Application of 1,4-Diaminoanthraquinone as a New Sensing Material for Fabrication of a Iron(III)-Selective Modified Carbon Paste Electrode

In the present work, a novel sensitive electrochemical potentiometric sensor for sensing Fe³⁺ ions based on 1,4-diaminoanthraquinone (DAQ) as a hydrophobic selector element was prepared to implement as an ion selective carbon paste electrode in the aqueous solutions. The adequate amounts of ionophore (5%), paraffin oil (25%) as a binder, Nanosilica (NS: 0.5%) multi-wall carbon nanotubes (MWCNTs: 1%) as a modifier, and graphite powder (68.5%) as an inert matrix was occupied to form the paste. This new FeCP sensor demonstrated a Nernstian slope of 19.7 ± 0.7 mV per decade over widish linear range between 1.0 × 10^–8 to 1.0 × 10^–2 mol L^–1 at working pH range of 1.9–5.0 in the optimized conditions. The average elapsed time to response of electrode was about ~6 s for concentrations from lower (1.0 × 10^?8 mol L^–1) to higher (1.0 × 10^?2 mol L^–1) of Fe³⁺ ion solution. The selectivity of electrode toward Fe³⁺ ions in comparison with other cations was studied by matched potential method. The making FeCP sensor has been put to use successfully as an indicator electrode in analytical applications such as the potentiometric titration and determination of iron(III) ion in blend of different ions.     

Flavonoids of Alcea rosea L. and their immune stimulant,antioxidant and cytotoxic activities on hepatocellular carcinoma HepG-2 cell line

Alcea rosea L. is widely cultivated in gardens of Egypt as an ornamental plant and it has a great history of folkloric medicinal uses. In the present work, phytochemical investigation of the alcoholic extract of the flowers of A. rosea L. led to the isolation of six flavonoids (1–6). Dihydrokaempferol-4′-O-β-d-glucopyranoside (1), dihydrokaempferol (2), kaempferol-3-O-[6″-(E-coumaroyl)]-β-d-glucopyranoside (3), kaempferol-3-O-β-d-glucopyranoside (4), Apigenin (5) and kaempferol-3-O-α-l-rhamnopyranosyl-(1′″→6″)-β-d-glucopyranoside (6). Four of the isolated compounds were evaluated for their antioxidant, immunostimulant and cytotoxic activities against HepG-2 cell line. Compound (3) showed potent cytotoxic activity against HepG-2 cell line with high selectivity towards hepatocellular carcinoma in vitro (with IC₅₀ = 3.8 μg/mL). Compounds 1 and 2 exhibited significant antioxidant activity and compound 4 showed a significant immune stimulant activity. Compound 1 is isolated for the first time from genus Alcea and this is the first report for its biological investigation.     

Computational investigation of the structure and antioxidant activity of some pyrazole and pyrazolone derivatives

Pyrazoles and pyrazolones constitute a group of organic compounds that have various medical applications such as antimicrobial, antipyretic, anti-inflammatory, antitumor and antioxidants. Pyrazolones can exist in different isomeric forms (CH, NH, OH) due to keto-enol, lactam-lactim and imine-enamine tautomerism. Determination of the most stable tautomeric form is thus important for understanding their biological roles at the molecular level. We performed a theoretical investigation of the structural and antioxidant properties of three synthetic pyrazolones (1–3), one synthetic pyrazole (4), one natural pyrazole (5) and two engineered hydroxyl derivatives of 1 (7, 8) and of 5 (9, 10) using the density functional theory at the B3LYP/6-311++G(d,p) level of theory in gas phase and in methanol (using the polarizable continuum model). It is found that substituents and solvents may influence the relative stability of pyrazolone isomers and that the CH tautomer is typically the least stable. Vertical ionization potentials, vertical electron affinities and X–H bond dissociation energies (X?=?C, N, O, S) are calculated for the global minimum structures and compared with those of the standard antioxidant flavonoid quercetin (6). Calculations predict that compounds 1 and 5 have antioxidant activity similar to 6 and that their mono and dihydroxyl derivatives (7–10) are more efficient antioxidants. Results also indicate that compounds 1–10 preferably interact with free radicals adopting the H atom transfer rather than the sequential electron transfer proton transfer mechanism. The study gives insight into the structural requirements for the design of highly efficient antioxidants.     

