1301
|
Chavez FA, Ho RYN, Pink M, Young VG, Kryatov SV, Rybak-Akimova EV, Andres H, Münck E, Que L, Tolman WB. Unusual peroxo intermediates in the reaction of dioxygen with carboxylate-bridged diiron(II,II) paddlewheel complexes. Angew Chem Int Ed Engl 2002; 41:149-52. [PMID: 12491468 DOI: 10.1002/1521-3773(20020104)41:1<149::aid-anie149>3.0.co;2-#] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Ferman A Chavez
- Department of Chemistry and Center for Metals in Biocatalysis, 207 Pleasant Street SE, University of Minnesota, Minneapolis 55455, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
1302
|
Chanda N, Laye RH, Chakraborty S, Paul RL, Jeffery JC, Ward MD, Lahiri GK. Dinuclear ruthenium(ii) complexes [{(L)ClRuII}2(μ-tppz)]2+(L = an arylazopyridine ligand) incorporating tetrakis(2-pyridyl)pyrazine (tppz) bridging ligand: synthesis, structure and spectroelectrochemical properties. ACTA ACUST UNITED AC 2002. [DOI: 10.1039/b204862k] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
1303
|
Lehnert N, Ho RY, Que L, Solomon EI. Electronic structure of high-spin iron(III)-alkylperoxo complexes and its relation to low-spin analogues: reaction coordinate of O-O bond homolysis. J Am Chem Soc 2001; 123:12802-16. [PMID: 11749538 DOI: 10.1021/ja011450+] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The spectroscopic properties of the high-spin Fe(III)-alkylperoxo model complex [Fe(6-Me(3)TPA)(OH(x))(OO(t)Bu)](x)(+) (1; TPA = tris(2-pyridylmethyl)amine, (t)Bu = tert-butyl, x = 1 or 2) are defined and related to density functional calculations of corresponding models in order to determine the electronic structure and reactivity of this system. The Raman spectra of 1 show four peaks at 876, 842, 637, and 469 cm(-1) that are assigned with the help of normal coordinate analysis, and corresponding force constants have been determined to be 3.55 mdyn/A for the O-O and 2.87 mdyn/A for the Fe-O bond. Complex 1 has a broad absorption feature around 560 nm that is assigned to a charge-transfer (CT) transition from the alkylperoxo to a t(2g) d orbital of Fe(III) with the help of resonance Raman profiles and MCD spectroscopy. An additional contribution to the Fe-O bond arises from a sigma interaction between and an e(g) d orbital of iron. The electronic structure of 1 is compared to the related low-spin model complex [Fe(TPA)(OH(x))(OO(t)Bu)](x)(+) and the reaction coordinate for O-O homolysis is explored for both the low-spin and the high-spin Fe(III)-alkylperoxo systems. Importantly, there is a barrier for homolytic cleavage of the O-O bond on the high-spin potential energy surface that is not present for the low-spin complex, which is therefore nicely set up for O-O homolysis. This is reflected by the electronic structure of the low-spin complex having a strong Fe-O and a weak O-O bond due to a strong Fe-O sigma interaction. In addition, the reaction coordinate of the Fe-O homolysis has been investigated, which is a possible decay pathway for the high-spin system, but which is thermodynamically unfavorable for the low-spin complex.
Collapse
Affiliation(s)
- N Lehnert
- Department of Chemistry, Stanford University, Stanford, CA 94305-5080, USA
| | | | | | | |
Collapse
|
1304
|
Lukoyanov D, Burger RM, Scholes CP. ENDOR determination of the distance between bleomycin-bound iron and 19F of 2'-fluorocytidine in a DNA target sequence. J Am Chem Soc 2001; 123:12742-3. [PMID: 11741465 DOI: 10.1021/ja016943t] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- D Lukoyanov
- Department of Chemistry, and Center for Biological Macromolecules, State University of New York at Albany, Albany, New York 12222, USA
| | | | | |
Collapse
|
1305
|
Simaan AJ, Banse F, Girerd JJ, Wieghardt K, Bill E. The electronic structure of non-heme iron(III)-hydroperoxo and iron(III)-peroxo model complexes studied by Mössbauer and electron paramagnetic resonance spectroscopies. Inorg Chem 2001; 40:6538-40. [PMID: 11735458 DOI: 10.1021/ic010635e] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- A J Simaan
- Laboratoire de Chimie Inorganique, UMR CNRS 8613, Université Paris-Sud, F-91405 Orsay, France
| | | | | | | | | |
Collapse
|
1306
|
Hikichi S, Yoshizawa M, Sasakura Y, Komatsuzaki H, Moro-oka Y, Akita M. Structural Characterization and Intramolecular Aliphatic C−H Oxidation Ability of MIII(μ-O)2MIII Complexes of Ni and Co with the Hydrotris(3,5-dialkyl-4-X-pyrazolyl)borate Ligands TpMe2,X (X=Me, H, Br) and TpiPr2. Chemistry 2001. [DOI: 10.1002/1521-3765(20011203)7:23%3c5011::aid-chem5011%3e3.0.co;2-c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
|
1307
|
Hikichi S, Yoshizawa M, Sasakura Y, Komatsuzaki H, Moro-oka Y, Akita M. Structural characterization and intramolecular aliphatic C-H oxidation ability of M(III)(mu-O)2M(III) complexes of Ni and Co with the hydrotris-(3,5-dialkyl-4-X-pyrazolyl)borate ligands TpMe2,X (X = Me, H, Br) and TpiPr2. Chemistry 2001; 7:5011-28. [PMID: 11775675 DOI: 10.1002/1521-3765(20011203)7:23<5011::aid-chem5011>3.0.co;2-c] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Reaction of the dinuclear M(II)-bis(mu-hydroxo) complexes of nickel and cobalt, [(M(II)(TpR)]2(mu-OH)2] (M = Ni; 3Ni M = Co: 3Co), with one equivalent of H2O2 yields the corresponding M(III)-bis(mu-oxo) complexes, [[M(III)(TpR)]2-(mu-O)2] (M=Ni; 2Ni, M=Co: 2Co). The employment of a series of TpMe2,X (TpMe2,X = hydrotris(3,5-dimethyl-4-X-1-pyrazolyl)borate; X = Me, H, Br) as a metal supporting ligand makes it possible to isolate and structurally characterize the thermally unstable M(III)-bis-(mu-oxo) complexes 2Ni and 2Co. Both the starting (3Ni and 3Co) and resulting complexes (2Ni and 2Co) contain five-coordinate metal centers with a slightly distorted square-pyramidal geometry. Characteristic features of the nickel complexes 2Ni, such as the two intense absorptions around 400 and 300 nm in the UV-visible spectra and the apparent diamagnetism, are very similar to those of the previously reported bis(mu-oxo) species of Cu(III) and Ni(III) with ligands other than TpR, whereas the spectroscopic properties of the cobalt complexes 2Co (i.e., paramagnetically shifted NMR signals and a single intense absorption appearing at 350 nm) are clearly distinct from those of the isostructural nickel compounds 2Ni. Thermal decomposition of 2Ni and 2Co results in oxidation of the inner saturated hydrocarbyl substituents of the TpR ligand. Large kH/kD values obtained from the first-order decomposition rates of the TpMe3 and Tp(CD3)2,Me derivatives of 2 evidently indicate that the rate-determining step is an hydrogen abstraction from the primary C-H bond of the methyl substituents. mediated by the M(III)2-(mu-O)2 species. The nickel complex 2Ni shows reactivity about 10(3) times greater than that of the cobalt analogue 2Co. The oxidation ability of the M(III)(mu-O)2M(III) core should be affected by the hindered TpR ligand system, which can stabilize the +2 oxidation state of the metal centers.
