Transfer Redox Research Articles

Laser heated boron doped diamond electrodes: effect of temperature on outer sphere electron transfer processes.

Thermoelectrochemical experiments can reveal significant information about electrochemical processes compared to ambient only measurements. Typical thermoelectrochemistry is performed using resistively heated wires or laser heated electrodes, both of which can suffer drawbacks associated with the electrode material employed. Boron doped diamond (BDD) is ideal for thermoelectrochemical investigations due to its extremely high thermal conductivity and diffusivity, extreme resistance to thermal ablation (can withstand laser power densities, Pd, of GW cm(-2) for nanosecond pulses) and excellent electrochemical properties (low background currents and wide potential window). In this paper we describe the use of a pulsed laser technique to heat the rear of a 1 mm diameter conducting BDD disc electrode, which drives electrochemical solution reactions at the front face. Maximum electrode temperatures of 90.0 °C were recorded experimentally and confirmed by finite element modelling (FEM). The effect of laser pulsed heating (maximum 3.8 kW cm(-2); 10 ms on and 90 ms off) on the cyclic voltammetric response of two fast (reversible) outer sphere electron transfer redox mediators (Ru(NH3)6(3+/2+) and IrCl6(2-/3-)) are investigated. In particular, we observe pulsed increases in the current, which increase with increasing Pd. The potential of the peak current is shifted positively for the Ru(NH3)6(3+/2+) couple (in accordance with a positive temperature coefficient, β, +0.68 mV K(-1)) and negatively for the IrCl6(3-/2-) couple (β = -0.48 mV K(-1)). Scanning backwards, in contrast to that observed for a macrodisc electrode in ambient solution, a cathodic peak is again observed for Ru(NH3)6(3+/2+) and an anodic peak for IrCl6(3-/2-) couple. We attribute this response to the entropy of the redox reaction and the time-dependant change in mass transport due to the induced thermal gradients at the electrode/electrolyte interface. The observed responses are in qualitative agreement with FEM simulations.

Effective Blockage of the Interfacial Recombination Process at TiO2 Nanowire Array Electrodes in Dye-Sensitized Solar Cells

Effective blockage of recombination electron transfer of a fast electron transfer redox couple (ferrocenium/ferrocene or Fc(+)/Fc) at TiO2 nanowire array electrodes is achieved by silanization of the dye loaded TiO2 nanowire array. FT-IR clearly shows the formation of polysiloxane network at fluorine doped tin electrodes covered with TiO2 nanowire arrays and the dye molecules. Compared to the commonly used TiO2 nanoparticle film electrodes, the TiO2 nanowire array has a more spatially accessible structure, facilitating the formation of uniform polysiloxane films. Energy-dispersive X-ray spectroscopy (EDS) also reveals the presence of Si over multiple spots at the cross sections of the silanized TiO2 nanowire array electrodes. As a result, a rather high open-cell voltage Voc (0.69 V) and an enhanced efficiency (0.749 %) for DSSC with the Fc(+)/Fc couple were obtained. Contrary to the passivated TiO2 nanoparticle film electrodes at which a complex, biphasic dependence of electron lifetime on Voc was observed, we recorded a logarithm linear dependence of the lifetime on Voc after the silanization treatment. The nanowire arrays with optimal salinization treatments afford a useful surface for the study of electron recombination and photovoltaic generation in DSSCs.

Ion‐Transfer Voltammetry at Carbon Nanofibre Membranes Produced by 500 °C Graphitisation/Graphenisation of Electrospun Poly‐Acrylonitrile

AbstractLow temperature carbonisation (500 °C) of poly‐acrylonitrile nanofibres (typically 100 nm diameter) electrospun into a nanoweb‐like deposit on tin‐doped indium oxide (ITO) substrates (or as free‐standing membrane over glass capillaries) yields active carbon film electrodes but with only relatively low electrochemical activity. Without resorting to higher carbonisation temperatures, substantial improvements in both electrical conductivity and electron transfer reactivity are observed after “surface‐graphenisation”, that is coating with graphene‐oxide prior to vacuum carbonisation. Improvements in voltammetric characteristics are demonstrated for both membranes mounted on ITO substrates and free‐standing membranes suspended over the end of a borosilicate glass capillaries for (i) the aqueous phase hydroquinone/benzoquinone redox system and (ii) the biphasic oil|aqueous ion transfer redox system tetraphenylporphyrinato‐Mn(III/II) in 4‐phenyl‐(3‐propyl)‐pyridine).

