Bioremediation of trace cobalt from simulated spent decontamination solutions of nuclear power reactors using E. coli expressing NiCoT genes

Removal of radioactive cobalt at trace levels (≈nM) in the presence of large excess (10⁶-fold) of corrosion product ions of complexed Fe, Cr, and Ni in spent chemical decontamination formulations (simulated effluent) of nuclear reactors is currently done by using synthetic organic ion exchangers. A large volume of solid waste is generated due to the nonspecific nature of ion sorption. Our earlier work using various fungi and bacteria, with the aim of nuclear waste volume reduction, realized up to 30% of Co removal with specific capacities calculated up to 1 μg/g in 6–24 h. In the present study using engineered Escherichia coli expressing NiCoT genes from Rhodopseudomonas palustris CGA009 (RP) and Novosphingobium aromaticivorans F-199 (NA), we report a significant increase in the specific capacity for Co removal (12 μg/g) in 1-h exposure to simulated effluent. About 85% of Co removal was achieved in a two-cycle treatment with the cloned bacteria. Expression of NiCoT genes in the E. coli knockout mutant of NiCoT efflux gene (rcnA) was more efficient as compared to expression in wild-type E. coli MC4100, JM109 and BL21 (DE3) hosts. The viability of the E. coli strains in the formulation as well as at different doses of gamma rays exposure and the effect of gamma dose on their cobalt removal capacity are determined. The potential application scheme of the above process of bioremediation of cobalt from nuclear power reactor chemical decontamination effluents is discussed.     

Theoretical investigations of the experimentally observed selectivity of a cobalt imprinted polymer

A cobalt imprinted polymer synthesised, for reducing the volume of radioactive waste generated during nuclear reactor decontaminations, using vinylbenzyl iminodiacetate (VbIDA) as the functional ligand, has been found to be selective for cobaltous ions over excess ferrous ions. The selectivity of the polymer has been investigated through theoretical calculation of the formation energies of complexes involved by using the ab-initio density functional theory (DFT) code SIESTA (Spanish Initiative for Electronic Simulations with Thousands of Atoms). The formation energies of complexes of Fe²⁺, Co²⁺, Cu²⁺ and Ni²⁺ with the free functional ligands as well as with ligands attached to the crosslinkers have been calculated. The calculations revealed that the ferrous forms an unstable complex with the ligands attached to the crosslinkers. The formation energy calculation results were found to corroborate the experimentally observed selectivity order.     

Hydrothermal syntheses, structural characterizations and magnetic properties of cobalt(II) and manganese(II) coordination polymeric complexes containing pyrazinecarboxylate ligand

Two novel coordination polymeric complexes [Co(pzca)₂(H₂O)]_n (1) and [Mn(pzca)₂]_n (2) (pzca=2-pyrazinecarboxylate) have been synthesized by hydrothermal reaction of M(CH₃COO)₂·4H₂O (M=Co, Mn) and 2-pyrazinecarboxylic acid. The complex 1 displays an infinite zigzag chain structure in which each cobalt(II) center was coordinated by three nitrogen and three oxygen atoms to generate a CoN₃O₃ octahedral geometry. The existence of hydrogen bond leads to the formation of the interpenetrating stacking structure. Complex 2 indicates a two-dimensional layer structure through the linkage of bridging oxygen atom of pzca ligand. Each Mn(II) center exhibits a distorted octahedral coordination environment with four oxygen atoms and two nitrogen atoms. The distances of adjacent Mn(II) atoms are 3.503 and 5.654 Å, respectively. The magnetic property analyses reveal that both complexes show weak antiferromagnetic exchange interactions between the metal centers.     

Mononuclear cobalt(II) carboxylate complexes: Synthesis, molecular structure and selective oxygenation study

