Abstract
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/SiO 2 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 H 2 O 2 as ligand. The difference UV–visible spectra of the bimetallic structures showed a very sensitive response to H 2 O 2 concentration with a Kapp 3.75 × 10 3 M −1 ( R : 0.9865; Std E : 2.6 × 10 −2 ) which was notoriously similar to K m value for peroxidase enzyme (2.5 × 10 3 M −1 ).
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