On the behavior of the carboxyphenylterpyridine(8-quinolinolate) thiocyanatoruthenium(II) complex as a new black dye in TiO2 solar cells modified with carboxymethyl-beta-cyclodextrin

Abstract A terpyridine ligand encompassing a terminal 4-carboxyphenyl group (cptpy), was employed in a new Ru(II) black dye, in the presence of 8-quinolinolate (Q) and SCN − as ancillary ligands. Such compound, here referred as [Ru(cptpy) (Q) (NCS)], was designed aiming its inclusion into carboxymethyl-beta-cyclodextrin, anchored on TiO 2 . This host–guest strategy was employed to prevent the formation of aggregates and protect the photoinjecting moiety against parallel deactivation events. Such expectation has indeed been fulfilled by the system. On the other hand, 8-quinolinolate as a strong electron donor ligand, effectively enhanced the light harvesting behavior of the dye, shifting and spreading the IPCE peaks over the entire visible region. Unfortunately, the red shift of visible charge-transfer bands was compensated by a decrease of the Ru(III)/(II) potentials, slowing down the electron transfer kinetics with the I 3 /I − redox mediator. Therefore, the observed counterbalance between charge transfer energies and redox potentials imposes a critical limit in the design of better mononuclear ruthenium-polypyridine dyes.

High-Frequency Electron Nuclear Double-Resonance Spectroscopy Studies of the Mechanism of Proton-Coupled Electron Transfer at the Tyrosine-D Residue of Photosystem II

The solar water-splitting protein complex, photosystem II, catalyzes one of the most energetically demanding reactions in Nature by using light energy to drive the catalytic oxidation of water. Photosystem II contains two symmetrically placed tyrosine residues, YD and YZ, one on each subunit of the heterodimeric core. The YZ residue is kinetically competent and is proposed to be directly involved in the proton-coupled electron transfer reactions of water oxidation. In contrast, the YD proton-coupled electron transfer redox poises the catalytic tetranuclear manganese cluster and may electrostatically tune the adjacent monomeric redox-active chlorophyll and β-carotene in the secondary electron transfer pathway of photosystem II. In this study, we apply pulsed high-frequency electron paramagnetic resonance (EPR) and electron nuclear double-resonance (ENDOR) spectroscopy to study the photochemical proton-coupled electron transfer (PCET) intermediates of YD. We detect the "unrelaxed" and "relaxed" photoinduced PCET intermediates of YD using high-frequency EPR spectroscopy and observe an increase of the g anisotropy upon temperature-induced relaxation of the unrelaxed intermediate to the relaxed state as previously observed by Faller et al. [(2002) Biochemistry 41, 12914-12920; (2003) Proc. Natl. Acad. Sci. U.S.A. 100, 8732-8735]. This observation suggests the presence of structural differences between the two intermediates. We probe the possible structural differences by performing high-frequency (2)H ENDOR spectroscopy experiments. On the basis of numerical simulations of the experimental (2)H ENDOR spectra, we confirm that (i) there is a significant change in the H-bond length of the tyrosyl radical in the unrelaxed (1.49 Å) and relaxed (1.75 Å) PCET intermediates. This observation suggests that the D2-His189 residue is deprotonated prior to electron transfer at the YD residue and (ii) there are negligible changes in the conformation of the tyrosyl ring in the unrelaxed and relaxed PCET intermediates of YD.

A low-potential glucose biofuel cell anode based on a toluidine blue modified redox polymer and the flavodehydrogenase domain of cellobiose dehydrogenase

A pH-dependent, two-electron transfer redox polymer was synthesized based on a methacrylate backbone with tunable properties covalently modified with toluidine blue (P017-TB). Entrapment of the isolated flavodehydrogenase domain of cellobiose dehydrogenase from Myriococcum thermophilum (FAD-MtCDH) within P017-TB is the basis for low-potential bioanode with an open circuit potential of −240mV vs. Ag/AgCl and a maximum current density of 60μAcm−2 at −150mV. Together with a bilirubin oxidase biocathode a biofuel cell with an open circuit voltage of 720mV and a power density of 6.1μWcm−2 was obtained.

