Sugar response of boronic acid-substituted azobenzene dye-modified polymer

We synthesized a boronic acid-appended azobenzene dye (BA) and attached it to poly(ethyleneimine) (polyBA) for studying its sugar response. The addition of d-glucose induced a significant change in the UV–visible absorption spectra of the polyBA solution. The binding constants for d-glucose (K_glu) and d-fructose (K_fru) were calculated to be 54 M^? 1 and 110 M^? 1, respectively. The selectivity for d-glucose was higher in polyBA as compared with that of monomeric BA (K_glu = 1.2 M^? 1, K_fru = 17 M^? 1). We also fabricated multilayered films composed of polyBA and polyanions {poly(vinyl sulfate) (PVS), carboxymethylcellulose (CMC)} using a layer-by-layer deposition technique. In (PVS/polyBA)₁₀ films, the affinity for d-glucose was relatively low (K_glu = 1.7 M^? 1, K_fru = 28 M^? 1). In contrast, (CMC/polyBA)₅ films showed a high affinity for d-glucose (K_glu = 18 M^? 1, K_fru = 42 M^? 1). The loosely packed structure of the (CMC/polyBA)₅ film and the suitable chemical structures of CMC probably led to a high affinity for d-glucose.     

Preparation and characterization of copper nanoparticles/zinc oxide composite modified electrode and its application to glucose sensing

We report a new method for selective detection of d(+)-glucose using a copper nanoparticles (Cu-NPs) attached zinc oxide (ZnO) film coated electrode. The ZnO and Cu-NPs were electrochemically deposited onto indium tin oxide (ITO) coated glass electrode and glassy carbon electrode (GCE) by layer-by-layer. In result, Cu-NPs/ZnO composite film topography was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. SEM and AFM confirmed the presence of nanometer sized Cu-NPs/ZnO composite particles on the electrode surface. In addition, X-ray diffraction pattern revealed that Cu-NPs and ZnO films were attached onto the electrode surface. Indeed, the Cu-NPs/ZnO composite modified electrode showed excellent electrocatalytic activity for glucose oxidation in alkaline (0.1 M NaOH) solution. Further, we utilized the Cu-NPs/ZnO composite modified electrode as an electrochemical sensor for detection of glucose. This glucose sensor showed a linear relationship in the range from 1 × 10^? 6 M to 1.53 × 10^? 3 M and the detection limit (S/N = 3) was found to be 2 × 10^? 7 M. The Cu-NPs/ZnO composite as a non-enzymatic glucose sensor presents a number of attractive features such as high sensitivity, stability, reproducibility, selectivity and fast response. The applicability of the proposed method to the determination of glucose in human urine samples was demonstrated with satisfactory results.     

New quaternary alkali metal,rare earth (3+) thiophosphate,K2SmP2S7 with both [P2S6]4− and [PS4]3− anions

A new quaternary alkali metal, rare earth thiophosphate was synthesized by the ceramic method and characterized by single crystal X-ray diffraction: K₂SmP₂S₇ crystallizes in the monoclinic space group C2 (no. 5) with the unit cell parameters a = 22.746(5) Å, b = 6.7362(13) Å, c = 8.9004(18) Å, β = 99.68(3)°, V = 1344.3(5) Å³ and Z = 2. The phase K₂SmP₂S₇ can be better described as K₄Sm₂[PS₄]₂[P₂S₆] because it contains in the crystal structure both discrete anions [PS₄]^3? and [P₂S₆]^4?. The crystal structure consists of infinite chains of ¹_∞[SmPS₄] that are linked together through the ethane-like [P₂S₆]^4? anions to form two-dimensional layers. The packing of K₂SmP₂S₇ is formed by layers of ²_∞[Sm₂[PS₄]₂[P₂S₆]]^4? separated by K⁺ cations. K₂SmP₂S₇ was characterized by Raman and Fourier transform infrared (FTIR) spectroscopy and SEM-EDX microprobe analyses. The optical band gap of K₂SmP₂S₇ was determined by UV–vis diffuse reflectance measurements to be 2.59 eV.     

