Large Electron Transfer Research Articles

Design of carbon nanotube fiber microelectrode for glucose biosensing

AbstractBACKGROUND: Carbon nanotube (CNT) fiber directly spun from an aerogel has a unique, well‐aligned nanostructure (nano‐pore and nano‐brush), and thus provides high electro‐catalytic activity and strong interaction with glucose oxidase enzyme. It shows great potential as a microelectrode for electrochemical biosensors.RESULTS: Cyclic voltammogram results indicate that post‐synthesis treatments have great influence on the electrocatalytic activity of CNT fibers. Raman spectroscopy and electrical conductivity tests suggest that fibers annealed at 250 °C remove most of the impurities without damaging the graphite‐like structure. This leads to a nano‐porous morphology on the surface and the highest conductivity value (1.1 × 105 S m−1). Two CNT fiber microelectrode designs were applied to enhance their electron transfer behaviour, and it was found that a design using a 30 nm gold coating is able to linearly cover human physiological glucose level between 2 and 30 mmol L−1. The design also leads to a low detection limit of 25 µmol L−1.CONCLUSIONS: The high performance of CNT fibers not only offers exceptional mechanical and electrical properties, but also provides a large surface area and electron transfer pathway. They consequently make excellent bioactive microelectrodes for glucose biosensing, especially for potential use in implantable devices. Copyright © 2011 Society of Chemical Industry

Fabrication, biomolecular assembly and electrochemical biosensing applications of highly ordered Ti–Pd alloy oxide nanotube arrays

Pd–TiO 2 nanotube arrays (Pd–TNTs) which are highly ordered and vertically grown on Ti–0.2Pd alloy were fabricated by electrochemical anodization for the first time. The obtained Pd–TNTs were utilized as a “super vessel” for assembly of myoglobin (Mb) and biosensing applications. Experimental results demonstrate that the resulting Pd–TNTs display an enhanced capability for the immobilization of myoglobin. The direct electrochemistry of the immobilized Mb is dramatically facilitated, indicated by a couple of well-defined redox peaks and a very large electron transfer rate constant ( k s) of 20.7 s − 1 . Furthermore, Mb/Pd–TNTs present excellent electrocatalytic activity for the detection of trichloroacetic acid with a wide linear range from 0.5 to 96 μM and a low detection limit of 94 nM (3 N/S). Pd–TNTs with highly ordered nanotubular structure open a facile way to obtain ideal materials for biomolecular assembly and construct electrochemical biosensors.

ZnS nanocrystals decorated single-walled carbon nanotube based chemiresistive label-free DNA sensor.

We fabricated ZnS nanocrystals decorated single-walled carbon nanotube (SWNT) based chemiresistive sensor for DNA. Since the charge transfer in the hybrid nanostructures is considered to be responsible for many of their unique properties, the role of ZnS nanocrystals toward its performance in DNA sensor was delineated. It was found that the free carboxyl groups surrounding the ZnS nanocrystals allowed large loading of single strand DNA (ssDNA) probe that provided an ease of hybridization with target complementary c-ssDNA resulting in large electron transfer to SWNT. Thus it provided a significant improvement in sensitivity toward c-ssDNA as compared to bare SWNT based DNA sensor.

Electrochemical detection of ultratrace nitroaromatic explosives using ordered mesoporous carbon

A sensitive electrochemical sensor has been fabricated to detect ultratrace nitroaromatic explosives using ordered mesoporus carbon (OMC). OMC was synthesized and characterized by scanning electron microscopy, transmission electron microscopy and nitrogen adsorption/desorption measurements. Glassy carbon electrodes functionalized with OMC show high sensitivity of 62.7 μA cm −2 per ppb towards 2,4,6-trinitrotoluene (TNT). By comparison with other materials such as carbon nanotubes and ordered mesoporous silica, it is found that the high performance of OMC toward sensing TNT is attributed to its large specific surface area and fast electron transfer capability. As low as 0.2 ppb TNT, 1 ppb 2,4-dinitrotoluene and 1 ppb 1,3-dinitrobenzene can be detected on OMC based electrodes. This work renders new opportunities to detect ultratrace explosives for applications of environment protections and home securities against chemical warfare agents.

