Effects of the Protonation State of Titratable Residues and the Presence of Water Molecules on Nocodazole Binding to β‐Tubulin

Regulation of microtubule assembly by antimitotic agents is a potential therapeutic strategy for the treatment of cancer, parasite infections, and neurodegenerative diseases. One of these agents is nocodazole (NZ), which inhibits microtubule polymerization by binding to β‐tubulin. NZ was recently co‐crystallized in Gallus gallus tubulin, providing new information about the features of interaction for ligand recognition and stability. In this work, we used state‐of‐the‐art computational approaches to evaluate the protonation effects of titratable residues and the presence of water molecules in the binding of NZ. Analysis of protonation states showed that residue E198 has the largest modification in its pK_a value. The resulting E198 pK_a value, calculated with pH‐REMD methodology (pK_a=6.21), was higher than the isolated E amino acid (pK_a=4.25), thus being more likely to be found in its protonated state at the binding site. Moreover, we identified an interaction between a water molecule and C239 and G235 as essential for NZ binding. Our results suggest that the protonation state of E198 and the structural water molecules play key roles in the binding of NZ to β‐tubulin.     

Adsorption of nickel on Enterococcus hirae cell walls

The metal affinity of Enterococcus hirae cell walls and the relation to the chemical composition of the wall constituents were investigated, by studying the nickel absorption on purified cell walls of Enterococcus hirae mutants. The strains of Enterococcus hirae are characterised by their penicillin resistance, the mother strains ATCC9790, the penicillin-sensitive mutant AS21 and the penicillin-resistant mutant R40 present an MIC (minimum inhibitory concentration of penicillin) of 1–2, 0·075 and 80μg cm⁻³, respectively. Preliminary results showed that the penicillin-resistant cell wall (R40) had more affinity for nickel than the others. The maximum amount of fixed nickel average 2·03 μmol of Ni mg⁻¹ of R40 cells walls, 1·06 μmol of Ni mg⁻¹ of AS21 cell walls and 0·96 μmol of Ni mg⁻¹ of ATCC cell walls. The Scatchard model showed at least two types of nickel fixation sites, with low and high affinity respectively, and a negative cooperativity between sites. Application of the BET isotherm implies a multilayer adsorption process in which one layer does not need to be completely saturated before the succeeding ones. The potentiometric titration curve showed the proton affinity distribution of the cell walls. Two protonation constants were obtained, one at pH 4·5 which corresponded to the pK_a of a weak acid, and one at pH 7·2 which corresponded to the pK_a of the couple of H₂PO₄⁻/HPO₄²⁻. ©1997 SCI     

γ‐Alumina supported Cu‐Ni bimetallic catalysts: Characterization and selective hydrogenation of 1,3‐butadiene

Addition of a second metal often improves the selectivity of a supported catalyst for the hydrogenation of 1,3‐butadiene. Catalysts containing 15 wt% Ni and varying amounts of Cu were prepared and characterized by TPR, XRD and XPS. The Cu‐Ni interaction affects the reduction behavior of the catalysts. TPR result shows that the synergetic effect of copper and nickel modifies the capability of metal to combine with hydrogen in bulk phase. The Ni 2p spectra in XPS shows significant shifts toward lower binding energies with increasing copper loading. From XRD results it is represented that aggregation of nickel occurs more easily due to the copper addition. The adding of copper on Ni/Al₂O₃ makes the conversion rate decreased and increases the selectivity to 1‐butene.     

Ni(ll) biosorption by Rhizopus arrhizus Env 3: the study of important parameters in biomass biosorption