An innovative process to fabricate copper/diamond composite films for thermal management applications

Diamond dispersed copper matrix (Cu/D) composite films with strong interfacial bonding were produced by tape casting and hot pressing without carbide forming additives. The tape casting process offers an original solution to obtain laminated materials with accurate thickness control, smooth surface finish, material net-shaping, scalability, and low cost. This study presents an innovative process of copper submicronic particles deposition onto diamond reinforcements prior to densification by hot pressing. Copper particles act as chemical bonding agents between the copper matrix and the diamond reinforcements during hot pressing, thus offering an alternative solution to traditionnal carbide-forming materials in order to get efficient interfacial bonding and heat-transfer in Cu/D composites. It allows high thermal performances with low content of diamond, thus enhancing the cost-effectiveness of the materials. Microstructural study of composites by scanning electron microscopy (SEM) was correlated with thermal conductivity and thermal expansion coefficient measurements. The as-fabricated films exhibit a thermal conductivity of 455 W m^?1 K^?1 associated to a coefficient of thermal expansion of 12 × 10^?6 °C^?1 and a density of 6.6 g cm^?3 with a diamond volume fraction of 40%, which represents a strong enhancement relative to pure copper properties (λ_Cu = 400 W m^?1 K^?1, α_Cu = 17 × 10^?6 °C^?1, ρ_Cu = 8.95 g cm^?3). The as-fabricated composite films might be useful as heat-spreading layers for thermal management of power electronic modules.     

Flux growth and thermal properties of LiBaB9O15 single crystal

A large LiBaB₉O₁₅ single crystal has been grown by the top-seeded solution growth (TSSG) method using a Li₂Mo₃O₁₀ flux system. The crystal obtained exhibits (1 1 0), (1 1 3) and (1 0 2) faces. For the first time, thermal properties of the as-grown crystal, including thermal expansion, specific heat and thermal conductivity, have been investigated as a function of temperature. The specific heat of the LiBaB₉O₁₅ crystal was measured to be 0.663–1.110 J g^?1 K^?1 over the temperature range of 20–400 °C. The crystal exhibits thermal expansion along the a- and b-axis, coupled with thermal contraction along the c-axis, over the measured temperature range of 25–500 °C. The average thermal expansion coefficients along the a- and c-axis of the LiBaB₉O₁₅ crystal from 25 to 500 °C are calculated to be α_a = 6.56 × 10^?6 K^?1 and α_c = ?4.82 × 10^?6 K^?1, respectively.     

Thermal conductivity and Kapitza resistance of cyanate ester epoxy mix and tri-functional epoxy electrical insulations at superfluid helium temperature

In the framework of the European Union FP7 project EuCARD, two composite insulation systems made of cyanate ester epoxy mix and tri-functional epoxy (TGPAP-DETDA) with S-glass fiber have been thermally tested as possible candidates to be the electrical insulation of 13 T Nb₃Sn high field magnets under development for this program. Since it is expected to be operated in pressurized superfluid helium at 1.9 K and 1 atm, the thermal conductivity and the Kapitza resistance are the most important input parameters for the thermal design of this type of magnet and have been determined in this study. For determining these thermal properties, three sheets of each material with different thicknesses varying from 245 to 598 μm have been tested in steady-state condition in the temperature range of 1.6–2.0 K. The thermal conductivity for the tri-functional epoxy (TGPAP-DETDA) epoxy resin insulation is found to be k = [(34.2 ± 5.5)?T ? (16.4 ± 8.2)] × 10^?3 Wm^?1 K^?1 and for the cyanate ester epoxy k = [(26.8 ± 4.8)?T ? (9.6 ± 5.2)] × 10^?3 Wm^?1 K^?1. For the Kapitza resistance, R_k, the best curve fitting the experimental data is described by R_k = (3057 ± 593) × 10^?6?T (?1.79 ± 0.34) m² KW^?1 for the TGPAP-DETDA insulation and R_k = (4114 ± 971) × 10^?6?T (?1.73 ± 0.41) m² KW^?1 for the cyanate ester epoxy insulation. Our results are compared with other epoxy based composite electrical insulation found in the literature.     