A hydrogen peroxide biosensor based on the direct electron transfer of hemoglobin encapsulated in liquid-crystalline cubic phase on electrode

Liquid crystal cubic phase formed with monoolein has been used as immobilizing matrix to host redox protein hemoglobin on glassy carbon electrode surface. The promoted direct electron transfer between hemoglobin and electrode was observed and a large average kinetic electron transfer rate constant k s of 3.03(±0.02) s −1 was estimated. The electrode modified with cubic phase containing hemoglobin retains the bioactivity of hemoglobin and shows excellent bioelectrocatalytic activity to the reduction of hydrogen peroxide with a small apparent Michaelis–Menten constant of 0.25(±0.03) mM. A novel reagentless hydrogen peroxide biosensor was constructed using the hemoglobin-containing cubic phase modified electrode and the proposed hydrogen peroxide biosensor shows a linear range of 7.0–239 μM with a detection limit of 3.1(±0.2) μM and good stability and reproducibility.

Specific features of the electronic structure of fluorinated multiwalled carbon nanotubes in the near-surface region

The C 1s and F 1s X-ray photoelectron spectra of fluorinated multiwalled carbon nanotubes with different fluorine contents have been measured using the equipment of the Russian-German beamline at the BESSY storage ring by varying the energy of exciting photons. It has been established that two fluorocarbon phases in which the chemical bonding is characterized by a different electron transfer from carbon atoms to fluorine atoms are formed in the near-surface region of nanotubes with fluorine concentrations of 10–39 wt %. The content of the dominant first phase with a large electron transfer in nanotubes remains unchanged with an increase in the probing depth. This phase is identified as a bulk phase formed as a result of the covalent attachment of fluorine atoms to graphene layers of the graphite skeleton without its destruction. The second phase with a small electron transfer is a near-surface phase, because it is predominantly located within two or three upper graphene monolayers and its contribution considerably decreases with an increase in the probing depth of fluorinated multiwalled carbon nanotubes.

Electrostatic Redesign of the [Myoglobin, Cytochrome b5] Interface To Create a Well-Defined Docked Complex with Rapid Interprotein Electron Transfer

Cyt b(5) is the electron-carrier "repair" protein that reduces met-Mb and met-Hb to their O(2)-carrying ferroheme forms. Studies of electron transfer (ET) between Mb and cyt b(5) revealed that they react on a "Dynamic Docking" (DD) energy landscape on which binding and reactivity are uncoupled: binding is weak and involves an ensemble of nearly isoenergetic configurations, only a few of which are reactive; those few contribute negligibly to binding. We set the task of redesigning the surface of Mb so that its reaction with cyt b(5) instead would occur on a conventional "simple docking" (SD) energy landscape, on which a complex exhibits a well-defined (set of) reactive binding configuration(s), with binding and reactivity thus no longer being decoupled. We prepared a myoglobin (Mb) triple mutant (D44K/D60K/E85K; Mb(+6)) substituted with Zn-deuteroporphyrin and monitored cytochrome b(5) (cyt b(5)) binding and electron transfer (ET) quenching of the (3)ZnMb(+6) triplet state. In contrast, to Mb(WT), the three charge reversals around the "front-face" heme edge of Mb(+6) have directed cyt b(5) to a surface area of Mb adjacent to its heme, created a well-defined, most-stable structure that supports good ET pathways, and apparently coupled binding and ET: both K(a) and k(et) are increased by the same factor of approximately 2 x 10(2), creating a complex that exhibits a large ET rate constant, k(et) = 10(6 1) s(-1), and is in slow exchange (k(off) << k(et)). In short, these mutations indeed appear to have created the sought-for conversion from DD to simple docking (SD) energy landscapes.

