碳纳米管-离子液体纳米流体修饰电极用于尿酸的测定

目的:用碳纳米管-离子液体纳米流体修饰玻碳电极,构建测定尿酸的电化学传感器。方法:将构建的电化学传感器置于尿酸的磷酸盐缓冲溶液中,实验结果表明,尿酸在修饰电极上产生一氧化峰,峰电位为0.570 V(vs.SCE),较裸电极负移0.170 V,且峰电流大大增强。据此,建立了测定UA的电化学分析方法。结果:在选定的最佳实验条件下,用线性扫描循环伏安法(LSV)测定尿酸的线性范围为5×10-6mol/L~8×10-4mol/L,检出限为5.5×10-7mol/L。结论:该方法可直接用于人体尿液中UA的测定,结果满意。     

Electrochemical determination of naltrexone on the surface of glassy carbon electrode modified with Nafion-doped carbon nanoparticles: Application to determinations in pharmaceutical and clinical preparations

A new sensitive and selective electrochemical sensor was developed for determination of naltrexone (NAL) in pharmaceutical dosage form and human plasma. Naltrexone is an opioid antagonist which is commonly used for the treatment of narcotic addiction and alcohol dependence. A voltammetric study of naltrexone has been carried out at the surface of glassy carbon electrode (GCE) modified with Nafion-doped carbon nanoparticles (CNPs). The electrochemical oxidation of naltrexone was investigated by cyclic and differential pulse voltammetric techniques. The dependence of peak currents and potentials on pH, concentration and the potential scan rate was investigated. The electrode characterization by electrochemical methods and atomic force microscopy (AFM) showed that CNPs enhanced the electroactive surface area and accelerated the rate of electron transfer. Application of the modified electrode resulted in a sensitivity enhancement of more than 20 times, relative to the bare GCE, in detection of NAL and a considerable negative shift in peak potential was achieved. Two linear dynamic ranges of 1–10 μM and 10–100 μM with a detection limit of 0.1 μM was obtained in phosphate buffer of pH = 3. Differential pulse voltammetry as a simple, rapid, sensitive and selective method was developed for the determination of NAL in dosage form and human plasma without any treatments. No electroactive interferences were found in biological fluids from the endogenous substances and additives present in capsules.     

Stripping coulometry determination of lead and mercury at screen-printed electrodes

The new possibilities of stripping coulometry method (SCM) using coulometric constant for the determination of the total electric charge are addressed. Since SCM is a method critical to the volume of the sample solution, the use of screen-printed electrodes (SPE) can significantly reduce the time of measurement. This work is devoted to the development of the new ways to define the coulometric constants and SCM determination of Pb and Hg at SPE.     

Solvent-effect on the interconversion among one-, two- and four-electron reduction waves for the 18-molybdodiphosphate complex, [(P2O7)Mo18O54]4−

For the [(P₂O₇)Mo₁₈O₅₄]^4? complex, the presence of small cations such as H⁺, Li⁺ and Na⁺ caused one-electron waves to be converted into four- and two-electron waves in a complex manner. With the addition of a trace amount of H⁺, a four-electron reduction wave was obtained in solvents of weaker basicity like acetone, acetonitrile and propylene carbonate (PC); the relative permittivity did not affect the appearance of the four-electron wave. On the other hand, two-electron waves were obtained in solvents of stronger basicity like N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), and N-methylpyrrolidinone (NMP). With the addition of Li⁺ or Na⁺, the one-electron waves were converted into two-electron waves only in acetone, indicating that the conversion can occur in solvents of both weak basicity and low relative permittivity.     

Electron transfer between a lutetium bisphthalocyanine and Fe across liquid|liquid interfaces between water and dichlorohexane or nitrobenzene; influence of coupling with ion transfer

The electron transfer across the liquid|liquid interface between aqueous solutions (W) of Fe^III/II compounds (hexacyanoferrates, chlorides) and a (t-butyl) substituted Lu^IIIbisphthalocyanine in dichlorohexane (DCH) or nitrobenzene (NB), has been studied by voltammetry at a microinterface and by spectrophotometry. The electron transfer wave has been observed only at the W|DCH. Coupling with an ion transfer facilitates this electron transfer: the Lu^IIIbisphthalocyanine has been oxidized or reduced across the W|NB interface, depending on the ion establishing the interfacial potential.     

