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1.
Wang Q Blake AJ Davies ES McInnes EJ Wilson C Schröder M 《Chemical communications (Cambridge, England)》2003,(24):3012-3013
The asymmetric binuclear complex [(dppe)Ni(mu-'S, S')Ni(L)](PF6)2 [L = (N, N'-diethyl-3,7-diazanonane-1,9-dithiolato)2-] shows a reversible one-electron reduction to afford a mixed-valent Ni(II) x Ni(I) species; the reduced complex has been characterised by EPR spectroscopy and mimics the redox active Nip site in the active A-cluster of acetyl coenzyme A synthase. 相似文献
2.
Dougherty WG Rangan K O'Hagan MJ Yap GP Riordan CG 《Journal of the American Chemical Society》2008,130(41):13510-13511
A series of binuclear NiNi complexes supported by a single thiolate bridge and containing a methylnickel moiety have been prepared and fully characterized. The complexes represent structural analogues for the proposed organonickel intermediate in the acetyl coenzyme A synthase catalytic cycle. Variable temperature 31P NMR spectroscopy was used to examine dynamic behavior of the thiolate bridging interaction in two of the derivatives. Kinetic analyses, independent exchange and crossover experiments support an intermolecular exchange mechanism. Carbonylation results in thioester formation via a reductive elimination pathway. 相似文献
3.
Harrop TC Olmstead MM Mascharak PK 《Journal of the American Chemical Society》2004,126(45):14714-14715
The Ni(II)-dicarboxamido-dithiolato complexes (Et4N)2[Ni(NpPepS)] (1) and (Et4N)2[Ni(PhPepS)] (2) were used as Nid metallosynthons in the construction of higher nuclearity dinuclear Ni-Cu and Ni-Ni species to model the bimetallic Mp-Nid site of the A-cluster of acetyl coenzyme A synthase/CO dehydrogenase (ACS/CODH). Reaction of 1 with [Cu(neo)Cl] and [Ni(terpy)Cl2] in MeCN affords the dinuclear complexes (Et4N)[Cu(neo)Ni(NpPepS)] (3) and [Ni(terpy)Ni(NpPepS)] (4), respectively. Reaction of 2 with [Ni(dppe)Cl2] in MeCN yields [Ni(dppe)Ni(PhPepS)] (6). The Ni-Cu complex 3 exhibits no redox chemistry at the Nid site and no reaction with CO. In contrast, the Nip sites in 4 and 6 are readily reduced (characterized by their Ni(I) EPR spectra) and bind CO, exhibiting nuco bands at 2044 and 1997 cm-1, respectively, indicating terminal CO binding. The present Ni-Ni systems replicate the structural and chemical properties of the A-cluster site in ACS/CODH and support the presence of Ni at Mp in the catalytically active enzyme. 相似文献
4.
Two metallosynthons, namely (Et4N)2[Ni(NpPepS)] (1) and (Et4N)2[Ni(PhPepS)] (2) containing carboxamido-N and thiolato-S as donors have been used to model the bimetallic M(p)-Ni(d) subsite of the A-cluster of the enzyme acetyl coenzyme A synthase/CO dehydrogenase. A series of sulfur-bridged Ni/Cu dinuclear and trinuclear complexes (3-10) have been synthesized to explore their redox properties and affinity of the metal centers toward CO. The structures of (Et4N)2[Ni(PhPepS)] (2), (Et4N)[Cu(neo)Ni(NpPepS)] x 0.5 Et2O x 0.5 H2O (3 x 0.5 Et2O x 0.5 H2O), (Et4N)[Cu(neo)Ni(PhPepS)] x H2O (4 x H2O), (Et4N)2[Ni{Ni(NpPepS)}2] x DMF (5 x DMF), (Et4N)2[Ni(DMF)2{Ni(NpPepS)}2] x 3 DMF (6 x 3 DMF), (Et4N)2[Ni(DMF)2{Ni(PhPepS)}2] (8), and [Ni(dppe)Ni(PhPepS)] x CH2Cl2 (10 x CH2Cl2) have been determined by crystallography. The Ni(d) mimics 1 and 2 resist reduction and exhibit no affinity toward CO. In contrast, the sulfur-bridged Ni center (designated Ni(C)) in the trinuclear models 5-8 are amenable to reduction and binds CO in the Ni(I) state. Also, the sulfur-bridged Ni(C) center can be removed from the trimers (5-8) by treatment with 1,10-phenanthroline much like the "labile Ni" from the enzyme. The dinuclear Ni-Ni models 9 and 10 resemble the Ni(p)-Ni(d) subsite of the A-cluster more closely, and only the modeled Ni(p) site of the dimers can be reduced. The Ni(I)-Ni(II) species display EPR spectra typical of a Ni(I) center in distorted trigonal bipyramidal and distorted tetrahedral geometries for 9(red) and 10(red), respectively. Both species bind CO, and the CO-adducts 9(red)-CO and 10(red)-CO display strong nu(co) at 2044 and 1997 cm(-1), respectively. The reduction of 10 is reversible. The CO-affinity of 10 in the reduced state and the nu(co) value of 10(red)-CO closely resemble the CO-bound reduced A-cluster (nu(co) = 1996 cm(-1)). 相似文献
5.
