Iron L-edge X-ray Absorption Spectroscopy of Oxy-Picket Fence Porphyrin: Electronic Structure of the Fe-O2 Bond
2013 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, no 3, 1124-1136 p.Article in journal (Refereed) Published
The electronic structure of the Fe-O-2 center in oxy-hemoglobin and oxy-myoglobin is a long-standing issue in the field of bioinorganic chemistry. Spectroscopic studies have been complicated by the highly delocalized nature of the porphyrin, and calculations require interpretation of multi-determinant wave functions for a highly covalent metal site. Here, iron L-edge X-ray absorption spectroscopy, interpreted using a valence bond configuration interaction multiplet model, is applied to directly probe the electronic structure of the iron in the biomimetic Fe-O-2 heme complex [Fe(pfp)-(1-Melm)O-2] (pfp ("picket fence porphyrin") = meso-tetra(alpha,alpha,alpha,alpha-o-pivalamidophenyl)porphyrin or TpivPP). This method allows separate estimates of sigma-donor, pi-donor, and pi-acceptor interactions through ligand-to-metal charge transfer and metal-to-ligand charge transfer mixing pathways. The L-edge spectrum of [Fe(pfp)(1-MeIm)O-2] is further compared to those of [Fe-II(pfp)(1-MeIm)(2)], [Fe-II(pfp)], and [Fe-III(tpp)(ImH)(2)]Cl (tpp = meso-tetraphenylporphyrin) which have Fe-II S = 0, Fe-II S = 1, and Fe-III S = 1/2 ground states, respectively. These serve as references for the three possible contributions to the ground state of oxy-pfp. The Fe-O-2 pfp site is experimentally determined to have both significant sigma-donation and a strong pi-interaction of the O-2 with the iron, with the latter having implications with respect to the spin polarization of the ground state.
Place, publisher, year, edition, pages
American Chemical Society (ACS), 2013. Vol. 135, no 3, 1124-1136 p.
IdentifiersURN: urn:nbn:se:uu:diva-198495DOI: 10.1021/ja3103583ISI: 000314141200029PubMedID: 23259487OAI: oai:DiVA.org:uu-198495DiVA: diva2:616337