Nickel Insertion Research Articles

Effect of the synthesis method on the performance of Ni-CeO2-ZrO2 catalysts for the hydrogenolysis of glycerol with endogenous hydrogen

In this work, we investigated the influence of the synthesis method of Ni-based CeZr catalysts on their physico-chemical and catalytic properties in the hydrogenolysis (HDO) of glycerol with H2 in-situ produced by the aqueous-phase reforming (APR). Conventional impregnation method involved surface nickel deposition (NiCeZr-IM). The one-pot methods, which involved nickel embedment into CeZr lattice, included sol-gel (NiCeZr-SC) and coprecipitation (NiCeZr-CA and ultrasound-assisted NiCeZR-CS) methods. Differences in textural, structural, morphological, redox, and surface properties, together with and catalytic performance in the glycerol APR-HDO, were investigated systematically. As well, spent catalysts were deeply characterized. There were notable differences among textural properties, which significantly affected their activity in glycerol conversion. The structural characterization confirmed the successful integration of Ni into the CeZr lattice, especially for the catalysts synthesized using one-pot methods. One-pot synthesized catalysts showed stronger Ni-CeZr interaction, which affect the reducibility. The catalysts prepared by coprecipitation contained the highest metal-to-acid ratio, making them very active for C-O bond hydrogenation. Post-reaction characterization discloses a leaching of the nickel, in greater amount for both coprecipitated catalysts. This study revealed the potential of Ni-based catalysts derived from subsurface insertion of nickel into the CeZr matrix for the hydrogenolysis of glycerol without external hydrogen.

Tribological properties and corrosion resistance of nickel-based composite mold inserts containing lubricant nanoparticles for micro-injection molding

During the micro-injection molding process, the lifetime of mold inserts is severely limited by high-pressure impact conditions and demolding friction. To investigate the tribological properties and durability of mold insert, nickel-based composite mold inserts have been fabricated by electroforming adding polytetrafluoroethylene (PTFE), molybdenum disulfide (MoS2) and tungsten disulfide (WS2) nanoparticles, respectively. The surface morphology of pure nickel (Ni) and composite mold inserts were characterized. The Ni grain sizes of the composite mold inserts significantly decreased without changing the grain orientation and phase composition. The maximum microhardness of Ni-WS2 mold inserts was increased from 278.2 HV of pure Ni to 456.0 HV, an increase of 1.64 times, while the minimum friction coefficient against Si3N4 ball was reduced to 0.25. In addition, Ni-WS2 mold inserts exhibited excellent tribological properties, and their wear resistances were further investigated at different sliding speeds and external loads. With the increase of sliding speed and load, the self-lubricating property of the composite mold inserts would gradually disappear and the wear rate would increase significantly. The formation of a uniform and dense friction transfer film is the key to reducing the friction coefficient and wear rate. Furthermore, the corrosion resistance of the mold inserts was improved to some extent with the addition of the three nanoparticles. In dynamic electrochemical tests, the corrosion current density of Ni-PTFE mold insert was 3.083 ± 0.228 × 10−6 A/cm2 and the corrosion rate was 0.036 ± 0.003 mm/year, which showed the best corrosion resistance.

Synthesis and characterization of (Co1-x Nix)3(BTC)2.12H2O (0 ≤ x ≤ 0.5) MOF based Janus chemical micromotors

