Graphene‐Functionalized 3D‐Carbon Fiber Electrodes – Preparation and Electrochemical Characterization

Graphene nanosheets were produced on the surface of carbon fibers by in situ electrochemical procedure including oxidative and reductive steps to yield first graphene oxide, later converted to graphene. The electrode material composed of graphene‐functionalized carbon fibers was characterized by scanning electron microscopy (SEM) and cyclic voltammery demonstrating superior electrochemical kinetics comparing with the original carbon paper. The interfacial electron transfer rate for the reversible redox process of [Fe(CN)₆]^3?/4? was found ca. 4.5‐fold higher after the electrode modification with the graphene nanosheets. The novel electrode material is suggested as a promising conducting interface for bioelectrocatalytic electrodes used in various electrochemical biosensors and biofuel cells, particularly operating in vivo.     

Electrochemical Performance of Transition Metal‐Coordinated Polypyrrole: A Mini Review

The conductive polymer of polypyrrole can be acted as electroactive electrode material of supercapacitor due to reversible redox behavior and high capacitance. It usually suffers from low electrochemical stability due to the breakdown of polymer molecule chain in the long‐term charge and discharge process. The monometallic or bimetallic‐coordinated polypyrrole usually exhibits the improved electrochemical performance. The transition metal ions such as ruthenium, iron, copper and cobalt are adopted for the coordination modification. The transition metal‐coordinated polypyrrole includes the intrachain and interchain coordination structure between transition metal ion and nitrogen atom of pyrrole ring. It is able to reinforce the polymer molecule chain strength to overcome excessive volumetric swelling and shrinking during charge‐discharge process, improving the cycling stability and rate capability of polypyrrole. Accordingly, the transition metal‐coordinated polypyrrole keeps simultaneously high capacitance performance and electrochemical stability, acting as the promising conductive polymer‐based supercapacitor electrode material for effective energy storage.     

Electrochemical Oxidation of 8‐Oxo‐2′‐Deoxyguanosine on Glassy Carbon,Gold, Platinum and Tin(IV) Oxide Electrodes

Cyclic voltammetry was used to investigate the oxidation of 8‐oxo‐2′‐deoxyguanosine (8‐oxo‐dG) on the glassy carbon (GC), platinum, gold and SnO₂ electrodes over a range of the sweep rate, 8‐oxo‐dG concentration and the solution pH. Reaction mechanism that is common to all these electrodes involves the two‐electron two‐proton charge transfer step followed by the irreversible chemical reaction(s). Rate of the charge transfer reaction decreases with the increasing solution pH (GC, Pt, Au), and depends on the nature of the electrode material following the sequence GC>Pt, Au>>SnO₂. These effects can be related to the degree of oxidation of the electrode surface (Pt, Au, SnO₂), or to the density of the active surface sites (GC). Any of these electrodes can be used for the fabrication of an amperometric detector for 8‐oxo‐dG .     

Functionalization of Multi‐Walled Carbon Nanotubes by Thermo‐Grafting with α‐Methylstyrene‐Containing Copolymers

The present article reports on a strategy for the functionalization of multi‐walled carbon nanotubes (MWCNTs) by grafting with various polymer chains. Copolymers consisting of α‐methylstyrene (AMS) and a second monomer, that is glycidyl methacrylate (GMA) or styrene (St), were synthesized in advance. The copolymers were heated in the presence of MWCNTs in solution, decomposition of the AMS sequences occurred, providing macroradicals, which further attacked the double bonds on the MWCNT surfaces. Grafting of the copolymer chains onto the surface of the MWCNTs was thus achieved, as demonstrated by FT‐IR, XPS and Raman technologies. The resulting poly(AMS‐co‐GMA)‐g‐MWCNTs could be uniformly dispersed in N,N‐dimethylformamide (DMF) and acetone, and the poly(AMS‐co‐St)‐g‐MWCNTs also could be uniformly dispersed in DMF.

