Download or read book Design Synthesis and Properties of Nickel Complexes that Replicate the Structural and Electronic Properties of the N3S2 Donor Set of Ni Containing Superoxide Dismutase written by Phan T. Truong and published by . This book was released on 2018 with total page 686 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nickel superoxide dismutase (NiSOD) is a metalloenzyme that can catalyze the disproportionation of superoxide (O2") to O2 and H2O2 at the diffusion-controlled rates. In the NiSOD active site, the Ni ion is situated in a mixed amine/peptide thiolates N3S2 coordination environment. The unique NiSOD active site promotes facile Ni(III/II) redox while prevents the oxidation/oxygenation of thiolates by the substrate and products of O2" disproportionation. This has prompted the development of relatively small synthetic analogues of NiSOD by our group and others to understand the role of mixed N/S donors in NiSOD. We reported the first five-coordinate (5C) analogue, K[Ni(N3S2)] (1), that replicates the N3S2 donor set of NiSOD structurally and electronically with a pendant pyridine as potential fifth ligand to Ni in the axial position. However, oxidation of 1 by ferrocenium hexafluorophosphate (FcPF6) yielded a disulfide-bridged complex. The increased in basicity as well as steric enforcement by incorporation of gem-(CH3)2 moiety in the second-generation analogue, Na[Ni(N3S2Me2)] (2), is expected to promote Ni-based redox while preventing disulfide formation at the S trans to carboxamide. However, the increase in steric enforcement in 2 led to a new oxidation pathway that yielded a thiazolidine ring rearrangement product that was not observed in 1. Since coordination of axial N-ligand to Ni is critical in promoting Ni-based redox in NiSOD, the pendant pyridine is replaced with N-ethylmorpholine (NEM) moiety in the third-generation analogue, Na[Ni(N3S2NEM)] (3). The more Lewis basic N-donor in 3 is expected to coordinate to both Ni2+ and Ni3+ oxidation state to promote Ni-based redox. Reactions of 3 with oxidants (air, FcPF6, and KO2) and Lewis acid (i.e. tris(pentafluorophenyl) borane) yielded stair-step trimetallic species with N-NEM poised to coordinate to terminal [NiN3S2] centers. CV of these trimetallic species exhibited multiple reversible redox couples assigned to the terminal [NiN3S2] centers. These results show that while 1-3 can replicate NiSOD active site electronically and structurally, reversible Ni(III/II) redox couple is not achievable unless the electron density on S-thiolates is sequestered by Lewis acids (i.e., Ni2+ and borane), which mimics the H-bond interactions in NiSOD active site.

Download or read book Synthesis and Properties of Nickel carboxamide and Thiolate Complexes for Modeling NiSOD and Ni II Sensing written by Ellen Patricia Broering and published by . This book was released on 2017 with total page 682 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nickel superoxide dismutase (NiSOD) is a metalloenzyme that disproportionates superoxide (O20́Ø0́2) to O2 and H2O2 by alternating between reduced and oxidized Ni states. NiSOD's coordination sphere also varies depending on oxidation states. In the reduced form, Ni(II) is coordinated in square-planar geometry by the primary amine of His1, carboxamide-N of Cys2, and two thiolate-S from Cys2 and Cys6. In the oxidized form, the imidazole-N of His1 binds axially in square pyramidal geometry that has proven crucial to accessing Ni(III) and maintaining the diffusion-controlled rate of disproportionation. Given the unusual coordination environment, Ni(II/III) redox, and O2 tolerance of the Cys-S ligands, we have turned to a synthetic approach to create low molecular weight mimics of the active site and gain insight into NiSOD. Using a metallosynthon precursor, we developed NiN2S2 complexes that model reduced NiSOD and vary at one coordination site to tune the electronic environment of the system. As a result of synthetic modifications in two systems, the S character in the redox active molecular orbital was sufficiently suppressed so as to allow access to a high valent Ni state. This is the first observation of a stable Ni(III) species in NiSOD synthetic analogues with structural and electronic donors that match the enzyme. Spectroscopic and computational evidence reveal that the high valent state is a resonance species of Ni(II)-thiyl radical and Ni(III)-thiolate character. Due to this resonance, the Ni complex exhibits unique reactivity with nitric oxide (NO), resulting in reductive nitrosylation and a dimeric {NiNO}10 species bridged by thiolates and N-nitrosamines. Turning to oxidized NiSOD models, a peptide-based His-Cysteamine ligand platform was developed, which contains His-NIm poised to bind to Ni in the apical position. However, this system coordinated Ni in an unidentified manner that did not involve the carboxamido-N, as evidenced by spectroscopic characterization. Taken together, these results highlight the reactivity of the amine/carboxamide/thiolate ligand environment of NiSOD. Ni is also found in other metalloenzymes and regulatory systems, and to better understand pathways of Ni trafficking, we have developed a novel N2S2 fluorescent sensor based upon the primary coordination sphere of reduced NiSOD to detect Ni(II) in solution.

