Electron Transfer

Multiple acyl-CoA dehydrogenase deficiency CoQ 10 deficiency Riboflavin Electron transfer flavoprotein ubiquinone oxidoreductase a b s t r a c t Multiple acyl-CoA dehydrogenase deficiency (MADD) is a metabolic disorder due to dysfunction of electron transfer flavoprotein (ETF) or ETF-ubiquinone oxidoreductase (ETF-QO). Mutations in ETFDH, encoding ETF-QO have been associated with both riboflavin-responsive and non-responsive MADD as well as a myopathic form of CoQ 10 deficiency, although pathomechanisms responsible for these different phenotypes are not well-defined. We performed mutation analysis in four Taiwanese MADD patients. Three novel ETFDH mutations were identified in four patients and all harbored the p.A84T mutation. Muscle CoQ 10 levels and respiratory chain activities measured in two patients were normal. Three patients improved on riboflavin together with carnitine. Our results show that not all MADD patients have CoQ 10 deficiency. Based upon our data, riboflavin and carnitine may be the first-line treatment for MADD.

A comparative study of direct and mediated electrochemistry of metalloproteins in bulk and membraneentrapped solutions is presented. This work reports the first electrochemical study of the electron transfer between a bacterial cytochrome c peroxidase and horse heart cytochrome c. The mediated catalysis of the peroxidase was analysed both using the membrane electrode configuration and with all proteins in solution. An apparent Michaelis constant of 66 ± 4 and 42 ± 5 lM was determined at pH 7.0 and 0 M NaCl for membrane and bulk solutions, respectively. The data revealed that maximum activity occurs at 50 mM NaCl, pH 7.0, with intermolecular rate constants of (4.4 ± 0.5) 9 10 6 and (1.0 ± 0.5) 9 10 6 M -1 s -1 for membrane-entrapped and bulk solutions, respectively. The influence of parameters such as pH or ionic strength on the mediated catalytic activity was analysed using this approach, drawing attention to the fact that careful analysis of the results is needed to ensure that no artefacts are introduced by the use of the membrane configuration and/or promoters, and therefore the dependence truly reflects the influence of these parameters on the (mediated) catalysis. From the pH dependence, a pK of 7.5 was estimated for the mediated enzymatic catalysis. Membrane electrode Á Mediated catalysis Á Bacterial cytochrome c peroxidase Á Horse cytochrome c Abbreviations AUME Gold membrane electrode BCCP Bacterial cytochrome c peroxidase ME Membrane electrode

Photobinding of drugs to biomolecules constitutes an important early event in the onset of photoallergy. In the present work, UV irradiation of human serum albumin in the presence of either suprofen (SUP) or its major photoproduct, decarboxylated suprofen (DSUP), has been studied as a model system for drug-photosensitised protein binding. Both dark binding and binding in the presence of light were investigated since this will affect the mode, site and mechanism of drug interaction with the protein. In order to determine the binding features of SUP to albumin, competitive binding experiments were carried out using fluorescent probes specific for site I and II. Suprofen was found to selectively dark bind to site II on HSA. Photobinding of DSUP to HSA was more efficient than SUP. Parallel to this, the intrinsic tryptophan fluorescence of HSA decreased when the protein was previously irradiated in the presence of the photoactive compounds, again being DSUP more efficient compared with SUP. As fluorescence quenching involves electron transfer from the excited Trp to the ground state DSUP, it follows that the photoactive compound binding to HSA must be on (or in close proximity to) site I Trp 214 residue. It appears that photobinding of SUP is largely preceded by its photodecomposition to DSUP which, in turn, associates and photobinds to HSA.

The cofactor composition and electron-transfer kinetics of the reaction center (RC) from a magnesium chelatase (bchD) mutant of Rhodobacter sphaeroides were characterized. In this RC, the special pair (P) and accessory (B) bacteriochlorophyll (BChl)-binding sites contain Zn-BChl rather than BChl a. Spectroscopic measurements reveal that Zn-BChl also occupies the H sites that are normally occupied by bacteriopheophytin in wild type, and at least 1 of these Zn-BChl molecules is involved in electron transfer in intact Zn-RCs with an efficiency of >95% of the wild-type RC. The absorption spectrum of this Zn-containing RC in the near-infrared region associated with P and B is shifted from 865 to 855 nm and from 802 to 794 nm respectively, compared with wild type. The bands of P and B in the visible region are centered at 600 nm, similar to those of wild type, whereas the H-cofactors have a band at 560 nm, which is a spectral signature of monomeric Zn-BChl in organic solvent. The Zn-BChl H-cofactor spectral differences compared with the P and B positions in the visible region are proposed to be due to a difference in the 5th ligand coordinating the Zn. We suggest that this coordination is a key feature of protein-cofactor interactions, which significantly contributes to the redox midpoint potential of H and the formation of the charge-separated state, and provides a unifying explanation for the properties of the primary acceptor in photosystems I (PS1) and II (PS2). magnesium chelatase mutant ͉ photosynthetic bacterial reaction center ͉ photosystems I and II ͉ protein-cofactor interaction

