Redox Reactions Of Complexes Research Articles

Electrochemical characterization of a plasmonic effect ethanol sensor based on two-dimensional ZnO synthesized by green chemistry

This work describes the electrochemical performance of a novel sensor based on two-dimensional ZnO and activated by the plasmonic effect to calculate the ethanol content in bio-alcohol samples. The ZnO was prepared in a coffee extract at 90 °C. XRD and TEM showed the formation of hexagonal phase ZnO and its two-dimensional morphology, respectively. The sensor was formed by depositing the semiconductor on a sterling silver sheet. The sensor was immersed in 1 M KOH at 25 °C and illuminated with visible light to produce the plasmonic effect. The electrochemical analysis showed that the plasmonic effect activated the complex redox reactions of ethanol/CO2. A Figure of Merit of the sensor was proposed to obtain the calibration curve and calculate the molar concentration of ethanol in four bio-alcohol samples obtained from artisanal production. The accurate content of ethanol in each sample was measured by gas chromatography and was compared with the calculated values. The results show the feasibility of using sensors activated by the plasmonic effect to calculate the ethanol content in alcohols.

Hydrothermal catalytic conversion and metastable equilibrium of organic compounds in the Jinding Zn/Pb ore deposit

Hydrothermal organic reactions in the presence of mineral catalysts have been well established by laboratory experiments. However, little is documented about hydrothermal catalytic conversion (HTCC) and the metastable existence of complex molecules in continental hydrothermal systems. Five freshly mined ores containing oil and solid bitumen and associated unmineralised host sediment were sampled from the Beichang mine, Jinding Zn/Pb ore deposit, Lanping, near the Indo-Eurasian collisional margin, southeastern Tibetan Plateau. Here we show evidence for a wide range of mineral (ZnS/PbS) catalysis of polycyclic aromatic compounds in the natural subsurface.An interpretation of hydrothermal alteration (non-biodegradation) was made for the unresolved complex mixture. From unmineralised host sediment through oils to the solid bitumen, a stepwise interaction of organic compounds with metal-bearing hydrothermal fluids was demonstrated by the transformation of polycyclic aromatic hydrocarbons (PAHs) and phenyl/sulfur/oxygen-containing compounds that are thought to be generated through HTCC. Thermodynamically-unstable phenyl derivatives (ortho- or α-substituted) resulted from hydrothermal alteration (ring opening) of the middle and naphthenic (low energy) rings of peri-condensed parent PAHs, as supported by the dominance of 1-phenyldibenzothiophene, 1-phenyldibenzofuran, triphenyleno[1,12-bcd]thiophene, triphenyleno[1,12-bcd]furan, 9-phenylphenanthrene, 1,1′:2′,1′′:2′′,1′′′-quaterphenyl, and the corresponding thiophenes or furans over other isomers. Heteroatom addition to phenyl-derivatives generates abundant heterocyclic compounds, which can undergo further dehydrocyclisation. In the presence of ZnS/PbS, the abundance of three compound classes (unsubstituted PAHs, ‘aryl-aryl’ linked phenyl-derivatives, and S/O atom-containing compounds) is mainly hydrothermally controlled, rather than thermodynamically controlled. Various phenyl/sulfur/oxygen-containing compounds are the metastable equilibrium products of a series of complex redox reactions under specific hydrothermal conditions. We hypothesise that the ubiquitous triphenyleno[1,12-bcd]furan is an important marker for hydrothermal organic–inorganic interactions in the Zn/Pb deposit. The relative abundance of 9-phenylphenanthrene provides a measure of the degree of hydrothermal alteration and HTCC. Our data is consistent with a close interaction of ascending metalliferous hydrothermal fluids with indigenous organic matter/compounds. Hydrothermal fluids, in the presence of sphalerite (and/or galena), are highly effective for activation of the carbon–carbon bonds in PAHs.

Direct Mechanistic Evidence for a Nonheme Complex Reaction through a Multivariate XAS Analysis.