Download or read book Synthesis and Characterization of Nickel Complexes with Relevance to Nickel Acireductone Dioxygenase and Nickel Superoxide Dismutase written by Margo Nicole Montgomery and published by . This book was released on 2012 with total page 288 pages. Available in PDF, EPUB and Kindle. Book excerpt: This research presents an investigation of synthetic model complexes with relevance to the active site of Ni(II) acireductone dioxygenase (Ni-ARD) and Ni(II) superoxide dismutase (Ni-SOD). Acireductone dioxygenases (ARDs) are a unique set of enzymes found in the methionine salvage pathway that catalyze the oxidation reaction of acireductone (1, 2-dihydroxy-3-oxo-5-(methylthio)pent-1-ene). These enzymes share a common polypeptide sequence but bind different metal ions, Ni 2+ or Fe2+, at the active site. The Ni-ARD enzyme is responsible for the off pathway shunt in the pathway. Using the tridentate nitrogen donor ligands hydrotris(3,5-dimethyl-1-pyrazolyl)borate (Tp*) and the newly developed tris(1, 2-dimethyl-4-imadozyl)carbinol, (4-TIC Me, Me) several reactions involving the acireductone analog 2-hydroxy-1, 3-diphenylpropan-1, 3-dione and O2 were investigated for similarities to the Ni-ARD active site. Superoxide dismutases (SODs) play a key role in protecting cells against oxidative damage by regulating the cellular concentration of the superoxide radical (O2.- ) which is an unwanted byproduct of cellular metabolism. This process is accomplished by converting the superoxide radicals to hydrogen peroxide and molecular oxygen. Several small-molecule complexes were synthesized and characterized in an effort to model the reduced state of the Ni-SOD using the Tp* ligand. The structures for these complexes have been determined using X-Ray Crystallography.

Download or read book Synthesis Structure and Reactivity of Nickel nickel Complexes for Understanding the A Cluster in Acetyl Coenzyme A Synthase written by William G. Dougherty (Jr) and published by ProQuest. This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The synthesis and reactivity of a series of binuclear NiNi complexes designed to model the A cluster of Acetyl Coenzyme A Synthase (ACS) are reported. The complexes were synthesized by metathesis reactions between the diamido dithiolato complexes Ni(phmi) or Ni(phma), phmi = N, N'-1,2-phenylene-bis(2-sulfanyl-2-methylpropionamide), phma = N, N'-1,2-phenylenebis(2-mercaptoacetamide); and the phosphine complexes Ni(dRpe)Cl 2, R = phenyl, ethyl, isopropyl. The complexes were fully characterized including by X-ray diffraction analysis demonstrating both the structural and electronic effects resulting from varying the substituent on the chelating phosphine and the bridging thiolato donors. These steric and electronic effects were also evident when investigating the electrochemical properties of these complexes by cyclic voltammetry, which indicated that the compounds were able to undergo two successive one-electron reductions at the S 2 P 2 coordinated nickel site. Ni(phma)Ni(depe) was reduced chemically using Na/Hg amalgam or decamethylcobaltocene producing a mixed-valent Ni 2+ Ni 1+ binuclear complex in solution, supported by an EPR signal consistent with a Ni 1+ center coupled to two equivalent phosphorus atoms, that reacts with CO ultimately forming trinuclear [Ni3(phma)2] 2- and Ni(dppe)(CO) 2 . A series of new NiNi-Me binuclear complexes were synthesized by metathesis of K 2 [Ni(phmi)] and [Et 4 N] 2 [Ni(phma)] with the methylnickel complex, Ni(dppe)MeCl. The complexes were characterized fully and the [Et 4 N][Ni(phma)Ni(dppe)Me] derivative was characterized crystallographically. These complexes showed interesting fluxional behavior in solution, which was investigated by variable temperature NMR studies. The fluxionality is proposed to arise from the isomerization of the methylnickel fragment between the two thiolate donors of the N 2 S 2 ligand through a 5-coordinate transition state. A series of thiolate exchange reactions were performed to assess thiolate lability. When a solution of [Et 4 N][Ni(phma)Ni(dppe)Me] was exposed to 1 equivalent of K 2 [Ni(phmi)] a equimolar amount of [Ni(phmi)Ni(dppe)Me] 2- and [Ni(phma)Ni(dppe)Me] 2- are produced as monitored by NMR spectroscopy. A crossover experiment between K[Ni(phmi)Ni(dppe)Me] and [Et 4 N][Ni(phma)Ni(dppe)CD 3] was performed and resulted in an equilibrium mixture containing all four possible complexes with K eq = 1. The methyl complexes reacted with CO forming Ni-acyl species that decompose rapidly under excess CO generating an acylated (N 2 S 2) ligand. This observed thiolate lability might be relevant to the enzyme where the exchange of one of the bridging thiolates for the thiolate CoA could be part of the mechanism responsible for acyl group transfer.