When redox active molecules are covalently tethered to the surface of the n-doped silicon, light induces their oxidation by the semiconductor. To visualize this charge separation we have followed the formation and decay of the surface photovoltage by an auxiliary transparent electrode, which serves as a capacitive probe that picks up the transient surface photovoltage. This method has been used in electronics and biophysics but is novel for the surface redox chemistry. The probe provides both the direction of the charge transfer and the resolution of the dynamics. Its application is independent of the optical properties of the semiconductor. Laser initiation of the reaction permits quantitative measurements of the reactions with the rate constants ~108-103 s-1. The electron injection from covalently tethered NTCI(A) molecules into silicon was fast (k >109 s-1). The back electron transfer is poly-disperse with the components ranging from ~10 microseconds and up.

nature materials | VOL 3 | OCTOBER 2004 | www.nature.com/naturematerials I n the last decade we have witnessed a fast growth in the research, development and marketing of biosensors, although no clear decisions have been made in favour of specific materials 1 . An ideal biosensor should combine nature's sensitivity and specificity with the advantages of modern microelectronics. Because of its technological advancement, silicon has been used in most of the past and current developments 2-5 . However, its poor biocompatibility and chemical instability prevent silicon from becoming the ideal material for biosensor applications. In contrast, diamond is known as a biocompatible material in itself 6 , consisting of just carbon atoms. Efforts were therefore made in the past to functionalize diamond surfaces 7-9 . Nevertheless, economic considerations and a lack of information have prevented a clear judgement of the potential of diamond in this particular field.The advent of a new diamond thin-film deposition technology 10 and recent breakthroughs in substitutional doping of diamond 11,12 have generated renewed interest. Indeed, the possibility of depositing large-area thin films of nanocrystalline diamond (NCD) on diverse substrates at a relatively low cost, and the fact that NCD has nearly the same combination of exceptional properties as single-crystal diamond-such as biocompatibility, chemical inertness and superb electrochemical properties 13 -have quickly led to considerable progress 15 . For instance, Yang et al. have demonstrated the modification of NCD surfaces with DNA oligonucleotides, and shown that NCD as a substrate for DNA immobilization has superior properties to those of other materials such as glass, gold or silicon 15 .

In this paper, we present a summary of our work on highly photostable supramolecular ruthenium complexes, which may be incorporated into more complex systems for artificial solar energy conversion. We have used supramolecular chemistry and photochemistry to synthesize highly photostable ruthenium bipyridine cnronates and a bipyridazine podate complex and to enhance photoelectron-transfer reactions in physical model systems for artificial photosynthesis.

The kinetics of oxidation of 16 meta-, ortho-, and para-substituted anilines with nine oxo(salen)chromium(V) ions
have been studied by spectrophotometric, ESIMS, and EPR techniques. During the course of the reaction, two
new peaks with ìmax at 470 and 730 nm appear in the absorption spectrum, and these peaks are due to the
formation of emeraldine forms of oligomers of aniline supported by the ESIMS peaks with m/z values 274 and 365
(for the trimer and tetramer of aniline). The rate of the reaction is highly sensitive to the change of substituents in
the aryl moiety of aniline and in the salen ligand of chromium(V) complexes. Application of the Hammett equation
to analyze kinetic data yields a F value of -3.8 for the substituent variation in aniline and +2.2 for the substituent
variation in the salen ligand of the metal complex. On the basis of the spectral, kinetic, and product analysis
studies, a mechanism involving an electron transfer from the nitrogen of aniline to the metal complex in the rate
controlling step has been proposed. The Marcus equation has been successfully applied to this system, and the
calculated values are compliant with the measured values

An investigation of the electrochemical activity of human white blood cells (WBC) for biofuel cell (BFC) applications is described. WBCs isolated from whole human blood were suspended in PBS and introduced into the anode compartment of a proton exchange membrane (PEM) fuel cell. The cathode compartment contained a 50 mM potassium ferricyanide solution. Average current densities between 0.9 and 1.6 μA cm-2 and open circuit potentials (Voc) between 83 and 102 mV were obtained, which were both higher than control values. Cyclic voltammetry was used to investigate the electrochemical activity of the activated WBCs in an attempt to elucidate the mechanism of electron transfer between the cells and electrode. Voltammograms were obtained for the WBCs, including peripheral blood mononuclear cells (PBMCs - a lymphocyte-monocyte mixture isolated on a Ficoll gradient), a B lymphoblastoid cell line (BLCL), and two leukemia cell lines, namely K562 and Jurkat. An oxidation peak at about 363 mV vs...

