Effects of salicylate derivate on the competing reaction of chromium(III) complex [Cr(III)(R-SA)(en)2]Cl with apoovotransferrin

Four novel Cr(III) complexes, Bis(ethylenediamine-κ²N,N′)(R-SA-κ²O,O′)chromium(III) chloride (H₂SA = salicylic acid, R = 5-F, 5-Cl, 5-Br, 4-CH₃ ethylenediamine = en) have been synthesized and three of them are determined by X-ray crystallography. The competition reaction with EDTA and apoovotransferrin (apoOTf) was monitored by UV–Visible (UV–vis) and fluorescence spectra at 37 °C. The reaction with EDTA is only a simple competitive process and no specific selectivity was observed (k_EDTA/F410 = 4.07 × 10^?3–4.37 × 10^?3 M^?1 s^? 1). While for the reaction with apoOTf, an instable intermediate species (R-SA)–Cr(III)–OTf forms (k_OTf/F336 = 1.70 × 10^? 1–2.08 × 10^?1 M^?1 s^? 1), where R-SA^2? act as the role of synergistic anion. The intermediate is instable and the R-SA^2? ligand will then be released with the rate constants of 1.17 × 10^? 1 (5-F-SA^2?) ≈ 1.01 × 10^? 1 (4-CH₃-SA^2?) > 3.19 × 10^? 2 (5-Cl-SA^2?) > 3.25 × 10^? 3 (5-Br-SA^2?) M^?1 s^? 1. The substitutive groups R on SA have positive influence on charge density of O donor atom, which directly affect the stability of the (R-SA)–Cr(III)–OTf intermediate.     

The synthesis,cyclic voltammetry and spectroelectrochemical studies of Co(II) phthalocyanines tetra-substituted at the α and β positions with phenylthio groups

Non-peripherally substituted cobalt 1,(4)-(tetraphenylthiophthalocyaninato) and peripherally substituted cobalt 2,(3)-(tetraphenylthiophthalocyaninato) complexes were synthesized. Redox processes were observed at E_1/2 = ?1.44 V (I), ?0.39 V (II), +0.37 V (III), +0.78 V (IV) and 1.15 V (V) for the non-peripherally substituted and at E_1/2 = ?1.42 V (I), ?0.57, ?0.39 V (II), +0.27 V (III), +0.79 V (IV) and +1.10 V (V) for the peripherally substituted complexes, respectively. The couples were assigned to Co^IPc^?2/Co^IPc^?3 (I), Co^IIPc^?2/Co^IPc^?2 (II), Co^IIIPc^?2/Co^IIPc^?2 (III), and Co^IIIPc^?1/Co^IIIPc^?2 (IV) using spectroelectrochemistry. The last process (V) could not be ascertained by spectroelectrochemistry but is associated with ring oxidation. Upon reduction or oxidation, the Q band of the non-peripherally substituted complex became less red shifted compared to that of its peripherally substituted counterpart.     

Thermal expansion of EB-PVD yttria stabilized zirconia

Yttria stabilized zirconia (YSZ) layers, suited for thermal barrier coatings (TBCs) in turbine engines, were produced by electron-beam physical vapour deposition (EB-PVD) on metallic (Ni-based alloys) ceramic (Al₂O₃) substrates (typically at 1000 °C) using ingot compositions of about 4 mol% Y₂O₃–ZrO₂. Employing powdered samples, removed from the surface of the as-deposited YSZ layers, precision X-ray diffraction data sets were recorded between 60 and 900 °C and the lattice parameters of the metastable, tetragonal (t′) and the cubic (c) phases were refined using Rietveld's method. It was unambiguously verified that phase (c) was present in all investigated samples as a minority phase already in the as-deposited state.The thermal expansion coefficients of the tetragonal phase (t′) (α₁₁ = 9.3(2) × 10^?6 K^?1, α₃₃ = 10.8(1) × 10^?6 K^?1) and the cubic phase (c) (α₁₁ = 8.5(2) × 10^?6 K^?1) were evaluated from the refined temperature dependent lattice parameter values of this study, and turned out to be close to each other, but significantly different from the coefficient of the monoclinic phase (m) (α₁₁ = 9.0 × 10^?6 K^?1, α₂₂ = 1.2 × 10^?6 K^?1, α₃₃ = 11.9 × 10^?6 K^?1, α₁₃ = 0.0 × 10^?6 K^?1), which was derived from temperature dependent lattice parameter measurements published by Touloukian et al.⁵ The expansion coefficient of the monoclinic phase (m) exhibited a very pronounced anisotropy in contrast to the tetragonal phases (t′) and (t). Our values for (t′) and (c) were in excellent agreement with that of other tetragonal and cubic phases from the literature with quite different Y₂O₃ contents.     

