Block Electron Transfer Research Articles

Effect of structural modification on the performances of phenothiazine-dye sensitized solar cells

Three novel dyes DX1, DX2 and DX3 containing phenothiazine are designed and synthesized for dye-sensitized solar cells (DSSCs). Photophysical, electrochemical and photovoltaic properties of the three dyes have been systematically investigated. The results show that the DX1-based DSSC with 0.5 mM chenodeoxycholic acid (CDCA) obtains the power conversion efficiency (PCE) of 5.69%. When an additional electron-deficient benzothiadiazole (BT) unit is introduced into the molecular structures of the dyes DX2 and DX3, the absorption spectra are broadened. But the short-circuit photocurrent density (Jsc) of the devices are decreased due to the blocked electron transfer, so the DSSC device based on DX2 only obtains the PCE of 3.43%. Furthermore, a triphenylamine (TPA) unit with high electron-donating ability is joined onto the nitrogen atom of phenothiazine donor in DX3, which enhances the electron injection efficiency and reduces the dye aggregation. Thus, the Jsc is improved, resulting in a higher PCE of 4.41% in the DX3-based dye than the DX2-based one.

Enhanced detection of saccharide using redox capacitor as an electrochemical indicator via a redox-cycling and its molecular logic behavior

Enhanced saccharide electrochemical sensing using dopamine cross-linked chitosan film on the electrode as an indicator was achieved by coupling indicator displacement assay (IDA) with a redox cycling. The affinity of dopamine-chitosan films toward a simple receptor of 2-fluorophenylboronic acid (FPBA) was comparable to that of saccharide towards FPBA in solution. Evidence for redox-capacitor activity of the films was then studied. The electrochemical behaviors of the films binding to FPBA and the competition with saccharide were investigated by cyclic voltammetry. FPBA binding to 1,2-diols on the films blocked electron transfer of a soluble mediator mixture between electrode and the films via a redox-cycling, resulting in a decrease in amplified signal of the mediators. The increase of amplified signal was detected in proportion to the concentration of added saccharide, ascribing to the displaced 1,2-diols from the binding receptor by competition reaction. The sensing strategy was allowed detection of micromolar levels of saccharide. Based on these properties, a molecular level IMP gate with saccharide and FPBA as inputs could be successfully mimicked.

Cell size and the blockage of electron transfer in photosynthesis: Proposed endpoints for algal assays and its application to soil alga Chlorococcum infusionum

This study evaluated multiple endpoints of algal assays to identify sensitive and easy to use endpoints that could be applied to evaluate algal toxicity in metal-polluted soil extracts. Soil algae play an important role in trophic levels; thus, Chlorococcum infusionum was selected as the test species. Soil extracts were used because they might help identify potential soil retention and ecological hazards caused by pollutants that are present in the soil aqueous phase. The multi-endpoints measured were growth yield, photosynthetic activities, and cell viabilities. Nine parameters were measured to evaluate photosynthetic activity; namely, specific energy fluxes per quinone A-reducing photosystem II reaction center (absorption flux, trapped energy flux, electron transport flux, and dissipated energy flux per reaction center), quantum yields (maximum quantum yield of primary photochemistry, quantum yield of electron transport, quantum yield of energy dissipation, and average quantum yield of primary photochemistry), and the blockage of electron transfer from the reaction center to the quinone pool. Cell viability was evaluated by measuring cell size, cell granularity, and the autofluorescence of chlorophyll using flow cytometry. The results showed that heavy metals reduced growth yield, cell viability, and the photosynthetic activity of C. infusionum in soil extracts. Out of the 13 tested endpoints, the blockage of electron transfer from the reaction center to the quinone pool and cell size represented the most sensitive endpoints. We propose that both endpoints should be measured, along with conventional growth yield, to determine the effect of soil pollutants and to lower pollutant concentrations in soils.

