−1, which were only observed in the Cu(II) complex of TPyP/AuNPs–APTES/SiO2 suggesting that the CuTPyP molecule is tilted with respect to the substrate surface. The presence of FeTPyP produces changes in the geometry of the adsorbed CuTPyP porphyrins, indicating a flat accommodation of the porphyrinic rings in FeTPyP–CuTPyP composite that could be the reason of the differential tendency to include H2O2 as ligand. The difference UV–visible spectra of the bimetallic structures showed a very sensitive response to H2O2 concentration with a Kapp 3.75 × 103 M−1(R: 0.9865; Std E: 2.6 × 10−2) which was notoriously similar to Km value for peroxidase enzyme (2.5 × 103 M−1).