Electrochemical Potential Difference Research Articles

Respiratory complex I: A dual relation with H+ and Na+?

Respiratory complex I couples NADH:quinone oxidoreduction to ion translocation across the membrane, contributing to the buildup of the transmembrane difference of electrochemical potential. H+ is well recognized to be the coupling ion of this system but some studies suggested that this role could be also performed by Na+. We have previously observed NADH-driven Na+ transport opposite to H+ translocation by menaquinone-reducing complexes I, which indicated a Na+/H+ antiporter activity in these systems. Such activity was also observed for the ubiquinone-reducing mitochondrial complex I in its deactive form. The relation of Na+ with complex I may not be surprising since the enzyme has three subunits structurally homologous to bona fide Na+/H+ antiporters and translocation of H+ and Na+ ions has been described for members of most types of ion pumps and transporters. Moreover, no clearly distinguishable motifs for the binding of H+ or Na+ have been recognized yet.We noticed that in menaquinone-reducing complexes I, less energy is available for ion translocation, compared to ubiquinone-reducing complexes I. Therefore, we hypothesized that menaquinone-reducing complexes I perform Na+/H+ antiporter activity in order to achieve the stoichiometry of 4H+/2e−. In agreement, the organisms that use ubiquinone, a high potential quinone, would have kept such Na+/H+ antiporter activity, only operative under determined conditions. This would imply a physiological role(s) of complex I besides a simple “coupling” of a redox reaction and ion transport, which could account for the sophistication of this enzyme. This article is part of a Special Issue entitled Respiratory complex I, edited by Volker Zickermann and Ulrich Brandt.

Note: Inhibiting bottleneck corrosion in electrical calcium tests for ultra-barrier measurements.

A major failure mechanism is identified in electrical calcium corrosion tests for quality assessment of high-end application moisture barriers. Accelerated calcium corrosion is found at the calcium/electrode junction, leading to an electrical bottleneck. This causes test failure not related to overall calcium loss. The likely cause is a difference in electrochemical potential between the aluminum electrodes and the calcium sensor, resulting in a corrosion element. As a solution, a thin, full-area copper layer is introduced below the calcium, shifting the corrosion element to the calcium/copper junction and inhibiting bottleneck degradation. Using the copper layer improves the level of sensitivity for the water vapor transmission rate (WVTR) by over one order of magnitude. Thin-film encapsulated samples with 20 nm of atomic layer deposited alumina barriers this way exhibit WVTRs of 6 × 10(-5) g(H2O)/m(2)/d at 38 °C, 90% relative humidity.

Graphene decorated microelectrodes for simultaneous detection of ascorbic, dopamine, and folic acids by means of chemical vapor deposition

In this paper, high quality and large area graphene layers were synthesized using thermal chemical vapour deposition on copper foil substrates. We use graphene incorporated electrodes to measure simultaneously ascorbic acid, dopamine and folic acid. Cyclic voltammetry and differential pulse voltammetry methods were used to evaluate electrochemical behaviour of the grown graphene layers. The graphene-modified electrode shows large electrochemical potential difference compared to bare gold electrodes with higher current responses. Also our fabricated electrodes configuration can be used easily for microfluidic analysis.

Fabrication of high quality graphene nanosheets via a spontaneous electrochemical reaction process

A highly efficient graphene nanosheet (GNS) production process based on spontaneous electrochemical reactions – (i) spontaneous lithiation reaction through the direct contact between graphite powder and Li metal in an electrolyte due to the high electrochemical potential difference; and (ii) reaction of Li inside the lithiated graphite with water – is reported. This process, with the absence of supplied energies, is oxidation-free, very fast, scalable and produces a high quality GNS (C/O: 17.9 by EA, ID/IG: 0.55 by Raman spectroscopy) with a high yield (>95wt.%).

Characterization of the WC coatings deposited by plasma spraying

Tungsten monocarbide (WC) is deposited using a plasma jet on the martensitic noncorrosive steel support (Z12CNDV12), in three different thicknesses.The characteristics of the coatings are determined by: its chemical composition, optical microscopy, RX analysis, tensile adhesion strength, Vickers hardness, the nature and the processing degree of the substrate and the deposition conditions.The method used for determining the behaviour in a corrosive environment of the WC coatings deposited by plasma spraying consists in measuring the electrochemical potential difference between the coating and the substrate, which are immersed in a solution containing NaCl as a corrosive agent. The experimental results are then mathematically processed in order to determine a law and the mechanisms involved.

