I.e., Ni Research Articles

Electrochemically Modulated Separation of Olefin-Paraffin Gas Mixtures in Membrane Electrode Assemblies

Olefin-Paraffin separations are ubiquitous chemical processes used in purifying monomers for the manufacture of a large variety of polymers and chemical intermediates. Some of the highly demanded olefin-made products include polyethylene, ethylene oxide, vinyl acetate, polypropylene, acrylonitrile, propylene oxide, and acrylic acid. Olefin-paraffin mixtures are relatively difficult to separate because of the similarity in physical properties of each component. Currently, olefins are typically purified via cryogenic distillations, a highly energy-intensive process that liquifies the hydrocarbon gas mixture and re-vaporizes them repeatedly, requiring approximately 3.6 MJ per kg of olefin purified. Because of the large energy-intensive of the process, olefin separations are responsible for approximately 0.3% of the global energy consumption, to produce 200 and 130 million metric tons per year of ethylene and propylene respectively (2020).Alternative non-thermal olefin-paraffin separation methods have the potential to increase the efficiency of this separation, and thus increase its sustainability. In this presentation we will discuss an alternative separation method based on an electrochemically modulated swing absorption system. In this system, Nickel(II) maleonitriledithiolate, an electrochemically active organometallic complex, is dispersed in an ionogel and integrated in a membrane electrode assembly (MEA). The oxidation state of Nickel(II) maleonitriledithiolate can be electrochemically modulated based on potential. At its oxidized state [i.e., Ni (IV)], the complex has a strong affinity towards the olefin’s pi-bond, while at its reduced state [i.e., Ni (II)] the complex loses this affinity. Our results show that when exposed to propylene-propane gas mixtures, propylene was selectively captured by the organometallic species during oxidative phase, and then released or decoupled during reductive phase. Its paraffin counterpart, propane, behaved as spectator molecules throughout the whole process, demonstrating consistent olefin separation through this selective capture-and-release mechanism. I will discuss how varying the composition of the MEA exposed potential mass transport limitations that play an important role in the separation efficiency and throughput. Experiments conducted under varying potentials exhibited operational robustness of the MEA in gas separations if electric potentials are carefully tuned between 1-3V in the oxidative cycle, and at approximately -2V in the reductive cycle. This proof-of-concept demonstration represents an important step towards achieving high-performing electrochemically-modulated olefin-paraffin separations that can integrate renewable electricity sources directly and help decarbonize the chemical manufacturing industry. Figure 1

Molecular Engineering of Quinone-Based Nickel Complexes and Polymers for All-Organic Li-Ion Batteries.

All-organic Li-ion batteries appear to be a sustainable and safer alternative to the currently-used Li-ion batteries but their application is still limited due to the lack of organic compounds with high redox potentials toward Li+/Li0. Herein, we report a computational design of nickel complexes and coordination polymers that have redox potentials spanning the full voltage range: from the highest, 4.7 V, to the lowest, 0.4 V. The complexes and polymers are modeled by binding low- and high-oxidized Ni ions (i.e., Ni(II) and Ni(IV)) to redox-active para-benzoquinone molecules substituted with carboxyl- and cyano-groups. It is found that both the nickel ions and the quinone-derived ligands are redox-active upon lithiation. The type of Ni coordination also has a bearing on the redox potentials. By combining the complex of Ni(IV) with 2-carboxylato-5-cyano-1,4-benzoquinones as a cathode and Ni(II)-2,5-dicarboxylato-3,6-dicyano-1,4-benzoquinone coordination polymer as an anode, all-organic Li-ion batteries could be assembled, operating at an average voltage exceeding 3.0 V and delivering a capacity of more than 300 mAh/g.

