Equal Number Of Electrons Research Articles

Sea urchin-like Ni3(HITP)2 as the substrate of molecular imprinted polymer: the voltammetric mechanism for sensitive detection of dopamine.

An electrochemical sensor composed of conductive metal-organic framework [Ni3(HITP)2] and molecular imprinted polymers (MIP) is fabricated to detect dopamine. Ni3(HITP)2 promotes electrons transfer due to the structure of in-plane charge delocalization and layered expansion conjugation. The combination of MIP with Ni3(HITP)2 improves the selectivity and conductivity, exhibiting a wide detection range (0.06 ~ 200µM) and a low detection limit (0.109µM). The kinetic mechanism on the electrode surface is an adsorption controlled process, with the equal number of electrons and protons participating in oxidation in the electrocatalytic process of catechol converting to o-quinone.

Highly sensitive square wave voltammetric method for determination of brucine in artificial urine samples based on choline chloride modified glassy carbon electrode

This paper demonstrates a highly sensitive Voltammetric sensor for determination of brucine (BRU) in artificial urine sample based on choline chloride modified glassy carbon electrode (ChCl/GCE). The simple and cost effective modification was performed by electrodeposition of choline chloride on glassy carbon electrode surface using cyclic voltammetry technique. The modified electrode surface was characterized by electrochemical, spectroscopic and microscopic imaging. The electrode yields a well-resolved peak current for the irreversible oxidation of brucine in the first scan and a pair of quasi-reversible peaks during the second scan. The CV study indicates that brucine undergoes an adsorption controlled electrochemical process with equal number of electrons and protons transfer on the ChCl/GCE. The SWV result shows that the reduction peak current of BRU at the ChCl/GCE was linear in the range of 0.001 μM–10 μM with limit of detection 8 × 10−5 μM, limit of quantification 2.6 × 10−4 μM and sensitivity of 116.4 μA/μM. The ChCl/GCE also showed an excellent selectivity, reproducibility and long-time stability towards the electrochemical reduction of Brucine. Moreover, the practical applicability of the fabricated ChCl/GCE was examined in order to determine BRU in artificial urine samples with recovery ranging from 95.5 to 102.7%. The validity of the developed method was confirmed by chromatographic techniques, high-performance liquid chromatography (HPLC) and the results obtained are consistent the HPLC method.

Electrochemical determination of paracetamol at Cu doped ZnO/Nanoparticle with TX-100-surfactant MCPE: A cyclic voltammetric technique

Zinc oxide nanoparticles (ZnO/NPs) and Copper doped ZnO nanoparticles (Cu-ZnO/NPs) were prepared using the co-precipitation method and their characterizations were done with X-ray diffraction (XRD), Scanning electron microscope (SEM) and Energy dispersive spectroscopy (EDS) techniques. The prepared Cu-ZnO/NPs were used for the modification of the carbon paste electrode (CPE), the Cetyl Trimethyl Ammonium Bromide (CTAB) and Triton-X 100 (TX-100) surfactants were immobilization on the surface of Cu-ZnO/MCPE, the TX-100 modified electrode improved the more redox property with increasing the peak current for Paracetamol (PA) compare to Cu-ZnO/CTAB/MCPE. From the pH study confirms that the equal number of electrons and protons transfer mechanism involved at the MCPE. The cyclic voltammetry (CV) technique demonstrated the oxidation of both PA and Adrenaline (AD) was found to be adsorption controlled. The electrochemical response of PA and AD was linear in the µM concentration range and the limit of detection and limit of quantification was found to be 4.6 µM and 16.2 µM for PA and 3.9 µM and 13.2 µM for AD respectively, the effect of interference study was examined by using the differential pulse voltammetric technique (DPV), the Cu-ZnO/TX-100/MCPE shows an excellent selectivity towards PA in presence of different AD concentration. In present study commercial PA tablet also studied.

Tunneling-tip-induced collapse of the charge gap in the excitonic insulator Ta2NiSe5

Tuning many-body electronic phases by an external handle is of both fundamental and practical importance in condensed matter science. The tunability mirrors the underlying interactions, and gigantic electric, optical and magnetic responses to minute external stimuli can be anticipated in the critical region of phase change. The excitonic insulator is one of the exotic phases of interacting electrons, produced by the Coulomb attraction between a small and equal number of electrons and holes, leading to the spontaneous formation of exciton pairs in narrow-gap semiconductors/semimetals. The layered chalcogenide Ta$_2$NiSe$_5$ has been recently discussed as such an excitonic insulator with an excitation gap of ~250 meV below $T_c$ = 328 K. Here, we demonstrate a drastic collapse of the excitation gap in Ta$_2$NiSe$_5$ and the realization of a zero-gap state by moving the tip of a cryogenic scanning tunneling microscope towards the sample surface by a few angstroms. The collapse strongly suggests the many-body nature of the gap in the insulating state of Ta$_2$NiSe$_5$, consistent with the formation of an excitonic state. We argue that the collapse of the gap is driven predominantly by the electrostatic charge accumulation at the surface induced by the proximity of the tip and the resultant carrier doping of the excitonic insulator. Our results establish a novel phase-change function based on excitonic insulators.

