Carbon/λ-MnO2 composites for supercapacitor electrodes

In the present work a composite of carbon with λ-MnO₂ have been synthesized by a simple two-step route. In the first step, to obtain LiMn₂O₄/carbon material, mesoporous activated carbon was impregnated with the solution of precursor metal salts and heated subsequently. As-prepared materials were acid treated which resulted in the formation of λ-MnO₂/carbon. Physical properties, structure and specific surface area of electrode materials were studied by TEM, X-ray diffraction and nitrogen sorption measurements. Voltammetry cycling, galvanostatic charge/discharge and impedance spectroscopy measurements performed in two- and three-electrode cells have been applied in order to measure electrochemical parameters. TEM images confirmed well dispersed λ-MnO₂ particles on the surface of carbon material. The carbon in the composite plays an important role as the surface area enhancing component and a support of pseudocapacitive material. Furthermore, the through-connected porosity serves as a continuous pathway for electrolyte transport. A synergetic effect of the porous carbon framework and of the redox properties of the λ-MnO₂ is at the origin of improvement of specific capacitance values which has been observed for composites after delithiation.     

Synthesis of dipyrrolo[2,3-a:1′,2′,3′-fg]acridin-12(1H)-ones

Acylation reactions of 4,6-dimethoxyindoles with glyoxyloyl chlorides were achieved by the use of graphite powder in 1,2-dichloroethane at reflux. The products were monoketones as a result of decarbonylation, rather than the expected 1,2-diketones. Treatment of these monoketones with base led to their cyclisation and elimination of methanol to afford the novel dipyrrolo[2.3-a:1′,2′,3′-fg]acridin-12(1H)-ones.     

A novel nanocomposite matrix based on graphene oxide and ferrocene-branched organically modified sol–gel/chitosan for biosensor application

A novel platform for the fabrication of a glucose biosensor was successfully constructed by entrapping glucose oxidase (GOD) in a ferrocene (Fc)-branched organically modified silica material (ormosil)/chitosan (CS)/graphene oxide (GO) nanocomposite. The morphology, structure, and electrochemistry of the nanocomposite were characterized by transmission electron microscopy, X-ray powder diffraction, UV–vis spectroscopy, Fourier transform infrared spectroscopy, and electrochemical techniques. Results demonstrated that the proposed electrochemical platform not only provided an excellent microenvironment to maintain the bioactivity of the immobilized enzyme, but also effectively prevented the leakage of both the enzyme and mediator from the matrix and retained the electrochemical activity of Fc. Furthermore, dispersing GO within the Fc-branched ormosil/CS matrix could significantly improve the stability of GO and make it exhibit a positive charge, which was more favorable for the further immobilization of biomolecules, such as GOD, with higher loading. Moreover, it could also improve the conductivity of the matrix film and facilitate the electron shuttle between the mediator and electrode. Under optimal conditions, the designed biosensor to glucose exhibited a wide and useful linear range of 0.02 to 5.39 mM with a low detection limit of 6.5 μM. The value of K _M ^app was 4.21 mM, indicating that the biosensor possesses higher biological affinity to glucose. The present approach could be used efficiently for the linkage of other redox mediators and immobilize other biomolecules in the process of fabricating novel biosensors.     

A turn-on fluorescence-sensing technique for glucose determination based on graphene oxide–DNA interaction

Graphene is a two-dimensional carbon nanomaterial one atom thick. Interactions between graphene oxide (GO) and ssDNA containing different numbers of bases have been proved to be remarkably different. In this paper we propose a novel approach for turn-on fluorescence sensing determination of glucose. Hydrogen peroxide (H₂O₂) is produced by glucose oxidase-catalysed oxidation of glucose. In the presence of ferrous iron (Fe²⁺) the hydroxyl radical (?OH) is generated from H₂O₂ by the Fenton reaction. This attacks FAM-labelled long ssDNA causing irreversible cleavage, as a result of the oxidative effect of ?OH, producing an FAM-linked DNA fragment. Because of the weak interaction between GO and short FAM-linked DNA fragments, restoration of DNA fluorescence can be achieved by addition of glucose. Due to the excellent fluorescence quenching efficiency of GO and the specific catalysis of glucose oxidase, the sensitivity and selectivity of this method for GO-DNA sensing are extremely high. The linear range is from 0.5 to 10 μmol L^?1 and the detection limit for glucose is 0.1 μmol L^?1. The method has been successfully used for analysis of glucose in human serum. Figure

