Solid-state stability studies of faropenem based on chromatography,spectroscopy and theoretical analysis

Aim: The purpose of this study was to investigate the stability of faropenem in solid state.

Results: The kinetic and thermodynamic parameters of degradation of faropenem were studied using an RP-HPLC method while the changes of spectral properties were investigated using derivative UV and FT-IR. Quantum-chemical calculations, based on the density functional theory, were carried out to support the estimation of the intra-ring stresses of faropenem and for theoretical interpretation of the spectra. The degradation of faropenem was a first-order reaction depending on the substrate concentration at an increased relative humidity and in dry air. The dependence ln k = f(1/T) became the ln k?=?(2.03?±?3.22)?×?10⁴–(9761?±?3052)(1/T) in dry air and ln k?=?(1.25?±?0.22)?×?10⁵–(9004?±?3479)(1/T?) at 90.0% RH. The thermodynamic parameters E_a, ΔH^≠a, and ΔS^≠a of the degradation of faropenem were calculated. The dependence ln k?=?f(RH%) assumed the form ln k?=?(7.58?±?1.88)?×?10^?2 (RH%) – (5.90?±?3.90)?×?10^?8.

Conclusions: Stability studies of faropenem showed that the fusion of β-lactam and thiazolidine rings reduces the intra-ring stress, leading to a lower susceptibility to degradation in dry air and at increased RH.     

Crystal structure and negative thermal expansion of solid solution Yb2W3-xMoxO12

Abstract

A new series of solid solutions Yb₂W_3-xMo_xO₁₂ (0.5 ≤ x ≤ 2.5) were successfully synthesized by the high-temperature solid state method. Their crystal structure and negative thermal expansion properties were studied using high-temperature X-ray powder diffraction and the Rietveld method. All samples of rare earth tungstates and molybdates were found to crystallize in the same orthorhombic structure with space group Pnca, and show the negative thermal expansion phenomena related to transverse vibration of bridging oxygen atoms in the structure. Thermal expansion coefficients (TEC) of Yb₂W_3-xMo_xO₁₂ were determined as ?18.3×10^?6 K^?1 for x = 0.5 and ?19.6×10^?6 K^?1 for x = 2.5 comparing to ?19.1×10^?6 K^?1 and ?18.3×10^?6 K^?1 for unsubstituted Yb₂W₃O₁₂ and Yb₂Mo₃O₁₂ in the identical temperature range of 200–800°C. High temperature X-ray diffraction data and bond length analysis suggest that the difference between W—O and Mo—O bond is responsible for the change of TECs after the element substitution in this series of solid solutions.     

FATIGUE CRACK GROWTH IN D16T A1-ALLOY SHEET SUBJECTED TO BIAXIAL OUT-OF-PHASE LOADING

Abstract— Fractographic peculiarities of fatigue crack development are studied in cruciform specimens of D16T aluminium alloy under out-of-phase biaxial tension and tension-compression. In the range of the biaxial load ratios λ from ?0.5 to +0.5 and an R-ratio of 0.3, fatigue striation formation took place beyond a crack growth rate near to 4 × 10^?8 m/cycle. The striation spacing and the crack growth rate increase as the φ-angle of the out-of-phase biaxial loads increases in the range of φ-angles from 0° to 180°. The ratio between the increment of crack growth, da/dN, and the striation spacing, δ, is approximately 1 to 1 when da/dN is greater than 4 × 10^?8 m/cycle. The relationship between the number of cycles from the beginning of a test up to the growth rate of 10^?6 m/cycle (N_d), and the crack growth period, N_P, from when the crack initiates up to the instant when that growth rate is reached, was determined for different λ ratios and φ angles. The value of N_d decreases as the φ angle is increased in the range from 0° to 1807deg;. Cycle loading parameters must be taken into account in order to describe the crack growth period when using a unified method that involves an equivalent stress intensity factor K_e=K_IF₁(λ, R)F₂(φ). The values of F₂(φ) were determined. The calculated fatigue crack growth period, N_c, applicable up to and including the stage of fatigue striation formation (predicted by using both of the F₁(λ, R) and F₂(φ) functions) is correlated with the experimental data and the error is of the order of 15%.     