In this work, we propose a method to directly determine the mechanism of the reaction between the nonheme complex FeII(tris(2-pyridylmethyl)amine) ([FeII(TPA)(CH3CN)2]2+) and peracetic acid (AcOOH) in CH3CN, working at room temperature. A multivariate analysis is applied to the time-resolved coupled energy-dispersive X-ray absorption spectroscopy (EDXAS) reaction data, from which a set of spectral and concentration profiles for the reaction key species is derived. These “pure” extracted EDXAS spectra are then quantitatively characterized by full multiple scattering (MS) calculations. As a result, structural information for the elusive reaction intermediates [FeIII(TPA)(κ2-OOAc)]2+ and [FeIV(TPA)(O)(X)]+/2+ is obtained, and it is suggested that X = AcO– in opposition to X = CH3CN. The employed strategy is promising both for the spectroscopic characterization of reaction intermediates that are labile or silent to the conventional spectroscopic techniques, as well as for the mechanistic understanding of complex redox reactions involving organic substrates.

TiO2 electrocatalysis via three-electron oxygen reduction for highly efficient generation of hydroxyl radicals

The use of heterogeneous catalysts to improve the Electro-Fenton (EF) process has attracted significant attention. However, complex redox reactions and multiple mass transfer steps during the EF process result in limited current efficiency with only a low rate of generation of hydroxyl radicals (OH). Herein, we establish a three-electron oxygen reduction reaction (ORR) process coupling adsorbed H2O2 (H2O2ad) generation with an in situ EF-like reaction on TiO2 during cathodic electrolysis. Anatase TiO2 was composited with graphite, enabling the electrochemical reduction of Ti4+ to Ti3+. H2O2ad was formed during the ORR, electrocatalyzed by TiO2, then the H2O2ad was reduced in situ to OH without desorption. The generation and decomposition of Ti-OH during the electrochemical reduction were directly observed by in situ Raman spectroscopy. This result was further confirmed by density functional theory (DFT) calculations. Based on this three-electron ORR mechanism, the OH yield reached 2.69 μg cm−2 min−1 and the current efficiency approached 92.8% at a current density of −0.80 mA cm−2 within 2 h during ORR on the TiO2/graphite (TiO2/C) cathode.

Fast repetition rate fs pulsed lasers for advanced PLIM microscopy

Simultaneous metabolic and oxygen imaging is promising to follow up therapy response, disease development and to determine prognostic factors. FLIM of metabolic coenzymes is now widely accepted to be the most reliable method to determine cellular bioenergetics. Also, oxygen consumption has to be taken into account to understand treatment responses. The phosphorescence lifetime of oxygen sensors is able to indicate local oxygen changes. For phosphorescence lifetime imaging (PLIM) dyes based on ruthenium (II) coordination complexes are useful, in detail TLD1433 which possesses a variety of different triplet states, enables complex photochemistry and redox reactions. PLIM is usually reached by two photon excitation of the drug with a femtosecond (fs) pulsed Ti:Sapphire laser working at 80[Formula: see text]MHz repetition rate and (time-correlated single photon counting) (TCSPC) detection electronics. The interesting question was whether it is possible to follow up PLIM using faster repetition rates. Faster repetition rates could be advantageous for the induction of specific photochemical reactions because of similar light doses used normally in standard CW light treatments. For this, a default 2[Formula: see text]-FLIM–PLIM system was expanded by adding a second fs pulsed laser (“helixx”) which provides 50[Formula: see text]fs pulses at a repetition rate of 250[Formula: see text]MHz, more than 2.3[Formula: see text]W average power and tunable from 720[Formula: see text]nm to 920[Formula: see text]nm. The laser beam was coupled into the AOM instead of the default 80[Formula: see text]MHz laser. We demonstrated successful applications of the 250[Formula: see text]MHz laser for PLIM which correlates well with measurements done by excitation with the conventional 80[Formula: see text]MHz laser source.

To be or not to be oxidized: A case study of olivine behavior in the fusion crust of ureilite A 09368 and H chondrites A 09004 and A 09502.

