Iron Porphyrin Dications with Neutral Axial Ligands: DFT Calculations Delineate Similarities with Heme Protein Compound II Intermediates

详细信息    查看全文

• 作者：Adam C. Chamberlin ; Akira Ikezaki ; Mikio Nakamura ; Abhik Ghosh
• 刊名：Journal of Physical Chemistry B
• 出版年：2011
• 出版时间：April 7, 2011
• 年：2011
• 卷：115
• 期：13
• 页码：3642-3647
• 全文大小：881K
• 年卷期：v.115,no.13(April 7, 2011)
• ISSN：1520-5207

文摘

OLYP/TZP calculations on two symmetrized model complexes [Fe(TPP)(py)₂]²⁺ and [Fe(TPP)(PhNC)₂]²⁺ (TPP = meso-tetraphenylporphyrin, py = pyridine, PhNC = phenylisocyanide) reveal dense manifolds of low-energy electronic states. For the latter complex, broken-symmetry calculations successfully reproduce the unique S = 0 ground state that is expected on the basis of experimental measurements on a closely related complex; the S = 0 state arises from antiferromagnetic coupling between a low-spin d_xy¹(d_xz,d_yz)⁴ Fe(III) center and a porphyrin 鈥渁_2u鈥?radical. Furthermore, the calculations indicate low-energy Fe(IV) states for both complexes. Overall, the results contribute to our deepening understanding of the factors contributing to the stability of iron(IV) centers. Thus, a dianionic 蟺-donor oxo ligand is no longer deemed a requirement for the stability of heme-based Fe(IV) centers; iron(IV) intermediates of heme proteins such as chloroperoxidase, catalase, and MauG, having only monanionic ligands such as hydroxide, thiolate, and phenolate and/or (in the case of MauG) a neutral histidine as axial ligands, are now firmly established.