Collapse
Affiliation(s)
- S Hikichi
- Chemical Resources Laboratory, Tokyo Institute of Technology, Yokohama, Japan.
| | | | | | | | | | | |
Collapse
|
1308
|
Abstract
Aromatic dioxygenases have been found to catalyse single and tandem oxidation reactions of conjugated polyenes. Rational selection and design of dioxygenases, allied to substrate shape, size and substitution pattern, has been used to control regiochemistry and stereochemistry during the oxygenation process. The resulting enantiopure bioproducts have been increasingly utilised as precursors for new and alternative routes in chiral synthesis.
Collapse
Affiliation(s)
- D R Boyd
- School of Chemistry, The Queen's University of Belfast, Belfast, Northern Ireland BT9 5AG, UK.
| | | | | |
Collapse
|
1309
|
Clifton IJ, Hsueh LC, Baldwin JE, Harlos K, Schofield CJ. Structure of proline 3-hydroxylase. Evolution of the family of 2-oxoglutarate dependent oxygenases. EUROPEAN JOURNAL OF BIOCHEMISTRY 2001; 268:6625-36. [PMID: 11737217 DOI: 10.1046/j.0014-2956.2001.02617.x] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Iron (II)/2-oxoglutarate (2-OG)-dependent oxygenases catalyse oxidative reactions in a range of metabolic processes including the hydroxylation of proline and lysine residues during the post-translational modification of collagen. 2-OG oxygenases commonly require ascorbate for full activity. In the vitamin C deficient disease, scurvy, reduced activity of 2-OG oxygenases results in impaired formation of collagen. Here we report the crystal structure of bacterial proline 3-hydroxylase from Streptomyces sp., an enzyme which hydroxylates proline at position 3, the first of a 2-OG oxygenase catalysing oxidation of a free alpha-amino acid. Structures were obtained for the enzyme in the absence of iron (to 2.3A resolution, R=20.2%, Rfree=25.3%) and that complexed to iron (II) (to 2.4A resolution, R=19.8%, Rfree=22.6%). The structure contains conserved motifs present in other 2-OG oxygenases including a 'jelly roll' beta strand core and residues binding iron and 2-oxoglutarate, consistent with divergent evolution within the extended family. The structure differs significantly from many other 2-OG oxygenases in possessing a discrete C-terminal helical domain. Analysis of the structure suggests a model for proline binding and a mechanism for uncoupling of proline and 2-OG turnover.
Collapse
Affiliation(s)
- I J Clifton
- The Dyson Perrins Laboratory and the Oxford Centre for Molecular Sciences, Oxford, UK
| | | | | | | | | |
Collapse
|
1310
|
Baik MH, Lee D, Friesner RA, Lippard SJ. Theoretical studies of diiron(II) complexes that model features of the dioxygen-activating centers in non-heme diiron enzymes. Isr J Chem 2001. [DOI: 10.1560/8yug-v7ef-vhhp-6ug2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
|
1311
|
Bi S, Liu C, Hu H, Zhang C. Theoretical study on magnetic coupling interaction for Cu(II) binuclear systems with extended bridging groups. Chem Phys Lett 2001. [DOI: 10.1016/s0009-2614(01)01340-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
|
1312
|
Skrzypczak-Jankun E, Bross RA, Carroll RT, Dunham WR, Funk MO. Three-dimensional structure of a purple lipoxygenase. J Am Chem Soc 2001; 123:10814-20. [PMID: 11686682 DOI: 10.1021/ja011759t] [Citation(s) in RCA: 129] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Polyunsaturated fatty acid metabolism is governed primarily by two enzymes, prostaglandin H synthase and lipoxygenase. The crystal structure of the metastable product-oxidized purple form of soybean lipoxygenase-3 was determined at 2.0 A resolution. The data reveal that the chromophore corresponds to an iron-peroxide complex, a potential intermediate in the catalyzed reaction. A significant alteration of the iron site accompanies the formation of the complex. The structure, the first for a fatty acid-lipoxygenase complex, also reveals an unexpected mode of binding, and identifies amino acid residues that may play significant roles in catalysis, regio- and stereoselectivity.
Collapse
Affiliation(s)
- E Skrzypczak-Jankun
- Department of Chemistry, University of Toledo, 2801 West Bancroft Street, Toledo, OH 43606, USA.
| | | | | | | | | |
Collapse
|
1313
|
Borowski T, Król M, Chruszcz M, Brocławik E. First Principle Calculations for the Non-Heme Iron Centers of Lipoxygenases: Geometrical and Spectral Properties. J Phys Chem B 2001. [DOI: 10.1021/jp0123637] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Tomasz Borowski
- Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Kraków, Poland, Department of Biostatistics and Medicinal Informatics Collegium Medicum, Jagiellonian University, Kopernika 17, 31-501 Kraków, Poland, and Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Niezapominajek, 30-239 Kraków, Poland
| | - Marcin Król
- Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Kraków, Poland, Department of Biostatistics and Medicinal Informatics Collegium Medicum, Jagiellonian University, Kopernika 17, 31-501 Kraków, Poland, and Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Niezapominajek, 30-239 Kraków, Poland
| | - Maksymilian Chruszcz
- Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Kraków, Poland, Department of Biostatistics and Medicinal Informatics Collegium Medicum, Jagiellonian University, Kopernika 17, 31-501 Kraków, Poland, and Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Niezapominajek, 30-239 Kraków, Poland
| | - Ewa Brocławik
- Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Kraków, Poland, Department of Biostatistics and Medicinal Informatics Collegium Medicum, Jagiellonian University, Kopernika 17, 31-501 Kraków, Poland, and Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Niezapominajek, 30-239 Kraków, Poland
| |
Collapse
|
1314
|
Drechsel H, Fiallo M, Garnier-Suillerot A, Matzanke BF, Schünemann V. Spectroscopic studies on iron complexes of different anthracyclines in aprotic solvent systems. Inorg Chem 2001; 40:5324-33. [PMID: 11578175 DOI: 10.1021/ic0002723] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Iron complexes of daunorubicin, idarubicin, pirarubicin, and doxorubicin in anhydrous DMF were studied by UV/vis, CD, fluorescence, Mössbauer, and EPR spectroscopy. Titration studies of the metal-free anthracyclines showed one (UV-detectable) deprotonation step requiring 2 equiv of base, compared to 1 equiv for quinizarine. Metal complexation was studied at three different metal/ligand ratios, and with increasing amounts of base. The results obtained from optical spectroscopy show the existence of two different complex species and give clear indications for the requirements of metal complexation. Complex species I, formed at a low iron-to-ligand ratio, is less dependent on base addition than complex species II formed with equimolar ferric ion. EPR and Mössbauer experiments provide further insight into the structures of both complex species. Lack of spin density of the Mössbauer samples in EPR indicates spin coupling between the metal centers. Mössbauer spectra consist of single quadrupole doublets with values typical for high-spin ferric ion in an octahedral arrangement. The Mössbauer spectroscopic features at 7 T exclude the presence of S = 0 dimers. Complex I represents a monomeric ferric iron complex whereas complex II is consistent with a more or less aggregrated oligomeric Fe-anthracycline system.
Collapse
Affiliation(s)
- H Drechsel
- Institut für Physik, Medizinische Universität Lübeck, Ratzeburger Allee 160, D-23538 Lübeck, Germany.
| | | | | | | | | |
Collapse
|
1315
|
Lovell T, Li J, Noodleman L. Energetics of oxidized and reduced methane monooxygenase active site clusters in the protein environment. Inorg Chem 2001; 40:5267-78. [PMID: 11559091 DOI: 10.1021/ic010116b] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Using the density functional optimized active site geometries obtained in the accompanying paper (Lovell, T.; Li, J.; Noodleman, L. Inorg. Chem. 2001, 40, 5251), a combined density functional and electrostatics approach has been applied to further address attendant uncertainties in the protonation states of the bridging ligands for MMOH(ox). The acidities (pK(a)s) associated with the bridging H(2)O ligand in Methylococcus capsulatus and corresponding energetics of each active site cluster interacting with the protein environment have been evaluated. The pK(a) calculations in combination with the results of the gas phase DFT studies allow the active site cluster in Methylosinustrichosporium to be best described as a diiron unit bridged by 2OH(-) ligands having an overall neutral net cluster charge. The presence of the exogenous acetate in M. capsulatus reveals a diiron unit bridged by 1OH(-) and 1H2O which asymmetrically shares its proton with a second-shell acetate in a very short strong AcO..H...OH hydrogen bond. For all MMOH(ox) and MMOH(red) active sites examined, significant Fe-ligand covalency is evident from the ESP atom charges, consistent with very strong ligand --> metal charge transfer from the muOH(-) and mu-carboxylato bridging ligands. The magnitude of electrostatic interaction of the individual protein residues in the active domain with the active site has been assessed via an energy decomposition scheme. Important second-shell residues are highlighted for the next level of quantum mechanics based calculations or alternatively for site-directed mutagenesis studies. Finally, from the known structural and spectroscopic evidence and the DFT studies, a possible mechanism is suggested for the conversion of MMOH(ox) into MMOH(red) that involves a combination of protein residues and solvent-derived ligands from the second coordination sphere.