Some cobalt carboxylate (both mononuclear as well as binuclear) complexes have been prepared by using hindered hydrotris(3,5-diisopropyl-1-pyrazolyl)borate (Tp^iPr2) as supporting ligand. The reaction of [Tp^iPr2Co(NO₃)] (2) with sodium benzoate resulted in the formation of acetonitrile coordinated complex [Tp^iPr2Co(OBz)(CH₃CN)] (3) whereas the reaction of 2 with sodium fluorobenzoate gave coordinately unsaturated five coordinate complex of the type [Tp^iPr2Co(F-OBz)] (4). The oxidation of compound 4 in the presence of 3,5-diisopropylpyrazole resulted in the formation of a unique compound (5) where only one methine carbon of isopropyl group on pyrazole ring of hydrotris(3,5-diisopropyl-1-pyrazolyl)borate oxidized and coordinated with cobalt center. In compound 5, the binding behavior of fluorobenzoate also changes from bidentate to monodentate and the nonbonded oxygen atom formed intramolecular hydrogen bond with the hydrogen atom of the NH fragment of the coordinated . X-ray crystallography and IR studies confirmed the existence of hydrogen bonding in complex 5. The pyrazolato bridged binuclear cobalt(II) complex (6) was prepared by the reaction of hydrated cobalt(II) nitrate, 3,5-diisopropylpyrazole and sodium nitrobenzoate where, each cobalt is four coordinate. The X-ray structure of 6 showed that the NH fragment of terminally coordinated formed intramolecular hydrogen bonding with nonbonded oxygen atom of monodentately coordinated nitrobenzoate.     

Molecular modeling of cobalt(II) hyaluronate

Structural data for complexes of hyaluronic acid and 3d metals(II) of the fourth group of the periodic table are lacking. A combined QM/MM method was used to solve the structure of the first coordination sphere around the cobalt(II) ion. Some available experimental data were compared with the results obtained via computation and were found to be in good agreement. Our results open the way for using molecular modeling to solve the structure of other metal(II) hyaluronates.     

The interactions of cobalt(II) with mitochondria from rat liver

The interactions of Co²⁺ with mitochondria have been investigated. The results indicate that Co²⁺ inhibits ATP synthesis. Further investigations into ATP synthesis mechanisms indicated that inhibition is due to the opening of a transmembrane pore. The opening of this pore causes the collapse of the high-energy intermediate where, under a pH and a potential gradient, the energy is stored and subsequently utilized to form ATP from ADP.     

One-dimensional helical coordination polymers of cobalt(II) and iron(II) ions with 2,2′-bipyridyl-3,3′-dicarboxylate (BPDC)

One-dimensional (1-D) helical coordination polymers, [M^II(H₂O)₃(BPDC)]_n · nH₂O (M = Co (1), Fe (2)), have been prepared by the self-assembly of cobalt(II) and iron(II) ions, respectively, with 2,2′-bipyridyl-3,3′-dicarboxylic acid (H₂BPDC) in an aqueous solution. X-ray crystal structures of compounds 1 and 2 show that each metal ion displays a distorted octahedral coordination geometry including three water oxygen atoms, one oxygen atom of the carboxylate of a BPDC²⁻ belonging to the adjacent metal ion and two nitrogen atoms from the BPDC²⁻ acting as a chelating ligand. In 1 and 2, one carboxylate oxygen atom of coordinated BPDC²⁻ binds to the neighboring metal ion, which give rise to 1-D helical coordination polymers. The helical chains of 1 and 2 are linked by the hydrogen bonding interactions between the carboxylate oxygen atom of the BPDC²⁻ ion belonging to a chain and the water molecule of the adjacent helical chain, which lead to 2-D networks extending along the ab plane. The supramolecules 1 and 2 show isomorphous structures regardless of the metal ions.     

Competitive adsorption of Cu(II) and Cd(II) ions by chitosan crosslinked with epichlorohydrin-triphosphate

In this study, chitosan (CTS) was crosslinked with both epichlorohydrin (ECH) and triphosphate (TPP), by covalent and ionic crosslinking reactions, respectively. The resulting adsorbent (CTS-ECH-TPP) was characterized by SEM, CHN, EDS, FT-IR and TGA analyses, and tested for metal adsorption. The adsorbent was used in batch experiments to evaluate the adsorption of Cu(II) and Cd(II) ions in single and binary metal solutions. In single metal solutions the maximum adsorption capacities for Cu(II) and Cd(II) ions, obtained by Langmuir model, were 130.72 and 83.75 mg g?1, respectively. Adsorption isotherms for binary solutions showed that the presence of Cu(II) decreased Cd(II) adsorption due to a significant competition effect, that is, the adsorbent was selective towards Cu(II) rather than Cd(II).     

A facile method for preparing biodegradable chitosan derivatives with low grafting degree of poly(lactic acid)

Chemical modification of chitosan by grafting with PLA (CS-g-PLA) was developed via 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) mediated coupling reaction. The introduction of PLA disrupted the crystalline structure of chitosan, improved its solubility and thermal stability. Low degree of PLA substitution showed better degradation efficiency than chitosan and PLA. Weight loss of CS-g-PLA6 and CS-g-PLA4 was 87% and 94%, respectively, in 7 days enzymatic degradation study. CS-g-PLA2 was totally degraded in 1 day. Self-assembly behavior was studied using pyrene fluorescence dye technique and found to be PLA grafting level dependent. CS-g-PLA with low grafting degree showed hydrophilic, self-assembling properties and controllable biodegradability that may widen its applications.     

