Novel Fe2O3@CeO2 Coreshell‐based Electrochemical Nanosensor for the Voltammetric Determination of Norepinephrine

A new selective carbon paste electrode (CPE), was applied as an electrochemical sensor for the detection of norepinephrine (NOE). The sensor was modified with 6‐amino‐4‐(3,4‐dihydroxyphenyl)‐3‐methyl‐1,4‐dihydropyrano[2,3‐c],pyrazole‐5‐carbonitrile (ADPC) assisted Fe₂O₃@CeO₂ coreshell nanoparticles (CNs) synthesized by simple method. To identify the redox properties of the modified electrode, and to examine its electrochemical properties, cyclic voltammetry (CV), chronoamperometry and differential pulse voltammetry (DPV) were conducted. Through electrochemical investigations, the coefficient of electron transfer between ADPC and the CNs/CPE (i. e. carbon paste electrode which was modified with CNs), the apparent charge transfer rate constant (k_s), and the diffusion coefficient (D) were calculated. The NOE oxidation occurred at the optimum pH of 7.0 and a potential that was about 235 mV less positive than that of the unmodified carbon paste electrode. The interaction between the two metals in the Fe₂O₃@CeO₂ coreshell led to an increase in the surface area and, consequently a sharp increase in the current. The differential pulse voltammogram of NOE showed two linear dynamic ranges an excellent detection limit (3σ) of 40 nM. In addition, NOE, AC and Trp were simultaneously determined at the modified electrode. Finally, NOE was quantitated in a number of real samples.     

Hydrogen production via CO2-reforming of methane over Cu and Co doped Ni/Al2O3 nanocatalyst: impregnation versus sol–gel method and effect of process conditions and promoter

In this study, Cu and Co doped Ni/Al₂O₃ nanocatalyst was synthesized via impregnation and sol–gel methods. The physiochemical properties of nanocatalyst were characterized by XRD, field emission scanning electron microscopy (FESEM), particle size distribution, BET, fourier transform infrared spectroscopy (FTIR), TG–DTA and energy dispersive X-ray (EDX) analysis. The samples were employed for CO₂-reforming of methane in atmospheric pressure, temperature range from 550 to 850 °C, under various mixture of CH₄/CO₂ and different gas hourly space velocity. XRD patterns besides indicating the decline of the peaks intensity in sol–gel method, proved the potential of this procedure in diminishing the crystal size and preventing the NiAl₂O₄ spinel formation. Moreover, high surface area might derive of smaller particle size and uniform morphology of sol–gel prepared ones, confirmed by FESEM and BET analysis. TG–DTG analysis as well supported the higher surface area for sol–gel made ones, represented the proper calcination temperature (approximately 600 °C). Also, presence of the active phases and elemental composition of nanocatalysts determine via EDX analysis. Promoting the basicity and the adsorption rate of CO₂, is attributed to the higher amount of OH groups for sol–gel prepared samples, proved by FTIR. Ni–Co/Al₂O₃ due to the synergetic effect of sol–gel method and cobalt addition depicted excellent characterization such as higher surface area, smaller particle size, supplying more stable support and enhanced morphology. Therefore, this nanocatalyst represented the best products yield (H₂ = 98.21 and CO = 95.64), H₂/CO close to unit (0.92–1.05) and stable conversion during 1,440 min stability test. So, Ni–Co/Al₂O₃ among all of the prepared nanocatalysts demonstrated the best catalytic performance and presented it as a highly efficient catalyst for dry reforming of methane. Despite of the stable yield of Ni–Cu/Al₂O₃, it depicted the lower catalytic activity and H₂/CO ratio than the unprompted nanocatalysts.     

Multiwavelength spectrophotometric determination of acidity constants of some azo dyes

A multiwavelength spectrophotometric titration method was applied to study the acidity constants of some azo dyes in water. The UV-vis absorption spectra of azo dye solutions were recorded in the course of their pH-metric titration with a standard base solution. The protolytic equilibrium constants, spectral profiles, concentration diagrams and also the number of components have been calculated. The quantitative effects of the substituents on the acidity of the studied azo dyes were investigated by the linear free energy relationship (LFER) using Hammet sigma constant (sigma) and field and resonance effects of Kamlet and Taft (f and Re, respectively).     

High Selective Parathion Voltammetric Sensor Development by Using an Acrylic Based Molecularly Imprinted Polymer‐Carbon Paste Electrode

The design and construction of an extra high selective voltammetric sensor for parathion by using a molecularly imprinted polymer (MIP) as recognition element was introduced. A parathion selective MIP and a nonimprinted polymer (NIP) were synthesized and then incorporated in the carbon paste electrode. The MIP‐CP electrode showed very high recognition ability in comparison to NIP‐CP. It was shown that electrode washing after parathion extraction, led to enhanced selectivity. Some parameters affecting the sensor response were optimized and then the calibration curve was plotted. A dynamic linear range of 1.7–900 nM was obtained. The detection limit of the sensor was calculated as 0.5 nM. This sensor was used successfully for parathion determination in real samples such as ground water and vegetables.     

Sandwich-type Uranium-Substituted of Bismuthotungstate: Synthesis and Structure Determination of [Na(UO2)2(H2O)4(BiW9O33)2]13?

