Catalytic activity of nickel(II), copper(II) and oxovanadium(II)‐dihydroindolone complexes towards homogeneous oxidation reactions

Three novel paramagnetic metal complexes (MH₂ID) of Ni²⁺, Cu²⁺ and VO²⁺ ions with 3‐hydroxy‐3,3’‐biindoline‐2,2’‐dione (dihydroindolone, H₄ID) were synthesized and characterized by different spectroscopic methods. The ligand (H₄ID) was synthesized via homocoupling reaction of isatin in presence of phenylalanine in methanol. Complexation of low valent Ni²⁺, Cu²⁺ ions and high valent VO²⁺ ions with H₄ID carried out in 1: 2 molar ratios. A comparison in the catalytic potential of paramagnetic complexes of low and high valent metal ion was explored in the oxidation processes of cis‐cyclooctene, benzyl alcohol and thiophene by an aqueous H₂O₂, as a green terminal oxidant, in the presence and absence of acetonitrile, as an organic solvent, at 85 °C. NiH₂ID, CuH₂ID and VOH₂ID show good catalytic activity, i.e. good chemo‐ and regioselectivity. VOH₂ID has the highest catalytic potential compared to both Ni²⁺‐ and Cu²⁺‐species in the same homogenous aerobic atmosphere. Catalytic oxidation of other alkenes and alcohols was also studied using NiH₂ID, CuH₂ID or VOH₂ID as a pre‐catalyst by an aqueous H₂O₂. A mechanistic pathway for those oxidation processes was proposed.     

Molecular structure,molecular docking,thermal, spectroscopic and biological activity studies of bis‐Schiff base ligand and its metal complexes

Coordination compounds of Fe(III), Zn(II), Ni(II), Co(II), Cu(II), Cd(II) and Mn(II) ions were synthesized from the ligand [4,4′‐((((ethane‐1,2‐diylbis(oxy))bis(2,1‐phenylene))bis(methanylylidene))bis(azanylylidene))diphenol]ethane (H₂L) derived from the condensation of bisaldehyde and 4‐aminophenol. Microanalysis, magnetic susceptibility, infrared, ¹H NMR and mass spectroscopies, molar conductance, X ray powder diffraction and thermal analysis were used to confirm the structure of the synthesized chelates. According to the data obtained, the composition of the 1:1 metal ion–bis‐Schiff base ligand was found to be [M(H₂L)(H₂O)₂]Cl_n (M = Zn(II), Ni(II), Co(II), Cu(II), Cd(II) and Mn(II), n = 2; Fe(III), n = 3). Magnetic susceptibility measurements and reflectance spectra suggested an octahedral geometry for the complexes. Central metals ions and bis‐Schiff base coordinated together via O2 and N2 donor sites which as evident from infrared spectra. The Gaussian09 program was applied to optimize the structural formula for the investigated Schiff base ligand. The energy gaps and other important theoretical parameters were calculated applying the DFT/B3LYP method. Molecular docking using AutoDock tools was utilized to explain the experimental behaviour of the Schiff base ligand towards proteins of Bacillus subtilis (5 h67), Escherichia coli (3 t88), Proteus vulgaris (5i39) and Staphylococcus aureus (3ty7) microorganisms through theoretical calculations. The docked protein receptors were investigated and the energies of hydrogen bonding were calculated. These complexes were then subjected to in vitro antibacterial studies against several organisms, both Gram negative (P. vulgaris and E. coli) and Gram positive (S. pyogones and B. subtilis). The ligand and metal complexes exhibited good microbial activity against the Gram‐positive and Gram‐negative bacteria.     

Spectrophotometric Determination of Pyrithioxin in Pharmaceutical Preparations

Rapid direct and induced difference spectrophotometric methods for determination of pyrithioxin in single dosage forms (tablets and syrups) are reported. The direct methods depend upon measurement of the absorbance of pyrithioxin in different media at λ_max i-e at 296 nm in 0.1 M hydrochloric acid, at 328 nm in citric acid-phosphate buffer of pH 7 and at 314 nm in 0.1 M sodium hydroxide. The mean percentage recovery of the authentic samples were 100.55±0.43, 101.21±0.58 and 100.29±0.64 respectively (P=0.05). The absorbance difference methods are based upon either measurement of the difference between the acid and the alkaline solutions i-e. Δ A (Alk-Acid) at 318 nm with an accuracy of 100.72±0.88 or the absorbance difference between the acid and neutral solutions i-e Δ A (pH 7-acid) at 328 nm with an accuracy of 100.31±0.68.     

Entire large solutions of semilinear equations involving the fractional Laplacian

We investigate the existence and nonexistence of positive entire large solutions of a class of semilinear equations involving the fractional Laplacian. Sharp lower and upper bounds of the minimal solution, if it exists, are also given.     