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Novel Co/graphene oxide and Co/nanoporous graphene catalysts for Fischer–Tropsch reaction

For the first time, nanoporous graphene and graphene oxide sheets have been synthesized and used as supports for preparation of Co/graphene-based catalysts to evaluate their efficiency in Fischer–Tropsch synthesis and for comparison with the performance of Co/Al₂O₃ to study the effects of the carbon supports on the reaction. Outstanding results were obtained compared with the alumina counterpart. Application of nanoporous graphene yielded heavier hydrocarbons compared with the Co/Al₂O₃ catalyst, possibly due to the high surface area and intrinsic properties of the carbon nanostructures as effective hydrogen carriers. Use of graphene oxide and nanoporous graphene supports also resulted in high CO₂ selectivity. However, the graphene-supported catalysts displayed lower C₁–C₄ hydrocarbon selectivity compared with the Al₂O₃ catalyst.     

Three-dimensional supramolecular architecture based on 4,4’-methylene-bis(benzenamine) and aromatic carboxylic acid guests:Synthons cooperation,robust motifs and structural diversity

The two-component solid forms involving 4,4’-methylene-bis(benzenamine) included both salts and co-crystals,while 4,4’methylene-bis(benzenamine) crystallized exclusively as a salt,in agreement with the differences in the pK a values.Many of the crystal structures displayed either the neutral or the ionic form of the carboxylic acid-amino heterosynthon,and the similarity in crystal structures between the neutral and the ionized molecules makes the visual distinction between a salt and co-crystal dependent on the experimental location of the acidic proton.A variety of supramolecular hydrogen bonded motifs involving interactions between the aza molecules and carboxylic acid groups are observed rather than just the O-H···N/O-H···O motif.The motifs are identical in all the two compounds analyzed showing the robustness of these supramolecular synthons.In all adducts,recognition between the constituents is established through either N-H···O and/or O-H···O/O-H···N pairwise hydrogen bonds.In all adducts,COOH functional groups available on 1 and 2 interact with the N-donor compounds.The COOH moieties in 1 forms only single N-H···O hydrogen bonds,whereas in 2,it forms pairwise O-H···N/N-H···O hydrogen bonds.The supramolecular architectures are elegant and simple,with stacking of networks in 2,but a rather complex network with a threefold interpenetration pattern was found in 1.Thermal stability of these compounds has been investigated by thermogravimetric analysis(TGA) of mass loss.     

DBU as a scaffold for the synthesis of [1,3]oxazolo[2’,3’ : 2,3]pyrimido-[1,2-a]azepines: annulation with aromatic cyanopropargylic alcohols

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A twofold interpenetrating framework based on the α-metatungstates

A new compound based on polyoxometalates, [Cu(bbi)]₅H[H₂W₁₂O₄₀] (1) (bbi=1,1′-(1,4-butanediyl)bis(imidazole)), has been hydrothermally synthesized and characterized by elemental analyses, IR spectroscopy, thermogravimetric analyses, and single X-ray diffraction. Compound 1 shows a twofold 3D+3D topology, and it represents the first interpenetrating network based on the isopolytungstate. The electrochemical property of compound 1 modified carbon paste electrode (1−CPE) was investigated in 1 M H₂SO₄ solution, and the results indicate that 1−CPE exhibits the electrocatalytic activity toward the reduction of bromate and nitrite. Further, the non-isothermal kinetics of the thermal decomposition of compound 1 provides the dynamic parameters E (activation energy) and A (pre-exponential factor) for the pyrolytic reaction of the organic ligands.     