Excitatory action of N-methyl- -aspartate on the rat locus coeruleus is mediated by nitric oxide: an in vivo voltammetric study

Biochemical, electrophysiological and behavioural studies have provided evidence that activation of N-methyl- -aspartate (NMDA) receptors contributes to the hyperactivity of noradrenergic neurons of the locus coeruleus (LC) in precipitated opioid withdrawal. Recently, it was demonstrated that central administration of nitric oxide (NO) synthase inhibitors suppresses this hyperactivity suggesting that NO mediates the NMDA receptor activation of LC in opioid withdrawal. Using a combination of microdialysis and in vivo voltammetry, this study examined whether local application of NMDA to the LC in opioid naive animals mimics the NO-dependent LC response seen in opioid withdrawal. In the urethane anaesthetized rat, perfusion of the LC (2 μl min⁻¹) with a solution of NMDA (5 mmol) via a microdialysis probe for 9 min resulted in a rapid and robust increase (290.1±32.2% above baseline) in the catechol oxidation current (CA·OC) recorded from the LC using differential normal pulse voltammetry (DNPV). The NMDA microdialysis also produced a large increase in the blood pressure (150.4±6.9% above baseline). An injection of the non-competitive NMDA receptor antagonist (+)MK-801 (0.5 mg kg⁻¹ i.v.), given 45 min after the start of NMDA application, rapidly returned both the CA·OC signal and the blood pressure response to baseline levels. Pretreatment of animals with intraventricular nitric oxide synthase (NOS) inhibitor, N^ω-nitro- -arginine methyl ester ( -NAME) (100 μg) significantly inhibited NOS activity in the LC, PAG-PVG and cerebellum. This dose of -NAME, administered prior to application of NMDA by microdialysis abolished the NMDA-induced rise in the CAOC recorded in the LC and the increase in systolic blood pressure. The results show that in voltammetry experiments, NMDA produces hyperactivity of LC and hypertension, responses that are dependent upon the synthesis of NO. Thus, in opioid naive rats, regional NMDA application via microdialysis mimics characteristics of the LC response that occur during the antagonist-precipitated opioid withdrawal.     

Direct electrochemistry and enzymatic activity of bacterial polyhemic cytochrome c3 incorporated in clay films

Quartz crystal microbalance and voltammetric measurements are used to study the electroenzymatic activity of incorporated bacterial polyhemic cytochrome c₃ in clay minerals. Two different natural clays have been chosen, i.e., kaolinite and montmorillonite, which differ in structure, swelling property and cation exchange capacity. Comparative voltammetric studies of various electroactive species at clay-modified pyrolytic graphite electrodes are first undertaken, which allow the complete characterization of the clay deposit. Then, the incorporation process of bacterial polyhemic cytochrome c₃ in the two clays is studied coupling quartz crystal microbalance and voltammetric measurements. Based on their respective characteristics, each clay yields a different behavior of the incorporated cytochrome c₃, with significantly different electroactive fractions of the immobilized protein. The consequences of the interactions between the protein and the clays on the enzymatic activity of cytochrome c₃ is then further examined. Firstly, the influence of the incorporation of cytochromes in clays on the metal reductase activity developed by bacterial polyheme c-type cytochromes is discussed. Secondly, hydrogenase enzymatic reactions are studied inside the clay films. An electrode is constructed by immobilizing hydrogenase in the clay and progressively incorporating either artificial (methyl viologen) or physiological (cytochrome c₃) hydrogenase partner. It is shown that this modified electrode yields an efficient and stable response for either H₂ consumption or evolution over a large range of pH.     