Download or read book Synthesis and Characterization of Nickel Imine amine Complexes a Possible Model for Nickel Superoxide Dismutase written by Tom Muinde Mwania and published by . This book was released on 2012 with total page 86 pages. Available in PDF, EPUB and Kindle. Book excerpt: Superoxide dismutases are ubiquitous enzymes that efficiently catalyze the disproportionation of superoxide radical anions to protect biological molecules from oxidative damage. Several SODs have been identified having different metals at their active sites. These include Mn SOD, Fe SOD, Cu/Zn SOD and, most recently, Ni SOD. The catalytic center of Ni SOD resides in the N-terminal active-site loop, where a Ni(II) is coordinated by the amine N of His-1, the amide N of Cys-2, and two thiolate S atoms of Cys-2 and Cys-6. In the oxidized form, Ni(III) adds the imidazole N of His-1 as an axial ligand. For the past decade, we have been developing methodology using 2, 2'-dithiodibenzaldehyde (DTDB) for the synthesis of metal complexes with mixed N/S coordination. We are reporting on the application of this methodology to the synthesis of model complexes for the active site of NiSOD, in which we have successfully synthesized and characterized three NiIIN2S2 complexes of imine/amine N donors: Ni(NNS)SPh (1), Ni(NNS)SPhNO2 (2) and Ni(NNS)StBu (3). These may be used as a model for reduced NiSOD, with future plans of comparing to complexes with amide/amine N donors, thus establishing the role of the amide.