Meteorite fusion crusts are quenched melt layers formed during meteoroid atmospheric entry, mostly preserved as coating on the meteorite surface. Antarctic ureilite Asuka (A) 09368 and H chondrites A 09004 and A 09502 exhibit well preserved thick fusion crusts, characterized by extensive olivine crystallization. As olivine is one of the major components of most meteorites and its petrologic behavior is well constrained, it can be roughly considered as representative for the bulk meteorite. Thus, in this work, the evolution of olivine in fusion crusts of the above‐listed selected samples is investigated. The different shape and chemistry of olivine crystallized in the fusion crust, both as overgrown rim on relic olivine clasts and as new crystals, suggest a general temperature and cooling rate gradient. The occurrence of reverse and oscillatory zoning in individual olivine grains within the fusion crust suggests complex redox reactions. Overall, the investigated fusion crusts exhibit a general oxidation of the relatively reduced initial material. However, evidence of local reduction is preserved. Reduction is likely triggered by the presence of carbon in the ureilite or by overheating during the atmospheric entry. Constraining these processes provides a potential analog for interpreting features observed in cosmic spherules and micrometeorites and for calibrating experiments and numerical models on the formation of fusion crusts.

Facet-Dependent Reduction Reaction of Diruthenium Metal-String Complexes by Face-to-Face Linked Gold Nanocrystals.

The facet-dependent redox reactions of diruthenium metal–string complexes by gold nanoparticles (AuNPs) are explored by using the surface-enhanced Raman scattering (SERS) technique. Gold nano-rhombic dodecahedrons (AuRDs), gold nanocubes (AuNCs), and gold octahedrons (AuOhs) with exclusive facets {110}, {100}, and {111}, respectively, were synthesized. These AuNPs linked face-to-face by metal–string complexes Ru2M(dpa)4Cl2 (dpa = dipyridyl amino, M = Ni, Cu) with chloride axial ligands serve as both SERS substrates and reducing agents in the reactions. We employ the diruthenium core in these complexes with multiple redox states to study the reduction ability of varied AuNP facets upon plasmonic excitation. In Ru2Ni(dpa)4Cl2, the Ru–Ru stretching mode νRu–Ru str. lies at 327 cm–1 on the SERS substrate AuOh, but this band shifts to 313 cm–1 on the AuRD and AuNC. The diruthenium moiety was reduced to [Ru2]4+ by the AuRD facet {110} and the AuNC {100}. The gold nanorods in the solution prepared with metal–string complexes bridging head-to-head on {111} facets were used for the SERS substrate. The SERS curves of the complexes in these self-assembled head-to-head rods display νRu–Ru str. at 327 cm–1, which is assigned to having an [Ru2]5+ core. Hence, facets {110} and {100} have a reduction reactivity greater than that of {111}. In Ru2Cu(dpa)4Cl2, the νRu–Ru str. is observed to lie at 312 cm–1 on AuRD, but shifts to 320 cm–1 on the AuNC and AuOh. In the latter cases, the diruthenium moiety was reduced to having a charge of 4+ with electronic configuration π*2δ*2, whereas the former case band at 312 cm–1 with a weaker Ru–Ru bonding is also attributed to [Ru2]4+ but with electron configuration π*4. π*4 lies at an energy greater than π*2δ*2. The electrochemical SERS spectra of diruthenium complexes were recorded to verify their oxidation states. Conclusively, these results yield the reduction reactivity of the following facet: {110} > {100} > {111}. According to the results of the redox reactions, the valence states of the diruthenium metal–string complexes are verified. In the [Ru2]n+ core, n = 4 π*4, 4 π*2δ*2, 5 π*2δ*, and 6 π*δ*, and the νRu–Ru str. is 312, 320, 327, and 337 cm–1, respectively.

An integrated cathode with bi-functional catalytic effect for excellent-performance lithium-sulfur batteries

The high energy density of lithium-sulfur batteries (LSBs) is mainly based on the complex redox reactions and phase conversions. The sluggish redox kinetics and the large accumulation of soluble polysulfides in the electrolyte leads to low sulfur utilization and serious shuttle effect. Herein, an integrated sulfur cathode is constructed through a facile and large-scale method. It is composed of sulfur-N, S doped bamboo like CNTs@Co3S4 (CNTs@Co3S4) composites on polypropylene separator. The immobilized polysulfides on the CNTs@Co3S4 surface are further reduced/oxidized during the discharge/charge process via the efficient bi-functional catalytic effect of CNTs@Co3S4, resulting in the rapid conversion of LiPSs. Consequently, the integrated sulfur cathode delivers a high initial reversible capacity of 1,473.6 mAh·g−1 at 0.2 C and a high specific capacity of 979 mAh·g−1 at 1 C after 500 cycles as well as excellent cycling stability for 1,000 cycles with a high specific capacity of 362.5 mAh·g−1 at 5 C, which are superior to reported similar host materials.