Physical electrochemistry has undergone a remarkable evolution over the last few decades, integrating advanced techniques and theory from solid state and surface physics. Single-crystal electrode surfaces have been a core notion, opening for scanning tunnelling microscopy directly in aqueous electrolyte (in situ STM). Interfacial electrochemistry of metalloproteins is presently going through a similar transition. Electrochemical surfaces with thiol-based promoter molecular monolayers (SAMs) as biomolecular electrochemical environments and the biomolecules themselves have been mapped with unprecedented resolution, opening a new area of single-molecule bioelectrochemistry. We consider first in situ STM of small redox molecules, followed by in situ STM of thiol-based SAMs as molecular views of bioelectrochemical environments. We then address electron transfer metalloproteins, and multi-centre metalloenzymes including applied single-biomolecular perspectives based on metalloprotein/metallic nanoparticle hybrids.

The nitric-oxide synthases (NOS, EC 1.14.13.39) are modular enzymes containing attached flavoprotein and heme (NOSoxy) domains. To generate nitric oxide (NO), the NOS FMN subdomain must interact with the NOSoxy domain to deliver electrons to the heme for O 2 activation during catalysis. The molecular basis and how the interaction is regulated is unclear. We explored the role of eight positively charged residues that create an electropositive patch on NOSoxy in enabling the electron transfer by incorporating mutations that neutralized or reversed their individual charges. Stopped-flow and steady-state experiments revealed that individual charges at Lys 423 , Lys 620 , and Lys 660 were the most important in enabling heme reduction in nNOS. Charge reversal was more disruptive than neutralization in all cases, and the effects on heme reduction were not due to a weakening in the thermodynamic driving force for heme reduction. Mutant NO synthesis activities displayed a complex pattern that could be simulated by a global model for NOS catalysis. This analysis revealed that the mutations impact the NO synthesis activity only through their effects on heme reduction rates. We conclude that heme reduction and NO synthesis in nNOS is enabled by electrostatic interactions involving Lys 423 , Lys 620 , and Lys 660 , which form a triad of positive charges on the NOSoxy surface. A simulated docking study reveals how electrostatic interactions of this triad can enable an FMN-NOSoxy interaction that is productive for electron transfer.

Recently, conducting polymers have attracted much interest in the development of biosensors. The electrically conducting polymers are known to possess numerous features, which allow them to act as excellent materials for immobilization of biomolecules and rapid electron transfer for the fabrication of efficient biosensors. In the present review an attempt has been made to describe the salient features of conducting polymers and their wide applications in health care, food industries, environmental monitoring etc.

Two simple procedures for the synthesis of 2-deoxy-D-lyxo-hexono-1,4-lactone are described. Reductive cleavage of a 2-O-tosyl derivative of D-galactono-1,4-lactone in the presence of sodium iodide afforded the 2-deoxy derivative. On the other hand, a-deoxygenation of D-galactono-1,4-lactone was easily achieved by photochemical electron transfer deoxygenation of HO-2 as the 3-(trifluoromethyl)benzoate. Methyl 2-deoxy-b-D-lyxo-hexafuranoside ('methyl 2-deoxy-b-D-galactofuranoside') was synthesized and tested as substrate for exo b-D-galactofuranosidase from Penicillium fellutanum. The reaction was followed by HPAEC, showing that methyl 2-deoxy-b-D-galactofuranoside was not hydrolyzed by incubation with the enzyme. Neither the 2-deoxy lactone, nor the 2-deoxy-b-D-galactofuranoside acted as inhibitors of the reaction with the 4-nitrophenyl b-D-galactofuranoside. The present and our previous results show that the hydroxyl groups at C-2, C-3 and C-6 of the galactofuranoside are essential for interaction with the exo b-D-galactofuranosidase.

The oxidation of cyclohexadiene in a mixed aqueous solvent in the present of azide ion produced 4-azido-2-cyclohexene-1-one, 1, and 2-azido-3-cyclohexene-1-one, 2, in a four electron transfer in about a 70% yield. The overall reaction is a net air oxidation. These enantioselectivies are higher than any obtained previously for addition to 1,3-dienes. The conversion of 1 to 2 involves a [3,3]sigmatropic rearrangement.