Towards high throughput corrosion screening using arrays of bipolar electrodes

In this work we demonstrate the possibility of combining bipolar electrochemistry with arrays of samples as a fast and versatile method for comparing their corrosion resistances at a wide range of potentials. Several steel samples of different grades were arranged in a bipolar electrochemical cell and exposed to an electric field by applying a constant current. The gradient in electrochemical potential difference across each sample resulted in a pitting corrosion gradient on the anodic parts which was used as a simple, straightforward and qualitative method of screening the corrosion properties of several samples in one single experiment. In the cell, all samples acted as individual bipolar electrodes but interestingly, the current density for each sample was also found to be influenced by the corrosion resistances of its neighbours. Results from the bipolar array were also compared with standard polarisation curves and the pitting resistance equivalent number (PREN) for each steel type.

Comparison of enhancement of transdermal permeability of Carvedilol through physical and chemical methods

Background The aim of the study was to overcome the difficulties raised in oral therapy; there is a need for the development of new drug delivery system that will improve the therapeutic efficacy. Because of its low dose and extensive hepatic metabolism, Carvedilol is a suitable candidate for transdermal administration. Objective The ultimate aim of this study was to administer Carvedilol through a transdermal patch and to evaluate by chemical method and iontophoresis by means of in-vitro drug release and ex-vivo permeation studies. Materials and methods The matrix type transdermal patches were prepared by solvent evaporation technique. Various formulations composed of hydroxypropyl methylcellulose (HPMC E15), Eudragit (ERL 100) in different ratios were prepared. All formulations consist of 15% v/w of dibutyl phthalate as plasticizer. Results and conclusion The prepared patches were characterized for various physicochemical parameters. The penetration-enhancing mechanism of iontophoresis was found to increase solvent flow through electro-osmosis and pore enlargement in the skin barrier, together with enhancement of electrochemical potential difference across the skin. The effect of chemical enhancer d-limonene and iontophoretic transdermal transport of drug using a current density of 1 mA/cm 2 was investigated. Increasing the applied current density from 0.5 to 1 mA/cm 2 resulted in a 2.2-fold increase in iontophoretic flux. Results demonstrated that iontophoresis exhibited a great ability to enhance the flux of drug in comparison with the chemical method. The optimized formulations F2 and F3 containing 8% d-limonene as chemical enhancer showed maximum skin permeation, 979.45 ± 3.16 and 900.57 ± 2.8 μg/cm 2 , respectively, whereas formulations F9 and F10 with iontophoresis showed the skin permeation, 1048.7 ± 3.8 and 1476.7.7 ± 4.8 μg/cm 2 , respectively, and obtained flux greater than F2.

Role of Charge Transfer States in P3HT-Fullerene Solar Cells

By examining poly(3-hexylthiophene)-fullerene blend solar cells with controlled variations of the active layer using subgap external quantum efficiency combined with intensity dependent quantum efficiency at short circuit, a direct correlation between trap-assisted recombination parameters and the charge transfer state absorption strength is established. Most significantly, by comparing devices with different polymer molecular weight, regioregularity, C60 derivative chemistry, and film drying speed, we find that samples with higher trap-assisted recombination exhibit higher charge generation efficiency. Both findings are in support of the general view that the charge transfer states are involved in both processes. In addition, we find that the traps are full at about 100 mW/cm2, which suggests, together with the correlation with the charge transfer states, that the electrochemical potential difference in the bulk exceeds the open circuit voltage and that the loss of voltage is probably due to recombination associated with charge extraction at the electrodes.

Effects of ageing on mechanical durability of round clinched steel/aluminium joints