Electrochemical oxidation of adenosine-5′-triphosphate on a chitosan–graphene composite modified carbon ionic liquid electrode and its determination

In this paper a new electrochemical method was proposed for the determination of adenosine-5′-triphosphate (ATP) based on a chitosan (CTS) and graphene (GR) composite film modified carbon ionic liquid electrode (CTS–GR/CILE). CILE was fabricated by using ionic liquid 1-butyl-3-methylimidazolium dihydrogen phosphate ([BMIM]H₂PO₄) as the binder, which was further modified by GR and CTS composite. The modified electrode exhibited an excellent electrocatalytic activity toward the oxidation of ATP with the increase of the oxidation peak current and the decrease of the oxidation peak potential. The electrochemical parameters of ATP on CTS–GR/CILE were calculated with the electron transfer coefficient (α) as 0.329, the electron transfer number (n) as 2.15, the apparent heterogeneous electron transfer rate constant (ks) as 3.705 × 10^? 5 s^? 1 and the surface coverage (Γ_T) as 9.33 × 10^? 10 mol cm^? 2. Under the optimal conditions the oxidation peak current was proportional to ATP concentration in the range from 1.0 × 10^? 6 to 1.0 × 10^? 3 M with the detection limit of 0.311 μM (S/N = 3). The proposed electrode showed excellent reproducibility, stability, anti-interference ability and further successfully applied to the ATP injection sample detection.     

Beneficial effect of minor Al substitution on the magnetocaloric effect of Mn1 − xAlxAs

Magnetocaloric effect near room temperature is enhanced by minor Al substitution in Mn_1 ? xAl_xAs compounds (x = 0, 0.015, 0.03). The Curie temperature and magnetic entropy change can be tuned by Al concentration. Under a field change of 2 T, which is below the critical field of metamagnetic transition and easy to reach in applications, a large reversible magnetic entropy change 28.5 J kg^? 1 K^? 1, and a huge magnetic entropy change 65.7 J kg^? 1 K^? 1 under a field change of 5 T is obtained at x = 0.015 near room temperature. Compared with that of MnAs mother alloy, it is concluded that minor Al substitution is beneficial for enhancing the magnetic entropy in Mn_1 ? xAl_xAs alloys.     

Site-specific Eu(III) binding affinities to a Datura innoxia biosorbent

The binding of Eu(III) to a biosorbent derived from cultured cells of the plant Datura innoxia, have been investigated through elucidation of apparent affinity constants associated with different chemical environments present on the cell wall. Adsorption isotherms for separate types of binding sites were generated using metal ion luminescence measurements. Application of regularized regression analysis to these isotherm data for four chemically distinguishable sites revealed the presence of sites exhibiting both low (mean log K_app = ?0.3 to 0.6) and higher (mean log K_app = 3.2–3.5) apparent affinities for pH conditions of 2.0, 4.0, and 5.0. Low affinity sites were observed for all pH conditions and attributed to non-specific binding of the metal ions to the negatively charged biomaterial. The pH-dependent higher affinity sites are ascribed to specific sites involving either an ion-exchange mechanism or formation of weak surface–metal ion complexes. These results differed significantly from a similar analysis of total metal binding isotherms that indicated mean log K_app values of ?0.5 to 0.25 (low affinity) and 5.6–6.0 (high affinity).     

Shock propagation in a tape wrapped carbon fibre composite

The use of carbon fibre composites has become more prevalent in recent years. As such, detailed knowledge of the material behaviour over a range of conditions is needed. In particular, knowledge of the high strain rate response is desirable. The shock response of a tape wrapped carbon fibre composite of density 1.46 g cm^?3 has been determined using both lateral and longitudinal Manganin stress gauges. The U_S ? u_p Hugoniot was found to be U_S = 3.69 + 0.59u_p. Deviation from the Hugoniot was observed in the P–V/V₀ plane for impact stresses above 5 GPa. Further, use of lateral gauges allowed the Hugoniot elastic limit to be estimated; this was found to be approximately 1.53 GPa, comparable to other composite materials. In addition, oscillations were observed in multiple traces, and found to be a function of the thickness of the carbon fibre weave.     