The interaction of a CO molecule with the Fe(100) surface is analyzed by the topology of the Laplacian of the electronic charge density −V2r. This analysis shows that the atomic graph of the top atoms of the Fe(100) surface is a cube that exposes a face, F top , with a ''hole'' of charge or (3,+1) critical point of −V2r, whereas the corresponding graph for the second layer atoms is an octahedron that exhibits a vertex, V sec , protruding above the Fe(100) surface, with a ''peak'' of charge or (3,−3) critical point of −V2r. Atomic graphs determined for the CO molecule show that the carbon atom has a non-bonded vertex, C Vnb , and a torus, C torus , of charge depletion perpendicular to the C-O bond direction. As the CO molecule approaches the surface, electron transfer towards the tilted CO in turn induces two non-bonded critical points, O Vnb , on the O atom. In accordance with experimental and theoretical results, the topological theory of the Laplacian suggests that the preferred pathway for CO dissociation corresponds to the tilted orientation on the surface, in which the attractive interaction C torus -V sec is enhanced by the interaction of the two O Vnb with the F top on two Fe top atoms of the (100) surface.

Silicon-based devices are currently the most attractive group because they are functioning at room temperature and can be easily integrated into conventional silicon microelectronics. There are many models and simulation programs available to compute CV curves with quantum correction [Choi C-H, This work deals with the simulation of electron transfer through SiO 2 barrier of metal-oxide-semiconductor structure (MOS). The carrier density is given by a self consistent resolution of Schro¨dinger and Poisson equations and then the MOS capacitance is deduced and compared with results available in literature. As it is well known, the MOS capacitance-voltage profiling provides a simple determination of structure parameters. The extracted tunnel oxide thickness and substrate doping are compared with those used in the simulation. For the purpose to investigate the electron tunnelling through the barrier, we have used the transfer matrix approach. Using I-V simulations, we have shown that the traps in SiO 2 matrix have a drastic influence on electron tunnelling through the barrier. The trap-assisted contribution to the tunnelling current is included in many models [Maserjian J, Zamani N. this is the basis for the interpretation of stress induced leakage current (SILC) and breakdown events. Memory effect becomes typical for this structure. We have studied the I-V dependence with trap parameters. r

Ammonia was synthesized by reducing NO À 3 /NO À 2 over several bimetallic surfaces, supported on H + conducting Nafion-117 polymer. When Pd was used alone as a cathode, the cent percent product was ammonia but the process was kinetically unfavorable (2.3 Â 10 À3 min À1 ) during nitrite reduction. Under the same experimental conditions, Pt-Pd, Ni-Pd, Ag-Pd and Cu-Pd cathodes were mainly selective to NH þ 4 (69-82%) but nitrite reduction activity was still low (68.1 Â 10 À3 min À1 ). The Rh-Pd was only one cathode, which simultaneously enhanced nitrate (21.1 Â 10 À3 min À1 ) and nitrite (25.6 Â 10 À3 min À1 ) reduction yielding ca. 75% of NH þ 4 . The cyclic voltammetric investigations as well as catalytic hydrogenation experiments indicated that the surface to substrate electron transfer reaction was the main reason of ammonia formation. It was noticed that multi functional roles of the Nafion membrane enhanced the ammonia synthesis performance of the electrolyte reactor.

The treatment of ß-and?-cyclodextrins with the half-sandwich complexes of iron afford the inclusion compounds CpFe (L 2) X· CD (ß and?)(X= Cl, I; L= CO; L 2= dppe, dppe=(Ph) 2 P (CH 2) 2 P (Ph) 2),[CpFe (L 2) L-] PF 6· CD (ß and?) L-neutral donor ligands and [(Cp ( ...

A simple procedure was developed to prepare a glassy carbon (GC) electrode modified with carbon nanotubes (CNTs) and catechol compounds. First, 25 μL of DMSO–CNTs solutions (0.4 mg/mL) was cast on the surface of GC electrode and dried in air to form a CNTs film. Then the GC/CNTs modified electrode immersed into a chlorogenic acid, catechine hydrate and caffeic acid solution (electroless deposition) for a short period of time (2–80 s). The cyclic voltammogram of the modified electrode in aqueous solution shows a pair of well-defined, stable and nearly reversible redox couple (quinone/hydroquinone) with surface confined characteristics. The combination of unique electronic and electrocatalytic properties of CNTs and catechol compounds results in a remarkable synergistic augmentation on the response. The electrochemical reversibility and stability of modified electrode prepared with incorporation of catechol compound into CNTs film was evaluated and compared with usual methods for attachment of catechols to electrode surfaces. The transfer coefficient (α), heterogeneous electron transfer rate constants (ks) and surface concentrations (Γ) for GC/CNTs/catechol compound modified electrodes were calculated through the cyclic voltammetry technique. The modified electrodes showed excellent catalytic activity, fast response time and high sensitivity toward oxidation of hydrazine in phosphate buffer solutions at pH range 4–8. The modified electrode retains its initial response for at least 2 months if stored in dry ambient condition. The properties of modified electrodes as an amperometric sensor for micromolar or lower concentration detection of hydrazine have been characterized.

