Central Cobalt Atom Research Articles

Characterization of the PduS Cobalamin Reductase of Salmonella enterica and Its Role in the Pdu Microcompartment

Salmonella enterica degrades 1,2-propanediol (1,2-PD) in a coenzyme B12 (adenosylcobalamin, AdoCbl)-dependent fashion. Salmonella obtains AdoCbl by assimilation of complex precursors, such as vitamin B12 and hydroxocobalamin. Assimilation of these compounds requires reduction of their central cobalt atom from Co3+ to Co2+ to Co+, followed by adenosylation to AdoCbl. In this work, the His6-tagged PduS cobalamin reductase from S. enterica was produced at high levels in Escherichia coli, purified, and characterized. The anaerobically purified enzyme reduced cob(III)alamin to cob(II)alamin at a rate of 42.3±3.2 μmol min(-1) mg(-1), and it reduced cob(II)alamin to cob(I)alamin at a rate of 54.5±4.2 nmol min(-1) mg(-1) protein. The apparent Km values of PduS-His6 were 10.1±0.7 μM for NADH and 67.5±8.2 μM for hydroxocobalamin in cob(III)alamin reduction. The apparent Km values for cob(II)alamin reduction were 27.5±2.4 μM with NADH as the substrate and 72.4±9.5 μM with cob(II)alamin as the substrate. High-performance liquid chromatography (HPLC) and mass spectrometry (MS) indicated that each monomer of PduS contained one molecule of noncovalently bound flavin mononucleotide (FMN). Genetic studies showed that a pduS deletion decreased the growth rate of Salmonella on 1,2-PD, supporting a role in cobalamin reduction in vivo. Further studies demonstrated that the PduS protein is a component of the Pdu microcompartments (MCPs) used for 1,2-PD degradation and that it interacts with the PduO adenosyltransferase, which catalyzes the terminal step of AdoCbl synthesis. These studies further characterize PduS, an unusual MCP-associated cobalamin reductase, and, in conjunction with prior results, indicate that the Pdu MCP encapsulates a complete cobalamin assimilation system.

Synthesis and Electrochemistry of Schiff Base Cobalt(III) Complexes and Their Catalytic Activity for Copolymerization of Epoxide and Carbon Dioxide

A series of cobalt complexes with N,N,O,O-tetradentate Schiff base ligands were prepared. All the complexes were characterized by spectroscopy and electrochemical methods. An X-ray crystal structure analysis revealed that L1-CoIII-dnp was monomeric with a six-coordinated central cobalt(III) atom in the solid state. The complexes were employed as catalysts for the alternating copolymerization of CO2 and racemic propylene oxide. End group analysis of the resulting polymer provided strong evidence for a monomer insertion mechanism for the propagation step. The catalytic activity was interpreted using the redox potential of cobalt(II/III) for the L-CoIII-dnp complexes, which offered a measure of the bond strength, or the degree of inertness of the axial ligand, to promote or suppress the monomer insertion.

Synthesis and Characterization of New M‐Triazole Complexes (M = Co, Cu, Zn)

AbstractThree new complexes with the ligand 3,5‐diamino‐1,2,4‐triazole (Hdatrz), [Co3(μ2‐Hdatrz)6(H2O)6]·(NO3)8·4H2O (1), [Cu3(μ2‐Hdatrz)4(μ2‐Cl)2(H2O)2Cl2]·Cl2·4H2O·2C2H5OH (2) and {[Zn2(μ2‐SO4) (μ3‐datrz)2]·2H2O}n (3) have been synthesized and structurally characterized. Complex 1 has a linear trinuclear mixed‐valence cobalt structure with six neutral triazole ligands in the N(1), N(2)‐bridging mode. The central cobalt atom, Co(1), is coordinated to six nitrogen atoms (octahedral) whereas the terminal cobalt atom, Co(2), is coordinated to an N3O3 moiety (octahedral). In complex 1, the uudd cyclic water clusters, nitrate anions and the trimeric cations are linked to a supramolecular structure. Complex 2 features a linear trinuclear copper(II) core, with four N(1), N(2)‐bridging triazole ligands and two chlorido bridges. The central copper atom is coordinated to an N4Cl2 moiety (octahedral) whereas the terminal copper is coordinated to an N2Cl2O moiety (square‐pyramidal). In complex 2, tetrahedral hydrogen bonding interactions play an important role to form a supramolecular network. Complex 3 exhibits a polymeric structure, with N(1), N(2), N(4)‐bridging triazolate ligands and sulfate bridges, in which zinc is coordinated to an N3O moiety (tetrahedral). In complex 3, water molecules and sulfate anions construct the sulfate‐water supramolecular chain with hydrogen bonding interactions. In addition, the complexes were investigated by elemental analyses, IR spectroscopic, and thermogravimetric measurements.

