Phase stability,mechanical and thermodynamic properties of orthorhombic and trigonal MgSiN2: an ab initio study

Structural stability and mechanical and thermodynamic properties of the orthorhombic and trigonal MgSiN₂ polymorphs (or-MgSiN₂ and tr-MgSiN₂) were investigated through density functional theory and quasi-harmonic Debye model (QHDM). Our calculations show that or-MgSiN₂ is energetically the stable polymorph at low pressure, in agreement with previous experimental and theoretical study. Under pressure, a crystallographic transition from the orthorhombic structure to the trigonal one occurs around 25, 17.45 and 19.05 GPa as obtained from the generalized gradient approximation of Perdew-Wang (GGA-PW91), the generalized gradient approximation parameterized recently by Perdew et al (GGA-PBEsol) and the local density approximation developed by Ceperley and Alder and parameterized by Perdew and Zunger (LDA-CAPZ), respectively. Single-crystalline and polycrystalline elastic constants and related properties, namely Vickers hardness, acoustic Grüneisen parameter, minimum thermal conductivity, isotropic sound velocities and Debye temperature, were numerically estimated for both or-MgSiN₂ and tr-MgSiN₂. We have showed that the hardness of tr-MgSiN₂ is comparable to that of the harder materials like c-BN and B₆O. Temperature and pressure dependencies of volume, bulk modulus, thermal expansion, Grüneisen parameter, heat capacities and Debye temperature were investigated using QHDM.     

Sequential determination of iron(II) and iron(III) in pharmaceutical by flow-injection analysis with spectrophotometric detection.

A flow injection procedure for the sequential spectrophotometric determination of iron(II) and iron(III) in pharmaceutical products is described. The method is based on the catalytic effect of iron(II) on the oxidation of iodide by bromate at pH = 4.0. The reaction was monitored spectrophotometrically by measuring the absorbance of produced triiodide ion at 352 nm. The activating effect for the catalysis of iron(II) was extremely exhibited in the presence of oxalate ions, while oxalate acted as a masking agent for iron(III). The iron(III) in a sample solution could be determined by passing through a Cd-Hg reductor column introduced in the FIA system to reduce iron(III) to iron(II), which allows total iron determination. Under the optimum conditions, iron(II) and iron(III) could be determined over the range of 0.05 - 5.0 and 0.10 - 5.0 microg ml(-1), respectively with a sampling rate of 17 +/- 5 h(-1). The experimental limits of detection were 0.03 and 0.04 microg ml(-1) for iron(II) and iron(III), respectively. The proposed method was successfully applied to the speciation of iron in pharmaceutical products.     

A mathematical modelling to extract active ingredients from Oliveria decumbens by supercritical fluid extraction through using ultrasonic process

The experimental feasibility of extracting carvacrol or cymophenol from local and medicinal Oliveria decumbens by supercritical carbon dioxide through using ultrasound waves was investigated in this study. The extraction modelling was carried out in two forms: Internal and external. The internal model was adopted to simulate the concentration distribution of the phytochemicals in the plant particles. In this model, the extracted cell was assumed to be a filled substrate and two mechanisms of molecular permeability and mass transfer had the greatest effect. The comparison of the experimental data obtained from modelling revealed that both the internal and external models are compatible with the experimental data as much as 80%, indicating an acceptable accuracy. Furthermore, the empirical data is completely in line with the model at the final time (40 min), which is the time to reach the equilibrium.     

Effects of Seed Roasting Temperature on Sesame Oil Fatty Acid Composition,Lignan, Sterol and Tocopherol Contents,Oxidative Stability and Antioxidant Potential for Food Applications