Collapse
Affiliation(s)
- T Lovell
- Department of Molecular Biology TPC-15, The Scripps Research Institute, La Jolla, California 92037, USA.
| | | | | |
Collapse
|
1316
|
Lovell T, Li J, Noodleman L. Density functional studies of oxidized and reduced methane monooxygenase. Optimized geometries and exchange coupling of active site clusters. Inorg Chem 2001; 40:5251-66. [PMID: 11559090 DOI: 10.1021/ic010115j] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The conflicting protein crystallography data for the oxidized form (MMOH(ox)) of methane monooxygenase present a dilemma regarding the identity of the solvent-derived bridging ligands within the active site: do they comprise a diiron unit bridged by 1H2O and 1OH(-) as postulated for Methylococcus capsulatus or 2OH(-) ligands as suggested for Methylosinus trichosporium? Using models derived explicitly from the M. capsulatus and M. trichosporium protein data, spin-unrestricted density functional methods have been used to study two structurally characterized forms of the hydroxylase component of methane monooxygenase. The active site geometries of the oxidized (MMOH(ox)) and two-electron-reduced (MMOH(red)) states have been geometry optimized using several quantum cluster models which take into account the antiferromagnetic (AF) and ferromagnetic (F) coupling of electron spins. Trends in cluster geometries, energetics, and Heisenberg J values have been evaluated. For the majority of models, calculated geometries are in good agreement with the X-ray analyses and appear relatively insensitive to the F or AF alignment of electron spins on adjacent Fe sites. Discrepancies between calculation and experiment appear in the orientation of the coordinated His and Glu amino acid side chains for both MMOH(ox) and MMOH(red) and also in unexpected intramolecular proton transfer in the MMOH(ox) cluster models. There is additional dispersion between (and among) calculated and experimental Fe(3+)-OH(-) distances with relevance to the correct protonation state of the solvent-derived ligands. In an accompanying paper (Lovell, T.; Li, J.; Noodleman, L. Inorg. Chem. 2001, 40, 5267), a comparison of the related energetics of the active site models examined herein is further evaluated in the full protein and solvent environment.
Collapse
Affiliation(s)
- T Lovell
- Department of Molecular Biology TPC-15, The Scripps Research Institute, La Jolla, California 92037, USA.
| | | | | |
Collapse
|
1317
|
Kodera M, Taniike Y, Itoh M, Tanahashi Y, Shimakoshi H, Kano K, Hirota S, Iijima S, Ohba M, Okawa H. Synthesis, characterization, and activation of thermally stable mu-1,2-peroxodiiron(III) complex. Inorg Chem 2001; 40:4821-2. [PMID: 11531426 DOI: 10.1021/ic0155434] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Affiliation(s)
- M Kodera
- Department of Molecular Science and Technology, Doshisha University, Kyotanabe, Kyoto 610-0321, Japan
| | | | | | | | | | | | | | | | | | | |
Collapse
|
1318
|
Stenmark P, Grünler J, Mattsson J, Sindelar PJ, Nordlund P, Berthold DA. A new member of the family of di-iron carboxylate proteins. Coq7 (clk-1), a membrane-bound hydroxylase involved in ubiquinone biosynthesis. J Biol Chem 2001; 276:33297-300. [PMID: 11435415 DOI: 10.1074/jbc.c100346200] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ubiquinone (UQ) is an essential cofactor for respiratory metabolism. In yeast, mutation of the COQ7 gene results in the absence of UQ biosynthesis and demonstrates a role for this gene in the step leading to the hydroxylation of 5-demethoxyubiquinone. Intriguingly, the disruption of the corresponding gene in Caenorhabditis elegans, clk-1, results in a prolonged life span and a slowing of development. Because of the pleiotropic effect of this disruption, the small size of the protein, and the lack of obvious homology to other known hydroxylases, it has been suggested that Coq7 may be a regulatory or structural component in UQ biosynthesis, rather than acting as the hydroxylase per se. Here we identify Coq7 as belonging to a family of a di-iron containing oxidases/hydroxylases based on a conserved sequence motif for the iron ligands, supporting a direct function of Coq7 as a hydroxylase. We have cloned COQ7 from Pseudomonas aeruginosa and Thiobacillus ferrooxidans and show that indeed this gene complements an Escherichia coli mutant that lacks an unrelated 5-demethoxyubiquinone hydroxylase. Based on the similarities to other well studied di-iron carboxylate proteins, we propose a structural model for Coq7 as an interfacial integral membrane protein.
Collapse
Affiliation(s)
- P Stenmark
- Department of Biochemistry and Biophysics, Stockholm University, Svante Arrhenius väg 12, S-106 91 Stockholm, Sweden
| | | | | | | | | | | |
Collapse
|
1319
|
Lehnert N, Ho RY, Que L, Solomon EI. Spectroscopic properties and electronic structure of low-spin Fe(III)-alkylperoxo complexes: homolytic cleavage of the O-O bond. J Am Chem Soc 2001; 123:8271-90. [PMID: 11516278 DOI: 10.1021/ja010165n] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The spectroscopic properties, electronic structure, and reactivity of the low-spin Fe(III)-alkylperoxo model complex [Fe(TPA)(OH(x))(OO(t)Bu)](x+) (1; TPA = tris(2-pyridylmethyl)amine, (t)Bu = tert-butyl, x = 1 or 2) are explored. The vibrational spectra of 1 show three peaks that are assigned to the O-O stretch (796 cm(-1)), the Fe-O stretch (696 cm(-)(1)), and a combined O-C-C/C-C-C bending mode (490 cm(-1)) that is mixed with upsilon(FeO). The corresponding force constants have been determined to be 2.92 mdyn/A for the O-O bond which is small and 3.53 mdyn/A for the Fe-O bond which is large. Complex 1 is characterized by a broad absorption band around 600 nm that is assigned to a charge-transfer (CT) transition from the alkylperoxo pi*(upsilon) to a t(2g) d orbital of Fe(III). This metal-ligand pi bond is probed by MCD and resonance Raman spectroscopies which show that the CT state is mixed with a ligand field state (t(2g) --> e(g)) by configuration interaction. This gives rise to two intense transitions under the broad 600 nm envelope with CT character which are manifested by a pseudo-A term in the MCD spectrum and by the shapes of the resonance Raman profiles of the 796, 696, and 490 cm(-1) vibrations. Additional contributions to the Fe-O bond arise from sigma interactions between mainly O-O bonding donor orbitals of the alkylperoxo ligand and an e(g) d orbital of Fe(III), which explains the observed O-O and Fe-O force constants. The observed homolytic cleavage of the O-O bond of 1 is explored with experimentally calibrated density functional (DFT) calculations. The O-O bond homolysis is found to be endothermic by only 15 to 20 kcal/mol due to the fact that the Fe(IV)=O species formed is highly stabilized (for spin states S = 1 and 2) by two strong pi and a strong sigma bond between Fe(IV) and the oxo ligand. This low endothermicity is compensated by the entropy gain upon splitting the O-O bond. In comparison, Cu(II)-alkylperoxo complexes studied before [Chen, P.; Fujisawa, K.; Solomon, E. I. J. Am. Chem. Soc. 2000, 122, 10177] are much less suited for O-O bond homolysis, because the resulting Cu(III)=O species is less stable. This difference in metal-oxo intermediate stability enables the O-O homolysis in the case of iron but directs the copper complex toward alternative reaction channels.