Capillary electrophoresis of boron cluster compounds in aqueous and nonaqueous solvents

The electrophoretic properties of boron cluster compounds were determined in water, methanol and ACN as solvents of the BGE and discussed based on the principles of ion migration. Two types of boron cluster compounds were investigated. One type consisted of derivatives of the nido-7,8-dicarbaundecaborate cluster, the other types are derivatized cobalt bis(dicarbollide) ions (COSANs) whose central cobalt atom is sandwiched by two 7,8-dicarbaundecaborate clusters. The BGE in all solvents was acetate/acetic acid buffer with pH 4.75 in water, 9.7 in methanol and 22.3 in ACN, respectively, at different ionic strength between 5 and 30 mM. The dependence of the mobility on ionic strength could not be explained by the theory of Debye, Hückel and Onsager, but good agreement was found upon considering an ion size parameter. Limiting mobilities were derived by curve fitting, and by the aid of the solvent viscosities the hydrodynamic radii of the analyte anions were calculated. They are between 0.25 and 0.48 nm, and were nearly independent of the solvent. Electrophoresis of the analytes in a BGE consisting of 6 mM perchloric acid in ACN allows the conclusion that the present boron cluster compounds behave as stronger acids than perchloric acid.

Synthesis and Crystal Structure of a Mixed-Ligand Cobalt(II) Complex with 2-Aminobenzimidazole

The cobalt(II) complex, [Co(abz)2(SCN)2] 1, has been synthesized by the reaction of cobalt(II) nitrate with ammonium thiocyanate and abz ligands (abz = 2-aminobenzimidazole), and was fully structurally characterized by elemental analysis, IR spectra, X-ray diffraction and thermogravimetric experiments. It crystallizes in the triclinic P-1 space group with a = 8.6316(10), b = 9.3426(10), c = 13.254(2) A, α = 95.793(2), β = 95.870(2), γ = 115.7380(10), V = 945.1(2) A3, and Z = 2. The central cobalt(II) atom is four-coordinated to nitrogen donors from two neutral abz ligands and two isothiocyanate anions respectively, adopting a slightly distorted tetrahedral geometry. In addition, the intermolecular N–H···N and N–H···S hydrogen bonds interactions link the discrete mononuclear units into infinite three-dimensional networks. The essence sentence of the paper: In the mixed-ligand mononuclear complex, [Co(abz)2(SCN)2], the four coordinated cobalt(II) atom exhibits a slightly distort tetrahedron, which is further assembled into 3D infinite network by intermolecular hydrogen interactions.

The PduX Enzyme of Salmonella enterica Is an l-Threonine Kinase Used for Coenzyme B12 Synthesis

Here, the PduX enzyme of Salmonella enterica is shown to be an L-threonine kinase used for the de novo synthesis of coenzyme B(12) and the assimilation of cobyric acid (Cby). PduX with a C-terminal His tag (PduX-His(6)) was produced at high levels in Escherichia coli, purified by nickel affinity chromatography, and partially characterized. (31)P NMR spectroscopy established that purified PduX-His(6) catalyzed the conversion of l-threonine and ATP to L-threonine-O-3-phosphate and ADP. Enzyme assays showed that ATP was the preferred substrate compared with GTP, CTP, or UTP. PduX displayed Michaelis-Menten kinetics with respect to both ATP and l-threonine and nonlinear regression was used to determine the following kinetic constants: V(max) = 62.1 +/- 3.6 nmol min(-1) mg of protein(-1); K(m)(, ATP) = 54.7 +/- 5.7 microm and K(m)(,Thr) = 146.1 +/- 8.4 microm. Growth studies showed that pduX mutants were impaired for the synthesis of coenzyme B(12) de novo and from Cby, but not from cobinamide, which was the expected phenotype for an L-threonine kinase mutant. The defect in Cby assimilation was corrected by ectopic expression of pduX or by supplementation of growth medium with L-threonine-O-3-phosphate, providing further support that PduX is an L-threonine kinase. In addition, a bioassay showed that a pduX mutant was impaired for the de novo synthesis of coenzyme B(12) as expected. Collectively, the genetic and biochemical studies presented here show that PduX is an L-threonine kinase used for AdoCbl synthesis. To our knowledge, PduX is the first enzyme shown to phosphorylate free L-threonine and the first L-threonine kinase shown to function in coenzyme B(12) synthesis.