The clinching is one of the most common metal joining processes in the manufacturing of metal plate based products (similar or dissimilar, pre-coated or galvanized), especially when the assembly without adding major joining elements is required. When the clinched joints work in an aggressive environment, particular attention would be placed on the electrochemical stability and corrosion resistance of the metal constituents (Mizukoshi and Okada 1997). In joining design, an appropriate material selection reduces the electrochemical potential differences and prevents significant galvanic currents (Kruger and Mandel 2011; Calabrese et al. 2014). The durability of the metal joints could be heavily influenced in a corrosive environment, whereas the less noble material will tend to increase its corrosion rate; instead the more noble one will reduce its electrochemical dissolution (He et al. 2008; Bardal 2004). Accelerated ageing tests (i.e. salt fog test) were carried out to evaluate the durability of the joints in highly aggressive environments (Calabrese et al. 2013; LeBozec et al. 2012). Although the durability for a long time of the clinched joint in a corrosion environment is a known problem, few works focus the attention on the relationship between durability of joints and electrochemical behaviour of the metal constituents. The aim of the present work is to evaluate the durability at long ageing time in salt spray test (according to ASTM B117) of carbon steel/aluminium alloy joints, obtained by clinching. The investigation has been conducted on one total thickness (2.5 mm) of unsymmetrical joints (i.e. thickness sheets of 1.5 mm and 1 mm) to inquire about the effect of corrosion on the two different unsymmetrical configurations (St1.5/Al1 and St1/Al.5). The joint resistance has been determined, by means of shear tests of single-lap joints in according to ISO/CD 12996. The samples were exposed to critical environmental conditions following the ASTM B 117 standard. To inquire the damage evolution of the samples, 0, 1, 2,3, 5, 7, 10 and 15 weeks of ageing time have been chosen. Seven samples for each combination and for each ageing time were realized. A Design of Experiment has been performed, followed by the ANOVA of the results to analyse the influence of the two factors, thickness combinations and ageing time, on the mechanical properties of the joints. The two sets of joints show a different behaviour at increasing ageing time: the St1.5/Al1 batch shows a constant decay of the load values, instead the St1/Al1.5 set maintains acceptable values of resistance for several weeks of ageing, at tenth week the mechanical stability is strongly impaired. In the latter case the presence of the thin oxide layer at the overlapping interface, which behaves as an adhesive interlayer, and the larger thickness of the aluminium plate improve the resistance of the St1/Al1.5 joints. Statistical analysis confirms that the two thickness combinations and ageing time are the significant factors. At zero weeks, neglecting the effect of ageing, the maximum load values of all samples belong to the same population. This means that the resistance of the clinched joints is the same regardless the combination of thicknesses, but by considering both the ageing and thickness, the analysis of variance shows that both thickness and weeks are significant parameters distinguishing two different populations in the distribution of loads. The experimental results evidenced that the corrosion degradation phenomena influence significantly both the performance and the failure of the joints. This is also confirmed by statistical analysis according to which the two thickness combinations and ageing time are the significant factors.

Semiquinone-induced Maturation of Bacillus anthracis Ribonucleotide Reductase by a Superoxide Intermediate

Ribonucleotide reductases (RNRs) catalyze the conversion of ribonucleotides to deoxyribonucleotides, and represent the only de novo pathway to provide DNA building blocks. Three different classes of RNR are known, denoted I-III. Class I RNRs are heteromeric proteins built up by α and β subunits and are further divided into different subclasses, partly based on the metal content of the β-subunit. In subclass Ib RNR the β-subunit is denoted NrdF, and harbors a manganese-tyrosyl radical cofactor. The generation of this cofactor is dependent on a flavodoxin-like maturase denoted NrdI, responsible for the formation of an active oxygen species suggested to be either a superoxide or a hydroperoxide. Herein we report on the magnetic properties of the manganese-tyrosyl radical cofactor of Bacillus anthracis NrdF and the redox properties of B. anthracis NrdI. The tyrosyl radical in NrdF is stabilized through its interaction with a ferromagnetically coupled manganese dimer. Moreover, we show through a combination of redox titration and protein electrochemistry that in contrast to hitherto characterized NrdIs, the B. anthracis NrdI is stable in its semiquinone form (NrdIsq) with a difference in electrochemical potential of ∼110 mV between the hydroquinone and semiquinone state. The under anaerobic conditions stable NrdIsq is fully capable of generating the oxidized, tyrosyl radical-containing form of Mn-NrdF when exposed to oxygen. This latter observation strongly supports that a superoxide radical is involved in the maturation mechanism, and contradicts the participation of a peroxide species. Additionally, EPR spectra on whole cells revealed that a significant fraction of NrdI resides in its semiquinone form in vivo, underscoring that NrdIsq is catalytically relevant.

Nonlinear coupled equations for electrochemical cells as developed by the general equation for nonequilibrium reversible-irreversible coupling.