We report the synthesis and characterization of Metal–Organic Framework (MOF)-Based Janus chemical Micro motors that self-propel at 26 and 25 µms−1 in 5% and 12% of H2O2, respectively, via ionic diffusiophoresis. The synthesis of this MOF was achieved by solvothermal method. The TG -DT analysis study on (Co1-x Nix)3(BTC)2·12H2O (0 ≤ x ≤ 0.5) micro motors, showed that water ligands can be easily removed. The Co3(BTC)2·12H2O crystallized in orthorhombic crystal system with Pmmm space group and (Co0.8Ni0.2)3(BTC)2·12H2O, (Co1.5Ni1.5)3(BTC)2·12H2O crystallized in monoclinic crystal system with C2 space group. The lattice constants, dislocation density and micro strain of the micro motors were calculated and the structure is discussed in detail using crystal viewer. The morphology of (Co1-x Nix)3(BTC)2·12H2O (0 ≤ x ≤ 0.5) micro motors were scrutinized using the field emission scanning electron microscopy (FE-SEM). Energy dispersion X-ray (EDX) analysis was employed for the elemental analysis and chemical characterization. The vibrational characterization was studied by utilizing Fourier Transform Infrared Spectroscopy (FT-IR) and Raman spectroscopy. The asymmetric and symmetric stretching vibrations of 1,3,5 trisubstituted aromatic ring appeared as three bands at 1368, 1428 and 1219 cm−1. The optical properties were explored using UV–Visible DRS and the absorption edge of Co-BTC, Co0.8Ni0.2-BTC and Co0.5Ni0.5-BTC were observed at approximately 300 nm, 450 nm and 500 nm respectively. The direct band gap for (Co1-x Nix)3(BTC)2.12 H2O (0 ≤ x ≤ 0.5) micromotors was found to be 3.84 eV, 3.76 eV and 3.66 eV respectively. The pore-size distribution and specific surface areas were calculated using Barrett–Joyner–Halenda, BJH and Brunauer Emmett-Teller method respectively. The average pore diameter 8.727 nm and total pore volume of 2.467 × 10−2cm3g−1 was obtained for the material. Insertion of nickel in the lattice of cobalt further accelerates the speed from 0.08 µms−1 to 26µms−1, which leads to a force of 7.29 fN and a power of 4.9 × 10−9 fW, which resembles bio molecular motors. Considering the investigation of MOFS as Microbots/Micromotors so far, Co0.8Ni0.2BTC in both 5% and 12% H2O2 can be represented as the best example of clear observation of bubble tails propelling spherical Janus micromotors.

Microstructure of a nickel insert, a special copper alloy, and a cast joint between them

Abstract in English This work deals with the characterisation of the microstructure of a nickel insert, a special copper alloy and the cast joint between them after their use as a glass manufacturing mould. The microstructure was characterised by optical microscopy, scanning electron microscopy and microanalysis by energy dispersive X-ray spectroscopy. It was found that the nickel insert contained 7 at. % Si and 0.3 at. % Fe. The special copper alloy contains undesirable phases or compounds, including lead, aluminium-based oxides and borides. The borides are either iron-, iron-chromium- or chromium-based with different stoichiometries between metal components and boron. The cast joint between the nickel insert and the special copper alloy has evidence of mixing the two alloys, while only in some areas porosity and oxides prevented the formation of a suitable cast joint. Aluminium-based oxides and some borides could be the cause of the formation of cracks due to their morphology.

Using a high-throughput, whole-cell hydrogenase assay to identify potential small molecule inhibitors of [NiFe]-hydrogenase.

[NiFe]-hydrogenases are used by several human pathogens to catalyze the reversible conversion between molecular hydrogen and protons and electrons. Hydrogenases provide an increased metabolic flexibility for pathogens, such as Escherichia coli and Helicobacter pylori, by allowing the use of molecular hydrogen as an energy source to promote survival in anaerobic environments. With the rise of antimicrobial resistance and the desire for novel therapeutics, the [NiFe]-hydrogenases are alluring targets. Inhibiting the nickel insertion pathway of [NiFe]-hydrogenases is attractive as this pathway is required for the generation of functional enzymes and is orthogonal to human biochemistry. In this work, nickel availability for the production and function of E. coli [NiFe]-hydrogenase was explored through immunoblot and activity assays. Whole-cell hydrogenase activities were assayed in high throughput against a small molecule library of known bioactives. Iodoquinol was identified as a potential inhibitor of the nickel biosynthetic pathway of [NiFe]-hydrogenase through a two-step screening process, but further studies with immunoblot assays showed confounding effects dependent on the cell growth phase. This study highlights the significance of considering the growth phenotype for whole-cell based assays overall and its effects on various cellular processes influenced by metal trafficking and homeostasis.