An access to α, β-unsaturated ketones via dual cooperative catalysis

A dual cooperative organocatalytic approach for the synthesis of α, β-unsaturated ketones is described. This one pot transformation is realized via a domino Knoevenagel-Michael-retro Michael reaction sequence. Various aliphatic ketones reacted smoothly with aromatic as well as aliphatic aldehydes in presence catalytic amount of Meldrum’s acid and bifunctional amine. The highlights of this protocol are the easy availability of catalysts, high selectivity, and functional group tolerance. The reaction proved to highly E-selective with no side products emanating from self-condensation, unlike the base-mediated reactions.     

High-performance liquid chromatographic enantioseparation of cyclic β-aminohydroxamic acids on zwitterionic chiral stationary phases based on Cinchona alkaloids

Cyclic β-aminohydroxamic acid enantiomer pairs were stereoselectively separated by high-performance liquid chromatography on the recently developed Cinchona alkaloid-based zwitterionic chiral stationary phases Chiralpak ZWIX(+)™, ZWIX(−)™, ZWIX(+A) and ZWIX(−A). The results of variation of the applied chromatographic conditions, such as the bulk solvent composition, the concentrations and ratio of the acid and base additives, the presence of water as mobile phase additive and the counter-ion concentration furnished a better understanding of the retention mechanism. A thermodynamic study in the temperature range 5–50 °C revealed enthalpy-controlled enantiodiscrimination in all cases. The structure–selectivity relationships clearly indicated the importance of the strereochemistry of the functional groups. From an enantiorecognition aspect, the diexo position of the functional groups always proved more favorable than the diendo position. The elution sequence was determined in all cases and was found to reversed when ZWIX(+)™ was changed to ZWIX(−)™ or ZWIX(+A) to ZWIX(−A).     

Synthesis of polyamidines based on 1,4-dicyanobenzene and 4,4′-diaminodiphenyl oxide in ionic liquids

1,4-Dicyanobenzene and 4,4′-diaminodiphenyl oxide at 190–200°C in ionic liquids form polyamidines of different molecular weights, whose T _10% in air is in the range 250–270 °C.     

Temperature-dependent molecular-recognizable membranes based on poly(N-isopropylacrylamide) and β-cyclodextrin

A novel temperature-dependent molecular-recognizable membrane, poly(N-isopropylacylamide-co-glycidyl methacrylate/cyclodextrin)-grafted-polyethylene terephthalate (P(NIPAM-co-GMA/CD)-g-PET) membrane, is prepared by the combination of plasma-induced pore-filling grafting polymerization and chemical reaction. Scanning electron microscope (SEM) images show that the surfaces and cross-sections of the prepared membranes are uniformly grafted by polymeric layer. Fourier transform infrared (FT-IR) results show that CDs are successfully induced onto the P(NIPAM-co-GMA) grafted chains through reaction with epoxy groups. When the environmental temperature increases from 25 °C to 45 °C, the contact angle of prepared P(NIPAM-co-GMA/CD)-g-PET membrane increases from 65° to 76.9°; whereas, that of substrate membrane decreases from 84.8° to 77.1°. During the dynamic adsorption experiments, the guest 8-anilino-1-naphthalenesulfonic acid ammonium salt (ANS) molecules are adsorbed onto the P(NIPAM-co-GMA/CD)-g-PET membrane at lower temperature (25 °C) and desorbed from it at higher temperature (40 °C) with good repeatability. This phenomenon of adsorption at low temperature and desorption at high temperature of the P(NIPAM-co-GMA/CD)-g-PET membrane is attributable to both the “swollen–shrunken” configuration change of P(NIPAM-co-GMA) grafted chains and the molecular recognition of CD toward ANS. The P(NIPAM-co-GMA/CD)-g-PET membrane show both good thermo-responsibility and temperature-dependent molecular-recognizable characteristics toward guest molecules, which is highly potential to be applied in temperature-controlled affinity separations.     

