Top PDF Direct Electron Transfer to Cytochrome c Induced by a Conducting Polymer

Direct Electron Transfer to Cytochrome c Induced by a Conducting Polymer

Direct Electron Transfer to Cytochrome c Induced by a Conducting Polymer

24 electrochemical injection of positive charge through the PEDOT backbone could induce additional electrostatic repulsions pulling the segment away from the conducting polymer interface. This effect is detected as a vanishing of the corresponding vibrational modes in the FTIR spectrum of Fig. 8a. On the other hand, it is remarkable the absence of differential infrared bands coming from type III β-turn (residues 14-19 and 67-70). Such a behaviour reveals that these protein sites remain unmodified upon oxidation and, probably, they are preferred positions for the protein to interact with the conducting polymer. As shown in Fig. 9, the proposed orientation favours the approach of cyt c to the surface through positively-charged Lys 13, 27, 72 and 86, which seem active residues facilitating the electron transfer from the conducting polymer to the heme group. The interaction of positive Lys residues with the polymer substrate seems favoured by the excess of dopant PSS anions relative to EDOT monomers (ratio close to 4:1, as deduced from XPS data in Fig. 2). In addition, the alignment proposed in Fig. 9 agrees with that reported previously for cyt c adsorbed on bare gold electrodes 77 . It was demonstrated that this particular configuration hampers the direct electron transfer to cyt c due to the suppressed rotation of the adsorbed protein. Since, in the present case, the electron transfer takes place from a PEDOT-PSS layer under similar protein alignment, the rotation of cyt c should be not confined after its interaction with this particular conducting substrate.
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Direct Electron Transfer of Glucose Oxidase in Carbon Paper for Biofuel Cells and Biosensors

Direct Electron Transfer of Glucose Oxidase in Carbon Paper for Biofuel Cells and Biosensors

practical value, findings from such studies could aid in understanding the fundamental mechanisms of biological redox reactions [1-5]. Owing to its high sensitivity to glucose, glucose oxidase (GOx) has received considerable attention as a potential enzymatic component of BFCs, and for use in real-time glucose monitoring related applications. However, establishing direct electron transfer (DET) between the immobilized GOx and conventional electrodes is a challenge due to the inaccessibility of GOx active centers, which are deeply embedded within a thick insulating protein shell [6,7]. Many attempts at immobilization have been employed to reduce the distance and to improve electron transfer between the active center of GOx and the electrodes [8-11]. These attempts have incorporated various immobilization methods (e.g., physical adsorption [12], cross-linking [13], covalent binding entrapment in gels [14] or membranes [15], self-assembly [16] and layer-by-layer [17] processes), and inorganic/organic matrixes (e.g., metal nanoparticles [18], nanostructured metal oxides [19], carbon nanotubes [10, 20-24], grapheme [25-28], semiconductor nanoparticles [29-32] and conducting polymer nanowires [33]).
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A Novel Tri-Protein Bio-Interphase Composed of Cytochrome c, Horseradish Peroxidase and Concanavalin A: Electron Transfer and Electrocatalytics

A Novel Tri-Protein Bio-Interphase Composed of Cytochrome c, Horseradish Peroxidase and Concanavalin A: Electron Transfer and Electrocatalytics

than that of the other electrodes. The results indicated that the co-entrapped Cyt c-HRP in tri-protein bio-interphase could greatly promote the electron transfer between proteins and the electrode. It was because that the sugar-lectin biospecific interaction between HRP and Con A provided a stable immobilization of Cyt c-HRP and the synergistic interactions between these two proteins resulted in optical conformation and a porous structure. According to previous results for the arrangement of Cyt c and sulfonated polyaniline [23] and LBL arrangement of Cyt c and sulfite oxidase [15], long-distance electron transfer process might be ascribed to one of the following mechanisms: (1) electron transfer occurred by direct interaction between neighboring Cyt c or HRP molecules, while Con A wass responsible for stabilization of the arrangement; (2) Cyt c and HRP could be wired by Con A, which would be a conductive polymer under specific conditions; (3) electron transfer occurred by a face-to- face electron hopping between Cyt c and HPR or Cyt c.
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Direct Electron Transfer of Cytochrome c on ZrO2 Nanoparticles Modified Glassy Carbon Electrode

Direct Electron Transfer of Cytochrome c on ZrO2 Nanoparticles Modified Glassy Carbon Electrode