BACKGROUND: The removal of toxic metals from wastewaters by biosorption, based on the metal‐binding capacities of various biological materials, has attracted much interest. However, the success of this approach depends on economic feasibility, which can be obtained by optimisation of the environmental conditions. In this study, Ni(II) biosorption experiments were carried out using a preformed biomass of Rhizopus arrhizus. A pure culture of previously isolated R. arrhizus Env 3 was used for maximum biosorption of nickel metal from nickel‐electroplating industrial effluent. RESULTS: Various environmental factors such as nickel concentration, pH, temperature, mycelial pellet weight, pretreatment of fungal biomass, dead and living fungal biomass and time course of biosorption by R. arrhizus Env 3 were optimised for maximum removal of nickel from the effluent. The maximum nickel removal rate of 618.5 mg g^?1 was observed with living biomass at pH 8, temperature 35 °C, nickel concentration 500 mg L^?1, pellet size 3 g wet weight and shaker velocity 150 rpm. Maximum nickel biosorption was obtained after 72 h. CONCLUSION: Statistical analysis of different factors such as temperature, pH, mycelial pellet size, concentration of nickel in effluent and residual nickel level showed that all these factors had significant effects on the biosorption of nickel metal by R. arrhizus Env 3 from nickel‐electroplating industrial effluent. Copyright © 2008 Society of Chemical Industry     

Electropolishing of metals in alcoholic solution of sulphuric acid

The potentiodynamic polarization curves of iron, nickel, cobalt, molybdenum, copper and iron-nickel and cobalt-nickel alloys were measured in the polishing solution of 1M H₂SO₄ in CH₃OH. The above mentioned metals and alloys may be divided into three groups: metals and alloys with high dissolution rate in the active state in which the polishing follows immediately behind the active dissolution region (Fe, Co and Ni-Fe and NiCo alloys with a low nickel content), metals and alloys with low passivating current density that become passive at first and the polishing takes place behind the region of localized corrosion (nickel and NiFe and NiCo alloys with a high nickel content) are metals that are polished in the transpassive region (molybdenum).     

Evaluation of electroactive intermediate states in anodic O2 evolution at chemically formed nickel oxide: Comparison with behaviour at nickel metal anodes

The behaviour of the kinetically involved intermediate states arising in the electrocatalysis of anodic oxygen evolution at chemically formed, high-area nickel oxide (NiO·OH) films on nickel metal as substrate is examined by means of analysis of potential (V) decay transients, following interruption of anodic polarization currents at various overpotentials. The potential decay behaviour is treated in terms of the dependence ofV(t) on log (time,t), and of ln (–dV/dt) as f[V(t)]. The pseudocapacitance associated with the potential-dependence of the coverage or surface density of the overpotential-deposited species involved as intermediates in the reaction at the oxide electrode surface is evaluated jointly from the potential decay and Tafel polarization behaviour, following procedures developed recently.In anodic O₂ evolution on oxide surfaces, such as NiO·OH, the intermediate states in the kinetics of the reaction are to be identified as OH or O species coupled with potential-dependent Ni(III) and Ni(IV) oxidation states of nickel, and the surface density of these states can be evaluated experimentally.The results obtained for anodic O₂ evolution on the chemically formed nickel oxide films are compared with the behaviour at anodically formed thin oxide films on nickel metal.     

The effect of non‐ideal mixing on the number of steady states and dynamic behaviour for autocatalytical reactions in a CSTR

In this paper, we analyze the concentration multiplicity and dynamic behavior for an autocatalytical reaction, A + R → (n + 1)R + products with an overall rate expression given by – γ_a= kc_a^pc_r^r(p > 0 and r > 0) in a imperfectly mixed (Cholette's model) CSTR. We proved that non‐ideal mixing had an effect on the number of steady states and dynamic behavior for the reaction orders r > 1 and r = 1. However, the above‐mentioned effect does not happen for the reaction order r < 1. Furthermore, a simulated example was used to demonstrate our results.     

Nickel(II) complexes bearing the bis(β‐ketoamino) ligand for the copolymerization of norbornene with a higher 1‐alkene

