Spectroscopic Study of the Dimerization Process οf Iron Protoporphyrin IX

Abstract

The commercial protoporphyrin IX, iron-ferriprotoporphyrin IX-chloride and synthesized iron porphyrin µ-oxo-dimers were examined by UV/vis absorption and fluorescence, Fourier transformed infrared spectroscopy, resonance Raman, X-ray absorption, Mössbauer spectroscopy and SQUID. The evidence of Fe-O-Fe antiferromagnetic coupling concluded from SQUID and Mössbauer in the case of samples containing dimerized forms confirmed the presence of the oxo-bridges. In this paper the results of UV/vis, fluorescence, Fourier transform infrared FTIR and Raman spectroscopies are reported and discussed. The study is based on the comparison of the free-base protoporphyrin IX, Fe-PPIX-Cl and the synthesized dimerized specimen. The vibrational modes in two energy regions i.e. 330-650 cm −1 and 750-900 cm −1 , reportedly characteristic of the existence of Fe-O-Fe bridges, are discussed. A significant photoluminescence emission, strongly Stokes shifted from the Soret band, absent in the protoporphyrin IX and the iron-ferriprotoporphyrin IX-chloride, is observed. The strong Stokes shift and the mismatch of the excitation spectrum to the Soret band suggest that is does not have origin in the de-excitation of the porphyrin moiety and that it could have origin in an Fe-O-Fe charge transfer state.

Spectroscopic study and electronic structure of prototypical iron porphyrins and their μ-oxo-dimer derivatives with different functional configurations

“…Iron porphyrin dimers were prepared by insertion of iron atoms from 57 FeCl 3 into protoporphyrin IX (PPIX) (Sigma-Aldrich) precipitated from a water-N,N-dimethylformamide (DMF) solution, according to the modied Adler and Fleisher procedure. 17 The reactant solvent obtained in a basic synthetic procedure was treated with a stoichiometric amount of NaOH and diluted with distilled water and centrifuged. Supernatant and sediment were checked at every stage by UV/Vis absorption spectroscopy to monitor the metallization/dimerisation process and later lyophilized.…”

“…15 Also Mössbauer spectroscopy studies, performed on the complexes we investigated, claimed the occurrence of a solvation effect. 16 As an ideal local structural probe, the X-ray absorption spectroscopy was already used to investigate local structural congurations of porphyrins, [17][18][19] as well as to identify spin-structures combining Mössbauer data and other magnetic and spectroscopic measurements, etc. 19 Metalloporphyrins are networking molecules with strong internal N-H hydrogen bonds that may be used to substitute a metal ion inside a porphyrin ring, forming a metallo complex.…”

Cryogenically induced signal enhancement of Raman spectra of porphyrin molecules

“…Previous studies have successfully reduced the photothermal degradation by mixing the pure porphyrin sample with a KBr at 1% concentration and pressing into a pellet, which acts as a heat sink. 27 In this experiment, the heat sink is provided by the Linkam cooling stage, which reduces the sample temperature to cryogenic levels and thus limits the photothermal degradation. As the results do not indicate any contribution of photochemical degradation reduction to the signal enhancement, it is reasonable to assume that the observed effect can be entirely assigned to the reduction in photothermal degradation.…”