     

Electrochemical Characterization of Screen‐Printed Carbon Electrodes by Modification with Chitosan Oligomers

The kinetics on the current amplification of the disposable screen‐printed carbon electrodes (SPCEs) by modification with chitosan oligomers (COs), coupled with the Fe(CN) redox system, were characterized with the variation of electron‐transfer rate constant (k°) and the electroactive area (A_ea) at electrode surface. The nonlinear response characteristics of peak currents with increase in Fe(CN) bulk concentrations complicated the estimation of A_ea in cyclic voltammetric analysis. Upon the modification with COs, the rate constant of SPCEs was not much influenced and the current amplification was characterized with the increase of a better estimated A_ea, obtained from electrochemical impedance measurements and verified with the reciprocal of electron‐transfer resistances linearly proportional to the Fe(CN) bulk concentrations. It is hereby provided for an evaluation of the carbon based electrodes with modification.     

Investigation of the Electrochemical Behavior of Mesalazine on the Surface of a Glassy Carbon Electrode Modified with CNT/PPY Doped by 1,5‐Naphthalenedisulfonic Acid

A glassy carbon electrode (GCE) was modified with a thin layer of multiwalled carbon nanotubes (MWCNTs) and subsequently, electrochemically deposited poly‐pyrrole. The electrochemical behavior of mesalazine was studied on the surface of the modified electrode by applying linear sweep voltammetry (LSV). The electropolymerization process and the electrochemical response toward mesalazine were investigated in the presence of different aromatic anion dopants including, benzenesulfonic acid (BSA), 1,3‐benzenedisulfonic acid (1,3‐BDSA), 1,5‐naphthalenedisulfonic acid (1,5‐NDSA) and new coccine (NC). By using 1,5‐NDSA as dopant, a significant increase (～418 times) in the peak current of mesalazine was observed, in comparison to the bare GCE. Experimental variables such as drop size of the cast MWCNTs suspension, pH of the supporting electrolyte, accumulation conditions and the number of scans in the electropolymerization process were optimized by monitoring the LSV responses of mesalazine. Under the optimum conditions, two linear dynamic ranges of 0.01–0.1 µmol L^?1 and 0.1–1.0 µmol L^?1 with a detection limit of 3 nmol L^?1 were resulted for the voltammetric determination of mesalazine. The prepared electrode showed high sensitivity, stability and good reproducibility for determination of mesalazine. These properties made the prepared sensor suitable for the determination of mesalazine in pharmaceutical and clinical preparations.     

Electrochemical synthesis of poly(3‐methylthiophene): A kinetic study

Poly(3‐methylthiophene) (P3MT) films were electrogenerated on both platinum and carbon‐felt working electrodes. The kinetic equation was determined by the monomer and electrolyte concentrations being changed for different reaction times. For each sample, the weight of the polymer obtained was measured along with the polymerization charge, the oxidation charge, the ratio (R) between the two magnitudes, the charge storage efficiency (SE), and the doping level. The results obtained from the kinetic study indicate significant electrolyte participation in the electropolymerization process. The SE and the doping level decreased inversely proportionately to both the reaction time and the concentrations of the monomer and electrolyte. The ratio R increased with reaction time as well as with monomer or electrolyte concentrations for all P3MTs generated on the carbon‐felt electrodes, whereas for those films generated on platinum electrodes, the highest values were obtained for the lowest monomer and electrolyte concentrations. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1258–1266, 2000     

Electrochemical Studies of the Interaction of 2‐Nitroacridone with DNA and Determination of DNA

A new acridone derivate 2‐nitroacridone (NAD) was synthesized and a new method of electrochemical probe has been proposed for the determination of salmon sperm DNA based on its interaction with NAD. The electrochemical behavior of interaction of NAD with DNA was investigated on glassy carbon electrode (GCE). In the presence of DNA, the peak current of NAD decreases and the peak potential shifts to a more positive potential without appearance of a new peak. The binding ratio between NAD and salmon sperm DNA was calculated to be 2 : 1 and the binding constant was 3.19×10⁵ L/mol. The decrease of the peak current (ΔI_p) of NAD was proportional to the concentration of DNA in the range from 1.55×10^?7 M to 2.02×10^?6 M with the detection limit of 3.10×10^?8 M, and DNA of synthetic sample was determined satisfactorily. Additionally, the binding mechanism was preliminarily discussed. The mode of interaction between NAD and DNA was found to be intercalation binding.     

