Carbon Nanotube Electrodes for Electrochemical Detection of Dopamine

Carbon nanotubes (CNTs) are suited for neurochemistry because of their biological inertness, ability to withstand biofouling, and superior electron transport kinetics. Dopamine, the canonical monoaminergic neuromodulator, contributes to reward, cognition and attention, however, its detection in real-time is challenging due to its low basal concentration in the brain (100nM L-1). In our present work, we fabricate pyrolytic carbon electrodes and perform a CNT coating to improve the electrochemical kinetics of dopamine. Upon CNTs coating, dopamine shows a sensitivity of 9±18nA/μM for a cylindrical electrode having a mean surface diameter of 8±4μm. Increasing the scan frequency from 10-100 Hz shows that dopamine electron transfer kinetics improves; wherein dopamine is oxidized at 0.35±0.09V and reduced to -0.10±0.05V for 10 Hz. Increasing the frequency results in a shift of oxidation peak towards the anodic region, wherein dopamine oxidizes at 0.08±3V and reduces at -0.1±0.05V for 100 Hz, thus showing that dopamine redox is reversible which can be attributed to the superior electron transport kinetics of CNTs. The sensor was able to distinguish dopamine signals against other neurochemicals like serotonin and foulant 3,4-Dihydroxyphenylacetic acid (DOPAC). The minimum chemical detection that can be performed using these nanopipettes is 50±18nM L-1, which is well below the physiological concentrations of dopamine in the brain.Graphical AbstractA: Pictorial view of background-subtracted voltammetry. The waveform used was -0.4V to 1.3 V and cycled back to -0.4V at 10 Hz. B: The voltammogram was converted as a 2-D representation, into current, voltage, and repetition to understand the dopamine oxidation. C: Background subtracted voltammetry for dopamine using 100 Hz waveform. D: The 2-D representation of current, voltage, and repetition.

Triphenylantimony(V) Catecholates of the Type (3-RS-4,6-DBCat)SbPh3-Catechol Thioether Derivatives: Structure, Electrochemical Properties, and Antiradical Activity

A new series of triphenylantimony(V) 3-alkylthio/arylthio-substituted 4,6-di-tert-butylcatecholates of the type (3-RS-4,6-DBCat)SbPh3, where R = n-butyl (1), n-hexyl (2), n-octyl (3), cyclopentyl (4), cyclohexyl (5), benzyl (6), phenyl (7), and naphthyl-2 (8), were synthesized from the corresponding catechol thioethers and Ph3SbBr2 in the presence of a base. The crystal structures of 1, 2, 3, and 5 were determined by single-crystal X-ray analysis. The coordination polyhedron of 1–3 is better described as a tetragonal pyramid with a different degree of distortion, while that for 5- was a distorted trigonal bipyramid (τ = 0.014, 0.177, 0.26, 0.56, respectively). Complexes demonstrated different crystal packing of molecules. The electrochemical oxidation of the complexes involved the catecholate group as well as the thioether linker. The introduction of a thioether fragment into the aromatic ring of catechol ligand led to a shift in the potential of the “catechol/o-semiquinone” redox transition to the anodic region, which indicated the electron-withdrawing nature of the RS group. The radical scavenging activity of the complexes was determined in the reaction with DPPH radical.

The Influence of Ni Content on the Corrosion Resistance of Cu-Ni-Sn-C-P Sintered Alloys in Poor Quality Fuel

The copper alloys, which were added Nickel show high corrosion resistance. Therefore, they are generally used in environments of poor quality fuel. However, it is expected that we reduce the amount of Ni in copper alloy, due to increase of Nickel consumption in recent years. We used five different types of sintered material samples that are different in the content of Nickel in the present study, to investigate the influence of Ni content to corrosion resistance quantitatively. These samples were used for the experiment of open circuit potentials, anodic and cathodic polarization curves measurements. To simulate environment in poor quality fuel we employed solution of 0.5 M Na2S + 0.1 M NaOH (pH = 13.05). The experiment of open circuit potentials shows that samples that the content of Nickel is less than 42 mass% were formed passivation film on surface of sample during aeration. The experiment of polarization curves measurements show that the each sample was implied behavior of forming passivation film corresponding to potential-pH diagram of Cu in anodic region basically. In addition, the 36.4 mass% Nickel was remarkably improved corrosion resistance.

