Titanium dioxide anchored graphene oxide nanosheets for highly selective voltammetric sensing of dopamine

The authors report on an efficient method for the voltammetric sensing of dopamine (DA) by using an electrode modified with alternating monolayers of graphene oxide (GO) and Titanium dioxide (TiO₂) nanoparticles anchored GO nanosheets (NSs)). The as-prepared nanostructures were characterized by photoluminescence spectroscopy, powder X-ray diffraction, Raman spectroscopy, FT-IR spectroscopy, transmission electron microscopy, scanning electron microscopy, atomic force microscopy and Energy Dispersive X-ray Analysis (EDAX) techniques. The GO/TiO₂ nanocomposite (NC) was deposited on a glassy carbon electrode (GCE), where it displayed an excellent electrocatalytic activity toward the oxidation of DA, owing to its excellent conductivity, high specific surface area, enhanced interfacial contact and more negative zeta potential. Figures of merit include (a) a fast response (5 s), (b) a wide linear range (between 0.2 and 10 μM of DA) (c) a particularly low detection limit (27 nM), (d) a working potential as low as 0.25 V (vs. Ag/AgCl) and (e) a sensitivity of 1.549 μA·μM^?1·cm^?2. The GO/TiO₂/GCE exhibited excellent selectivity over the other interferences as revealed by the differential pulse voltammetric and amperometric studies. The analysis of spiked urine samples resulted in recoveries in the range of 96 to 106%, with RSDs between 3.8 and 5.2%.

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Graphical abstract A GO/TiO₂ (graphene oxide/titanium dioxide) nanocomposite (NC) was prepared and exploited as electrochemical probes in DA detection. It displays a low detection limit, wide linear range and excellent selectivity.

     

trans‐Di­aqua(C‐meso‐5,12‐di­methyl‐1,4,8,11‐tetra­aza­cyclo­tetra­decane‐N,N′,N′′,N′′′)copper(II) dichloride dihydrate

The crystal structure of the title complex, [Cu(C₁₂H₂₈N₄)(H₂O)₂]Cl₂·2H₂O, has been determined. The Cu^II atom is octahedrally coordinated by the four N atoms of the tetradentate macrocyclic ligand in equatorial positions and by the O atoms of two water mol­ecules in axial positions. The crystal structure is stabilized by a three‐dimensional network of hydrogen bonds.     

(12‐Hydro­xy­methyl‐5,5,7,12,14‐penta­methyl‐1,4,8,11‐tetra­aza­cyclo­tetra­decane‐N‐acetato‐N,N′,N′′,N′′′,O,O′)cobalt(III) chloride perchlorate monohydrate

In the title compound, [Co(C₁₈H₃₇N₄O₃)](ClO₄)Cl·H₂O, the Co^III ion has a distorted octahedral geometry, with four N atoms and two O atoms constituting the coordination sphere. The crystal structure is stabilized by a three‐dimensional network of hydrogen bonds.     

Molybdenum trioxide catalyzed oxidative cross-dehydrogenative coupling of benzylic sp3 C–H bonds: synthesis of α-aminophosphonates under aerobic conditions

Molybdenum trioxide (MoO₃) catalyzed efficient oxidative cross-dehydrogenative-coupling (CDC) method for C–H functionalization of N-aryl tetrahydroisoquinolines has been explored. This user-friendly method of synthesizing α-aminophosphonates employs 1.1 equiv of dialkyl-H-phosphonate under aerobic condition. Formation of new C–P bonds from unfunctionalized starting materials under environmentally benign conditions provides an excellent avenue for the synthesis of biologically active α-aminophosphonates.     

C-H functionalization of tertiary amines by cross dehydrogenative coupling reactions: solvent-free synthesis of α-aminonitriles and β-nitroamines under aerobic condition

A solvent-free synthesis of α-aminonitriles and β-nitroamines by oxidative cross-dehydrogenative coupling under aerobic condition is reported. A catalytic amount of molybdenum(vi) acetylacetonoate was found to catalyze cyanation of tertiary amines to form α-aminonitriles, whereas vanadium pentoxide was found to promote aza-Henry reaction to furnish β-nitroamines. Both of these environmentally benign reactions are performed in the absence of solvents using molecular oxygen as an oxidant.     

Solid state structure of the hydrated potassium thiocyanate complex of benzodinaphthopyridino 21-crown-7, C37H31NO6·KSCN·H2O (1 : 1 : 1)

Single crystal X-ray analysis of the hydrated KSCN complex of benzodinaphthopyridino-21-crown-7 (1) (1 : 1 : 1) is reported. Crystals of the complex are orthorhombic,Pnma, with = 16.946(4),b = 22.298(4),c = 10.390(8) Å andD _c = 1.184 g cm^–1,Z = 4. The host macroring (1) has a mirror symmetry and exists in a so-called dentists chair conformation. The cation (K^–) is coordinated to all the six ether oxygen atoms and also weakly to the pyridine N atom. The SCN^– anion group has a statistical type of disorder with opposite orientations of S and N such that nitrogen and sulphur are coordinated to K⁺. Packing of the host molecules is in columns to form quasi channels with K⁺, SCN^–, and H₂O being located inside the stacks. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82132 (9 pages).     