The most commonly used carbon-based electrode in the analytical laboratory is glassy carbon (GC). It is made by pyrolyzing (Pyrolysis is the decomposition of organic compounds by heating to high temperatures in the absence of oxygen) a carbon polymer, under carefully controlled conditions, to a high temperature like 2000◦C [35]. An intertwining ribbon-like material results with retention of high conductivity, hardness, and inertness. Glassy carbon electrode (GCE, dia. 3mm) was polished with 1 μm and 0.05 μm alumina slurries sequentially and then rinsed with distilled water. After that, the electrode was sonicated in deionized water and finally dried under ambient conditions.
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Direct Electron Transfer of Cytochrome C on Cadmium Oxide Nanoparticles Modified Carbon Paste Electrode

Direct Electron Transfer of Cytochrome C on Cadmium Oxide Nanoparticles Modified Carbon Paste Electrode

waste products, are the building blocks for the organ systems in the body. The functional status of an organ system is determined by measuring the chemical input and output analytes of the cells3. Therefore, the majority of tests made in the hospital or the physician’s office deal with analyzing the chemistry of the body19-21. Cadmium oxide (CdO) is n-type semiconductor used as a transparent conductive material prepared as a transparent conducting film back. Cadmium oxide has been used in applications such as photodiodes, phototransistors, photovoltaic cells, transparent electrodes, liquid crystal displays, IR detectors, and anti-reflection coat4.in this research we used of cadmium oxide nanoparticles as facile electron transfer between cytochrome c and carbon paste electrode. Carbon paste electrodes (CPEs) belong to promising electrochemical or bioelectrochemical sensors of wide applicability22-23. It is well accepted that Cyt c exhibits peroxidase activities, which can catalyze the reductive reaction of hydrogen peroxide.
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A Membrane Bound Cytochrome Enables Methanosarcina acetivorans To Conserve Energy from Extracellular Electron Transfer

A Membrane Bound Cytochrome Enables Methanosarcina acetivorans To Conserve Energy from Extracellular Electron Transfer

Tools are available for genetic manipulation of the methanogen Methanosarcina acetivorans (27–29). A methyl ᎑ coenzyme M reductase from an uncultured ANME was introduced into M. acetivorans to generate a strain that could convert methane to acetate with simultaneous reduction of Fe(III) (30). Most of the electrons from the methane consumed were recovered in acetate (30), and it was not shown that energy was conserved from Fe(III) reduction. In vitro reactions catalyzed by membrane vesicles of wild-type M. acetivorans suggested that the membrane-bound heterodisulfide re- ductase HdrDE reduced Fe(III)-citrate and AQDS and that an outer-surface multiheme c-type cytochrome might also function as a potential electron donor for Fe(III)-citrate reduction (31). However, in vitro assays with cell components are not a definitive approach for determining the physiologically relevant mechanisms involved in the reduction of Fe(III) and AQDS. This is because constituents that do have access to extracellular electron acceptors in vivo are exposed to extracellular electron acceptors in vitro and many reduced cofactors and redox-proteins, including c-type cytochromes, can nonspecifically reduce these electron acceptors (32). Analysis of the phenotypes of intact cells that result from specific gene deletions can provide more conclusive evidence.
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Cytochrome c Provides an Electron-Funneling Antenna for Efficient Photocurrent Generation in a Reaction Center Biophotocathode

Cytochrome c Provides an Electron-Funneling Antenna for Efficient Photocurrent Generation in a Reaction Center Biophotocathode

contrast, the RC adsorbs on the electrode via hydrophobic regions that are normally embedded in the membrane interior. The fi nding that high cyt c loading yields larger photocurrents and more positive onset potentials is important for improving the short-circuit currents and open-circuit voltages of cyt c- based biophotovoltaic systems. We suggest this is due to an interconnected cyt c layer, which acts as an electron-funneling antenna and electron-storing capacitor for delivery of electrons to the RC. Our data show that cyt c mobility is crucial for ET from the cyt c to the surface-bound RCs, likely due to reorientation of the heme group from the electrode surface for lateral cyt c − cyt c exchange, or toward the photo-oxidized RC primary electron donor cofactors. Finally, we have obtained de fi nitive evidence on the central role of cyt c-mediated ET to RCs immobilized on electrodes. We show the cyt c indeed gates ET to the RC, via the shift in the half-wave potential that is consistent with the positive shift in cyt c formal potential.
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Visualizing changes in electron distribution in coupled chains of cytochrome bc1 by modifying barrier for electron transfer between the FeS cluster and heme c1