A self-healing polymer network based on reversible covalent bonding

A self-healing polymer network for potential coating applications was designed based on the concept of the reversible Diels–Alder (DA) reaction between a furan functionalized compound and a bismaleimide. The network allows local mobility in a temperature window from ca. 80 °C to 120 °C by shifting the DA equilibrium towards the initial building blocks. Changing the spacer length in the furan functionalized compound leads to tailor-made properties. Elastomeric model systems were chosen to evaluate the kinetic parameters by Fourier transform infrared spectroscopy. For the DA reaction a pre-exponential factor ln(A_DA in kg mol^?1 s^?1) equal to 13.1 ± 0.8 and an activation energy (E_DA) of 55.7 ± 2.3 kJ mol^?1 are found. For the retro-DA reaction, ln(A_rDA) and E_rDA are 25.8 ± 1.8 s^?1 and 94.2 ± 4.8 kJ mol^?1, respectively. The enthalpy and entropy of reaction are calculated as ?38.6 kJ mol^?1 and ?105.3 J mol^?1 K^?1. The kinetic results are validated by micro-calorimetry. Non-isothermal dynamic rheometry provides the gel-point temperature of the reversible network. The sealing capacity is evaluated by atomic force microscopy for micro-meter sized defects. Repeatability of the non-autonomous healing is checked by micro-calorimetry, ruling out side-reactions below 120 °C.     

Physical properties of carbon nanotube sheets drawn from nanotube arrays

We report mechanical, thermal, and electrical properties of novel sheet materials composed of multiwalled carbon nanotubes, drawn from a CNT array. At low loading there is some slippage of CNTs but at higher loading tensile strength σ₀ = 7.9 MPa and Young’s modulus E = 310 MPa. The room-temperature thermal conductivity of the CNT sheet was 2.5 ± 0.5 W m^?1 K^?1, giving a thermal conductivity to density ratio of κ/ρ = 65 W m^?1 K^?1 g^?1 cm³. The heat capacity shows 1D behavior for T > 40 K, and 2D or 3D behavior at lower temperatures. The room-temperature specific heat was 0.83 J g^?1 K^?1. The iV curves above 10 K have Ohmic behavior while the iV curve at T = 2 K is non-Ohmic, and a model to explain both ranges is presented. Negative magnetoresistance was found, increasing in magnitude with decreasing temperature (?15% at T = 2 K and B = 9 T). The tensile strength, Young’s modulus and electrical conductivity of the CNT sheet are low, in comparison with other CNT materials, likely due to defects. Thermal conductivity is dominantly phononic but interfacial resistance between MWCNTs prevents the thermal conductivity from being higher.     

Theoretical investigation of mechanical and thermal properties of MPO4 (M = Al,Ga)

Minimum lattice thermal conductivities and mechanical properties of polymorphous MPO₄ (M = Al, Ga) are investigated by first principles calculations. The theoretical minimum thermal conductivities are found to be 1.02 W (m K)^?1 for α-AlPO₄, 1.20 W (m K)^?1 for β-AlPO₄, 0.87 W (m K)^?1 for α-GaPO₄ and 0.88 W (m K)^?1 for β-GaPO₄. The lower thermal conductivities in comparison to YSZ can be attributed to the lattice phonon scattering due to the framework of heterogeneous bonds. In addition, the low shear-to-bulk modulus ratio for both β-AlPO₄ (0.38) and β-GaPO₄ (0.30) is observed. Our results suggest their applications as light-weight thermal insulator and damage-tolerant/machinable ceramics.     