Collapse
Affiliation(s)
- N Lehnert
- Department of Chemistry, Stanford University, Stanford, CA 94305-5080, USA
| | | | | | | |
Collapse
|
1320
|
Torrent M, Mogi K, Basch H, Musaev DG, Morokuma K. A Density Functional Study of Possible Intermediates of the Reaction of Dioxygen Molecule with Non-Heme Iron Complexes. 1. N-Side versus O-Side Mechanism with Water-Free Model. J Phys Chem B 2001. [DOI: 10.1021/jp0114743] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Maricel Torrent
- Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, Georgia 30322, and Department of Chemistry, Bar Ilan University, Ramat Gan, 52900, Israel
| | - Koichi Mogi
- Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, Georgia 30322, and Department of Chemistry, Bar Ilan University, Ramat Gan, 52900, Israel
| | - Harold Basch
- Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, Georgia 30322, and Department of Chemistry, Bar Ilan University, Ramat Gan, 52900, Israel
| | - Djamaladdin G. Musaev
- Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, Georgia 30322, and Department of Chemistry, Bar Ilan University, Ramat Gan, 52900, Israel
| | - Keiji Morokuma
- Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, Georgia 30322, and Department of Chemistry, Bar Ilan University, Ramat Gan, 52900, Israel
| |
Collapse
|
1321
|
Blomberg MRA, Siegbahn PEM. A Quantum Chemical Approach to the Study of Reaction Mechanisms of Redox-Active Metalloenzymes. J Phys Chem B 2001. [DOI: 10.1021/jp010305f] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
| | - Per E. M. Siegbahn
- Department of Physics, Stockholm University, Box 6730, S-113 85 Stockholm, Sweden
| |
Collapse
|
1322
|
Gomes CM, Le Gall J, Xavier AV, Teixeira M. Could a diiron-containing four-helix-bundle protein have been a primitive oxygen reductase? Chembiochem 2001; 2:583-7. [PMID: 11828492 DOI: 10.1002/1439-7633(20010803)2:7/8<583::aid-cbic583>3.0.co;2-5] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- C M Gomes
- Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Rua da Quinta Grande 6, Apt 127, 2780-156 Oeiras, Portugal.
| | | | | | | |
Collapse
|
1323
|
Merkx M, Kopp DA, Sazinsky MH, Blazyk JL, Müller J, Lippard SJ. Dioxygen Activation and Methane Hydroxylation by Soluble Methane Monooxygenase: A Tale of Two Irons and Three Proteins. Angew Chem Int Ed Engl 2001. [DOI: 10.1002/1521-3773(20010803)40:15%3c2782::aid-anie2782%3e3.0.co;2-p] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
|
1324
|
Merkx M, Kopp DA, Sazinsky MH, Blazyk JL, Müller J, Lippard SJ. Aktivierung von Disauerstoff und Hydroxylierung von Methan durch lösliche Methan-Monooxygenase: eine Geschichte von zwei Eisenatomen und drei Proteinen. Angew Chem Int Ed Engl 2001. [DOI: 10.1002/1521-3757(20010803)113:15<2860::aid-ange2860>3.0.co;2-2] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
|
1325
|
Merkx M, Kopp DA, Sazinsky MH, Blazyk JL, Müller J, Lippard SJ. Dioxygen Activation and Methane Hydroxylation by Soluble Methane Monooxygenase: A Tale of Two Irons and Three Proteins. Angew Chem Int Ed Engl 2001; 40:2782-2807. [PMID: 29711993 DOI: 10.1002/1521-3773(20010803)40:15<2782::aid-anie2782>3.0.co;2-p] [Citation(s) in RCA: 461] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2001] [Revised: 05/03/2001] [Indexed: 11/11/2022]
Affiliation(s)
- Maarten Merkx
- Department of Chemistry Massachusetts Institute of Technology 77 Massachusetts Avenue 18-590 Cambridge, MA 02139 (USA) Fax: (+1) 617-258-8150
| | - Daniel A Kopp
- Department of Chemistry Massachusetts Institute of Technology 77 Massachusetts Avenue 18-590 Cambridge, MA 02139 (USA) Fax: (+1) 617-258-8150
| | - Matthew H Sazinsky
- Department of Chemistry Massachusetts Institute of Technology 77 Massachusetts Avenue 18-590 Cambridge, MA 02139 (USA) Fax: (+1) 617-258-8150
| | - Jessica L Blazyk
- Department of Chemistry Massachusetts Institute of Technology 77 Massachusetts Avenue 18-590 Cambridge, MA 02139 (USA) Fax: (+1) 617-258-8150
| | - Jens Müller
- Department of Chemistry Massachusetts Institute of Technology 77 Massachusetts Avenue 18-590 Cambridge, MA 02139 (USA) Fax: (+1) 617-258-8150
| | - Stephen J Lippard
- Department of Chemistry Massachusetts Institute of Technology 77 Massachusetts Avenue 18-590 Cambridge, MA 02139 (USA) Fax: (+1) 617-258-8150
| |
Collapse
|
1326
|
Zhou J, Kelly WL, Bachmann BO, Gunsior M, Townsend CA, Solomon EI. Spectroscopic studies of substrate interactions with clavaminate synthase 2, a multifunctional alpha-KG-dependent non-heme iron enzyme: correlation with mechanisms and reactivities. J Am Chem Soc 2001; 123:7388-98. [PMID: 11472170 DOI: 10.1021/ja004025+] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Using a single ferrous active site, clavaminate synthase 2 (CS2) activates O(2) and catalyzes the hydroxylation of deoxyguanidinoproclavaminic acid (DGPC), the oxidative ring closure of proclavaminic acid (PC), and the desaturation of dihydroclavaminic acid (and a substrate analogue, deoxyproclavaminic acid (DPC)), each coupled to the oxidative decarboxylation of cosubstrate, alpha-ketoglutarate (alpha-KG). CS2 can also catalyze an uncoupled decarboxylation of alpha-KG both in the absence and in the presence of substrate, which results in enzyme deactivation. Resting CS2/Fe(II) has a six-coordinate Fe(II) site, and alpha-KG binds to the iron in a bidentate mode. The active site becomes five-coordinate only when both substrate and alpha-KG are bound, the latter still in a bidentate mode. Absorption, CD, MCD, and VTVH MCD studies of the interaction of CS2 with DGPC, PC, and DPC provide significant molecular level insight into the structure/function correlations of this multifunctional enzyme. There are varying amounts of six-coordinate ferrous species in the substrate complexes, which correlate to the uncoupled reaction. Five-coordinate ferrous species with similar geometric and electronic structures are present for all three substrate/alpha-KG complexes. Coordinative unsaturation of the Fe(II) in the presence of both cosubstrate and substrate appears to be critical for the coupling of the oxidative decarboxylation of alpha-KG to the different substrate oxidation reactions. In addition to the substrate orientation relative to the open coordination position on the iron site, it is hypothesized that the enzyme can affect the nature of the reactivity by further regulating the binding energy of the water to the ferrous species in the enzyme/succinate/product complex.