A re-evaluation of the two-step spin crossover in the trinuclear cation [Co3(dipyridylamido)4Cl2]+

Density functional theory is used to explore the electronic states involved in the remarkable two-step spin crossover (S = 0 --> S = 1 --> S = 2) in the cationic extended metal atom chain [Co(3)(dpa)(4)Cl(2)](+) (dpa = the anion of 2-dipyridylamine) (R. Clérac, F. A. Cotton, K. R. Dunbar, T. Lu, C. A. Murillo and X. Wang, J. Am. Chem. Soc., 2000, 122, 2272). The calculations are consistent with a model in which all three spin states share one common feature-a vacancy in the d(xy) orbital on the central cobalt atom which is stabilised by pi donation from four amide groups. As a result, all three can be considered to contain a Co(2+)-Co(3+)-Co(2+) chain. The singlet and triplet states arise from antiferromagnetic and ferromagnetic coupling, respectively, between the unpaired electron in this d(xy) orbital and another localised entirely on the terminal cobalt centres (the antisymmetric combination of Co d(z(2))). The singlet-triplet transition does not, therefore, populate any additional antibonding orbitals, and as a result the structure is almost invariant around the characteristic temperature of the singlet-triplet transition. In the most stable quintet, in contrast, the symmetry of the Co-Co-Co chain is broken, giving rise to a localised high-spin Co(II) centre (S = 3/2), ferromagnetically coupled to a Co(III)-Co(II) dimer (S = 1/2). The structural changes associated with this transition are apparent in the X-ray data in subtle changes in both Co-N and Co-Cl bond lengths, although their magnitude is damped by the relatively low population (18%) of the quintet even at 300 K.

Synthesis, Crystal Structure and Antitumor Study of a Cobalt(II) Complex of the 2-Acetylpyrazine Thiosemicarbazone

The title complex [Co(C7H8N5S)2]·2H2O has been synthesized and characterized by IR and UV spectral studies. The structure of the compound has been determined by single-crystal X-ray diffraction. The complex consists of discrete monomeric molecules with octahedrally hexacoordinate cobalt(II) ions, where two acetylpyrazine thiosemicarbazones act as NNS tridentate ligands coordinated to the central cobalt atom via the pyrazine nitrogen, azomethine nitrogen and sulfur atoms. Hydrogen bonds link the different components to stabilize the crystal structure. The antitumor activity of the title complex was tested against A549 lung cancer cell line. The complex exhibited lower antitumor activity, as compared to the free ligand.

Preparation and biodistribution of 32P‐labelled hydroxocobalamin and comparison with 57Co‐labelled cobinamide and cyanocobalamin

AbstractTo study whether in biodistribution studies the phosphorus‐containing side‐chain of cobalamin and the central cobalt atom behave differently, 32P‐ and 57Co‐labelled hydroxocobalamins were biosynthesized. A considerably higher specific activity of the 32P‐labelled compound was achieved than before. Both labelled hydroxocobalamins were administered in physiological quantities subcutaneously and orally to rats. The distributions of the two isotopes did not differ significantly. To explain previously observed slight deviations from this pattern, radiolabelled dicyano cobinamide and cyanocobalamin were prepared and studied in an analogous manner. Generally they behaved as hydroxocobalamin, but with greater accumulation in the liver, possibly reflecting the cyanide‐detoxifying function of this organ. Copyright © 2008 John Wiley & Sons, Ltd.

Coordination Chemistry of Acrylamide. 6 Synthesis and Coordination Compounds of N‐Pyrazolylpropanamide – a Versatile Acrylamide‐derived Ligand

AbstractThe syntheses, spectroscopy and single crystal X‐ray structures of the multifunctional acrylamide‐derived ligand N‐pyrazolylpropanamide (= L) (1), and its complexes [L2CuCl2] (2) and [L4Co3Cl6] (3) with copper(II) and cobalt(II) chlorides, respectively, are described. The ligand 1 is easily obtained in one step by the reaction of pyrazole with acrylamide in a 1:1 molar ratio in the presence of trimethylbenzylammonium hydroxide as a basic catalyst. The reaction of CuCl2·2H2O with 1 in a 1:2 metal salt:ligand molar ratio in ethanol/‐triethylorthoformate solution gave coordination compound 2. The crystal structure of 2 contains two seven‐membered chelate rings formed by two nitrogen atoms of the pyrazolyl groups and two weakly coordinated carbonyl oxygen atoms of the substituted amide moieties. Two chloride ions in the axial positions complete a distorted octahedral coordination environment around the CuII atom. The reaction of CoCl2·6H2O with 1 in a 1:2 metal salt:ligand molar ratio afforded the unusual zwitterionic complex 3. The crystal structure of 3 contains a central cobalt atom in an octahedral coordination surrounded by four ligands in which two of them act as chelate ligands and the other two, coordinated via the carbonyl oxygen atoms of the amide moieties to this metal center, act as bridging ligands bonded to two CoCl3− units.