Preparation and application of epoxy–chitosan/alginate support in the immobilization of microbial lipases by covalent attachment

The aim of this work was the preparation and application of highly hydrophobic epoxy–chitosan/alginate as a support to immobilize microbial lipases from Thermomyces lanuginosus commercially available as Lipolase® (TLL1) and Lipex® 100L (TLL2) and Pseudomonas fluorescens (PFL). The catalytic properties of the biocatalysts were assayed in olive oil hydrolysis and butyl butyrate synthesis. The results indicated that 12 h was enough for TLL1 to be immobilized on the support. Covalent attachment of TLL1 turned biocatalysts highly active and around 6-fold more stable than free lipase. Based on the results, a time of incubation of 24 h was selected for further studies about the maximum immobilized protein amount and butyl butyrate synthesis. Maximum protein loading immobilized was found to be 25.4 mg g^?1 support for TLL1, followed by TLL2 (20.5 mg g^?1) and PFL (15.5 mg g^?1) offering 80 mg protein g^?1 support. The immobilization of TLL1 and TLL2 resulted in highly active biocatalysts (around 1300 IU g^?1 gel), almost fivefold higher than PFL (272.4 IU g^?1 gel). In butyl butyrate synthesis, PFL showed similar activity to TLL1 and TLL2 derivatives, up to 60 mmol L^?1. The biocatalysts displayed high activity after five successive cycles, retaining around 95% of the initial activity.     

High-temperature compressive creep of spark-plasma sintered additive-free polycrystalline β-SiC

The high temperature mechanical behaviour of additive-free nano-size power of β-SiC sintered by spark-plasma sintering (SPS) technique has been studied. Samples had a mean grain size of 0.58 μm and 97.4% of relative density. They were deformed by means of constant load compression (creep) tests at temperatures between 1750 and 1850 °C and stresses between 200 and 500 MPa. The strain rates ranged from 1 × 10^?7 s^?1 to 1 × 10^?6 s^?1 depending on the test conditions. The activation energy Q and the stress exponent n parameters, which characterize the deformation mechanisms, were evaluated. The values obtained for the activation energy Q in the whole temperature range was 540 kJ mol^?1, and the stress exponent n values were between 1.2 and 1.3 for T = 1750 °C and 2.6 for T = 1800 °C. The values of these parameters, together with the results of microscopy of the deformed samples, suggested that there are two mechanisms operating simultaneously: (i) grain boundary sliding (GBS) accommodated by diffusion of Si along the grain boundary and (ii) dislocation glide and climb (power law creep (PLC)). The contribution of the latter mechanism increases with temperature.     

Effects of mechanical milling on preparation and properties of CuAl1−xFexO2 thermoelectric ceramics

CuAl_1?xFe_xO₂ (x = 0, 0.1, and 0.2) thermoelectric ceramics produced by a reaction-sintering process were investigated. Pure CuAlO₂ and CuAl_0.9Fe_0.1O₂ were obtained. Minor CuAl₂O₄ phase formed in CuAl_0.8Fe_0.2O₂. Addition of 10 mol% Fe lowered the sintering temperature obviously and enhanced the grain growth. At x = 0.1, electrical conductivity = 3.143 Ω^?1 cm^?1, Seebeck coefficient = 418 μV K^?1, and power factor = 5.49 × 10^?5 W m^?1 K^?2 at 600 °C were obtained. The reaction-sintering process is simple and effective in preparing CuAlO₂ and CuAl_0.9Fe_0.1O₂ thermoelectric ceramics for applications at high temperatures.     

