NADH coenzyme model compound as photocatalyst for the direct arylation of (hetero)arenes

9,10-Dihydro-10-methylacridine (AcrH₂), a NADH coenzyme model compound, as an organo-photoredox catalyst is demonstrated for the cross-coupling of aryl diazonium salts with (hetero)arenes. Under mild and operationally simple conditions, this new photocatalytic protocol has been applied to arylation of a wide variety of (hetero)arenes and tolerates various functional groups.     

Controlled Electrodeposition of Au‐Copper Oxide Nanocomposite on a Renewable Carbon Ceramic Electrode for Sensitive Determination of NADH in Serum Samples

In this study, a sensitive nicotinamide adenine dinucleotide (NADH) biosensor based on Au‐Copper oxide nanocomposite modified carbon ceramic electrode (Au?CuO/CCE) was introduced. The developed NADH biosensor was prepared by controlled electrodeposition of copper and Au nanoparticles on the surface of a renewable CCE and was turned to Au?CuO/CCE by cycling the potential in alkaline media. The prepared electrode was carefully characterized with scanning electron microscopy, X‐ray diffraction, atomic force microscopy and cyclic voltammetry techniques. According to scan rate study, surface coverage (Γ) of the fabricated Au?CuO/CCE was calculated to be 1.54×10^?8 mol cm^?2 which was 3 time more than CuO/CCE. The fabricated electrode is well stable which could be reliably utilized for the determination of NADH with amperometry technique over the concentration range of 1–29 μM with sensitivity and detection limit (S/N=3) of 0.1025 μA μM^?1 and 0.09 μM respectively. The prepared biosensor was used for NADH determination in serum samples with fast response time and satisfactory analytical results.     

Electrochemical and Photoelectrochemical Sensing of NADH and Ethanol Based on Immobilization of Electrogenerated Chlorpromazine Sulfoxide onto Graphene‐CdS Quantum Dot/Ionic Liquid Nanocomposite

Here, a simple one‐step solvothermal procedure was employed to synthesize a nanocomposite containing graphene‐nanosheets and CdS quantum dots (GNs‐CdS QDs). The electrochemical oxidation of chlorpromazine (CPZ) to chlorpromazine‐sulfoxide (CPZ‐SO) onto a GNs‐CdS QDs/ionic liquid (IL) nanocomposite modified glassy carbon (GC) electrode give rise to redox‐active products which showed excellent electrocatalytic and photoelectrocatalytic activity toward NADH oxidation at reduced overpotential. A linear response up to 200 µM was obtained for photoamperometric determination of NADH with detection limit 1 µM. Immobilizing alcohol dehydrogenase(ADH) onto the modified electrode via a simple cross linking procedure, the photoelectrochemical capability of the proposed system toward ethanol biosensing was clearly shown.     

Electrocatalytic adsorptive voltammetry for fludarabine determination in urine

Fludarabine (F-Ara-A, 9-β-d-arabinofuranosyl-2-fluoroadenine) is an arabinosyl nucleoside with potent cytotoxic activity against chronic lymphocytic leukemia. Herein, its electrochemical behavior is investigated on pyrolytic graphite electrodes (PGEs); and a novel catalytic adsorptive differential-pulse-voltammetric method for its determination is developed based on the strong electrocatalytic effect on nicotinamide adenine dinucleotide (NADH) oxidation exhibited by the oxidation products of F-Ara-A. This approach was applied to human urine samples, which required a previous solid-phase extraction. The F-Ara-A recovery was of 89.7%. The method proposed is fast, simple and permits detection of F-Ara-A concentrations up to 72 h after infusion.     

Intercalation of methylene blue into barium phosphate—synthesis and electrochemical investigation

Methylene blue (MB) was strongly retained inside the cavity of host layered barium phosphate, without leaching, and the intercalated compound was characterized through X-ray power diffraction (XRD), IR spectra and electrochemical measurements. The intercalated dye compound was incorporated into a carbon paste electrode and, by means of cyclic voltammetry and amperometry, its electrochemical properties were investigated. In various electrolyte solutions, changing the pH between 3 and 9, the midpoint potential remained practically constant at −0.15 V. This is not the usual behavior for MB, since it is known that in the solution phase the midpoint potential changes considerably with pH. These data suggest that methylene blue behaves as a guest molecule in the lamellar structure of the barium phosphate. The electrode formed by this host/guest composition was used to investigate NADH electrochemical oxidation.     

1,4-Dihydropicolinic acid derivatives: novel NADH analogues with an altered connectivity pattern

Sodium dithionite reduction of α-substituted N-alkylpyridinium salts (derived from picolinic acid derivatives) afforded the corresponding 1,4-dihydropyridines with a new substitution pattern, in which the electron-withdrawing group is at the α-position. These compounds promote biomimetic reductions and are hence considered functional NADH analogues.     