Role of diffusion-annealing temperature on the microstructural and superconducting properties of Cu-doped MgB2 superconductors

This study deals with not only investigate the effect of the copper diffusion on the microstructural and superconducting properties of MgB₂ superconducting samples employing dc resistivity as a function of temperature, scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements but also calculate the diffusion coefficient and the activation energy of copper for the first time. Electrical-resistivity measurements indicate that both the room-temperature resistivity value and zero resistivity transition temperatures (T _c ) increase with increasing the diffusion-annealing temperature from 650 to 850?°C. SEM measurements show that not only the surface morphology and grain connectivity improve but also the grain size of the samples increases with the increase in the diffusion-annealing temperature up to 850?°C. As for the XRD results, all the samples contain the MgB₂ phase only and exhibit the polycrystalline superconducting phase with more intensity of diffraction lines, leading to the increasement in the lattice parameter a and c. Additionally, the diffusion coefficient is observed to increase from 6.81?×?10^?8 to 4.69?×?10^?7?cm²?s^?1 as the diffusion-annealing temperature increases, confirming that the Cu diffusion at lower temperatures is much less significant. Temperature dependence of the Cu diffusion coefficient is described with the aid of the Arrhenius relation D?=?3.75?×?10^?3 exp (?1.15?±?0.10?eV/k _B T) and the corresponding activation energy of copper in MgB₂ system is found to be about 1.15?eV. The possible reasons for the observed improvement in microstructural and superconducting properties of the samples due to Cu diffusion are also discussed.     

A Novel Fullerene Hydroxamic Acid for the Liquid–Liquid Extraction,Separation, Preconcentration,and Spectrophotometric and ICP‐AES Determination of Vanadium

Abstract

A new reagent N‐phenyl‐(1,2 methanofullerene C₆₀)61‐formohydroxamic acid (PMFFA) is reported for extraction and trace determination of vanadium(V) in nutritional and biological substrates. The extraction mechanism of vanadium from 6 M HCl media is investigated. The influence of PMFFA, diverse ions, and temperature on the distribution constant of vanadium examined. The over all stability constant (log β₂ K _e ) and extraction constant (K _ex) are 20.89 ± 0.02 and 8.0 ± 0.02 × 10^?15, respectively in chloroform. The thermodynamics parameters are calculated and kinetics of vanadium transport is discussed. The system obeys Beer's law in the range of 3.2–64.0 ng mL^?1 of vanadium(V). The molar absorptivity is 7.96 × 10⁵ L mol^?1 cm^?1, at 510 nm. The PMFFA–vanadium(V) complex chloroform extract in chloroform was directly inserted into plasma for ICP‐AES measurement, which increases the sensitivity by 50 folds and obey Beer's law in the range of 50–1200 pg mL^?1 of vanadium(V). The method is applied for determination vanadium in real standard samples, sea water, and environmental samples.     

Plutonium dioxide catalyzed reaction between H<Subscript>2</Subscript> and O<Subscript>2</Subscript>

The kinetic characteristics of the reaction between H₂ and O₂ were calculated to more adequately simulate the radiolysis of water adsorbed on PuO₂. The rate constants of this reaction were determined via comparison of the calculated results with the published experimental data. It was found that, with the amount of the adsorbed water increasing from 2 × 10^?4 to 5 × 10^?3%, the rate constant of the reaction decreases from 6.0 × 10^?4 to 1.7 × 10^?5 mol^?1 s^?1. At the water content over 5 × 10^?3%, the rate constant is ≤1 × 10^?5 mol^?1 s^?1. A new mathematical model of the radiation-chemical and physicochemical processes occurring in the PuO₂-H₂O system was presented; the amounts of hydrogen and oxygen yielded by α-radiolysis of the adsorbed water were calculated, taking into account the reaction between H₂ and O₂.     

Predictive models for drugs exhibiting negative food effects based on their biopharmaceutical characteristics

Context: A drug is defined to exhibit food effects if its pharmacokinetic parameter, area under the curve (AUC_0–∞) is different when co-administered with food in comparison with its administration on a fasted stomach. Food effects of drugs administered in immediate release dosage forms were classified as positive, negative, and no food effects.

Objective: In this study, predictive models for negative food effects of drugs that are stable in the gastrointestinal tract and do not complex with Ca²⁺ are reported.