Electronic structure of fluorinated multiwalled carbon nanotubes studied using x-ray absorption and photoelectron spectroscopy

This paper presents the results of combined investigation of the chemical bond formation in fluorinated multiwalled carbon nanotubes (MWCNTs) with different fluorine contents (10-55 wt %) and reference compounds (highly oriented pyrolytic graphite crystals and white graphite fluoride) using x-ray absorption and photoelectron spectroscopy at C 1s and F 1s thresholds. Measurements were performed at BESSY II (Berlin, Germany) and MAX-laboratory (Lund, Sweden). The analysis of the soft x-ray absorption and photoelectron spectra points to the formation of covalent chemical bonding between fluorine and carbon atoms in the fluorinated nanotubes. It was established that within the probing depth (similar to 15 nm) of carbon nanotubes, the process of fluorination runs uniformly and does not depend on the fluorine concentration. In this case, fluorine atoms interact with MWCNTs through the covalent attachment of fluorine atoms to graphene layers of the graphite skeleton (phase 1) and this bonding is accompanied by a change in the hybridization of the 2s and 2p valence electron states of the carbon atom from the trigonal (sp(2)) to tetrahedral (sp(3)) hybridization and by a large electron transfer between carbon an fluorine atoms. In the MWCNT near-surface region the second fluorine-carbon phase with weak electron transfer is formed; it is located mainly within two or three upper graphene monolayers, and its contribution becomes much poorer as the probing depth of fluorinated multiwalled carbon nanotubes (F-MWCNTs) increases. The defluorination process of F-MWCNTs on thermal annealing has been investigated. The conclusion has been made that F-MWCNT defluorination without destruction of graphene layers is possible. (Less)

Light-induced Hydrogen Bonding Pattern and Driving Force of Electron Transfer in AppA BLUF Domain Photoreceptor

The AppA BLUF (blue light sensing using FAD) domain from Rhodobacter sphaeroides serves as a blue light-sensing photoreceptor. The charge separation process between Tyr-21 and flavin plays an important role in the light signaling state by transforming the dark state conformation to the light state one. By solving the linearized Poisson-Boltzmann equation, I calculated E(m) for Tyr-21, flavin, and redox-active Trp-104 and revealed the electron transfer (ET) driving energy. Rotation of the Gln-63 side chain that converts protein conformation from the dark state to the light state is responsible for the decrease of 150 mV in E(m) for Tyr-21, leading to the significantly larger ET driving energy in the light state conformation. The pK(a) values of protonation for flavin anions are essentially the same in both dark and light state crystal structures. In contrast to the ET via Tyr-21, formation of the W state results in generation of only the dark state conformation (even if the initial conformation is in the light state); this could explain why Trp-104-mediated ET deactivates the light-sensing yield and why the activity of W104A mutant is similar to that of the light-adapted native BLUF.

Studies on catalytic behavior of Co–Ni–B in hydrogen production by hydrolysis of NaBH 4

Catalyst powders of Co–B, Ni–B, and Co–Ni–B, with different molar ratios of Co/Ni, were synthesized by chemical reduction of cobalt and nickel salts with sodium borohydride at room temperature. Surface morphology and structural properties of the catalyst powders were studied using scanning electron microscopy (SEM) and X-ray diffraction (XRD) respectively. Surface electronic states and composition of the catalysts were studied by X-ray photoelectron spectroscopy (XPS). The catalytic activity of the powders has been tested by measuring the H 2 generation rate and yield by the hydrolysis of NaBH 4 in basic medium. Co–Ni–B with the Co/(Co + Ni) molar ratio ( χ Co) of 0.85 exhibited much superior activity with highest H 2 generation rate as compared to the other powder catalysts. The enhanced activity obtained with Co–Ni–B ( χ Co = 0.85) powder catalyst could be attributed to: large active surface area and electron transfer by alloying large quantity of B to active Co and Ni sites on the surface of the catalyst. The electron enrichment, detected in the XPS spectra on active Co and Ni sites in Co–Ni–B, higher than that of Co–B and Ni–B seems to be able to facilitate the catalysis reaction by providing the negative charge electron required by the reaction. Synergetic effect of the Co and Ni atoms in Co–Ni–B catalyst is able to lower the activation energy up to 34 kJ mol −1 as compared to 45 kJ mol −1 obtained with Co–B powder. Structural modification, caused by the heat-treatment at 773 K for 2 h in Ar atmosphere, was not able to change the activity of the Co–Ni–B powder.