Collapse
Affiliation(s)
- J Zhou
- Contribution from the Departments of Chemistry, Stanford University, Stanford, California 94305, USA
| | | | | | | | | | | |
Collapse
|
1327
|
Baldwin J, Voegtli WC, Khidekel N, Moënne-Loccoz P, Krebs C, Pereira AS, Ley BA, Huynh BH, Loehr TM, Riggs-Gelasco PJ, Rosenzweig AC, Bollinger JM. Rational reprogramming of the R2 subunit of Escherichia coli ribonucleotide reductase into a self-hydroxylating monooxygenase. J Am Chem Soc 2001; 123:7017-30. [PMID: 11459480 DOI: 10.1021/ja002114g] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The outcome of O2 activation at the diiron(II) cluster in the R2 subunit of Escherichia coli (class I) ribonucleotide reductase has been rationally altered from the normal tyrosyl radical (Y122*) production to self-hydroxylation of a phenylalanine side-chain by two amino acid substitutions that leave intact the (histidine)2-(carboxylate)4 ligand set characteristic of the diiron-carboxylate family. Iron ligand Asp (D) 84 was replaced with Glu (E), the amino acid found in the cognate position of the structurally similar diiron-carboxylate protein, methane monooxygenase hydroxylase (MMOH). We previously showed that this substitution allows accumulation of a mu-1,2-peroxodiiron(III) intermediate, which does not accumulate in the wild-type (wt) protein and is probably a structural homologue of intermediate P (H(peroxo)) in O2 activation by MMOH. In addition, the near-surface residue Trp (W) 48 was replaced with Phe (F), blocking transfer of the "extra" electron that occurs in wt R2 during formation of the formally Fe(III)Fe(IV) cluster X. Decay of the mu-1,2-peroxodiiron(III) complex in R2-W48F/D84E gives an initial brown product, which contains very little Y122* and which converts very slowly (t1/2 approximately 7 h) upon incubation at 0 degrees C to an intensely purple final product. X-ray crystallographic analysis of the purple product indicates that F208 has undergone epsilon-hydroxylation and the resulting phenol has shifted significantly to become a ligand to Fe2 of the diiron cluster. Resonance Raman (RR) spectra of the purple product generated with 16O2 or 18O2 show appropriate isotopic sensitivity in bands assigned to O-phenyl and Fe-O-phenyl vibrational modes, confirming that the oxygen of the Fe(III)-phenolate species is derived from O2. Chemical analysis, experiments involving interception of the hydroxylating intermediate with exogenous reductant, and Mössbauer and EXAFS characterization of the brown and purple species establish that F208 hydroxylation occurs during decay of the peroxo complex and formation of the initial brown product. The slow transition to the purple Fe(III)-phenolate species is ascribed to a ligand rearrangement in which mu-O2- is lost and the F208-derived phenolate coordinates. The reprogramming to F208 monooxygenase requires both amino acid substitutions, as very little epsilon-hydroxyphenylalanine is formed and pathways leading to Y122* formation predominate in both R2-D84E and R2-W48F.
Collapse
Affiliation(s)
- J Baldwin
- Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
1328
|
Assarsson M, Andersson ME, Högbom M, Persson BO, Sahlin M, Barra AL, Sjöberg BM, Nordlund P, Gräslund A. Restoring proper radical generation by azide binding to the iron site of the E238A mutant R2 protein of ribonucleotide reductase from Escherichia coli. J Biol Chem 2001; 276:26852-9. [PMID: 11328804 DOI: 10.1074/jbc.m008190200] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The enzyme activity of Escherichia coli ribonucleotide reductase requires the presence of a stable tyrosyl free radical and diiron center in its smaller R2 component. The iron/radical site is formed in a reconstitution reaction between ferrous iron and molecular oxygen in the protein. The reaction is known to proceed via a paramagnetic intermediate X, formally a Fe(III)-Fe(IV) state. We have used 9.6 GHz and 285 GHz EPR to investigate intermediates in the reconstitution reaction in the iron ligand mutant R2 E238A with or without azide, formate, or acetate present. Paramagnetic intermediates, i.e. a long-living X-like intermediate and a transient tyrosyl radical, were observed only with azide and under none of the other conditions. A crystal structure of the mutant protein R2 E238A/Y122F with a diferrous iron site complexed with azide was determined. Azide was found to be a bridging ligand and the absent Glu-238 ligand was compensated for by azide and an extra coordination from Glu-204. A general scheme for the reconstitution reaction is presented based on EPR and structure results. This indicates that tyrosyl radical generation requires a specific ligand coordination with 4-coordinate Fe1 and 6-coordinate Fe2 after oxygen binding to the diferrous site.
Collapse
Affiliation(s)
- M Assarsson
- Department of Biochemistry and Biophysics, Stockholm University, S-10691 Stockholm, Sweden
| | | | | | | | | | | | | | | | | |
Collapse
|
1329
|
Solomon EI. Invited award contribution for ACS Award in Inorganic Chemistry. Geometric and electronic structure contributions to function in bioinorganic chemistry: active sites in non-heme iron enzymes. Inorg Chem 2001; 40:3656-69. [PMID: 11442362 DOI: 10.1021/ic010348a] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Spectroscopy has played a major role in the definition of structure/function correlations in bioinorganic chemistry. The importance of spectroscopy combined with electronic structure calculations is clearly demonstrated by the non-heme iron enzymes. Many members of this large class of enzymes activate dioxygen using a ferrous active site that has generally been difficult to study with most spectroscopic methods. A new spectroscopic methodology has been developed utilizing variable temperature, variable field magnetic circular dichroism, which enables one to obtain detailed insight into the geometric and electronic structure of the non-heme ferrous active site and probe its reaction mechanism on a molecular level. This spectroscopic methodology is presented and applied to a number of key mononuclear non-heme iron enzymes leading to a general mechanistic strategy for O2 activation. These studies are then extended to consider the new features present in the binuclear non-heme iron enzymes and applied to understand (1) the mechanism of the two electron/coupled proton transfer to dioxygen binding to a single iron center in hemerythrin and (2) structure/function correlations over the oxygen-activating enzymes stearoyl-ACP Delta9-desaturase, ribonucleotide reductase, and methane monooxygenase. Electronic structure/reactivity correlations for O2 activation by non-heme relative to heme iron enzymes will also be developed.
Collapse
Affiliation(s)
- E I Solomon
- Department of Chemistry, Stanford University, Stanford, California 94305-5080, USA.
| |
Collapse
|
1330
|
Miyake H, Chen K, Lange SJ, Que L. "Intermolecular" trapping of a nonheme Fe(IV)=O intermediate. Inorg Chem 2001; 40:3534-8. [PMID: 11421702 DOI: 10.1021/ic000935g] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The reactions of Fe(III)(TPA) (TPA = tris(2-pyridylmethyl)amine) complexes with 2-methyl-1-phenyl-2-propyl-hydroperoxide (MPPH) delivered by syringe pump under anaerobic conditions afford nearly quantitative conversion of MPPH to products derived from the benzyl radical. These results unequivocally show that MPPH breaks down by O-O bond homolysis, leading to the formation of the benzyl radical and a high valent Fe(IV)=O species. Without added substrates, the benzyl radical reacts with the high valent species to form benzyl alcohol or benzyl halides. The Fe(IV)=O species can also effect the two-electron oxidation of added substrates such as thioanisole, cyclohexanol, and cyclooctene under appropriate conditions. The oxidation of thioanisole and cyclohexanol is likely facilitated by pre-equilibrium binding of the substrate to the metal center, allowing these substrates to intercept the high valent iron-oxo species as it forms. These results suggest the importance of close proximity to direct the high valent metal center down a desired pathway.