Roasting is a key step for preparing sesame oil that leads to important changes in its organoleptic properties and quality. In this study, white sesame seeds were roasted for 20 min in an electric oven at different temperatures (120, 150, 180, 210, 250 and 300 °C). The oils extracted from unroasted and roasted seeds were compared for their chemical composition: fatty acids (including trans isomers), phytosterols, lignans (sesamin and sesamolin), tocopherols and total phenolic compounds, as well as their oxidative stability and antiradical capacity. There were no obvious differences in the oil densities, refractive indexes or iodine values, but the saponification values were affected by temperature. Relevant primary and secondary lipid oxidation were observed at T > 250 °C, resulting in a higher p-anisidine value and K232 as well as K268 values. Roasting improved oil yield (from 33.5 to 62.6%), increased its induction period (from 5.5 to 10.5 h) and enhanced the total phenolic content (from 152 to 194 mg/100 g) and antiradical activity of the extracted oil. Depending on roasting temperature, a gradual decline was recorded in total amounts of phytosterols (up to 17.4%), γ-tocopherol (up to 10.6%), sesamolin (maximum of 27.5%) and sesamin (maximum of 12.5%). All the investigated oils presented a low quantity in triglyceride polymers, clearly below the maximum tolerated quantity according to the European regulation. The optimal roasting temperature for obtaining high nutritional grade oil within the permissible values was 210 °C. The unsaponifiable components (including lignans and sterols) extracted from roasted seeds have been shown to be natural additives to fresh meatball products to extend shelf life. The results of this study may help to boost the nutritional content of plant-based diets by allowing for the use of roasted sesame seed oil and its components.     

Investigation of inclusion complex of metformin into selective cyclic peptides as novel drug delivery system: Structure,electronic properties,AIM, and NBO study via DFT

In this study, the density functional theory computational method is used to investigate the encapsulation process of metformin into three types of the cyclic peptides composed of eight serine (CP1), eight glycine (CP2), and four serine‐glycine (CP3) cyclic peptides as a new model in the process of drug delivery in the gas phase. The obtained results using the B3LYP/6‐31++G (d,p) method indicate that the complexes formed are energetically favored. Furthermore, results reveal that the drug encapsulation process is typically chemisorption. The natural bonding orbital analysis shows that the intermolecular interaction of the C2 complex (metformin/CP2) is stronger than the C1 (Metformin/CP1) and C3 (Metformin/CP3) complexes due to greater total charge transfer energy, and the C1 complex is found to be the most favored complex. The theory of atoms in molecule (AIM) method is used to analyze the nature of interactions in different molecular systems. The results show the investigated cyclic peptides as effective carriers of metformin in the nanomedicine field.     

Silicon-29 NMR Study of Alkaline Aqueous and Alcoholic Tri-butylmethyl Ammonium (TBMA) Silicate Solutions

Silicon-29 NMR spectroscopy was used to characterize aqueous and alcoholic alkaline solutions of tri-butylmethyl ammonium (TBMA) silicates. The effect of TBMA cation on the equilibrium of silicate oligomers in aqueous alkaline silicate solutions was investigated using ²⁹Si NMR spectra. It was found that TBMA cation has a structure directing role and directs the silicate species to form minor amounts of silicate anion in the presence of high concentration of silicon. Silicon-29 NMR spectra of TBMA silicate solutions indicate that considerable changes occurred by changing the Si/TBMA ratio. The distribution of silicate species was affected by the presence of the alcohols, specifically methanol.     

Asymmetric α-hydroxy ketone synthesis by direct ketone oxidation using a bimetallic palladium(II) complex

The oxidation of ketones by a chiral bimetallic palladium(II) complex in the presence of CuCl₂ in THF–water solvents gave an enantioselective synthesis of α-hydroxyketones in catalytic oxidation utilizing an atmosphere of oxygen. The ee’s ranged from 61% to 92%. The reaction was accelerated by addition of strong acid that presumably increases the rate of enolization.     

Fabrication of Membrane Sensitive Electrodes for the Validated Electrochemical Quantification of Anti-Osteoporotic Drug Residues in Pharmaceutical Industrial Wastewater

Accurate and precise application of ion-selective electrodes (ISEs) in the quantification of environmental pollutants is a strenuous task. In this work, the electrochemical response of alendronate sodium trihydrate (ALN) was evaluated by the fabrication of two sensitive and delicate membrane electrodes, viz. polyvinyl chloride (PVC) and glassy carbon (GC) electrodes. A linear response was obtained at concentrations from 1 × 10⁻⁵ to 1 × 10⁻² M for both electrodes. A Nernstian slope of 29 mV/decade over a pH range of 8–11 for the PVC and GC membrane electrodes was obtained. All assay settings were carefully adjusted to obtain the best electrochemical response. The proposed technique was effectively applied for the quantification of ALN in pure form and wastewater samples, acquired from manufacturing industries. The proposed electrodes were effectively used for the determination of ALN in real wastewater samples without any prior treatment. The current findings guarantee the applicability of the fabricated ISEs for the environmental monitoring of ALN.