Mapping orbital changes upon electron transfer with tunnelling microscopy on insulators.

Electron transfer plays a crucial part in many chemical reactions1,2, including photosynthesis, combustion and corrosion. But even though redox-state transitions change the electronic structure of the molecules involved, mapping these changes at the single-molecule level is challenging. Scanning tunnelling microscopy provides insights into the orbital structure3 of single molecules and their interactions4,5, but requires the use of a conductive substrate that keeps molecules in a given charge state and thereby suppresses redox-state transitions. Atomic force microscopy can be used on insulating substrates to obtain structural6 and electrostatic7,8 information but does not generally access electronic states. Here we show that when synchronizing voltage pulses that steer electron tunnelling between a conductive atomic force microscope tip and a substrate with the oscillation of the tip, we can perform tunnelling experiments on non-conductive substrates and thereby map the orbital structure of isolated molecules as a function of their redox state. This allows us to resolve previously inaccessible electronic transitions in space and energy and to visualize the effects of electron transfer and polaron formation on individual molecular orbitals. We anticipate that our approach will prove useful for the investigation of complex redox reactions and charging-related phenomena with sub-ångström resolution.

Redox reactions of cationic nitrosyl iron complexes with thiourea and its aliphatic derivatives: The experiment and DFT investigation

Redox reactions of cationic nitrosyl iron complexes with thiourea and its aliphatic derivatives have been studied using cyclic voltammetry technique and DFT investigation. Experimental values of the redox potentials have been determined and compared with results of DFT calculations. Using quantum-chemical modeling, structures of the forming reduced and oxidized forms have been obtained and their electronic structures have been studied. The redox processes in these systems were shown to be complicated and accompanied by the complexes decomposition. It is very important for understanding of their reactivity.

The Ataxia telangiectasia-mutated and Rad3-related protein kinase regulates cellular hydrogen sulfide concentrations

The ataxia telangiectasia-mutated and Rad3-related (ATR) serine/threonine kinase plays a central role in the repair of replication-associated DNA damage, the maintenance of S and G2/M-phase genomic stability, and the promotion of faithful mitotic chromosomal segregation. A number of stimuli activate ATR, including persistent single-stranded DNA at stalled replication folks, R loop formation, hypoxia, ultraviolet light, and oxidative stress, leading to ATR-mediated protein phosphorylation. Recently, hydrogen sulfide (H2S), an endogenous gasotransmitter, has been found to regulate multiple cellular processes through complex redox reactions under similar cell stress environments. Three enzymes synthesize H2S: cystathionine-β-synthase, cystathionine γ-lyase, and 3-mercaptopyruvate sulfurtransferase. Since H2S can under some conditions cause DNA damage, we hypothesized that ATR activity may regulate cellular H2S concentrations and H2S-syntheszing enzymes. Here we show that human colorectal cancer cells carrying biallelic knock-in hypomorphic ATR mutations have lower cellular H2S concentrations than do syngeneic ATR wild-type cells, and all three H2S-synthesizing enzymes show lower protein expression in the ATR hypomorphic mutant cells. Additionally, ATR serine 428 phosphorylation is altered by H2S donor and H2S synthesis enzyme inhibition, while the oxidative-stress induced phosphorylation of the ATR-regulated protein CHK1 on serine 345 is increased by H2S synthesis enzyme inhibition. Lastly, inhibition of H2S production potentiated oxidative stress-induced double-stranded DNA breaks in the ATR hypomorphic mutant compared to ATR wild-type cells. Our findings demonstrate that the ATR kinase regulates and is regulated by H2S.

Comparative Computational and Experimental Detection of Adenosine Using Ultrasensitive Surface-Enhanced Raman Spectroscopy.