Visible Light Mediated Activation and O-Glycosylation of Thioglycosides

Visible light catalysis allows the efficient construction of single electron transfer (SET) redox cycles that result in minimal formation of byproducts and proceed under exogenous control of a removable light source. The O-glycosylation of thioglycosides via visible light photoredox chemistry is reported. Mechanistic studies show that the reaction is fully light responsive and support a mechanism involving decomposition of an oxidatively generated sulfur radical cation and propagation via reduction of the thiol side product.

Anthraquinone derivatives as electron-acceptors with liquid crystalline properties

Dialkoxy derivatives of anthraquinone (AQ), dicyano-anthraquinone (DCAQ) and tetracyanoanthraquinone (TCAQ) were synthesized and their associated electrochemical, optical and self-assembling properties were investigated as candidates for n-type materials. AQ shows UV absorption features, whereas both DCAQ and TCAQ exhibit bathochromic and hyperchromic electronic transitions into the visible region. The electron accepting strength of the three compounds was established by cyclic voltammetry as -1.52 V, -1.3 V and -0.9 V vs. ferrocene/ferricenium for AQ, DCAQ and TCAQ, respectively. All three quinones displayed quasireversible, two sequential one-electron transfer redox reactions. DFT calculations of DCAQ and TCAQ demonstrate structural changes upon reduction, which is supported by spectroelectrochemical experiments. Furthermore, the structural changes result in different absorption profiles and show potential as electrochromic materials. Finally, both AQ and DCAQ show liquid crystalline phases and importantly, DCAQ exhibits both a smectic liquid crystalline and a soft crystal phase between -6 °C and 85 °C, which offers promise as a self-assembling n-type material.

Screening of bacterial cytochrome P450s responsible for regiospecific hydroxylation of (iso)flavonoids

Screening of cytochrome P450 monoxygenases responsible for the regiospecific hydroxylation of flavones, isoflavones and chalcones was attempted using a P450 library constructed from Streptomyces avermitilis MA4680, Bacillus and Nocardia farcinica IFM10152 strains. As electron transfer redox partners with the P450s in Escherichia coli system, putidaredoxin reductase (PdR) and putidaredoxin (Pdx) from Pseudomonas putida were used. Among the 50 soluble P450s in the library screened, three cytochrome P450s, i.e. CYP107Y1, CYP125A2 and CYP107P2 from S. avermitilis MA4680 showed good hydroxylation activities towards flavones and isoflavones. However, low product yields prevented us from identifying complete structure of the products. By using S. avermitilis MA4680 as their expression host, further analysis identified that CYP107Y1(SAV2377), CYP125A2(SAV5841) and CYP107P2(SAV4539) showed good regiospecific hydroxylation activities towards genistein (4′,5,7-trihydroxyisoflavone), chrysin (5,7-dihydroxyisoflavone) and apigenin (4′,5,7-dihydroxyisoflavone) to produce 3′,4′,5,7,-tetrahydroxyisoflavone, B-ring hydroxylated 5,7-dihydroxyflavone and 3′,4′,5,7,-tetrahydroxyflavone, respectively. Analyses of the reaction products were performed using HPLC, ESI-MS–MS and GC–MS and 1H NMR.

Spectroscopic Characterization and Quantitative Estimation of Ropinirole Hydrochloride Through Charge Transfer Complex Formation and Redox Reaction

Two spectrophotometric methods for the estimation of ropinirole hydrochloride (RP) in bulk drug and in its tablet formulations are described. Method A based on charge transfer (CT) interactions between RP as amino heterocyclic donor and chloranilic acid (CLA) as π-acceptor showing absorption maximum at 528 nm. Factors controlling the CT-reactions were studied, optimized and composition of the formed CT-complexes was identified. Job’s method of continuous variation was used to detect the stoichiometric ratios of the formed complexes and they showed that 1:1 complexes were produced between RP and CLA. Also the solid CT-complexes were characterized by FTIR spectroscopy where the formed complexes included proton and electron transfer. The method B is based on the formation of blue colored chromogen due to the reaction of RP with Folin Ciocalteu (FC) reagent in presence of alkali which exhibits an absorption maximum at 633 nm. Beer’s law range is 1–100 μg /ml and 5–40 μg /ml for methodA and method B respectively. Under the optimum conditions, linear relationships with good correlation coefficients were identified with high accuracy and precision. The proposed methods were successfully applied to the determination of RP in formulations.