Acetyl coenzyme A synthase (ACS) is an alpha2beta2 tetramer in which the active-site A-cluster, located in the alpha subunits, consists of an Fe4S4 cubane bridged to a {Nip Nid} binuclear site. The alpha subunits exist in two conformations. In the open conformation, Nip is surface-exposed, while the proximal metal is buried in the closed conformation. Nip is labile and can be replaced by Cu. In this study, the effects of Zn are reported. ACS in which Zn replaced Nip was inactive and did not exhibit the so-called NiFeC EPR signal nor the ability to accept a methyl group from the corrinoid-iron-sulfur protein (CoFeSP). Once Zn-bound, it could not be replaced by subsequently adding Ni. The Zn-bound A-cluster cannot be reduced and bound with CO or become methylated, probably because Zn (like Cu) is insufficiently nucleophilic for these functions. Unexpectedly, Zn replaced Nip only while ACS was engaged in catalysis. Under these conditions, replacement occurred with kapp approximately 0.6 min-1. Replacement was blocked by including EDTA in the assay mix. Zn appears to replace Nip when ACS is in an intermediate state (or states) of catalysis but this(these) state(s) must not be present when ACS is reduced in CO alone, or in the presence of CoA, CoFeSP, or reduced methyl viologen. Nip appears susceptible to Zn-attack when the alpha subunit is in the open conformation and protected from attack when it is in the closed conformation. This is the first evidence that the structurally-characterized conformations of the alpha subunit change during catalysis, indicating a mechanistic role for this conformational change. 相似文献
6.
Prabu R Vijayaraj A Suresh R Shenbhagaraman R Kaviyarasan V Narayanan V 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,78(2):601-606
The five binuclear nickel(II) complexes have been synthesized by the Schiff base condensation of 1,8-[bis(3-formyl-2-hydroxy-5-methyl)benzyl]-l,4,8,11-tetraazacyclo-tetradecane (PC) with appropriate aliphatic diamines and nickel(II) perchlorate. All the five complexes were characterized by elemental and spectral analysis. The electronic spectra of the complexes show three d-d transition in the range of 550-1055 nm due to 3A2g→3T2g(F), 3A2g→3T1g(F) and 3A2g→3T1g(P). These spin allowed electronic transitions are characteristic of an octahedral Ni2+ center. Electrochemical studies of the complexes show two irreversible one electron reduction waves at cathodic region. The reduction potential of the complexes shifts towards anodically upon increasing the chain length of the macrocyclic ring. All the nickel(II) complexes show two irreversible one electron oxidation waves at anodic region. The oxidation potential of the complexes shift towards anodically upon increasing the chain length of the macrocyclic ring. The catalytic activities of the complexes were observed to be increase with increase the macrocyclic ring size. The observed rate constant values for the catalytic hydrolysis of 4-nitrophenyl phosphate are in the range of 5.85×10(-3) to 9.14×10(-3) min(-1). All the complexes were screened for antimicrobial activity. 相似文献
7.
Stopped-flow was used to evaluate the methylation and reduction kinetics of the isolated alpha subunit of acetyl-Coenzyme A synthase from Moorella thermoacetica. This catalytically active subunit contains a novel Ni-X-Fe4S4 cluster and a putative unidentified n = 2 redox site called D. The D-site must be reduced for a methyl group to transfer from a corrinoid-iron-sulfur protein, a key step in the catalytic synthesis of acetyl-CoA. The Fe4S4 component of this cluster is also redox active, raising the possibility that it is the D-site or a portion thereof. Results presented demonstrate that the D-site reduces far faster than the Fe4S4 component, effectively eliminating this possibility. Rather, this component may alter catalytically important properties of the Ni center. The D-site is reduced through a pathway that probably does not involve the Fe4S4 component of this active-site cluster. 相似文献
8.