To establish a proteomic reference map of date palm leaves (Deglet Nour cultivar), we separated and identified leaf proteins using two-dimensional polyacrylamide gel electrophoresis and mass spectrometry, respectively. In total, 284 spots were excised from gel and analyzed by liquid chromatography tandem mass spectrometry (LC-MS/MS). Among them, 158 were successfully identified (i.e, a success rate of 55.6%) conducting to the identification of 126 unique proteins. These proteins were then clustered according to their functional annotations. Identified proteins were involved in metabolism, electron transport, photosynthesis, protein synthesis, cell structure or defence. However, 29.4 % of the identifications gave unknown function. We then compared the proteome map of female and male trees. Only one discriminated spot was found to be specific of the gender. We identified the corresponding protein as an ABC superfamily ATP binding cassette transporter, ABC protein, a protein whose an ortholog in Arabidopsis thaliana was already reported as required for male fertility and pollen formation. The relevance of this protein as gender biomarker was then confirmed in four other cultivars, i.e., Aligue, Khouet Aligue, Kentichi and Kenta. Such biomarker should be helpful in rapidly distinguishing date palm gender of immature trees.

A abordagem mais promissora para o desenvolvimento de biossensores eletroquímicos é a busca da comunicação elétrica direta entre as biomoléculas e a superfície do eletrodo. Esta revisão apresenta as principais abordagens, estratégias e avanços no desenvolvimento de biossensores eletroquímicos de terceira geração. Os temas discutidos englobam uma breve descrição sobre os fundamentos do fenômeno de transferência de elétrons e sobre o desenvolvimento de biossensores amperométricos (diferentes tipos e novas técnicas de imobilização orientada de enzimas). Um enfoque especial foi dado para as enzimas e proteínas redox capazes de eletrocatalisar reações via transferência direta de elétrons. Também foram apresentadas e discutidas as aplicações analíticas e tendências futuras dos biossensores de terceira geração.

The transient reflectivity of bismuth crystal excited by a 45 fs laser pulse in the near-infrared range has been recovered with an accuracy of 10 −5 , at initial sample temperatures ranging from 50 to 510 K, and at pump fluences from 2 mJ/ cm 2 to 21 mJ/ cm 2. The coherent phonon excitation and decay processes were imprinted into the time-dependent reflectivity and this allows us to uncover the temporal phonon history preceding the structural transformation of solid Bi. Analysis showed that the first coherent atomic displacement was produced by the polarization force and the electron pressure force during the laser pulse, and that manifests itself by a negative change in the reflectivity. The frequency of the subsequent reflectivity oscillations was chirped, redshifted from the initial value due to the lattice heating. The amplitude decreased gradually while electrons transferred their energy to the lattice. Heating and thermal expansion of the lattice transformed the initially coherent harmonic vibrations of atoms into strongly nonlinear chaotic motion that signifies the onset of disordering of the solid. This process was identified through measurement of the damping rate of the reflectivity oscillations and interpretation of this rate as the decay rate of an optical phonon into two acoustic phonons. The analysis of the reflectivity oscillations provides evidence that the overheated solid experiences only the onset of the solid-liquid phase transition but did not proceed into the liquid phase. General relations between the laser-exerted forces, the atomic motion, and the optical parameters were established. The proposed theory reproduces well the measured transient reflectivity across a wide range of crystal temperatures and laser excitation fluences.

Low dimensional semiconductor crystals structures otherwise known as quantum dots are in possession of unique optoelectronic properties that allow the flow of electrons to be harvested instantaneously. The advent of quantum dot for various technological applications is motivated by their flexibility of their bandgap supporting their capability to tap power from the visible spectrum as well as the invisible infrared through absorbable wavelength ranges from about 700 nanometre to 10 micron. Besides the wide energy harvesting range, quantum dot utilizes small to area for high energy production. The emergence of quantum dot and its application in optoelectronic device such as solar is set to improve the efficiency limit of traditional devices. The configuration of quantum dot in solar cell is discussed as well as electron transfer processes. Their three unique advantages for solar-to-electric energy conversion such as provision of large surface and interfacial areas per unit volume for...