A novel bis(β‐ketoamino)Ni(II) complex catalyst, Ni{CF₃C(O)CHC[N(naphthyl)]CH₃}₂, was synthesized, and the structure was solved by a single‐crystal X‐ray refraction technique. The copolymerization of norbornene with higher 1‐alkene was carried out in toluene with catalytic systems based on nickel(II) complexes, Ni{RC(O)CHC[N(naphthyl)]CH₃}₂(R?CH₃, CF₃) and B(C₆F₅)₃, and high activity was exhibited by both catalytic systems. The effects of the catalyst structure and comonomer feed content on the polymerization activity and the incorporation rates were investigated. The reactivity ratios were determined to be r_1‐octene = 0.009 and r_norbornene = 13.461 by the Kelen–Tüdõs method for the Ni{CH₃C(O)CHC[N(naphthyl)]CH₃}₂/B(C₆F₅)₃ system. The achieved copolymers were confirmed to be vinyl‐addition copolymers through the analysis of ¹H‐NMR and ¹³C‐NMR. The thermogravimetric analysis results showed that the copolymers exhibited good thermal stability (decomposition temperature, T_dec > 400°C), and the glass‐transition temperature of the copolymers were observed between 215 and 275°C. The copolymers were confirmed to be noncrystalline by wide‐angle X‐ray diffraction analysis and showed good solubility in common organic solvents. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Characterization of highly dispersed Ni/Al2O3 catalysts by EXAFS analysis of higher shells

The size and morphology of Ni/Al₂O₃ catalysts in the oxidic, reduced, and passivated state were determined by EXAFS analysis of the higher shells around the Ni atoms. In the oxidic state, the Ni cations were present in small NiO_x particles with predominant (111) plane. Below 4.5 wt% Ni loading, the NiO_x particles consisted of one Ni layer, and of two or three Ni layers above 4.5 wt% Ni. A Ni–Al contribution was observed in samples with low Ni loading. The layer which is in contact with the Al₂O₃ surface is affected by the support surface and its structure is highly distorted, while the other layers were not distorted and have a structure similar to that in bulk NiO. In the reduced state, the number of Ni metal atoms in the reduced Ni particles was smaller than 100 with a narrow distribution below a loading of 15.6 wt% Ni. Above this loading, the particle size suddenly increased and the distribution became wider. The distances and Debye–Waller factors were similar to those of bulk nickel which suggested a weak interaction between the particles and the support. In the passivated state, Ni kernels with 20–40 metal atoms were covered by a one layer thick NiO skin. This revised version was published online in June 2006 with corrections to the Cover Date.     

Formation of Ni(CO)4 during the Interaction between CO and Silica-Supported Nickel Catalyst: an FTIR Spectroscopic Study

The formation of Ni(CO)₄ during interaction of CO with silica-supported highly dispersed nickel metal (d _av4 nm) was investigated by FTIR spectroscopy. At temperatures below 145 K, in addition to linear and bridged nickel carbonyls, CO adsorption on Ni⁰/SiO₂ leads to the formation of Ni(CO) _x (x=2, 3) subcarbonyls (band at ca. 2090 cm^–1) and negligible amounts of Ni(CO)₄ adsorbed on SiO₂ (band at 2048 cm^–1). Up to this temperature CO causes no detectable erosion of the metal surface. Above 145 K the rate of interaction between CO and the nickel particles significantly increases. Until 235 K Ni(CO)₄ mainly remains in the adsorbed state, while at still higher temperatures the equilibrium between adsorbed and gaseous Ni(CO)₄ (band at 2058 cm^–1) is shifted towards the latter. It is assumed that subcarbonyls formed on defect sites of the metal surface are precursors of the nickel tetracarbonyl. Successive adsorption–evacuation cycles of CO at room temperature result in a decrease in the amount of the Ni(CO)₄ formed, probably due to a reduction of the number of defect metal sites. On the basis of ¹²CO and ¹³CO coadsorption, an alternative interpretation of the band at 2048 cm^–1 to species containing isolated Ni(CO)₃ groups is proposed.     

