cis‐Dioxomolybdenum(VI) complexes with unsymmetric linear tetradentate ligands: syntheses,structures and bromoperoxidase activities

Reactions of [MoO₂(acetylacetonate)₂], 2‐((2‐(2‐hydroxyethylamino)ethylamino)methyl)‐4‐R‐phenols (H₂Lⁿ, n = 1–5 for R = H, Me, OMe, Cl and Br, respectively) and KOH in 1:1:2 mole ratio in methanol afford a series of complexes having the general formula cis‐[MoO₂(Lⁿ)] ( 1 , 2 , 3 , 4 , 5 ) in 81–86% yields. The complexes have been characterized using elemental analysis, spectroscopy (infrared, UV–visible, and ¹H NMR, ¹³C NMR and ¹³C‐DEPT NMR) and electrochemical measurements. The molecular structures of 1 , 2 , 3 , 4 have been determined using single‐crystal X‐ray crystallography. In each of 1 , 2 , 3 , 4 , the ONNO‐donor 6,5,5‐membered fused chelate rings forming (Lⁿ)²⁻ and the two mutually cis oxo groups assemble a distorted octahedral N₂O₄ coordination sphere around the metal centre. In the crystal lattice, each of 1 , 2 , 3 , 4 forms a one‐dimensional infinite chain structure via intermolecular N  H⋅⋅⋅O hydrogen bonding interactions. In cyclic voltammograms, the diamagnetic complexes display an irreversible metal‐centred reduction in the potential range −0.73 to −0.88 V (vs Ag/AgCl). The physicochemical data are consistent with a very similar gross molecular structure for all of 1 , 2 , 3 , 4 , 5 . All the complexes exhibit decent bromoperoxidase activities and are also able to effectively catalyse benzoin and methyl(phenyl)sulfide oxidation reactions. Copyright © 2015 John Wiley & Sons, Ltd.     

Nitrogen‐Doped Carbon Nanotube Arrays for High‐Efficiency Electrochemical Reduction of CO2: On the Understanding of Defects,Defect Density,and Selectivity

Nitrogen‐doped carbon nanotubes (NCNTs) have been considered as a promising electrocatalyst for carbon‐dioxide‐reduction reactions, but two fundamental chemistry questions remain obscure: 1) What are the active centers with respect to various defect species and 2) what is the role of defect density on the selectivity of NCNTs? The aim of this work is to address these questions. The catalytic activity of NCNTs depends on the structural nature of nitrogen in CNTs and defect density. Comparing with pristine CNTs, the presence of graphitic and pyridinic nitrogen significantly decreases the overpotential (ca. −0.18 V) and increases the selectivity (ca. 80 %) towards the formation of CO. The experimental results are in congruent with DFT calculations, which show that pyridinic defects retain a lone pair of electrons that are capable of binding CO₂. However, for graphitic‐like nitrogen, electrons are located in the π* antibonding orbital, making them less accessible for CO₂ binding.     

A glassy carbon electrode modified with a copper tungstate and polyaniline nanocomposite for voltammetric determination of quercetin

A binary nanocomposite of type copper tungstate and polyaniline (CuWO₄@PANI) is described that was obtained by single step polymerization on the surface of a glassy carbon electrode (GCE). The resulting electrode is shown to be a viable tool for voltammetric sensing of quercetin (Qn) in blood, urine and certain food samples. The nanocomposite was characterized by UV-visible absorption spectroscopy, Fourier-transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction and high-resolution transmission electron microscopy. Differential pulse voltammetry was applied to quantify Qn, typically at the relatively low working potential of 0.15 V (vs. Ag/AgCl). The modified GCE has a wide analytical range (0.001–0.500 μM) and a low detection limit (1.2 nM). The sensor is reproducible, selective and stable. This makes it suitable for determination of Qn in real samples without complicated sample pretreatment.

Open image in new window

Graphical abstract Schematic of a copper tungstate and polyaniline nanocomposite modified glassy carbon electrode for voltammetric determination of quercetin in real samples.

     

Intercalated Poly (2-acrylamido-2-methyl-1-propanesulfonic Acid) into Sulfonated Poly (1,4-phenylene ether-ether-sulfone) Based Proton Exchange Membrane: Improved Ionic Conductivity