Visualizing changes in electron distribution in coupled chains of cytochrome bc1 by modifying barrier for electron transfer between the FeS cluster and heme c1

Flash-activated turnover kinetics of cytochrome bc 1 were per- formed essentially as described in refs. [34 –36] , on a home-built double wavelength time-resolved spectrophotometer. The spectro- photometer consisted of a SP-20 Flash Lamp System (Rapp OptoElec- tronic, GmbH) and an optical assembly equipped with two H-20Vis monochromators (JY Horiba) (a generous gift of Prof. P. Leslie Dutton, University of Pennsylvania, Philadelphia, USA) and the two 9828SB07 photomultipliers in QL30 housing (Electron Tubes). An activation of the sample and an acquisition of the data were controlled by a locally written program using the NI PXI-1042Q interface (National Instru- ments). The electronic assembly was designed by T. Ole ś and J. Kozioł (Jagiellonian University). For the measurements, chromatophore membranes were suspended in appropriate buffer: 50 mM MES (for pH 6), 50 mM MOPS (for pH 7), or 50 mM Tris (for pH 9) containing 100 mM KCl, 3.5 μM valinomycin, and redox mediators: 7 μM 2,3,5,6- tetramethyl-1,4-phenylenediamine, 1 μM phenazine methosulfate, 1 μM phenazine ethosulfate, 5.5 μM 1,2-naphthoquinone, 5.5 μM 2- hydroxy-1,4-naphthoquinone. The sample was poised at an ambient potential of 150 mV, 100 mV, or -20 mV for pH 6, 7, or 9, respectively. Transient cytochrome c and b reduction kinetics initiated by a short saturating flash (10 μs) from a xenon lamp were followed at 550– 540 nm and 560 –570 nm, respectively. Inhibitors antimycin A, myxothiazol, and stigmatellin were used at final concentrations of 7, 7 and 1.5 μM, respectively.
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Structural and conducting properties of proton conducting tri-blend polymer electrolytes

Structural and conducting properties of proton conducting tri-blend polymer electrolytes

In our recent years solid polymer electrolyte is expected to replace the conventional liquid electrolytes due to its better durability, flexibility and long life time. Liquid electrolytes have been known as better candidates for various applications due to their considerable ionic conductivities. At the onset of introducing batteries, liquid electrolytes had shown good performance. Due to some disadvantages such as leakage and corrosion, attention has been diverted towards solid electrolytes [1] . Various research

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The Conducting Bological Pigment; Melanin Polymer

The Conducting Bological Pigment; Melanin Polymer

changed the electrical properties and the conductivities obtained are most likely due to differing water content in their respective samples. Baraldi et al. and Bridelli et al. [7] found evidence for two types of water in melanin: ‘structural’ water, probably within the structure of melanin; and ‘physical’ water, probably on the surface of melanin. They also found that water is a major factor in the electrical properties of melanin. Hall voltage measurements by Trukhan et al. [7] indicated that the charge carrier in melanin was positive. However, once again no hydration levels were recorded. It is most likely that the experiments were performed at ambient conditions; possibly indicating water’s role in the result. They suggested that the charge carriers were holes but conceded that protons were also a likely interpretation [7]. Coulometric studies by Powell et al. [7] suggested that synthetic melanin carried charges that were 65% protonic and 35% electronic over a hydration range of 12% to 35% weight gained in water. Due to the thermoelectric measurements, they tried to explain the conductivity of melanin in terms of conformational changes in melanin’s structure, which allows the electrons to hop more frequently. Further studies by Strzelecka investigated the supposed semiconductor properties of both natural and synthetic eumelanin. It was implied that the dominant charge carrier was a positively charged hole. In 1995, Jastrzebska et al [11] attempted to map out the direct current conductivity of melanin systematically as a function of hydration. They assumed that the hydration of melanin was proportional to relative humidity (RH). For this reason, they used various salt solutions to control the RH over a range of values. (Figure 2.5) shows the results obtained. They suggested that at low hydration the main charge carriers were electrons, but at higher hydration levels the carriers were positively charged polarons1 [7].
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Identifying involvement of Lys251/Asp252 pair in electron transfer and associated proton transfer at the quinone reduction site of Rhodobacter capsulatus cytochrome bc1

Identifying involvement of Lys251/Asp252 pair in electron transfer and associated proton transfer at the quinone reduction site of Rhodobacter capsulatus cytochrome bc1