The aim of this work is to the study the influence of the isomer structures of butyl acrylate monomer on the single-electron transfer/degenerative chain transfer mediated living radical polymerization (SET-DTLRP). The kinetic of isobutyl acrylate is determined for the first time by SET-DTLRP in water catalyzed by sodium dithionite. The plots of number-average molecular weight versus conversion and ln([M]0/[M]) versus time are linear, demonstrating a controlled polymerization. The influence of the isomer t-butyl, i-butyl, and n-butyl on the kinetics, properties, and stereochemistry of the reactions was assessed. To the best of our knowledge, there is no previous report dealing with the synthesis of PiBA by any LRP approach in aqueous medium. The results presented in this work suggest that the stability provided by the acrylate side group has an important influence in the polymerization process. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6542–6551, 2008

The lead dioxide electrodeposition (LDE) from nitrate electrolytes is studied by the rotating disk electrode, cyclic voltammetry, and electrode impedance methods. A four-stage kinetic scheme of the LDE reaction is proposed: (1) the electron transfer and generation of oxygen-containing species on the electrode surface; (2) the species interact with lead ions, forming an oxygen-containing intermediate product of Pb(III) of the type Pb(OH)2+, which is not fixed on the electrode surface; (3) the product is oxidized, with the transfer of the second electron, forming compounds of Pb(IV) associated with oxygen (of the type Pb(OH)2+2); and (4) the latter decomposes via a chemical mechanism to form PbO2. The rate-determining stage of the LDE process is essentially dependent on the potential and state of the electrode surface, concentration of Pb(II) ions in solution, and hydrodynamic conditions of experiment. The proposed scheme explains within a unified mechanism of the LDE reaction all the...

We report cloning and sequencing of gene ps1 encoding a versatile peroxidase combining catalytic properties of lignin peroxidase (LiP) and manganese peroxidase (MnP) isolated from lignocellulose cultures of the white-rot fungus Pleurotus eryngii. The gene contains 15 putative introns, and the deduced amino acid sequence consists of a 339-residue mature protein with a 31-residue signal peptide. Several putative response elements were identified in the promoter region. Amino acid residues involved in oxidation of Mn 2 and aromatic substrates by direct electron transfer to heme and long-range electron transfer from superficial residues as predicted by analogy with Phanerochaete chrysosporium MnP and LiP, respectively. A dendrogram is presented illustrating sequence relationships between 29 fungal peroxidases.

We have fabricated a dye-sensitized solar cell (DSSC) with a pair of carbon-based electrodes using a transparent, conductive carbon nanotubes (CNTs) film modified with ultra-thin titanium-sub-oxide (TiO x ) as the working electrode and a bilayer of conductive CNTs and carbon black as the counter electrode. Without TiO x modification, the DSSC is almost nonfunctional whereas the power conversion efficiency (PCE) increases significantly when the working electrode is modified with TiO x . The performance of the cell could be further improved when the carbon black film was added on the counter electrode. The improved efficiency can be attributed to the inhibition of the mass recombination at the working electrode/electrolyte interface by TiO x and the acceleration of the electron transfer kinetics at the counter electrode by carbon black. The DSSC with a pair of carbon-based electrodes gives the PCE of 1.37%.

The electrocatalytic properties of cubic palladium nanoparticles towards the electrochemical reduction of oxygen were studied in acid and alkaline solutions and compared with those of spherical nanoparticles and bulk Pd. The synthesised Pd nanoparticles were characterised by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Electrooxidation of pre-adsorbed CO was employed for cleaning the palladium catalyst surface. Oxygen reduction was studied using the rotating disk electrode (RDE) method and enhanced electrocatalytic activity of Pd nanocubes was revealed both in acid and alkaline solutions, which was attributed to the prevalence of Pd(1 0 0) facets. The mechanism of oxygen reduction on Pd nanoparticles was similar to that on bulk Pd, the first electron transfer being the rate-limiting step, and the reaction predominantly followed a four-electron pathway in both solutions.

First-principle calculations are carried out to investigate the structural, elastic and electronic properties of Fe 2 C. We use the plane-wavebased-pseudo-potential method, in which both the local-density approximation (LDA) and the generalized gradient approximation (GGA) implanted in the CASTP code are employed. The internal positions of atoms in the unit cell are optimized and the ground state properties such as lattice parameter, elastic constants, bulk modulus and the final enthalpy of g-Fe 2 C and e-Fe 2 C are calculated. The calculated values compare favorably with the available experimental data. From the calculated results, we confirm that the mechanical and energetic stability of g-Fe 2 C are prior to e-Fe 2 C at ambient conditions. The density of state (DOS) reveals that both g-Fe 2 C and e-Fe 2 C are strong metallic carbides. The electronic structure explains that the bonds of Fe 2 C are of the unusual mixtures of metallic, covalent, and ionic. It is found that the e-Fe 2 C has no magnetic character from the spin-polarized site-projected densities of states. The g-Fe 2 C has magnetic character with atom-averaged magnetic moment of 1.09 l B , which is little smaller than that within the Slater-Pauling-Friedel (SPF) model.