Imidazole-based nickel(II) and cobalt(II) coordination complexes for potential use as models for histidine containing metalloproteins

It has been established that small molecule model complexes have been useful in studying more complex biological systems of metalloproteins. Because many metalloproteins have active sites that contain multiple histidine residues bound to a metal center, a series of imidazole-containing scorpionate ligands and the associated Co and Ni complexes have been developed to investigate the bonding parameters of histidine containing active sites. The tris(2-imidazolyl) carbinol (2-TIC, 6) and tris[2-(N-methylimidazolyl)] carbinol (2-^MeTIC, 7) complexes of Ni²⁺ and Co²⁺, namely [Co(2-^MeTIC)₂]Cl₂ (8), [Co(2-^MeTIC)₂](NO₃)₂ (9), [Ni(2-^MeTIC)₂]Cl₂ (10), [Ni(2-^MeTIC)₂](NO₃)₂ (11), [Co(2-TIC)₂](NO₃)₂ (12), and [Ni(2-TIC)₂](NO₃)₂ (13), have been prepared from the reaction of the appropriate ligand and appropriate metal salt in polar solvent. These complexes have been characterized by single crystal X-ray diffraction, spectroscopic techniques, and magnetic susceptibility. In each solid-state structure the metal center in the cation coordinates to three N atoms from two ligands and adopts a pseudo-octahedral coordination geometry. The X-ray characterization of tris[2-(N-methylimidazolyl)] carbinol is also reported.     

Kinetics of adsorption of Zn(II) ion on chitosan derivatives

The adsorption of Zn(II) ions from aqueous solution by chitosan derivatives (KCTS and HKCTS) was studied in a batch adsorption system. The adsorption capacities and rates of Zn(II) ions onto chitosan derivatives were evaluated. The adsorption isothermal data could be well interpreted by the Langmuir and Freundlich models. The kinetic experimental data properly correlated with the second-order kinetic model, which indicates that the chemical adsorption is the rate-limiting step. The apparent adsorption activation energy were 25.47 kJ mol⁻ and 5.473 kJ mol⁻, respectively, and the second-order adsorption constant for KCTS and HKCTS were 0.00311 g (mg min)⁻¹ and 0.005 g (mg min)⁻¹, respectively.     

Synthesis and characterisation of copper(II), zinc(II) and cobalt(II) complexes of salicylglycine, a metabolite of aspirin

Copper(II), nickel(II) and cobalt(II) complexes of the aspirin metabolite salicylglycine (H₂L), of stoichiometry M(HL)₂·solvate, have been prepared and characterised. In these complexes salicylglycinate is coordinated to the metal via its carboxylato group and possibly also its amide oxygen in the copper(II) complex. Under basic conditions copper(II) forms the complex Cu(LH₋₁)·2H₂O·MeOH, in which the ligand is coordinated to the metal via its carboxylate and phenolate oxygen atoms and the deprotonated peptide nitrogen atom.     

Cobalt(II) salophen-modified carbon-paste electrode for potentiometric and voltammetric determination of cysteine

A chemically modified electrode constructed by incorporating N,N(')-bis(salicylidene)-1,2-phenylenediaminocobalt(II) into carbon-paste matrix was used as a sensitive electrochemical sensor for detection of cysteine. The resulting electrode exhibits catalytic properties for the electrooxidation of cysteine and lowers the overpotential for the oxidation of this compound. The faster rate of electron transfer results in a near-Nernstian behavior of the modified electrode and makes it a suitable potentiometric and voltammetric sensor for the fast and easy determination of cysteine. A linear response in concentration range from approximately 2 microM to 0.01 M was obtained with a detection limit of 1 microM for the potentiometric detection of cysteine. The modified electrode was also used for the amperometric and differential pulse voltammetric determination of cysteine and the results were compared with those of the potentiometric method.     