Treatment of aqueous solutions containing nickel using crandallite‐type compounds

The removal of nickel from aqueous solutions streams has been investigated using an artificial amorphous crandallite‐type compound, CaAl₃(OH)₆(HPO₄)(PO₄) (Ca‐crandallite), synthesized in our laboratory. Equilibrium ion‐exchange isotherms in an aqueous medium of Ca²⁺/Ni²⁺ at different pH values at 293 K have been determined. The experimental equilibrium data were satisfactorily correlated using a Langmuir‐type empirical equation. At low pH values, the hydrogen ion competes with the heavy metal cation and the percentage removal of metal declines. It was found that the operating capacity of Ca‐crandallite with respect to the metal ion increased with the pH of the solution, in accordance with a second‐degree polynomial equation. However, the pH should not be allowed to rise to levels at which chemical precipitation as nickel hydroxide would occur, with 7.00 the highest value tested. Taking into account the variation of operating capacity with pH, the system exhibited a unique separation factor, namely all the experimental points can be described by a unique isotherm in a dimensionless form. The Ca‐crandallite showed a high capacity, 2.176 meq g^?1, for the exchange of Ni(II) from nickel nitrate solutions and the rate of exchange of metal increases with increasing solution temperature due to the enhancement of effective intraparticle diffusivity. Copyright © 2005 Society of Chemical Industry     

Synthesis of High Temperature Stable Carbon Coated Metal Nanoparticles in AlPO4 Based Matrix In Situ in Oxidative Atmosphere

In this work, we have reported a universal method for the synthesis of metal nanoparticles coated with graphite layer in AlPO₄ based matrix. As an example, graphitized carbon coated Ag, Pt, Cu and Ni nanoparticles were synthesized in the amorphous AlPO₄ based matrix. The metal nanoparticles were protected from oxidation up to very high temperatures due to the low oxygen diffusivity in AlPO₄ based matrix and carbon coating over the metal nanoparticles. The oxidation states of the Ag and Ni nanoparticles were detected with the help of X‐ray photoelectron spectroscopy. The synthesis technique followed very simple methodology. The entire processing including heat treatments at higher temperatures were carried out in oxidative atmosphere. The mechanism for the formation of metal particle in AlPO₄ based matrix has also been addressed. This approach can be a universal approach to achieve metal nanoparticles in AlPO₄ based matrix. Finally, catalyzing activities of the AlPO₄‐Cu nanocomposites in the oxidation of cyclohexane, AlPO₄‐Ni and AlPO₄‐Pt nanocomposites in the reduction in 4‐nitrophenol were successfully investigated.     

A computational and experimental study on the effective properties of Al2O3‐Ni composites

It has been demonstrated that effective medium approximation and mean field homogenization technique is a useful computational tool to predict the effective thermal and structural properties of alumina‐nickel (Al₂O₃‐Ni) composites. Nickel particle size and volume fraction, thermal interface resistance and porosity are found significant factors that affect thermal conductivity, elastoplastic behavior, elastic modulus and thermal expansion coefficient of Al₂O₃‐Ni composite. To complement the computational design, Al₂O₃‐Ni composite samples with designed range of volume fractions and nickel particle size are developed using spark plasma sintering process and properties are measured for model verification.     

Novel Ni/polypyrrole and Cu/polypyrrole composites prepared in the presence of different acids: Synthesis and investigation of thermal stability

We report the synthesis and characterization of new organic/inorganic hybrid materials constituted of Ni(0) and Cu(0) nanoparticles and polypyrrole (PPy). Copper and nickel nanoclusters were synthesized by a chemical reduction of aqueous metal salt solutions by sodium borohydride. PPy/Ni(0) and PPy/Cu(0) composites were obtained in the presence of two different acids (H₃BO₃, CH₃COOH), by polymerizing pyrrole‐Ni and pyrrole‐Cu particles by using iron (III) chloride. The composites have been characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and magnetic susceptibility techniques. Conductivity measurements of samples were taken using four‐probe devices. The PPy/Ni(0) and PPy/Cu(0) nanocomposites doped with different acids exhibited higher conductivity values than those of homopolymers. Among all samples, Ni/PPy‐H₃BO₃ has the highest conductivity (1.42 S cm^?1). Homopolymers and composites showed a stable and increasing conductivity with increasing temperature, except Ni(0). We observed that from TGA analysis of polymers, metal composites of PPy synthesized in two different media are more stable than those of PPy‐CH₃COOH and PPy‐H₃BO₃. The magnetic susceptibility values of homopolymers and Cu are negative, whereas the other samples are positive. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Atomic Scale Mechanisms of the Reduction of Nickel–Magnesium Aluminate Spinels

