Axial ligation in water-soluble copper porphyrinates: contrasts between EPR and UV–vis

• Published in: Inorganic chemistry communications Vol. 18; pp. 1 - 3
• Main Authors: Mot, Augustin C., Syrbu, Sergei A., Makarov, Sergei V., Damian, Grigore, Silaghi-Dumitrescu, Radu
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-04-2012
• Subjects: Copper porphyrin; DFT; EPR; EPR; Copper porphyrin; DFT
• ISSN: 1387-7003; 1879-0259
• DOI: 10.1016/j.inoche.2011.12.030

Copper porphyrinates are generally known to display a less diverse reactivity compared to their iron counterparts. Here, we examine a water-soluble copper porphyrinate for its ability to engage in reactions involving axial ligation to the copper or possible redox cycling. Although UV–vis spectra indicate an expected lack of reactivity, electron paramagnetic resonance spectra (EPR) reveal an unexpected wealth of changes in electronic structures at the copper, induced by potential ligands such as imidazole or nitrite, but also by seemingly unexpected candidates for ligands, such as 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) and guaiacol, as well as by dithionite.
Reactions of water-soluble copper porphyrinates appear much more sensitively examined by EPR than by UV–vis; dithionite and ABTS are among unexpected ligands [Display omitted]
► Reactions of a water-soluble copper porphyrin are investigated with UV–vis and EPR. ► Ligands and redox partners leave the UV–vis spectrum almost or entirely unaffected. ► Drastic changes in the EPR spectrum are noted, by contrast to UV–vis. ► ABTS and dithionite are surprisingly shown by EPR to ligate the copper porphyrin.