We show how the Butler-Volmer and Nernst equations, as well as Peltier effects, are contained in the general equation for nonequilibrium reversible and irreversible coupling, GENERIC, with a unique definition of the overpotential. Linear flux-force relations are used to describe the transport in the homogeneous parts of the electrochemical system. For the electrode interface, we choose nonlinear flux-force relationships. We give the general thermodynamic basis for an example cell with oxygen electrodes and electrolyte from the solid oxide fuel cell. In the example cell, there are two activated chemical steps coupled also to thermal driving forces at the surface. The equilibrium exchange current density obtains contributions from both rate-limiting steps. The measured overpotential is identified at constant temperature and stationary states, in terms of the difference in electrochemical potential of products and reactants. Away from these conditions, new terms appear. The accompanying energy flux out of the surface, as well as the heat generation at the surface are formulated, adding to the general thermodynamic basis.

CFD prediction of scalar transport in thin channels for reverse electrodialysis

Reverse electrodialysis (RED) is a very promising technology allowing the electrochemical potential difference of a salinity gradient to be directly converted into electric energy. The fluid dynamics optimization of the thin channels used in RED is still an open problem. The present preliminary work focuses on the computational fluid dynamics simulation of the flow and concentration fields in these channels. In particular, three different configurations were investigated: a channel unprovided with a spacer (empty channel) and two channels filled with spacers, one made of overlapped filaments and the other of woven filaments. The transport of two passive scalars, representative of the ions present in the solution, was simulated in order to evaluate concentration polarization phenomena. Computational domain effects were also addressed. Results show that: (i) the adoption of a computational domain limited to a single unit cell along with periodic boundary conditions provides results very close to those obtained in a larger domain; (ii) the woven spacer-filled channel is the best compromise between pressure drop and concentration polarization. Future work will address the inclusion of electrical effects along with the migrative transport of the ions in the channel.

Computational Modeling of Electrolyte/Cathode Interface for Li-Ion Batteries

Since the electrochemical potential difference and the charge capacity largely determine the energy density of a Li-ion battery, a major and concurrent factor in the choice of electrode materials for high-voltage Li-ion chemistry is the insight gained from studying and understanding the electrochemical reactions which take place at the electrode/electrolyte interface. The extreme electrochemical potential of high-voltage cathode materials marks a limit on the oxidation stability window of the state-of-the-art nonaqueous electrolytes used in Li-ion chemistry. In addition, the properties of the passivation layer for any particular cathode electrode material are determined by the composition of the electrolyte and electrolyte additives. The importance of understanding how the electrode surface reacts with the electrolyte for advancing Li-ion energy storage capacity is evidenced, in part, by kinetics measurements which have demonstrated that the activation energy of Li+ charge transfer rates varies with differing electrode materials. This clearly suggests that the different electrodes create distinct chemical interfaces in the same electrolyte. Spinel dissolution and cathodic capacity losses in metal-oxide cells as a function of varying electrolyte solution setting, comprising different mixtures of solvents, Li salts and additives, is a major area of current research. It has been shown that spinel dissolution is induced by acids resulting from electrochemical oxidation of solvent molecules on composite cathodes. The widely utilized carbonate based solvents are considered to be relatively inert, whereas other related solvents such as various ethers are readily oxidized to produce acids. Experimental charge/discharge cycling of spinel-loaded composite cathodes found the acid concentration and the extent of spinel dissolution to be significantly higher in ether-containing electrolytes in comparison to their carbonate based counterparts. Further experimental evidence indicates that Li and transition-metal ion extraction is facilitated by an acid induced degradation of the cathode material, where continued spinel dissolution leads to oxygen loss from the Li-metal-oxide lattice. The nature of added Li salts largely influences solvent oxidation and spinel dissolution. Although solvent induced acid production for electrolytes containing fluorinated salts is not significant, the appreciable spinel dissolution in these cathode/electrolyte systems strongly suggests that acid is generated through various reaction pathways. A thorough understanding of the reactions on the electrode surface of lithium batteries is central to the designing of new electrode interface material components to achieve efficiency and durability in high-voltage settings. In the present computational modeling work, we focus on the high-voltage lithium nickel manganese spinel (LiNi0.5Mn1.5O4) cathode material, where an experimental investigation of the voltage-dependent electrochemical reactions of a 1-M LiPF6/EC:DMC:DEC electrolyte on a LiNi0.5Mn1.5O4-based electrode, through characterization of the surface species by XPS and FTIR-ATR, showed that the increase in current flow coincides with changes to the surface chemistry of the cathodes and displayed a clear trend of increasing polyethylenecarbonate formation with increasing voltage. In order to provide predictive understanding in complement to experimental work, we performed high-level Quantum Chemical (QC) calculations and DFT-based Born-Oppenheimer Molecular Dynamics (BOMD) simulations on a series of non-aqueous, mainly carbonate-based electrolytes featuring a combination of solvents, salts, electrolyte additives, and cathode materials. Initial BOMD calculations of molecule/surface systems (EC, DEC, FEC, DMC, PF6 -, HFIB) served as a guide for subsequent unconstrained BOMD simulations of electrolyte mixtures on the delithiated LiNi0.5Mn1.5O4 [111] and [100] surfaces to capture spontaneous electrochemical reactions. Nudged Elastic Band and Path Minimization calculations were employed to study the chemisorption characteristics of each electrolyte, such as the internal bond-breaking/bond-making evolution of the electrolyte and the electrolyte coordination to surface metal ions. Then, DFT potential-of-mean-force (PMF) simulations were conducted on explicit liquid electrolyte/electrode interfaces at finite temperature to investigate the previously determined pathways. From the PMF calculations, potential key reaction steps such as the transfer of protons and the lowering of the reaction barrier in the explicit liquid environment were determined. In particular, the two mechanisms of main interest in regard to interfacial electrolyte/cathode chemistry studied in the simulations is the retrieval of an oxygen ion from the cathode surface by an oxidized electrolyte molecular fragment and the proton transfer from the carbonate electrolyte to the metal-oxide. Our DFT based molecular dynamics simulations conducted at liquid EC/cathode interfaces are consistent with the view that reactions and electron transfer occur at the electrode interface.