Electrochemical Behaviors of Hexathiadipentalene Ring, Dithiol Ring, and Methyl Sulfide Groups on Anthracene Derivatives Confined on Electrode

Hexathiadipentalenoanthracene (hexathioanthracene) and related-structure compounds which are based on anthracene (ANT) containing redox-active organosulfur unit were synthesized, and their redox-activities of trithiapentalene ring, dithiol ring, and its methyl sulfide function groups linked on the ANT molecule were examined with the cyclic voltammetric method using their coated electrodes. The electrochemical oxidation processes for their neutral compounds (hexathiadipentalenoanthracene, 1,4,5,8-tetra(methylthio)anthracene and anthra-bis-[1,2]dithiole) are electrochemically reversible and exhibit stepwise two one-electron transfer redox responses in an ethylene carbonate (EC): diethylcarbonate (DEC) (1:3 volume ratio) solution containing in the potential range from (versus ).

Synthesis and characterization of heterooligonuclear ruthenium complexes with tri(phenanthrolino)hexaazatriphenylene ligands

A homologous series of homo- and heterooligonuclear ruthenium/palladium complexes of 9,10,19,20,29,30-hexaazahexapyrido[3,2-a:2′,3′-c:3′′,2′′-k:2′′′,3′′′-m:-3′′′′,2′′′′-u:2′′′′′,3′′′′′-w]-trinaphthylene (PHAT) with the formula [{Ru(tbbpy)2} n (μ-phat)]2n+ (n = 1, 2, 3) and [{Ru(tbbpy)2} m (μ-phat){PdCl2}3- m ]2m+ (m = 1, 2) was prepared and characterized, where TBBPY = 4,4′-di-tert-butyl-2,2′-bipyridine. Toward this aim, a new synthetic route was developed for which a microwave-assisted successive complexation reaction of the multitopic ligand was used. In accordance to the only known complex of this kind, [{Ru(phen)2}3(μ-phat)]6+, only the outer 1,10-phenanthroline (PHEN) like coordination spheres of the ligand could be substituted with octahedral ruthenium and square planar palladium fragments. This allows the construction of new supramolecular structures with at least three metal centers that are potentially capable of intramolecular multielectron transfer and photocatalytic redox activity. Electrochemical investigations show that the metal centers in the homonuclear ruthenium complex do not interact and that the ligand-based redox steps are reversible. Preliminary investigations also show that PHAT may be photochemically reduced as seen by UV-Vis spectroscopy; however, no catalytic activity for photochemical hydrogen production could be observed.

Free radical facilitated damage of ungual keratin

Thioglycolic acid (TA) and urea hydrogen peroxide (urea H 2O 2) are thought to disrupt α-keratin disulfide links in the nail. However, optimal clinical use of these agents to improve the treatment of nail disorders is currently hindered by a lack of fundamental data to support their mechanism of action. The aim of this study was to investigate how the redox environment of ungual keratin, when manipulated by TA and urea H 2O 2, influenced the properties of the nail barrier. Potentiometric and voltammetric measurements demonstrated that urea H 2O 2 obeyed the Nernst equation for a proton coupled one-electron transfer redox process while TA underwent a series of redox reactions that was complicated by electrode adsorption and dimer formation. The functional studies demonstrated that nail permeability, measured through TBF penetration (38.51 ± 10.94 μg/cm 2/h) and nail swelling (244.10 ± 14.99% weight increase), was greatest when relatively low concentrations of the thiolate ion were present in the applied solution. Limiting the thiolate ion to low levels in the solution retards thiolate dimerisation and generates thiyl free radicals. It appeared that this free radical generation was fundamental in facilitating the redox-mediated keratin disruption of the ungual membrane.