Cobalt(II), nickel(II) and zinc(II) do not bind to intra-helical N(7) guanine positions in the B-form crystal structure of d(GGCGCC)

Three novel X-ray crystal structures for the DNA hexamer d(GGCGCC) in the B-form complexed to divalent cobalt, nickel and zinc ions have been determined to a resolution of 2.9–3.0 Å. The structures were isomorphous and had five DNA strands and five metal cations per asymmetric unit. In all three cases, divalent metal cations were coordinated only to the terminal guanine residue at the N(7) position, with no metal ions binding to non-terminal guanine positions. Water molecules bound to the metal cations interacted with neighboring guanine residues 3 to the ones to which the cations were coordinated, affecting the propeller twist. Even though DNA occupied only about 35% of the unit cell volume, it is interesting that the few interactions involving the metal cations were sufficient to stabilize the crystal lattice. As well as lending support to the proposal that these metals do not coordinate to B-DNA in a stable manner, the results presented here also extend the crystallographic evidence for this phenomenon to the GGC and CGC sequences for all three metal cations.Electronic Supplementary Material Supplementary material is available for this article if you access the article at . A link in the frame on the left on that page takes you directly to the supplementary material.Abbreviations MPD 2-methyl-2,4-pentanediol - TAPS N-[tris(hydroxymethyl)methyl]-3-aminopropanesulfonate     

Synthesis, structural aspects and magnetic properties of an unusual 2D thiocyanato-bridged cobalt(II)-Schiff base network

A new two-dimensional (2D) thiocyanato-bridged cobalt(II) network formulated as [LCo₂(NCS)₂]_n (1), has been synthesized with the Schiff base ligand N,N′-bis(3-methoxysalicylidenimino)-1,3-diaminopropane (H₂L) and thiocyanate anions. This novel layered compound has been completely characterized by elemental analysis, FT-IR, UV-Vis spectroscopy and the structure has been established by single crystal X-ray diffraction studies. The structure of 1 consists of a doubly phenoxo-bridged dimer comprising two different cobalt(II) centers with different coordination geometries (octahedral and tetrahedral). The 2D network is accomplished by bridging thiocyanate ligands, connecting the dimeric motifs in an end-to-end fashion. Variable-temperature magnetic susceptibility and EPR measurements reveal predominant antiferromagnetic exchange interaction in the complex.     

Synthesis and structural characterization of a novel seven-coordinate cobalt(II) complex: 2,9-Bis(ethanolamine)-1,10-phenanthrolinechlorocobalt(II) chloride

Condensation reaction of 2,9-dicarboxaldehyde-1,10-phenanthroline with 2-aminoethanol followed by NaBH₄ reduction yielded the polydentate Schiff base ligand 2,9-bis(ethanolamine)-1,10-phenanthroline in its reduced form. This ligand was characterized by elemental analysis, LC-MS, IR, UV-Vis and NMR spectroscopy. Reaction of the reduced Schiff base ligand with aqueous solution of cobalt(II) chloride affords 2,9-bis(ethanolamine)-1,10-phenanthrolinechlorocobalt(II) chloride in high yield. Single crystals of the cobalt(II) complex were obtained from the crystallization in ethanol and its structure was elucidated by X-ray structural analysis. The cobalt(II) complex ion was found to be seven-coordinated in a pentagonal bipyramidal geometry, whereby cobalt(II) ion is surrounded by the six donor atoms in the ligand molecule and a chloride ion.     

Synthesis and characterization of ion‐imprinted resin for selective removal of UO2(II) ions from aqueous medium

In this work, uranyl ion‐imprinted resin based on 2‐(((4‐hydroxyphenyl)amino)methyl)phenol was synthesized by condensation polymerization of its uranyl complex in presence of resorcinol and formaldehyde cross‐linkers. Numerous instrumental techniques including elemental analysis, Fourier transform infrared spectroscopy, ultraviolet, ¹H along with ¹³C nuclear magnetic resonance spectroscopy have been employed for complete characterization of the synthesized ligand and its uranyl complex. Additionally, the obtained ion‐imprinted and non‐imprinted resins were investigated using scanning electron microscope and Fourier transform infrared spectroscopy. The effects of various essential parameters such as pH, temperature and contact time on removal of uranyl ions have been examined, and the results indicated that the obtained resin exhibited the optimum activity at pH 5. Furthermore, the adsorption process was spontaneous at all studied temperatures and followed the second‐order kinetics model. Also, Langmuir adsorption isotherm exhibited the best fit with the experimental results with maximum adsorption capacity 139.3 mg/g. Moreover, the selectivity studies revealed that the ion‐imprinted resin exhibited an obvious affinity toward the uranyl ions in presence of other metal ions compared with the non‐imprinted resin. Copyright © 2015 John Wiley & Sons, Ltd.     