Download or read book Design Synthesis and DNA Reactivity of Nickel Complexes Containing DNA Binding Groups written by Ren-Hwa Yeh and published by . This book was released on 1997 with total page 278 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Studies in Bioinorganic Chemistry written by Roxanne Michelle Jenkins and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: As inspired by the coordination environment of nickel in NikR and NiSOD, imidazole ligands were incorporated into N2SNiII square planar complexes in order to investigate the electronic and structural features of NiII species containing both imidazole and thiolate ligation. Rare examples of nickel complexes containing such ligand sets in continuous tetradentate (N2N'S) and discontinuous (N2S---N') coordination were synthesized and characterized. A significant finding in these studies is that the plane of the imidazole ligand is oriented perpendicular to the N2SNi plane. Further investigations addressed the orientational preference and stereodynamic nature of flat monodentate ligands (L = imidazoles, pyridine and an N-heterocyclic carbene) bound to planar N2SNi moieties. The solid state molecular structures of planar [N2SNiL]n+ complexes accessed through bridge-splitting reactions of dimeric, thiolate-S bridged [N2SNi]2 complexes, reveal that the plane of the added monodentate ligand orients largely orthogonal to the N2SNiL square plane. Variable temperature 1H NMR characterization of dynamic processes and ground state isomeric ratios of imidazole complexes in their stopped exchange limiting spectra, readily correlate with DFT-guided interpretation of Ni-L rotational activation barriers. Full DFT characterization relates the orientation mainly to steric hindrance derived both from ligand and binding pocket. In the case of the imidazole ligands a minor electronic contribution derives from intramolecular electrostatic interactions (imidazole C-2 C-H[superscript delta]- - S[superscript delta]− interaction). Our group has firmly established the versatility of the (bme-daco)2−, (bme-dach)2−, and (ema)4− ligands to accommodate a number of metals (M = Ni, Zn, Cu, and Fe), and have demonstrated reactivity of such N2S2M complexes occurs predominately at the S-thiolate sites. As vanadium is of interest for its biological, pharmacological and spectroscopic/analytical probe abilities, vanadyl analogues were explored as mimics of possible chelates formed from Cys-X-Cys binding sites in vivo. The structural and electronic changes from the incorporation of V=O2 in such dianionic and tetraanionic N2S2 binding pockets is investigated and compared to Ni2+ and Zn2+ in similar N2S2 environments. The nucleophilicity of the S-thiolate in these systems is explored with alkylating agents and W(CO)x. Furthermore, the vanadyl interaction with the CGC peptide, the biological analogue of the tetraanionic N2S2 ligand, was produced and characterized by EPR; its W(CO)x adducts were indentified by [upsilon](CO) infrared spectroscopy.

Download or read book Nickel Amine imine and Amine amide Bisthiolate Complexes as Models for the Active Site of Nickel Superoxide Dismutase written by Nilmini K. Senaratne and published by . This book was released on 2017 with total page 199 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nickel Superoxide Dismutase (NiSOD) catalyzes disproportionation of cytotoxic superoxide radical to H2O2 and molecular O2. The mononuclear nickel center in the active site undergoes alternate oxidation and reduction during the catalytic cycle and, the coordination geometry around the Ni changes accordingly. The four-coordinate reduced state of the NiSOD is coordinated by the N-terminal amine of His1, carboxamido N of Cys2 and, two thiolato S atoms from Cys2 and Cys6 in a square-planar geometry. The oxidized state contains an additional N donor arise from the imidazole of His1 giving a five-coordinate square-pyramidal geometry. The highly unusual coordination environment of the NiSOD makes it distinct among other known SODs and motivates researchers to study about it. This research is mainly focused on to understand the role of the amide N coordination in the NiSOD which is only found in very few metalloenzymes. Through a synthetic model approach we have synthesized two types of model systems which contain amine/amide and amine/imine bisthiolate coordination. The imidazole N from His is the common N donor found in metalloenzymes and we made imine N containing models to represent the normal His imidazole N. The imine containing complexes, [Ni(NNimS]SR] were compared with the amide containing complexes, [Ni(NNamS)SR] utilizing X-ray crystallography, spectroscopic techniques, electrochemical measurements, and reactivity studies. Different thiolates with varying electron donating ability were used to study the effect of nature of the thiolates on the properties of the Ni center. This comparison allows us to understand the effective role of the amide N donation in NiSOD. In addition to our attempts at synthesizing four-coordinate NiN2S2 model complexes, this work describes our attempts at synthesizing NiN3S2 complexes as models for the oxidized state of the NiSOD.

Download or read book New Nickel II Complexes with N donor Ligands and Anions as Coligands written by Vladislav Abramov and published by . This book was released on 2010 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Synthesis Structural and Electronic Properties and Reactivity of Group 5 Metal Complexes Incorporating the Redox active ONO Ligand Platform written by Steven Paul Hananouchi and published by . This book was released on 2014 with total page 67 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis describes the synthesis, electronic and structural properties, and reactivity of Group 5 metal complexes incorporating the [ONO] ligand platform. A study of the electronic and structural properties of the Group 5 metal complexes incorporating the [ONO] ligand is performed. Once the electronic properties of the complexes are known, the reactivity of the complexes is compared. Chapter 1 describes a brief history of redox-active ligands. The previously published results of redox-active ligands acting as an electron source are discussed. In Chapter 2, the synthesis and electronic and structural properties of metal dichlorides and trichlorides of Group 5 metal complexes incorporating the [ONO] ligand and comparing the metal-ligand cooperativity are performed. In Chapter 3, the synthesis and reactivity of [ONO]NbMe2 and the reactivity of reduced species of [ONO]V(L)n are discussed.