The ␤-cyclodextrin (␤-CD) polyiodide inclusion complex (␤-CD) 2 •Co 0.5 •I 7 •21H 2 O has been synthesized, characterized and further investigated via FT-Raman spectroscopy in the temperature range of 30-120 • C. The experimental results point to the coexistence of I − 7 units (I 2 •I − 3 •I 2) that seem not to interact with the Co 2+ ions and I − 7 units that display such interactions. The former units exhibit a disorder-order transition of both their I 2 molecules above 60 • C due to a symmetric charge-transfer interaction with the central I − 3 [I 2 ← I − 3 → I 2 ], whereas in the latter units only one of the two I 2 molecules becomes well-ordered above 30 • C. The other I 2 molecule remains disordered presenting no charge-transfer phenomena. The Co 2+ ion induces a considerable asymmetry on the geometry of the I − 3 anion and a significant modification of its Lewis base character. Complementary dielectric measurements suggest no important involvement of H•••I contacts in the observed modification of the I − 3 electron-transfer properties.

In this paper, we show the unique role of bicarbonate ion in stimulating the electron transfer of photosystem II (PS II) in formate-treated leaf discs from spinach. This is referred to as the "bicarbonate effect" and is independent of the role of CO 2 in CO 2 fixation. It is shown to have two sites of action: (1) the first, described here for the first time, stimulates the electron flow between the hydroxylamine donation site ("Z" or "D") and QA, the first plastoquinone electron acceptor and (2) the other accelerates the electron flow beyond QA, perhaps at the QAQB complex, where QB is the second plastoquinone electron acceptor. The first site of inhibition by formate-treatment is detected by the decrease of the rate of oxygen evolution and the simultaneous quenching of the variable chlorophyll a (Chl a) fluorescence of leaf discs infiltrated with 100 mM formate for about 10 s followed by storage for 10 min in dark. This is referred to as short-term formate treatment. Addition of bicarbonate reverses this short-term formate effect and restores fully both Chl a fluorescence and oxygen evolution rate. Reversible quenching of variable Chl a fluorescence of heated and short-term formate treated leaf discs, in the presence of hydroxylamine as an artificial electron donor to PS II, is also observed. This suggests that the first site of action of the anion effect is indeed between the site of donation of hydroxylamine to PS II (i.e. "Z" or "D") and QA-The second site of the effect, where bicarbonate depletion has its most dramatic effect, as well known in thylakoids, is shown by an increase of Chl a fluorescence of leaf discs infiltrated with 100 mM formate for about 10 min followed by storage for 10 min in dark. This is referred to as the long-term formate treatment. Addition of bicarbonate fully restores the variable Chl a fluorescence of these leaf discs. Chl a fluorescence transient of DCMU-infiltrated (10 min) leaf discs is similar to that of long-term formate-treated one suggesting that the absence of bicarbonate, like the presence of DCMU, inhibits the electron flow beyond QA

Trends in electrocatalytic activity of the oxygen evolution reaction (OER) are investigated on the basis of a large database of HO* and HOO* adsorption energies on oxide surfaces. The theoretical overpotential was calculated applying standard density functional theory in combination with the computational standard hydrogen electrode model (SHE). We show that by the discovery of a universal scaling relation between the adsorption energies of HOO* vs. HO* it is possible to analyze the reaction free energy diagrams of all the oxides in a general way. This gives rise to an activity volcano that is the same for a wide variety of oxide catalyst materials and a universal descriptor for the oxygen evolution activity. This suggests a fundamental limitation on the maximum oxygen evolution activity for a class of planar oxide catalysts. [a] Chem.