Chitosan gel beads immobilized Cu (II) for selective adsorption of amino acids

Chitosan (CS) gel beads were prepared by using phase inversion and precipitation technique. The gel beads could bind copper (II), by which Cu (II) ion-immobilized chitosan gel beads (CS-Cu²⁺ gel beads) were prepared, and the amount of the immobilized Cu (II) was about 35 mg/g when the CS gel beads were incubated in 150 ppm cupric sulfate solution. The CS-Cu²⁺ gel beads could selectively adsorb histidine (His) from the mixed solution containing His and tryptophan (Trp); and the selective coefficient which was defined as the adsorbed amount ratio of His to Trp was about 8.0 at the pH value of 7.4. The effect of the pH value on the amino acid adsorption was also studied. In order to investigate the relationship of the amino acid adsorption and protein adsorption, the adsorbed amounts for IgG and albumin were determined; and the results indicated that the CS-Cu²⁺ gel beads could adsorb a larger amount of IgG than albumin due to the larger amount of the exposed residual His. The study provided a sorbent and a method to selectively remove His and IgG.     

Structural and spectroscopic comparison of five-coordinate cobalt(II) and nickel(II) thiolato complexes with the related four-coordinate complexes

Five-coordinate thiolato complexes, [L1M(SMeIm)] (M = Co and Ni) (L1 = hydrotris(3,5-diisopropyl-1-pyrazolyl)borate anion and HSMeIm = 2-mercapto-1-methylimidazole), were synthesized. These complexes were compared with the corresponding Cu(II) and Zn(II) complexes with the same ligands and were also compared with the related four-coordinate complexes [L1M(SC₆F₅)] (HSC₆F₅ = pentafluorobenzenthiol). All the complexes were characterized by X-ray crystallography and UV-Vis absorption, IR, ¹H NMR, and other spectroscopic techniques. All five-coordinate thiolato complexes, [L1M(SMeIm)] (M = Co, Ni, and Cu), form a distorted square pyramidal structure with a high spin state, and only [L1Zn(SMeIm)] takes a four-coordinate structure with a distorted tetrahedral configuration. The N21-M-S bond angles of the obtained five-coordinate complexes were proportional to the corresponding d value, which comes from between the equatorial basal plane with N4S ligand donor sets and metal ion. These observations and M-S bond distances affect on UV-Vis and far-IR spectral behavior.     

Five-coordinate cobalt(II) complexes of tris(2-pyridylmethyl)amine (TPA): Synthesis, structural and magnetic characterization of a terephthalato-bridged dinuclear cobalt(II) complex

The cobalt(II) complexes [Co(TPA)Cl]ClO₄ (1), [Co(TPA)Br]ClO₄ (2), [Co(TPA)(H₂O)]Cl(ClO₄) (3) and [Co₂(TPA)₂(μ-tp)](ClO₄)₂ · 2H₂O (4) (TPA = tris(2-methylpyridyl)amine and tp = terephthalate dianion) were synthesized and structurally characterized by UV-vis and IR spectroscopy. The molecular structures of complexes 1 and 4 were determined by X-ray crystallography and their magnetic properties were measured over the temperature range 2-300 K. The coordination geometry around the central Co(II) in these compounds has a distorted trigonal bipyamidal geometry with four nitrogen atoms from the TPA ligand and the fifth coordination site is occupied by Cl⁻ ion in 1, Br⁻ ion in 2, coordinated oxygen atom from H₂O in 3 and by an oxygen atom supplied by the carboxylate group of the bridged terephthalato ligand in 4. The visible spectra of the complexes 1-3 in MeOH show strong distortion toward tetrahedral geometry. For complex 4, analysis of the infrared spectral data for the ν(COO⁻) stretching frequencies of the tp-carboxalato groups reveals the existence of the bis(monodentate) coordination mode for the bridged tp. X-ray data for 1 and 4 show that the former is mononuclear while the latter is dinuclear. The electronic spectrum of 4 in MeOH is in complete agreement with the assigned X-ray geometry around the Co(II) centers. The magnetic behavior of the mononuclear complex 1 is indicative of a high-spin compound with zero-field splitting. The best fit was obtained with ∣D∣ = 7.3 cm⁻¹, g = 2.25. The dinuclear complex 4 exhibits weak antiferromagnetic coupling with a coupling constant J = −0.8 cm⁻¹. The magnetic properties and the structural parameters of 4 are discussed in relation to the other related μ-terephthalato dinuclear Co(II) compounds. The geometry of the coordination sphere around 4 is unique - the CSD compilation listing only one other compound with such a geometry around the dinuclear Co(II) complex and its composition is far different from that in 4. However, they share a common feature of having a weakly antiferromagnetic coupling between Co(II) centers.