Methods: An empirical model was developed using five drugs exhibiting negative food effects and seven drugs exhibiting no food effects by multiple regression analysis, based on biopharmaceutical properties generated from in vitro experiments. An oral absorption model was adopted for simulating negative food effects of model compounds using in situ rat intestinal permeability.

Results: Analysis of selected model drugs indicated that percent food effects correlated to their dissociation constant, K (K_a or K_b) and Caco-2 permeabilities. The obtained predictive equation was: Food effect (%)?=?(2.60?×?10⁵·P_app) ? (2.91?×?10⁵·K) ? 8.50. Applying the oral absorption model, the predicted food effects matched the trends of published negative food effects when the two experimental pH conditions of fed and fasted state intestinal environment were used.

Conclusion: A predictive model for negative food effects based on the correlation of food effects with dissociation constant and Caco-2 permeability was established and simulations of food effects using rat intestinal permeability supported the drugs’ published negative food effects. Thus, an empirical and a mechanistic model as potential tools for predicting negative food effects are reported.     

Improvement of electrical properties and thermal conductivity of ethylene propylene diene monomer (EPDM)/barium titanate (BaTiO<Subscript>3</Subscript>) by carbon blacks and carbon fibers

The aim of the study was to use carbon fibers and carbon blacks to improve the thermal conductivity, mechanical and dielectric properties of ethylene propylene diene monomer (EPDM)/barium titanate (BaTiO₃) composites. It was found that 7.5 vol% carbon blacks, with high specific surface area, can make complex viscosity of EPDM/BaTiO₃ compound to become non-sensitive to varying shear. Due to the sulfuric atom and C=C groups on surface of carbon blacks, 10 vol% carbon blacks can enhance the tensile strength and tear strength of EPDM/BaTiO₃ (70/30) from 9.00 MPa and 21.06 kN m^?1 to 14.32 MPa (59% increase) and 30.02 kN m^?1 (43% increase). It was found that the 10 vol% spherical carbon blacks with high specific area can partially contact BaTiO₃ and fill the gap between BaTiO₃ particles to increase thermal conductivity and dielectric constant of EPDM/BaTiO₃(70/30) from 0.323 W m^?1 K^?1and 7 at 5 MHz to 0.632 W m^?1 K^?1 (95% increase) and 746 (106 times increase) at 5 MHz, respectively. When the filler content was 10 vol%, carbon blacks and carbon fibers can decrease the volume resistivity of EPDM/BaTiO₃ (70/30) from 2.23?×?10¹³ to 6.37?×?10⁵ Ω m (eight order of magnitude drop) and 4.25?×?10¹¹ Ω m (two order of magnitude drop), respectively.     

A simple and sensitive method for determination of vitamins D3 and K1 in rat plasma: application for an in vivo pharmacokinetic study

Purpose: To develop and to validate a simple but sensitive method for determination of vitamins D₃ and K₁ in rat plasma.

Methods: The sample treatment included protein precipitation by cold acetonitrile, evaporation, reconstitution with methanol and filtration. The chromatography conditions included Xterra RP18 3.5?µm 4.6?×?100?mm column at ambient temperature and mobile phase consisting of methanol/water (93/7, v/v) at 0.5?mL/min flow rate. Vitamin D₃ and probucol were detected at 265?nm and vitamin K₁ at 239?nm. Rats were administered intravenously by 0.1?mg/kg of vitamin D₃ or K₁ and the blood samples were withdrawn pre-administration and at pre-determined time points post-administration. The pharmacokinetic analysis was performed using a non-compartmental approach.

Results: The calibration curves in rat plasma were linear up to 5000?ng/mL for both vitamins. The limit of quantification (LOQ) was 20?ng/mL for vitamin D₃ and 40?ng/mL for K₁. Inter- and intra-day precision and accuracy were below 15%. The pharmacokinetic parameters of vitamin D₃ following intravenous administration were: AUC_0?∞?=?11323?±?1081?h?×?ng/mL, V_d?=?218?±?80?mL/kg, CL?=?8.9?±?0.8?mL/h/kg, t_1/2?=?16.8?±?5?h; and of vitamin K₁: AUC_0?∞?=?2495?±?297?h?×?ng/mL, V_d?=?60?±24?mL/kg, CL?=?40.5?±?5.1?mL/h/kg, t_1/2?=?1.1?±0.5?h.