Metal ion-promoted fabrication of melanin-like poly(L-DOPA) nanoparticles for photothermal actuation

Melanin-inspired polymers are currently the focus of growing interest for a wide range of applications ranging from energy to biomedical area. Whilst researchers have made numerous attempts to prepare and utilize polydopamine nanoparticles (PDA NPs), they have made limited progress in developing and discovering another typical functional mimic of natural melanin, poly (levodopa) (P(L-DOPA)) NPs, probably due to the lack of facile synthetic strategies towards satisfactory structural and functional control of melanin-like NPs. Herein, we reported a one-pot preparation method towards P(L-DOPA) NPs with good yields and controllable size/property in an aqueous solution assisted by various metal ions (i.e., Ni(II), Mg(II), Ca(II), Fe(III), Mn(II), Co (II), Zn(II) and Cd(II)). Interestingly, the resulting P(L-DOPA) NPs exhibited enhanced light absorption and photothermal behaviors compared with well-established PDA NPs, which can be employed to further fabricate kinds of photothermal composite actuators with promising performances such as folding, switching, and forward-moving. This study offers a facile and robust way to synthesize new synthetic melanins beyond PDA, and facilitates further functional discovery and evolution of melanin-inspired polymers and composites.

Synthesis, Structural, Spectral and Intriguing Electrochemical Redox Properties of π-Extended Chlorins and Porphyrins

Meso-tetraarylporphyrins are widely explored due to their facile synthesis, characteristic deep colors, intense fluorescence, and high photochemical stability. Moreover, porphyrinoids have ability to chelate a wide variety of metal ions in their inner core.1 The electronic properties of porphyrins can be easily modulated by appending different substituents at β-and/or meso-positions. The substituents at β-positions of the porphyrins exert much larger steric and electronic effects on the porphyrin π-system than substituents at the meso-aryl positions.2 The optical properties of porphyrin π-system can be tuned by the modification of macrocyclic core through extended π-conjugation3a or by converting into chlorins3b or by tuning the conformation of the macrocycle.3c Chart 1. Molecular structures synthesized monofused porphyrins and difused chlorins/porphyrins. Herein, we report the facile regioselective synthesis of monofused porphyrin and difufused chlorins/porphyrins (Chart 1) in good to excellent yields. Single crystal X-ray diffraction analysis revealed the quasi planar to moderate nonplanar conformation of difused chlorins due to trans-orientation of β-substituents (Figure 1), whereas difused porphyrin exhibited higher mean plane deviation from 24-atom core (Δ24) as compared to chlorins.4 Figure 1. ORTEP diagrams showing top and side views of NiDFP(IND)2 (a and c) and trans-NiDFC(MN)2 (b and d), respectively. Difused porphyrins exhibited large red-shift (Δλmax = 40-55 nm) in their Soret band as compared to their precursors, i.e. Ni(II) chlorins whereas difused chlorins showed marginal red-shift (Δλmax = 16-22 nm) as compared to the corresponding precursors, i.e. free base trans-chlorins. The significant red-shift in the Soret band was attributed to the twisted macrocyclic core as shown in the ORTEP side views (Figures 1c and 1d). Figure 2. Comparative electronic absorption spectra of trans-Ni(II)chlorin, NiTPC[CH(CN)2]2 and the corresponding difused porphyrin, NiDFP. These fused porphyrinoids have shown interesting electrochemical redox properties. Notably, antipodal-NiDFP(IND)2(Ph)2 exhibited three oxidations, whereas H2DFC(IND)2X2 and NiDFP(IND)2X2 (X = Br, Ph) have shown three reversible reductions. These multiple oxidations and reductions aroused due to combined ‘push-pull’ effect of β-substituents and fusion induced twisted macrocyclic core. The first oxidation and reduction potentials of H2DFC(IND)2 were cathodically shifted (130 mV and 240 mV) as compared to their precursors, i.e H2TPC(IND)2 due to extended π-conjugation. In this presentation, the synthesis, spectral, intriguing redox properties will be discussed in detail. Figure 3. Comparative cyclic voltammograms of (a) NiDFPs (b) H2DFCs. References The Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds.; Academic Press: San Diego, 2000−2003; Vol. 1−20.(a) Medforth, C. J.; Senge, M. O.; Smith, K. M.; Sparks, L. D.; Shelnut, J. A. Am. Chem. Soc. 1992, 114, 9859−9869. (b) Retsek, J. L.; Medforth, C. J.; Nurco, D. J.; Gentemann, S.; Chirvony, V. S.; Smith, K. M.; Holten, D. J. Phys. Chem. B 2001, 105, 6396−6411.(a) Akhigbe, J.; Luciano, M.; Zeller, M.; Brückner, C. Org. Chem. 2015, 80, 499−511. (b) Brückner, C.; Samankumara, L.; Ogikubo, J. In Handbook of Porphyrin Science; Kadish, K. M., Smith, K. M., Guilard, R., Eds.; World Scientific: River Edge, NY, 2012; Vol. 17, pp 1−112. (c) Kojima, T.; Nakanishi, T.; Harada, R.; Ohkubo, K.; Yamauchi, S.; Fukuzumi, S. Chem. Eur. J. 2007, 13, 8714−8725.(a) Chaudhri, N.; Grover, N.; Sankar, M.; Chem. 2017, 56, 11532–11545. (b) Chaudhri, N.; Grover, N.; Sankar, M.; (Submitted for Publication). MS sincerely thanks DST, India and Indo-US Science and Technology Forum (IUSSTF), New Delhi for financial support. Figure 1