Monolayer-Protected Nanoparticle Film Assemblies as Platforms for Controlling Interfacial and Adsorption Properties in Protein Monolayer Electrochemistry

Assembled films of nonaqueous nanoparticles, known as monolayer-protected clusters (MPCs), are investigated as adsorption platforms in protein monolayer electrochemistry (PME), a strategy for studying the electron transfer (ET) of redox proteins. Modified electrodes featuring MPC films assembled with various linking methods, including both electrostatic and covalent mechanisms, are employed to immobilize cytochrome c (cyt c) for electrochemical analysis. The background signal (non-Faradaic current) of these systems is directly related to the structure and composition of the MPC films, including nanoparticle core size, protecting ligand properties, as well as the linking mechanism utilized during assembly. Dithiol-linked films of Au225(C6)75 are identified as optimal films for PME by sufficiently discriminating against detrimental background current and exhibiting interfacial properties that are readily engineered for cyt c adsorption and electroactivity (Faradaic current). Surface concentrations and denaturation rates of adsorbed cyt c are dictated by specific manipulation of the individual MPCs composing the outer layer of the film. The use of specially designed, hydrophilic MPCs as a terminal film layer results in near-ideal cyt c voltammetry, attributed to a high degree of molecular level control of the necessary interfacial interactions and flexibility needed to create a uniform and effective binding of protein across large areas of a substrate. The electrochemical properties of cyt c at MPC films, including ET rate constants that are unaffected by the large ET distance introduced by MPC assemblies, are compared to traditional strategies employing self-assembled monolayers to immobilize cyt c. The incorporation of nanoparticles as protein adsorption platforms has implications for biosensor engineering as well as fundamental biological ET studies.

Low-Energy Driven Electrochromic Devices Using Radical Polymer as Transparent Counter Electroactive Material

Electroactive and transparent organic radical polymers offered a novel design of materials for electrochromic (EC) devices. A radical polymer containing 2,2,6,6-tetramethylpiperidinoxyl (TEMPO) groups as redox active sites per repeating unit was spin-coated on a counter ITO/glass electrode of the EC device which was also comprised of Prussian blue (PB) as an electrochromic material on ITO and ion-con-ducting polymer gel between the two electrodes. Electrochemical switching of the cell was monitored using the visible absorption of PB (λmax = 700 nm) that appeared in the oxidized (mixed-valence) state, while the radical polymer was transparent in the visible region in both redox states. PB and the radical polymer were concurrently reduced and oxidized, respectively, on each electrode during the charging process, which corresponded to the decoloration of the cell. The coloration was effected by a discharging process. The electrochromic switching and stability of the cell was characterized by a low driving voltage ΔV and, consequently, a small driving energy ∫ΔVi(t)dt, as a result of a small potential gap between PB and the radical polymer. The optical switch was fast and fully reversible by virtue of the large heterogeneous electron transfer rate constant of the TEMPO center (kp ≈ 10-1 cm/s). The polymeric counter electrode material, without dissolution into the electrolyte layer, led to a good open circuit memory that did not require refreshing charges to maintain the redox states of PB.