If Photoinhibition of Soybean Photosystem II Enhances the Hypersensitive Response, It is Not Solely Due to Blockage of Electron Transfer Flow at D1

Previous studies have suggested that photoinhibition, through inactivation of photosystem II (PSII), could be beneficial to plants during defense to pathogens through enhanced reactive oxygen (ROS), especially during the hypersensitive response (HR). In this study, we addressed this question by focusing on a possible role of turnover and inhibition of the PSII subunit D1, in defense to the compatible and incompatible strains of the bacterial pathogen Pseudomonas syringae in soybean leaves. Expression of the D1 encoding gene, psbA, as well as 14 other chloroplast encoded genes, was down regulated in response to P. syringae. This down regulation is consistent with reduced production of PSII components leading to increased photoinhibition of existing photocenters, and is also consistent with multiple studies showing a concerted down regulation of nuclear-encoded chloroplast genes during pathogen attack. However, although expression of the psbA transcript was reduced in response to pathogen within 8 hours of inoculation, the level of the psbA product, the D1 protein, showed no significant changes via western blots, and did not show any signs of degradation. Additionally, infiltrating leaves with the D1 inhibiting herbicide bentazon (competitive inhibitor of QB binding to D1, stopping photosynthesis by blocking electron transfer from QA to QB) together with P. syringae inoculation, showed that D1 inhibition did not enhance defense as expected (if photoinhibition enhanced defense), but actually rendered the host slightly more susceptible. The results reflect two possibilities. One is that PSII inhibition through blockage of electron flow through D1 of PSII, does not enhance resistance to P. syringae. The second possibility supported by the data is that the mechanism of photoinhibition during pathogen defense is not due solely to the blockage of electron flow, but through another means of stimulating photoinhibition, such as an inefficient degradation, removal, and replacement of damaged D1 from the PSII complex.

A novel photoelectrochemical aptasensor based on the modulation of a dye sensitized TiO2 photoelectrode

Both N719 dye labeled chain release and bound thrombin blocking electron transfer resulted in a decreased photocurrent.

Simultaneous determination of carcinoembryonic antigen and α-fetoprotein using an ITO immunoelectrode modified with gold nanoparticles and mesoporous silica

We report on an electrochemical immunoassay for simultaneous detection of the tumor markers carcinoembryonic antigen (CEA) and α-fetoprotein (AFP). Gold nanoparticles (AuNPs) were synthesized inside the internal pore walls of mesoporous silica (MPS). Then, Methylene blue (MB) and 6-ferrocenylhexanethiol (FeC), which act as electrochemical substrates, were incorporated into the channels via the formation of Au-S bonds. Finally, monoclonal antibodies against CEA (anti-CEA) and AFP (anti-AFP) were immobilized in the channels of MB-AuNPs-MPS and FeC-AuNPs-MPS, respectively. Suspensions of anti-CEA/MB-AuNPs-MPS and of anti-AFP/FeC-AuNPs-MPS were deposited on two different sites of the ITO electrode. When incubated with samples containing the two analytes, the formation of electrically nonconductive immunoconjugates blocks electron transfer. Simultaneous detection of CEA and AFP was accomplished by monitoring the current change before and after an immunoreaction has occurred. The AuNPs confined inside the channels are promoting the electron transport and thus improve detection limits. The immunoelectrode responds to CEA in the 0.5–50 ng mL−1 concentration range, and to AFP in concentrations between 0.5 and 100 ng mL−1. The detection limits (at an S/N of 3) are 0.1 ng mL−1 in both cases.

A thin pristine non-triarylamine hole-transporting material layer for efficient CH3NH3PbI3perovskite solar cells

A new non-traditional organic hole-transporting material (HTM), 4-(4-phenyl-4-α-naphthylbutadienyl)-N,N-bis(4-benzyl)-aniline (PNBA), has been employed in CH3NH3PbI3 perovskite solar cells for the first time. The pore filling of PNBA into mesoporous TiO2/CH3NH3PbI3 scaffold is investigated in detail. As high as 11.4% of light-to-electricity conversion efficiency has been achieved, comparable to corresponding spiro-OMeTAD-based devices under the same conditions. It is revealed that the uniform and thin PNBA film is sufficient as a HTM for perovskite solar cells, and can facilitate hole transport to the metal cathode and also block electron transfer from the perovskite to the metal cathode.

Preparation and characterization of alkylphosphonic acid self-assembled monolayers on titanium alloy by chemisorption and electrochemical deposition.

Ti-6Al-4V alloy is the most commonly used alloy for dental and orthopedic implants. In order to improve osseointegration, different surface modification methods are usually employed, including self-assembled monolayers (SAMs). This study presents an investigation of both active (electroassisted) and passive (adsorption) approaches for the modification of Ti-6Al-4V using alkylphosphonic acid. The monolayers were characterized by cyclic voltammetry, double-layer capacitance, contact angle measurements, X-ray photoelectron spectroscopy, polarization modulation infrared reflection adsorption spectroscopy, electrochemical impedance spectroscopy, and corrosion potentiodynamic polarization measurements. It is shown that the electrochemically assisted monolayers, which are assembled faster, exhibit better control over surface properties, a superior degree of order, and a somewhat higher packing density. The electrosorbed SAMs also exhibit better blockage of electron transfer across the interface and thus have better corrosion resistance.