Spray-drying as a tool to disperse conductive carbon inside Na<Subscript>2</Subscript>FePO<Subscript>4</Subscript>F particles by addition of carbon black or carbon nanotubes to the precursor solution

In this work, Na₂FePO₄F-carbon composite powders were prepared by spray-drying a solution of inorganic precursors with 10 and 20 wt% added carbon black (CB) or carbon nanotubes (CNTs). In order to compare the effect of CB and CNT when added to the precursor solutions, the structural, electrochemical, and morphological properties of the synthesized Na₂FePO₄F-xCB and Na₂FePO₄F-xCNT samples were systematically investigated. In both cases, X-ray diffraction shows that calcination at 600 °C in argon leads to the formation of Na₂FePO₄F as the major inorganic phase. ⁵⁷Fe Mössbauer spectroscopy was used as complementary technique to probe the oxidation states, local environment, and identify the composition of the iron-containing phases. The electrochemical performance is markedly better in the case of Na₂FePO₄F-CNT (20 wt%), with specific capacities of about 100 mAh/g (Na₂FePO₄F-CNT) at C/4 rate vs. 50 mAh/g for Na₂FePO₄F-CB (20 wt%). SEM characterization of Na₂FePO₄F-CB particles revealed different particle morphologies for the Na₂FePO₄F-CNT and Na₂FePO₄F-CB powders. The carbon-poor surface observed for Na₂FePO₄F-CB could be due to a slow diffusion of carbon in the droplets during drying. On the contrary, Na₂FePO₄F-CNT shows a better CNT dispersion inside and at the surface of the NFPF particles that improves the electrochemical performance.     

A new disposable biosensor platform: carbon nanotube/poly(o-toluidine) nanocomposite for direct biosensing of urea

The development of new techniques for rapid and continuous monitoring of urea in biomedical and clinical analysis is very important. Thus, conductive polymer-supported carbon nanotube as an effective electrochemical biosensing platform for direct detection of urea in blood samples was designed. For the assay optimization, several conductive polymers were synthesized and tested as electrode modifiers; among the tested polymers, poly-o-toluidine (PoT) showed the highest electrochemical signals. However, after the enzyme immobilization, direct bioelectrochemical signals were not obtained when the PoT was used alone. Due to the lower electrocatalytic feature of PoT, integration of carbon nanotube, to form a composite with the PoT, was exploited to enable the direct electron transfer. Successfully, using the hybrid, the catalytic activity of the immobilized urease enzyme was retained. Consequently, a sensitive and specific chronoamperometric signals were achieved after the bioassay optimization. Eventually, a standard calibration curve for urea determination was obtained. A linear range was found from 0.1 to 11 mM with the limit of detection of 0.03 mM. Successfully, several blood samples were analyzed and urea level was correlated with the reference analytical method.

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Graphical abstract Scheme 1: Schematic representation of screen-printed electrode-modified urease biosensors. Three-layer functionalized surface (multi-walled carbon nanotube/poly(o-toluidine) nanocomposite, with glutaraldehyde (cross-linker and urease-immobilized enzyme), was designed for urea biosensors.

     

Method Development and Quantitative Elemental Analysis of Mentha Longifolia L. Leaves from Saudi Arabia by Total Reflection X-Ray Fluorescence

A method has been developed for the quantitative elemental analysis of Mentha longifolia L. leaves collected from different cities in Saudi Arabia using total reflection X-ray fluorescence. Using a microwave digestion system, 100?mg of each sample was completely digested using 3?mL of nitric acid and 2?mL of hydrogen peroxide. The stabilization of the digested samples on the silicon reflectors was studied using a silicone solution and polyvinyl alcohol. 5?µL of either silicone solution or polyvinyl alcohol (1% m/v) was pipetted and dried on the silicon reflector prior to the deposition of the digested samples. It was recognized that there is some enhancement on the intensity of the peak area with the silicone solution at photon energies less than 11?keV. However, the obtained results confirm the ability of using silicone solution or polyvinyl alcohol (1% m/v) as the stabilizer prior to the deposition of the sample droplet on the quartz reflector. However, the silicone solution was more applicable. Based on the developed method, 15 elements were quantified, namely, P, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Cu, Zn, Br, Rb, Sr, and Ba. Based on the present quantitative analysis results, M. longifolia samples collected from Al-Madina city had the highest concentration of P, Cl, K, Ti, Fe, Ni, and Cu. The lowest concentrations of P, S, Cl, K, Mn, Ni, and Br were found in Taif-Shafa.     