ChemInform Abstract: Organometallic Electron Reservoir Sandwich Iron Complexes as Potential Agents for Redox and Electron Transfer Chain Catalysis

Abstract Among the various properties of transition metal organometallic compounds is the ease with which they can withstand redox changes. This property led to the concept of ‘organometallic electron-reservoir’. These organometallic electron-reservoirs are used to perform different types of catalytic reactions. The first mentioned is electron transfer chain (ETC) catalysis also called electrocatalysis, which uses them as initiators in reactions that implicate the electron itself as the real and effective catalyst. Examples will illustrate this principle in organometallic chemistry using Fe sandwich complexes: (i) ligand substitution in [Fe(II)Cp(arene)] + PF 6 − by two-electron donors; (ii) intramolecular disproportionation of dinuclear fulvalene carbonyl complexes and selective discrimination of metal centers; (iii) design of a system in which both ETC and organometallic catalyses are coupled (the first known example concerns the polymerization of terminal alkynes by a W 0 complex); (iv) intramolecular dithiocarbamate ligand chelation in Fe(II) piano stool complexes which can be initiated either by reduction or by oxidation, both chain pathways being explained. A second application of these organometallic complexes in catalysis takes place in redox catalysis: when they are used in catalytic amount they act as electron carriers lowering the overpotential existing between an electrode and a substrate. Two cases were examined: (i) redox catalysis of the reduction of water and (ii) redox catalysis of the reduction of nitrogen derivatives: nitrates and nitrites.

Spinning into control

Spin transitions are the most common mechanism for switching molecules between two distinct energy states, for uses as diverse as memory devices and displays. How the transition is triggered is crucial, and a pentanuclear cluster has now been reported in which the spin transition is promoted by redox transfer between different metal ions.

CYP2C9-CYP3A4 Protein-Protein Interactions: Role of the Hydrophobic N Terminus

Cytochromes P450 (P450s) interact with redox transfer proteins, including P450 reductase (CPR) and cytochrome b(5) (b5), all being membrane-bound. In multiple in vitro systems, P450-P450 interactions also have been observed, resulting in alterations in enzymatic activity. The current work investigated the effects and mechanisms of interaction between CYP2C9 and CYP3A4 in a reconstituted system. CYP2C9-mediated metabolism of S-naproxen and S-flurbiprofen was inhibited up to 80% by coincubation with CYP3A4, although K(m) values were unchanged. Increasing CYP3A4 concentrations increased the degree of inhibition, whereas increasing CPR concentrations resulted in less inhibition. Addition of b5 only marginally affected the magnitude of inhibition. In contrast, CYP2C9 did not alter the CYP3A4-mediated metabolism of testosterone. The potential role of the hydrophobic N terminus on these interactions was assessed by incubating truncated CYP2C9 with full-length CYP3A4, and vice versa. In both cases, the inhibition was fully abolished, indicating an important role for hydrophobic forces in CYP2C9-CYP3A4 interactions. Finally, a CYP2C9/CYP3A4 heteromer complex was isolated by coimmunoprecipitation techniques, confirming the physical interaction of the proteins. These results show that the N-terminal membrane binding domains of CYP2C9 and CYP3A4 are involved in heteromer complex formation and that at least one consequence is a reduction in CYP2C9 activity.

Bi- and tetranuclear ligational deeds of a polyaza macrocycle having four diazine (N2) bridging components headed for CoII, NiII, CuII and ZnII ions: An emphasis on electrochemistry of non-innocent ligand system

Novel bi- and tetranuclear CoII, NiII, CuII and ZnII complexes having diazine bridging units have been prepared and characterised on the basis of analytical and spectroscopic techniques. With the help of electronic spectra and magnetic moment measurements, it is predicted that the CoII and NiII complexes have octahedral geometry while CuII and ZnII complexes found to be square pyramidal. Present ZnII and CuII complexes are binuclear in nature, where as CoII and NiII complexes are tetranuclear with feeble antiferromagnetic exchange interactions. UV–visible spectral studies, in the range 275–425 nm, evidence the significant blue shift in π → π* transition which provide the ease of stabilization of bonding molecular orbitals in the complexes. All complexes are monomeric in nature. Ligand and all complexes were found to be electrochemically active compounds. One electron transfer process is observed in ligand similarly, there is no significant change in the cyclic voltammograms of CoII and ZnII complexes, while CuII and NiII complexes show one and two electron transfer redox behaviours, respectively in the present macrocyclic ligand field.

