Electrocatalytic oxidation of NADH by Brilliant Cresyl Blue-DNA intercalation adduct

A new and simple electrochemical method capable to detect single-base mutations in DNA has been developed. It relies on the electrocatalytic oxidation of NADH by the intercalator Brilliant Cresyl Blue (BCB). Whereas negligible catalytic responses were obtained with graphite electrodes modified by BCB-single-stranded DNA, high catalytic activity is obtained at electrodes modified by the complexes between double-stranded DNA and BCB. The proposed explanation for these results is that charge transport from the intercalated BCB through the DNA base stack is a necessary event for the electrocatalytic activity as disruption by a single-base mismatch leads to a complete suppression of the electrocatalytic voltammetric response. These finds open new possibilities for the detection of DNA hybridization and mutation.     

Electrochemical oxidation of 2′,3′-dideoxyadenosine at pyrolytic graphite electrode

The oxidation chemistry of 2′,3′-dideoxyadenosine (I) has been studied at a pyrolytic graphite electrode (PGE) in the pH range 2.4-10.9 and a well defined oxidation peak was noticed. The peak potential of the peak was linearly dependent on pH with dE_p/dpH as 42 mV/pH. Voltammetric, coulometric, spectral studies and product analysis indicate that the oxidation of (I) occurs in an EC reaction involving 6e⁻, 6H⁺ process at pH 7.2 to give allantoin, C-C dimer and dideoxyribose as the major products and a C-O-O-C linked dimer as a minor product. Tentative mechanisms for the formation of the products have also been suggested. A comparison of peak potential value of 2′,3′-dideoxyadenosine with adenosine and 2′-deoxyadensoine indicated that the difference is insignificant which has further been supported by the calculations of difference of energies of lowest unoccupied and highest occupied molecular orbitals.     

Electrocatalytic activity of 2,3,5,6-tetrachloro-1,4-benzoquinone/multi-walled carbon nanotubes immobilized on edge plane pyrolytic graphite electrode for NADH oxidation

This work reports the electrocatalytic activity of 2,3,5,6-tetrachloro-1,4-benzoquinone (TCBQ)/multi-walled carbon nanotubes (MWCNT) immobilized on an edge plane pyrolytic graphite electrode for nicotinamide adenine dinucleotide (NADH) oxidation. Scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS) were used to confirms the presence of chloro after the nanotube modification with 2,3,5,6-tetrachloro-1,4-benzoquinone. The surface charge transfer constant, k_s, and the charge transfer coefficient for the modified electrode, α, were estimated as 98.5 (±0.6) s⁻¹ and 0.5, respectively. With this modified electrode the oxidation potential of the NADH was shifted about 300 mV toward a less positive value, presenting a peak current much higher than those measured on an unmodified edge plane pyrolytic graphite electrode (EPPG). Cyclic voltammetry and rotating disk electrode (RDE) experiments indicated that the NADH oxidation reaction involves 2 electrons and a heterogenous rate constant (k_obs) of 3.1 × 10⁵ mol⁻¹ l s⁻¹. The detection limit, repeatability, long-term stability, time of response and linear response range were also investigated.     

Electrocatalytic oxidation of NADH on a glassy carbon electrode modified with MWCNT-Pd nanoparticles and poly 3,4-ethylenedioxypyrrole

An NADH biosensor based on MWCNTs-Pd nanoparticles and polymerized 3,4-ethylenedioxypyrrole (PEDOP) was developed and characterized. PEDOP/MWCNTs-Pd/GCE was prepared quickly and simply and showed improved sensitivity to NADH. Comparable results were obtained by cyclic voltammetric (CV) and amperometric methods for NADH determination. The amperometric method gave short response times, and linear regression was observed at concentrations below 1.0 mM. The proposed NADH biosensor exhibited a wide linear response range of 1 μM–13 mM during amperometric testing using an applied potential of 0.42 V, with a low detection limit of 0.18 μM (S/N = 3). The sensor demonstrated fast responses and good stability.     