Available online 12 July 2016 Describing dynamics of proton transfers in proteins is challenging, but crucial for understanding processes which use them for biological functions. In cytochrome bc 1 , one of the key enzymes of respiration or photosynthesis, proton transfers engage in oxidation of quinol (QH 2 ) and reduction of quinone (Q) taking place at two distinct catalytic sites. Here we evaluated by site-directed mutagenesis the contribution of Lys251/Asp252 pair (bacterial numbering) in electron transfers and associated with it proton uptake to the quinone reduction site (Q i site). We showed that the absence of protonable group at position 251 or 252 significantly changes the equilibrium levels of electronic reactions including the Q i -site mediated oxidation of heme b H , reverse reduction of heme b H by quinol and heme b H /Q i semiquinone equilibrium. This implicates the role of H-bonding network in binding of quinone/semiquinone and defining thermodynamic properties of Q /SQ /QH 2 triad. The Lys251/Asp252 proton path is disabled only when both protonable groups are removed. With just one protonable residue from this pair, the entrance of protons to the catalytic site is sustained, albeit at lower rates, indicating that protons can travel through parallel routes, possibly involving water molecules. This shows that proton paths display engineering tolerance for change as long as all the elements available for functional cooperation secure efficient proton delivery to the catalytic site.
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Direct Simulation of Proton-Coupled Electron Transfer Reaction Dynamics and Mechanisms

Direct Simulation of Proton-Coupled Electron Transfer Reaction Dynamics and Mechanisms

In both limiting regimes for the electronic coupling (Figs. 1.6(b) and 1.6(d)), the RPMD trajec- tories reveal concerted PCET reaction mechanisms that are implicit in the associated PCET rate theories (Eqs. (1.19) and (1.16)). However, the RPMD simulations additionally reveal a distinct – and to our knowledge, previously undiscussed – mechanism for concerted PCET in the inter- mediate coupling regime, in which the tunneling electron partially localizes about three sites: the positions of the electron donor site, the electron acceptor site, and the proton that is simultaneously undergoing transfer (Fig. 1.6(c)). This intermediate mechanism, which might be called “transient- proton-bridge” PCET, exhibits hybrid features of the PCET mechanisms from both limiting regimes (Figs. 1.6(b) and 1.6(d)), and it reflects the changing parameters that are employed to modulate the electronic coupling in Systems 2a-2f (Table 1.7); in this sense, it appears to be a physically reasonable mechanism for PCET in systems with intermediate electronic coupling, rather than an artifact of the approximate RPMD dynamics. Nonetheless, the transient-proton-bridge mechanism is certainly one for which no previous PCET rate theory has been been derived, and it remains to be seen whether an unambiguous kinetic signature of this new mechanism can be identified and observed in a physical system.
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Potential for Direct Interspecies Electron Transfer in Methanogenic Wastewater Digester Aggregates

Potential for Direct Interspecies Electron Transfer in Methanogenic Wastewater Digester Aggregates

ABSTRACT Mechanisms for electron transfer within microbial aggregates derived from an upflow anaerobic sludge blanket reac- tor converting brewery waste to methane were investigated in order to better understand the function of methanogenic consor- tia. The aggregates were electrically conductive, with conductivities 3-fold higher than the conductivities previously reported for dual-species aggregates of Geobacter species in which the two species appeared to exchange electrons via interspecies electron transfer. The temperature dependence response of the aggregate conductance was characteristic of the organic metallic-like con- ductance previously described for the conductive pili of Geobacter sulfurreducens and was inconsistent with electron conduction through minerals. Studies in which aggregates were incubated with high concentrations of potential electron donors demon- strated that the aggregates had no significant capacity for conversion of hydrogen to methane. The aggregates converted formate to methane but at rates too low to account for the rates at which that the aggregates syntrophically metabolized ethanol, an im- portant component of the reactor influent. Geobacter species comprised 25% of 16S rRNA gene sequences recovered from the aggregates, suggesting that Geobacter species may have contributed to some but probably not all of the aggregate conductivity. Microorganisms most closely related to the acetate-utilizing Methanosaeta concilii accounted for more than 90% of the se- quences that could be assigned to methane producers, consistent with the poor capacity for hydrogen and formate utilization. These results demonstrate for the first time that methanogenic wastewater aggregates can be electrically conductive and suggest that direct interspecies electron transfer could be an important mechanism for electron exchange in some methanogenic sys- tems.
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Photon Induced Electron Transfer in Quantum Dot Solar Cell