Amperometric hydrogen peroxide sensor based on the use of CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> hollow nanostructures

The authors report on the preparation of a hollow-structured cobalt ferrite (CoFe₂O₄) nanocomposite for use in a non-enzymatic sensor for hydrogen peroxide (H₂O₂). Silica (SiO₂) nanoparticles were exploited as template for the deposition of Fe₃O₄/CoFe₂O₄ nanosheets, which was followed by the removal of SiO₂ template under mild conditions. This leads to the formation of hollow-structured Fe₃O₄/CoFe₂O₄ interconnected nanosheets with cubic spinel structure of high crystallinity. The material was placed on a glassy carbon electrode where it acts as a viable sensor for non-enzymatic determination of H₂O₂. Operated at a potential of ?0.45 V vs. Ag/AgCl in 0.1 M NaOH solution, the modified GCE has a sensitivity of 17 nA μM^?1 cm^?2, a linear response in the range of 10 to 1200 μM H₂O₂ concentration range, and a 2.5 μM detection limit. The sensor is reproducible and stable and was applied to the analysis of spiked urine samples, where it provided excellent recoveries.

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Graphical abstract Schematic of a cobalt ferrite (CoFe₂O₄) hollow structure for use in electrochemical determination of H₂O₂. The sensor shows a low detection limit, a wide linear range, and excellent selectivity for H₂O₂.

     

Efficient synthesis of carbonyl compounds: oxidation of azides and alcohols catalyzed by vanadium pentoxide in water using tert-butylhydroperoxide

Catalytic amount of vanadium reagent with tert-butylhydroperoxide as the oxidant was found to be an excellent oxidizing agent in aqueous medium. Vanadium pentoxide with aq tert-butylhydroperoxide readily oxidizes primary benzylic azides to the corresponding acids and secondary benzylic azides to the corresponding ketones in excellent yields. Further, vanadium pentoxide and aq tert-butylhydroperoxide combination turned out to be an effective catalyst for the oxidation of alcohols. Using vanadium pentoxide and aq tert-butylhydroperoxide primary alcohols were oxidized to the corresponding acids, whereas secondary alcohols underwent a smooth transformation to furnish corresponding ketones in excellent yields. All the oxidations are performed in water.     

Dimeric cyclopalladated azobenzenes: structural differences between 2-hydroxypyridine and 2-mercaptopyridine bridged complexes

Binuclear chloro-bridged cyclopalladated azobenzenes [Pd(A)Cl]₂ (A=ortho-metallated azobenzene or its derivatives) have been reacted with aqueous (aq.) AgNO₃ followed by the addition of 2-hydroxypyridine (2-PyOH; donor centres of deprotonated form abbreviated N,O)/2-mercaptopyridine (2-PySH; donor centres of deprotonated form abbreviated N,S) in presence of Et₃N to synthesise bridged dinuclear compound [Pd(A)(μ-N,O)]₂–[Pd(A)(μ-N,S)]₂. The compositions of the complexes have been established by elemental analyses, IR, UV–vis, ¹H and ¹³C-NMR spectral data. The structural confirmation has been carried out by X-ray crystallography. The structures show anti-symmetric metallacycle in the dimer and N,O/N,S bridging arrangement. The dimer [Pd(A₁)(μ-N,X)]₂ shows strong PdPd interaction (A₁=2-(phenylazo)benzene). The coordination mode in [Pd(A₁)(μ-N,O)]₂ shows trans pyridine-N to Pd---N(azo) bond while in [Pd(A₁)(μ-N,S)]₂ pyridine-N is trans to the Pd---C bond. The square planes are convergent towards heterocyclic bridging side.     

N-Heterocyclic carbene as a Brønsted base catalyst for the amination of naphthol derivatives and alcoholysis of glutaric anhydrides

A non-covalent Brønsted-basic N-heterocyclic carbene catalyzed (NHC) Friedel-Crafts type amination of naphthol derivatives using dialkyl azodicarboxylates as the aminating source and alcoholysis of various glutaric anhydrides using alcohol as pronucleophile is presented. Both of these reactions are performed in the presence of either commercially available free-carbene catalyst or in situ-generated carbene catalyst. Friedel-Crafts type amination reaction is an example of a hydroxy group facilitated amination reaction. Both reactions proceed via in situ activations of –OH group by the carbene catalyst through hydrogen bonding interaction and furnish the relevant products in moderate to excellent yields.