Unusual temperature effect on the stability of nickel anodes in molten carbonates

The stability of nickel anode in a eutectic molten Li2CO3-Na2CO3-K2CO3 electrolysis cell was systematically investigated over the temperature range of 450°C to 750°C. An unusual temperature effect was observed involving a critical activation-passivation transition temperature at 575°C for the nickel in the melt; rapid dissolution of nickel was found to occur below 575°C under anodic polarization, whereas its surface became passivated above this temperature, and the stability of the passivation film was further improved by increasing the temperature up to 750°C. A blackish oxide film forms on nickel surfaces that retard the anodic dissolution of nickel. The composition and structure of the oxide film, as well as its formation mechanism, were studied by electrochemical measurements combined with X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) characterization. Two temperature sensitive oxidation states of nickel (i.e., Ni(II) and Ni(III)) formed during the anodic polarization. Ni(III) tended to combine with Li2CO3 to form the more soluble LiNiO2 during anodic polarization at lower temperature, and its content in the film decreased dramatically with increasing temperature. Thus, a stable and protective film consisting of NiO can form at temperatures above 575°C.

Nickel adsorption onto polyurethane ethylene and vinyl acetate sorbents.

The present study was conducted to appraise the efficiencies of polyurethane ethylene sorbent (PES) and vinyl acetate sorbent (VAS) for nickel (Ni) adsorption. Process variables, i.e. Ni(II) ions initial concentration, pH, contact time and adsorbent dosage were optimized by response surface methodology (RSM) approach. The Ni(II) adsorption was fitted to the kinetic models (pseudo-first-order and pseudo-second-order) and adsorption isotherms (Freundlich and Langmuir). At optimum conditions of process variables, 171.99 mg/g (64.7%) and 388.08 mg/g (92.7%) Ni(II) was adsorbed onto PES and VAS, respectively. The RSM analysis revealed that maximum Ni(II) adsorption can be achieved at 299 mg/L Ni(II) ions initial concentration, 4.5 pH, 934 min contact time and 1.3 g adsorbent dosage levels for PES, whereas the optimum values for VAS were found to be 402 mg/L Ni(II) ions initial concentration, 4.6 pH, 881 min contact time and 1.2 g adsorbent dosage, respectively. The -OH and -C = O- were involved in the Ni(II) adsorption onto PES and VAS adsorbents. At optimum levels, up to 53.67% and 80.0% Ni(II) was removed from chemical industry wastewater using PES and VAS, respectively, which suggest that PES and VAS could possibly be used for Ni(II) adsorption from industrial wastewater.