Summary Binuclear NiII and CoII complexes derived from 2,6-diformyl-4-methylphenol and various aromatic monoamines have been prepared and investigated. The NiII complexes have Ni2LCl3 composition while the CoII complexes have Co2L2Cl2 composition, where L represents the organic ligand. The complexes are active catalysts in the oxidation of 3,5-di-t-butylcatechol (3,5-DTBC) by dioxygen, but less so than their Cu analogues. This result is attributed to the absence of antiferromagnetic coupling between the metal centres. 相似文献
9.
The influence of structural parameters on the exchange coupling J between metal atoms in end-to-end azido-bridged binuclear complexes of Cu(II) and Ni(II) has been studied by means of density functional calculations. For the case of double-bridged Cu(II) compounds, four ideal pentacoordinate models have been employed in which the coordination spheres of the two metal atoms are either a trigonal bipyramid or a square pyramid, connected through equatorial or axial bridges. The distortion from those ideal geometries along a Berry pathway has also been analyzed. For the hexacoordinate Ni(II) compounds, models with two or one bridging ligands have been studied. The effect of the bridging M-N-N bond angles on the exchange coupling has been analyzed for both the Cu(II) and Ni(II) complexes. 相似文献
10.
Linck RC Spahn CW Rauchfuss TB Wilson SR 《Journal of the American Chemical Society》2003,125(29):8700-8701
Models for the active site of the acetyl CoA synthase (ACS) were synthesized by attachment of Cu+ and Ni(0) to nickel diaminodithiolate (S2N2) and diamidodithiolate (S2N2') complexes. The Ni-Ni species form stable CO adducts, i.e., [{(CO)2Ni}{NiS2N2'}]2-, whereas the Cu-NiS2N2 and Cu-NiS2N2' models do not. These results provide supporting evidence for a biological role for reduced nickel in ACS. 相似文献
11.
Treatment of the N-P ligand ArPN(SiMe3)2 with TiCl4 affords the imido-bridged binuclear titanium complex [TiCl2(THF)(micro-NArP)]2 (ArP = m-C6H4PR2) which reacts with Ni(0) or Pd(ii) to give heterotrinuclear compounds, while activation with methylaluminoxane generates a new type of imido-based ethene polymerisation catalyst that is tolerant of -PR2 functional groups. 相似文献
12.
South Africa is a mineral-rich country and one area in which minerals can be very important is catalysis. Over an extended period of time, homogeneous catalysis has grown to become very useful, particularly in the chemical and pharmaceutical industries. The organometallic compounds required in the catalysis industry have advanced from metallocenes to an alternative in the form of a-diimines. Most a-diimines are prepared from iminopyridyl moieties and are most active with nickel and palladium transition metals. This review providesa history of homogeneous catalysis and a discussion on iminopyridines, with the main focus on the nickel and palladium complexes formed from them. There follows a discussion of the bimetallic nickel and palladium complexes in various catalytic applications such as Suzuki and Heck coupling, with the main focus on ethylene polymerisation. The limitations are addressed and possible solutions presented to overcome those challenges. Several reviews in the related topics are to be found in the literature but not the a-diimine with iminopyridines and bimetallic nickel and palladium metals. 相似文献
13.
S. Sreedaran K. Shanmuga Bharathi A. Kalilur Rahiman R. Suresh R. Jegadeesh N. Raaman V. Narayanan 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2009,74(4):849-854
Five binuclear nickel(II) complexes have been prepared by simple Schiff base condensation of the compound 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-l,4,8,11-tetraazacyclotetradecane (L) with appropriate aliphatic or aromatic diamine, nickel(II) perchlorate and triethylamine. All the complexes were characterized by elemental and spectral analysis. Positive ion FAB mass spectra show the presence of dinickel core in the complexes. The electronic spectra of the complexes show red shift in the d–d transition. Electrochemical studies of the complexes show two irreversible one electron reduction processes in the range of 0 to −1.4 V. The reduction potential of the complexes shifts towards anodically upon increasing chain length of the macrocyclic ring. All the nickel(II) complexes show two irreversible one electron oxidation waves in the range 0.4–1.6 V. The observed rate constant values for catalysis of the hydrolysis of 4-nitrophenyl phosphate are in the range of 1.36 × 10−2–9.14 × 10−2 min−1. The rate constant values for the complexes containing aliphatic diimines are found to be higher than the complexes containing aromatic diimines. Spectral, electrochemical and catalytic studies of the complexes were compared on the basis of increasing chain length of the imine compartment. All the complexes show higher antimicrobial activity than the ligand and metal salt. 相似文献
14.
