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排序方式: 共有212条查询结果,搜索用时 15 毫秒
31.
Francisco Berbel José Manuel Dı́az-Cruz Cristina Ariño Miquel Esteban 《Journal of electroanalytical chemistry (Lausanne, Switzerland)》1999,475(2):99-106
An extension of a voltammetric model for the complexation between metal ions and mixtures of ligands (either simple or macromolecular, labile or inert) is proposed for the study of the Zn(II)+oxalate system. The model considers the presence of species of low solubility that can be assumed to behave as soluble inert complexes. As well as the solubility problem, a loss of reversibility in the zinc reduction process occurs. This problem is overcome by increasing the effective time scale of the measurements. The application of the model to experimental data has produced reliable results, which can be used to estimate complexation constants and solubility products, as long as the irreversible processes that influence the current and potential measurement are avoided. 相似文献
32.
A relatively high level of extracellular ascorbate in the striatum, which is known to modulate impulse flow in striatal neurons, originates primarily from glutamate-containing corticostriatal afferents. Increasing evidence suggests that ascorbate release from these fibers is regulated by a multisynaptic loop that includes γ-aminobutyric acid (GABA) mechanisms in the substantia nigra. To assess the role that nigral GABA plays in striatal ascorbate release, extracellular ascorbate was monitored voltammetrically in the striatum during infusions of GABA into the substantia nigra pars reticulata (SNr) of awake, unrestrained rats. Compared to vehicle infusions, intranigral GABA lowered striatal ascorbate by >50%. In contrast, intranigral application of picrotoxin, a GABA antagonist, had the opposite effect. Neither GABA nor picrotoxin altered striatal 3,4-dihydroxyphenylacetic acid (DOPAC), a major dopamine metabolite. Collectively, these results indicate that intranigral GABA exerts a tonic inhibitory influence on ascorbate release in the striatum. 相似文献
33.
34.
Jorge García-Cañadas Ivan Mora-Seró Francisco Fabregat-Santiago Juan Bisquert Germà Garcia-Belmonte 《Journal of electroanalytical chemistry (Lausanne, Switzerland)》2004,565(2):329-334
The main features of cyclic voltammograms (CVs) of thin electrochromic films based on a-WO3 were investigated. First, the chemical capacitance is defined in terms of the electrochemical potential variation with the insertion level, x, and is measured under galvanostatic (chronopotentiometry) quasi-equilibrium conditions. An equilibrium capacitance increasing rapidly with respect to insertion level or negative potential is observed, respectively Cch∝xa at x>10?3(a≈0.74) and Cch∝Vα(α≈3). Simulation methods used to generate the observed CVs are described in detail. Major CV peaks can be simply understood as charging and discharging of the variable capacitor, in conjunction with a distortion of the voltage scale due to a series transport process. Therefore a simple RC equivalent circuit allows us to explain the principal CVs characteristics of lithium intercalation and deintercalation in amorphous films. 相似文献
35.
Jaume Puy Joan Cecilia Josep Galceran Raewyn M. Town Herman P. van Leeuwen 《Journal of electroanalytical chemistry (Lausanne, Switzerland)》2004,571(2):121-132
The voltammetric lability of a complex system, where a metal ion M and a ligand L form the species ML and ML2, is examined. Together with the rigorous numerical simulation of the problem, two limiting cases are analysed for the overall process ML2 → M: (i) the most common case for aqueous complexes, where ML → M is the kinetically limiting step and (ii) the case where ML2 → ML is limiting. In both cases, analytical expressions for the lability criteria are provided which show good agreement with the results obtained from the rigorous numerical simulation of the problem. 相似文献
36.
Jian-jun Zhang Artur H. Swiergiel Vitaliy S. Palamarchouk Adrian J. Dunn 《Brain research bulletin》1998,47(3):277-284
Previous studies have indicated that intracerebroventricular (i.c.v.) infusions of corticotropin-releasing factor (CRF) activate locus coeruleus (LC) noradrenergic neurons and increase the metabolism and extracellular concentrations of norepinephrine (NE) in several brain regions, suggesting increased release. To examine the temporal aspects and mechanism of the presumed release of NE, CRF was infused i.c.v. and the oxidation current was recorded using carbon fiber voltammetric electrodes placed in rat hippocampus or cortex. The CRF (1 μg, i.c.v.) caused a significant increase of oxidation current with a delay of approximately 5 min, and a peak at approximately 35 min. Similar responses were observed in the medial prefrontal cortex. The hippocampal response was markedly attenuated when CRF was infused into rats pretreated with DSP-4 to deplete NE, suggesting that the observed changes in current resulted from oxidation of NE. The increase of NE-like current did not occur when 25 μg alpha-helical CRF9–41 (ahCRF) was injected immediately before 1 μg CRF, suggesting that the response was mediated by cerebral CRF-receptors. Subcutaneous pretreatment with the ganglionic blocker, chlorisondamine, at a dose of 3 mg/kg had no effect on the voltammetric response to CRF, but a 6 mg/kg dose completely prevented the response. The β-adrenoceptor antagonists, S-propranolol (5 mg/kg), nadolol (5 and 10 mg/kg), and timolol (5 mg/kg) attenuated the NE response to i.c.v. CRF to varying degrees. When chlorisondamine (3 μg) or nadolol (5 μg) were given i.c.v. before the CRF, the hippocampal responses were not blocked. These results suggest peripheral actions of ganglionic and β-adrenergic blockers. We conclude that peripheral autonomic mechanisms, and probably both central and peripheral β-adrenoceptors, contribute to the increased secretion of hippocampal NE in response to i.c.v. CRF. 相似文献
37.