The dynamics of the reduction reaction of Ni_xMg_1?xAl₂O₄ to form nickel metal and a remnant oxide was quantified to understand spinel behavior in catalysis applications. X‐ray diffraction, thermogravimetry, and pycnometry were employed to track the evolution of high‐Ni spinels to metastable nonstiochiometric spinels during reduction, but before the phase transformation to theta alumina. Rietveld refinements of X‐ray diffraction data were used to quantify structural changes in the spinel and the phase fraction, crystallite size, and microstrain of all phases during H₂ reduction. During reduction, one O^2? is lost for each Ni²⁺ reduced to Ni metal. Ni_0.25Mg_0.75Al₂O₄ and Ni_0.5Mg_0.5Al₂O₄ were shown to form Ni metal and a non‐stoichiometric spinel of the same Mg‐Al ratio as the starting composition. NiAl₂O₄ and Ni_0.75Mg_0.25Al₂O₄ were found to become unstable as full reduction was approached, and metastable spinel, Θ‐Al₂O₃, and α‐Al₂O₃ formed sequentially given sufficient time at temperature.     

Preparation and electrical properties of ZnO‐Bi2O3‐based multilayer varistors with base metal nickel inner electrodes

In this study, ZnO‐Bi₂O₃‐based multilayer varistors (MLVs) cofired with nickel (Ni) inner electrodes were prepared by tape‐casting method. Samples were sintered in pure nitrogen (N₂) to keep Ni from being oxidized, and then reoxidized in air to obtain the nonlinear properties (reduction‐reoxidation method). The EDAX results showed that Ni inner electrodes are stable and have no evident migration into ZnO‐Bi₂O₃‐based ceramics when sintered in N₂. The influence of reoxidation temperature on microstructures and nonlinear properties of samples were studied. Samples reoxidized at the temperatures lower than 650°C showed poor nonlinear properties. After reoxidized in air at 700°C for 2 hours, samples exhibited nonlinear properties of V_1 mA=16.3 V, α=26.5, I_L=0.68 μA. At the reoxidation temperature higher than 750°C, the oxidation of Ni inner electrodes deteriorated the nonlinear properties of samples. It demonstrated that ZnO‐Bi₂O₃‐based MLVs with base metal Ni inner electrodes proposed in this work are suitable for reduction‐reoxidation method. The replacement of noble metals Pt or Ag/Pd alloys by base metal Ni is expected to lower the cost of ZnO‐Bi₂O₃‐based MLVs.     

Gas Recombination in Sealed Ni–MHx Cells

This paper focuses on investigation of gas recombination in a positive-limited-sealed Ni–MH_x cell. The positive electrodes were prepared by electrochemical impregnation of fibrous nickel plaques. The metal hydride negative electrodes were made by pasting the mixture of rare-earth hydrogen storage alloy powders, conducting and binding agents on foamed nickel substrates. The measurement of the positive capacity at different charge times was used to estimate the partial current for oxygen evolution at the same time. The effects of charge rate, electrolyte saturation level and initial state of charge of the positive electrodes on the recombination were investigated in sealed Ni–MH_x cells. By determining the differential capacity of nickel hydroxide electrodes, an improved mathematical model was used to evaluate the gas recombination parameters during charge, overcharge, rest and discharge of the positive-limited-sealed Ni–MH_x cell. The gas recombination during rest, discharge and overdischarge was also examined. The oxygen recombination on the nickel hydroxide electrodes can be neglected due to the consumption of water when the nickel hydroxide electrodes were discharged. The longer overdischarge produced an increase in cell pressure for the sealed Ni–MH_x cell at an electrolyte unsaturated level and the evolving gas can be recombined by a following recharge operation. © 1997 SCI.     