Polyethylenimine-Multi-Walled Carbon Nanotubes/Glassy Carbon Electrode as an Efficient Sensing Platform for Promethazine

A sensor based on polyethylenimine-functionalized multi-walled carbon nanotubes/glassy carbon electrode (fMWCNT-PEI/GCE) was developed for promethazine hydrochloride (PMZ) detection in pharmaceutical samples. PMZ is oxidized at the modified electrode at more negative potentials and with higher sensitivity than at the bare electrode. The morphological characterization of the sensor surface showed a homogeneous layer with size distribution of the diameters of the PEI-fMWCNT ranging from 22–47 nm. The characterization of the electrochemical behavior suggested that an equal number of electrons and protons participate in the PMZ irreversible oxidation on the fMWCNT-PEI/GCE. The optimized conditions were Sörensen buffer at pH 2.0, frequency of 90 s−1, amplitude of the pulse of 40 mV, and height of the potential step of 2 mV. Based on the most sensitive peak, at ca. −0.75 V, which is related to the formation of the phenazothiazonium ion, the PMZ calibration curve was obtained with sensitivity of 3.21 × 10−3 A mol−1 l, a linearity range of 4.97 × 10−7 to 5.03 × 10−6 mol l−1, and a detection limit of 2.31 × 10−7 mol−1 l. This methodology was successfully validated in pharmaceutical samples by comparison with the standard method of the Pharmacopoeia, showing high potential applicability of the fMWCNT-PEI/GCE.

ZnO/functionalized MWCNT and Ag/functionalized MWCNT modified carbon paste electrodes for the determination of dopamine, paracetamol and folic acid

In this study, functionalized multiwalled carbon nanotubes (FMWCNT), Ag nanocomposite FMWCNT (Ag/FMWCNT) and ZnO nanoparticles (NPs) were prepared and characterized by different characterization techniques. The prepared materials, pristine-MWCNT (MWCNT), ZnO composite with MWCNT and FMWCNT were used as modifiers of carbon paste electrode (CPE) to study the electrochemical behavior of dopamine (DA) in phosphate buffer solution (pH7.4) by using cyclic voltammetric technique. In that ZnO NPs incorporated with FMWCNT modified CPE (ZnO/FMWCNT MCPE) shows enhanced electrocatalytic activity compared to bare and all other modified CPEs. As a result the ZnO/FMWCNT MCPE was used for further electrochemical studies. From the pH study, it was found that an equal number of electrons and protons are involved in the electrochemical reaction of DA. The calibration curve for DA was obtained in the concentration range of 0.2–5μM. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.025 and 0.08μM, respectively. The ZnO/FMWCNT MCPE showed good stability, repeatability and reproducibility towards DA. Moreover the ZnO/FMWCNT MCPE, Ag/FMWCNT MCPE and bare CPE were used for the study of electrochemical response of paracetamol (PC) and folic acid (FA). At Ag/FMWCNT MCPE, no characteristics voltammetric peaks appeared for PC and FA. The ZnO/FMWCNT MCPE showed good electrocatalytic activity towards PC and FA when compared to bare CPE. The effect of scan rate shows that the electrode process is diffusion controlled for DA, PC and FA. The LOD and LOQ for PC were found to be 0.23 and 0.79μM with a linear range of 0.5–13μM. ZnO/FMWCNT MCPE was effectively applied towards the determination of DA and PC in pharmaceutical samples. The fabricated electrode proved to be an effective sensor for electrochemical investigation of DA in presence of PC and FA.