Structure and stability of endohedral X@Si 20H 20 complexes (X = Li 0/+, Na 0/+, K 0/+, Be 0/2+, Mg 0/2+, Ca 0/2+)

The structure and stability of endohedral X@Si 20H 20 complexes (X = Li 0/+, Na 0/+, K 0/+, Be 0/2+, Mg 0/2+, Ca 0/2+) have been studied at the B3LYP/6-31G* level of density functional theory. It is found that complexes with X = Na 0/+, K 0/+, Mg and Ca 0/2+ are energy minimum structures with X at the cage center in I h symmetry, while those with X = Li 0/+, Be 0/2+, Mg 2+ have off-centered structures with X towards one pentagon face in C 5v symmetry. Large electron or charge transfer between the Si 20H 20 cage and the encapsulated X has been observed.

Ab initio study of the electronic properties of the planar Ga 5 N 5 cluster

The first-principles, all-electron, ab initio calculations have been performed for an the amazing stable planar structure of Ga5N5 cluster based on the density functional theory. Electronic structure, electron affinity, ionization potential and binding energy are obtained. No spin magnetic moment is found. The results show that the planar structure of the Ga5N5 cluster is stable. It is found that for the planar structure of Ga5N5 cluster, three nitrogen atoms in the N3 subunit bind together with large electron transfer although no free N3 can exist. This may be important to the stability of the planar structure of the Ga5N5 cluster which has the lowest ground-state energy.

Covalent layer-by-layer type modification of electrodes using ferrocene derivatives and crosslinkers

A series of mono-substituted ferrocenes (Fecp 2 R, R = CONHCH 2N(C 2H 4NH 2) 2 ( 4), R = CH 2NHCH 2N(C 2H 4NH 2) 2 ( 5)) and di-substituted ferrocenes (Fe(cp R) 2, R = COF ( 3)) have been prepared, with 4 and 5 representing new compounds. The ferrocenes were grown layer-by-layer on metal oxide electrodes and crosslinked. The underlying principle of synthesis is based on repetitive and fast amide forming reactions between trimesic acid chloride ( 2) or Fe(cp COF) 2 ( 3) and tris(2-aminoethyl)amine ( 6), or one of the amine-substituted ferrocenes 4 or 5 on a 3-aminopropyl triethoxysilane (APS) ( 1) modified ITO, FTO or ATO electrode. Linear growth of the films electroactivity with the number of cascade steps is observed for up to 12 cascade steps yielding 1.1 × 10 −8 ferrocene centers/cm 2 on a flat ITO electrode, whereas 3 cascade steps yield 2.2 × 10 −7 ferrocene centers/cm 2 on a mesoporeous ATO electrode. In case of the ATO electrode, the inner walls of the mesopores exhibiting a very large surface are completely modified in the procedure. Beside this large coulometry fast electron transfer kinetics, high stability and low optical density in both oxidation states is observed. The electrodes were checked for their potential use as optically transparent counter electrodes in electrochromic devices.

Comparison of Catalytic Electrochemistry of Glucose Oxidase between Covalently Modified and Freely Diffusing Phenothiazine-Labeled Poly(ethylene oxide) Mediator Systems

The enzyme catalytic reaction is electrochemically compared under a substrate-saturated and diffusion-limited condition between native glucose oxidase (GOx) mixed with phenothiazine-labeled poly(ethylene oxide) (PT-PEO) and GOx-(PT-PEO) hybrid with PT-PEO covalently bonded to lysine residues on the enzyme surface. Although the catalytic current (icat) increases with the ratio of [PT-PEO]/[GOx] in both systems, the dependence of the icat on the molecular weight of PT-PEO is totally different. In the mixed systems, the icat decreases with increasing the molecular weight of PT-PEO, which reflects the decreases in the diffusion coefficient (D) of PT-PEO and the intermolecular electron transfer (ET) rate from FADH2/FADH to PT+-PEO. In the hybrids, on the other hand, the icat reveals a maximum at the molecular weight of 3000 (PT-PEO3000), which originates from the dependence of the intramolecular ET rate from FADH2/FADH to PT+ on the molecular weight of PT-PEO. The greater ET rate is enough to make up for the smaller D of PT groups attached on GOx in the hybrid with PT-PEO3000, yielding to the slightly larger icat than that of the corresponding mixed system. The active local motion of the long and hydrophilic PEO chain, the higher local concentration of PT groups due to their immobilization on the GOx surface, and the simultaneous oxidation of multiple attached PT groups at the electrode are possible reasons for the large ET rate constant of the hybrid systems.