Synthesis of a phosphotyrosyl analogue having χ1, χ2 and φ angles constrained to values observed for an SH2 domain-bound phosphotyrosyl residue

Src homology 2 (SH2) domains provide connectivity in protein-tyrosine kinase (PTK)-dependent signaling through their high affinity association with phosphotyrosyl (pTyr)-containing peptide sequences. Because recognition of pTyr residues is central to SH2 domain-binding affinity, design of pTyr-mimicking residues has been one component of SH2 domain signaling antagonist development. Reported herein is the synthesis of (±)-(rel-1R,2R,5S)-3-acetyl-1,2,3,4,5,6-hexahydro-8-O-phosphoryl-1,5-methano-3-benzazocine-2-carboxylic acid methyl ester (3c) as a monomeric pTyr-mimicking analogue that constrains three torsion angles (χ₁=168°; χ₂=−85°; φ₁=−113°) to values approximating those observed for a pTyr residue bound to the Grb2 SH2 domain (χ₁=182°; χ₂=−89°; φ₁=−132°). Compound 3c differs from our previously reported analogue, (±)-(rel-1R,2R,5S)-3-acetyl-1,2,3,4,5,6-hexahydro-1-methyl-1,5-methano-3-benzazocin-8-ol, in lacking a methyl substituent at the bridgehead 1-position. Molecular modeling studies had indicated that this methyl group could potentially hinder SH2 domain binding. Synthesis of the desmethyl derivative was achieved by formation of the methanobenzazocine ring system using an intramolecular electrophilic cyclization that proceeds through an activated acyliminium intermediate. Importantly, the correct relative (2R) stereochemistry at the ‘α-carboxyl’-bearing carbon is obtained through base-catalyzed equilibration of a (2S/2R) diastereomeric mixture that results from intramolecular ring closure. Comparison of Grb2 SH2 domain-binding affinity of 3c (IC₅₀=1167 μM) with conformationally flexible phosphorylated (±)-N-acetyl-tyrosine methyl ester (15; IC₅₀=1469 μM) revealed no apparent enhancement in affinity. This apparent ineffectiveness of ‘local conformational constraint’ on SH2 domain-binding affinity of the monomeric pTyr mimetic is consistent with previous reports obtained by conformationally constraining pTyr-mimicking residues that were contained within peptide platforms. Although not providing high binding affinity in its current form, the novel 1,5-methano-3-benzazocine ring system may afford a novel platform for further elaboration and development of small molecule SH2 domain signaling antagonists.     

A sensitive amperometric sensor for hydrazine based on Pt nanoparticles-reduced graphene oxide–multi-walled carbon nanotubes composite

The platinum nanoparticles-reduced graphene oxide-multi-walled carbon nanotubes composite (PtNPs-rGO-MWCNTs) has been synthesised by one-step chemical co-reduction strategy in ethylene glycol (EG) system using sodium citrate as reducing agent. The X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), as well as the electrochemical methods have been used for the characterisation of this composite. Benefiting from the large effective surface and good carrier function of rGO-MWCNTs, PtNPs in this nanocomposite have some excellent characteristics such as small particle size, good dispersion, as well as high electrocatalytic activity. Based on this, a new electrochemical sensor for hydrazine has been fabricated using dropping method. Under the optimum conditions, the linear range for the determination of hydrazine by amperometry at 0.20 V (vs. SCE) in phosphate buffer (pH 7.0) is from 2.0 × 10^?7 mol L^?1 to 2.3 × 10^?3 mol L^?1. The detection limit and sensitivity is 4.5 × 10^?8 mol L^?1 (S/N = 3) and 219.7 μA mM^?1, respectively. This sensor has some attractive analytical features such as low detection limit, wide linear range, high sensitivity, as well as good stability.     

Experimental and ab initio infrared study of χ-, κ‐ and α-aluminas formed from gibbsite

χ-, κ- and α-alumina phases formed by dehydration of micro-grained gibbsite between 773 and 1573 K are studied using infrared spectroscopy (IR). The structural transitions evidenced by X-ray diffraction (XRD) were interpreted by comparing IR measurements with ab initio simulations (except for the χ form whose complexity does not allow a reliable simulation). For each phase, IR spectrum presents specific bands corresponding to transverse optical (TO) modes of Al-O stretching and bending under 900 cm⁻¹. The very complex χ phase, obtained at 773 K, provides a distinctive XRD pattern in contrast with the IR absorbance appearing as a broad structure extending between 200 and 900 cm⁻¹ resembling the equivalent spectra for γ-alumina phase. κ-alumina is forming at 1173 K and its rich IR spectrum is in good qualitative agreement with ab initio simulations. This complexity reflects the large number of atoms in the κ-alumina unit cell and the wide range of internuclear distances as well as the various coordinances of both Al and O atoms. Ab initio simulations suggest that this form of transition alumina demonstrates a strong departure from the simple pattern observed for other transition alumina. At 1573 K, the stable α-Αl₂Ο₃ develops. Its IR spectra extends in a narrower energy range as compared to transition alumina and presents characteristics features similar to model α-Αl₂Ο₃⋅ Ab initio calculations show again a very good general agreement with the observed IR spectra for this phase. In addition, for both κ- and α-Αl₂Ο₃, extra modes, measured at high energy (above 790 cm⁻¹ for κ and above 650 cm⁻¹ for α), can originate from either remnant χ-alumina or from surface modes.     

