title: Spectroscopic and catalytic characterization of a functional Fe(III)Fe(II) biomimetic for the active site of uteroferrin and protein cleavage.
abstract: A mixed-valence complex, [Fe(III)Fe(II)L1(μ-OAc)(2)]BF(4)·H(2)O, where the ligand H(2)L1 = 2-{[[3-[((bis(pyridin-2-ylmethyl)amino)methyl)-2-hydroxy-5-methylbenzyl](pyridin-2-ylmethyl)amino]methyl]phenol}, has been studied with a range of techniques, and, where possible, its properties have been compared to those of the corresponding enzyme system purple acid phosphatase. The Fe(III)Fe(II) and Fe(III)(2) oxidized species were studied spectroelectrochemically. The temperature-dependent population of the S = 3/2 spin states of the heterovalent system, observed using magnetic circular dichroism, confirmed that the dinuclear center is weakly antiferromagnetically coupled (H = -2JS(1)·S(2), where J = -5.6 cm(-1)) in a frozen solution. The ligand-to-metal charge-transfer transitions are correlated with density functional theory calculations. The Fe(III)Fe(II) complex is electron paramagnetic resonance (EPR)-silent, except at very low temperatures (<2 K), because of the broadening caused by the exchange coupling and zero-field-splitting parameters being of comparable magnitude and rapid spin-lattice relaxation. However, a phosphate-bound Fe(III)(2) complex showed an EPR spectrum due to population of the S(tot) = 3 state (J= -3.5 cm(-1)). The phosphatase activity of the Fe(III)Fe(II) complex in hydrolysis of bis(2,4-dinitrophenyl)phosphate (k(cat.) = 1.88 × 10(-3) s(-1); K(m) = 4.63 × 10(-3) mol L(-1)) is similar to that of other bimetallic heterovalent complexes with the same ligand. Analysis of the kinetic data supports a mechanism where the initiating nucleophile in the phosphatase reaction is a hydroxide, terminally bound to Fe(III). It is interesting to note that aqueous solutions of [Fe(III)Fe(II)L1(μ-OAc)(2)](+) are also capable of protein cleavage, at mild temperature and pH conditions, thus further expanding the scope of this complex's catalytic promiscuity.
authors.affiliation: School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane 4072, Australia.
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Smith
authors.forename: Rosely A
authors.initials: RA
authors.lastname: Peralta
authors.forename: Rafael
authors.initials: R
authors.lastname: Jovito
authors.forename: Adolfo
authors.initials: A
authors.lastname: Horn
authors.forename: Adailton J
authors.initials: AJ
authors.lastname: Bortoluzzi
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Noble
authors.forename: Graeme R
authors.initials: GR
authors.lastname: Hanson
authors.forename: Robert
authors.initials: R
authors.lastname: Stranger
authors.forename: Vidura
authors.initials: V
authors.lastname: Jayaratne
authors.forename: Germán
authors.initials: G
authors.lastname: Cavigliasso
authors.forename: Lawrence R
authors.initials: LR
authors.lastname: Gahan
authors.forename: Gerhard
authors.initials: G
authors.lastname: Schenk
authors.forename: Otaciro R
authors.initials: OR
authors.lastname: Nascimento
authors.forename: Angélica
authors.initials: A
authors.lastname: Cavalett
authors.forename: Tiago
authors.initials: T
authors.lastname: Bortolotto
authors.forename: Guilherme
authors.initials: G
authors.lastname: Razzera
authors.forename: Hernán
authors.initials: H
authors.lastname: Terenzi
authors.forename: Ademir
authors.initials: A
authors.lastname: Neves
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Riley
mesh_terms: D000135:Acid Phosphatase / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D040761:Biomimetic Materials / Q000737:chemistry / Q000378:metabolism; D020134:Catalytic Domain; D002417:Cattle; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D005290:Ferric Compounds / Q000737:chemistry* / Q000378:metabolism; D005296:Ferrous Compounds / Q000737:chemistry* / Q000378:metabolism; D006023:Glycoproteins / Q000737:chemistry* / Q000378:metabolism; D006868:Hydrolysis; D008958:Models, Molecular; D011725:Pyridines / Q000737:chemistry / Q000378:metabolism; D012710:Serum Albumin, Bovine / Q000378:metabolism
chemical_list: D005290:Ferric Compounds; D005296:Ferrous Compounds; D006023:Glycoproteins; D011725:Pyridines; D012710:Serum Albumin, Bovine; C091137:purple acid phosphatase; D000135:Acid Phosphatase; C023666:pyridine