Understanding the Effect of Metal Centers on Charge Transport and Delocalization in Conducting Metallopolymers

A series of conducting polymers, formed from an electropolymerizable Schiff-base ligand, N,N′-((2,2′-dimethyl)propyl)bis(2-thiophenyl)salcylidenimine, and the corresponding metal complexes (i.e., Ni(II), Cu(II), V(IV)═O, Co(II), and Zn(II)) have been prepared, characterized, and studied in detail. Our successful synthesis of the ligand polymer helps to make a direct comparison between the properties of metal-free conducting polymers and the corresponding metallopolymers. This enables the role of metal centers in these Schiff-base conducting metallopolymers (CMPs) in particular, and in Wolf type III CMPs in general, to be unambiguously elucidated. Vis–NIR absorption spectroelectrochemical studies show that longer distances for charge delocalization were found in the CMPs when compared to the metal-free counterpart, an indication of the contribution of the metal centers in extending the effective conjugation length of these electroactive polymers. The systematic use of both redox-active and redox-inactive f...

Electrochemical and spectroelectrochemical behavior of N-methyl-phenothiazinyl meso-substituted porphyrins and their complexes with Ni(II), Cu(II) and Pd(II)

The electrochemical and spectroelectrochemical properties of 11 new N-methyl phenothiazinyl meso-substituted porphyrins, H2PtzxPh4−xPorph (where Ptz stands for N-methyl phenothiazinyl, Ph for phenyl and Porph for porphyrin; x=0, 1, 2 or 4), and their complexes with Ni(II), Cu(II) and Pd(II) were investigated. The half wave potentials of the redox processes yielding the anion, dianion or π-cation and dication radicals were estimated from square-wave voltammetry measurements, performed in CH2Cl2 containing 0.1M TBAPF6 as supporting electrolyte. Two opposite effects decide the electrochemical behavior of the metal complexes corresponding to the Ptz-substituted porphyrins: (i) the electron attracting ability of the Ptz substituent and (ii) the decrease of the electronic affinity of the porphyrin macrocycle induced by the presence of the metallic ion, i.e. Ni(II), Cu(II) or Pd(II). The electrochemical data were rationalized by using the Hammett’s linear free energy relationship. The spectral data, obtained from in situ spectroelectrochemical measurements, confirmed the characteristic behavior of the porphyrin derivatives and were found in good agreement with the electrochemical results.

The influence of Fe(II) competition on the sorption and migration of Ni(II) in MX-80 bentonite

► We model the diffusion of Ni(II) through bentonite using different sorption models. ► We examine sorption competition of Fe(II) and Ni(II) at different concentrations. ► Ni(II) breakthrough is 15 times earlier with Fe(II) sorption competition. ► Ni(II) sorption is non-linear and depends on the Fe(II) concentration levels. ► Sorption competition is important and has to be modelled by reactive transport codes. The results from batch sorption experiments on montmorillonite systems have demonstrated that bivalent transition metals compete with one another for sorption sites. For safety analysis studies of high level radioactive waste repositories with compacted bentonite near fields, the importance of competitive sorption on the migration of radionuclides needs to be evaluated. Under reducing conditions, the bentonite porewater chosen has a Fe(II) concentration of ∼5.3 × 10 −5 M through saturation with siderite. The purpose of this paper is to assess the influence of such high Fe(II) concentrations on the transport of Ni(II) through compacted bentonite, Ni(II) was chosen as an example of a bivalent transition metal. The one-dimensional calculations were carried out at different Ni(II) equilibrium concentrations at the boundary (Ni(II) EQBM ) with the reactive transport code MCOTAC incorporating the two site protolysis non electrostatic surface complexation/cation exchange sorption model, MCOTAC-sorb. At a Ni(II) EQBM level of 10 −7 M without Fe(II) competition, the reactive transport calculations using a constant K d approach and the MCOTAC-sorb calculation yielded the same breakthrough curves. At higher Ni(II) EQBM (10 −5 M), the model calculations with MCOTAC-sorb indicated a breakthrough which was shifted to later times by a factor of ∼5 compared with the use of the constant K d approach. When sorption competition was included in the calculations, the magnitude of the influence depended on the sorption characteristics of the two competing sorbates and their respective concentrations. At background Fe(II) concentrations of 5.3 × 10 −5 M, and a Ni(II) EQBM level of 10 −7 M, the Ni(II) breakthrough time was ∼15 times earlier than in the absence of competition. At such Fe(II) concentrations the Ni(II) breakthrough curves at all source concentrations less than 3.5 × 10 −5 M (fixed by the NiCO 3,S solubility limit) are the same i.e. Ni(II) exhibits linear (low) sorption. Competitive sorption effects can have significant influences on the transport of radionuclides through compacted bentonite i.e. reduce the migration rates. Since, for the case considered here, the Fe(II) concentration in the near field of a high-level radioactive waste repository may change in time and space, the transport of bivalent transition metal radionuclides can only be properly modelled using a multi-species reactive transport code which includes a sorption model.