Impactor designed to increase mass output rate of nanoparticles from a pneumatic nebulizer

A modular impactor was designed to remove large droplets from aerosols generated by a pneumatic nebulizer, the Six-Jet Atomizer from TSI Inc. (Shoreview, MN), with the aim of generating dry nanoparticles. Three interchangeable nozzle heads were designed to provide droplet cutoff diameters of 0.5, 1, and 2 μm at an air flow rate of 8.3×10^?4 m³ s^?1 (50 L min^?1), which corresponds to all six jets of the nebulizer operated at 25 °C and an air pressure of 241 kPa (35 psi). The collection and output characteristics of the 0.5 μm impactor were evaluated from dry particle size distributions produced by nebulizing an aqueous solution with a NaCl mass fraction of 1% both with and without the impactor present. The impactor characteristic cutoff curve was sharp (impactor geometric standard deviation, GSD_imp=1.15–1.19) with a 50% cutoff diameter d₅₀ that ranged from 0.48 μm at 3.0×10^?4 m³ s^?1 to 0.74 μm at 11.7×10^?4 m³ s^?1. The rate of dry NaCl particle generation ranged from 0.5 to 5 g s^?1 (0.04 to 0.4 g day^?1) with mass median diameters MMD_p=80–123 nm and geometric standard deviations GSD_p=1.6–1.8 (depending on flow rate). Anomalous negative impactor efficiencies were observed at flow rates >8.3×10^?4 m³ s^?1 for 100 to 400 nm droplets and at all flow rates for droplets smaller than 100 nm. This phenomenon will be investigated further as a way to increase the generation rate of nanoparticles. A step-by-step procedure is presented for the selection of an appropriate impactor design and operating flow rate for a desired maximum aerosol particle size.     

Synthesis and characterization of molecularly imprinted polymers with metallic zinc center for enrofloxacin recognition

A molecularly imprinted polymer with a metallic center (MIPc) was prepared and characterized. The template molecule for MIPc was a complex [Zn(Aza-f)(Enr)]NO₃?H₂O, Com, based on the ligands: enrofloxacin (Enr) and azabis(oxazoline) functionalized with styrene. Com was characterized before preparing MIPc. Moreover, the polymer prepared via non-covalent (MIPe) was prepared using Enr as the template molecule while no template molecules were used to prepare the non-imprinted polymer (NIP).MIPc was characterized using different spectroscopic techniques. In addition, the polymer molecular recognition capacity was studied by using rebinding kinetic studies. The kinetics shows that MIPc reach the equilibrium before the MIPe and NIP and the amount of Enr adsorbed is approximately 5 times higher that MIPe and NIP.Scatchard plots analysis for NIP, MIPe and MIPc shows K_d = 0.4768, 0.020, 0.0067 (mmol L^?1) respectively. In comparison with the MIPe the binding affinity is nearly 100 times higher taking into account the high affinity sites. The selectivity of MIPc for Enr was higher than that for ofloxacin or flumequin, isotherms were fit to the Langmuir–Freundlich model, and the Enr showed a value of K_o = 21.38 mM^?1, while the ofloxacin had a value of 2.2 × 10^?8 mM^?1 and the flumequin of 1.6 × 10^?5 mM^?1.     

Tuning the selectivity for ring-opening reactions of methylcyclopentane over Pt catalysts: A mechanistic study from first-principles calculations

Using density functional calculations, we studied the conversion of methylcyclopentane to its ring-opening products: branched hexanes [2-methylpentane (2MP), 3-methylpentane (3MP)], as well as unbranched n-hexane (nHx). We employed flat Pt(1 1 1) and stepped Pt(2 1 1) to describe terrace-rich large and defect-rich small Pt particles, respectively. On Pt(1 1 1), the barriers of all elementary steps for the paths leading to branched hexanes lie below 90 kJ mol^?1, while the formation of nHx features a barrier of 116 kJ mol^?1 in its C–C bond scission step. This higher barrier impedes the formation of nHx on Pt(1 1 1) and thus rationalizes the experimental observations that terrace-rich large Pt particles selectively produce branched hexanes. However, on Pt(2 1 1), the barrier of C–C scission for the formation of nHx decreases to 94 kJ mol^?1, thus implying enhanced formation of nHx over the defects, in agreement with the essentially statistical product distribution observed with defect-rich small Pt particles.     