An in vitro reconstitution system to monitor iron transfer to the active site during the maturation of [NiFe]-hydrogenase

[NiFe]-hydrogenases (Hyds) comprise a small and a large subunit. The latter harbors the biologically unique [NiFe](CN)2CO active-site cofactor. The maturation process includes the assembly of the [Fe](CN)2CO cofactor precursor, nickel binding, endoproteolytic cleavage of the large subunit, and dimerization with the small subunit to yield active enzyme. The biosynthesis of the [Fe](CN)2CO moiety of [NiFe]-Hyd-1 and Hyd-2 occurs on the scaffold complex HybG–HypD (GD), whereas the HypC–HypD complex is specific for the assembly of Hyd-3. The metabolic source and the route for delivering iron to the active site remain unclear. To investigate the maturation process of O2-tolerant Hyd-1 from Escherichia coli, we developed an enzymatic in vitro reconstitution system that allows for the synthesis of Hyd-1 using only purified components. Together with this in vitro reconstitution system, we employed biochemical analyses, infrared spectroscopy (attenuated total reflection FTIR), mass spectrometry (MS), and microscale thermophoresis to monitor the iron transfer during the maturation process and to understand how the [Fe](CN)2CO cofactor precursor is ultimately incorporated into the large subunit. We demonstrate the direct transfer of iron from 57Fe-labeled GD complex to the large subunit of Hyd-1. Our data reveal that the GD complex exclusively interacts with the large subunit of Hyd-1 and Hyd-2 but not with the large subunit of Hyd-3. Furthermore, we show that the presence of iron in the active site is a prerequisite for nickel insertion. Taken together, these findings reveal how the [Fe](CN)2CO cofactor precursor is transferred and incorporated into the active site of [NiFe]-Hyd.

Characterization of the Nickel‐inserting Cyclometallase LarC from Moorella thermoacetica and Identification of a CMPylated Reaction Intermediate

The nickel‐pincer nucleotide (NPN) cofactor is required for lactate racemase (LarA) activity1, and LarB, LarE, and LarC are needed to generate this coenzyme2. LarC catalyzes the last step of the biosynthesis pathway by inserting nickel into pyridinium‐3,5‐dithiocarboxylic acid mononucleotide (P2TMN), resulting in the mature NPN cofactor3. Previously, LarC from Lactobacillus plantarum was shown to be a CTP‐dependent, single‐turnover nickel insertase or cyclometallase, but a structure was only obtained for its C‐terminal domain and its reaction mechanism was not identified. We characterized LarC from Moorella thermoacetica(LarCMt) and identified a novel reaction intermediate in which the precursor P2TMN is CMPylated. We propose that LarCMt uses CTP to generate the CMP‐P2TMN species that is properly positioned in the active site for nickel insertion, analogous to the molybdenum insertion step during molybdenum cofactor biosynthesis4. LarCMt variants were characterized to further elucidate the mechanism of the transient CMPylation process. Additionally, we generated preliminary structural data for the full‐length LarCMt through cryo‐electron microscopy. Our results highlight the role of CTP in the nickel insertion reaction and provide a better structural and mechanistic understanding of the LarC reaction.1. Desguin, B. et al. A tethered niacin‐derived pincer complex with a nickel‐carbon bond in lactate racemase. Science. 349, 66–69 (2015).2. Desguin, B. et al. Lactate racemase is a nickel‐dependent enzyme activated by a widespread maturation system. Nat. Commun. 5, 3615 (2014).3. Desguin, B. et al. Biosynthesis of the nickel‐pincer nucleotide cofactor of lactate racemase requires a CTP‐dependent cyclometallase. J. Biol. Chem. 293, 12303–12317 (2018).4. Llamas, A., Mendel, R. R. & Schwarz, G. Synthesis of adenylated molybdopterin: An essential step for molybdenum insertion. J. Biol. Chem. 279, 55241–55246 (2004).

