Peculiarities of DRX in a Highly-Alloyed Austenitic Stainless Steel

The features of discontinuous dynamic recrystallization (DRX) in a highly-alloyed austenitic stainless steel were studied at temperatures of 800 °C to 1100 °C. Hot deformation accompanied by DRX was characterized by an activation energy of 415 kJ/mol. The frequency of the sequential DRX cycles depended on the deformation conditions; and the largest fraction of DRX grains with small grain orientation spread below 1° was observed at a temperature of around 1000 °C and a strain rate of about 10⁻³ s⁻¹. The following power law relationships were obtained for DRX grain size (D_DRX) and dislocation density (ρ) vs. temperature-compensated strain rate (Z) or peak flow stress (σ_P): D_DRX ~ Z^−0.25, ρ ~ Z^0.1, σ_P ~ D_DRX^−0.9, σ_P ~ ρ^1.4. The latter, i.e., σ_P ~ ρ^1.4, was valid in the flow stress range below 300 MPa and changed to σ_P ~ ρ^0.5 on increasing the stress. The obtained dependencies suggest a unique power law function between the dislocation density and the DRX grain size with an exponent of −0.5.     

Synthesis,Crystal Structure and Luminescent Property of Mg(II) Complex with N-Benzenesulphonyl-L-Leucine and 1,10-Phenanthroline

A new complex [Mg(L)₂(phen)(H₂O)₂](phen)(H₂O)₂ [L= N-benzenesulphonyl-L-leucine] was synthesized by the reaction of magnesium chloride hexahydrate with N-benzenesulphonyl-L-leucine and 1,10-phenanthroline in the CH₃CH₂OH/H₂O (v:v = 5:1). It was characterized by elemental analysis, IR and X-ray single crystal diffraction analysis. The crystal of the title complex [Mg(L)₂(phen)(H₂O)₂](phen)(H₂O)₂ belongs to triclinic, space group P-1 with a = 0.72772(15) nm, b = 1.4279(3) nm, c = 1.4418(3) nm, α = 63.53(3)°, β = 79.75(3)°, γ = 81.83(3)°, V = 1.3163(5) nm³, Z =1, D_c= 1.258 μg·m⁻³, μ = 0.177 mm⁻¹, F(000) = 526, and final R₁ = 0.0506, ωR₂ = 0.1328. The complex comprises a six-coordinated magnesium(II) center, with a N₂O₄ distorted octahedron coordination environment. The molecules are connected by hydrogen bonds and π-π stacking to form one dimensional chain structure. The luminescent property of the Mg(II) complex has been investigated in solid.     

Nonlinear Optical Properties of Porphyrin,Fullerene and Ferrocene Hybrid Materials

In this research, we investigated the second-order nonlinear optical (NLO) properties of multicomponent hybrid materials formed by meso-tetraphenylporphyrin P (both as free base and Zn^II complex), carrying in 2 or 2,12 β-pyrrolic position an electron donor ferrocene (Fc), and/or an electron acceptor fullerene (C60) moiety, connected to the porphyrin core via an ethynyl or an ethynylphenyl spacer. We measured the NLO response by the electric-field-induced second-harmonic generation (EFISH) technique in CH₂Cl₂ solution with a 1907 nm incident wavelength, recording for all the investigated compounds unexpected negative values of μβ₁₉₀₇. Since density functional theory (DFT) calculations evidenced for P-Fc dyads almost null ground state dipole moments and very low values for P-C60 dyads and Fc-P-C60 triads, our EFISH results suggested a significant contribution to γ_EFISH of the purely electronic cubic term γ(−2ω; ω, ω, 0), which prevails on the quadratic dipolar orientational one μβ(−2ω; ω, ω)/5kT, as confirmed by computational evidence.     