Conclusion: The developed HPLC–UV assay is a simple and sensitive method for the determination of vitamins D₃ and K₁ in rat plasma. A higher dose of vitamin K₁ should be used in future studies for accurate estimation of pharmacokinetic parameters. The data show the suitability of the assay for pharmacokinetic studies in rats.     

Properties of TiNxfilms reactively sputtered in an argon-nitrogen atmosphere

The dependence of the resistivity and temperature coefficient of resistivity (TCR) of TiN_x films on nitrogen pressure is described. The partial nitrogen pressure was varied from 10^?5 Torr to 2×10^?4 Torr. The maximum value of the resistivity (216 μΩ cm) and the lowest negative value of TCR (?33ppmK^?1) were obtained in the nitrogen pressure range (2?4)×10^?5 Torr. The minimum value of the resistivity (44 μΩ cm) and the highest positive value of the TCR (1160 ppm K^-1 were obtained in the nitrogen pressure range (4?10)×10^?5 Torr. The influence of aging temperature up to 573 K on the resistance changes are shown. X-ray diffraction analysis indicated the presence of oriented or non-oriented TiN in these films.     

The temperature dependence of permittivity in MgO and Fe-MgO single crystals

The permittivities (ε′) of undoped MgO and iron-doped Fe-MgO single crystals have been measured over the temperature range 20 to 650? C for frequencies between 500 Hz and 50 kHz. From 25 to around 200? C the temperature dependence of ε′ fits well with Havinga's formula and the value of [(ε′ ? 1) (ε′ + 2)]^?1 (?ε′/?T) = 1.02 × 10^?2K^?1 found for undoped MgO agrees closely with data published for lower temperature ranges; this increases considerably with the addition of iron, rising to 2.85×10^?5K^?1 for MgO single crystals doped with 12 900 p.p.m. iron. Above 200? C the permittivity changes much more rapidly than the Havinga formula predicts, the variation being greater in iron-doped specimens. The frequency dependence ofε′ is also temperature-dependent; below 200? Cε′ follows [ε′(Ω) ? ε′ _∞] ∫Ω ^(n?1) withn=0.98±0.02 for all samples, but above 200? C the value ofε′ falls more rapidly with frequency than would be expected from this law. The effect is more pronounced for MgO with 12 900 p.p.m. iron. The results are discussed in terms of a contribution to the measured permittivity arising from temperature-enhanced conductivity.     

Analysis of reversible resistivity changes during structural relaxation in Co58Fe5Ni10Si11B16 metallic glass using different kinetic forms

Resistivity changes during structural relaxation in pre-annealed Co₅₈Fe₅Ni₁₀Si₁₁B₁₆ metallic glass were measured as functions of annealing temperature (280 to 400° C) and time and their kinetics were analysed using two different kinetic forms. In the case of the non-linear kinetic form which is expressed as ω = exp [- (t/?_m) ⁿ ], the values of mean activation energy,E _a, and mean pre-exponential factor, ?₀, are 1.84 eV and 2.88 × 10^?13 sec, respectively, and it was found that the quality of data fitting to the calculated curve with a constant value ofn = 0.35 was excellent. In the case of the log normal kinetic form which was developed by Nowick and Berry, the values ofE _a and ?₀ are 1.75 eV and 2.4 × 10^?12 sec, respectively, and the quality of data fitting to the calculated curve with a constant value ofβ = 4.5 was good, except for the slight deviation in the large value of log (t/?_m), whereβ is the width of the distribution of relaxation times. The kinetic parameters obtained in the present study were compared with various reported values.     

Prediction of frequency effect in high temperature fatigue crack growth using damage factors

An earlier modification of the Paris law for the growth of deep cracks in the linear elastic fracture mechanics regime is extended to include a term enabling the prediction of cyclic crack growth rates at low frequencies. The relation requires (i) a reference growth law under continuous cycling at the appropriate elevated temperature and (ii) a specified, dimensionless degradation term, defined as D_c, the creep/oxidation damage per cycle, which increases as the applied frequency decreases or as the dwell time at peak load is prolonged. The relationship is validated against data from the previous analysis on low alloy ferritic and austenitic steels in the range 538–650°C and against further published results on Ni-based alloys at temperatures up to 700°C. It appears that for the former series oxidation is the dominant damaging mode, whereas a linear creep damaging mechanism is manifest in the Ni-based alloys. Moreover, levels of cyclic damage in terms of D_c are higher in the latter, ranging between 10^?3 and 5 × 10^?1 compared with 10^?4 to 5 × 10^?2 for the steels. A brief comparison is made with damage factors arising from the high strain fatigue deformation mode at elevated temperatures and other models for the prediction of frequency effects are discussed.     