A series of hybrid proton exchange membranes were synthesized via in situ polymerization of poly (2-acrylamido-2-methyl-1-propanesulfonic acid) PMPS with sulfonated poly (1,4-phenylene ether-ether-sulfone) (SPEES). The insertion of poly (2-acrylamido-2-methyl-1-propanesulfonic acid) PMPS, between the rigid skeleton of SPEES plays a reinforcing role to enhance the ionic conductivity. The synthesized polymer was chemically characterized by fourier-transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance ¹H NMR spectroscopy to demonstrate the successful grafting of PMPS with the pendent polymer chain of SPEES. A variety of physicochemical properties were also investigated such as ion exchange capacity (IEC), proton conductivity, water uptake and swelling ratio to characterize the suitability of the formed polymer for various electrochemical applications. SP-PMPS-03, having the highest concentration of all PMPS, shows excellent proton conductivity of 0.089 S cm⁻¹ at 80 °C which is much higher than SPEES which is ~0.049 S cm⁻¹. Optimum water uptake and swelling ratio with high conductivity is mainly attributed to a less ordered arrangement polymer chain with high density of the functional group to facilitate ionic transport. The residual weight was 93.35, 92.44 and 89.56%, for SP-PMPS-01, 02 and 03, respectively, in tests with Fenton’s reagent after 24 h. In support of all above properties a good chemical and thermal stability was also achieved by SP-PMPS-03, owing to the durability for electrochemical application.     

Are Guessing,Source Coding and Tasks Partitioning Birds of A Feather?

This paper establishes a close relationship among the four information theoretic problems, namely Campbell source coding, Arikan guessing, Huleihel et al. memoryless guessing and Bunte and Lapidoth tasks’ partitioning problems in the IID-lossless case. We first show that the aforementioned problems are mathematically related via a general moment minimization problem whose optimum solution is given in terms of Renyi entropy. We then propose a general framework for the mismatched version of these problems and establish all the asymptotic results using this framework. The unified framework further enables us to study a variant of Bunte–Lapidoth’s tasks partitioning problem which is practically more appealing. In addition, this variant turns out to be a generalization of Arıkan’s guessing problem. Finally, with the help of this general framework, we establish an equivalence among all these problems, in the sense that, knowing an asymptotically optimal solution in one problem helps us find the same in all other problems.     

Structural Elucidation of Alkali Degradation Impurities of Favipiravir from the Oral Suspension: UPLC-TQ-ESI-MS/MS and NMR

A novel stability-indicating, reversed-phase, high-performance liquid chromatography (RP-HPLC) method was developed and validated for the determination of favipiravir in an oral suspension. The effective separation of favipiravir and its degradation products was achieved on a Zorbax Eclipse Plus C18 column (5 μm particle size, 150 mm length × 4.6 mm diameter). The mobile phase was prepared by mixing 5 mM of phosphate buffer (pH 3.5) and methanol in a 75:25 v/v ratio delivered at a 1.0 mL/min flow rate. The eluents were monitored using a photodiode array detector at a wavelength of 322 nm. The stability-indicating nature of this method was evaluated by performing force degradation studies under various stress conditions, such as acidic, alkali, oxidative, thermal, and photolytic degradation. Significant degradation was observed during the alkali stress degradation condition. The degradation products generated during various stress conditions were well separated from the favipiravir peak. In addition, the major degradation product formed under alkali stress conditions was identified using UPLC-ESI-TQ-MS/MS and NMR. Method validation was performed according to the ICH Q2 (R1) guideline requirements. The developed method is simple, accurate, robust, and reliable for routine quality control analysis of favipiravir oral suspensions.     

Liquid anion exchanger study of gold (III) from aqueous halide media with N-n-octylaniline

N-n-octylaniline in xylene is used for the extractive separation of gold(III) from halide media. Gold(III) was extracted quantitatively with 10 ml of 2% reagent in xylene from 0.5-10 M and 0.5-8 M hydrochloric acid and hydrobromic acid, respectively. It was stripped from the organic phase with ammonia buffer solution (pH 10.1) and estimated spectrophotometrically with stannous chloride. The effect of metal ion, acids, reagent concentration and of various foreign ions has been investigated. Method is applicable to the analysis of synthetic mixtures containing platinum metals and alloy samples. The method is fast, accurate and precise.     

Nickel-Impregnated Silica Nanoparticle Synthesis and Their Evaluation for Biocatalyst Immobilization

In the present investigation, impact of nickel-impregnated silica paramagnetic particles (NSP) as biocatalyst immobilization matrices was investigated. These nanoparticles were synthesized by sol–gel route using a nonionic surfactant block co polymer [poly (ethylene glycol)-block-poly-(propylene glycol)-block-poly (ethylene glycol)]. Diastase enzyme was immobilized on these particles (enzyme-impregnated NSP) as model enzyme and characterized using Fourier-transform infrared spectroscopy and X-ray crystallography. Analysis of enzyme-binding nature with these nanoparticles at different physiological conditions revealed that binding pattern and activity profile varied with the pH of the reaction mixture. The immobilized enzyme was further characterized for its biocatalytic activity with respect to kinetic properties such as Km and Vmax and compared with free enzyme. Paramagnetic nanoparticle-immobilized enzyme showed more affinity for substrate compared to free one. The nature of silica and nickel varied from amorphous to crystalline nature and vice versa upon immobilization of enzyme. To the best of our knowledge, this is the first report of its kind for change of nature from one form to other under normal temperatures upon diastase interaction with NSP.