Electrocatalytic properties of NDGA and NDGA/FAD hybrid film modified electrodes for NADH/NAD redox reaction

The fabrication of monolayers composed of nordihydroguaiaretic acid (NDGA), and hybrid films composed of NDGA-flavin adenine dinucleotide (FAD) adsorbed films was performed in neutral aqueous solutions to produce electrochemically active thin films exhibiting one and two redox couples, respectively. An electrochemical quartz crystal microbalance and cyclic voltammetry were used to study the in situ growth of the NDGA and hybrid NDGA/FAD film monolayers. The NDGA modified film electrocatalytically oxidized NADH, ascorbic acid, dopamine, and N₂H₄ in neutral aqueous solutions. Well-separated voltammetric peaks were observed for dopamine and uric acid mixtures, and also for ascorbic acid and uric acid mixtures using the NDGA/GC modified electrode. When transferred to various aqueous buffered solutions, the two redox couples of the NDGA/FAD hybrid film and their formal potentials were observed to be pH-dependent. The electrocatalytic oxidation and reduction of NADH and NAD⁺ by a NDGA/FAD hybrid film in neutral aqueous solutions was carried out, and the electrocatalytic oxidation of NADH was performed using a NDGA/FAD hybrid film.     

New Cu(I) complexes with 2,2′-biquinolyl and 2,2′-quinolyl-pyridine containing polymer ligands as electrocatalysts for O2 activation in the oxidation of aliphatic amines

A series of polynuclear Cu(I) complexes with various types of polymer ligands containing 2,2′-biquinolyl (biQ) or 2,2′-quinolyl-pyridine (QPy) fragments in the polymer backbone was synthesized using sacrificial Cu anode. Cyclic voltammetry investigation of the obtained complexes revealed the formation of two types of Cu(I) coordination units, depending on the polymer's structure and electrolysis conditions. The first type of complexes, with only one biQ ligand per Cu(I) center, showed high oxidase activity in the air oxidation of primary and secondary amines to corresponding aldehydes with concomitant reduction of molecular oxygen to water. The reactions proceed in acetonitrile or N-methylpyrrolidone in the presence of O₂ at a potential of Cu^II/Cu^I electroreduction (−0.55 V vs. Ag/AgCl/KCl) with the high preparative yield and current efficiency. The possible scheme of the electrocatalytic process is discussed.     

聚亚甲基蓝/纳米二氧化硅修饰电极的制备及其对NADH的电催化氧化

通过电化学方法制备了聚亚甲基蓝/纳米二氧化硅复合膜修饰电极(PMB-nano-SiO2/GCE),采用扫描电子显微镜(SEM)和交流阻抗法(EIS)对复合膜界面进行了表征,并研究了烟酰胺腺嘌呤二核苷酸(NADH)在修饰电极表面的电化学行为。结果表明,在pH 7.0的磷酸盐缓冲溶液中,NADH氧化峰电位降低和峰电流明显增加,表明该修饰电极对NADH具有良好的电催化氧化性能。NADH浓度在1.0～100.0μmol/L浓度范围内与峰电流呈良好的线性关系,相关系数为0.997。     

Electrocatalytic activity of arylthio tetra-substituted oxotitanium(IV) phthalocyanines towards the oxidation of nitrite

This paper investigates the catalytic activities of arylthio substituted oxotitanium phthalocyanine (OTiPc) complexes that are immobilized on the glassy carbon electrode by electropolymerization, towards the oxidation of nitrite. The complexes are peripherally and non-peripherally substituted with phenylthio and benzylthio groups, namely 1a, 1b, 2a and 2b. All the modified electrodes exhibited improved electrocatalytic oxidation of nitrite than the unmodified electrodes by a two-electron mechanism producing nitrate ions. Catalytic currents are enhanced and nitrite overpotential reduced to ∼0.60 V. Kinetic parameters are determined for all complexes and a mechanism is proposed.     