Modification of Gold Electrode via Electrografting of the in situ Generated 3‐Carboxy‐1,2,4‐triazoldiazonium Salt for Label‐free Determination of Carcinoembryonic Antigen

In present study electrografting of the in situ generated 3‐carboxy‐1,2,4‐triazoldiazonium chloride on the Au disk electrode have been studied. The electrode film thickness differences between electrodeposited due to the aryl radical structure 3‐carboxy‐1,2,4‐triazoldiazonium chloride and 4‐carboxyphenyldiazonium salt was shown. The mechanism of 3‐carboxy‐1,2,4‐triazoldiazonium chloride electrografting has been proposed. 4‐nitroanilin was used to investigate the carbodiimide crosslinking capacity. It was established that electrodeposited films are suitable for carbodiimide crosslinking but the reaction proceed only on the “external” electrografted layer. Under the chosen optimal parameters, the label‐free electrochemical immunosensor have been developed. 3‐carboxy‐1,2,4‐triazoldiazonium chloride electrografting provided improvement of analytical characteristics in respect to electrodeposited 4‐carboxyphenyldiazonium salt. The linear range for carcinoembryonic antigen (CEA) detection is 10–10⁴ ng ? ml^?1, the limit of detection estimated as 0.2 ng ? ml^?1. The developed immunosensor is stable during 30 day′s storage and selective against excess of bovine serum albumin as an interfering reagent.     

Optimization of an Electrochemical Sensor for Determination of Imidacloprid Based on β‐cyclodextrin Electropolymerization on Glassy Carbon Electrode

An electrochemical sensor based on electropolymerization of β‐cyclodextrin (β‐CD) on a glassy carbon electrode (GCE) was developed for the determination of imidacloprid (IMP). That insecticide is the most commonly used insecticides globally and has been related to the death of bee colonies around the world are imperative. So the development of a simple, cheap and sensitive method for IMP determination is essential. This work aims the modification of a GCE by β‐CD film. The analytical response obtained with GCCE/β‐CD in the presence of the IMP showed an increase in the peak current variation of 947 % in relation to the bare GCE, indicating that the analyte was encapsulated in the β‐CD increasing the detection sensitivity. The followed experimental conditions were optimized: potential range (−1.3 to 0.9 V), presence or absence of dissolved oxygen (presence) and stirring during the electropolymerization (with agitation), number of cycles (5 scans), electrolyte pH (pH=5.0), scan rate (100 mV s⁻¹) and concentration of β‐CD (6 mol L⁻¹). The optimization promoted a peak current variation increase of 57 %, developing a more sensitivity methodology.     

A Comparative Study of Modifying Gold and Carbon Electrode with 4‐Sulfophenyl Diazonium Salt

A comparison of the reductive adsorption behavior of 4‐sulfophenyl diazonium salt and subsequent electrochemical reactivity on gold relative to carbon was studied with some significant differences observed. The ability of the 4‐sulfophenyl layer adsorbed onto gold to block access of the redox probe ferricyanide to the underlying electrodes, as determined via cyclic voltammetry was inferior to the same layers formed on glassy carbon electrodes thus indicating a more open, porous layer formed on gold. More significantly, the 4‐sulfophenyl layers are shown to be far less electrochemically stable on gold than on glassy carbon. Electrochemical and X‐ray photoelectron spectroscopy (XPS) evidence suggests the instability is due to cleavage of the bond between sulfonate functional group and phenyl ring. These results provide further evidence that although aryl diazonium salt layers are relatively stable on gold surfaces compared with alkanethiol based self‐assembled monolayer (SAMs), the stability is not as high as is observed on carbon.     

Kinetic Studies Prove High Catalytic Activity of a Diene–Rhodium Complex in 1,4‐Addition of Phenylboronic Acid to α,β‐Unsaturated Ketones

In the 1,4‐addition of phenylboronic acid to α,β‐unsaturated ketones, [Rh(OH)(cod)]₂ has a much higher catalytic activity than [Rh(OH)(binap)]₂ (cod=1,5‐cyclooctadiene, binap=2,2′‐bis(diphenylphosphanyl)‐1,1′‐binaphthyl). Kinetic studies revealed that the rate‐determining transmetalation step in the catalytic cycle has a large rate constant when [Rh(OH)(cod)]₂ is used.     