Electrocatalytic Drug Metabolism by CYP2C9 Bonded to A Self-Assembled Monolayer-Modified Electrode

Cytochrome P450 (P450) enzymes typically require the presence of at least cytochrome P450 reductase (CPR) and NADPH to carry out the metabolism of xenobiotics. To address whether the need for redox transfer proteins and the NADPH cofactor protein could be obviated, CYP2C9 was bonded to a gold electrode through an 11-mercaptoundecanoic acid and octanethiol self-assembled monolayer (SAM) through which a current could be applied. Cyclic voltammetry demonstrated direct electrochemistry of the CYP2C9 enzyme bonded to the electrode and fast electron transfer between the heme iron and the gold electrode. To determine whether this system could metabolize warfarin analogous to microsomal or expressed enzyme systems containing CYP2C9, warfarin was incubated with the CYP2C9-SAM-gold electrode and a controlled potential was applied. The expected 7-hydroxywarfarin metabolite was observed, analogous to expressed CYP2C9 systems, wherein this is the predominant metabolite. Current-concentration data generated with increasing concentrations of warfarin were used to determine the Michaelis-Menten constant (K(m)) for the hydroxylation of warfarin (3 microM), which is in good agreement with previous literature regarding K(m) values for this reaction. In summary, the CYP2C9-SAM-gold electrode system was able to carry out the metabolism of warfarin only after application of an electrical potential, but in the absence of either CPR or NADPH. Furthermore, this system may provide a unique platform for both studying P450 enzyme electrochemistry and as a bioreactor to produce metabolites without the need for expensive redox transfer proteins and cofactors.

Comparative Study of Metal‐Catalyzed Iminations of Sulfoxides and Sulfides

A comparative study of the imination of sulfur compounds with various metal catalysts in combination with isolated or in situ generated iminoiodinanes (PhI==NR) as nitrogen sources is presented. The influence of the metal catalyst towards the imination of a variety of substituted sulfoxides has been evaluated. Moreover, the effect of the different oxidation states of sulfur on the reactivity and selectivity of the nitrogen transfer redox process in the formation of sulfilimines and sulfoximines was studied. Depending on both the specific metal catalyst as well as the employed nitrene precursor, the sulfide/sulfoxide imination ratio varied in transformations of thianthrene-5-oxide and substituted para-thio phenylsulfoxides.

Exploring Mitochondria in the Intact Ischemic Heart

In describing human nature, the Irish author and satirist Jonathan Swift noted that “vision is the art of seeing what is invisible to others.” In the biological sciences, “vision” is transformed into a “science” as progress in imaging technology enables the uncovering of previously “invisible” intracellular programs. This capacity to “see inside cells” is improving in lock-step with advancing technologies that enable fluorophore-labeling of genes, proteins, cells, substrates, and metabolites. Thus, biomedical imaging is expanding our understanding of cellular function and disease pathophysiology. In this issue of Circulation , the practical application of 2-photon scanning laser microscopy is used to directly assess the mitochondrial inner membrane potential in the intact rat heart in response to cardiac ischemia and reperfusion.1 Article p 1497 Before discussing this study, I will digress for a moment to review the relevance of mitochondrial function and the proposed role of the inner mitochondrial membrane potential on cardiac function and in its response to ischemia and reperfusion. The mitochondrion is central to cardiac function, as it modulates cardiac energetics, reactive radical biology, calcium homeostasis, and apoptosis.2 The inner mitochondrial membrane potential in turn reflects a composite of mitochondrial functioning, which means the maintenance of this electrochemical potential requires: (1) the functional integrity of electron transfer redox centers of oxidative phosphorylation; (2) the catalytic integrity of enzymes of β-oxidation and the Kreb’s cycle; and (3) the appropriate functioning of transport mechanisms linking the cytosol and the mitochondrial matrix. The mitochondrial inner membrane potential is not static; rather, the modulation of this electrochemical gradient directly controls mitochondrial adenosine triphosphate generation, Ca2+ flux, and the production and control of reactive oxygen species (ROS).3 Interestingly, modest modulation of the mitochondrial membrane potential appears to confer cellular adaptations that enhance …