Download or read book Model Complexes for Nickel Containing Enzymes written by Joshua Robert Zimmerman and published by . This book was released on 2009 with total page 209 pages. Available in PDF, EPUB and Kindle. Book excerpt: Carbon Monoxide Dehydrogenase / Acetyl CoA Synthase (CODH/ACS) is a bifunctional enzyme that catalyzes the reduction of CO2́2 to CO and the assembly of Acetyl CoA. The A-cluster active site, which catalyzes the Acetyl CoA synthesis, contains a Fe-S cubane bridged by a cysteine thiolate to a dinuclear Ni(℗æ-S)2́2Ni cluster (Fig. 1). The proximal nickel, Nip, has S2́3X coordination, while the distal nickel, Nid, has N2́2S2́2 coordination. This project focuses on the synthesis of model complexes for the asymmetric dinuclear metal center in order to understand the electronic characteristics of this cluster and investigate the feasibility of proposed intermediates. The initial target compound is shown in Figure 2. We have developed an efficient method for synthesizing metal complexes with mixed N/S coordination through the use of 2-2'-dithiodibenzaldehyde, DTDB. Symmetric nickel complexes with NS2́3 coordination have previously been synthesized using DTDB and various bidentate NS ligands. Herein we present our results upon incorporating N,N-dimethylethylenediamine into this methodology.

Download or read book Synthesis Structure and Reactivity of mu 3 Sn Capped Trinuclear Nickel Clusters written by Nicole Torquato and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Chapter 1. This section presents an overview of literature pertaining to low-valent/low-oxidation state tin hydrides, transition metal coordinated tin hydrides, and group 10 trinuclear metal cluster synthesis, characterization, and reactivity. Chapter 2. Treatment of the trichlorotin-capped trinuclear nickel cluster, [Ni3(dppm)3([mu]3-Cl)([mu]3-SnCl3)], 1, with 4 eq. NaHB(Et)3 yields a [mu]3-SnH capped trinuclear nickel cluster, [Ni3(dppm)3([mu]3-H)([mu]3-SnH)], 2 [dppm = bis(diphenylphosphino)methane]. Single-crystal X-ray diffraction, nuclear magnetic resonance (NMR) spectroscopy, and computational studies together support that cluster 2 is a divalent tin hydride. Complex 2 displays a wide range of reactivity including oxidative addition of bromoethane across the Sn center. Addition of 1 eq. iodoethane to complex 2 releases H2 (g) and generates an ethyltin-capped nickel cluster with a [mu]3-iodide, [Ni3(dppm)3([mu]3-I)([mu]3-Sn(CH2CH3))], 4. Notably, insertion of alkynes into the Sn-H bond of 2 can be achieved via addition of 1 eq. 1-hexyne to generate the 1-hexen-2-yl-tin-capped nickel cluster, [Ni3(dppm)3([mu]3H)([mu]3-Sn(C6H11))], 5. Addition of H2 (g) to 5 regenerates the starting material, 2, and hexane. The formally 44-electron cluster 2 also displays significant redox chemistry with two reversible one-electron oxidations (E = -1.3 V, -0.8 V vs. Fc0/+) and one-electron reduction process (E = -2.7 V vs. Fc0/+) observed by cyclic voltammetry. Chapter 3. H2 and D2 exchange by a [mu]3-SnH, [mu]3-H capped trinuclear nickel cluster, [Ni3(dppm)3([mu]3-H)([mu]3-SnH)], 1, (dppm = bis(diphenylphosphino)methane) was investigated through a variety of nuclear magnetic resonance (NMR) spectroscopy studies. Mechanistic studies reveal reversible exchange upon addition of D2/H2 between 1 and the deuteride species, [Ni3(dppm)3([mu]3-D)([mu]3-SnD)], 1D. Furthermore, these studies suggest a conformational change at the Ni-H functionality upon addition of H2. Variable temperature (VT) NMR studies of 1 demonstrate a temperature dependence of the Sn-H and the Ni-H resonances, with the Ni-H experiencing the largest perturbation in chemical shift. Further mechanistic insights were obtained with VT NMR studies performed under an atmosphere H2 and HD. Overall, these studies provide evidence of H2/D2 exchange by complex 1 and suggest a novel mechanism for hydrogen activation and exchange processes. Chapter 4. Spectroscopic and structural comparisons are made between a series of (OR)3Sn capped trinuclear nickel clusters. The synthesis of the (OEt)3Sn and (OPh)3Sn capped nickel clusters, [Ni3(dppm)3([mu]3-Cl)([mu]3-Sn(OEt)3)] (1), [Ni3(dppm)3([mu]3-Cl)([mu]3-Sn(OPh)3)] (2), was realized by the treatment of [Ni3(dppm)3([mu]3-Cl)([mu]3-SnCl3] with 6 eq. of KOEt or NaOPh, respectively. Treatment of complex 1 with 10 eq. glycerol results in the synthesis of the (C3H5O3)Sn capped trinuclear nickel cluster, [Ni3(dppm)3([mu]3-Cl)([mu]3-Sn(C3H5O3))] (3). The crystallographic studies of these clusters allow a detailed structural comparison. In addition, cyclic voltammetric data were obtained for complexes 1, 2, and 3 and their electrochemical properties are compared. Complex 1 and 3 exhibit reversible oxidation and reduction events. Complex 2 displays a reversible oxidation and a pseudo-reversible reduction. Chapter 5. The focus of this chapter is to briefly describe project ideas based on main group coordinated polynuclear clusters that future researchers may find worthwhile.