Preparation,crystal structure and characterization of α-NaSbP2S6 and β-NaSbP2S6 phases

The new phases α-NaSbP₂S₆ and β-NaSbP₂S₆ were synthesized by ceramic and reactive flux methods at 773 K. The structures of α-NaSbP₂S₆ and β-NaSbP₂S₆ were determined by the single-crystal X-ray diffraction technique. α-NaSbP₂S₆ crystallizes in the monoclinic space group P2₁/c with a = 11.231(2) Å, b = 7.2807(15) Å, c = 11.640(2) Å, β = 108.99(3)°, V = 900.0(3) Å³ and z = 4. β-NaSbP₂S₆ crystallizes in the monoclinic space group P2₁ with a = 6.6167(13) Å, b = 7.3993(15) Å, c = 9.895(2) Å, β = 92.12(3) °, V = 484.10(17) Å³ and z = 2.The α- and β-phases of NaSbP₂S₆ are closely related, the main difference lies in the stacking of the [Sb[P₂S₆]]_nⁿ⁻ layers. The structure of α-NaSbP₂S₆ consists of two condensed layers (MPS₃ type) to give an ABAB… sequence with Na⁺ cations located in the interlayer space. The packing of β-NaSbP₂S₆ is formed by monolayers of [Sb[P₂S₆]]_nⁿ⁻ stacked in an AA… fashion separated by a layer of Na⁺ cations. Both phases are derivates of the M¹⁺M³⁺P₂Q₆ family.The optical band gaps of α-NaSbP₂S₆ and β-NaSbP₂S₆ were determined by UV–vis diffuse reflectance measurements to be 2.17 and 2.25 eV, respectively.     

Both initial concentrations of Fe(II) and monovalent cations jointly determine the formation of biogenic iron hydroxysulfate precipitates in acidic sulfate-rich environments

In order to accurately predict the types of biogenic iron hydroxysulfate precipitates in acidic, sulfate-rich environments facilitated by Acidithiobacillus ferrooxidans, different initial concentrations of Fe^2 +, K⁺, Na⁺, and NH₄⁺ are selected and tested in batch experiments for the formation of the precipitates. The critical equations of jarosite formation in FeSO₄–K₂SO₄–H₂O system or FeSO₄–(NH₄)₂SO₄–H₂O system could be described as Y = ? 22120.8077 ? 0.04257x + 0.006170x² (R² = 0.9979) or Y = 0.03540 ? 0.002950x + 7.407E ? 5x² (R² = 0.9934), respectively, where Y is the threshold or critical values of the molar ratio of Fe/K or Fe/NH₄ for jarosite formation, and x (mmol/L) is the initial concentration of Fe(II). Schwertmannite is the sole biogenic secondary ferric mineral when molar ratio of Fe/K or Fe/NH₄ is higher than Y in the system with a given initial Fe(II) concentration. The precipitates are an admixture of schwertmannite and jarosite, or pure jarosite when the Fe/M molar ratio is lower than Y. The crystallinity of the secondary ferric minerals increased with the increase of initial Fe(II) concentration in the medium with a fixed K⁺ concentration. It is observed that the capacity of monovalent cation in promoting jarosite formation is K⁺ > NH₄⁺ > Na⁺, as exhibiting that the capacity of K⁺ in this process is about 75 and 200 times greater than NH₄⁺ and Na⁺, respectively. Obviously, both the initial concentration of Fe(II) and molar ratio of Fe to monovalent cation determine the types of biogenic iron hydroxysulfate precipitates.     

EPR and optical absorption studies of Cr3+ doped lithium potassium sulphate single crystals

X-band electron paramagnetic resonance (EPR) studies of Cr³⁺ doped lithium potassium sulphate single crystals have been done at room temperature. The Cr³⁺ crystal field and spin Hamiltonian parameters have been evaluated by employing resonance line positions observed in the EPR spectra for different orientations of external magnetic field. The evaluated g, D and E values are: g_x = 2.0763 ± 0.0002, g_y = 1.9878 ± 0.0002, g_z = 1.8685 ± 0.0002 and D = 549 ± 2 × 10^?4 cm^?1, E = 183 ± 2 × 10^?4 cm^?1. Using EPR data the site symmetry of Cr³⁺ ion in the crystal is discussed. Cr³⁺ ion enters the lattice substitutionally replacing K⁺ site. The optical absorption study of the single crystal is also done in 195–925 nm wavelength range at room temperature. By correlating optical and EPR data the nature of bonding in the crystal is discussed. The calculated values of Racah parameters (B and C), crystal field parameter (D_q) and nephelauxetic parameters (h and k) are obtained as: B = 697, C = 3247, D_q = 2050 cm^?1, h = 1.146 and k = 0.21.     