Selectively facilitated transport of Zn(II) through a novel polymer inclusion membrane containing Cyanex 272 as a carrier reagent

This paper describes the selectively facilitated transport of Zn(II) through a novel polymer inclusion membrane (PIM) containing Cyanex 272 as a carrier reagent. The prepared PIM was characterized by using Fourier Transform Infrared (FT-IR) spectroscopy and Atomic Force Microscopy (AFM) techniques and contact angle measurements. The effects of Zn(II) (in feed phase), HCl (in stripping phase) and Cyanex 272 (in membrane) concentrations on the transport were investigated. When the feed phase contained 1 × 10 − 4 M Zn (II) at pH 3.4, 99% of Zn(II) was transported through the PIM (prepared with 1.0% carrier solution) by using 0.5 M of HCl as a stripping phase. Furthermore, Zn(II) was preferably transported in the presence of various metal ions (i.e., Ni(II), Cu(II), Pb(II) and Co(II), etc.). The results also showed that transport efficiency of the PIM was reproducible and it could be efficiently used in the long-term separation processes.

Relationship between the chemical form of nickel applied to the soil and its uptake and toxicity to barley plants ( Hordeum vulgare L.)

Synthetic chelating agents, such as organic acids and amino acids, are used in remediation of soil contaminated with heavy metals, including Ni. It has not been clearly shown that the complexation of Ni by organics may increase the effectiveness of phytoremediation; the Ni complexation may increase the removable metal concentration, but may decrease its uptake by plants. The objective of this research was to investigate the Ni toxicity and the dynamics of its uptake by the barley plants ( Hordeum vulgare L.) from medium and heavy clay soils contaminated with inorganic Ni (as NiSO 4·7H 2O) and organic Ni(II) complexes, i.e. Ni(II)-citrate, Ni(II)-Glu and Ni(II)-EDTA (molar ratio Me/L was 1:1). In the pot experiment, Ni in these chemical forms was applied to the soils in the concentration of 75 mg Ni·kg −1. With respect to both absorption and phytotoxicity, the examined chemical forms of nickel can be put in the following order: NiSO 4·7H 2O>Ni(II)-citrate>Ni(II)-Glu>Ni(II)-EDTA. The molar ratio of Me/L (i..e. Ni/Ligands) in the plants differed from that in the soil; in the plants, the Ni concentration was higher than ligand concentrations. Thus, molar ratio Me/L was higher than 1:1. The highest concentration of nickel in the dry matter of plants, supplied from all examined forms of this element, was found in the initial growth stages (i.e. in emergence stage), and it declined with the progressing growth. No matter what the chemical form of Ni was supplied, the barley plants absorbed more Ni from the medium soil than from the heavy soil. Despite the fact that the degree of phytotoxicity of the chemical forms of nickel used in the experiment differed, the types of morphological and anatomical damages of plants were similar. Phytotoxicity of the examined chemical forms of Ni corresponded to the concentration of Ni absorbed from these forms by the barley plants.