Collapse
Affiliation(s)
- H Miyake
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, USA
| | | | | | | |
Collapse
|
1331
|
Jo DH, Chiou YM, Que L. Models for extradiol cleaving catechol dioxygenases: syntheses, structures, and reactivities of iron(II)-monoanionic catecholate complexes. Inorg Chem 2001; 40:3181-90. [PMID: 11399191 DOI: 10.1021/ic001185d] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Crystallographic and spectroscopic studies of extradiol cleaving catechol dioxygenases indicate that the enzyme-substrate complexes have both an iron(II) center and a monoanionic catecholate. Herein we report a series of iron(II)-monoanionic catecholate complexes, [(L)Fe(II)(catH)](X) (1a, L = 6-Me(3)-TPA (tris(6-methyl-2-pyridylmethyl)amine), catH = CatH (1,2-catecholate monoanion); 1b, L = 6-Me(3)-TPA, catH = DBCH (3,5-di-tert-butyl-1,2-catecholate monoanion); 1c, L = 6-Me(2)-bpmcn (N,N'-dimethyl-N,N'-bis(6-methyl-2-pyridylmethyl)-trans-1,2-diaminocyclohexane), catH = CatH; 1d, L = 6-Me(2)-bpmcn, catH = DBCH), that model such enzyme complexes. The crystal structure of [(6-Me(2)-bpmcn)Fe(II)(DBCH)](+) (1d) shows that the DBCH ligand binds to the iron asymmetrically as previously reported for 1b, with two distinct Fe-O bonds of 1.943(1) and 2.344(1) A. Complexes 1 react with O(2) or NO to afford blue-purple iron(III)-catecholate dianion complexes, [(L)Fe(III)(cat)](+) (2). Interestingly, crystallographically characterized 2d, isolated from either reaction, has the N-methyl groups in a syn configuration, in contrast to the anti configuration of the precursor complex, so epimerization of the bound ligand must occur in the course of isolating 2d. This notion is supported by the fact that the UV-vis and EPR properties of in situ generated 2d(anti) differ from those of isolated 2d(syn). While the conversion of 1 to 2 in the presence of O(2) occurs without an obvious intermediate, that in the presence of NO proceeds via a metastable S = (3)/(2) [(L)Fe(catH)(NO)](+) adduct 3, which can only be observed spectroscopically but not isolated. Intermediates 3a and 3b subsequently disproportionate to afford two distinct complexes, [(6-Me(3)-TPA)Fe(III)(cat)](+) (2a and 2b) and [(6-Me(3)-TPA)Fe(NO)(2)](+) (4) in comparable yield, while 3d converts to 2d in 90% yield. Complexes 2b and anti-2d react further with O(2) over a 24 h period and afford a high yield of cleavage products. Product analysis shows that the products mainly derive from intradiol cleavage but with a small extent of extradiol cleavage (89:3% for 2b and 78:12% for anti-2d). The small amounts of the extradiol cleavage products observed may be due to the dissociation of an alpha-methyl substituted pyridyl arm, generating a complex with a tridentate ligand. Surprisingly, syn-2d does not react with O(2) over the course of 4 days. These results suggest that there are a number of factors that influence the mode and rate of cleavage of catechols coordinated to iron centers.
Collapse
Affiliation(s)
- D H Jo
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, MN 55455, USA
| | | | | |
Collapse
|
1332
|
Liu A, Ho RY, Que L, Ryle MJ, Phinney BS, Hausinger RP. Alternative reactivity of an alpha-ketoglutarate-dependent iron(II) oxygenase: enzyme self-hydroxylation. J Am Chem Soc 2001; 123:5126-7. [PMID: 11457355 DOI: 10.1021/ja005879x] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- A Liu
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis 55455, USA
| | | | | | | | | | | |
Collapse
|
1333
|
Ho RY, Mehn MP, Hegg EL, Liu A, Ryle MJ, Hausinger RP, Que L. Resonance Raman studies of the iron(II)--alpha-keto acid chromophore in model and enzyme complexes. J Am Chem Soc 2001; 123:5022-9. [PMID: 11457330 DOI: 10.1021/ja0041775] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The bidentate coordination of an alpha-keto acid to an iron(II) center via the keto group and the carboxylate gives rise to metal-to-ligand charge-transfer transitions between 400 and 600 nm in model complexes and in alpha-ketoglutarate-dependent dioxygenases. Excitation into these absorption bands of the Fe(II)TauD(alpha-KG) complex (TauD = taurine/alpha-ketoglutarate dioxygenase, alpha-KG = alpha-ketoglutarate) elicits two resonance Raman features at 460 and 1686 cm(-1), both of which are sensitive to (18)O labeling. Corresponding studies of model complexes, the six-coordinate [Fe(II)(6-Me(3)-TPA)(alpha-keto acid)](+) and the five-coordinate [Fe(II)(Tp(Ph2))(alpha-keto acid)] (6-Me(3)-TPA = tris[(6-methyl-2-pyridyl)methyl]amine, Tp(Ph2) = hydrotris(3,5-diphenylpyrazol-1-yl)borate), lead to the assignment of these two features to the Fe(II)(alpha-keto acid) chelate mode and the nu(C==O) of the keto carbonyl group, respectively. Furthermore, the chelate mode is sensitive to the coordination number of the metal center; binding of a sixth ligand to the five-coordinate [Fe(II)(Tp(Ph2))(benzoylformate)] elicits a 9--20 cm(-1) downshift. Thus, the 10 cm(-1) upshift of the chelate mode observed for Fe(II)TauD(alpha-KG) upon the addition of the substrate, taurine, is associated with the conversion of the six-coordinate metal center to a five-coordinate center, as observed for the iron center of clavaminate synthase from X-ray crystallography (Zhang, Z.; et al. Nat. Struct. Biol. 2000, 7, 127-133) and MCD studies (Zhou, J.; et al. J. Am. Chem. Soc. 1998, 120, 13539--13540). These studies provide useful insights into the initial steps of the oxygen activation mechanism of alpha-ketoglutarate-dependent dioxygenases.
Collapse
Affiliation(s)
- R Y Ho
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, USA
| | | | | | | | | | | | | |
Collapse
|
1334
|
Lee D, Lippard SJ. Oxidative N-dealkylation of a carboxylate-bridged diiron(II) precursor complex by reaction with O2 affords the elusive [Fe2(mu-OH)2(mu-O2CR)](3+) core of soluble methane monooxygenase hydroxylase. J Am Chem Soc 2001; 123:4611-2. [PMID: 11457252 DOI: 10.1021/ja0100930] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Affiliation(s)
- D Lee
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | | |
Collapse
|
1335
|
Kryatov SV, Rybak-Akimova EV, MacMurdo VL, Que L. A mechanistic study of the reaction between a diiron(II) complex [FeII(2)(mu-OH)2(6-Me3-TPA)2](2+) and O2 to form a diiron(III) peroxo complex. Inorg Chem 2001; 40:2220-8. [PMID: 11327894 DOI: 10.1021/ic001300k] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A kinetic study of the reaction between a diiron(II) complex [Fe(II)(2)(mu-OH)(2)(6-Me(3)-TPA)(2)](2+) 1, where 6-Me(3)-TPA = tris(6-methyl-2-pyridylmethyl)amine, and dioxygen is presented. A diiron(III) peroxo complex [Fe(III)(2)(mu-O)(mu-O(2))(6-Me(3)-TPA)(2)](2+) 2 forms quantitatively in dichloromethane at temperatures from -80 to -40 degrees C. The reaction is first order in [Fe(II)(2)] and [O(2)], with the activation parameters DeltaH(double dagger) = 17 +/- 2 kJ mol(-1) and DeltaS(double dagger) = -175 +/- 20 J mol(-1) K(-1). The reaction rate is not significantly influenced by the addition of H(2)O or D(2)O. The reaction proceeds faster in more polar solvents (acetone and acetonitrile), but the yield of 2 is not quantitative in these solvents. Complex 1 reacts with NO at a rate about 10(3) faster than with O(2). The mechanistic analysis suggests an associative rate-limiting step for the oxygenation of 1, similar to that for stearoyl-ACP Delta(9)-desaturase, but distinct from the probable dissociative pathway of methane monoxygenase. An eta(1)-superoxo Fe(II)Fe(III) species is a likely steady-state intermediate during the oxygenation of complex 1.