Complementary Approaches for Enhancing Polystyrene Hydrophobicity: Additives Development and Replication of Micro/Nanotextures

This work aims at developing polymer surfaces with enhanced hydrophobicity by controlling both the surface chemistry and the surface structure. As a first step, a chemical surface modification is achieved by the incorporation of a synthetized tailored fluorinated copolymer, named POISE-a (Polymer prOcessing Interface StabilizEr), in a commercial polystyrene matrix. Then, a complementary physical approach based on micro-structuration of a polymer surface is used. Polystyrene films containing various contents of POISE-a were elaborated by a solvent casting method. The structuration of the films was conducted by replicating a texture from a nickel insert using a hot-embossing technique with optimized processing conditions. The beneficial effect of POISE-a on both the wettability properties and the replication efficiency was evaluated by the water/polymer static contact angle and the quantification of the replication rate, respectively. The use of this tailored additive, even at low percentages (i.e., 1 wt.%), associated with the structuration of the PS surface, improves both the hydrophobicity of polystyrene and the robustness of the replication process.

Revisiting the CooJ family, a potential chaperone for nickel delivery to [NiFe]‑carbon monoxide dehydrogenase

Nickel insertion into nickel-dependent carbon monoxide dehydrogenase (CODH) represents a key step in the enzyme activation. This is the last step of the biosynthesis of the active site, which contains an atypical heteronuclear NiFe4S4 cluster known as the C-cluster. The enzyme maturation is performed by three accessory proteins, namely CooC, CooT and CooJ. Among them, CooJ from Rhodospirillum rubrum is a histidine-rich protein containing two distinct and spatially separated Ni(II)-binding sites: a N-terminal high affinity site (HAS) and a histidine tail at the C-terminus. In 46 CooJ homologues, the HAS motif was found to be strictly conserved with a H(W/F)XXHXXXH sequence. Here, a proteome database search identified at least 150 CooJ homologues and revealed distinct motifs for HAS, featuring 2, 3 or 4 histidines. The purification and biophysical characterization of three representative members of this protein family showed that they are all homodimers able to bind Ni(II) ions via one or two independent binding sites. Initially thought to be present only in R. rubrum, this study strongly suggests that CooJ could play a significant role in CODH maturation or in nickel homeostasis.

Probing the transport of Ni(II) ions through the internal tunnels of the Helicobacter pylori UreDFG multimeric protein complex

The survival of several pathogenic bacteria, such as Helicobacter pylori (Hp), relies on the activity of the nickel-dependent enzyme urease. Nickel insertion into urease is mediated by a multimeric chaperone complex (HpUreDFG) that is responsible for the transport of Ni(II) from a conserved metal binding motif located in the UreG dimer (CPH motif) to the catalytic site of the enzyme. The X-ray structure of HpUreDFG revealed the presence of water-filled tunnels that were proposed as a route for Ni(II) translocation. Here, we probe the transport of Ni(II) through the internal tunnels of HpUreDFG, from the CPH motif to the external surface of the complex, using microsecond-long enhanced molecular dynamics simulations. The results suggest a “bucket-brigade” mechanism whereby Ni(II) can be transported through a series of stations found along these internal pathways.

Experimental Investigation and Molecular Dynamics Simulation on the Anti-Adhesion Behavior of Alkanethiols on Nickel Insert in Micro Injection Molding

Due to the adhesion between the polymer melt and nickel (Ni) mold insert in the micro injection molding process, deformation defects frequently occur when the microstructures are demolded from the insert. In this study, self-assembled alkanethiols were applied to modify the surface of Ni mold insert to reduce its surface energy. Experimental trials were undertaken to explore the effect of alkanethiols coating on the replication quality. After that, molecular dynamics (MD) simulation was then used to investigate the adhesion behavior between the self-assembled coating and polypropylene (PP) by establishing three different types of alkanethiol material. The interaction energy, the potential energy change and radial distribution function were calculated to study the anti-adhesion mechanism. Experimental results show that all the three coatings can effectively decrease the adhesion and therefore promote the replication fidelity. It is demonstrated in MD simulation that the adhesion mainly comes from the van der Waals (vdW) force at the interface. The arrangement of sulfur atom on the Ni surface results in different absorbing behaviors. Compared with that of the PP–Ni interface, the interfacial energy and adhesion work after surface treatment is significantly reduced.

