5,10,15,20-meso-tetrapiridilporfirina de európio: síntese, caracterização e investigações espectroscópicas

Abstract

Increasingly, porphyrins have gained a position of detached interest in scientific circles. Its high biological compatibility, being a molecule found naturally in plants and many red blood animals, coupled with the possibility of forming complexes with lanthanide atoms, makes these compounds are particularly attractive in a branch of medicine quite promising in terms respect to combat cancer, called photodynamic therapy. The lanthanide-porphyrin complex act as photosensitizers in the production of singlet oxygen, a cytotoxic species, may be soaked in organic tissue of interest, promoting the cancer cell death. The synthesis of some Ln-porphyrin complexes [Ln (Ln = Gd, Er, Yb)] are already reported in the literature. However, with increasing ionic radius of metal that is intended to complex in the porphyrin, the energy barrier which prevails opposite the occurrence of this synthesis also increases, hindering the occurrence of the metalation process. Thus, this study seeks to promote metalation with europium, in 5,10,15,20 - meso - tetrapyridilporphyrin (H2TPyP). Was used the europium acetylacetonate salt [Eu(acac)3] in the synthesis as a source of Eu3+ ion. The obtained compound was purified by column chromatography on elution of alumina (Al2O3) and further characterized by absorption spectroscopy in the ultraviolet-visible region (UV-VIS) and infrared region (IR), luminescence and termogravimetric analysis (TG). The results obtained for the UV-vis spectra show for complex synthesized 3 Q bands, a lower number compared to the spectrum of the free base porphyrin, which has 4 Q bands, which discloses the formation of a compound with higher symmetry, which rose from D2h to D4h due to insertion of the metal ion in the porphyrin ring. It was observed also a bathochromic shift of the Soret band in the complex shifted from 417 to 429nm, consistent with the fact that the metallation occurred. The IR results and suggest the occurrence of metalation of the suppression band 3304cm-1, indicating deprotonation of the central atoms of Nytrogen, also suggested maintaining the acetylacetonate ion in stabilizing the structure of the complex. The luminescence showed that there was enhancement of emission bands, which is consistent with the formation of a metal complex. In the TG results, it was found that the compound formed to the amount of residue obtained was much higher than that for H2TPyP, suggesting the formation of metal oxide in the first case, consistent with the fact that formation of europium metalloporphyrin.