Collapse
Affiliation(s)
- S V Kryatov
- Department of Chemistry, Tufts University, Medford, MA 02155, USA
| | | | | | | |
Collapse
|
1336
|
He C, DuBois JL, Hedman B, Hodgson KO, Lippard SJ. A Short Copper-Copper Distance in a (μ-1,2-Peroxo)dicopper(II) Complex Having a 1,8-Naphthyridine Unit as an Additional Bridge. Angew Chem Int Ed Engl 2001; 40:1484-1487. [DOI: 10.1002/1521-3773(20010417)40:8<1484::aid-anie1484>3.0.co;2-z] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2000] [Revised: 02/06/2001] [Indexed: 11/06/2022]
|
1337
|
He C, DuBois JL, Hedman B, Hodgson KO, Lippard SJ. A Short Copper-Copper Distance in a (μ-1,2-Peroxo)dicopper(II) Complex Having a 1,8-Naphthyridine Unit as an Additional Bridge. Angew Chem Int Ed Engl 2001. [DOI: 10.1002/1521-3757(20010417)113:8<1532::aid-ange1532>3.0.co;2-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
|
1338
|
Gao* EQ, Liao* DZ, Jiang ZH, Yan SP. Synthesis, crystal structure and magnetic properties of novel copper(II)–nickel(II) complexes of macrocyclic oxamides. Polyhedron 2001. [DOI: 10.1016/s0277-5387(01)00755-0] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
|
1339
|
Poussereau S, Blondin G, Chottard G, Guilhem J, Tchertanov L, Rivière E, Girerd JJ. Synthesis, Structure and Characterization of the New Complex [L1(H2O)Fe(μ-O)Fe(OH2)L1]4+ [L1 =N,N′-Bis(1-methylimidazolyl-2-methyl)-N,N′-Bismethyl-1,2-ethanediamine] − Formation of the (μ-O)(μ-H3O2) Complex upon Deprotonation. Eur J Inorg Chem 2001. [DOI: 10.1002/1099-0682(200104)2001:4<1057::aid-ejic1057>3.0.co;2-a] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
|
1340
|
Abstract
Spectroscopic methods covering many energy regions together provide complementary insight into metalloenzyme active sites. These methods probe geometric and electronic structure and define these contributions to reactivity. Two recent advances--determination of the polarizations of electronic transitions in solution using magnetic circular dichroism, electron paramagnetic resonance and quantum chemistry, and experimental estimation of covalency using metal L-edges and ligand K-edges--are particularly important.
Collapse
Affiliation(s)
- N Lehnert
- Department of Chemistry, Stanford University, CA 94305, USA
| | | | | |
Collapse
|
1341
|
Tolman WB, Spencer DJ. New advances in ligand design for synthetic modeling of metalloprotein active sites. Curr Opin Chem Biol 2001; 5:188-95. [PMID: 11282346 DOI: 10.1016/s1367-5931(00)00189-7] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Judicious control of ligand steric bulk and auxiliary structural elements enables the construction of novel synthetic complexes that model the properties of metalloprotein active sites, thus providing insight into their structure and function. Major recent developments include the synthesis of a number of unusual and biologically relevant complexes of copper and iron using elaborate N-donor and O-donor ligands.
Collapse
Affiliation(s)
- W B Tolman
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis 55455, USA.
| | | |
Collapse
|
1342
|
Gao EQ, Yin LH, Tang JK, Cheng P, Liao DZ, Jiang ZH, Yan SP. Synthesis, crystal structure and magnetic properties of a new dialkoxo-bridged diiron(III) complex. Polyhedron 2001. [DOI: 10.1016/s0277-5387(01)00731-8] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
|
1343
|
Jackson HL, Shoner SC, Rittenberg D, Cowen JA, Lovell S, Barnhart D, Kovacs JA. Probing the influence of local coordination environment on the properties of Fe-type nitrile hydratase model complexes. Inorg Chem 2001; 40:1646-53. [PMID: 11261975 PMCID: PMC4485621 DOI: 10.1021/ic001271d] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A series of four structurally related cis-dithiolate-ligated Fe(III) complexes, [Fe(III)(DITpy)2]Cl (1), [Fe(III)(DITIm)2]Cl (2), [Fe(III)(ADIT)2]Cl (3), and [Fe(III)(AMIT)2]Cl (4), are described. The structural characterization of 3 as well as the spectroscopic properties of 3 and 4 has been previously reported. Crystal data for 1, 2, and 4 are as follows: 1.3H2O crystallizes in the orthorhombic space group Pca2(1) with a = 19.800(4) A, b = 18.450(4) A, c = 14.800(3) A, and Z = 8. 2.(1/2)EtOH.1/2H2O crystallizes in the monoclinic space group Cc with a = 24.792(4) A, b = 14.364(3) A, c = 17.527(3) A, beta = 124.91(2) degrees, and Z = 8. 4 crystallizes in the triclinic space group P1 with a = 8.0152(6) A, b = 10.0221(8) A, c = 11.8384(10) A, alpha = 73.460(3) degrees, beta = 71.451(5) degrees, gamma = 72.856(4) degrees, and Z = 2. Complexes 1-4 share a common S2N4 coordination environment that consists of two cis-thiolates, two trans-imines, and two cis-terminal nitrogen donors: Nterm = pyridine (1), imidazole (2), and primary amine (3 and 4). The crystallographically determined mean Fe-S bond distances in 1-4 range from 2.196 to 2.232 A and are characteristic of low-spin Fe(III)-thiolate complexes. The low-spin S = 1/2 ground state was confirmed by both EPR and magnetic susceptibility measurements. The electronic spectra of these complexes are characterized by broad absorption bands centered near approximately 700 nm that are consistent with ligand-to-metal charge-transfer (CT) bands. The complexes were further characterized by cyclic voltammetry measurements, and all possess highly negative Fe(III)/Fe(II) redox couples ( approximately -1 V vs SCE, saturated calomel electrode) indicating that alkyl thiolate donors are effective at stabilizing Fe(III) centers. Both the redox couple and the 700 nm band in the visible spectra show solvent-dependent shifts that are dependent upon the H-bonding ability of the solvent. The implications of these results with respect to the active site of the iron-containing nitrile hydratases are also discussed.
Collapse
Affiliation(s)
| | | | | | | | | | | | - Julie A. Kovacs
- Author to whom correspondence should be addressed: Dr. Julie A. Kovacs, Department of Chemistry, University of Washington, Box 351700, Seattle, WA 98195-1700. . Fax: 206-685-8665
| |
Collapse
|
1344
|
Kurosaki H, Yoshida H, Ito M, Koike H, Higuchi E, Goto M. Synthesis and characterization of bis(mu-hydroxo)diiron(III) complex of N-(4-nitro-2-hydroxy)phenylmethyl-N-(2-pyridylethyl)-N-(2-pyridylmethyl)amine and hydroxylation reaction of alkane. Bioorg Med Chem Lett 2001; 11:785-8. [PMID: 11277520 DOI: 10.1016/s0960-894x(01)00070-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Bis(mu-hydroxo)diiron(III) complex, [Fe2III(mu-OH)2(NE)2](NO3)2 x 3H2O (3) (N-(4-nitro-2-hydroxy)phenylmethyl-N-(2-pyridylethyl)-N-(2-pyridylmethyl)amine = HNE, where H denotes a dissociable proton of the p-nitrophenol group), has been prepared and characterized by X-ray crystallography, electronic and magnetic spectroscopies.
