A Heterobimetallic FeIIIMnII Complex of an Unsymmetrical Dinucleating Ligand: A Structural and Functional Model Complex for the Active Site of Purple Acid Phosphatase of Sweet Potato

Summary, in English

The heterodinuclear mixed-valence complex [FeMn(ICIMP)(OAc)(2)Cl] (1) {H2ICIMP = 2-(N-carboxylmethyl)-[N-(N-methylimidazolyl-2-methyl)aminomethyl]-[6-(N-isopropylmethyl)-[N-(N-methylimidazolyl-2-methyl)]aminomethyl-4-methylphenol], an unsymmetrical N4O2 donor ligand} has been synthesized and fully characterized by several spectroscopic techniques as well as by X-ray crystallography. The crystal structure of the complex reveals that both metal centers in 1 are six-coordinate with the chloride ion occupying the sixth coordination site of the Mn-II ion. The phenoxide moiety of the ICIMP ligand and both acetate ligands bridge the two metal ions of the complex. Mossbauer spectroscopy shows that the iron ion in 1 is high-spin Fe-III. Two quasi-reversible redox reactions for the complex, attributed to the (FeMnII)-Mn-III/(FeMnII)-Mn-II (at -0.67 V versus Fc/Fc(+)) and (FeMnII)-Mn-III/(FeMnIII)-Mn-III (at 0.84 V), were observed by means of cyclic voltammetry. Complex 1, with an Fe-III-Mn-II distance of 3.58 angstrom, may serve as a model for the mixed-valence oxidation state of purple acid phosphatase from sweet potato. The capability of the complex to effect organophosphate hydrolysis (phosphatase activity) has been investigated at different pH levels (5.5-11) by using bis(2,4-dinitrophenyl)phosphate (BDNPP) as the substrate. Density functional theory calculations indicate that the substrate coordinates to the Mn-II ion. In the transition state, a hydroxide ion that bridges the two metal ions becomes terminally coordinated to the Fe-III ion and acts as a nucleophile, attacking the phosphorus center of BDNPP with the concomitant dissociation of the leaving group.

• Författare: Biswanath Das; Henrik Daver; Amrendra Singh; Reena Singh; Matti Haukka; Serhiy Demeshko; Franc Meyer; George Lisensky; Martin Jarenmark; Fahmi Himo; Ebbe Nordlander
• Avdelning/ar: Kemisk fysik
• Publiceringsår: 2014
• Språk: Engelska
• Sidor: 2204-2212
• Publikation/Tidskrift/Serie: European Journal of Inorganic Chemistry
• Volym: 2014
• Issue: 13
• Länkar: http://dx.doi.org/10.1002/ejic.201301375
• Dokumenttyp: Artikel i tidskrift
• Förlag: John Wiley & Sons Inc.
• Ämne: Atom and Molecular Physics and Optics
• Nyckelord: Metalloenzymes; Mixed-valent compounds; Moessbauer spectroscopy; Density; functional calculations; Transition states; Hydrolysis
• Status: Published
• ISBN/ISSN/Övrigt: ISSN: 1099-0682