Electrochemical sensing of trifluralin in water by fluconazole-immobilized Fe3O4/SiO2 nanomagnetic core–shell linked to carbon nanotube modified glassy carbon electrode; an experimental and theoretical modeling

A novel and sensitive method has been described for voltammetric study and determination of trifluralin, commonly used herbicide, based on its electrochemical oxidation on modified glassy carbon electrode (GCE) with multi-walled carbon nanotubes (MWCNT) and nanomagnetic core–shell coated with fluconazole (Fe3O4/SiO2 ~ FLU). CV studies indicated that the amine group of trifluralin oxidation process has a quasi-reversible and adsorption-like behavior in a mechanism with equal number of electrons and protons. The proposed sensor was found to quantify trifluralin by SWV in the range of 1.0 × 10−9–2.0 × 10−7 mol L−1, R2 = 0.998, detection limit (1.0 × 10−9 mol L−1) and repeatability (RSD = 1.99%, n = 10, for 1.0 × 10−7 mol L−1 trifluralin). The interpretations of the theoretical calculations and experimental results have shown good adaptation to discuss the outer sphere electron transfer (ET) process on the fluconazole-immobilized Fe3O4/SiO2 core–shell linked to carbon nanotube modified glassy carbon electrode. To further validate its possible application, the method was used for the quantification of trifluralin in water samples.

Multiwall carbon nanotube modified glassy carbon electrode as voltammetric sensor for the simultaneous determination of ascorbic acid and caffeine

Simultaneous determination of ascorbic acid (AA) and caffeine (CAF) in pharmaceutical preparation is important and it has been achieved by square wave voltammetry (SWV) using a glassy carbon electrode (GCE) modified with multiwall carbon nanotubes (MWCNT). The oxidation of AA and CAF at MWCNT occurred at ∼−10mV and ∼1103mV at a much lower potential, than that observed (∼202mV and ∼1402mV) for their oxidation at bare GCE. The mechanistic study has shown that the equal number of electrons and protons are involved in the oxidation of drugs. The electrodes could be used for the determination of AA and CAF in a wide concentration range 10–500μM, respectively, whereas the detection limit has been found to be 1.0×10−2μM and 3.52×10−3μM respectively. In view of high sensitivity for the detection of the drugs, the technique has been used for the reliable determination of AA and CAF in tea leaves, coffee, cold drink (mountain dew), pharmaceutical preparations and urine samples.

Deterministic Single InGaN Quantum Dots grown on GaN Micro-Pyramid Arrays

InGaN quantum dots (QDs) formed on top of GaN pyramids have been fabricated by means of selective area growth employing hot wall MOCVD. Upon regrowth of a patterned substrate, the growth will solely occur in the holes, which evolve into epitaxially grown wurtzite based pyramids. These pyramids are subsequently overgrown by a thin optically active InGaN well. The QDs are preferably nucleating at the apices of the pyramids as evidenced by the transmission electron microscopy (TEM). The emission from these QDs have been monitored by means of microphotoluminescence (μPL), in which single emission lines have been detected with a sub-meV line width. The μPL measurements undoubtedly reveal that the QDs are located in the apexes of the pyramids, since the sharp emission peaks can only be monitored as the excitation laser is focused on the apices in the µPL. It is also demonstrated that the emission energy can be changed in a controlled way by altering the growth conditions, like the growth temperature and/or composition, for the InGaN layers. The tip of the GaN pyramid is on the nm scale and can be made sharp or slightly truncated. TEM analysis combined with µPL results strongly indicate that the Stranski-Krastanow growth modepreferably is taking place at the microscopic c-plane truncation of the GaN pyramid. Single emission lines with a high degree of polarization is a common feature observed for individual QDs. This emission remains unchanged with increasing the excitation power and sample temperature. An in-plane elongated QD forming a shallow potential with an equal number of electrons and holes is proposed to explain the observed characteristics of merely a single exciton emission with a high degree of polarization.

The Effect of Applied Voltage on the Carrier Effective Mass in ABA Trilayer Graphene Nanoribbon

Density of states which is an important parameter for the carrier statistics study of Trilayer Graphene Nanoribbon with ABA stacking is modeled in this paper. Analytical model for the density of states of ABA trilayer graphene nanoribbon is proposed and a numerical solution is obtained. In addition, applied voltage effect on carrier effective mass is simulated. The simulation results indicate that by increasing the applied voltage, the carrier effective mass (m?) increases and thus to obtain equal number of electrons and holes, the location of the intrinsic Fermi level will be moved far from the band gap centre.