Optical spectra of anionic boron cluster compounds and their utilization for photometric detection

The article presents first collection of UV–vis absorption spectra of purely synthetic boron cluster compounds. Single-cage compounds have at least 11 cluster atoms; cobaltadicarboranes consists of 2 substituted 11-vertex bis(dicarbollide) clusters sandwiching the central cobalt atom. Spectrum of any of 18 investigated compounds has absorption maximum between 200 and 210 nm; its molar extinction coefficient is of the order of 10 3–10 4 L/mol cm. Second maximum exists in a spectrum of a single-cage compound if its exo-skeletal substituent absorbs UV-light above 200 nm. Spectra of cobaltadicarbaboranes both bridged and unbridged have pronounced second maxima between 270 and 300 nm. Their molar extinction coefficients range from 10 4 to 10 5 L/mol cm. First light absorption minimum is close to 254 nm in spectra with two and more absorption maxima. Several correlations are derived between structure of investigated compounds and their UV–vis absorption spectra.

Synthesis and characterization of two novel cobalt (II) phosphine complexes: crystal structures of [CoCl 3(Cy 2PCH 2PCy 2H)] and [Co(NO 3) 2(Cy 2PCH 2PCy 2O)]. Cy = cyclohexyl, C 6H 11

The complexes [(Cy 2PCH 2PCy 2H)CoCl 3] ( 1) and [(Cy 2PCH 2PCy 2O)Co(NO 3) 2] ( 2), Cy = cyclohexyl (C 6H 11), have been prepared and characterized by EPR, UV–Vis, microanalysis and X-ray crystallography. The reaction CoCl 2 · 6H 2O and dcpm, dcpm = bis(dicyclohexylphosphino)methane, was found to form the monomeric, four coordinate, thermochromic and paramagnetic complex [(Cy 2PCH 2PCy 2H)CoCl 3] ( 1). Of particular interest is the formation of a zwitterion, or inner salt, in which the dangling phosphine adds a hydrogen atom, giving the phosphorus a +1 formal charge. The molecule adopts a pseudo-tetrahedral geometry around the central cobalt atom to which the cyclohexyl groups bind in an equatorial fashion to the phosphine. The reaction of Co(NO 3) 2 · 6H 2O and dcpm in a toluene/methanol/methylene chloride mixture yields the pseudo-octahedral complex [(Cy 2PCH 2PCy 2O)Co(NO 3) 2] ( 2). The cobalt is in the +2 oxidation state with one of the phosphorus atoms again having a +1 formal charge. The complex adopts a pseudo-octahedral geometry around the central cobalt atom with the cyclohexyl groups binding in an equatorial fashion to the phosphine similar to [(Cy 2PCH 2PCy 2H)CoCl 3].

Fate of nickel and cobalt sulfophthalocyanines under oxidizing conditions: a spectroscopic investigation

Two water-soluble metal sulfophthalocyanines, namely Ni (II) PcS and Co (II) PcS , were structurally characterized by electrospray ionization mass spectrometry (ESI-MS) and UV-vis and NMR spectroscopy. The dominant ion in ESI-MS was a penta-protonated monomeric Ni (II) complex and a tetra-protonated form with the Co (II) ion being oxidized to Co (III), confirming the facile oxidation of the central cobalt atom of the phthalocyanine ring by a soft ionization method as ESI. Experiments at various ESI voltages were also performed to ascertain the target of the oxidation, whether it was the metal or the phthalocyanine unsaturated system. Addition of small amounts of oxidizing agents, like potassium persulfate, resulted in a definite attenuation of the Q band in the UV-vis spectra, while ESI-MS detected a variety of complexes, containing at least one oxygen atom, which rapidly replaced the initial complexes.