Download or read book Nickel Superoxide Dismutase written by and published by . This book was released on 2015 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt: Crystal structures of nickel-dependent superoxide dismutases (NiSODs) reveal the presence of a H-bonding network formed between the NH group of the apical imidazole ligand from His1 and the Glu17 carboxylate from a neighboring subunit in the hexameric enzyme. This interaction is supported by another intrasubunit H-bond between Glu17 and Arg47. In this study, four mutant NiSOD proteins were produced to experimentally evaluate the roles of this H-bonding network and compare the results with prior predictions from density functional theory calculations. The X-ray crystal structure of H1A-NiSOD, which lacks the apical ligand entirely, reveals that in the absence of the Glu17-His1 H-bond, the active site is disordered. Characterization of this variant using X-ray absorption spectroscopy (XAS) shows that Ni(II) is bound in the expected N2S2 planar coordination site. Despite these structural perturbations, the H1A-NiSOD variant retains 4% of wild-type (WT) NiSOD activity. Three other mutations were designed to preserve the apical imidazole ligand but perturb the H-bonding network: R47A-NiSOD, which lacks the intramolecular H-bonding interaction; E17R/R47A-NiSOD, which retains the intramolecular H-bond but lacks the intermolecular Glu17-His1 H-bond; and E17A/R47ANiSOD, which lacks both H-bonding interactions. These variants were characterized by a combination of techniques, including XAS to probe the nickel site structure, kinetic studies employing pulse-radiolytic production of superoxide, and electron paramagnetic resonance to assess the Ni redox activity. The results indicate that in addition to the roles in redox tuning suggested on the basis of previous computational studies, the Glu17-His1 H-bond plays an important structural role in the proper folding of the "Ni-hook" motif that is a critical feature of the active site.

Download or read book Development of Nickel II Complexes of Oxime Containing Ligands for the Activation of Dioxygen written by Michael Joseph Goldcamp and published by . This book was released on 2002 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Ligands containing two oxime donor groups with a variable third group in a tripodal amine motif have been designed and synthesized. Their Ni(II) complexes, and some Zn(II), Cu(II), and Fe(III) complexes, have been structurally and spectroscopically characterized. Deprotonation of the oxime groups gives Ni(II)--Polyoximate complexes that form bis(N-O) oximate bridged dimers with significantly low oxidation potentials for Ni(II). These Ni(II)-polyoximate complexes react with dioxygen, consuming multiple equivalents. This is unusual chemistry for Ni(II), especially in the absence of ligand oxidation. The Ni(II) / O 2 reaction system promotes oxidation of triphenyl phosphine, with oxygen atom transfer, benzyl alcohol, and 3,5-di-tert-butylcatechol. Reaction of the Ni(II)-polyoximate complexes with o-quinones causes the formation of high-valent nickel complexes of the reduced dioxolenes, semiquinones and catecholates.