Changes of chloroplast ultrastructure and total chlorophyll concentration in cabbage leaves caused by excess of organic Ni(II) complexes

Leaf chlorophyll concentration, chloroplast ultrastructure, Ni concentration in leaves and Ni accumulation in chloroplasts were examined in cabbage plants treated with Ni as organic complexes, i.e. Ni(II)–Glu, Ni(II)–citrate and Ni(II)–EDTA, in the concentrations of 40 and 85 μM. The plants were grown on half-strength Hoagland's nutrient solution at pH 5.3 for a period of 21 days. The Ni(II) complexes have different effects on leaf chlorophyll concentration and degree and specificity of ultrastructural changes of chloroplasts. After Ni(II)–Glu and Ni(II)–citrate treatment at both concentrations of Ni, the leaf chlorophyll concentration was reduced. After Ni(II)–EDTA treatment, it was reduced only at the concentration of 85 μM Ni. After Ni(II)–Glu and Ni(II)–citrate treatment, the electron density of chloroplast stroma and the number of grana were reduced. Accumulation of starch was observed only in those chloroplasts that were located close to vascular bundles. After Ni(II)–Glu treatment, the thylakoids were swollen, but after Ni(II)–citrate treatment, the thylakoids were condensed. After Ni(II)–EDTA treatment, an accumulation of starch and an increase of the number of plastoglobuli were observed. Damage of the thylakoids was observed sporadically. The experiment also showed that there is a relationship between the degree of toxicity of the examined Ni complexes and Ni concentration in leaves. As far as toxicity and Ni bioaccumulation is concerned, the Ni complexes can be put in the following order: Ni(II)–Glu≥Ni(II)–citrate≫Ni(II)–EDTA. The tissue localization of Ni by the silver sulphide method showed differences in Ni accumulation in the chloroplasts. After Ni(II)–Glu and Ni(II)–citrate treatment, Ni accumulation in chloroplasts was higher than after Ni(II)–EDTA treatment.

Structural, spectroscopic and electrochemical studies of nickel(II) “sandwich” complexes with ligands featuring tethered 1,4,7-triazacyclononane macrocycles †

A structural and electrochemical study of the nickel(II) complexes, [Ni(tacn)2](ClO4)2 (1), [NiLeth](ClO4)2 (2), [NiLox](ClO4)2·H2O (3), [Ni2Ldur](ClO4)4·2H2O (4), [Ni3Ldur(H2O)3](ClO4)6·9H2O (5) and [Ni2Lisomes(H2O)3](ClO4)4·7H2O (6) [tacn = 1,4,7-triazacyclononane, Leth = 1,2-bis(1,4,7-triazacyclonon-1-yl)ethane, Lox = 1,2-bis(1,4,7-triazacyclonon-1-ylmethyl)benzene, Ldur = 1,2,4,5-tetrakis(1,4,7-triazacyclonon-1-ylmethyl)benzene, Lisomes = 1,2,3-tris(1,4,7-triazacyclonon-1-ylmethyl)benzene] is reported. Single-crystal X-ray crystallography has established that 2 and 6 feature nickel(II) centres in a distorted octahedral geometry, which are sandwiched between pairs of tacn rings. In 6, a second nickel(II) centre coordinates the third tacn ring of Lisomes and three water molecules complete the distorted octahedral coordination sphere. For the sandwiched Ni(II) centres, steric contraints introduced by the ethane and ortho-oriented tacn rings in Lisomes cause significant distortions to the Ni(II) coordination spheres. Cyclic, square-wave and near steady-state voltammetric studies on 1–6 indicate that the sandwiched nickel(II) centres may be reversibly oxidised to the nickel(III) state, with the potential for the nickel(II)/(III) couple showing a dependence on the nature of the tether linking the sandwiching tacn rings. Complex 4 undergoes oxidation in two overlapping one-electron processes [i.e., Ni(II)Ni(II) → Ni(III)Ni(II) → Ni(III)Ni(III)], indicating that the two nickel centres within the complex behave in an essentially independent fashion.