To better understand detection and monitoring of the important neurotransmitter adenosine at physiological levels, this study combines quantum chemical density functional modeling and ultrasensitive surface-enhanced Raman spectroscopic (SERS) measurements. Combined simulation results and experimental data for an analyte concentration of about 10−11 molar indicate the presence of all known molecular forms resulting from adenosine’s complex redox-reaction. Detailed analysis presented here, besides assessing potential Raman signatures of these adenosinic forms, also sheds light on the analytic redox process and voltammetric detection. Examples of adenosine Raman fingerprints for different molecular orientations with respect to the SERS substrate are the vibrational line around 920 ± 10 cm−1 for analyte physisorption through the carbinol moiety and around 1600 ± 20 cm−1 for its fully oxidized form. However, both hydroxyl/oxygen sites and NH2/nitrogen sites contribute to molecule’s interaction with the SERS environment. Our results also reveal that contributions of partially oxidized adenosine forms and of the standard form are more likely to be detected with the first recorded voltammetric oxidation peak. The fully oxidized adenosine form contributes mostly to the second peak. Thus, this comparative theoretical–experimental investigation of adenosine’s vibrational signatures provides significant insights for advancing its detection, and for future development of opto-voltammetric biosensors.

“Carbon-Air Secondary Battery” System By Combining Direct Carbon Fuel Cells and CO2 Electrolysis As Large Scale Energy Storage

Introduction The large scale installations of renewable energy are required to prevent global warming problem. Since the cost of solar cells has reduced remarkably, the key issue becomes the management of unstable power generation based on renewable energy, which depends on time, weather conditions and location. Therefore, large scale energy storage becomes more important for stable power supply and for further installations of renewable energy. Secondary batteries such as lithium ion battery are the most popular one but their high cost limits the large scale installations. Novel batteries such as lithium-air battery have been reported, but the critical issues are their large overvoltage and instability during charge/discharge cycles due to their complex redox reactions with dissolution/precipitation. “Power to gas system” is another approach that is producing hydrogen by water electrolysis. By transporting hydrogen, surplus energy can be delivered. But the storage system requires ultra-low temperature (< 20 K) or high pressure (several tens MPa). In the paper, we proposed “Carbon-air secondary battery” system as another approach, and we demonstrated the power generation and charging repeatedly. Furthermore, we evaluated the charge/discharge efficiency. Carbon-air secondary battery system The system is focused on the redox reaction of carbon, C + O2 ⇄ CO2. Because carbon has high specific energy (2500 Wh/kg and 1940 Wh/L based on liquid CO2) and CO2 can be much easier and safer to be stored by liquidation (5.7 MPa at 293 K) than hydrogen, the system is expected as large scale energy storage to solve the problems of hydrogen storage. To construct the system with high efficiency, the electrochemical devise requires high temperature. Direct carbon fuel cells (DCFC) using solid carbon as fuel, such as molten carbonate type, solid oxide type (SOFC), and their hybrid type, have been studied [1]. Because the ratio of Gibbs free energy to enthalpy of the reaction (C + O2 → CO2) is near to 1 and carbon fuel utilization ideally can reach almost 1, DCFC potentially has high efficiency. The way to deliver solid carbons to the three phase boundary (TPB) are critical in development of DCFC. We had proposed rechargeable DCFC (RDCFC) based on SOFC delivering solid carbon to TPB by using hydrocarbon pyrolysis [2-4]. As shown in Fig. 1 (left), three electrochemical reactions (1-3) occur on the fuel electrode. Direct carbon electrochemical oxidation reactions (1, 2) require larger overvoltage than that of the reaction (3), but the produced CO2 induces Boudouard equilibrium reaction (4) that leads the reaction (3) to proceed preferentially, which contributes to the reduction of total overvoltage with high fuel utilization. In this paper, we propose a novel “secondary battery” system with power generation by RDCFC, and charging by CO2 electrolysis and store of both solid carbon and liquid CO2. In the case of CO2 electrolysis (Fig. 1 (right)), the reaction (5) has large overvoltage. But if the reaction (5) proceeds easier, the efficient secondary battery system can be constructed. Experiment al The cells were consisted of Ni / GDC (Gd0.10Ce0.90O2- δ) composite fuel electrode, LSM (La0.8Sr0.2MnO2) air electrode and YSZ (8 mol% Y2O3 – stabilized ZrO2) or ScSZ (10 mol% Sc2O3 and 1 mol% CeO2 –stabilized ZrO2) disk electrolytes. The image of experimental setup is shown in Fig. 2. The fuel electrode side and the air electrode side were filled with Ar and air respectively at 800℃. The initial fuel of solid carbon was deposited on the fuel electrode by supplying propane for 5 minute, and the fuel electrode side was subsequently filled by CO2 and closed. Finally power generation and electrolysis at constant current were carried out repeatedly. Results and discussions We succeeded in stable cycle of power generation at 100 mA/cm2 over 30 times. The coulomb efficiency was ranged from 0.8 to 1 and the maximum charge/discharge efficiency was 0.35. When the current density were varied between 50 mA/cm2 to 175 mA/cm2, the maximum power density and average power density reached to 88 mW/cm2 at 150 mA/cm2 and 47 mW/cm2 at 100 mA/cm2 respectively. The power generation of our proposed “Carbon-air secondary battery” system could be demonstrated. Reference [1] T. M. Gür, Chem. Rev, 113, (2013), 6179-6206 [2] M. Ihara, K. Matsuda, H. Sato and C. Yokoyama, Solid State Ionics, 175, (2004), 51-54 [3] M. Ihara and S. Hasegawa, J. Electrochem. Soc., 153 (8), (2006), A1544-A1546 [4] S. Hasegawa and M. Ihara, J. Electrochem. Soc., 155 (1), (2008), B58-B63 Figure 1