Electrochemical characterization of tenoxicam using a bare carbon paste electrode under stagnant and forced convection conditions

From potentiostatic current transients and voltammetry studies, carried out under both stagnant and forced convection conditions, the tenoxicam electrochemical behavior on a bare carbon paste rotating disk electrode was assessed in an aqueous solution (pH = 0.403). It was found that tenoxicam's electrochemical oxidation is a mass transfer-controlled process where a current peak is clearly formed at around 0.74 V when the potential scan was varied in the positive direction. However, when the potential was switched to the negative direction, up to the initial potential value, no reduction peak was formed. Tenoxicam's electrochemical oxidation follows an EC mechanism where the electrodic and chemical kinetics are fast. From sample-current voltammetry both the number of electrons, n, that tenoxicam losses during its electro-oxidation and its half-wave potential, E_1/2, were determined to be 2 and 0.770 V vs. Ag/AgCl, respectively. Moreover, from differential pulse voltammetry plots it was confirmed that effectively in this case n = 2. Considering 2 electrons and both the Randles-Sevcik and Cotrell equations, the tenoxicam's diffusion coefficient, D, was determined to be (3.745 ± 0.077) × 10^?6 and (4.116 ± 0.086) × 10^?6 cm² s^?1, respectively. From linear sweep voltammetry plots recorded under forced convection conditions, it was found that Levich's equation describes adequately the limiting current recorded as a function of the electrode rotation rate, from where the D value was also found to be (4.396 ± 0.058) × 10^?6 cm² s^?1. Therefore, the average D value was (4.09 ± 0.33) × 10^?6 cm² s^?1. Furthermore, from the radius of the tenoxicam molecule, previously optimized at M052X/6-31 + G(d,p) level of theory, and using the Stokes–Einstein approach, D was also estimated to be 4.54 × 10^?6 cm² s^?1 which is similar to the experimentally estimated values, under both stagnant and forced convection hydrodynamic conditions.     

Use and recycling of Ca-alginate biocatalyst for removal of phenol from wastewater

The objective of the current work is the exhaustive study of the phenol degradation potential in both free cell and immobilized bacterium (Pseudomonas aeruginosa) in calcium alginate beads (biocatalyst) was investigated for its ability to grow and degrade phenol as its sole source of carbon and energy.The biodegradation assays were performed in liquid medium with phenol being the only substrate. It was found that P. aeruginosa is able to degrade phenol up to 500 mg L^?1 in 50 h as free cell and 900 mg L^?1 in 80 h when immobilized in the calcium alginate beads. However, for 1200 mg L^?1 concentration, the immobilized cells took much more time (290 h) for a complete degradation.The reuse of these beads in different concentrations of phenol (100–900 mg L^?1) showed that the cells keep their phenol degradation ability up to 900 mg L^?1in 78.5 h with 99% removal efficiency.Similarly, the reuse of the biocatalyst in the same initial phenol concentration (500 mg L^?1), allows us to get 9 cycles.     