Spinel structure of activated carbon supported MFe2O4 composites as an economic and efficient electrocatalyst for oxygen reduction reaction in neutral media

For more sustainability and marketing of microbial fuel cells (MFCs) in wastewater treatment, the sluggish kinetics of cathode oxygen reduction reaction (ORR) and platinum scarcity (with its high cost) should be swept away. So, this work aimed to synthesize metal ferrite (MFe₂O₄; M = Mn, Cu, and Ni) -based activated carbon composites as inexpensive ORR cathode catalysts. The composites were synthesized using a facile modified co-precipitation approach with low-thermal treatment and labeled as MnFe₂O₄/AC, CuFe₂O₄/AC, and NiFe₂O₄/AC. The as-synthesized catalysts are physicochemically characterized by X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared microscopy (FTIR), Barrett-Joyner-Halenda (BJH), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and electron spin resonance (ESR). The electrochemical catalytic performance toward ORR was studied in a phosphate buffer solution (PBS) at neutral media via cyclic voltammetry (CV) and linear sweep voltammetry (LSV). MnFe₂O₄/AC has the highest onset potential (E_onset) value of − 0.223 V compared to CuFe₂O₄/AC (− 0.280 V) and NiFe₂O₄/AC (− 0.270 V). MnFe₂O₄/AC also has the highest kinetic current density (j_K) and lowest Tafel slope (− 5 mA cm⁻² and − 330 mV dec⁻¹) compared to CuFe₂O₄/AC (− 3.05 mA cm⁻² and − 577 mV dec⁻¹) and NiFe₂O₄/AC (− 2.67 mA cm⁻² and − 414 mV dec⁻¹). The ORR catalyzed by MnFe₂O₄/AC at pH = 7 proceeds via a 4e⁻ -kinetic pathway. The ESR is in good agreement with the electrochemical analysis due to the highest ∆H_ppvalue for MnFe₂O₄/AC compared to CuFe₂O₄/AC and NiFe₂O₄/AC. Thus, MnFe₂O₄/AC is suggested as a promising alternative to Pt- electrocatalyst cathode for MFCs at neutral conditions.

Graphical Abstract

     

Triazoles and fused triazoles,III: Facile and efficient synthesis of 2,5-disubstituted-s-triazolo[3,4-b]-1,3,4-thiadiazoles

Summary The development of a facile and efficient method for the synthesis of 2,5-diaryl-s-triazolo[3,4-b]-1,3,4-thiadiazoles4 a–e from the corresponding 3-aryl-4-amino-5-mercapto-s-triazole (2), is described. 3-Aryl-4-arylideneamino-5-mercapto-s-triazoles (3 a–e) were cyclized to compounds4 a–e by heating in nitrobenzene for a few minutes.Part II: See Ref. [11]     

Biologically Active Polymers, 6

Various copolymers were prepared by the copolymerization of 2‐chloroethyl vinyl ether (CEVE) with methyl methacrylate (MMA), hydroxyethyl methacrylate (HEMA) and vinylbenzyl chloride (VBC). The copolymers were further modified by quaternization with triethylamine, triphenylphosphine, and tributylphosphine. The antimicrobial activities of the prepared, quaternized copolymers were evaluated against Candida albicans, Fusarium oxysporium, Aspergillus flavus, Bacillus subtilis, Escherichia coli, and Staphylococcus aureus. The antimicrobial activity was explored by the cut plug method, viable cell counting (surviving ratio), transmission electron microscopy, and potassium leakage tests. The results indicated that the prepared polymers had a high antimicrobial activity, and control experiments on the main polymer without ammonium, phenyl, or butyl and/or phosphonium groups were carried out. The phosphonium containing polycationic biocides are more effective than the quaternary ammonium salt polymers. Examining the C. albicans and S. aureus polymer‐treated cells by electron microscopy indicated disruption for the cytoplasmic membrane and release of potassium ion as shown by the assay of potassium leakage.

Growth inhibition of different concentrations of polymer (X_b).     

Potentiometric studies of binary and ternary complexes of Zn(II) with triethylenetetramine as primary ligand and selected amino acids and DNA units as secondary ligands

The acid-base equilibria of triethylenetetramine. (Trien) and the formation equilibria of binary and ternary complexes of Zn(II) with Trien as primary ligand and some selected arnino acids and DNA units as secondary ligands have been investigated. The results showed the formation of a 11 Zn (Trien)²⁺ complex. At higher pH, the Zn (Trien)²⁺ complex is hydrolysed to give Zn (Trien) (OH)⁺ and Zn(Trien)(OH)₂ complexes. The fraction of the monohydroxo species attains a maximum of 81.3% at pH 10. The stability constantsK _Zn(Trien)A ^Zn(Trien) for the ternary complexes were determined. Histidine coordinates in a histamine-like way. Lysine and ornithine ligate by the two amino groups. Serine and methionine are bound in a glycine-like mode. However, penicillamine, cysteine and glutathione ligate partly like mercaptoethylamine and partly like mercaptopropionic acid. In the case of DNA complexes, inosine is bound through the n₁ atom. However, uracil, undine, thymine and thymidine ligate through the N₃ atom. The relative stabilities of ternary complexes are compared with those of the corresponding binary complexes in terms of logK values. The concentration distribution diagrams of the complexes are evaluated.