Research on Nitrate Removal by Graphene Loaded With Iron Nanoparticles for Groundwater Remediation

Abstract Nitrate is one of the most frequent pollutants of groundwater, and in some areas, nitrate pollution is becoming a serious problem. Seeking new material and methods for improved efficiency of groundwater nitrate removal is a hot topic of environmental research. While graphene has been widely used in the processing of heavy metal ions in aqueous solution, its role in nitrate removal remains largely unexplored. In this study, we loaded micrometer-sized graphene with nanoscale iron particles (G-Fe) by liquid-phase reduction. The characteristics of nitrate reduction by the G-Fe composites were determined under different conditions using static experiments to reveal the reaction mechanism of G-Fe in removing nitrates. Results showed that the optimal load ratio of graphene with nanoscale iron was 5:1. Lower initial pH improved nitrate removal efficiency (NRE) to varying degrees and 100 % removal was obtained at pH 2.15. Dissolved oxygen (DO) had no effect on NRE. The effect of coexisting anions on NRE descended as follows: PO43−, SO42−, and Cl−. Kinetic studies showed that the reaction order between G-Fe and nitrate was about 0.45, indicating that the reaction involved complex redox reactions and adsorption/desorption processes, other than a simple first-order reaction. This study demonstrates the effectiveness of G-Fe composites in nitrate removal and establishes an advanced technology for groundwater remediation.

In situ determination of potential-driven structural changes in a redox-active plumbagin polymer film on a glassy carbon electrode using PM IRRAS under electrochemical control

Complex redox reactions occurring in the poly(plumbagin) involve reversible reduction and oxidation of the quinone moiety accompanied by parallel oxidation reactions taking place both, in the polymer backbone and in side chains. In acidic medium the methyl side chain undergoes oxidation to a carboxylic acid. In neutral solution the diaryl ether bond is oxidized to unstable hemiacetals, leading to the breakdown of the ether bond and finally to the degradation of the polymer film. Understanding of potential-dependent changes in the composition and structure of redox-active polymers adsorbed on an electrode surface requires a concerted use of spectroscopic and electrochemical techniques. Infrared reflection-absorption spectroscopy techniques are often used in in situ electrochemical experiments, but require surfaces strongly reflecting IR radiation (e.g. gold). Here a glassy carbon electrode (GCE) is used for in situ polarization modulation infrared reflection-absorption spectroscopy (PM IRRAS) experiments with electrochemical control. Due to a weak reflection of the IR light from the GCE surface, the sensitivity of the PM IRRAS decreases compared to metallic surfaces but was sufficient for the analysis of a redox-active polymer film. Electrochemical studies show that the mechanism of the redox reaction of the quinone/hydroquinone couple depends on the used solvent (D2O, H2O) and on the pD (pH) of the electrolyte solution. In H2O a two electron transfer reactions are accompanied by two protonation reactions. The first protonation reaction takes place after the first electron transfer and is the rate-determining step. The dependence of the redox potential on pD shows that the transfer of two electrons is accompanied by one deuteration reaction. Deuterium ions produced during the parallel oxidation reactions of the polymer backbone serve as the substrate for the chemical step of the quinone reduction reaction. In D2O, similarly to H2O, the rate-determining step is a chemical reaction. The rate-determining reaction depends on pD of the electrolyte solution. This work shows clearly that the isotopic substitution, often used in spectroscopic experiments, may have a large impact on the electrochemical behavior of redox-active compounds.