The sandwich-type [Na(UO₂)₂(H₂O)₄(BiW₉O₃₃)₂]¹³⁻ uranium (VI) has been synthesized by reacting the trivacant species of B-α-[BiW₉O₃₃]⁹⁻ with and investigated by IR and UV–Vis spectroscopy, and elemental analysis. The X-ray single crystal analysis was carried out on Na₁₃[Na(UO₂)₂(H₂O)₄(BiW₉O₃₃)₂] · 33H₂O (I) which crystallizes in the orthorhombic system, space group Pna2₁ with a = 33.8454(19) ?, b = 21.1484(12) ?, c = 13.2403(7) ?, α = 90°, β = 90°, γ = 90°, and Z = 4. The polyanion consists of two lacunary B-α-[BiW₉O₃₃]⁹⁻ groups which sandwich two uranyl cations and one sodium cation. The uranium atoms adopt distorted pentagonal–bipyramidal coordination, achieved by two equatorial bonds to each BiW₉O₃₃ unit and one external water ligand. The coordination of each uranium atom is evident by the shift of ν_as(W–O_b–W) and ν_as(Bi–O) stretching vibrational bonds. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Electrografting of 4‐tert‐Butylcatechol on GC Electrode. Selective Electrochemical Determination of Homocysteine

A new sensor based on the grafting of 4‐tert‐butylcatechol on the surface of a glassy carbon electrode (GC) was developed for the catalytic oxidation of homocysteine ( Hcy ). The GC‐modified electrode exhibited a reversible redox response at neutral pH. Under the optimum conditions cyclic voltammetric results indicated the excellent electrocatalytic activity of modified electrode toward the oxidation of Hcy at reduced over‐potential about 350 mV. A linear dynamic range of 0.01–3.0 mM and a detection limit of 1.0 µM were obtained for Hcy . The modified electrode was used as an electrochemical sensor for selective determination of Hcy in human blood.     

Synthesis and Dynamic NMR Study of New Stable Ylides Derived from the Reaction of Triphenylphosphine,Dialkyl Acetylenedicarboxylates,and 5-ACYL Meldrum’s Acid

Abstract

Triphenylphosphine and dialkyl acetylenedicarboxylate react smoothly in the presence of 5-acyl Meldrum's acid in dichloromethane at room temperature and lead to synthesis of new stable ylide derivatives of dimethyl (5-acetyl-2,2-dimethyl-4,6-dioxo-1,3-dioxane-5-yl)-3-(triphenyl-λ⁵-phosphanylidene) succinate. Dynamic NMR study results of rotamers are reported and compared with the previous-related reports.     

A One‐Pot Synthesis of 1,2‐Dihydroisoquinoline Derivatives from Isoquinoline via a Four‐Component Reaction

A four‐component reaction for the synthesis of 1,2‐dihydroisoquinoline derivatives is described. The Huisgen 1,4‐dipolar intermediate, which is produced from isoquinoline and an electron‐deficient acetylene compound 1 , reacts with H₂O in the presence of diketene to produce 1,2‐dihydroisoquinoline derivatives 2 (Scheme 1). In addition, reaction of isoquinoline, dibenzoylacetylene (=1,4‐diphenylbut‐2‐yne‐1,4‐dione), and diketene in the presence of H₂O leads to pyrroloisoquinoline derivative 7 . The structures of the compounds 2a – f and 7 were corroborated spectroscopically (IR, ¹H‐ and ¹³C‐NMR, EI‐MS) and by elemental analyses. A plausible mechanism for the reaction is proposed (Schemes 2 and 3).     

A Simple Approach to the Synthesis of 1,4-Bis(arylsulfonyl)tetrahydropyrazine-2,5-diones

Summary.  The addition of triphenylphosphine to dimethyl acetylenedicarboxylate in the presence of arylsulfonylglycyl chlorides leads to 1,4-bis-arylsulfonyl-tetrahydropyrazine-2,5-diones and dimethyl (E)-2-chloro-2-butenedioate. Corresponding author. E-mail: isayavar@yahoo.com Received June 3, 2002; accepted June 10, 2002     

Application of an Hg2+ selective imprinted polymer as a new modifying agent for the preparation of a novel highly selective and sensitive electrochemical sensor for the determination of ultratrace mercury ions

A simple and very selective electrode, based on a mercury ion imprinted polymer (IIP), and its application for the determination of Hg(2+) ions in the real samples is introduced. Mercury ion selective cavities were created in the vinyl pyridine based cross-linked polymer. In order to fabricate the sensor carbon particles and polymer powder were mixed with melted n-eicosane. An explicit difference was observed between the responses of the electrodes modified with IIP and non imprinted polymer (NIP), indicating proper performance of the recognition sites of the IIP. Various factors, known to affect the response behavior of selective electrode, were investigated and optimized. The interference of different ionic species with the response of the electrode was also studied. The results revealed that, compared to previously developed mercury selective sensors, the proposed sensor was more selective, regarding the common potential interferer. This sensor showed a linear response range of 2.5 × 10(-9)-5.0 × 10(-7) M and lower detection limit of 5.2 × 10(-10) M (S/N). The sensor was successfully applied to the determination of mercury in real samples.