Density functional studies of [(alkoxy-carbonyl)methyl]cobalt tricarbonyl triphenylphosphine complexes: an α-ester η 3-coordination

Spectroscopic and structural data of 15 complexes with the general formula of RO(O)CCH 2Co(CO) 3PPh 3 indicate a novel coordination mode of the α-ester group to the central cobalt atom, which was found to be crucial in the formation of configurational chirality of the ester carbon atom. Stereoselective self-assembly, elongated ester carbonyl bond lengths, reduced carbonyl stretching frequencies, and 13C/ 31P NMR coupling constants show an activated α-ester group compared to the uncoordinated ester or to that in a more distal position. Density functional calculations were carried out to describe the nature of this new bonding, termed earlier as ‘autosolvation’.

Impact of vitamin B-12 deficiency during lactation on maternal and infant health.

Vitamin B-12 is a “cobalamin”, a term that describes structures with a corrin ring which has a central cobalt atom, phosphate, a base, and ribose. One of several groups can be attached to the cobalt: cyanide, forming vitamin B-12; 5’deoxyadenosine, forming 5’ deoxyadenosylcobalamin; or a methyl group, forming methylcobalamin. Methylcobalamin is a cofactor for the conversion of homocysteine to methionine, and adenosylcobalamin is required for the conversion of methyl malonyl CoA to succinyl CoA. These cofactor functions explain why in vitamin B-12 deficiency there is elevated methylmalonic acid (MMA) in urine and serum, and plasma homocysteine (Hcy).

Structure and characterization of tris(4-morpholinedithiocarbamato-S,S′)cobalt(·)acetonitrile solvate complex: [Co(S2CNC4H8O)3]·CH3CN

The crystal and molecular structure of the complex [Co(S2CNC4H8O)3]·CH3CN has been determined by X-ray crystallography. The compound crystallizes in the triclinic system, space group P\overline 1 , with lattice parameters a = 10.561(2), b = 11.114(2), c = 13.011(3) A, α = 103.88(3), β = 101.58(3), γ = 114.91(1)°, and Z = 2. X-ray analysis reveals that the cobalt(III) atom is located at the apparent intersection of D3 symmetry. Despite the apparent presence of the rotational axes, all of the atoms in the structure were found to be unique; there are no symmetry-related atoms. The central cobalt atom is octahedrally coordinated by an arrangement of six S atoms. The octahedron is distorted as a result of the forced configuration of the four-membered chelate ring. The average Co–S distance is 2.273 A. The FT-IR spectra clearly show there are acetonitrile molecules in the crystal lattice.

Di-tert-butyl phosphate complexes of cobalt(II) and zinc(II) as precursors for ceramic M(PO3)2 and M2P2O7 materials: synthesis, spectral characterization, structural studies, and role of auxiliary ligands.

Reaction of the metal acetates M(OAc)2xH2O with di-tert-butyl phosphate (dtbp-H) (3) in a 4:6 molar ratio in methanol or tetrahydrofuran followed by slow evaporation of the solvent results in the formation of metal phosphate clusters [M4(mu 4-O)(dtbp)6] (M = Co (4, blue); Zn (5, colorless)) in nearly quantitative yields. The same reaction, when carried out in the presence of a donor auxiliary ligand such as imidazole (imz) and ethylenediamine (en), results in the formation of octahedral complexes [M(dtbp)2(imz)4] (M = Co (6); Ni (7); Zn (8)) and [Co(dtbp)2-(en)2] (9). The tetrameric clusters 4 and 5 could also be converted into mononuclear 6 and 8; respectively, by treating them with a large excess of imidazole. The use of slightly bulkier auxiliary ligand 3,5-dimethylpyrazole (3,5-dmp) in the reaction between cobalt acetate and 3 results in the isolation of mononuclear tetrahedral complex [Co(dtbp)2(3,5-dmp)2] (10) in nearly quantitative yields. Perfectly air- and moisture-stable samples of 4-10 were characterized with the aid of analytical, thermoanalytical, and spectroscopic techniques. The molecular structures of the monomeric pale-pink compound 6, colorless 8, and deep-blue 10 were further established by single-crystal X-ray diffraction studies. Crystal data for 6: C28H52CoN8O8P2, a = 8.525(1) A, b = 9.331(3) A, c = 12.697(2) A, alpha = 86.40(2) degrees, beta = 88.12(3) degrees, gamma = 67.12(2) degrees, triclinic, P1, Z = 1. Crystal data for 8: C28H52N8O8P2Zn, a = 8.488(1) A, b = 9.333(1) A, c = 12.723(2) A, alpha = 86.55(1) degrees, beta = 88.04(1) degrees, gamma = 67.42(1) degrees, triclinic, P1, Z = 1. Crystal data for 10: C26H52CoN4O8P2, a = b = 18.114(1) A, c = 10.862(1) A, tetragonal, P4(1), Z = 4. The Co2+ ion in 6 is octahedrally coordinated by four imidazole nitrogens which occupy the equatorial positions and oxygens of two phosphate anions on the axial coordination sites. The zinc derivative 8 is isostructural to the cobalt derivative 6. The crystal structure of 10 reveals that the central cobalt atom is tetrahedrally coordinated by two phosphate and two 3,5-dmp ligands. In all structurally characterized monomeric compounds (6, 8, and 10), the dtbp ligand acts as a monodentate, terminal ligand with free P=O phosphoryl groups. Thermal studies indicate that heating the samples at 171 (for 4) or 93 degrees C (for 5) leads to the loss of twelve equivalents of isobutene gas yielding carbon-free [M4(mu 4-O)(O2P(OH)2)6], which undergoes further condensation by water elimination to yield a material of the composition Co4O19P6. This sample of 4 when heated above 500 degrees C contains the crystalline metaphosphate Co(PO3)2 along with amorphous pyrophosphate M2P2O7 in a 2:1 ratio. Similar heat treatment on samples 6-8 results in the exclusive formation of the respective metaphosphates Co(PO3)2, Ni(PO3)2, and Zn(PO3)2; the tetrahedral derivative 10 also cleanly converts into Co(PO3)2 on heating above 600 degrees C.