Stabilization of the ethane oxidation catalytic activity of Cu-ZSM-5

The state of isolated copper ions in Cu-ZSM-5 containing additions of La, Ce, and Co was monitored in-situ by ESR under flow conditions. Treatment by steam at 630°C for 17 h or high-temperature dry calcination at 850°C induce an irreversible change in coordination for practically all square-planar Cu²⁺ ions in mono-cationic Cu-ZSM-5 without agglomeration or encapsulation of the isolated ions. All Cu²⁺ ions remain accessible to gas-phase molecules, but the catalytic reactivity of these altered copper sites decreases drastically. A stabilizing effect is noted for samples modified by a relatively large amount, ca. 5.0 wt.-%, of multivalent rare-earth ions La or Ce. Here a part of the copper ions (20–30%) preserves the parent square-planar Cu²⁺ state even after calcination at 850°C for 0.5 h. The effect of ca. 1% La or Ce is much less pronounced. The catalytic activity in the complete oxidation of ethane correlates well with the number of square-planar cupric cations retained by the samples after different treatments. The introduction of cobalt sharply increases the ethane oxidation activity of samples calcined at 500–650°C.     

Electrocatalytic activity of surface adsorbed ruthenium-alizarin complexone toward the oxidation of benzyl alcohol

The surface electrochemical behavior of an adsorbed alizarin complexone (abbreviated as AC) and its surface coordination with Ru(II) were studied in aqueous solution at a pH range of 0-6. The surface complex of ruthenium with AC displays strong electrocatalytic activities toward benzyl alcohol. Based on the rotating disk electrode measurement, it is believed that the electrocatalytic oxidation of benzyl alcohol is a two-electron and two-proton process with benzaldehyde as a major product. On the other hand, ruthenium-AC surface complex has also shown catalytic activities toward electro-oxidation of several small organic molecules such as methanol, formic acid, formaldehyde, ethanol, and acetaldehyde.     

An electrochemical study of poly(2,2′-dithiodianiline) in acidic aqueous media

Poly(2,2′-dithiodianiline) [poly(DTDA)], which is a conducting polymer interconnected with disulfide (SS) bonds, was studied electrochemically in acidic aqueous media. Redox reactions and structural changes of the poly(DTDA) in acidic aqueous solutions at various applied potentials and pH values were investigated. A Pourbaix diagram [potential (E)-pH profile] for the poly(DTDA) was plotted in order to distinguish the structures of the poly(DTDA) for the applied potentials and the pH values. The detailed structural changes were characterized using in situ UV-vis and surface-enhanced Raman spectroscopies.     

Electrochemical properties of benzylmercapto and dodecylmercapto tetra substituted nickel phthalocyanine complexes: Electrocatalytic oxidation of nitrite

Nickel tetrakis(benzylmercapto)phthalocyanine (NiTBMPc) and nickel tetrakis(dodecylmercapto)phthalocyanine (NiTDMPc) complexes were synthesized and their spectral and electrochemical properties reported. The CV showed four or five redox processes for NiTBMPc and NiTDMPc, respectively. For the first time, spectroelectrochemistry gave evidence for the formation of Ni^II/Ni^I process in a NiPc complex. The rest of the processes were ring based. The NiTBMPc complex was successfully deposited on both gold and glassy carbon electrodes by electropolymerisation while NiTDMPc complex was deposited on gold electrode only. The films were electro-transformed in aqueous 0.1 M NaOH solution to the O–Ni–O oxo bridged form. The modified electrodes were characterized using electrochemical impedance spectroscopy and the results showed typical behavior for modified electrodes. Electrodes with poly-Ni(OH)Pcs films exhibited higher charge transfer resistance values, R_p than their corresponding poly-NiPcs films counterparts. All the modified electrodes showed improved catalytic activities than the unmodified electrodes towards nitrite ions electrooxidation. Better catalytic activities were observed for the modified electrodes when they were transformed to O–Ni–O oxo bridge form. All the modified electrodes exhibited high resistance to electrode surface passivation.     