Long-range structure of Cu(InxGa1−x)3Se5: A complementary neutron and anomalous x-ray diffraction study

Distinguishing the scattering contributions of isoelectronic atomic species by means of conventional x-ray- and/or electron diffraction techniques is a difficult task. Such a problem occurs when determining the crystal structure of compounds containing different types of atoms with equal number of electrons. We propose a new structural model of Cu(InxGa1−x)3Se5 which is valid for the entire compositional range of the CuIn3Se5–CuGa3Se5 solid solution. Our model is based on neutron and anomalous x-ray diffraction experiments. These complementary techniques allow the separation of scattering contributions of the isoelectronic species Cu+ and Ga3+, contributing nearly identically in monoenergetic x-ray diffraction experiments. We have found that CuIII3Se5 (III=In,Ga) in its room temperature near-equilibrium modification exhibits a modified stannite structure (space group I4¯2m). Different occupation factors of the species involved, Cu+, In3+, Ga3+, and vacancies have been found at three different cationic positions of the structure (Wyckoff sites 2a, 2b, and 4d) depending on the composition of the compound. Significantly, Cu+ does not occupy the 2b site for the In-free compound, but does for the In-containing case. Structural parameters, including lattice constants, tetragonal distortions, and occupation factors are given for samples covering the entire range of the CuIn3Se5–CuGa3Se5 solid solution. At the light of the result, the denotation of Cu-poor 1:3:5 compounds as chalcopyrite-related materials is only valid in reference to their composition.

A Structural Determinant for the Control of PIP2 Sensitivity in G Protein-gated Inward Rectifier K+ Channels

Inward rectifier K+ (Kir) channels are activated by phosphatidylinositol-(4,5)-bisphosphate (PIP2), but G protein-gated Kir (KG) channels further require either G protein βγ subunits (Gβγ) or intracellular Na+ for their activation. To reveal the mechanism(s) underlying this regulation, we compared the crystal structures of the cytoplasmic domain of KG channel subunit Kir3.2 obtained in the presence and the absence of Na+. The Na+-free Kir3.2, but not the Na+-plus Kir3.2, possessed an ionic bond connecting the N terminus and the CD loop of the C terminus. Functional analyses revealed that the ionic bond between His-69 on the N terminus and Asp-228 on the CD loop, which are known to be critically involved in Gβγ- and Na+-dependent activation, lowered PIP2 sensitivity. The conservation of these residues within the KG channel family indicates that the ionic bond is a character that maintains the channels in a closed state by controlling the PIP2 sensitivity.

Poly(brilliant cresyl blue) modified glassy carbon electrodes: Electrosynthesis, characterisation and application in biosensors

The phenoxazine dye, brilliant cresyl blue (BCB) has been polymerised on glassy carbon electrodes by potential cycling, and the resulting poly(brilliant cresyl blue) (PBCB) film has been studied by cyclic voltammetry, differential pulse voltammetry and electrochemical impedance spectroscopy. A differential pulse voltammetry study in different supporting electrolytes with different pH values revealed that the current intensity of the oxidation peak of the resulting polymer increases with increase in pH up to pH 4.1 where the highest response is exhibited and then begins to decrease. It was also observed that the peak potential moves to more negative values with increase in pH with a slope of −51 mV/pH, indicating an equal number of electrons and protons in the redox process. The electrode modified with poly(brilliant cresyl blue) was successfully applied to the determination of hydrogen peroxide in amperometric mode at 0.0 V vs. SCE. Glucose oxidase enzyme was then immobilised by crosslinking with glutaraldehyde and bovine serum albumin (BSA): the polymer functions as a redox mediator in a glucose biosensor allowing determination of glucose at small negative potentials with low interferences.

Metal-Insulator-Like Behavior in Semimetallic Bismuth and Graphite

When high quality bismuth or graphite crystals are placed in a magnetic field directed along the c axis (trigonal axis for bismuth) and the temperature is lowered, the resistance increases as it does in an insulator but then saturates. We show that the combination of unusual features specific to semimetals, i.e., low carrier density, small effective mass, high purity, and an equal number of electrons and holes (compensation), gives rise to a unique ordering and spacing of three characteristic energy scales, which not only is specific to semimetals but which concomitantly provides a wide window for the observation of apparent field-induced metal-insulator behavior. Using magnetotransport and Hall measurements, the details of this unusual behavior are captured with a conventional multiband model, thus confirming the occupation by semimetals of a unique niche between conventional metals and semiconductors.

Ion Beam Sputter Deposition Of Optical Coatings

A beam of 500 to 1200 eV argon and oxygen ions, neutralized with an equal number of electrons, strikes a target, and the sputtered particles form a deposited layer of SiO2, Ta205, or TiO2. A second beam at lower energy is aimed at the substrate and used for stress modification and predeposition sputter cleaning. Deposited films are mechanically stable and extremely adherent; internal stress is compressive. The primary contaminant is carbon, which is less than one percent. Refractive indices near 1 µm are 1.47 for SiO2, 2.03 for Ta205, and 2.27 for Ti02. Optical absorptance of half-wavelength films at 1.06 Am is near 10-4 for SiO2 and Ta205 and near 4 X 10-4 for TiO2. Damage tests with a 114 um radius, 5 ns pulse length, 1.06 um wavelength laser show an onset energy flux for visible damage in the 12 to 30 J/cm2 range for single-layer films, and slightly less for a three-layer structure.

