Spectroscopic Investigation of the Selective Interaction of Mercuric and Cupric Ions with a Porphyrin Active Layer

Abstract

The mechanisms of interaction between a tetrapyridyl-substituted porphyrin and Hg(II) and Cu(II) ions have been investigated by means of different spectroscopic techniques. Reflection spectroscopy investigations of the porphyrin Langmuir floating film and by polarization modulation infrared (IR) reflection adsorption spectroscopy at the air–water interface provided evidence of the active role played by the pyridyl substituents of the porphyrin in the interaction with the analyte. Such behavior seems to be very selective toward Cu2+ and Hg2+ ions, as demonstrated by the IR measurements in difference mode. UV–vis and IR characterizations suggest a deeply different interaction between the active molecules and the two analytes. In fact, the interaction of Hg2+ ions with the tetrapyrrolic derivative molecules involves both the pyridyl substituents and the central bite of the ring. On the other hand, in the case of Cu2+ ions, spectroscopic evidence suggests that the cupric ions interact with only the porphyrin peripheral substituents. A relevant fluorescence quenching of the Langmuir–Schaefer (LS) film is observed when even a 0.5 nM HgCl2 or 0.5 nM CuCl2 aqueous solution is fluxed on the LS film.

The influence of combination mode on the structure and properties of porphyrin–graphene oxide composites

“…1-3 with the reported rationales [13,38], we find three different binding mechanisms rule the interaction between the GO and the porphyrins (THPP, TPP and TPPOH). Based on the structural characteristics of the TPPOH and the GO and our previous report about the interaction between TPPOH zinc and titanate nanotubes [39], it is deduced that the interaction between the TPPOH and the GO is mainly occurs on the peripheries of the GO.…”

ZnO‐Porphyrin Composite Nanostructures as Discriminating Adducts for Metallic Ions in Aqueous Matrices

“…This region is dominated by the typical TPyP vibration modes. The porphyrin spectrum is mainly characterized by a sharp peak at about 1590 cm −1 , due to the combination of the stretching modes of C=C and C=N groups of the pyridyl substituents, another important asymmetric peak centered at about 1480 cm −1 , ascribable to C=C and C=N stretching modes of both substituents and porphyrin core, and a signal at about 1405 cm −1 attributable to an overlap of pyridine and pyrrole groups …”

“…Such chemical groups are well‐known to be involved in binding and sensing phenomena and were expected to be influenced by the interaction with ZnO. In fact, the corresponding IR signals vary in the ZnO@TPyP spectrum (grey line Figure a).…”

“…A possible rationale of these evidences is that a different interactions of TPyP with metal ions takes place, according to already reported conclusions . Cupric ions mainly interact with the pyridyl substituents that are already involved in the binding with ZnO surface reducing the strength of the physical adsorption of TPyP on zinc oxide surface, increasing the weight percent of excited electrons that shows a longer lifetime, quenching the SERS effect.…”

“…Porphyrins are well‐known macrocycles used as active layers for sensors of many different analytes both in liquid and in vapor phase . TPyP was already used to detect cupric and mercuric ions . The resonance effect between TPyP and ZnO is the consequence of a charge transfer from the porphyrin towards the inorganic semiconductor and it is affected by the presence of cupric and mercuric ions.…”