Development of amperometric laccase biosensor through immobilizing enzyme in copper-containing ordered mesoporous carbon (Cu-OMC)/chitosan matrix

A functionalized copper-containing ordered mesoporous carbon (Cu-OMC) which shows good electrical properties was synthesized by carbonization of sucrose in the presence of cupric acetate inside SBA-15 mesoporous silica template. Based on this, a facilely fabricated amperometric biosensor by entrapping laccase into the Cu-OMC/chitosan (CS) film was developed. Laccase from Trametes versicolor was assembled on a composite film of Cu-OMC/chitosan (CS) modified Au electrode and the electrode was characterized. The optimum experimental conditions of biosensor for the detection of catechol were studied in details. Under the optimal conditions, the detection limit was 0.67 μM and the linear detection range was from 0.67 μM to 15.75 μM for catechol. The apparent Michaelis–Menten (K_M^app) was estimated using the Lineweaver–Burk equation and the K_M^app value was 40.2 μM. This work demonstrated that the Cu-OMC/CS composite provides a suitable support for laccase immobilization and construction of biosensor.     

Above room temperature magnetocaloric effect in perovskite Pr0.6Sr0.4MnO3

The dependence of magnetization M on the applied magnetic field H and temperature T was measured carefully, near the Curie temperature T_C for the perovskite manganite sample Pr_0.6Sr_0.4MnO₃. The experimental results indicate that this specimen exhibit ferromagnetic (FM) to paramagnetic (PM) transition at T_C ~ 320 K. In the 200 K–45 K temperature range the spontaneous magnetization was decreasing, probably due to spin canted state between manganese and praseodymium spin systems. At 46 K the magnetization presents a second little transition, which can be ascribed to very weak traces of secondary Mn₃O₄ phase, and remains constant between 10 K and 46 K. The maximum value of the magnetic entropy change obtained from the M(H) plot data is |ΔS_M^max| = 2.3 Jkg^? 1 K^? 1 for applied magnetic field of 2.5 T. At this value of magnetic field the relative cooling power (RCP) is 34.5 Jkg^? 1. The temperature corresponding to ΔS_M maximum value is almost equal to T_C. The large entropy change can be attributed to the fact that the ferromagnetic transition enhances the effect of the applied magnetic field greatly. It is suggested by the results that this compound can be used as the working material in an active magnetic regenerative refrigerator above room temperature.     

Structure and magnetism in Pr3RuO7

The crystal structure of the ordered fluorite, Pr₃RuO₇, was refined from powder neutron diffraction data in Cmcm. An interesting structural feature is the presence of relatively well separated zig-zag chains of corner sharing RuO₆ octahedra, Ru–Ru interchain distance 6.61 Å vs. Ru–Ru intrachain distance of 3.76 Å. Magnetic susceptibility data show a Curie–Weiss behavior for T>225 K with C=5.96(4) emu K mol⁻¹ and θ_c=+11(2) K. In an attempt to separate the contributions of Pr(3+) and Ru(5+), the properties of isostructural Pr₃TaO₇ were also measured, yielding C=4.63(3) emu K mol⁻¹. Thus, the contribution of Ru(5+), 4d³, S=3/2, to the measured Curie constant is estimated to be 1.33 emu K mol⁻¹, not far from the spin-only value of 1.87 emu K mol⁻¹. This supports the view that the Ru 4d electrons are localized and magnetic, not itinerant. A susceptibility maximum at about 50 K is attributed to long-range magnetic order and this is substantiated by neutron diffraction data. There is little evidence for one-dimensional antiferromagnetic correlations in this material but behavior characteristic of short-range ferromagnetic correlations attributed to Pr–Ru exchange interactions are found in the temperature range 50–200 K, consistent with the positive θ_c.     