Reconstitution of respiratory complex I on a biomimetic membrane supported on gold electrodes.

For the first time, respiratory complex I has been reconstituted on an electrode preserving its structure and activity. Respiratory complex I is a membrane-bound enzyme that has an essential function in cellular energy production. It couples NADH:quinone oxidoreduction to translocation of ions across the cellular (in prokaryotes) or mitochondrial membranes. Therefore, complex I contributes to the establishment and maintenance of the transmembrane difference of electrochemical potential required for adenosine triphosphate synthesis, transport, and motility. Our new strategy has been applied for reconstituting the bacterial complex I from Rhodothermus marinus onto a biomimetic membrane supported on gold electrodes modified with a thiol self-assembled monolayer (SAM). Atomic force microscopy and faradaic impedance measurements give evidence of the biomimetic construction, whereas electrochemical measurements show its functionality. Both electron transfer and proton translocation by respiratory complex I were monitored, simulating in vivo conditions.

New Analytical Tool for Electrochemical Interfaces – in Situ Neutron Reflectometry

Interfacial reactions between intercalation electrodes and electrolyte have attracted much attention to achieve high current drain and long-term stability of lithium batteries, fuel cells, and metal-air batteries. However, there is no common strategy for the design of materials produced under an electrochemical potential field. Neutron reflectometry (NR) is a new experimental technique that gives useful information of the concentration gradient of diffusing species from the electrode to the electrolyte on battery operation [1]. Here we have detected a defect-rich phase in the 10–20 nm region from the surface of lithium intercalation electrodes, Li4Ti5O12, LiMn1/3Co1/3Ni1/3O2, and LiFePO4. The defective phase formation has been directly related to the electrochemical activity of nanosized electrode materials. Epitaxial films of each electrode material were grown on Nb:SrTiO3(111) substrates using a pulsed laser deposition apparatus [1-2]. Thicknesses of the films were 25 to 45 nm. NR measurements were performed on SOFIA (BL-16, J-PARC), which is a time-of-flight reflectometer [3]. A deuterated propylene carbonate electrolyte containing 1 M LiPF6 was used as an electrolyte solution to prevent incoherent scattering of 1H. The neutron reflectivity spectra were collected at pristine and at open circuit voltage condition. The models of interfacial structure were refined by the Parratt32 data analysis program using roughness, thickness, and scattering length density (SLD) of each layer as parameters. The SLD in the surface region of Li4Ti5O12(111) increased from the pristine to the cell-construction conditions. As nLi ions have a negative coherent scattering length of -1.9 fm, the increase in the SLD indicated a formation of lithium vacancies in the surface region prior to electrochemical cycling. The lithium vacancy-type (VLi') defect formation was confirmed by lattice contraction observed by surface X-ray diffraction [4]. Similar to Li4Ti5O12, a lithium vacancy-type defect phase was detected for LiMn1/3Co1/3Ni1/3O2(1-18). In contrast, LiFePO4(100) films showed a decrease in the SLD value at the electrochemical interface formation, indicating a defect phase of interstitial lithium type (Lii .). The type of defects generated may be related to the electrochemical potentials of the electrode and the electrolyte. The difference in electrochemical potential causes a gradual change in the structure at the interfacial region to equilibrate the potentials of the two materials. Lithium is the mobile species in these electrodes; therefore, lithium may participate in charge compensation with formation of the defect phase. The defective phase was related to an extremely high lithium storage capacity of nanosized Li4Ti5O12[5] and an isotropic lithium diffusion in nanosized LiFePO4. The results suggest how to create a defect phase at the electrochemical interface and the concept of interfacial defect phase control is extended to nanosize material control for next-generation battery materials. References M. Hirayama, et al., Electrochemistry, 78 (2010) 413.M. Hirayama, et al., Dalton Trans., 40 (2011) 2882.M. Koji et al., J. Phys.: Conf. Ser., 272 (2011) 012017.M. Hirayama, et al., J. Am. Chem. Soc., 132, (2010) 15268; K. Sakamoto, et al., Phys. Chem. Chem. Phys., 12 (2010) 3815; K. Sakamoto, et al., Chem. Mater., 21 (2009) 2632.Wagemaker, et al., J. Am. Chem. Soc., 131 (2009) 17786.