X-ray dosimetric properties of vapor-grown CdGa<Subscript>2</Subscript>S<Subscript>4</Subscript> single crystals

CdGa₂S₄ single crystals have been grown from a presynthesized source material by closed-tube iodine vapor transport, and their X-ray dosimetric properties have been studied. Their X-ray sensitivity coefficient K ranges from K = 1.26 × 10⁻¹¹ to 1.39 × 10⁻¹⁰ A min/(V R) at effective X-ray hardnesses V _a = 25–50 keV and dose rates E = 0.75–78.05 R/min, and increases with X-ray dose. The K(V _a) curve has a negative slope, in contrast to the K(E) curve. The photocurrent-dose curves of the CdGa₂S₄ single crystals demonstrate that the steady-state X-ray photocurrent is a power-law function of X-ray dose rate: ΔI _E,0 ∼ E ^α . With increasing V _a, the slope of the curves sharply decreases and α approaches unity.     

Catalytic decomposition of organic anions in alkaline radioactive waste: IV. Oxidation of glycolate with persulfate in the presence of Ru(III)

Oxidation of glycolate ions with Na₂S₂O₈ + RuCl₃ mixture in 0.2 M NaOH was studied by spectrophotometry. Glycolate is oxidizd to oxalate at 20–70°C. The reaction of glycolate with persulfate follows the first-order rate law with respect to [S₂O ₈ ^2? ], weakly depends on the glycolate concentration, and accelerates with increasing the Ru(III) content from 2 × 10^?5 to 1 × 10^?4 M. Further increase in the Ru(III) concentration does not affect the reaction rate. Probable reaction mechanism was considered.     

Removal of nitrophenols from water using cellulose derived nitrogen doped graphitic carbon material containing titanium dioxide

Nitrophenols (NPs) and their derivatives are highly toxic, mutagenic and bio-refractory pollutants commonly present in natural water resources and industrial wastewater. To remove NPs from water, N-doped graphitic carbon (NGC) and NGC adsorbent containing titanium dioxide (NGC–TiO₂) were synthesized by pyrolysis of microcrystalline cellulose and dopamine mixture, and the mixture along with TiO₂ at 500°C, respectively. NCG-TiO₂ was thoroughly characterized using various analytical techniques. NP adsorption on the NGC–TiO₂ adsorbent surface was studied by varying the pH, initial concentration of NP, and adsorbent dose. The results showed that the most efficient adsorption was achieved at pH 3. After 4?h sonication at pH 3, 80% 4-NP adsorption was achieved using NGC–TiO₂ compared to 74% with NGC adsorbent. The percentage removal of 4-NP was higher than 3-NP which was also higher than 2,4-DNP using NGC–TiO₂. 4-NP adsorption best fitted to the Langmuir isotherm plot with R² value of 0.9981 and adsorption capacity of 52.91?mg?g^?1. The adsorption process of NP was found to follow a pseudo-second-order kinetic model. The rate constant value for the adsorption of 10^?4?M 4-NP at pH 3 using 10?mg of NGC–TiO₂ adsorbent was found to be 3.76?×?10^?5?g.mg^?1.min^?1     

Design of electrical probe memory with TiN capping layer

The concept of electrical probe memory using phase-change media has recently received considerable attention due to its promising potential for next-generation data storage device. However, the physical performances of the conventional electrical probe memory are strongly limited by its diamond-like carbon capping layer ascribed to its large contact resistance and sharp difference between the theoretically optimized properties values and the experimentally measured values. Therefore, the diamond-like carbon capping layer is replaced by a titanium nitride layer here, and the modified device architecture is re-optimized by a newly developed three-dimensional model, resulting in a media stack consisting of a 2-nm Ge₂Sb₂Te₅ layer sandwiched by 2-nm titanium nitride layer with an electrical conductivity of 2?×?10⁵ Ω^?1 m^?1 and a thermal conductivity of 12 W m^?1 K^?1, and a 40-nm titanium nitride bottom layer with an electrical conductivity of 2?×?10⁶ Ω^?1 m^?1 and a thermal conductivity of 12 W m^?1 K^?1. The advantageous features of such a device on the writing of both crystalline and amorphous bits are also demonstrated according to the developed model.     