Bisphosphorylated ligands based on isomeric N,N’-phenylenedibenzimidoyl dichlorides

The Arbuzov reaction of N,N’-phenylenedibenzimidoyl dichlorides furnished new tetradentate ligands, viz., N,N’-bis[(diphenylphosphoryl)phenylmethylidene]benzenediamines, which form complexes with lanthanides.     

Redox system for perfluoroalkylation of arenes and α-methylstyrene derivatives using titanium oxide as photocatalyst

Photoirradiation of titanium oxide (TiO₂) excites the electrons from the valence band to the conduction band, leaving holes in the valence band. Using these holes and electrons, it is possible to perform one-electron oxidations and reductions. We developed a method for the photocatalytic perfluoroalkylation of aromatic rings such as benzene and its derivatives, naphthalene and benzofuran with perfluoroalkyl iodide by the combination of reduction and oxidation reactions with TiO₂. Perfluoroalkyl iodide was reduced to a perfluoroalkyl radical by the excited electrons in the conduction band of TiO₂, and the resulting radical reacted with an aromatic ring to form an arenium radical that was successively oxidized to a cation by the holes in the valence band of TiO₂. Similarly, the photocatalytic reaction of α-methylstyrene with perfluoroalkyl iodide afforded perfluoroalkylated α-methylstyrene, in which the perfluoroalkyl group is on a methyl carbon.     

High-Pressure Synthesis and Crystal Structures of β-MNX (M=Zr, Hf; X=Br, I)

The single crystals of four kinds of metal nitride halides, β-MNX (M=Zr, Hf; X=Br, I), were prepared in Pt (or Au) capsules by the reaction of MN or α-MNX powders with NH₄X as fluxes under a high pressure of 3-5 GPa at 1000-1100°C. Their crystal structures were determined by single-crystal X-ray diffraction techniques. All four compounds crystallize in a rhombohedral space group R-3m, Z=6 with a=3.6403(6) Å, c=29.270(5) Å for β-ZrNBr, a=3.718(2) Å, c=31.381(9) Å for β-ZrNI, a=3.610(1) Å, c=29.294(6) Å for β-HfNBr, and a=3.689(1) Å, c=31.329(6) Å for β-HfNI. β-ZrNBr is isotypic with SmSI and the others are isotypic with YOF. Both structure variants are composed of structural slabs [X-M-N-N-M-X] (M=Zr, Hf; X=Br, I) stacked together by X…X van der Waals forces, but the ways of the layer stacking sequence are different: X_AM_cN_BN_CM_bX_A∣X_CM_bN_AN_BM_aX_C∣X_BM_aN_CN_AM_cX_B∣ in the SmSI-type and X_AM_bN_CN_BM_cX_A∣X_CM_aN_BN_AM_bX_C∣X_BM_cN_AN_CM_aX_B∣ in the YOF-type polymorphs.     

Facile synthesis of α, β-unsaturated esters through a one-pot copper-catalyzed aerobic oxidation-Wittig reaction

An efficient one-pot synthesis of α, β-unsaturated esters through the aerobic oxidation – Wittig tandem reaction of alcohols and phosphorous ylide is developed. This new method operates under mild reaction conditions, and uses CuI/TEMPO (TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxyl) as co-catalyst and air (O₂) as the oxidant. It tolerates a wide range of functionalized benzylic alcohol and aliphatic alcohols.