Angle of Insertion and Torsional Resistance of Nickel-Titanium Rotary Instruments.

Previously published studies have investigated the influence of instrument access on cyclic fatigue resistance. However, no studies have evaluated the relationship between angulated access and torsional resistance. The aim of this study was to investigate the influence of the angle of access on the torsional resistance of endodontic instruments. One hundred and eighty instruments were selected: 90 F-One Blue 25/04 and 90 HeroShaper 25/04 instruments. Three subgroups (n = 30) for each instrument type (A and B) were established according to the angle of insertion of the instruments inside the artificial canal (0°, 10° and 20°). The tests were performed using a custom-made device consisting of the following: a motor that can record torque values of 0.1 s; interchangeable stainless-steel canals with different curvature (0°, 10° and 20°) that allow the instrument’s angulated insertion and keep it flexed during testing procedures; and a vise used to secure the instrument at 3 mm from the tip. Torque limit was set to 5.5 Ncm, and each instrument was rotated at 500 rpm until fracture occurred. Torque to fracture (TtF) was registered by the endodontic motor, and the fragment length (FL) was measured with a digital caliper. Fractographic analysis was performed using a scanning electron microscopy (SEM) evaluation to confirm the cause of failure. TtF values and fragment length (FL) values were statistically analyzed using one-way analysis of variance (ANOVA) test and the Bonferroni correction for multiple comparisons across the groups with significance set to a 95% confidence level. Regarding the F-One Blue instruments, the results showed a higher TtF for group A3 (20°) than for group A1 (0°) and group A2 (10°), with a statistically significant difference between group A3 and the other two groups (p < 0.05), whereas no statistically significant difference was found between group A1 and group A2 (p > 0.05). Regarding the HeroShaper instrument, the results showed the highest TtF for group B3, with a statistically significant difference between the three subgroups B1, B2 and B3 (p < 0.05). The results showed that the torsional resistance increases as the angle of instrument access increases with a varying intensity, according to the crystallographic phase of the instrument selected.

Self-Assembled Monolayers of Alkanethiols on Nickel Insert: Characterization of Friction and Analysis on Demolding Quality in Microinjection Molding.

When the part geometry scaling down from macro to microscale level, the size-induced surface effect becomes significant in the injection molding process. The adhesion between polymer and nickel (Ni) mold insert during the process can lead to defects in necking, warping and deformation of microstructure. In this study, the self-assembled monolayers (SAMs) with low surface energy were deposited on the Ni surface to reduce the adhesion and further improve the demolding quality of the microstructure. Results show that the alkyl mercaptan SAMs with chemical bonds and close alignment can be successfully deposited on the surface of Ni by the solution deposition method. The contact angle, surface free energy, and friction coefficient before and after anti-adhesion treatment on the surface of mold insert were measured. In addition, the anti-adhesion properties of different alkyl mercaptan materials and the correspondingly replication quality of microstructure parts after injection molding were analyzed. It is found that the Ni mold insert treated by the perfluorodecanethiol has the best wear resistance and still shows good reproducibility at the 100th demolding cycle.

Metal specificity of the Ni(II) and Zn(II) binding sites of the N-terminal and G-domain of E. coli HypB.