Tunneling ultramicroelectrode: nanoelectrodes and nanoparticle collisions.

We describe the fabrication of a nanometer-size electrode based on an insulating TiO2 film and a metal nanoparticle (NP). The TiO2 film is deposited on the conducting Pt surface of an ultramicroelectrode (UME) to block electron transfer (ET) to solution species. The film thickness is, however, thin enough to enable tunneling to Pt NPs; thus, the subsequent contact of metal NP to the TiO2 film restores the ET to solution species solely on the NP surface via facile electron tunneling. Consequently, the composite of UME/metal oxide film/NP offers nm-scale active area. The TiO2 film is electrochemically deposited on the Pt UME (Pt UME/TiO2), monitoring the cyclic voltammetry (CV) of ferrocenemethanol until the oxidation wave just disappears. A single Pt NP is captured in a collision experiment by observing the current increase upon contact of the Pt NP with the Pt UME/TiO2 by means of Pt NP-mediated electrochemical reduction of Fe(CN)6(3-). The resultant Pt UME/TiO2/Pt NP (or tunneling UME, T-UME) showed long-term stability and robustness with well-defined electrochemical response, suggesting applicability as a novel nm-size electrode for CV and steady-state measurements such as those with scanning electrochemical microscopy (SECM). Here, we employed the T-UME to measure SECM approach curves and showed remarkable approach capability for a nm-size SECM probe.

A mouse model of mitochondrial complex III dysfunction induced by myxothiazol

Myxothiazol is a respiratory chain complex III (CIII) inhibitor that binds to the ubiquinol oxidation site Qo of CIII. It blocks electron transfer from ubiquinol to cytochrome b and thus inhibits CIII activity. It has been utilized as a tool in studies of respiratory chain function in in vitro and cell culture models. We developed a mouse model of biochemically induced and reversible CIII inhibition using myxothiazol. We administered myxothiazol intraperitoneally at a dose of 0.56mg/kg to C57Bl/J6 mice every 24h and assessed CIII activity, histology, lipid content, supercomplex formation, and gene expression in the livers of the mice. A reversible CIII activity decrease to 50% of control value occurred at 2h post-injection. At 74h only minor histological changes in the liver were found, supercomplex formation was preserved and no significant changes in the expression of genes indicating hepatotoxicity or inflammation were found. Thus, myxothiazol-induced CIII inhibition can be induced in mice for four days in a row without overt hepatotoxicity or lethality. This model could be utilized in further studies of respiratory chain function and pharmacological approaches to mitochondrial hepatopathies.

Peak and steady-state photocurrents in a molecular diode

It has been shown that the time evolution of a photocurrent under the conditions of the irradiation of a photochromic molecule by moderate-intensity light includes the fast and slow stages of the kinetic process. The fast stage corresponds to an increase in the current and is associated with the charging of the molecule, which is in a singlet excited state after a phototransition. The slow stage includes electron transfer between electrodes involving both charged and excited (singlet and triplet) states of the molecule. When the exchange interaction of unpaired electrons on the HOMO and LUMO levels of the photoexcited molecule is weak, the steady-state photocurrent is close in magnitude to the maximum transient current, whereas the steady-state current is suppressed when the exchange interaction is strong. The reason is that a molecule in the triplet state can block electron transfer between electrodes. The conditions have been found under which such blocking is a manifestation of the peak transient photocurrent that is formed immediately after the beginning of the irradiation of the molecule.