Structure and Dielectric Behavior of Yb2O3-MgO Co-Doped 0.92BaTiO3-0.08(Na0.5Bi0.5)TiO3 Ferroelectric Relaxor

Dielectric properties and structure of 0.015Yb₂O₃-xMgO doped 0.92BaTiO₃-0.08(Na_0.5Bi_0.5)TiO₃ ceramics with x = 0.0–0.025 have been investigated. As Yb₂O₃-MgO was added into the BT-NBT, the phase changes from tetragonal to pseudo-cubic, with the tetragonality c/a decreases from 1.011 to 1.008 and XRD peaks broadened. The combined study of XRD and TEM image revealed a formation of core–shell structure in grains with core of 400–600 nm and the shell of a thickness 60–200 nm. There is a slowly phase transition against temperature from the variable temperature Raman analysis. The ferroelectric relaxor peak of BT-NBT decreases from ~4000 to ~2000 and a new broad dielectric peak with an equivalent maximum (ε_r′~2300) appears in the temperature dependent dielectric constant curve (ε_r′-T), which produces a flat ε_r′-T curve. Sample 0.92BaTiO₃-0.08(Na_0.5Bi_0.5)TiO₃-0.015Yb₂O₃-0.005 MgO and 0.92BaTiO₃-0.08(Na_0.5Bi_0.5)TiO₃-0.015Yb₂O₃-0.01MgO give a ε_r′ variation within ±14% and ±10% in 20–165 °C. The core–shell microstructure should take account for the flattened ε_r′–T behavior of these samples.     

Crystal and molecular structure of n,n'-diethyl-n,n'-diphenylurea

N,N′-diphenyl-N,N′-diethylurea (C₁₇H₂₀N₂O) crystallizes in the space group P2₁/c. The unit cell constants are: a = 10.42 ± 0.01 Å, b = 16.86 ± 0.02 Å, c = 10.66 ± 0.001 Å, β = 125°16′ ± 5′; Z = 4, D_x = 1.16 g·cm^-3, D_meas = 1.16 ± 0.01 g·cm^-3. Data for 1392 reflections were collected at room temperature on a Picker automated diffractometer. The crystal structure was solved by direct methods and refined by bloc-diagonalized matrix least-squares calculations. The molecule is characterized by a pseudo C₂ symmetry; both phenyl groups are trans with respect to the oxygen atom. The hybridization of the two nitrogen atoms is intermediate between trigonal and tetrahedral; the nonplanar distortion of the amide groups is about 30°. The amide C-N bond lengths are 1.37 Å.     

Synthesis,Crystal Structure and Luminescent Property of Cd (II) Complex with N-Benzenesulphonyl-L-leucine

A new trinuclear Cd (II) complex [Cd₃(L)₆(2,2-bipyridine)₃] [L = N-phenylsulfonyl-L-leucinato] has been synthesized and characterized by elemental analysis, IR and X-ray single crystal diffraction analysis. The results show that the complex belongs to the orthorhombic, space group P2₁2₁2₁ with a = 16.877(3) Å, b = 22.875(5) Å, c = 29.495(6) Å, α = β = γ = 90°, V = 11387(4) ų, Z = 4, D_c= 1.416 μg·m⁻³, μ = 0.737 mm⁻¹, F (000) = 4992, and final R₁ = 0.0390, ωR₂ = 0.0989. The complex comprises two seven-coordinated Cd (II) atoms, with a N₂O₅ distorted pengonal bipyramidal coordination environment and a six-coordinated Cd (II) atom, with a N₂O₄ distorted octahedral coordination environment. The molecules form one dimensional chain structure by the interaction of bridged carboxylato groups, hydrogen bonds and π-π interaction of 2,2-bipyridine. The luminescent properties of the Cd (II) complex and N-Benzenesulphonyl-L-leucine in solid and in CH₃OH solution also have been investigated.     

Dependence of Heat Transport in Solids on Length-Scale,Pressure, and Temperature: Implications for Mechanisms and Thermodynamics