Collapse
Affiliation(s)
- H Kurosaki
- Faculty of Pharmaceutical Sciences, Kumamoto University, Japan
| | | | | | | | | | | |
Collapse
|
1345
|
He C, Lippard SJ. Synthesis and electrochemical studies of diiron complexes of 1,8-naphthyridine-based dinucleating ligands to model features of the active sites of non-heme diiron enzymes. Inorg Chem 2001; 40:1414-20. [PMID: 11261945 DOI: 10.1021/ic000975k] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A bis(mu-carboxylato)(mu-1,8-naphthyridine)diiron(II) complex, [Fe2(BPMAN)(mu-O2CPhCy)2](OTf)2 (1), was prepared by using the 1,8-naphthyridine-based dinucleating ligand BPMAN, where BPMAN = 2,7-bis[bis(2-pyridylmethyl)aminomethyl]-1,8-naphthyridine. The cyclic voltammogram (CV) of this complex in CH2Cl2 exhibited two reversible one-electron redox waves at +296 mV (DeltaE(p) = 80 mV) and +781 mV (DeltaE(p) = 74 mV) vs Cp2Fe+/Cp2Fe, corresponding to the FeIIIFeII/FeIIFeII and FeIIIFeIII/FeIIIFeII couples, respectively. This result is unprecedented for diiron complexes having no single atom bridge. Dinuclear complexes [Fe2(BPMAN)(mu-OH)(mu-O2CPhCy)](OTf)2 (2) and [Mn2(BPMAN)(mu-O2CPhCy)2](OTf)2 (3) were also synthesized and structurally characterized. The cyclic voltammogram of 2 in CH2Cl2 exhibited one reversible redox wave at -22 mV only when the potential was kept below +400 mV. The CV of 3 showed irreversible oxidation at potentials above +900 mV. Diiron(II) complexes [Fe2(BEAN)(mu-O2CPhCy)3](OTf) (4) and [Fe2(BBBAN)(mu-OAc)2(OTf)](OTf) (6) were also prepared and characterized, where BEAN = 2,7-bis(N,N-diethylaminomethyl)-1,8-naphthyridine and BBBAN = 2,7-bis[2-[2-(1-methyl)benzimidazolylethyl]-N-benzylaminomethyl]-1,8-naphthyridine. The cyclic voltammograms of these complexes were recorded. The Mössbauer properties of the diiron compounds were studied.
Collapse
Affiliation(s)
- C He
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | | |
Collapse
|
1346
|
Basch H, Musaev DG, Mogi K, Morokuma K. Theoretical Studies on the Mechanism of the Methane → Methanol Conversion Reaction Catalyzed by Methane Monooxygenase: O-Side vs N-Side Mechanisms. J Phys Chem A 2001. [DOI: 10.1021/jp004032k] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Harold Basch
- Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, Georgia 30322, and Department of Chemistry, Bar Ilan University, Ramat Gan 52900, Israel
| | - Djamaladdin G. Musaev
- Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, Georgia 30322, and Department of Chemistry, Bar Ilan University, Ramat Gan 52900, Israel
| | - Koichi Mogi
- Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, Georgia 30322, and Department of Chemistry, Bar Ilan University, Ramat Gan 52900, Israel
| | - Keiji Morokuma
- Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, Georgia 30322, and Department of Chemistry, Bar Ilan University, Ramat Gan 52900, Israel
| |
Collapse
|
1347
|
Whittington DA, Lippard SJ. Crystal structures of the soluble methane monooxygenase hydroxylase from Methylococcus capsulatus (Bath) demonstrating geometrical variability at the dinuclear iron active site. J Am Chem Soc 2001; 123:827-38. [PMID: 11456616 DOI: 10.1021/ja003240n] [Citation(s) in RCA: 143] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The oxidation of methane to methanol is performed at carboxylate-bridged dinuclear iron centers in the soluble methane monooxygenase hydroxylase (MMOH). Previous structural studies of MMOH, and the related R2 subunit of ribonucleotide reductase, have demonstrated the occurrence of carboxylate shifts involving glutamate residues that ligate the catalytic iron atoms. These shifts are thought to have important mechanistic implications. Recent kinetic and theoretical studies have also emphasized the importance of hydrogen bonding and pH effects at the active site. We report here crystal structures of MMOH from Methylococcus capsulatus (Bath) in the diiron(II), diiron(III), and mixed-valent Fe(II)Fe(III) oxidation states, and at pH values of 6.2, 7.0, and 8.5. These structures were investigated in an effort to delineate the range of possible motions at the MMOH active site and to identify hydrogen-bonding interactions that may be important in understanding catalysis by the enzyme. Our results present the first view of the diiron center in the mixed-valent state, and they indicate an increased lability for ferrous ions in the enzyme. Alternate conformations of Asn214 near the active site according to redox state and a distortion in one of the alpha-helices adjacent to the metal center in the diiron(II) state have also been identified. These changes alter the surface of the protein in the vicinity of the catalytic core and may have implications for small-molecule accessibility to the active site and for protein component interactions in the methane monooxygenase system. Collectively, these results help to explain previous spectroscopic observations and provide new insight into catalysis by the enzyme.
Collapse
Affiliation(s)
- D A Whittington
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | | |
Collapse
|
1348
|
Wolfe MD, Parales JV, Gibson DT, Lipscomb JD. Single turnover chemistry and regulation of O2 activation by the oxygenase component of naphthalene 1,2-dioxygenase. J Biol Chem 2001; 276:1945-53. [PMID: 11056161 DOI: 10.1074/jbc.m007795200] [Citation(s) in RCA: 129] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Naphthalene 1,2-dioxygenase (NDOS) is a three-component enzyme that catalyzes cis-(1R,2S)-dihydroxy-1,2-dihydronaphthalene formation from naphthalene, O2, and NADH. We have determined the conditions for a single turnover of NDOS for the first time and studied the regulation of catalysis. As isolated, the alpha3beta3 oxygenase component (NDO) has up to three catalytic pairs of metal centers (one mononuclear Fe2+ and one diferric Rieske iron-sulfur cluster). This form of NDO is unreactive with O2. However, upon reduction of the Rieske cluster and exposure to naphthalene and O2, approximately 0.85 cis-diol product per occupied mononuclear iron site rapidly forms. Substrate binding is required for oxygen reactivity. Stopped-flow and chemical quench analyses indicate that the rate constant of the single turnover product-forming reaction significantly exceeds the NDOS turnover number. UV-visible and electron paramagnetic resonance spectroscopies show that during catalysis, one mononuclear iron and one Rieske cluster are oxidized per product formed, satisfying the two-electron reaction stoichiometry. The addition of oxidized or reduced NDOS ferredoxin component (NDF) increases both the product yield and rate of oxidation of formerly unreactive Rieske clusters. The results show that NDO alone catalyzes dioxygenase chemistry, whereas NDF appears to serve only an electron transport role, in this case redistributing electrons to competent active sites.
Collapse
Affiliation(s)
- M D Wolfe
- Department of Biochemistry, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | | | | | | |
Collapse
|
1349
|
Lovell T, Stranger R, McGrady JE. Mutual interdependence of spin crossover and metal-metal bond formation in M2Cl9(3-) (M = Fe, Ru, Os). Inorg Chem 2001; 40:39-43. [PMID: 11195385 DOI: 10.1021/ic0004737] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Broken-symmetry density functional theory is used to examine the coupling between metal ions in the face-shared bioctahedral complexes M2Cl9(3-), M = Fe, Ru, Os. In the ruthenium and osmium systems, the metal ions have low-spin configurations, and strong coupling results in the formation of a metal-metal sigma bond. In contrast, the iron system contains two weakly coupled high-spin FeIII centers, the different behavior being due to the high spin-polarization energy in the smaller Fe atom. At Fe-Fe separations shorter than 2.4 A, however, an abrupt transition occurs and the ground state becomes very similar to that for the heavier congeners (i.e., strongly coupled low-spin FeIII). The intrinsic link between high-spin/low-spin transitions on the individual metal centers and the onset of metal-metal bond formation is traced to the spin-polarization energy, which plays a central role in both processes.
Collapse
Affiliation(s)
- T Lovell
- Department of Chemistry, The Faculties, Australian National University, Canberra, ACT 0200, Australia
| | | | | |
Collapse
|
1350
|
Torrent M, Musaev DG, Morokuma K. The Flexibility of Carboxylate Ligands in Methane Monooxygenase and Ribonucleotide Reductase: A Density Functional Study. J Phys Chem B 2000. [DOI: 10.1021/jp003692m] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Maricel Torrent
- Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, Georgia 30322
| | - Djamaladdin G. Musaev
- Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, Georgia 30322
| | - Keiji Morokuma
- Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, Georgia 30322
| |
Collapse
|