Structure and function of the bi-directional bacterial flagellarmotor.

The bacterial flagellum is a locomotive organelle that propels the bacterial cell body in liquid environments. The flagellum is a supramolecular complex composed of about 30 different proteins and consists of at least three parts: a rotary motor, a universal joint, and a helical filament. The flagellar motor of Escherichia coli and Salmonella enterica is powered by an inward-directed electrochemical potential difference of protons across the cytoplasmic membrane. The flagellar motor consists of a rotor made of FliF, FliG, FliM and FliN and a dozen stators consisting of MotA and MotB. FliG, FliM and FliN also act as a molecular switch, enabling the motor to spin in both counterclockwise and clockwise directions. Each stator is anchored to the peptidoglycan layer through the C-terminal periplasmic domain of MotB and acts as a proton channel to couple the proton flow through the channel with torque generation. Highly conserved charged residues at the rotor–stator interface are required not only for torque generation but also for stator assembly around the rotor. In this review, we will summarize our current understanding of the structure and function of the proton-driven bacterial flagellar motor.

The 2014 Joseph W. Richards Summer Research Fellowship -- Summary Report: Thermogalvanic Waste Heat Recovery in Transportation Energy Systems

Waste heat recovery remains an inviting subject for research. Solid state thermoelectric devices have been widely investigated for this purpose, but their practical application remains challenging due to high cost and the inability to fabricate them in geometries that are easily compatible with heat sources. An alternative to solid-state thermoelectric devices are thermogalvanic cells.1-7 The temperature difference between the hot and the cold electrodes creates a difference in electrochemical potential of the redox couples at the electrodes. Once connected to a load, electrical current and power is delivered, converting thermal energy into electrical energy. The aim of this summer project is to extend ongoing research to study the feasibility of incorporating thermogalvanic systems into automobiles. A climate-controlled wind tunnel (Fig. 1) was built to provide equivalent conditions to the ambient air stream under the car. Temperature was controlled using a window air conditioner, while an air mover drove the flow up to 6 m s−1. A heat gun provided the equivalent of a low-temperature exhaust gas stream (~110 oC). The annular cell was bound by concentric copper pipes (electrodes) and CPVC bulkheads; all sealed with silicone. K-type thermocouples were attached with epoxy onto electrode surfaces to measure the electrode temperature, which were monitored and recorded by a Campbell Scientific CR23X Micrologger. The cell potential (E) was probed using a Fluke 8846A Digital Multimeter. An Elenco RS-500 resistor box (Rext) was connected in parallel to measure power output, P = E/Rext. A 0.7 M CuSO4 aqueous electrolyte was used, with 0.1 M H2SO4 as the supporting electrolyte. The Tcold was varied based on the quad-monthly average ambient air temperature (Tambient) in Phoenix, AZ of 31.6, 22.5, and 14.1 oC. Because thermal resistance from the hot air stream to the inner copper pipe is large relative to the thermal resistance of the cell, the Thot was measured to be less than the hot air stream’s temperature. Reducing this resistance would greatly improve the system performance. The experimental values of Thot and Tcold are shown next to their resultant plots in Fig. 2. These results showed that higher Tambient yielded a higher P, because of the higher average cell temperature, Tavg = (Thot+ Tcold)/2. This trend agreed with our previous study.8 Since the resistor could only be Fig 1. 3D CAD drawings of the wind tunnel and the cross-sectional diagram of the annular Cu/Cu2+ thermogalvanic cell.