Accurate laser-flash measurements of thermal diffusivity (D) of diverse bulk solids at moderate temperature (T), with thickness L of ~0.03 to 10 mm, reveal that D(T) = D_∞(T)[1 − exp(−bL)]. When L is several mm, D_∞(T) = FT^−G + HT, where F is constant, G is ~1 or 0, and H (for insulators) is ~0.001. The attenuation parameter b = 6.19D_∞^−0.477 at 298 K for electrical insulators, elements, and alloys. Dimensional analysis confirms that D → 0 as L → 0, which is consistent with heat diffusion, requiring a medium. Thermal conductivity (κ) behaves similarly, being proportional to D. Attenuation describing heat conduction signifies that light is the diffusing entity in solids. A radiative transfer model with 1 free parameter that represents a simplified absorption coefficient describes the complex form for κ(T) of solids, including its strong peak at cryogenic temperatures. Three parameters describe κ with a secondary peak and/or a high-T increase. The strong length dependence and experimental difficulties in diamond anvil studies have yielded problematic transport properties. Reliable low-pressure data on diverse thick samples reveal a new thermodynamic formula for specific heat (∂ln(c_P)/∂P = −linear compressibility), which leads to ∂ln(κ)/∂P = linear compressibility + ∂lnα/∂P, where α is thermal expansivity. These formulae support that heat conduction in solids equals diffusion of light down the thermal gradient, since changing P alters the space occupied by matter, but not by light.     

Molecular dynamics study displays near in-line attack conformations in the hammerhead ribozyme self-cleavage reaction

We have performed molecular dynamics (MD) calculations by using one of the recently solved crystal structures of a hammerhead ribozyme. By rotating the α, β, γ, δ, , and ζ torsion angles of the phosphate linkage of residue 17, the nucleobase at the cleavage site was slightly rotated out of the active site toward the solution. Unconstrained MD simulations exceeding 1 ns were performed on this starting structure solvated in water with explicit counter ions and two Mg²⁺ ions at the active site. Our results reveal that near attack conformations consistently were formed in the simulation. These near attack conformations are characterized by assumption of the 2′-hydroxyl to a near in-line position for attack on the -O-(PO₂⁻)-O- phosphorous. Also during the time course of the MD study, one Mg²⁺ moved immediately to associate with a pro-R phosphate oxygen in the conserved core region, and the second Mg²⁺ remained associated with the pro-R oxygen on the phosphate linkage undergoing hydrolysis. These results are in accord with a one-metal ion mechanism of catalysis and give insight into the possible roles of many of the conserved residues in the ribozyme.     

Spectroscopic identification and stability of the intermediate in the OH + HONO2 reaction

The reaction of nitric acid with the hydroxyl radical influences the residence time of HONO₂ in the lower atmosphere. Prior studies [Brown SS, Burkholder JB, Talukdar RK, Ravishankara AR (2001) J Phys Chem A 105:1605–1614] have revealed unusual kinetic behavior for this reaction, including a negative temperature dependence, a complex pressure dependence, and an overall reaction rate strongly affected by isotopic substitution. This behavior suggested that the reaction occurs through an intermediate, theoretically predicted to be a hydrogen-bonded OH–HONO₂ complex in a six-membered ring-like configuration. In this study, the intermediate is generated directly by the association of photolytically generated OH radicals with HONO₂ and stabilized in a pulsed supersonic expansion. Infrared action spectroscopy is used to identify the intermediate by the OH radical stretch (ν₁) and OH stretch of nitric acid (ν₂) in the OH–HONO₂ complex. Two vibrational features are attributed to OH–HONO₂: a rotationally structured ν₁ band at 3516.8 cm⁻¹ and an extensively broadened ν₂ feature at 3260 cm⁻¹, both shifted from their respective monomers. These same transitions are identified for OD–DONO₂. Assignments of the features are based on their vibrational frequencies, analysis of rotational band structure, and comparison with complementary high level ab initio calculations. In addition, the OH (v = 0) product state distributions resulting from ν₁ and ν₂ excitation are used to determine the binding energy of OH–HONO₂, D₀ ≤ 5.3 kcal·mol⁻¹, which is in good accord with ab initio predictions.     