Nanoscale control of interfacial processes for latent fingerprint enhancement

Latent fingerprints on metal surfaces may be visualized by exploiting the insulating characteristics of the fingerprint deposit as a "mask" to direct electrodeposition of an electroactive polymer to the bare metal between the fingerprint ridges. This approach is complementary to most latent fingerprint enhancement methods, which involve physical or chemical interaction with the fingerprint residue. It has the advantages of sensitivity (a nanoscale residue can block electron transfer) and, using a suitable polymer, optimization of visual contrast. This study extends the concept in two significant respects. First, it explores the feasibility of combining observation based on optical absorption with observation based on fluorescence. Second, it extends the methodology to materials (here, polypyrrole) that may undergo post-deposition substitution chemistry, here binding of a fluorophore whose size and geometry preclude direct polymerization of the functionalised monomer. The scenario involves a lateral spatial image (the whole fingerprint, first level detail) at the centimetre scale, with identification features (minutiae, second level detail) at the 100-200 microm scale and finer features (third level detail) at the 10-50 microm scale. However, the strategy used requires vertical spatial control of the (electro)chemistry at the 10-100 nm scale. We show that this can be accomplished by polymerization of pyrrole functionalised with a good leaving group, ester-bound FMOC, which can be hydrolysed and eluted from the deposited polymer to generate solvent "voids". Overall the "void" volume and the resulting effect on polymer dynamics facilitate entry and amide bonding of Dylight 649 NHS ester, a large fluorophore. FTIR spectra demonstrate the spatially integrated compositional changes. Both the hydrolysis and fluorophore functionalization were followed using neutron reflectivity to determine vertical spatial composition variations, which control image development in the lateral direction.

In vitro reactive oxygen species production by mitochondria from the rabbitfish Siganus fuscessens livers and the effects of Irgarol-1051

In this study, the mitochondria from the livers of Siganus fuscessens were exposed to the Irgarol-1051with or without respiratory chain inhibitors using succinate or malate as the substrate, and the effects on mitochondrial ROS production were tested. The mitochondrial ROS production was significantly enhanced by antimycin A with an increase of more than three folds but not by rotenone and NaN3, and this may suggest complex III is the major ROS-producing site. Irgarol-1051 treatments gave a somewhat contradictory result: this chemical can inhibit the mitochondrial ROS production but the inhibition decreased with the increase of doses. These contradictory data about Irgarol-1051 may be explained by the balance between the effects of inhibition through the opening of small-size pores and stimulation through blocking electron transfer, but the mechanism laid behind needs more evidence to support. As Irgarol-1051 was continuously used in antifouling and its bio-concentration factor is up to 160 in fish, the toxic effect of Irgarol-1051 on aquatic animals should be paid more attention to.

Effect of sodium cyanide on the activities of some oxidative enzymes and metabolites in Clarias gariepinus

-1 ) of sodium cyanide. Fish showed a gradual decrease in respiratory rate, increase in LDH and decrease in SDH levels, and lactic acid followed a similar trend with pyruvate in an eight-day trial. The changes in the levels of these enzyme activities may be as a result of impaired oxidative metabolism and cellular damage, which had effect on the release of these enzymes. Elevation in the level of lactic acid and decrease in pyruvic acid was due to shift from aerobic to anaerobic metabolism which resulted to a severe drop in the respiratory rate of the fish. It may be as a result of blockage of electron transfer from cytochrome-c oxidase to molecular oxygen which might lead to cellular hypoxia even in the presence of normal oxygenation of hemoglobin. Thus, inhibition of oxidative metabolism by sodium cyanide in C. garipenus was reconfirmed. Behavioral changes caused by sodium cyanide exposure in the fish were probably due to the combination of lactate acidosis with cytotoxic hypoxia, which might depress the central nervous system.

Modulation of gene expression of carotene biosynthesis‐related protein by photosynthetic electron transport for the acclimation of intertidal macroalga Ulva fasciata to hypersalinity and excess light

A gene (UfCBR) encoding carotene biosynthesis-related (CBR) protein that potentially functions for the dissipation of excessive energy has been cloned from the intertidal green macroalga Ulva fasciata Delile. Hypersalinity and high light ≥300 µmol m(-2) s(-1) increased both UfCBR mRNA level and non-photochemical quenching (NPQ). The increase of UfCBR mRNA level and NPQ by high light was inhibited by treatment of photosynthetic electron transport inhibitor, 3-(3,4-dichlorophenyl)-1,1-dimethylurea or 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, but not by stigmatellin, an inhibitor that blocks electron transfer from quinol oxidase to iron-sulfur protein in cytochrome b(6) f complex. Treatment of dimethylthiourea, an H(2) O(2) scavenger, under 1200 µmol m(-2) s(-1) condition inhibited H(2) O(2) accumulation but did not affect UfCBR mRNA level, while treatment of H(2) O(2) in 150 µmol m(-2) s(-1) condition decreased UfCBR mRNA level. Thus, an reactive oxygen species-independent redox control via a more reduced state downstream the cytochrome b(6) f complex is involved in high light up-regulation of UfCBR expression in U. fasciata. The expression of UfCBR in U. fasciata against oxidative stress occurring in high light or high salinity in relation to NPQ is discussed.

