Síntese e caracterização espectroscópica de adutos obtidos com porfirinas, ácido esquárico e os metais de transição Co(II), Ni(II), Cu(II) e Zn(II)

Abstract

In the present work it has been described the syntheses, spectroscopic and biological properties of metalloporphyrins derived from three different porphyrins: (5,10,15,20-tetraphenyl)-21H,23H porphyrin [H2TPP], (5,10,15,20-tetrapiridil)-21H,23H porphyrin [H2TPyP] and (ρ-tetrakis-hidroxiphenyl)-21H,23H porphyrin [H2TKP]. Thirty three compounds have been synthesized, where eighteen are new, and were obtained from the reaction between metalloporphyrins containing metal ions from the first transition series [Co2+, Ni2+, Cu2+ and Zn2+], the oxocarbon squaric acid, and the Schiff base 1,2-N,N-bis(4methoxibenzylidene) ethylenodiimine (MBDA).Several techniques were used to characterize the compounds: vibrational spectroscopy (Raman and infrared absorption), electronic spectroscopy, nuclear magnetic and electron paramagnetic resonances, and thermogravimetry; such techniques provided information that allowed us to propose structural arrangements for the compounds obtained. It is noteworthy that both the metal and the squaric acid have a key role in the final arrangement archived. The proposed structures are distorted, as suggested by electronic spectroscopy, through the shift of the Soret band. PCA chemometric analysis was useful in predicting that the most energetic secondary bands in the electronic spectra of porphyrins (N, L and M bands ≤ 200 nm) are more susceptible to variations in water content of the medium. The class of compounds formed by the respective metalloporphyrins and the coordination of one or two squaric acid molecules in the axial positions of the metal (M) are named “oxocarbonporphyrins” [MTKP(SQ)]. For the first time, metalloporphyrins together with oxocarbon ion are classified as a new family of compounds and this proposal was based on a comparative method. It was also observed the lability of zinc(II) complexes in solution as well as the instability of the cobalt(II) complexes, for all the synthesized derivatives. These data strongly suggest that the accommodation of the metal ion inside the macrocyclic ligand is ion size dependent. However, the [ZnTKP(SQ)] complex showed up as the most positive and promising species for photodynamic trials, with electronic transitions above 650 nm in the therapeutic window.