Inhibiting Effects of Two Derivatives of Amino-Thiophenol on the Corrosion of Copper by Electrochemical Methods

Corrosion inhibition of the two thio compounds, 2-{[(2-sulfanyl-phenyl)imino]methyl}phenol (SIMP) and 2-{[(Z)-1-(4-methyl-phenyl)methylidene]amino}-1-benzenthiol (MMAB), as corrosion inhibitors for copper in 15% hydrochloric acid (HCl) have been investigated by potentiodynamic polarization measurements and electrochemical impedance spectroscopy. Potentiodynamic polarization results show that corrosion potentials shift more toward the anodic region in the presence of thio compounds than that of blank solution. The adsorption of inhibitors on the copper surface follows from Langmuir adsorption isotherm. Activation energy (Ea), Gibbs free energy (ΔGads0), enthalpy (ΔH*), and entropy (ΔS*) of corrosion process are calculated by using the experimental measurements.

The Effect of Cd Addition on NDE of As-Cast Mg-Cd Alloy in 0.1M NaCl Solution

The effect of Cd additions on NDE of an as-cast Mg-Cd alloy in 0.1M NaCl solution was investigated using the gas collection method, potentiostatic current decay test and in-situ Laser Raman Spectroscopy. The experimental results showed that, in the cathodic region the addition of Cd reduced the hydrogen evolution and the magnesium hydride formation; in the anodic region the addition of Cd restrained the NDE but slightly increased the anodic dissolution.

Butadiynyl-bridged Diphenothiazines – Redox-active Fluorophores and Self-assembly on HOPG

Ethynyl phenothiazines are oxidatively coupled to symmetrical dumbbell-shaped butadiynylbridged diphenothiazines in good yields. These molecules show intense absorption bands, intense blue-green luminescence with large Stokes shifts, and reversible oxidation potentials in the anodic region. Thermally, these butadiynes do not undergo topochemical polymerization, but oligomerizations to oligomeric polycyclic heterocycles with complex structures in the melt. STM images of two representatives on HOPG (highly oriented pyrolytic graphite) show the formation of monolayers adsorbed by attractive π-π interactions.

Direct current electrical degradation of iron-doped titania ceramics

An anomalous increase of current was found in Fe-doped titania ceramics subjected to a constant field of 105 V/m. It is suggested that the space charge rises from blockage of O2(g) → O2−(s) ion transfer at the cathode. This leads to an increase of n-conductivity in the cathodic region and p-conductivity in the anodic region according to the specific defect equilibrium. This viewpoint was reinforced by two newly observed phenomena: (i) the I-V plot shows a linear feature at the initial stage, but it gradually becomes a rectifying feature with time; and (ii) an edge-located electrode shows lower current density and faster current saturation compared with a normal electrode.

ISOENZYMATIC POLYMORPHISM AND ACTIVITY OF PEROXIDASES OF COMMON BEAN (Phaseolus vulgaris L.) UNDER SALINE STRESS

One of the uses of the technique of tissue culture for plant breeding is the identification of cell lines tolerant to salt stress.In order to study the biochemical mechanisms involved in the genetic expression to salt tolerance, callus from embryo axis of four bean cultivars (cv. IAC-carioca; cv. IAPAR-14; cv. JALO-EEP558; CV. BAT-93) were grown in Murashige & Skoog (1962) medium, supplemented with NaCl in the concentrations of 0, 20, 40, 60 and 80 mM. After 14 days callus were harvested and analyzed according to their isoenzymatic patterns and peroxidase activities. BAT and IAPAR cultivars showed two common activity zones in the anodic region, with only one specific enzymatic band to each one (the two fastest migration band); it is possible that the two middle anodic zones detected are products of the same enzymatic locus but from different alleles with different eletrophoretic mobilities. Cv. JALO showed two anodic activities in common with cvs IAC and IAPAR with an exclusive anodic zone of slower migration which showed the most intense activity of all cultivars analyzed. This cv. still showed a dimeric heterozygotic catodic zone in all treated samples. Probably this is the same zone which occurs in homozygosis with fixation of the slower allele for all cvs BAT and IAPAR submitted to all treatments. Cv. IAC showed two anodic bands in common with Cv. IAPAR and cv. JALO. It still showed a faster anodic band in common with cv. IAPAR and an exclusive anodic band of slower migration. It is interesting to say that for this cv. IAC resulting from cultivation in NaCl 20 mM did not show activity in the three slower anodic zones. Cv. IAC showed only one dimeric heterozygotic catodic zone in all treatments. This zone is probably composed by two different alleles from the same locus detected in cv. JALO. Samples from cv. IAC treated with 40 and 60 mM showed a more intense enzymatic activity in the catodic zone. Analyses of the peroxidase activity in the crude extract of the different bean cultivars analysed showed different reations to salt concentration in the cultivation procedures as well as a high increasing of peroxidase activity in cv. IAC and JALO.