Fluorescence Quenching in Electron-Donating Solvents. 1. Influence of the Solute−Solvent Interactions on the Dynamics

The electron transfer (ET) quenching dynamics of excited perylene (Pe), cyanoperylene (PeCN), methanolperylene (PeOH), and methylperylene (PeMe) in N,N-dimethylaniline (DMA) has been investigated using ultrafast fluorescence up-conversion. Measurements of the rotational dynamics of PeCN and PeMe in nonpolar and polar inert solvents using optically heterodyned polarization spectroscopy are also presented. The fluorescence decay in DMA is strongly nonexponential and about 10 times faster with PeCN than with the other electron acceptors. The quenching dynamics has been analyzed with a model distinguishing three types of donor molecules surrounding the acceptor: those with optimal orientation for ET and those requiring orientational or translational diffusion prior to ET. According to this model, which can account for the whole fluorescence decay, the faster quenching dynamics of PeCN is not due to a larger ET rate constant, but to a larger number of donor molecules, typically three to four, with an optimal ...

The nature of the chemical bonding in the D3h and C2v isomers of Fe3(CO)12

The bonding in the D3h and C2v isomers of Fe3(CO)12 has been studied with two complementary topological approaches, namely the atoms-in-molecules (AIM) theory and the analysis of the electron localization function (ELF). Both methods indicate that the stabilization of the C2v isomer is mostly due to the presence of two ligands in bridging positions, which take advantage of a rather large electron transfer from the iron atoms. Within the ELF framework, each of these latter ligands is involved in three-center (3c–4e) bonds with the two adjacent iron atoms.

Synthesis and Antibacterial Activity of .ALPHA.-Methylene-.GAMMA.(.BETA.)-carboxy-.GAMMA.-butyrolactones.

α-Methylene-γ(β)-carboxy-γ-butyrolactones (5 and 10) are considered to have strong antibacterial activity owing to large absolute electronegativity (χ), electron transfer(ΔΝ) and stabilization energy(ΔE) compared to potent cyclopentanone antibiotics. α-Methylene-γ-carboxy-γ-butyrolactone(5) was synthesized starting from L-glutamic acid and α-methylene-β-carboxy-γ-butyrolactone (α-methylene paraconic acid 10) was obtained via ethyl α-formylsuccinate(6) or hydroxymethylation of ethyl α-carbethoxysuccinate(11). α-Methylenationed 5 and 10 showed no strong antibacterial activity as we expected formerly.

Measured and Calculated Electronic Structure of Ni0.40Pd0.400P0.20 and Cu0.400Pd0.400P0.20

ABSTRACTX-ray Photoemission spectra of Ni0.40Pd0.40P0.20 and Cu0.40Pd0.40P0.20 in the amorphous states are compared to each other and to first principles calculations of the electronic density of states. The electronic structure is calculated for a previously validated amorphous model of Ni0.40Pd0.40P0.20 and for the same amorphous structure but with Cu replacing Ni. The measured and calculated electronic structures of Ni0.40Pd0.40P0.20 agree and exhibit very little charge transfer to Pd. However, the measured and calculated electronic structures of Cu0.40Pd0.40P0.20 differ considerably. In Cu0.40Pd0.40P0.20 there is a large electron transfer to Pd. The local densities of states on Pd atoms in different CuPdP local environments that arise in the amorphous model shed light on this dramatic charge redistribution.