Reductive Electropolymerization and Electrochromism of Iron(II) Complex with Styrene-Based Ligand

The benzimidazole-based ligand containing polymerizable styrene group has been prepared via condensation of picolinaldehyde derivative containing styrene moiety and benzimidazole-based hydrazine. The ligand reacted with iron(II) tetrafluoroborate and iron(II) trifluoromethanesulfonate giving red-brown complexes of Fe(II) ions of formula [FeL₂]X₂, where X = CF₃SO₃⁻ (1) or BF₄⁻ (2). Reductive electropolymerization was used to obtain a thin layer of the polymeric complex, poly-1. Further investigation of electrochemical properties of the compound by cyclic voltammetry showed two quasi-reversible redox processes assigned to electrooxidation and electroreduction of the polymer. Spectroelectrochemical measurements confirmed that the polymer undergoes the color changes during oxidation and reduction process. The polymer in its neutral state (Fe(II)) is yellow and it exhibits absorption band at 370 nm, after oxidation to Fe(III) state absorption band shifts to 350 nm and the polymer is almost colorless. While the metal ions are reduced to Fe(I) absorption band at around 410 nm has been observed and the polymer changed its color to intense yellow. The stability of the polymer during multiple oxidation/reduction cycles has also been investigated.     

Fe–Doped TiO2–Carbonized Medium–Density Fiberboard for Photodegradation of Methylene Blue under Visible Light

Fe–doped titanium dioxide–carbonized medium–density fiberboard (Fe/TiO₂–cMDF) was evaluated for the photodegradation of methylene blue (MB) under a Blue (450 nm) light emitting diode (LED) module (6 W) and commercial LED (450 nm + 570 nm) bulbs (8 W, 12 W). Adsorption under daylight/dark conditions (three cycles each) and photodegradation (five cycles) were separately conducted. Photodegradation under Blue LED followed pseudo-second-order kinetics while photodegradation under commercial LED bulbs followed pseudo-first-order kinetics. Photodegradation rate constants were corrected by subtracting the adsorption rate constant except on the Blue LED experiment due to their difference in kinetics. For 8 W LED, the rate constants remained consistent at ~11.0 × 10⁻³/h. For 12 W LED, the rate constant for the first cycle was found to have the fastest photodegradation performance at 41.4 × 10⁻³/h. After the first cycle, the rate constants for the second to fifth cycle remained consistent at ~28.5 × 10⁻³/h. The energy supplied by Blue LED or commercial LEDs was sufficient for the bandgap energy requirement of Fe/TiO₂–cMDF at 2.60 eV. Consequently, Fe/TiO₂–cMDF was considered as a potential wood-based composite for the continuous treatment of dye wastewater under visible light.     

The Effects of Zr Doping on the Optical,Electrical and Microstructural Properties of Thin ZnO Films Deposited by Atomic Layer Deposition

Transparent conducting oxides (TCOs), with high optical transparency (≥85%) and low electrical resistivity (10⁻⁴ Ω·cm) are used in a wide variety of commercial devices. There is growing interest in replacing conventional TCOs such as indium tin oxide with lower cost, earth abundant materials. In the current study, we dope Zr into thin ZnO films grown by atomic layer deposition (ALD) to target properties of an efficient TCO. The effects of doping (0–10 at.% Zr) were investigated for ~100 nm thick films and the effect of thickness on the properties was investigated for 50–250 nm thick films. The addition of Zr⁴⁺ ions acting as electron donors showed reduced resistivity (1.44 × 10⁻³ Ω·cm), increased carrier density (3.81 × 10²⁰ cm⁻³), and increased optical gap (3.5 eV) with 4.8 at.% doping. The increase of film thickness to 250 nm reduced the electron carrier/photon scattering leading to a further reduction of resistivity to 7.5 × 10⁻⁴ Ω·cm and an average optical transparency in the visible/near infrared (IR) range up to 91%. The improved n-type properties of ZnO: Zr films are promising for TCO applications after reaching the targets for high carrier density (>10²⁰ cm⁻³), low resistivity in the order of 10⁻⁴ Ω·cm and high optical transparency (≥85%).     