Electrocatalytic activity and stability of substituted iron phthalocyanines towards oxygen reduction evaluated at different temperatures

A significant amount of work has been done in the field of the transition metal (TM) macrocyclic-catalyzed oxygen reduction reaction (ORR), but not as a function of temperature and substitution in an acidic electrolyte to simulate the environment of an operating PEM fuel cell. The electrocatalytic activity of several iron-based phthalocyanine macrocycles for the ORR were evaluated using cyclic voltammetric (CV) and rotating disc electrode (RDE) techniques. The activities of these substituted iron phthalocyanines were compared to those of the unsubstituted species in the temperature range of 20-80 °C. The activity was also evaluated in the presence of hydrogen peroxide, both a possible by-product of the ORR and potential de-activator of iron phthalocyanines. The kinetics and corresponding parameters such as overall ORR electron transfer numbers, reaction rate constants, Tafel slopes, electron transfer numbers in the rate-determining step, and electron transfer coefficients were all measured in the temperature range of 20-80 °C. A mechanism for the different FePc-catalyzed ORR's was suggested based on the experimental results. The effect of substitution and temperature on ORR kinetics was also studied in this paper.     

Synergistic effect of a catechin-immobilized poly(3,4-ethylenedioxythiophene)-modified electrode on electrocatalysis of NADH in the presence of ascorbic acid and uric acid

Catechin is a polyphenolic flavonoid that can be isolated from a variety of natural sources, including tea leaves, grape seeds, and the wood and bark of trees such as acacia and mahogany. In our experiments, catechin was immobilized on PEDOT/GC (poly(3,4-ethylenedioxythiophene)/glassy carbon)-modified electrodes and used as a mediator for NADH (nicotinamide adenine dinucleotide) oxidation. The effect of the PEDOT thickness on the surface coverage of the catechin molecules was studied using cyclic voltammetry. The electrochemical properties and the effect of pH on the redox properties of the immobilized catechin molecules were studied by cyclic voltammetry in phosphate solution. The electrocatalytic oxidation of NADH at different electrode surfaces such as the bare GC-, the PEDOT/GC-, the catechin/GC- and the catechin/PEDOT/GC-modified electrodes was explored in phosphate solution at pH 7. In the catechin/PEDOT/GC-modified electrode, the PEDOT film plays an important role in resolving the oxidation potentials of ascorbic acid and NADH into two peaks that occur at the same potential for the catechin/GC-modified electrode surface. The heterogeneous electron transfer rate constant for NADH oxidation at the catechin/PEDOT/GC-modified electrode was determined using the rotating disk electrode technique and found to be 9.88 × 10³ M⁻¹ s⁻¹. The amperometric determination of NADH at the catechin/PEDOT/GC electrode was tested. The sensitivity of the electrode was 19 nA/μM.     

Characterization and activity of Fe-ZSM-5 catalysts for the total oxidation of phenol in aqueous solutions

Fe-ZSM-5 zeolites with of Si/Fe ratios varying from 40 to 200 were synthesized and characterized by IR, XRD, SEM, ESR and ion-exchange techniques. From the obtained results, it is possible to conclude that, these zeolites have a good crystallinity and that the incorporation of Fe³⁺ ions into the MFI-structure depends on the Si/Fe ratios in the gel: the higher the Si/Fe ratio, the more the percentage of Fe³⁺ions is incorporated into the MFI lattice.

Catalytic properties of Fe-ZSM-5 were studied in the oxidation of phenol. The reaction was performed in a static system, at the atmospheric pressure, 343 K, and with H₂O₂ concentration, which exceeds stoichiometric concentration for complete oxidation of phenol to carbon dioxide and water. From the catalytic results, it can be concluded that framework Fe can catalyze more completely phenol oxidation than the extra-framework Fe does.     