The active site of Acetyl CoA Synthase utilizes a square planar NiN2S2 complex in the form of NiII(CGC)2− (CGC = the cysteine-glycine-cysteine tripeptide motif within the protein) to serve as a bidentate sulfur-donor ligand to chelate a second, catalytically active Ni atom responsible for the C-C and C-S coupling reactions for the production of Acetyl CoA. Metalloenzymes, such as this, which house stable catalytic complexes within intricately designed pockets accessible by solvent channels, have inspired design of resin-bound complexes. Through the use of TentaGel S-RAM® resin beads, the O-Ni(CGC)2− ligand has been synthesized and derivatized with the RhI(CO)2 moiety. The identification of the adduct on these resin beads is afforded by attenuated total reflectance FTIR spectroscopy in the ν(CO) region and compared to solution analogues. The goal of this study is to establish a quantitative measure of the loading of nickel and rhodium on the tripeptide modified resin beads, O-(CGC). The extent of CGC derivatization was determined by Fmoc cleavage of the Fmoc protected O-(CGC). Nickel and rhodium loading were determined by Neutron Activation Analysis. This work provides evidence that the TentaGel S-RAM® resin beads greatly decrease the air sensitivity of the Ni-Rh complex as compared to the unsupported solution phase analogue. The derivatized beads have also been studied for their ability to withstand a number of physical stresses, i.e., for leaching. 相似文献
15.
16.
G. A. Tolstikov N. R. Popod'ko A. A. Pozdeeva R. I. Khusnutdinov S. I. Zhdanov D. K. Galeev U. M. Dzhemilev 《Russian Chemical Bulletin》1984,33(6):1186-1189
Conclusions By electrochemical methods, it was shown that -organonickel complexes stabilized by organoaluminum compounds are present in homogeneous three-component systems consisting of NiX2 (X=Cl or acac), an organophosphorus activator [PR3, P(OR)3, where R=Et, i-Pr, Bu,Ph], and an organoaluminum reducing agent.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1293–1295, June, 1984. 相似文献
17.
Todd C. Harrop 《Coordination chemistry reviews》2005,249(24):3007-3024
Acetyl coenzyme A synthase/carbon monoxide dehydrogenase (ACS/CODH) is a bifunctional enzyme present in a number of anaerobic bacteria. The enzyme catalyzes two separate reactions namely, the reduction of atmospheric CO2 to CO (CODH activity at the C-cluster) and the synthesis of acetyl coenzyme A (ACS activity at the A-cluster) from CO, CH3 from a corrinoid iron-sulfur protein, and the thiol coenzyme A. The structure(s) of the A-cluster of ACS/CODH from Moorella thermoacetica revealed an unprecedented structure with three different metallic subunits linked to each other through bridging Cys-S residues comprising the active site. In these structure(s) a Fe4S4 cubane is bridged via Cys-S to a bimetallic metal cluster. This bimetallic cluster contains a four-coordinate Ni, Cu, or Zn as the proximal metal (to the Fe4S4 cluster; designated Mp), which in turn is bridged through two Cys-S residues to a terminal square planar Ni(II) (Nid, distal to Fe4S4) ligated by two deprotonated carboxamido nitrogens from the peptide backbone. It is now established that Ni is required at the Mp site for the ACS activity. Over the past several years modeling efforts by several groups have provided clues towards understanding the intrinsic properties of the unique site in ACS. To date most studies have focused on dinuclear compounds that model the Mp-Nid subsite. Synthesis of such models have revealed that the Nip sites (a) are readily removed when mixed with 1,10-phenanthroline (phen) and (b) can be reduced to the Ni(I) and/or Ni(0) oxidation state (deduced by EPR or electrochemical studies) and bind CO in terminal fashion with νco value similar to the enzyme. In contrast, the presence of Cu(I) centers at these Mp sites do not bind CO and are not removable with phen supporting a non-catalytic role for Cu(I) at the Mp site in the enzyme. The Nid site (coordinated by carboxamido-N/thiolato-S) in these models are very stable in the +2 oxidation state and not readily removed upon treatment with phen suggesting that the source of ‘labile Ni’ and the NiFeC signal arises from the presence of Ni at the Mp site in ACS. This review includes the results and implications of the modeling studies reported so far. 相似文献
18.
