Electrochemical Preparation of Poly(acriflavine) Film‐Modified Electrode and Its Electrolcatalytic Properties Towards NADH,Nitrite and Sulfur Oxoanions

Electrochemical polymerization of acriflavine (AF) was carried out onto glassy carbon electrodes (GCE) from the aqueous buffer solution containing 1.5×10^?3 M AF monomer (pH 3.5) which produced a thin electrochemically active film. This is noted as poly(AF) film modified electrodes (PAF/GCE). This modified electrode was shown a stable reversible redox couple centered at +0.22 V in pH 3.5 buffer solutions. PAF/GCE was found to be more stable in acidic solutions and its formal potential was found to be pH dependent with a slope close to ?60 mV/pH. The electrochemical deposition kinetics of poly(AF) onto gold coated quartz crystal was studied by using electrochemical quartz crystal microbalance (EQCM) combined with cyclic voltammetry (CV). PAF/GCE was found be good mediator for electrochemical oxidation of reduced nicotinamide adenine dinucleotide (NADH) in pH 5 buffer solutions. The electrocatalytic oxidation of SO and electrocatalytic reduction of NO , SO and S₂O were carried out at PAF/GCE electrode in acidic aqueous solutions. The electrocatalytic oxidation of NADH was also investigated by using amperometric method.     

Electrochemical Behaviour of Microwave‐assisted Oxidized MWCNTs Based Disposable Electrodes: Proposal of a NADH Electrochemical Sensor

The effect of the oxidation degree of multiwalled carbon nanotubes (MWCNTs) for the detection of NADH was evaluated in this paper. MWCNTs were oxidized by microwave‐assisted sulfonitic treatment at different times (5, 10, 15, and 30 min) and deposited onto a graphite screen printed electrodes. Oxidized MWCNTs were characterized and the electrochemical performance evaluated. The best sensor in terms of sensitivity and stability was obtained after 15 minutes of oxidation (SPE/CNT15). A significant reduction of the NADH oxidation potential was recorded for oxidized MWCNTs compared with unmodified MWCNTs (0.270 V and 0.500 V, respectively vs. Ag/AgCl pseudo reference electrode), increasing the selectivity of the system. Chronoamperometric calibration curves carried out applying a potential of 0.3 V for 1 min were linear in the 4–35 μM range of NADH. A limit of detection of 1 μM was achieved with negligible surface fouling (three consecutive calibration curves, 30 total measurements: slope decrease 5.9 %). Inter electrode reproducibility (n=13) was good resulting in RSD of 15.2 % and 5.0 % for the peak intensity and the oxidation potential, respectively. Quantification of glucose in white wine samples was carried out to demonstrate the ability of the NADH sensor to work in real samples. A good correlation with a spectrophotometric kit for the glucose quantification was achieved.     

耐尔兰共价键合修饰石墨电极的电化学行为及对NADH的响应研究

本文报道了耐尔兰Ａ键合型石墨修饰电极的制作方法,详细研究了修饰电极的电化学行为及对ＮＡＤＨ的响应情况。在ｐＨ７．４的磷酸盐缓冲溶液中,用该电极在０ｍＶ（ｖ．ｓＳＣＥ）电位下检测ＮＡＤＨ,响应电流与ＮＡＤＨ浓度在４．３×１０－６～５．２×１０－４ｍｏｌ·Ｌ－１范围内成线性关系,检测下限为１．２×１０－６ｍｏｌ·     

天青Ⅰ修饰玻碳电极的电化学性质及其对NADH的催化氧化

本文利用滴涂于玻碳表面的Nafion膜中负电性的磺酸基与天青I阳离子之间的静电作用,以实现天青I的固定化,从而制备出Nafion/天青I电催化型烟酰胺腺嘌呤二核苷酸(NADH)传感器。采用循环伏安法考察了传感器的电化学性质,并研究了该修饰电极对NADH的电催化作用。实验结果表明:该修饰电极对NADH有良好的电催化作用,NADH氧化峰电位比未修饰的玻碳电极负移了660 mV,响应电流与NADH的浓度在8.7×10-5~1.5×10-2mol/L范围内呈良好的线性关系。该方法检出限为3.0×10-5mol/L。     

运动训练大鼠的自体荧光研究

首次通过激光诱导荧光光谱技术(LIF)研究运动训练大鼠心脏、肾脏、肝脏、脂肪以及前腿肌和后腿的比目鱼肌和腓肠肌的自体荧光光谱特性。测量所用的激发光波长为250～650 nm而发射波长为300～700 nm。比较参照组和3组不同运动状态组的三维荧光光谱,主要在腓肠肌的光谱中发现了和运动相关且位于激发波长(340±10)nm和发射波长(460±10)nm区域的特有荧光峰。根据这一荧光峰可以判别其对应的荧光物质是NADH(还原态烟酰胺腺嘌呤二核苷酸)。比较3组不同运动模式组的荧光光谱,发现运动模式与其峰强具有明显的相关性。研究结果表明,运动大鼠腓肠肌的能量代谢强于前腿、比目鱼肌及其他脏器,且NADH自体荧光光谱特性是判断肌肉代谢程度的有效的指标之一。     