Dynamics of Various Metal-Octaethylporphyrins in Solution Studied by Resonance Raman and Low-Temperature Optical Absorption Spectroscopies. Role of the Central Metal

The temperature dependence of the Soret band of various metal-octaethylporphyrins [i.e., Ni(II), Cu(II), and Pd(II)] dissolved in the glass-forming mixture 50% (v/v) isopentane/ethyl ether in the temperature range 300−40 K was studied. Co(II)-octaethylporphyrin dissolved in dichloromethane was also investigated in the temperature range 300−180 K. The aim of the work was to investigate the role of the central metal in the conformational flexibility of porphyrins and in communicating solvent motions to their macrocycle. We used resonance Raman spectroscopy to determine the vibronic coupling of high-frequency modes to the electronic transition into the porphyrin B state. The corresponding coupling of a “bath” of low-frequency porphyrin/solvent motions was taken into account by a temperature-dependent Gaussian width (σ) of the Soret band. Following the approach of Melchers et al. (Biophys. J. 1996, 70, 2092−2099), the mean square fluctuations (MSF) of the central metal atom with respect to the porphyrin plane...

Neoplastic transformation of a human kidney epithelial cell line transfected with V‐HA‐ras oncogene

We have recently shown that normal human kidney epithelial (NHKE) cells were immortalized by treatment with Ni(II) alone. In the present study the immortalized human kidney cell line (IHKE) was transfected with a plasmid construct containing the v-Ha-ras oncogene (pZipras). After transfection, the cell lines formed tumors in athymic nude mice, whereas the ZipNeoSV(X)-transfected IHKE control cultures formed no tumors. Tumor cell lines (THKE) were established from the tumors in nude mice. These cells appear to be of human epithelial origin and express high levels of Ha-ras transcript. Karyotypic analysis was performed. The cell lines were tri-, tetra- or pentaploid. A consistent finding in the IHKE, IHKZE and THKE cells was increased numbers of chromosomes 17 and 7p+. Some marker chromosomes were identical in the IHKE and THKE cell lines, underlining their common origin and their possible importance in the carcinogenic process. This shows that the combined action of a chemical carcinogen [i.e., Ni(II)] and v-Ha-ras oncogene resulted in fully transformed human kidney epithelial cells, consistent with a step-wise progression of human epithelial cell transformation.