Organic Electrochemistry Goes to Work: Genotoxicity Sensor Arrays

This paper focuses on fundamental concepts derived from the technical evolution of organic electrochemistry that have helped us to develop sensors for the chemistry of genotoxicity, which is essentially the damage of DNA by chemicals and their metabolites. This research is driven by the need to screen for the possibility of genotoxicity of new environmental chemicals and drug candidates, about 30% of which have toxicity issues that do not manifest until clinical trials on humans. A major issue is metabolic chemistry driven mainly by cytochrome (cyt) P450s and other metabolic enzymes. Metabolic chemistry involves catalysis of organic reactions, oxidations in the case of cyt P450s. We found ways to inject electrons into cyt P450s in thin films via their native reductase electron-transfer partners to catalyze metabolic reactions electrochemically via mechanisms that are the same as in our livers. This is organic electrochemistry. For the sensors, we needed a way to detect the resulting metabolite-related DNA damage in sensors combining thin LbL films of metabolic enzymes and DNA in which the metabolites are generated and react with DNA. We found that guanines in DNA chains can react in an electrocatalytic process involving a Ru metallopolymer (RuPVP) and provide a strong visible light output via electrochemiluminescence (ECL). This electrocatalytic process oxidizes RuII in the polymer to RuIII to oxidize guanine moieties in the DNA, and a complex redox reaction sequence produces the light. The catalytic oxidation current can also be measured. Organic electro-oxidations are responsible for these outputs. Similar approaches can be used to design sensor arrays that monitor DNA oxidation. Electrocatalytic Cyt P450 oxidations and ECL generation are combined in our most sophisticated genotoxicity sensor arrays. When DNA is damaged, its double-stranded structure is disrupted and RuIII sites in the film gain better access to guanine moieties to produce more ECL light, or more catalytic current. Examples, including the genotoxic potential of e-cigarettes, will be discussed.

Lithium - Redox Battery Using a Solvate Ionic Liquid

Redox flow batteries have been expected as the large scale storage battery. Redox flow batteries utilize the oxidation and reduction of two soluble redox couples for charging and discharging without the solid phase reaction. Therefore, the cycle lives of the redox flow batteries are expected to be much longer than those of rechargeable lithium batteries using insertion-type active materials. Currently, vanadium redox flow batteries have been put into practical use to stabilize the supply of renewable energy. Vanadium redox flow batteries have low energy density compared to other batteries. Since aqueous solution is used for the electrolyte, the electrochemical window of the water limits the cell voltage. Although there has been various studies using an organic electrolyte in order to enlarge the cell voltage, the flammability and volatility of the organic solvents can be disadvantageous from the point of view of safety. 1) Recently, aprotic ionic liquids have attracted attention as nonaqueous electrolytes. Especially, aprotic ionic liquids containing bis(trifluoromethylsulfonyl)amide (TFSA-) have been studied extensively in the electrochemical field because they show favorable features such as incombustibility, involatility and wide electrochemical potential window. We have already reported the redox reactions of various metal complexes in the ionic liquids and their applicability to redox flow batteries. 2) However, there are a few reports regarding the redox battery using the ionic liquids probably due to lack of the suitable ion exchange membrane that can move the career ion in the ionic liquids. In the present study, a new redox battery, namely “lithium-redox battery”, was proposed using a redox reaction of an iron complex for a cathode reaction, dissolution and deposition of lithium for an anode reaction, and LiTFSA – tetraglyme (G4) solvate ionic liquid for an electrolyte. In addition, lithium ion conductive solid electrolyte (LICGCTM) was used as the diaphragm, which prevents penetration of the redox species and enables transfer of lithium ions. Tris(2,2'-bipyridine)iron(II) complex ([Fe(bpy)2]2+) was found to be soluble and stable in the solvate ionic liquid. The redox reaction between [Fe(bpy)3]2+ and [Fe(bpy)3]3+ was confirmed to be reversible by cyclic voltammetry. The formal potential of [Fe(bpy)3]3+/2+ was 4.1 V vs. Li|Li(I). Reversible charge-discharge cycling of the lithium redox battery having an average cell voltage of 3.9 V was possible for 30 cycles with a coulombic efficiency of more than 95%. References 1) Y. Matsuda, K. Tanaka, M. Okada, Y. Takasu, and M. Morita, J. Appl. Electrochem., 18, 909 (1988). 2) Y. Katayama, M. Yoshihara, and T. Miura, J. Electrochem. Soc., 162, H501 (2015).