Phosphatidylinositol 4,5-bisphosphate (PIP2) stimulates the electrogenic Na/HCO3 cotransporter NBCe1-A expressed in Xenopus oocytes

Bicarbonate transporters are regulated by signaling molecules/ions such as protein kinases, ATP, and Ca²⁺. While phospholipids such as PIP₂ can stimulate Na-H exchanger activity, little is known about phospholipid regulation of bicarbonate transporters. We used the patch-clamp technique to study the function and regulation of heterologously expressed rat NBCe1-A in excised macropatches from Xenopus laevis oocytes. Exposing the cytosolic side of inside-out macropatches to a 5% CO₂/33 mM HCO₃⁻ solution elicited a mean inward current of 14 pA in 74% of macropatches attached to pipettes (−V_p = −60 mV) containing a low-Na⁺, nominally HCO₃⁻-free solution. The current was 80–90% smaller in the absence of Na⁺, approximately 75% smaller in the presence of 200 μM DIDS, and absent in macropatches from H₂O-injected oocytes. NBCe1-A currents exhibited time-dependent rundown that was inhibited by removing Mg²⁺ in the presence or absence of vanadate and F⁻ to reduce general phosphatase activity. Applying 5 or 10 μM PIP₂ (diC8) in the presence of HCO₃⁻ induced an inward current in 54% of macropatches from NBC-expressing, but not H₂O-injected oocytes. PIP₂-induced currents were HCO₃⁻-dependent and somewhat larger following more NBCe1-A rundown, 62% smaller in the absence of Na⁺, and 90% smaller in the presence of 200 μM DIDS. The polycation neomycin (250–500 μM) reduced the PIP₂-induced inward current by 69%; spermine (100 μM) reduced the current by 97%. Spermine, poly-D-lysine, and neomycin all reduced the baseline HCO₃⁻-induced inward currents by as much as 85%. In summary, PIP₂ stimulates NBCe1-A activity, and phosphoinositides are regulators of bicarbonate transporters.     

Linking the Electrical Conductivity and Non-Stoichiometry of Thin Film Ce1−xZrxO2−δ by a Resonant Nanobalance Approach

Bulk ceria-zirconia solid solutions (Ce_1−xZr_xO_2−δ, CZO) are highly suited for application as oxygen storage materials in automotive three-way catalytic converters (TWC) due to the high levels of achievable oxygen non-stoichiometry δ. In thin film CZO, the oxygen storage properties are expected to be further enhanced. The present study addresses this aspect. CZO thin films with 0 ≤ x ≤ 1 were investigated. A unique nano-thermogravimetric method for thin films that is based on the resonant nanobalance approach for high-temperature characterization of oxygen non-stoichiometry in CZO was implemented. The high-temperature electrical conductivity and the non-stoichiometry δ of CZO were measured under oxygen partial pressures pO₂ in the range of 10⁻²⁴–0.2 bar. Markedly enhanced reducibility and electronic conductivity of CeO₂-ZrO₂ as compared to CeO_2−δ and ZrO₂ were observed. A comparison of temperature- and pO₂-dependences of the non-stoichiometry of thin films with literature data for bulk Ce_1−xZr_xO_2−δ shows enhanced reducibility in the former. The maximum conductivity was found for Ce_0.8Zr_0.2O_2−δ, whereas Ce_0.5Zr_0.5O_2-δ showed the highest non-stoichiometry, yielding δ = 0.16 at 900 °C and pO₂ of 10⁻¹⁴ bar. The defect interactions in Ce_1−xZr_xO_2−δ are analyzed in the framework of defect models for ceria and zirconia.     

Influence of Cu Content on Structure,Thermal Stability and Magnetic Properties in Fe72−xNi8Nb4CuxSi2B14 Alloys