Electrochemical Detection of Duplex DNA Using Intercalation‐Triggered Decomplexation of Ferrocene with β‐Cyclodextrin

The redox peak of ferrocenylnaphthalene diimide used as a threading intercalator shifted positively due to the formation of its complex with β‐cyclodextrin. This complex collapsed upon the addition of double‐stranded DNA, and its redox potential shifted negatively. This behavior was applied for the homogenous detection of a polymerase chain reaction (PCR) product from Porphyromonas gingivalis, which is important for the diagnosis of periodontal disease, and its quantitative detection was achieved with a detection limit of 2.7 nM.     

A Sensitive Electrochemical Immunosensor for α‐Fetoprotein Detection with Colloidal Gold‐Based Dentritical Enzyme Complex Amplification

A sensitive and specific electrochemical immunosensor was developed with α‐fetoprotein (AFP) as the model analyte by using gold nanoparticle label for enzymatic catalytic amplification. A self‐assembled monolayer membrane of mercaptopropionic acid (MPA) was firstly formed on the electrode surface through gold‐sulfur interaction. Monoclonal mouse anti‐human AFP was covalently immobilized to serve as the capture antibody. In the presence of the target human AFP, gold nanoparticles coated with polyclonal rabbit anti‐human AFP were bound to the electrode via the formation of a sandwiched complex. With the introduction of goat anti‐rabbit IgG conjugated with alkaline phosphatase, the dentritical enzyme complex was formed through selective interaction of the secondary antibodies with the colloidal gold‐based primary antibody at the electrode, thus affording the possibility of signal amplification for AFP detection. Current response arising from the oxidation of enzymatic product was significantly amplified by the dentritical enzyme complex. The current signal was proportional to the concentration of AFP from 1.0 ng mL^?1 to 500 ng mL^?1 with a detection limit of 0.8 ng mL^?1. This system could be extended to detect other target molecules with the corresponding antibody pairs.     

Kinetic Stabilization and Reactivity of π Single‐Bonded Species: Effect of the Alkoxy Group on the Lifetime of Singlet 2,2‐Dialkoxy‐1,3‐diphenyloctahydropentalene‐1,3‐diyls

Kinetic stabilization and reactivity of π single‐bonded species have been investigated in detail by generating a series of singlet 2,2‐dialkoxy‐1,3‐diphenyloctahydropentalene‐1,3‐diyls ( DR s). The lifetime at 293 K in benzene was found to increase when the carbon chain length of the alkoxy groups was increased; 292 ns ( DRb ; OR=OR′=OCH₃) <880 ns ( DRc ; OR=OR′=OC₂H₅) <1899 ns ( DRd ; OR=OR′=OC₃H₇) ≈2292 ns ( DRe ; OR=OR′=OC₆H₁₃) ≈2146 ns ( DRf ; OR=OR′=OC₁₀H₂₁). DRh (OR=OC₃H₇, OR′=OCH₃; 935 ns) with the mixed‐acetal moiety is a longer‐lived species than another diastereomer DRg (OR=OCH₃, OR′=OC₃H₇; 516 ns). Activation parameters determined for the first‐order decay process reveal that the enthalpy factor plays a crucial role in determining the energy barrier of the ring‐closing reaction, that is, from the π‐bonding to the σ‐bonding compounds. Computational studies using density functional theory provided more insight into the structures of the singlet species with π single‐bonded character and the transition states for the ring‐closing reaction, thereby clarifying the role of the alkoxy group on the lifetime and the stereoselectivity of the ring‐closing reaction.     