HypB is one of the chaperones required for proper nickel insertion into [NiFe]-hydrogenase. Escherichia coli HypB has two potential Ni(II) and Zn(II) binding sites-the N-terminal one and the so-called GTPase one. The metal-loaded HypB-SlyD metallochaperone complex activates nickel release from the N-terminal HypB site. In this work, we focus on the metal selectivity of the two HypB metal binding sites and show that (i) the N-terminal region binds Zn(II) and Ni(II) ions with higher affinity than the G-domain and (ii) the lower affinity G domain binds Zn(II) more effectively than Ni(II). In addition, the high affinity N-terminal domain, both in water and membrane mimicking SDS solution, has a larger affinity towards Zn(II) than Ni(II), while an opposite situation is observed at basic pH; at pH 7.4, the affinity of this region towards both metals is almost the same. The N-terminal HypB region is also more effective in Ni(II) binding than the previously studied SlyD metal binding regions. Considering that the nickel chaperone SlyD activates the release of nickel and blocks the release of zinc from the N-terminal high-affinity metal site of HypB, we may speculate that such pH-dependent metal affinity might modulate HypB interactions with SlyD, being dependent on both pH and the protein's metal status.

Influence of Diamond-Like Carbon Coating on the Channel Deformation of Injection-Molded Microfluidic Chips during the Demolding Process.

Injection molding is one of the main techniques for manufacturing microfluidic chips. As an important stage, the demolding process in injection molding will directly affect the quality of the functional unit of microfluidic chips (polymer microchannels), thus limiting the realization of its functions. In this study, molecular dynamics (MD) simulations on the demolding process were carried out to investigate the influence of diamond-like carbon (DLC) coating on the channel deformation. The channel qualities of polystyrene (PS), polymethyl methacrylate (PMMA), cyclic olefin copolymer (COC) and polycarbonate (PC) were analyzed after demolding with nickel (Ni) and DLC-coated mold inserts, respectively. In particular, the non-bonded interfacial interaction energy, elastic recovery and gyration radius of polymer molecular chains were further studied. The results showed that the non-bonded interfacial interaction energies could be significantly reduced by DLC-coating treatment on the mold insert. Moreover, common channel defects such as molecular chain separation, surface burrs and necking did not occur. The treatment of DLC coating could also significantly reduce the change in the gyration radius of polymer molecular chains, so the morphology of the polymer channel could be maintained well. However, the change in the elastic recovery of the polymer channel was increased, and the opening width became larger. In a word, DLC-coating treatment on the mold insert has great application potential for improving the demolding quality of injection-molded microfluidic chips.

Simultaneous Catalytic Oxidation of a Lean Mixture of CO-CH4 over Spinel Type Cobalt Based Oxides

A series of nickel-cobalt bimetal oxides in varying molar ratios and its single metal oxides were synthesized by reactive calcination of coprecipitated basic-carbonates. Several characterization techniques, such as: Bruneuer Emmett Teller (BET), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infra Red (FTIR), and Hydrogen Temperature Programmed Reduction (H2-TPR), were performed over the oxides. Activities of oxides were evaluated in methane total oxidation in the presence or the absence of CO. The best catalytic performance was observed over NiCo catalyst with a Ni/Co molar ratio of 1:1, and the complete conversion of CO-CH4 mixture was achieved at 390 °C. Moreover, the presence of carbon monoxide improves CH4 total oxidation over nickel-cobalt mixed oxides. Structural analysis reveals that the insertion of nickel into the spinel lattice of cobalt oxide causes the structural disorder, which probably caused the increase of the amount of octahedrally coordinated divalent nickel cations that are responsible for catalytic activity. Stability of the best-performed catalyst has been tested in the two conditions, showing remarkable long-term stability and thermal stability, however, showed deactivation after thermally ageing at 700 °C. Copyright © 2020 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Aminomethylation of Oxabenzonorbornadienes via the Merger of Photoredox and Nickel Catalysis.

The first aminomethylation of oxabenzonorbornadienes using dual photoredox/nickel catalysis has been disclosed. This cascade reaction allowed the preparation of the cis-aminomethyl dihydronaphthalenols without any prefunctionalization or any use of nucleophilic organometallic species. The control of the regio- and stereoselectivity might be explained by a sequence involving insertion of nickel(0) into the C-O bond followed by the formation of a π-allyl intermediate.