Analysis of [formula omitted] charge recombination with the Arrhenius, Eyring and Marcus theories

The Q band of photosynthetic thermoluminescence, measured in the presence of a herbicide that blocks electron transfer from PSII, is associated with recombination of the S 2 Q A - charge pair. The same charge recombination reaction can be monitored with chlorophyll fluorescence. It has been shown that the recombination occurs via three competing routes of which one produces luminescence. In the present study, we measured the thermoluminescence Q band and the decay of chlorophyll fluorescence yield after a single turnover flash at different temperatures from spinach thylakoids. The data were analyzed using the commonly used Arrhenius theory, the Eyring rate theory and the Marcus theory of electron transfer. The fitting error was minimized for both thermoluminescence and fluorescence by adjusting the global, phenomenological constants obtained when the reaction rate theories were applied to the multi-step recombination reaction. For chlorophyll fluorescence, all three theories give decent fits. The peak position of the thermoluminescence Q band is correct by all theories but the form of the Q band is somewhat different in curves predicted by the three theories. The Eyring and Marcus theories give good fits for the decreasing part of the thermoluminescence curve and Marcus theory gives the closest fit for the rising part.

Photocatalytic Hydrogen Production from Noncovalent Biohybrid Photosystem I/Pt Nanoparticle Complexes

A photocatalytic hydrogen-evolving system based on intermolecular electron transfer between native Photosystem I (PSI) and electrostatically associated Pt nanoparticles is reported. Using cytochrome c6 as the soluble mediator and ascorbate as the sacrificial electron donor, visible-light-induced H2 production occurs for PSI/Pt nanoparticle biohybrids at a rate of 244 μmol H2 (mg chlorophyll)−1 h−1 or 21 034 mol H2 (mole PSI)−1 h−1. These results demonstrate that highly efficient photocatalysis of H2 can be obtained for a self-assembled, noncovalent complex between PSI and Pt nanoparticles; a molecular wire between the terminal acceptor of PSI, the [4Fe−4S] cluster FB, and the nanoparticle is not required. EPR characterization of the electron-transfer reactions in PSI/Pt nanoparticle biohybrids shows blocked electron transfer to flavodoxin, the native acceptor protein of PSI, and presents evidence of low-temperature photogenerated electron transfer between PSI and the Pt nanoparticle. This work demonstrate...

On the Monolayer Adsorption of Thiol‐Terminated Dendritic Oligothiophenes onto Gold Surfaces

AbstractThe self‐assembled monolayer formation of a series of thiophene dendron thiols with different generations and alkyl chain lengths onto gold surfaces is studied. Average film thicknesses and dielectric constants were calculated from SPR using a two‐subphase differential method. The in situ adsorption of the thiophene dendron thiols was monitored by SPR kinetics measurements and fitted using an empirical three‐step model. Electrochemical redox molecular probing experiments provided additional insight into surface coverage, which showed different abilities to block electron transfer at the monolayer/electrode interfaces. The surface coverage of the films was also estimated by QCM measurements and supported by static WCA measurements. magnified image

Blocked Electron Transfer and Suppressed Blinking of Single CdSe/ZnS Quantum Dots in Agarose Gel

AbstractFluorescence blinking is an interesting phenomenon commonly observed in single molecule/particle spectroscopy and has attracted wide interest recently. Such behavior in quantum dots is undesirable for applications as fluorescence markers. In this report, we observed suppressed blinking for single CdSe/ZnS quantum dots mixed in agarose gel. We attributed the suppression to an increase in activation energy so that the charge transfer is blocked from the neutral light state to the charged dark state as the gel concentration increases.

Synthetic atpenin analogs: Potent mitochondrial inhibitors of mammalian and fungal succinate-ubiquinone oxidoreductase

Atpenins and harzianopyridone represent a unique class of penta-substituted pyridine-based natural products that are potent inhibitors of complex II (succinate-ubiquinone oxidoreductase) in the mitochondrial respiratory chain. These compounds block electron transfer in oxidative phosphorylation by inhibiting oxidation of succinate to fumarate and the coupled reduction of ubiquinone to ubiquinol. From our investigations of complex II inhibitors as potential agricultural fungicides, we report here on the synthesis and complex II inhibition for a series of synthetic atpenin analogs against both mammalian and fungal forms of the enzyme. Synthetic atpenin 2e provided optimum mammalian and fungal inhibition with slightly higher potency than natural occurring atpenin A5.