Download or read book Invesitgation of Nickel II oximate Complexes that React with Molecular Oxygen written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Ni(II) complexes containing amidates and thiolates have been shown to react with O2 via irreversible ligand oxidation. We have constructed a series of Ni(II) complexes based on a tripodal amine bis(oxime) ligand framework. These complexes display oxygen reactivity upon deprotonation of the oximes without requiring irreversible ligand oxidation. This project investigated the reaction involving one of the complexes in the library, [Ni(TRISOXH3)(NO3)(H2O)](NO3)ʺ (H2O), where TRISOXH3 = (tris(1-propan-2-onyl oxime)amine). It was discovered that the reaction of this complex with molecular oxygen is contingent upon the presence of a source of hydrogen atoms. This two-hydrogen atom donor acts as a substrate. Several primary alcohols, including the relatively inert methanol, and amines were catalytically oxidized by this reaction. Spectroscopic analysis using a variety of techniques has demonstrated that reversible oxidation occurs on the oximate nitrogen to form an iminoxyl radical. Many of the other complexes in the series were also investigated to examine their electronic structure, their electrochemical properties, and their ability to oxidize methanol.

Download or read book Active Oxygen in Biochemistry written by Valentine Angelou and published by Springer Science & Business Media. This book was released on 2013-03-09 with total page 480 pages. Available in PDF, EPUB and Kindle. Book excerpt: The field of "Oxygen Activation" has attracted considerable interest recently, not only because it presents challenges in those fields of basic research that aim to understand the fundamental aspects of chemical and biological reactions that involve dioxygen, but also because of its wide range of practical implications in such diverse fields as medicine, synthesis of pharmaceuticals and other organic compounds, materials science, and atmospheric science. This is the second of two volumes that focus on the subject of oxygen activation, the first slanted toward chemistry and the second toward biological chemistry. We planned these volumes to be more general than many monographs of this sort, not as detailed summaries of the authors' own research but rather as general overviews of the field. Our choice of topics was strongly influenced by our syllabus for a course entitled "Oxygen Chemistry," which two of us have twice taught jointly at UCLA. Definition of important issues, horizons, and future prospects was an important goal, and, although totally comprehensive coverage was not possible, we believe that we have chosen a representative selection of research topics current to the field. We have targeted this work to a diverse audience ranging from professionals in fields from physics to medicine to beginning graduate students who are interested in rapidly acquiring the basics of this field.

Download or read book Nickel and Its Surprising Impact in Nature written by Astrid Sigel and published by John Wiley & Sons. This book was released on 2007-03-13 with total page 728 pages. Available in PDF, EPUB and Kindle. Book excerpt: Helmut Sigel, Astrid Sigel and Roland K.O. Sigel, in close cooperation with John Wiley & Sons, launch a new Series “Metal Ions in Life Sciences”. The philosophy of the Series is based on the one successfully applied to a previous series published by another publisher, but the move from “biological systems” to “life sciences” will open the aims and scope and allow for the publication of books touching on the interface between chemistry, biology, pharmacology, biochemistry and medicine. Volume 2 focuses on the vibrant research area concerning nickel as well as its complexes and their role in Nature. With more than 2,800 references and over 130 illustrations, it is an essential resource for scientists working in the wide range from inorganic biochemistry all the way through to medicine. In 17 stimulating chapters, written by 47 internationally recognized experts, Nickel and Its Surprising Impact in Nature highlights critically the biogeochemistry of nickel, its role in the environment, in plants and cyanobacteria, as well as for the gastric pathogen Helicobacter pylori, for gene expression and carcinogenensis. In addition, it covers the complex-forming properties of nickel with amino acids, peptides, phosphates, nucleotides, and nucleic acids. The volume also provides sophisticated insights in the recent progress made in understanding the role of nickel in enzymes such as ureases, hydrogenases, superoxide dismutases, acireductone dioxygenases, acetyl-coenzyme A synthases, carbon monoxide dehydrogenases, methyl-coenzyme M reductases...and it reveals the chaperones of nickel metabolism.