The effect of substitution of Fe by Cu on the crystal structure and magnetic properties of Fe_72−xNi₈Nb₄Cu_xSi₂B₁₄ alloys (x = 0.6, 1.1, 1.6 at.%) in the form of ribbons was investigated. The chemical composition of the materials was established on the basis of the calculated minima of thermodynamic parameters: Gibbs free energy of amorphous phase formation ΔG^amorph (minimum at 0.6 at.% of Cu) and Gibbs free energy of mixing ΔG^mix (minimum at 1.6 at.% of Cu). The characteristic crystallization temperatures T_x1onset and T_x1 of the alpha-iron phase together with the activation energy E_a for the as-spun samples were determined by differential scanning calorimetry (DSC) with a heating rate of 10–100 °C/min. In order to determine the optimal soft magnetic properties, the wound cores were subjected to a controlled isothermal annealing process in the temperature range of 340–640 °C for 20 min. Coercivity Hc, saturation induction Bs and core power losses at B = 1 T and frequency f = 50 Hz P_10/50 were determined for all samples. Moreover, for the samples with the lowest Hc and P_10/50, the magnetic losses were determined in a wider frequency range 50 Hz–400 kHz. The real and imaginary parts of the magnetic permeability µ′, µ″ along with the cut-off frequency were determined for the samples annealed at 360, 460, and 560 °C. The best soft magnetic properties (i.e., the lowest value of Hc and P_10/50) were observed for samples annealed at 460 °C, with Hc = 4.88–5.69 A/m, Bs = 1.18–1.24 T, P_10/50 = 0.072–0.084 W/kg, µ′ = 8350–10,630 and cutoff frequency at 8–9.3 × 10⁴ Hz. The structural study of as-spun and annealed ribbons was carried out using X-ray diffraction (XRD) and a transmission electron microscope (TEM).     

Spectroscopic sensitivity of linear-benzoadenine nucleotides to divalent metal counterions, side chain conformations, micelles, and enzymes

From pK_a data for lin-benzoadenosine 5′-mono-, 5′-di-, and 5′-triphosphates, which are fluorescent “stretched-out” analogues of adenine nucleotides, it was possible to designate the cases of interaction of phosphate with the heteroaromatic moiety. The addition of divalent metal cations or quaternary ammonium micelles diminishes the direct intramolecular interaction between the phosphate(s) and base and consequently brings the pK_a values close to that of lin-benzoadenosine. Fluorescence spectroscopy was used to investigate the interaction of lin-benzoadenine nucleotides with Mg²⁺, Mn²⁺, and Co²⁺. The association constants for the formation of such complexes were obtained from measurements of steady-state fluorescence quenching. Phase and modulation measurements of the fluorescence lifetimes of lin-benzoadenine nucleotides as a function of Co²⁺ concentration permitted determination of the static component of the quenching due to intramolecular complex formation. The association constants of the lin-benzoadenine nucleotides with all of the divalent metal ions studied were greater than those observed for the corresponding adenine nucleotides and were in the order: lin-benzo-ATP > lin-benzo-ADP > lin-benzo-AMP. Fourier transform ¹H NMR of lin-benzo-ATP in the presence of Co²⁺ showed broadening of the aromatic proton signals, the 2-H signal (corresponding to the 8-H in ATP) being the most affected. Models are proposed to explain the phosphate-base interaction, the influence of metal ions on base protonation, and the intramo- the intramolecular quenching observed in the complexes due to paramagnetic ion (Co²⁺, Mn²⁺) and base interaction.     

Fast events in protein folding: Relaxation dynamics of secondary and tertiary structure in native apomyoglobin

We report the fast relaxation dynamics of “native” apomyoglobin (pH 5.3) following a 10-ns, laser-induced temperature jump. The structural dynamics are probed using time-resolved infrared spectroscopy. The infrared kinetics monitored within the amide I absorbance of the polypeptide backbone exhibit two distinct relaxation phases which have different spectral signatures and occur on very different time scales (ν = 1633 cm⁻¹, τ = 48 ns; ν = 1650 cm⁻¹, τ = 132 μs). We assign these two spectral components to discrete substructures in the protein: helical structure that is solvated (1633 cm⁻¹) and native helix that is protected from solvation by interhelix tertiary interactions (1650 cm⁻¹). Folding rate coefficients inferred from the observed relaxations at 60°C are k_f(solvated) = (7 to 20) × 10⁶ s⁻¹ and k_f(native) = 3.6 × 10³ s⁻¹, respectively. The faster rate is interpreted as the intrinsic rate of solvated helix formation, whereas the slower rate is interpreted as the rate of formation of tertiary contacts that determine a native helix. Thus, at 60°C helix formation precedes the formation of tertiary structure by over three orders of magnitude in this protein. Furthermore, the distinct thermodynamics and kinetics observed for the apomyoglobin substructures suggest that they fold independently, or quasi-independently. The observation of inhomogeneous folding for apomyoglobin is remarkable, given the relatively small size and structural simplicity of this protein.