Charge transfer transitions in extended correlated electronic systems

The positions are intensities of dipole-allowed charge transfer (CT) excitations are found exactly for model hamiltonians with one valence state per site, nearest-neighbor electron transfer, and equal number of electrons N e and sites N. Diagrammatic valence bond (VB) methods yield the complete analysis of configuration interactions in free-radical stacks of N 3 = N = 4 and 6 sites and in donor-acceptor stacks of N e = N = 4, 6 and 8 sites, which suffice for N → ∞ extrapolarations. The previously used dimer model ( N e = N = 2) of CT transitions is significantly modified in extended systems when, as in π-molecular free-radical or CT solids or in linear polyenes, the correlations are comparable to the bandwidth and there is extensive configuration interaction mixing of VB states with different electron distributions. The roles of correlations, of nearest-neighbor interactions, and of temperature are discussed, and constrasted to dimer results, for CT transition in both segregated an mixed stacks.

Topology of the Fermi Surface of Zinc from Galvanomagnetic Measurements

High-field magnetoresistance and Hall effect measurements have been made on high-purity single crystals of zinc at 4.2\ifmmode^\circ\else\textdegree\fi{}K in magnetic fields up to 18kG. For an arbitrary field direction there is an equal number of electrons and holes but at special field directions there are open orbits. There is clear evidence that magnetic breakdown occurs at points $H$ and $K$ of the Brillouin zone at quite low fields. The topology of the multiply connected sheet of the Fermi surface is similar to that predicted by the free-electron model.

The ion distribution above the F2maximum

Observations of the ion distribution in the ionosphere indicate that the distribution up to 550 km is controlled in part by changes in the recombination rate with altitude, although diffusion exerts an increasingly important influence above the F2 maximum. It is further concluded that the ion distribution above 550 km is controlled by diffusion and not by recombination, although a further reduction in recombination rate with increasing altitude does occur. Charge-exchange reactions between oxygen ions and hydrogen atoms at an altitude near the base of the exosphere provide a source of thermal protons which move upward along the magnetic field lines together with an equal number of electrons and produce a medium for the propagation of radio whistlers. The computed distribution of protons and electrons is in reasonable agreement with whistler observations. The whistler medium is of telluric origin, and the source of ionization is the same as that for the F region. It is suggested that the region above 1800 km in which protons predominate over all other ions be called the protonosphere, to distinguish it from the lower ionized region normally referred to as the ionosphere.

Discussion on isotopes

Sir J. J. Thomson: I think I shall best open the discussion this afternoon if, instead of attempting a history of the subject of isotopes, I confine myself to a few special points. The conception of isotopes—that is, of two elements which have different atomic weights but chemical properties so closely resembling each other that they have not yet been separated by chemical methods—was, I believe, first reached by Prof. Soddy in connection with radio-active substances. In the few remarks which I have to make this afternoon, I shall not deal with these substances; I will leave them to others who are better acquainted with them than myself; I propose to confine myself to the consideration of the isotopes, or with some points connected with the isotopes, of the lighter elements. Before doing so, I should like to say just a word about the conception of isotopes on the electron theory of an atom. On that theory the atoms of the isotopes contain an equal number of electrons. The difference in the atomic weight is supposed to be due to the simultaneous entry into the core of the atom of one or more positive charges, and an equal number of electrons, so that the electric charge on the core is not affected. In reference to this, I would like to say that it by no means follows that an electron and a positive charge will neutralise each other at the distances that occur in the atom, however close together they might be placed; and, though one would expect that the residual effect would not be large, yet I think it might easily be appreciable, and might produce some difference between the properties, chemical or physical, of the isotopes. For example, though I do not think it would affect the number of electrons in the outer layer, I think it would affect the distance of the outer layer from the core of the atom. And the statement that the chemical properties of an element depend only on the outer layer of the atom, is one with which I should agree if it is recognised that, even if the number of electrons in the outer layer is unaltered, differences in the distance of this layer from the centre may result in different chemical properties. For example, we, or at any rate some of us, believe that the valency of an element fixes the number of electrons in the outer layer. Thus, there are the same number of electrons in the outer layer of the atoms of silicon and of carbon, and yet there are well-marked differences in the chemical properties of these two substances.