Oxidations of a trigonal-bipyramidal, high-spin Ni(II) dithiolate complex of a pentadentate, N3S2-donor ligand, N1,N9-bis(imino-2-mercaptopropane)-1,5,9-triazanonane) nickel(II), and the structurally analogous Zn(II) complex, lead to oxidations of the ligand. Oxidation of the Ni(II) complex with I2 produces a novel Ni(II) macrocyclic cationic complex containing a monodentate disulfide ligand (2). Crystals of the I3- salt of the complex form in the triclinic space group P(1) with cell dimensions a=8.508(3) A, b=9.681(2) A, c=14.066(4) A, angles alpha=90.97(2) degrees , beta=91.61(3) degrees , gamma=90.83(2) degrees , and Z=2. The structure was refined to R=6.31% and Rw=16.63% (I > 2sigma(I)). Oxidation of the Ni(II) complex with O2 leads to the formation of a novel pentadentate bis-iminothiocarboxylate complex with trigonal-bipyramidal geometry (3). This neutral product crystallizes in the monoclinic space group P21/c with cell dimensions a=13.625(3) A, b=7.605(5) A, c=14.902(4) A, angles alpha=gamma=90 degrees, beta=102.81(2) degrees , and Z=4. The structure was refined to R=7.18% and Rw=17.86% (I > 2sigma(I)). Oxidation of the Zn(II) dithiolate analogue with O2 leads to the formation of the Zn(II) complex of the pentadentate bis-iminothiocarboxylate ligand. The neutral complex is isomorphous with the Ni(II) complex and crystallizes in the monoclinic space group P2(1)/c with cell dimensions a=13.8465(4) A, b=7.6453(2) A, c=15.0165(6) A, angles alpha=gamma=90 degrees , beta=103.2140(11) degrees , and Z=4. The structure was refined to R=3.96% and Rw=9.45% (I > 2sigma(I)). Details of the crystal structures are reported. Kinetics of the O2 reactions show that the reactions of the Ni(II) and Zn(II) dithiolates follow the rate law, Rate=k2[1][O2], with k2=1.81 M(-1) s(-1) for the Ni(II) complex and k2=1.93 x 10(-2) M(-1) s(-1) for the Zn(II) complex. The O2 oxidation of the high-spin Ni(II) thiolate complex was found to follow a similar oxidation mechanism to those of low-spin Ni(II) complexes, which form transient persulfoxide intermediates that yield S-oxidation products. In the case of the high-spin system reported here, the transient persulfoxide intermediate gives rise to an alternative ligand oxidation product, a bis-iminothiocarboxylate complex, because of the reactivity of the ligand, which contains a methylene with acidic H atoms alpha to the thiolate sulfur. The proposed mechanism is supported by studies of the analogous Zn dithiolate complex, which gives rise to the analogous bis-iminothiocarboxylate product (5). 相似文献
19.
20.
Harmer J Finazzo C Piskorski R Ebner S Duin EC Goenrich M Thauer RK Reiher M Schweiger A Hinderberger D Jaun B 《Journal of the American Chemical Society》2008,130(33):10907-10920
Methanogenic archaea utilize a specific pathway in their metabolism, converting C1 substrates (i.e., CO2) or acetate to methane and thereby providing energy for the cell. Methyl-coenzyme M reductase (MCR) catalyzes the key step in the process, namely methyl-coenzyme M (CH3-S-CoM) plus coenzyme B (HS-CoB) to methane and CoM-S-S-CoB. The active site of MCR contains the nickel porphinoid F430. We report here on the coordinated ligands of the two paramagnetic MCR red2 states, induced when HS-CoM (a reversible competitive inhibitor) and the second substrate HS-CoB or its analogue CH3-S-CoB are added to the enzyme in the active MCR red1 state (Ni(I)F430). Continuous wave and pulse EPR spectroscopy are used to show that the MCR red2a state exhibits a very large proton hyperfine interaction with principal values A((1)H) = [-43,-42,-5] MHz and thus represents formally a Ni(III)F430 hydride complex formed by oxidative addition to Ni(I). In view of the known ability of nickel hydrides to activate methane, and the growing body of evidence for the involvement of MCR in "reverse" methanogenesis (anaerobic oxidation of methane), we believe that the nickel hydride complex reported here could play a key role in helping to understand both the mechanism of "reverse" and "forward" methanogenesis. 相似文献