Caffeic acid modified glassy carbon electrode for electrocatalytic oxidation of reduced nicotinamide adenine dinucleotide (NADH)

A new modified electrode was prepared by electrodeposition of caffeic acid (CFA) at the surface of an activated glassy carbon electrode. Cyclic voltammetry was used to investigate the redox properties of this electrode at various solution pH values and at various scan rates. The pH dependence of the electrode response was found to be 58.5 mV/pH, which is very close to the expected Nernstian value. The electrode was also employed to study electrocatalytic oxidation of reduced nicotinamide adenine dinucleotide (NADH), using cyclic voltammetry, chronoamperometry and rotating disk voltammetry as diagnostic techniques. It was found that the modified electrode exhibits potent and persistent electrocatalytic properties toward NADH oxidation in phosphate buffer solution (pH 7.0) with a diminution of the overpotential of about 450 mV compared to the process at an unmodified electrode. The electrocatalytic current increases linearly with NADH concentration in the range tested from 0.05 to 1.0 mM. The apparent charge transfer rate constant and transfer coefficient for electron transfer between the electrode surface and immobilized CFA were calculated as 11.2 s⁻¹ and 0.43, respectively. The heterogeneous rate constant for oxidation of NADH at the CFA-modified electrode surface was also determined and found to be about 3 × 10³ M⁻¹ s⁻¹. Finally, the diffusion coefficient of NADH was calculated as 3.24 × 10⁻⁶ cm² s⁻¹ for the experimental conditions, using chronoamperometric results. Received: 6 January 1999 / Accepted: 11 May 1999     

Comparative Studies on Electrocatalytic Activities of Chemically Reduced Graphene Oxide and Electrochemically Reduced Graphene Oxide Noncovalently Functionalized with Poly(methylene blue)

This study compares the electrocatalytic activities of chemically reduced graphene oxide (crGO) and electrochemically reduced graphene oxide (erGO), which are both noncovalently functionalized with a polyaromatic dye, poly(methylene blue) (polyMB), toward the oxidation of β‐nicotinamide adenine dinucleotide (NADH). PolyMB‐crGO and polyMB‐erGO composites were obtained via electropolymerization of methylene blue on crGO and GO modified glassy carbon (GC) electrodes, respectively. Cyclic voltammetry (CV) results indicate that these two types of integrated electrodes reveal different electrocatalytic activities. PolyMB‐crGO integrated electrode possesses lower catalytic oxidation potential, suggesting higher catalytic activity. The present study is helpful for the understanding and screening of graphene‐based advanced carbon nanomaterials for potential electrochemical applications.     

Theoretical Study of One-electron Redox Potentials of Some NADH Model Compounds

Several 1‐benzyl‐1,4‐dihydronicotinamide derivatives, which are important NADH model compounds were studied theoretically in acetonitrile. The performances of various DFT methods including B3LYP, B1B95, B3PW91, MPW1B95, MPWKCIS, and M06 were tested to calculate the redox potentials. The first theoretical protocol to predict the redox potentials of these derivatives is B1B95, whose reliability has been tested against almost all the available experimental data. Strikingly, the mean absolute derivations (MAD) and root mean square (RMS) error of the current theoretical model equal 0.015 and 0.017, respectively. By using this method, the important thermodynamic properties of BNAHs were investigated and the mechanisms of hydride transfer progress were explained. Besides, para‐substituents that have a big effect on these redox potentials of BNAH were systematically studied and carefully demonstrated.     

Stereomodulating effect of remote groups on the NADH-mimetic reduction of alkyl aroylformates with 1,4-dihydronicotinamide-β-lactam amides

Conformationally restricted NADH peptidomimetics 4a-e, characterized by the presence of a (1,4-dihydronicotinamide)-(β-lactam) moiety, have been synthesized and used to study the Mg²⁺ cation-promoted asymmetric reduction of alkyl aroylformates in acetonitrile. Increasing the bulkiness of peripheral substituents at the nitrogen atom of the β-lactam ring, at the 1,4-dihydronicotinamide moiety, or at the aroylformate ester group, was found to cause weak but clearly detectable variations of the enantiomeric excess of the reaction. A rational for these observations was consistent with a chelated NADH/Mg²⁺/ArCOCO₂R³ ternary complex model, according to DFT calculations computed at a B3LYP/6-31G^∗ theory level.     

Direct Modification of a Glassy Carbon Electrode with Toluidine Blue Diazonium Salt: Application to NADH Determination and Biosensing of Ethanol

We describe here the covalent modification of a glassy carbon electrode with toluidine blue (TB) diazonium salt, which is generated in situ from the reaction between the aromatic amino phenyl group of TB and sodium nitrite. TB is attached directly to the electrode surface without any cross‐linking agent or complex matrices. The resulting TB films exhibit excellent electrocatalytic behavior toward NADH oxidation. Low potential detection of NADH is performed at 0.15 V vs. Ag/AgCl. Furthermore, an ethanol biosensor is developed using the TB modified electrode and alcohol dehydrogenase. The great stability and reusability, excellent electrochemical reversibility, technically simple preparation and short preparation time make this method suitable for low‐cost bioelectronical devices.