CfbA promotes insertion of cobalt and nickel into ruffled tetrapyrroles in vitro.

The nickel chelatase CfbA is the smallest member of the chelatase family, but the mechanism by which this enzyme inserts nickel into sirohydrochlorin is unknown. In order to gain mechanistic insight, metal binding, tetrapyrrole binding, and enzyme activity were characterized for a variety of substrates using several spectroscopic and computational approaches. Mass spectrometery and magnetic circular dichroism experiments revealed that CfbA binds an octahedral, high-spin metal substrate. UV/Vis absorption spectroscopy demonstrated that the enzyme binds a wide range of tetrapyrrole substrates and perturbs their electronic structures. Based upon activity assays, CfbA promotes insertion of cobalt and nickel into several tetrapyrroles, including cobalt insertion into protopophyrin IX. Finally, density functional theory models were developed which strongly suggest that observed spectral changes upon binding to the enzyme can be explained by tetrapyrrole ruffling, but not deprotonation or saddling. The observation of an octahedral, high-spin metal bound to CfbA leads to a generalization for all class II chelatases: these enzymes bind labile metal substrates and metal desolvation is not a rate-limiting step. The conclusion that CfbA ruffles its tetrapyrrole substrate reveals that the CfbA mechanism is different from that currently proposed for ferrochelatase, and identifies an intriguing correlation between metal substrate specificity and tetrapyrrole distortion mode in chelatases.

Structural insight into metallocofactor maturation in carbon monoxide dehydrogenase

The nickel-dependent carbon monoxide dehydrogenase (CODH) employs a unique heterometallic nickel-iron-sulfur cluster, termed the C-cluster, to catalyze the interconversion of CO and CO2 Like other complex metalloenzymes, CODH requires dedicated assembly machinery to form the fully intact and functional C-cluster. In particular, nickel incorporation into the C-cluster depends on the maturation factor CooC; however, the mechanism of nickel insertion remains poorly understood. Here, we compare X-ray structures (1.50-2.48 Å resolution) of CODH from Desulfovibrio vulgaris (DvCODH) heterologously expressed in either the absence (DvCODH-CooC) or presence (DvCODH+CooC) of co-expressed CooC. We find that the C-cluster of DvCODH-CooC is fully loaded with iron but does not contain any nickel. Interestingly, the so-called unique iron ion (Feu) occupies both its canonical site (80% occupancy) and the nickel site (20% occupancy), with addition of reductant causing further mismetallation of the nickel site (60% iron occupancy). We also demonstrate that a DvCODH variant that lacks a surface-accessible iron-sulfur cluster (the D-cluster) has a C-cluster that is also replete in iron but lacks nickel, despite co-expression with CooC. In this variant, all Feu is in its canonical location, and the nickel site is empty. This D-cluster-deficient CODH is inactive despite attempts to reconstitute it with nickel. Taken together, these results suggest that an empty nickel site is not sufficient for nickel incorporation. Based on our findings, we propose a model for C-cluster assembly that requires both CooC and a functioning D-cluster, involves precise redox-state control, and includes a two-step nickel-binding process.

Study of structural and dielectric properties of Nickel-doped BaTiO3 material

In this work, the effect of nickel (Ni) insertion on the structural and dielectric properties of BaTiO3 material was investigated. A series of powders of composition Ba1-xNixTiO3 (x = 0, 0.05, 0.1, 0.15 and 0.20) were synthesized by solid method. The analysis by X-Ray Diffraction (XRD) shows that the obtained compounds crystallize in a phase of perovskite type. All the peaks are indexed in a phase of quadratic symmetry. Characterization by the Scanning Electron Microscope (SEM) indicates a heterogeneous microstructure of the grains. The study by spectroscopy of impedance in the frequency range [500Hz-1MHz] highlighted the effect of the nickel insertion on the transition temperature and the dielectric constant value.