CO methanation toward the production of synthetic natural gas over highly active Ni/TiO2 catalyst

The sonochemical synthesis and characterization of highly active and stable Ni nanoparticles supported on TiO₂ as a CO methanation catalyst for the production of synthetic natural gas are reported. The catalyst synthesized by sonication showed higher activity for CH₄ formation than the catalyst synthesized via the conventional wet impregnation method. The activation energy was found to be 79 and 94 kJ mol^?1 for the catalyst synthesized with sonication and wet impregnation method, respectively. The combined results of x‐ray photoelectron spectroscopy and x‐ray diffraction show that the enhancement in activity of the sample synthesized by sonication method is due to partial substitution of Ni in TiO₂ lattice. This creates oxide vacancies and facilitates hydrogen adsorption and spillover from nickel to support. H₂‐ temperature‐programmed reduction study corroborates the intimate contact of Ni with support, thus rendering strong metal support interactions. The mechanism involving Langmuir–Hinshelwood kinetics with hydrogen‐assisted CO dissociation was used to correlate experimental data. © 2013 American Institute of Chemical Engineers AIChE J, 60: 1027–1035, 2014     

Mullite–Nickel Magnetic Nanocomposite Fibers Obtained from Electrospinning Followed by Thermal Reduction

Mullite–nickel nanocomposite fibers with Ni nanoparticles of controllable size, dispersion, and consequent magnetic properties were fabricated using sol–gel/electrospinning method, followed by thermal reduction. The fibers were electrospun from an aqueous solution containing sol–gel mullite precursor and nickel nitrate. These fibers were then heat treated in the reducing atmosphere between 550°C and 750°C to achieve fine‐dis persed metallic Ni nanoparticles (NPs). After the Ni²⁺ was reduced to Ni NPs at 750°C for 10 h, the fibers were then directly transformed to the mullite fibers at 1000°C without the undesirable intermediate spinel phase. In many high‐temperature applications, mullite is the desired phase than spinel. If not fully reduced, the Ni²⁺ cations induce early precipitation of spinel phase before mullite can be formed. This spinel phase was a solid solution between Al₂NiO₄ and Al‐Si spinels, which later reacted with the residual silica and formed a mixture of mullite and spinel at 1400°C. The formation of spinel phase was suppressed or fully eliminated with chemically reducing Ni²⁺ to metal NPs. The average size of nickel NPs within the fibers was ~20 nm, insensitive of the Ni concentration and reducing temperature. However, the Ni NPs on the fiber surface grew as large as ~80 nm due to fast surface diffusion. The magnetic nanocomposites exhibited ferromagnetism with saturation magnetization (M_s) close to pure nickel of the same nominal weight, but coercivity (H_c) much smaller than the bulk nickel, indicating the nature of bimodal magnetic nanoparticle distributions. The majority of small Ni NPs (~20 nm) within the fibers exhibited superparamagnetism, while the minor portion of relatively large NPs (50–80 nm) showed ferromagnetism.     

Studies on Energetic Compounds Part 27: Kinetics and Mechanism of Thermolysis of Bis(Ethylenediamine)Metal Nitrates and Their Role in the Burning Rate of Solid Propellants

Four bis(ethylenediamine)metal(II) nitrate (BEMN) complexes, i.e. [M(EDA)₂](NO₃)₂, where M=Cu, Co, Ni and Zn, have been prepared and characterized. Thermolysis of these complexes induced by heat and drop‐weight impact has been investigated by TG‐DTG, DTA, explosion delay (D_E), explosion temperature (T_E) and impact sensitivity measurement. The kinetics of early thermolysis reaction prior to fast decomposition have been evaluated. Contracting area (CA, n=2) and contracting cube (CC, n=3) equations were found to give the best fits in isothermal TG data among all tested nine mechanism‐based kinetic models. The values of activation energy (E_a), T_E, D_E and activation energy for explosion (E*) have been found to be quite lower for the copper complex as compared to cobalt, nickel and zinc complexes. A mechanism of thermolysis has also been proposed. All these complexes were found to be insensitive towards impact of 2 kg weight up to the height of 110 cm. These complexes were used as energetic burning rate modifiers in the combustion of hydroxy‐terminated polybutadiene (HTPB)‐ammonium perchlorate (AP) composite solid propellants. A two‐fold increase in burning rate was observed with copper and cobalt complexes at low concentration (2% by wt.). The in situ freshly formed metal oxides with large number of active sites in their crystallites seem to be better additives for combustion of propellants.