Electrodeposited hybrid films of polyaniline and manganese oxide in nanofibrous structures for electrochemical supercapacitor

Hybrid films of polyaniline (PANI) and manganese oxide (MnO_x) were obtained through potentiodynamic deposition from solutions of aniline and MnSO₄ at pH 5.6. The hybrid films demonstrated characteristic redox behaviors of PANI in acidic aqueous solution. Characterization of the hybrid films by XRD indicated the amorphous nature of MnO_x in the films in which manganese existed in oxidation states of +2, +3 and +4, based on XPS measurement. Hybrid film of PANI and MnO_x, PM120 obtained from the solution of 0.1 M aniline and 120 mM Mn²⁺ displayed a well opened nanofibrous structure which showed an 44% increase in specific capacitance from that of PANI (408 F g^?1) to 588 F g^?1, measured at 1.0 mA cm^?2 in 1 M NaNO₃ (pH 1). The hybrid film kept more than 90% of its capacitance after 1000 charging-discharging cycles, with a coulombic efficiency of 98%. The specific capacitance of a symmetric capacitor using PM120 as the electrodes is 112 F g^?1.     

Adsorption of chromate and para-nitrochlorobenzene on inorganic–organic montmorillonite

Batch studies of chromate and para-nitrochlorobenzene (p-NCB) on montmorillonite modified by poly(hydroxo aluminium) ions (Al) and cetyl trimethylammonium bromide (CTMAB) are reported. The amounts adsorbed decreased in the order Al-CTMA-mont > CTMA-mont > Al-mont > montmorillonite. Adsorption of chromate on Al-CTMA-mont reached a maximum at pH = 4 while p-NCB was pH independent. The adsorption kinetics could be described by the pseudo-second-order model. The adsorption rates for chromate and p-NCB were 9.73 and 5.78 mg g^? 1 min^? 1, respectively. The adsorption capacity of chromate and p-NCB on Al-CTMA-mont calculated by the Langmuir model was 2.3 × 10^? 4 and 2.2 × 10^? 4 mol/g, the values of the adsorption energy of the Dubinin-Radushkevitch (D-R) model were 13.9 and 7.8 kJ/mol. These results implied that the chromate adsorption proceeded as chemisorption, mainly by ion exchange whereas p-NCB was bound by van der Waals forces.     

Flow injection analysis of free glycerol in biodiesel using a copper electrode as an amperometric detector

The main goal of this work was to develop a simple analytical method for quantification of glycerol based on the electrocatalytic oxidation of glycerol on the copper surface adapted in a flow injection system. Under optimal experimental conditions, the peak current response increases linearly with glycerol concentration over the range 60–3200 mg kg^?1 (equivalent to 3–160 mg L^?1 in solution). The repeatability of the electrode response in the flow injection analysis (FIA) configuration was evaluated as 5% (n = 10), and the detection limit of the method was estimated to be 5 mg kg^?1 in biodiesel (equivalent to 250 μg L^?1 in solution) (S/N = 3). The sample throughput under optimised conditions was estimated to be 90 h^?1. Different types of biodiesel samples (B100), as in the types of vegetable oils or animal fats used to produce the fuels, were analysed (seven samples). The only sample pre-treatment used was an extraction of glycerol from the biodiesel sample containing a ratio of 5 mL of water to 250 mg of biodiesel. The proposed method improves the analytical parameters obtained by other electroanalytical methods for quantification of glycerol in biodiesel samples, and its accuracy was evaluated using a spike-and-recovery assay, where all the biodiesel samples used obtained admissible values according to the Association of Official Analytical Chemists.     

Kinetic studies of the oxidation of quercetin,rutin and taxifolin in the basic medium by (ethylenediaminetetraacetato) cobalt(III) complex

The quercetin in 0.01 M NaOH solution underwent steady oxidation when it was exposed to air with the formation of the quinone product. For the taxifolin and rutin, the oxidation occurred only when the solutions were saturated with O₂, but very slowly. The kinetics of the oxidation of flavonoids in 0.01 M NaOH solution by Co(edta)^? complex was carried out and the rate constants are 3.44 × 10², 1.04 × 10^? 1 and 1.46 × 10^? 2 M^? 1 s^? 1 for quercetin, rutin and taxifolin, respectively, at μ = 0.10 M LiClO₄. The deprotonation of the C₃ hydroxyl group and the conjugation between pyrone and catechol rings account for the reactivity of quercetin.