Evolutionary Perspective on the Coupling Mechanism of Complex I and Related Enzymes

Complex I is an energy transducing enzyme present in the three domains of life. This enzyme catalyzes the oxidation of NADH and the reduction of quinone coupled to charge translocation across the membrane. In this way, it contributes to the establishment of the transmembrane difference of electrochemical potential which is used for ATP synthesis, solute transport and motility. The research on this enzyme has gained a new enthusiasm, especially after the resolution of the crystallographic structures of bacterial and mitochondrial complexes. Most attention is now dedicated to the investigation of the energy coupling mechanism. In this work, we made a thorough investigation of complex I and group 4 [NiFe] hydrogenases and established a third member of this family of proteins: the energy-converting hydrogenase related complex. We observed that four subunits (NuoB, D, H and antiporter-like) are common to the 3 types of complexes and we have denominated these subunits as the universal adaptor. We further explored the properties of the adaptor by investigating the structural characteristics of the antiporter-like subunit. We observed that the adaptor contains an antiporter-like subunit with a long amphipathic α-helix. The long helix is a common denominator that has been conserved through evolution. This should reflect a key role of such helix in the coupling mechanism of this family of enzymes. We are currently investigating the structural motifs involved in Na+/H+ antiporter activity in complex I and related complexes. These findings are a step forward in the investigation of the coupling mechanism of complex I.

Substituent and Solvent Effects on the Electrochemical Properties and Intervalence Transfer in Asymmetric Mixed‐Valent Complexes Consisting of Cyclometalated Ruthenium and Ferrocene

Four heterodimetallic complexes [Ru(Fcdpb)(L)](PF6) (Fcdpb=2-deprotonated form of 1,3-di(2-pyridyl)-5-ferrocenylbenzene; L=2,6-bis-(N-methylbenzimidazolyl)-pyridine (Mebip), 2,2':6',2''-terpyridine (tpy), 4-nitro-2,2':6',2''-terpyridine (NO2tpy), and trimethyl-4,4',4''-tricarboxylate-2,2':6',2''-terpyridine (Me3tctpy)) have been prepared. The electrochemical and spectroelectrochemical properties of these complexes have been examined in CH2Cl2, CH3NO2, CH3CN, and acetone. These complexes display two consecutive redox couples owing to the stepwise oxidation of the ferrocene (Fc) and ruthenium units, respectively. The potential difference, ΔE(1/2)(E(1/2)(Ru(II/III))-E(1/2)(Fc(0/+))), decreased slightly with increasing solvent donocity. The mixed-valent states of these complexes have been generated by electrolysis and the resulting intervalence charge-transfer (IVCT) bands have been analyzed by Hush theory. Good linear relationships exist between the energy of the IVCT band, E(op), and ΔE(1/2) of four mixed-valent complexes in a given solvent.

Galvanic corrosion behaviour of hot-dipped zinc-aluminum alloy coated titanium-aluminum couples

The hot-dipped zinc–aluminum alloy coating was used to avoid galvanic corrosion problems of titanium–aluminum alloy. The microstructure and corrosion properties of the coating were investigated by scanning electron microscopy, electrochemical measurement, and immersion test. The microstructure indicated that the coating consisted of outermost layer and middle interdiffusion layer, which metallurgically combined with the substrate. The electrochemical properties indicated that the coating on the titanium alloy decreased the electrochemical potential difference of galvanic couple. The corrosion current density showed that aluminum alloy contact with the coating changed the electrode, in other words, aluminum alloy specimen turned out to be the cathode in the galvanic couple. Immersion test was carried out to evaluate the performance of coating for galvanic corrosion, results confirmed that aluminum alloy contacted with coating on titanium–aluminum alloy exhibited less surface corrosion.