FeAPO-5分子筛的合成及其催化氧化水溶液中苯酚的性能

以水热晶化法合成了铁磷铝分子筛FeAPO-5,并用XRD、SEM、FT-IR和 UV-vis等对分子筛样品进行了表征。结果表明,所合成的FeAPO-5分子筛样品结晶度高,晶粒大小均匀,FeAPO-5样品中存在骨架Fe和骨架外Fe物种,并以骨架Fe物种为主。FeAPO-5作为一种非均相催化剂能有效催化氧化水溶液中苯酚,在苯酚初始浓度200 mg•L-1 、H2O2初始含量1200 mg•L-1、pH 5.0及溶液温度80℃的条件下,处理240 min后苯酚去除率达99.0％,TOC去除率可达77.8％。ICP分析结果表明,催化剂上析出到溶液中的铁离子浓度很低,催化剂性能稳定。     

Electrochemical synthesis and spectroelectrochemical behavior of poly(diphenylamine-co-4,4′-diaminodiphenyl sulfone)

The electroactive copolymer of diphenylamine (DPA) and 4,4′-diaminodiphenyl sulfone (DADPS) was synthesized electrochemically in 4 M H₂SO₄ and ethanol medium. Both electrochemical synthesis and characterization of the copolymer deposited on a glassy carbon electrode (GCE) were carried out using cyclic voltammetry. The voltammograms exhibited different patterns of behavior with different feed concentrations of DPA. Equimolar concentrations of DPA and DADPS demonstrated very efficient growth of the copolymer film on the surface of the GCE. The copolymer exhibited high solubility in dimethyl sulfoxide (DMSO). The scan rate exerted little-effect on this GCE copolymer film, revealing the film's excellent electroactive adherent properties. The effect of pH on the copolymer film showed that the polymer was electrochemically active up to pH 7.0. Spectroelectrochemical analysis of the copolymer film, carried out on an indium tin oxide (ITO) plate, showed multicolor electrochromic behavior when the applied potential was changed. The copolymer was characterized by FTIR and ¹H NMR spectral data. The surface morphology was studied using SEM analysis, the grain size of the copolymer was measured using XRD studies and was found to be 56 nm. The electrical conductivity of the copolymer was 2.65 × 10⁻² S cm⁻¹, as determined using a four-probe conductivity meter.     

Electrocatalytic oxidation of chlorophenols by electropolymerised nickel(II) tetrakis benzylmercapto and dodecylmercapto metallophthalocyanines complexes on gold electrodes

This work reports on the use of nickel(II) tetrakis benzylmercapto (NiTBMPc) and dodecylmercapto (NiTDMPc) metallophthalocyanine complexes films on gold electrodes for the electrochemical oxidation of 4-chlorophenol (4-CP) and 2,4,5-trichlorophenol (TCP). Both NiTBMPc and NiTDMPc complexes were successfully deposited on gold electrodes by electropolymerisation. The films were electro-transformed in aqueous 0.1 M NaOH solution to the ‘O-Ni-O oxo’ bridged form. For both complexes, films with different thickness were prepared and characterised by electrochemical impedance and UV-vis (on indium tin oxide) spectroscopies and the results showed typical behaviour for modified electrodes with increasing charge transfer resistance values (R_p) with polymer thickness. The poly-Ni(OH)NiPcs showed better catalytic activity than their poly-NiPcs counterparts.     

Graphene-gold nanostructure composites fabricated by electrodeposition and their electrocatalytic activity toward the oxygen reduction and glucose oxidation

A gold nanoparticles (Au NPs)-graphene nanocomposite (Au-graphene nanocomposite) was prepared by electrochemically depositing Au NPs on the surface of graphene sheets, and characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray powder diffraction (XRD), and electrochemical methods. The morphology and size of the Au NPs could be easily controlled by adjusting the electrodeposition time and the concentration of precursor (AuCl₄⁻). The electrocatalytic activities of the nanocomposites toward oxygen reduction and glucose oxidation were investigated by cyclic voltammetry. The results indicated that the nanocomposites had a higher catalytic activity than the Au NPs or graphene alone, indicating the synergistic effect of graphene and Au NPs. Therefore, this study has provided a general route for fabrication of graphene-based noble metal nanomaterials composite, which could be potential utility to fuel cells and bioelectroanalytical chemistry.