1,4-与1,2-二氢NADH模型物反应活性的比较

合成了两类NADH模型物: p-G-1,4-2H-PNAH和p-G-1,2-2H-PNAH, 测得了它们在不同温度下的乙腈中分别与四氯苯醌及N,N,N',N'-四甲基对苯二胺自由基正离子(TMPA+·)反应的速率常数及反应的活化参数(ΔH≠, ΔS≠, ΔG≠). 动力学研究结果表明: 1,2-2H-PNAH和1,4-2H-PNAH的相对反应活性可以通过远位取代基调节; 1,2-2H-PNAH和1,4-2H-PNAH与四氯苯醌的反应是决速步骤的熵控反应, 而1,2-2H-PNAH和1,4-2H-PNAH与TMPA+·的反应决速步骤则是由焓和熵共同控制的反应; 通过lnk2~σ的相关分析可以看出1,2-2H-PNAH和1,4-2H-PNAH与四氯苯醌及TMPA+·反应决速步骤中反应中心是正电荷增加的过程, 而且1,2-2H-PNAH的取代基效应大于1,4-2H-PNAH的取代基效应.     

Electrocatalytic oxidation of NADH at gold nanoparticles loaded poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid) film modified electrode and integration of alcohol dehydrogenase for alcohol sensing

A new modified electrode is fabricated by dispersing gold nanoparticles onto the matrix of poly(3,4-ethylenedioxythiophene)–poly(styrene sulfonic acid), PEDOT–PSS. The electrocatalytic activity of the PEDOT–PSS-Au_nano electrode towards the oxidation of β-nicotinamide adenine dinucleotide (NADH) is investigated. A substantial decrease in the overpotential (>0.7 V) has been observed for the oxidation of NADH at the PEDOT–PSS-Au_nano electrode in comparison to the potential at PEDOT–PSS electrode. The Au nanoparticles dispersed in the PEDOT–PSS matrix prevents the fouling of electrode surface by the oxidation products of NADH and augments the oxidation of NADH at a less positive potential (+0.04 V vs. SCE). The electrode shows high sensitivity to the electrocatalytic oxidation of NADH. Further, the presence of ascorbic acid and uric acid does not interfere during the detection of NADH. Important practical advantages such as stability of the electrode (retains 95% of its original activity after 20 days), reproducibility of the measurements (R.S.D.: 2.8%; n = 5), selectivity and wide linear dynamic range (1–80 μM; R² = 0.996) are achieved at PEDOT–PSS-Au_nano electrode. The ability of PEDOT–PSS-Au_nano electrode to promote the electron transfer between NADH and the electrode makes us to fabricate a biocompatible dehydrogenase-based biosensor for the measurement of ethanol. The biosensor showed high sensitivity to ethanol with rapid detection, good reproducibility and excellent stability.     

Comparison of the Electrochemical Reactivity of Carbon Nanotubes Paste Electrodes with Different Types of Multiwalled Carbon Nanotubes

Carbon nanotubes (CNTs) are widely used in electrochemical studies. It is reported that CNTs with different source and dispersed in different agents [1] yield significant difference of electrochemical reactivity. Here we report on the electrochemical performance of CNTs paste electrodes (CNTPEs) prepared by multiwalled carbon nanotubes (MWNTs) with different diameters, lengths and functional groups. The resulting electrodes exhibit remarkable different electrochemical reactivity towards redox molecules such as NADH and K₃[Fe(CN)₆]. It is found that CNTPEs prepared by MWNTs with 20–30 nm diameter show highest catalysis to NADH oxidation, while CNTPEs prepared by MWNTs with carboxylate groups have best electron‐transfer rate (The peak‐peak separation (ΔE_p) is +0.108 V for MWNTs with carboxylate groups, +0.155 V for normal MWNTs, and +0.174 V for short MWNTs) but weak catalysis towards oxidation of NADH owing to the hydrophilicity of carboxylate groups. The electrochemical reactivity depends on the lengths of CNTs to some extent. The ‘long’ CNTs perform better in our study (The oxidation signals of NADH appear below +0.39 V for ‘long’ CNTs and above +0.46 V for the ‘short’ one totally). Readers may get some directions from this article while choose CNTs for electrochemical study.     

Single sample extraction protocol for the quantification of NAD and NADH redox states in Saccharomyces cerevisiae

A robust redox extraction protocol for quantitative and reproducible metabolite isolation and recovery has been developed for simultaneous measurement of nicotinamide adenine dinucleotide (NAD) and its reduced form, NADH, from Saccharomyces cerevisiae. Following culture in liquid media, yeast cells were harvested by centrifugation and then lysed under nonoxidizing conditions by bead blasting in ice-cold, nitrogen-saturated 50 mM ammonium acetate. To enable protein denaturation, ice cold nitrogen-saturated CH(3)CN/50 mM ammonium acetate (3:1 v/v) was added to the cell lysates. Chloroform extractions were performed on supernatants to remove organic solvent. Samples were lyophilized and resuspended in 50 mM ammonium acetate. NAD and NADH were separated by HPLC and quantified using UV-Vis absorbance detection. NAD and NADH levels were evaluated in yeast grown under normal (2% glucose) and calorie restricted (0.5% glucose) conditions. Results demonstrate that it is possible to perform a single preparation to reliably and robustly quantitate both NAD and NADH contents in the same sample. Robustness of the protocol suggests it will be (i) applicable to quantification of these metabolites in other cell cultures; and (ii) amenable to isotope labeling strategies to determine the relative contribution of specific metabolic pathways to total NAD and NADH levels in cell cultures.