Redox reactions of binuclear tetranitrosyl iron complexes with bridging N-C-S ligands

Reduction of neutral binuclear tetranitrosyl iron complexes of “μ-N-C-S” structural type of [Fe2(SR)2(NO)4] composition with R being functional azaheterocyclic thiolyls has been studied by cyclic voltammetry in aprotic solvents in a wide range of potential scan rates. Redox potentials of these reactions have been determined. The consecutive transfer of two electrons was shown to be typical for all the complexes. For some complexes the products of the first electron addition are unstable, while for the others the products of reduction by both the first and the second electrons are stable. The calculations of geometric and electronic structures of monoanions, dianions and intermediates forming upon the reduction of the complexes were performed by DFT methods. Using quantum-chemical modeling, electrochemical reduction of the complexes has been studied; their energy and theoretical redox potentials have been calculated.

Recovery of Palladium(II) from nitric acid medium using a natural resin prepared from persimmon dropped fruits residues

A natural resin, named “PPF resin”, was prepared by cross-linking persimmon tannin with formaldehyde and employed as adsorbents for selective recovery of Pd(II) from nitric acid medium. Parameters such as acidic media, HNO3 concentration, contact time, initial metal concentration and temperature were investigated in detail. The adsorption behavior followed the typical monolayer type of Langmuir model and the maximum adsorption capacity reached 259.7mgg−1 at 323K. The obtained thermodynamic parameters (ΔG, ΔH and ΔS) revealed that this adsorption process was feasible, spontaneous and endothermic process. After adequately characterizing the samples by FT-IR, XRD, XPS and SEM-EDS, the adsorption mechanism was proposed to be complex formation and redox reaction. The Pd(II) recovery from industrial nitric acid extract of printed circuit boards was effective and highly selective, and the loaded Pd(II) can be easily desorbed using acidic thiourea solutions. Therefore, the present results provide a new, low cost and effective approach for palladium recovery from e-wastes in nitric acid medium.

Ullmann‐Type and Related Redox Reactions of Nitrosyl Molybdenum Complexes Bearing a Large‐Bite‐Angle Diphosphine

AbstractThe reactions of ArX (X = Cl and Br) with [Mo(NO)(P∩P)(NCMe)3][BArF4] P∩P = 2,2′‐bis(diphenylphosphanyl)diphenyl ether (DPEphos), BArF4 = tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate at 120 °C resulted in the formation of biphenyl (through CAr–CAr reductive homocoupling) and the dinuclear halide salts [Mo2(NO)2(P∩P)2(NCMe)2(μ‐X)2][BArF4]2 (X = Cl, 1; Br, 2). Complexes 1 and 2 potentially show cisoid (1c and 2c) and transoid (1t and 2t) regioisomerism with respect to the position of the NO ligand. The crystal‐structure determinations of 1 and 2 revealed the presence of the transoid isomers 1t and 2t and MI–MI bonding in both cases. A proposed mechanism for the formation of 1t and 2t involves reductive CAr–CAr coupling to form biphenyl from two Ph–MoII centers. In addition, the complexes Mo(NO)(P∩P)(CO)2Cl (3) and [Mo(NO)(mer‐κ3‐P,P,O‐DPEphos)Cl(PR3)] (R = Me, 4; Ph, 5) were obtained through the reductions of [Mo2(NO)2(P∩P)2Cl4(μ‐Cl)2].