Photon Induced Electron Transfer in Quantum Dot Solar Cell

Abstract- Low dimensional semiconductor crystals structures otherwise known as quantum dots are in possession of unique optoelectronic properties that allow the flow of electrons to be harvested instantaneously. The advent of quantum dot for various technological applications is motivated by their flexibility of their bandgap supporting their capability to tap power from the visible spectrum as well as the invisible infrared through absorbable wavelength ranges from about 700 nanometre to 10 micron. Besides the wide energy harvesting range, quantum dot utilizes small to area for high energy production. The emergence of quantum dot and its application in optoelectronic device such as solar is set to improve the efficiency limit of traditional devices. The configuration of quantum dot in solar cell is discussed as well as electron transfer processes. Their three unique advantages for solar-to-electric energy conversion such as provision of large surface and interfacial areas per unit volume for light absorption and charge separation. The confinement process of charge carriers in quantum dot provides the ability to tune the optical and electronic properties of materials in ways that are not possible with bulk materials. The study shows that the incorporation of quantum into solar cell could enhance the performance of devices and as well, low their cost.
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Laser Pulse Deposited Nanosized Ceria for Direct Electron Transfer of Glucose Oxidase

Laser Pulse Deposited Nanosized Ceria for Direct Electron Transfer of Glucose Oxidase

can be seen by TEM (Fig. 2a). The high-resolution TEM, HR-TEM (Fig. 2b) shows well-defined crystallites with strong faceting and well-defined edges. Most of the nanoparticles have polyhedral shape confirming the presence of randomly-oriented ceria crystallites. The crystal size could be clearly observed and ranged between 2 to 5 nm. The lattice fringes could be observed in magnified images of different crystallites (Fig. 2b insets) and measured to be 1.9 and 3.2 Å, corresponding to the interplane distances between the (220) and (111) lattice planes of cubic CeO 2 . The selected-area electron
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Visualizing changes in electron distribution in coupled chains of cytochrome bc_{1} by modifying barrier for electron transfer between the FeS cluster and heme c_{1}

Visualizing changes in electron distribution in coupled chains of cytochrome bc_{1} by modifying barrier for electron transfer between the FeS cluster and heme c_{1}

© 2009 Elsevier B.V. 1. Introduction Bioenergetic enzymes use chains of cofactors to transfer electrons over long distances and connect catalytic sites with substrate redox pools. In such systems, the overall direction of electron flow is a resultant of reversible partial reactions. When one, linearly organized chain is involved and the system behaves in purely electrochemical manner without any gating, the distribution of electrons among cofactors is relatively simple to predict based on equilibrium thermo- dynamic calculations. However complications arise when more than one chain is involved and the electron flow in one chain is somehow linked with the electron flow in the other chain or the group of chains. One of the prominent examples of this sort of arrangement is a two- chain assembly in cytochrome bc 1 (complex III), a common component
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Structure of yeast cytochrome c oxidase in a supercomplex with cytochrome bc1

Structure of yeast cytochrome c oxidase in a supercomplex with cytochrome bc1

Membrane solubilisation and SC purification. Membranes were diluted in 50 mM HEPES, 150 mM NaCl, 1 mM PMSF, pH 8.0 to a CIII concentration of 45 nM and protein complexes were solubilised for 1 hour on ice by the addition of 1% GDN (glyco-diosgenin, Anatrace). After solubilisation, 350 mM NaCl (to make 500 mM final) and 5 mM imidazole are added. Insoluble material was removed by centrifugation at 120,000 × g for 30 minutes at 4˚C. Solubilised proteins were then loaded overnight in a cold room at a flow rate of approx. 0.6 mL/min using a peristaltic pump onto a 5 mL HisTrap HP column (GE Healthcare) previously equilibrated with 2 column volumes (CV) of 50 mM HEPES, 500 mM NaCl, 5 mM imidazole, 0.05% GDN, pH 8.0. After loading, the column was washed with 3 CV of 50 mM HEPES, 500 mM NaCl, 5 mM imidazole, 0.05% GDN, pH 8.0, and then with 5 CV of 50 mM HEPES, 150 mM NaCl, 0.05% GDN, 5 mM imidazole, pH 7.2. Bound proteins were eluted with 50 mM HEPES, 150 mM NaCl, 0.05% GDN, 100 mM imidazole, pH 7.2. The eluted proteins were concentrated by centrifugation using 100 kDa MWCO centrifugal concentrators (GE Healthcare). The resulting sample was then further purified by gel filtration, using an Äkta Pure 25 (GE Healthcare) operated at 4˚C with UV detection at 280 nm and automated fraction collection, by loading on a Superose 6 Increase column (GE Healthcare) equilibrated with 50 mM HEPES, 150 mM KCl, 0.05% GDN, pH 7.2. Fractions containing SCs were pooled and concentrated as above, and reapplied once to the same column.
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Electrochemical study of Conducting Polymer/Lignin Composites