J Kim T.D Chung Hasuck Kim 《Journal of electroanalytical chemistry (Lausanne, Switzerland)》2001,499(1):78-84
The reduction peak of quinone in aprotic media appears at a positively shifted potential in the presence of acids, which play a role as proton sources. Since the height of the newly developed peak shows a good correlation with the concentration of the acid, it can be utilized to determine the concentration of weak acids. Although the magnitude of the peak potential shift (ΔEp) decreases as the water content in the solution increases, the presence of a Brønsted acid still leads to a significantly large ΔEp in an acetonitrile+water mixture (9/1, v/v) when a proper quinone derivative is chosen. ΔEp depends on not only the acidity of proton sources but also the basicity in quinone derivatives. Among the various quinones examined in the present study, tetramethyl-1,4-benzoquinone (duroquinone) exhibits the largest ΔEp and is found to be a suitable redox-active additive for the selective analysis of a variety of organic acids. Based on these results, conventional voltammetric techniques, e.g. differential pulse voltammetry, square-wave voltammetry and linear sweep voltammetry, can be employed to determine various biologically important acids with protonated amine or carboxylate groups. The quantitative analyses of histamine, maleic acid and pyruvic acid are successfully demonstrated in the 10?5 M range with a high sensitivity of 17~19 μA mM?1 by linear sweep voltammetry. 相似文献
38.
Nitrogen-oxygen breathing mixtures, for pressures higher than 0.5 MPa, decrease the release of dopamine in the rat striatum, due to the narcotic potency of nitrogen. In contrast, high pressures of helium-oxygen breathing mixtures of more than 1-2 MPa induce an increase of the striatal dopamine release and an enhancement of motor activity, referred to as the high pressure nervous syndrome (HPNS), and attributed to the effect of pressure per se. It has been demonstrated that the effect of pressure could be antagonized by narcotic gas in a ternary mixture, but most of the narcotic gas studies measuring DA release were executed below the threshold for pressure effect. To examine the effect of narcotic gases at pressure on the rat striatal dopamine release, we have used two gases, with different narcotic potency, at sublethargic pressure, nitrogen at 3 MPa and argon at 2 MPa. In addition, to dissociate the effect of the pressure, we have used nitrous oxide at 0.1 MPa to induce narcosis at very low pressure, and helium at 8 MPa to study the effect of pressure per se. In all the narcotic conditions we have recorded a decrease of the striatal dopamine release. In contrast, helium pressure induced an increase of DA release. For the pressures used, the results suggest that the decrease of dopamine release was independent of such an effect of the pressure. However, for the same narcotic gas, the measurements of the extracellular DA performed in the striatum seem to reflect an opposing effect of pressure, since the decrease in DA release is lower with increasing pressure. 相似文献
39.
Sana Ansari M. Shahnawaze Ansari Soami P. Satsangee Rajeev Jain 《Journal of Pharmaceutical Analysis》2021,11(1):57
In the present work, a chemically modified electrode has been fabricated utilizing Bi2O3/ZnO nanocomposite. The nanocomposite was synthesized by simple sonochemical method and characterized for its structural and morphological properties by using XRD, FESEM, EDAX, HRTEM and XPS techniques. The results clearly indicated co-existence of Bi2O3 and ZnO in the nanocomposite with chemical interaction between them. Bi2O3/ZnO nanocomposite based glassy carbon electrode (GCE) was utilized for sensitive voltammetric detection of an anti-biotic drug (balofloxacin). The modification amplified the electroactive surface area of the sensor, thus providing more sites for oxidation of analyte. Cyclic and square wave voltammograms revealed that Bi2O3/ZnO modified electrode provides excellent electrocatalytic action towards balofloxacin oxidation. The current exhibited a wide linear response in concentration range of 150–1000 nM and detection limit of 40.5 nM was attained. The modified electrode offered advantages in terms of simplicity of preparation, fair stability (RSD 1.45%), appreciable reproducibility (RSD 2.03%) and selectivity. The proposed sensor was applied for determining balofloxacin in commercial pharmaceutical formulations and blood serum samples with the mean recoveries of 99.09% and 99.5%, respectively. 相似文献
40.
E Lojou P Bianco M Bruschi 《Journal of electroanalytical chemistry (Lausanne, Switzerland)》1998,452(2):167-177
Cyclic voltammetry was used to investigate the kinetics of the electron transfer between various soluble or solid metal oxides, and polyheme c-type cytochromes from Desulfuromonas acetoxidans and Desulfovibrio. The second order rate constant for the catalytic reduction of soluble chromate ions by Desulfuromonas acetoxidans cytochrome c7 was found to be 6×105 M?1 s?1. By using the membrane electrode technology, it has been shown that the catalytic process for Cr(VI) reduction is efficient even when the cytochrome is entrapped in the close vicinity of the electrode surface. Moreover, this proceeding allowed the catalytic reduction of solid metal oxides such as manganese(IV), vanadium(V) and iron(III) oxides to be performed. Results suggest that the metal reductase activity of a microorganism is governed by its c-type cytochrome content. Furthermore, only cytochromes with bishistidinyl heme iron coordination act as metal reducers whereas mitochondrial c-type cytochromes do not. This approach opens new pathways for the use of sulfur or sulfate bacteria in the bioremediation of metal contaminated waters and waste streams. Processes involving the use of entrapped enzymes reactors could be developed according to the metal reducing activity of their polyheme c-type cytochromes. 相似文献