Quenching of singlet oxygen ( 1Δ g) by cobalt complexes with four nitrogen atoms in the equatorial plane

The quenching of singlet oxygen ( 1Δ g) by cobalt(III)- bis-1,2-benzosemiquinone-diiminato complexes (general structure LCo (III)(BQDI) 2ClO 4) has been studied in different solvents by measuring the singlet oxygen phosphorescence decay in time-resolved experiments. The axial ligand (Ph 3As, Ph 3Sb, N-methyl-imidazole, pyrrolidine) has practically no influence on the quenching; however, the chlorinated benzosemiquinone-diiminato complex has a markedly lower quenching rate constant. The solvent effects can be fully explained by the difference in viscosity, which supports the assumption that the quenching is diffusion controlled. The reactive radius of the encounter pair has been estimated to be 0.3 nm, shorter than the radius of the complex itself, which points to the fact that singlet oxygen must approach the central cobalt atom at the (partially) open axial position. The significance of these results regarding the quenching of singlet oxygen by vitamin B 12 derivatives is discussed.

Interaction of Co(CO) x with surface sites of SiO 2: theoretical study

The interaction of Co(CO) 4 and Co(CO) 3 species with silica surface was modeled by a non-local density functional method. The geometries of the cobalt carbonyl complexes interacting with the silica surface via SiCo, SiOCCo and SiOCo bonds were optimised, and the interaction energies were calculated. The results of the adsorbate models and the surface complexes bonded via SiCo bonds were found to be in agreement with previously published theoretical data and with available experimental findings. According to our results, cobalt carbonyl species form strong bonds with silica sites and are plausible surface complexes. Bonding via carbonyl ligand was the weakest type of interaction, while bonding via surface oxygen was the strongest. The interaction energies of charged species were higher than those of the radical species. The bond distances between cobalt and its nearest neighbours decreased when there were fewer carbonyl ligands in the complex. The interaction energies and the bond distances between cobalt and its nearest neighbours correlated with the charge of the central cobalt atom.

Detection of NO

CHEMISTRY Nitrous oxide (NO) is implicated in many metabolic processes, yet current methods for in vivo detection of NO rely on measuring metabolites such as nitrite, nitrate, or NO x species. Franz et al. have now synthesized a transition metal complex which directly detects NO in the range of 100 mM. In the “off” state, four nitrogen ligands are bound to the central cobalt atom, and virtually no fluorescent signal is observed. Both quenching by the cobalt atom and excimer complex formation in the stacked fluorescent ligands may contribute to suppression of fluorescence. Replacing two of the imine nitrogens with NO molecules triggers a fluorescent response because one of the dansyl groups is displaced; this fluorescence may be enhanced by formation of a d10 Co-dinitrosyl species. This sensor does not react with O2 and may lead to a more sensitive and reversible sensor for in vivo NO detection. — JU Angew. Chem. Int . Ed . 39 , 2120 (2000).