Metallothionein: A diamagnetic metalthiolate cluster protein

Metallothionein (MT) is an ubiquitously occurring, extremely sulfur- and metal-rich protein (mol. wt 6–7000) which plays a role in the metabolism and the detoxification of several essential and nonessential trace metals. All mammalian forms consist of a single polypeptide chain with a total of 61 amino acid residues of which 20 are cysteines. Each molecule binds 7 bivalent metal ions, most commonly Zn(II) and Cd(II). All cysteine residues participate in metal coordination through formation of metalmercaptide bonds. Their position in the polypeptide chain is preserved in all mammalian forms. Unique features are the CysXCys sequences (where X stands for an amino acid other than Cys) occurring 7 times along the chain. MT is an elongated nonglobular protein with an axial ratio of about 6 [1, 2]. As documented by 1H NMR and IR spectroscopy, it is a compact molecule with some secondary structure; however, it has not been crystallized as yet [3]. Hence, detailed structural information comes exclusively from spectroscopic studies. The electronic absorption spectrum is dominated by contributions from the electron transfer transitions of the metalthiolate complexes superimposed upon the plain absorption spectrum of the polypeptide chain. The positions of the first electron transfer band are strongly metal-dependent. The locations displayed in the derivatives of MT containing Zn, Cd, Hg or Pb are in accordance with Jørgensen's optical electronegativity scale. They coincide very closely with the shifts predicted for tetrahedral tetrathiolate model complexes, thus suggesting the same metal coordination in MT [4]. This is corroborated by the spectroscopic properties of MT reconstituted with Co(II). The visible and near-IR absorption spectrum of the green-colored derivative shows, besides the Co(II)thiolate electron transfer bands, dd maxima at 600, 682 and 743 nm belonging to the ν 3[ 4A 2 → 4T 1(P)] transition and at 1230 nm belonging to the ν 2[ 4A 2 → 4T 1(F)] transition. These are diagnostic of distorted tetrahedral tetrathiolate high-spin Co(II) complexes, a conclusion further substantiated by the magnetic circular dichroism (MCD) and electron spin resonance (ESR) spectra [5]. Independent evidence for the tetrahedral structure is also available for Zn(II)MT based on extended X-ray absorption fine structure (EXAFS) measurements [6] and for Cd(II)MT based on perturbed angular correlation of gamma ray (PAC) ▪ measurements using MT which contains the shortlived excited isomer 111mCd(II) [7]. The involvement of four sulfur ligands in the coordination of each metal ion is reconcilable with the overall Me(II) 7(Cys −) 20 stoichiometry of the molecule only if the metal complexes are sharing some thiolate ligands, thereby forming metal-thiolate clusters. This conjecture is now also confirmed experimentally. Thus the partitioning of the metal-coordinating ligands into bridging and non-bridging (terminal) thiolate ligands is manifested in a substantial broadening of the sulfur core electron binding energy profile in the X-ray photoelectron spectrum (ESCA) of MT as compared to those of elemental sulfur or monothiols [3]. Direct proof for clustering of the metal centers comes from the demonstration of metalmetal interactions by magnetic resonance spectroscopy. Thus in 113Cd-enriched MT 113Cd NMR resonances are split into multiplets by 113Cd 113Cd scalar coupling [8] and in fully substituted Co(II)MT the ESR-resonances are largely suppressed due to antiferromagnetic spin-canceling. This latter effect is also confirmed by magnetic susceptibility measurements [9]. By monitoring the changes in ESR amplitude and in magnetic susceptibility attending the stepwise incorporation of Co(II) into the protein, it is moreover possible to follow the building-up of the cluster structure. This process is biphasic. Up to binding of 4 equivalents of Co(II) the paramagnetic signals increase as expected for magnetically noninteracting high-spin complexes. However, upon further addition of Co(II), these features are lost again, signalling the transition to the magnetically interacting oligonuclear structures [9]. This two-step mode of metal-binding in which separate Co(II) tetrathiolate complexes are formed first is compatible with the model of two separate metal-thiolate clusters in MT deduced for 113Cd NMR homonuclear decoupling experiments [10] and from proteolytic cleavages studies [11] as well as from a 113Cd NMR study on cluster formation in progress in this laboratory. However, the actual steric organization of these clusters remains to be determined. An attractive structure consistent with all spectroscopic information at hand is the cage-like adamantane decahedron built up of thiolate units of tetrahedral symmetry (Fig. 1). The remarkable simplicity of the spectra and the unique capacity of MT to accommodate stoichiometrically different paramagnetic and diamagnetic metal ions, i.e., Ni(II), Co(II), Zn(II), Cd(II), Hg(II), Pb(II) and Bi(III), and to force them into environments of tetrahedral microsymmetry could be optimally accounted for by such a model or a variation of it. The need for these regular bioinorganic structures in MT would explain the remarkable preservation of the positions of all cysteine residues throughout mammalian evolution.

Catalytic properties of nickel oxide and its solid solutions in magnesium oxide in hydrogen oxidation

Temperature dependence of the reaction rate of H2 oxidation on nickel oxide and solid solutions of nickel ions in MgO prepared at 573–1373 K, has been studied. The variation of the catalytic properties with temperature is attributed to the presence of nickel ions in different oxidation states simultaneously, i. e. Ni(II) and Ni(III).