Determination of the inhibitory effect of green tea extract on glucose‐6‐phosphate dehydrogenase based on multilayer capillary enzyme microreactor

Natural herbal medicines are an important source of enzyme inhibitors for the discovery of new drugs. A number of natural extracts such as green tea have been used in prevention and treatment of diseases due to their low‐cost, low toxicity and good performance. The present study reports an online assay of the activity and inhibition of the green tea extract of the Glucose 6‐phosphate dehydrogenase (G6PDH) enzyme using multilayer capillary electrophoresis based immobilized enzyme microreactors (CE‐IMERs). The multilayer CE‐IMERs were produced with layer‐by‐layer electrostatic assembly, which can easily enhance the enzyme loading capacity of the microreactor. The activity of the G6PDH enzyme was determined and the enzyme inhibition by the inhibitors from green tea extract was investigated using online assay of the multilayer CE‐IMERs. The Michaelis constant (K_m) of the enzyme, the IC₅₀ and K_i values of the inhibitors were achieved and found to agree with those obtained using offline assays. The results show a competitive inhibition of green tea extract on the G6PDH enzyme. The present study provides an efficient and easy‐to‐operate approach for determining G6PDH enzyme reaction and the inhibition of green tea extract, which may be beneficial in research and the development of natural herbal medicines. Copyright © 2016 John Wiley & Sons, Ltd.     

Comparative study between two fabricated potentiometric sensors to enhance selectivity towards ferrous ions

Electroanalytical methods are highly selective for measuring electrical quantities including the charge, potential and current with their relation to chemical parameters. They are widely applied in various fields such as biochemical analysis, industrial quality control and environmental monitoring. They have many advantages over other techniques in that they are not time consuming and are specific for certain oxidation states of certain elements which give these techniques high selectivity and sensitivity features. This paper is based on two parts: the first part describes the fabrication of screen‐printed electrodes (SPEs) modified with methyl red as electroactive material, while second part describes the preparation and characterization of Fe(II)–methyl red complex using various spectroscopic tools, the complex being used for the construction of carbon paste electrodes (CPEs). The two proposed electrodes were successfully applied for the determination of Fe(II) in water and pharmaceutical (pharovit) samples. The electrodes under investigation show potentiometric response for Fe(II) in the concentration range 8.0 × 10^?7–1.0 × 10^?2 and 5.0 × 10^?7–1.0 × 10^?2 M at 25°C for SPE and CPE, respectively, and the electrode response is independent of pH in the range 1.5–7.0. These sensors show Nernstian slopes of 29.1 ± 0.2 and 29.7 ± 0.16 mV decade^?1 with detection limit values of 8.0 × 10^?7 and 5.0 × 10^?7 M for SPE and CPE, respectively. These electrodes show fast response time of 6 and 4 s and exhibit a lifetime of 100 and 30 days for SPE and CPE, respectively. The mechanism of chemical reaction between modifier and Fe(II) on the SPE surface was studied using infrared spectra, scanning electron microscopy and energy‐dispersive X‐ray analysis. The proposed potentiometric method was validated according to the IUPAC recommendations. The results obtained using the proposed sensors were comparable with those obtained with inductively coupled plasma analysis.     

Promising photoluminescence optical approach for triiodothyronine hormone determination based on smart copper metal–organic framework nanoparticles

A copper metal–organic framework nanoparticles (Cu‐MOF‐NPs) synthesized via simple technique. The prepared Cu‐MOF‐NPs nanoparticles were further characterized using ¹H‐NMR, FE‐SEM/EDX and thermal study (DSC/TGA). The FE‐SEM/EDX, thermal analysis, and NMR spectrum data with the other analysis support the nano‐Cu‐MOF structure and the monomeric unit (n[Cu (AIP)₂(APY)(H₂O)₂].4H₂O) of Cu‐MOF‐NPs. The photoluminescence (PL) studies of triiodothyronine hormone (T3) based on the prepared Cu‐MOF‐NPs investigated. The results revealed that the Cu‐MOF‐NPs might be used as a biosensor in the determination of triiodothyronine hormone (T3) in biological fluids through a significant quenching of the photoluminescence intensity of Cu‐MOF‐NPs at excitation wavelength 492 nm. The calibration plot achieved over the concentration range 0.0–200.0 ng/dL T3 hormone with a correlation coefficient 0.996 and limit of detection (LOD) and quantification (LOQ) 0.198 and 0.60 ng/dL, respectively. The PL spectra are indicating that Cu‐MOF‐NPs has highly selective sensing properties for T3 hormone without interfering with other human many hormones types. This approach considered a promising analytical tool for early diagnosis of the cases of thyroid disease. The mechanism of quenching between the Cu‐MOF‐NPs, and T3 hormone studied. The mechanism was a dynamic type and obtained due to the energy transfer mechanism.