title: Synthesis and spectroscopy of micro-oxo (O(2)(-))-bridged heme/non-heme diiron complexes: models for the active site of nitric oxide reductase.
abstract: In this paper, we describe the synthesis and study of a series of heme/non-heme Fe-O-Fe' complexes supported by a porphyrin and the tripodal nitrogen ligand TMPA [TMPA = tris(2-pyridylmethyl)amine]. The complete synthesis of [((6)L)Fe-O-Fe(X)](+) (1) (X = OMe(-) or Cl(-), 69:31 ratio), where (6)L is the dianion of 5-(o-O-[(N,N-bis(2-pyridylmethyl)-2-(6-methoxyl)pyridinemethanamine)phenyl]-10,15,20-tris(2,6-difluorophenyl)porphine, is reported. The crystal structure for 1.PF(6) reveals an intramolecular heme/non-heme diferric complex bridged by an Fe-O-Fe' moiety; 90 degree angle (Fe-O-Fe') = 166.7(3) degrees, and d(Fe.Fe') = 3.556 A. Crystal data for C(70)H(57)ClF(12)Fe(2)N(8)O(3)P (1.PF(6)): triclinic, Ponemacr;, a = 13.185(3) A, b = 14.590 (3) A, c = 16.885(4) A, alpha = 104.219(4) degrees, beta = 91.572(4) degrees, gamma = 107.907(4) degrees, V = 2977.3(11) A(3), Z = 2, T = 150(2) K. Complex 1 (where X = Cl(-)) is further characterized by UV-vis (lambda(max) = 328, 416 (Soret), 569 nm), (1)H NMR (delta 27-24 [TMPA -CH(2)-], 16.1 [pyrrole-H], 15.2-10.5 [PY-3H, PY-5H], 7.9-7.2 [m- and p-phenyl-H], 6.9-5.8 [PY-4H] ppm), resonance Raman (nu(as)(Fe-O-Fe') 844 cm(-)(1)), and Mössbauer (delta(Fe) = 0.47, 0.41 mm/s; deltaE(A) = 1.59, 0.55 mm/s; 80 K) spectroscopies, MALDI-TOF mass spectrometry (m/z 1202), and SQUID susceptometry (J = - 114.82 cm(-)(1), S = 0). We have also synthesized a series of 3-, 4-, and 5-methyl-substituted as well as selectively deuterated TMPA(Fe') complexes and condensed these with the hydroxo complex (F(8))FeOH or (F(8)-d(8))FeOH to yield "untethered" Fe-O-Fe' analogues. Along with selective deuteration of the methylene hydrogens in TMPA, complete (1)H NMR spectroscopic assignments for 1 have been accomplished. The magnetic properties of several of the untethered complexes and a comparison to those of 1 are also presented. Complex 1 and related species represent good structural and spectroscopic models for the heme/non-heme diiron active site in the enzyme nitric oxide reductase.
authors.affiliation: Department of Chemistry, Johns Hopkins University, Charles and 34th Streets, Baltimore, Maryland 21218, USA.
authors.forename: Ian M
authors.initials: IM
authors.lastname: Wasser
authors.forename: Constantinus F
authors.initials: CF
authors.lastname: Martens
authors.forename: Claudio N
authors.initials: CN
authors.lastname: Verani
authors.forename: Eva
authors.initials: E
authors.lastname: Rentschler
authors.forename: Hong-Wei
authors.initials: HW
authors.lastname: Huang
authors.forename: Pierre
authors.initials: P
authors.lastname: Moënne-Loccoz
authors.forename: Lev N
authors.initials: LN
authors.lastname: Zakharov
authors.forename: Arnold L
authors.initials: AL
authors.lastname: Rheingold
authors.forename: Kenneth D
authors.initials: KD
authors.lastname: Karlin
mesh_terms: D001665:Binding Sites; D018360:Crystallography, X-Ray; D007202:Indicators and Reagents; D007501:Iron / Q000737:chemistry*; D007504:Iron Radioisotopes; D009682:Magnetic Resonance Spectroscopy; D008280:Magnetics; D008958:Models, Molecular; D019159:Nonheme Iron Proteins / Q000138:chemical synthesis* / Q000737:chemistry; D010088:Oxidoreductases / Q000737:chemistry*; D011487:Protein Conformation; D015204:Spectroscopy, Mossbauer; D013059:Spectrum Analysis, Raman
chemical_list: D007202:Indicators and Reagents; D007504:Iron Radioisotopes; D019159:Nonheme Iron Proteins; D007501:Iron; D010088:Oxidoreductases; C034747:nitric-oxide reductase