Electrochemical study of Conducting Polymer/Lignin Composites

Fig.3 (A) shows the cyclic voltammograms obtained at poly AHNSA modified GCE in 0.1 M HNO 3 by cycling the potential between - 0.20 and 0.80 V in the potential scan rate of 10 - 250 mV/s. The voltammograms show three reversible redox couples at potentials (E ap /E cp ) of 0.071/0.038, 0.206/0.161, and 0.364/0.28 V respectively, due to electroactive deposition of the polymer film at the electrode surface. As shown in Fig.3 (B) both the anodic and cathodic peak currents increases linearly with increasing scan rate, with a regression coefficient of r 2 = 0.99951/0.99984, r 2 = 0.99405/0.99963, and
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Lytic and non-lytic permeabilization of cardiolipin-containing lipid bilayers induced by cytochrome C.

Lytic and non-lytic permeabilization of cardiolipin-containing lipid bilayers induced by cytochrome C.

The release of cytochrome c (cyt c) from mitochondria is an important early step during cellular apoptosis, however the precise mechanism by which the outer mitochondrial membrane becomes permeable to these proteins is as yet unclear. Inspired by our previous observation of cyt c crossing the membrane barrier of giant unilamellar vesicle model systems, we investigate the interaction of cyt c with cardiolipin (CL)-containing membranes using the innovative droplet bilayer system that permits electrochemical measurements with simultaneous microscopy observation. We find that cyt c can permeabilize CL-containing membranes by induction of lipid pores in a dose-dependent manner, with membrane lysis eventually observed at relatively high ( m M) cyt c concentrations due to widespread pore formation in the membrane destabilizing its bilayer structure. Surprisingly, as cyt c concentration is further increased, we find a regime with exceptionally high permeability where a stable membrane barrier is still maintained between droplet compartments. This unusual non-lytic state has a long lifetime (.20 h) and can be reversibly formed by mechanically separating the droplets before reforming the contact area between them. The transitions between behavioural regimes are electrostatically driven, demonstrated by their suppression with increasing ionic concentrations and their dependence on CL composition. While membrane permeability could also be induced by cationic PAMAM dendrimers, the non-lytic, highly permeable membrane state could not be reproduced using these synthetic polymers, indicating that details in the structure of cyt c beyond simply possessing a cationic net charge are important for the emergence of this unconventional membrane state. These unexpected findings may hold significance for the mechanism by which cyt c escapes into the cytosol of cells during apoptosis.
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Direct observation of plasma waves and dynamics induced by laser-accelerated electron beams

Direct observation of plasma waves and dynamics induced by laser-accelerated electron beams

To further investigate this effect, we perform a third experiment that concentrates on the features of the cone. The large field of view of the shadowgraphy diagnostic allows us to study the evolution on a picosecond timescale. In order to spoil the electron driver as little as possible, we remove the tape and move the jets closer to each other. The configuration is similar to the first experiment, but with slightly increased separation and almost twice the density in the first jet (cf. Table I). This leads to more than 2 . 5 × the beam charge (520 pC, about 100 kA) and less transmitted laser energy. Accordingly, we observe only one plasma wave, always accompanied by a cone. As shown in Fig. 4(a) and figures in the Supplemental Material [47], its origin is located close to the tail of the plasma wave, starting after a few hundred femtoseconds, and it persists at least out to 50 ps, as confirmed by varying the probe pulse delay. We measure a half-opening angle α ¼ ð3 . 0 0 . 5Þ mrad of the cone in this specific configuration. To our knowledge, no similar observation has been reported for either LWFA or PWFA and the origin of the diffraction cone was initially unclear. Assuming a mostly perpendicular motion, a transverse (group) velocity of v ⊥ ¼ 0 . 0017 c can be inferred from the opening angle. If the ion background was static and this feature arose only from electron motion, the velocities would be far too low to sustain a charge separation and the restoring forces would lead to plasma oscillations. Yet, the latter are not observed and the feature has to be associated with ion motion.
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