Acetylcholinesterase voltammetric biosensors based on carbon nanostructure-chitosan composite material for organophosphate pesticides

A sensitive biosensor for chloropyrifos (CPF), an organophosphorus pesticide, was developed by immobilizing acetylcholinesterase (AChE) through covalent bonding to an oxidized exfoliated graphite nanoplatelet (xGnPs)–chitosan cross-linked composite. Because of the increased surface area and the conductive properties of the nanomaterial, AChE developed a high affinity for acetylthiocholine (ATCI) and formed thiocholine with a fast response. The response of the sensor was a linear function of ATCI concentration in two segments, one from 0.005 to 0.039 mM and the second from 0.064 mM to 0.258 mM. The corresponding equation for the first range was i_p(A) = 2.26 × 10^? 5c + 4.39 × 10^? 7 (R² = 0.992) and the equation for the second was i_p(A) = 6.80 × 10^? 6c + 1.30 × 10^? 6 (R² = 1.000), with a detection limit of 1.58 × 10^? 10 M. The fabrication of the sensor was simple, the response was fast and the stability acceptable. This sensor has many potential applications, the foremost being in organophosphorus pesticides.     

Synthesis and electrical conductivity of La0.6Sr0.4Ru1−xMgxO3−δ (x = 0–0.6) perovskite solid solution

Sr and Mg were doped at La- and Ru-sites of perovskite oxide LaRuO₃, respectively, to enhance electrical conductivity and catalytic property as a cathode material for a low temperature solid oxide fuel cell. Crystal structure and particle morphology of La_0.6Sr_0.4Ru_1?xMg_xO_3?δ powders (shorten as LSRM) and electrical conductivity of sintered LSRM were studied. LSRM powders (x = 0–0.6) were prepared by co-precipitation method using metal nitrate solutions and ammonium carbonate solution. The freeze-dried powders were heated at 1273 K in air to form LSRM solid solution of orthorhombic structure. The true densities and particle sizes of LSRM solid solution, where valence of Ru was estimated to be 3+, decreased with increasing Mg content. The electrical conductivity of LSRM at x = 0–0.3 was almost independent of temperature and was in a range of 19–360 S cm^?1 at 1073 K. Hole conduction contributed to the high electrical conductivities. LSRM at x = 0.4 and 0.5 was a mixed conductor of oxide ions and holes, and showed a conductivity of 11 S cm^?1 at 1073 K in air. This conductivity decreased at a lower oxygen pressure and reached a constant value below 10 Pa of oxygen pressure.     

Influence of defects on fatigue strength and failure mechanisms in the VHCF-region for quenched and tempered steel and nodular cast iron

Investigations are presented in this paper on quenched and tempered steel 42CrMoS4 from two batches, with two different tensile strengths (R_m = 1100 MPa, 1350 MPa) but with similar microstructure, and a nodular cast iron EN-GJS-900-2 (R_m = 930 MPa). Fatigue tests with smooth (K_t = 1) and notched (K_t = 1.75) specimens were performed at R = −1 and R = 0 up to the number of cycles N = 2·10⁹ in order to determine the fatigue strength behaviour and failure mechanisms, especially in the VHCF-region. Failure in smooth specimens often initiated at material defects such as oxides in the quenched and tempered steel and shrinkage holes in the nodular cast iron. Firstly, a fatigue strength analysis was performed that did not consider these defects. A possibility of analysis of experimental data including VHCF-results has been discussed. Next, a linear elastic fracture mechanics analysis was performed in order to describe the defect behaviour, assuming that the defects act like cracks. The results showed that there are lower limit or threshold values of the stress intensity factor range ΔK for crack propagation in both materials. Analysis of defects and defect distribution in run-out specimens confirmed this conclusion. From the comparison of the results with an S–N curve from the design code FKM-Guideline Analytical strength assessment of components, recommendations for design and assessment of components have been derived.     

Synthesis of tellurium nanowires and their transport property

By using Na₂TeO₃ and Na₂S₂O₃ as starting materials, tellurium nanowires with diameter around 25 nm were synthesized via a hydrothermal reaction at 160 °C, X-ray diffraction (XRD) showed that the product was a pure trigonal phase and TEM image indicated the widths of nanowires were in the range of 10–40 nm. Through further high-resolution TEM (HRTEM) analysis, a preferential growth direction along the [0 0 1] zone axis was observed. The intrinsic structure of tellurium, as well as the directing role of PVP leading to the formation of the 1D nanostructure was briefly discussed. Field effect transistor from individual nanowire was constructed, the nanowire device revealed a pronounced gating effect, and yield a threshold voltage of 40 V, an on–off ratio as high as 10³_, and a mobility of 163 cm² V^?1 S^?1 at V_ds = ?0.1 V.