Electrophilic Alkylations of Vinylsilanes: A Comparison of α‐ and β‐Silyl Effects

Kinetics of the reactions of benzhydrylium ions (Aryl₂CH⁺) with the vinylsilanes H₂C?C(CH₃)(SiR₃), H₂C?C(Ph)(SiR₃), and (E)‐PhCH?CHSiMe₃ have been measured photometrically in dichloromethane solution at 20 °C. All reactions follow second‐order kinetics, and the second‐order rate constants correlate linearly with the electrophilicity parameters E of the benzhydrylium ions, thus allowing us to include vinylsilanes in the benzhydrylium‐based nucleophilicity scale. The vinylsilane H₂C?C(CH₃)(SiMe₃), which is attacked by electrophiles at the CH₂ group, reacts one order of magnitude faster than propene, indicating that α‐silyl‐stabilization of the intermediate carbenium ion is significantly weaker than α‐methyl stabilization because H₂C?C(CH₃)₂ is 10³ times more reactive than propene. trans‐β‐(Trimethylsilyl)styrene, which is attacked by electrophiles at the silylated position, is even somewhat less reactive than styrene, showing that the hyperconjugative stabilization of the developing carbocation by the β‐silyl effect is not yet effective in the transition state. As a result, replacement of vinylic hydrogen atoms by SiMe₃ groups affect the nucleophilic reactivities of the corresponding C?C bonds only slightly, and vinylsilanes are significantly less nucleophilic than structurally related allylsilanes.     

Grafting of wheat straw fibers with poly (ε‐caprolactone) via ring‐opening polymerization for poly(lactic acid) reinforcement

The use of natural materials has grown in the last years in the plastics industry. Natural lignocellulose fibers derived from agricultural waste present potential to be used as a replacement for glass fibers for polymer reinforcement, leading to lower CO₂ footprint products. This work focuses on the modification of the cellulose fibers in order to improve the compatibility with poly(lactic acid) (PLA). The scoured wheat straw fibers were grafted with polycaprolactone (PCL) through ring opening polymerization. Thermal stability of the wheat straw fibers improved after chemical modifications enabling higher processing temperatures. Flexural and tensile moduli were improved by 23% and 15%, respectively, compared with neat PLA, using 20 wt% modified fibers. An improvement of 20% in the impact strength was obtained using PCL grafted fibers because of entanglements and molecular interactions between PCL grafted on the wheat straw fibers and PLA molecules. Copyright © 2015 John Wiley & Sons, Ltd.     

Oxidation of 2‐Phenylethylamine with N‐Bromosuccinimide in Acid and Alkaline Media: A Kinetic and Mechanistic Study

A kinetic study of oxidation of 2‐phenylethylamine (PEA), a bioactive compound, with potent oxidant, N‐bromosuccinimide (NBS) has been carried out in HCl and NaOH media at 313 K. The experimental rate laws obtained are: ‐d [NBS] /dt = k[NBS][PEA][H⁺] in hydrochloric acid medium and ‐d [NBS]/dt = k[NBS][PEA]^x[OH^?]^y in alkaline medium where x and y are less than unity. Accelerating effect of [Cl^?], and retardation of the added succinimide on the reaction rate have been observed in acid medium. Variation of ionic strength of the medium shows negligible effect on rate of reaction in both media. Decrease in dielectric permittivity of the medium decreased the rate in both media. The stoichiometry of the reaction was found to be 1:1 in acid medium and 1:2 in the case of alkaline medium. The oxidation products of PEA were identified as the corresponding aldehyde and nitrile in acid and alkaline medium, respectively. The reactions were studied at different temperatures and the activation parameters have been evaluated. The reaction constants involved in the proposed mechanisms were computed. The reaction was found to be faster in alkaline medium in comparison with the acid medium, which is attributed to the involvement of different oxidizing species. The proposed mechanisms and the derived rate laws are consistent with the observed experimental results.     

Hydride‐Donor Abilities of 1,4‐Dihydropyridines: A Comparison with π Nucleophiles and Borohydride Anions

How are dihydropyridines like indoles? Both groups of compounds have similar nucleophilicity parameters N and are therefore suitable substrates for iminium‐catalyzed reactions of α,β‐unsaturated aldehydes. The N parameters of 1,4‐dihydropyridines were derived from the rates of hydride transfer reactions to benzhydrylium ions (see scheme).