Properties of RBaCuFeO5+δ (R = Y, La, Pr, Nd, Sm-Lu)

The structural properties, thermal stability, thermal expansion, and electrical properties of the RBaCuFeO_5+δ (R = Y, La, Pr, Nd, Sm-Lu) layered ferrocuprates have been studied systematically. The linear thermal expansion coefficients of the RBaCuFeO_5+δ phases are ? 13 × 10^?6 and ? 13 × 10^?6 K^?1 for R = La-Eu and R = Gd-Lu, respectively. Their electrical conductivity varies widely, from σ = 2.0 × 10¹ S/cm for LaBaCuFeO_5.47 to σ = 8.4 × 10^?8 S/cm for TmBaCuFeO_5.06 at 300 K. The lattice parameters, thermal expansion, and conductivity of RBaCuFeO_5+δ vary nonmonotonically with the ionic radius of R³⁺ (atomic number of the rare earth), which is due to the fact that the 4f electrons of the rare-earth ions play a significant role in determining the structural and transport properties of these phases.     

Revisiting some chalcogenides for thermoelectricity

Abstract

Thermoelectric materials that are efficient well above ambient temperature are needed to convert waste-heat into electricity. Many thermoelectric oxides were investigated for this purpose, but their power factor (PF) values were too small (～10^?4 W m^?1 K^?2) to yield a satisfactory figure of merit zT. Changing the anions from O^2? to S^2? and then to Se^2? is a way to increase the covalency. In this review, some examples of sulfides (binary Cr–S or derived from layered TiS₂) and an example of selenides, AgCrSe₂, have been selected to illustrate the characteristic features of their physical properties. The comparison of the only two semiconducting binary chromium sulfides and of a layered AgCrSe₂ selenide shows that the PF values are also in the same order of magnitude as those of transition metal oxides. In contrast, the PF values of the layered sulfides TiS₂ and Cu_0.1TiS₂ are higher, reaching ～10^?3 W m^?1 K^?2. Apparently the magnetism related to the Cr–S network is detrimental for the PF when compared to the d⁰ character of the Ti⁴⁺ based sulfides. Finally, the very low PF in AgCrSe₂ (PF = 2.25 × 10^?4 W m¹ K^?2 at 700 K) is compensated by a very low thermal conductivity (κ = 0.2 W m^?1 K^?1 from the measured C_p) leading to the highest zT value among the reviewed compounds (zT_700K = 0.8). The existence of a glassy-like state for the Ag⁺ cations above 475 K is believed to be responsible for this result. This result demonstrates that the phonon engineering in open frameworks is a very interesting way to generate efficient thermoelectric materials.     

Large third-order nonlinearity of nonpolar A-plane GaN film at 800 nm determined by Z-scan technology

We report an investigation on the optical third-order nonlinear property of the nonpolar A-plane GaN film. The film sample with a thickness of ~2?μm was grown on an r-plane sapphire substrate by metal-organic chemical vapor deposition system. By performing the Z-scan method combined with a mode-locked femtosecond Ti:sapphire laser (800?nm, 50?fs), the optical nonlinearity of the nonpolar A-plane GaN film was measured with the electric vector E of the laser beam being polarized parallel (//) and perpendicular (⊥) to the c axis of the film. The results show that both the third-order nonlinear absorption coefficient β and the nonlinear refractive index n₂ of the sample film possess negative and large values, i.e. β_//?=??135?±?29?cm/GW, n_2//?=??(4.0?±?0.3)?×?10^?3?cm²/GW and β_⊥?=??234?±?29?cm/GW, n_2⊥?=??(4.9?±?0.4)?×?10^?3?cm²/GW, which are much larger than those of conventional C-plane GaN film, GaN bulk, and even the other oxide semiconductors.