Solute exchange in the rabbit myocardium: Ischaemia, reflow, and myocardial necrosis

Objective: Coronary occlusion in the rabbit reduces the delivery of particulate tracers to close to zero, but exchange of diffusible solutes, derived from non-arterial sources, continues at a significant level. We investigated the relationships between the exchange of diffusible solutes during coronary occlusion and the extent of myocardial necrosis and between duration of ischaemia and the extent of recovery of solute exchange during reflow. Methods: In an anaesthetised rabbit model of regional ischaemia and reflow, solute exchange is measured using the voltammetric hydrogen clearance technique. The area at risk and infarct size are determined ex vivo with monastral blue and nitroblue tetrazolium staining, respectively. Three groups are studied: control perfusion for 130 minutes (group A); 30 minutes coronary ligation followed by 90 minutes reflow (group B) and 40 minutes coronary ligation followed by 90 minutes reflow (group C). Results: There was no significant difference in area at risk between the groups B and C (50±2% and 45±5%; p=ns) or in infarct size when expressed relative to the area at risk (42±7% and 55±5%; p=ns). During coronary ligation hydrogen clearance remained constant at 22±4% of the control region in group B and 32±4% in group C, at the same time period in group A it was 87±2% (ANOVA=p<0.05, with a significant non-linear trend). Although the duration of ischaemia and the level of solute exchange during ischaemia did not correlate individually with the extent of myocardial necrosis, together they showed a significant correlation (ANOVA; p<0.05). Following coronary occlusion, hydrogen clearance recovered to 72±9% after 30 minutes ischaemia but only to 57±5% following 40 minutes ischaemia and was 95±2% in the control group (ANOVA between the three groups p<0.05 with a significant linear trend). Myocardial hydration fell in the apical region following coronary ligation by 27±5% in group B and by 25±5% in group C, and rose on reperfusion but only to 80±3% in group B and 83±3% in group C of their preligation values. Conclusion: In collateral deficient myocardium, the extent of myocardial necrosis is dependent on the level of solute exchange occurring during ischaemia. The level of solute exchange during reflow is dependent on the duration of ischaemia. Received: 4 December 1997, Returned for 1. revision: 12 January 1998, 1. Revision received: 16 April 1998, Accepted: 13 May 1998     

Electrocatalytic reduction of uranium by bacterial cytochromes: biochemical and chemical factors influencing the catalytic process

Cyclic voltammetry was used to investigate the kinetics of the electron transfer between uranium(VI) and polyheme c-type cytochromes of bacterial origin. Reduced cytochromes were oxidized by U(VI), either in homogeneous solution, or when cytochromes were entrapped by a dialysis membrane or immobilized within an ion-exchanger film. By using membrane electrode technology, several factors such as uranium complexation, pH, origin of the cytochrome and medium were examined. Results suggest that uranium(VI) reductase activity is strongly dependent upon experimental conditions. In particular, a narrow pH window and well-controlled complexation conditions are necessary to observe high electrocatalytic reduction of uranium(VI) by c-type cytochromes. It has been demonstrated that U(VI) electroreduction originates in the presence of hemin-containing groups in the partner species.     

Hydrogenases from the hyperthermophilic bacterium Aquifex aeolicus: electrocatalysis of the hydrogen production/consumption reactions at carbon electrodes

Two [NiFe] hydrogenases extracted from the hyperthermophilic bacterium Aquifex aeolicus (Aa) are studied at a pyrolytic graphite electrode using cyclic voltammetry. The two hydrogenases have been shown to exhibit very similar behavior. They are able to catalyze under a nitrogen or a hydrogen atmosphere, the direct hydrogen production from protons and the reverse reaction of hydrogen oxidation directly in the absence of any promoter. The effect of experimental parameters (enzyme concentration, pH, ionic strength) are investigated. The electrocatalytic activity has been shown to increase when the temperature is increased within the range 22–65 °C in agreement with the evolution of the enzymatic activity. Using electrochemical techniques concomitantly with quartz crystal microgravimetry, it is demonstrated that the electrocatalysis is largely governed by the strong adsorption of hydrogenases on the electrode surface. The similarity between the two Aa hydrogenases and the hydrogenase from another hyperthermophilic bacterium, Pyrococcus furiosus, is discussed.