Two cobalt complexes, [Co(L Se )(phen)] AE CH 2 Cl 2 (1) and [Co(L Se )(N,N-Me 2 en)(CH 3 COO ) )] (2) have been synthesized and characterized by elemental analyses, magnetic measurements, i.r. studies etc. Single crystal X-ray studies reveal that in complex (1) cobalt atom is in +2 oxidation state with trigonal bipyramidal geometry, while in complex (2) it is in +3 oxidation state and surrounded octahedrally. The asymmetric unit of complex (2) contains two crystallographically independent discrete molecules. Complex (1) was found to be paramagnetic with l eff = 2.19 BM indicating a low spin cobalt(II) d 7 system, whereas complex (2) is found to be diamagnetic with cobalt(III) in low spin d 6 state. The kinetic studies on the reduction of (2) by ascorbic acid in 80% MeCN-20% H 2 O (v/v) at 25°C reveal that the reaction proceeds through the rapid formation of inner-sphere adduct, probably by replacing the loosely coordinated AcO ) group, followed by electron transfer in a slow step and is supported by a large Q (formation constant) value.

. We examined the time-resolved and steady-state fluorescence quenching of N-acetyl-L-tryptophanamide NATA by acrylamide and iodide, over a range of viscosities in propylene glycol. The quenching of NATA by acrylamide and iodide results in heterogeneity of the intensity decay which increases with the quencher concentration. We attribute the complex decays of NATA to transient effects in diffusion and the nature of the fluorophore᎐quencher Ž . interaction. These data were compared using the phenomenological radiation boundary condition RBC and Ž . distance-dependent quenching DDQ models for collisional quenching. We used global analysis of the time-resolved frequency-domain and steady-state data to select between the models. Consideration of both the frequency-domain and steady state data demonstrate that the quenching rate depends exponentially on the fluorophore᎐quencher distance, indicating the validity of the DDQ model. The rate constants for acrylamide and iodide quenching, at the 13 y1 9 y 1 constant distance of 5 A, were found to be near 10 s and 10 s , respectively. These rates reflect electron transfer and exchange interactions as the probable quenching mechanisms, respectively. ᮊ

The TiO 2 /UV photocatalytic degradations of indigo and of indigo carmine have been investigated both in aqueous heterogeneous suspensions and in the solid state. In addition to prompt removal of the color, TiO 2 /UV-based photocatalysis was simultaneously able to oxidize the dye, with almost complete mineralization of carbon and of nitrogen and sulfur heteroatoms into CO 2 , NH + 4 , NO − 3 , and SO 2− 4 , respectively. A detailed degradation pathway has been determined by careful identification of intermediate products, in particular, carboxylic acids, whose decarboxylation by photo-Kolbe reactions constitutes the main source of CO 2 evolution. The only persistent organic compound was acetic acid, whose degradation required a longer period of time. These results suggest that TiO 2 /UV photocatalysis may be envisaged as a method for treatment of diluted wastewaters in textile industries. The irradiation of titania with visible light did produce a photoinduced decolorization of the dye, probably induced by the breaking of the double-bond conjugation system of the chromophoric group. However, this decolorization was not accompanied by any degradation of the molecule since no loss of total organic carbon (TOC) nor release of inorganic ions were observed. This corresponded to a stoichiometric reaction of an electron transfer from the dye molecule excited in visible irradiation to titania. Because indigo is very poorly soluble (≈2 ppm), it was tentatively degraded in its solid state, mixed with titania in a photocatalytic solid-solid-type reaction. Observation of the decolorization and of the degradation of solid indigo constitutes a surprising and encouraging result for the development of self-cleaning titania-coated objects (glasses, steel, aluminium, metals, walls, etc.) fouled by solid dirt particles.

We introduce a new, non-invasive technique to measure linear electron transfer in intact leaves under steady-state illumination. Dark-interval relaxation kinetic or 'DIRK' analysis is based on measurements of the initial rates of relaxation of steady-state absorbance signals upon a rapid light-dark transition. We show that estimates of electron flux by DIRK analysis of absorbance signals, reflecting redox changes in the photosynthetic electron transfer chain, can yield quantitative information about photosynthetic flux when the light-dependent partitioning of electrons among redox components of the electron transfer chain are considered. This concept is modeled in computer simulations and then demonstrated in vivo with tobacco plants under non-photorespiratory conditions resulting in linear relationships between DIRK analysis and gross carbon assimilation (A(G)). Estimation based on DIRK analysis of the number of electrons transferred through the photosynthetic apparatus for...

Two polyvinylidene¯uoride micro®ltration membranes (GVHP and GVWP: Millipore, Bedford, MA) with a nominal pore size of 0.22 mm were challenged with mixed microbial cultures present in Milli-Q TM water and in secondary ef¯uent, and with a Gram-negative model bacterium, SW8, to investigate bacterial passage. Total bacterial counts measured microscopically using the DNA¯uorochrome DAPI revealed that the small bacteria in Milli-Q TM water passed MF membranes totally. The model bacterium, SW8 and bacteria from secondary ef¯uent were mostly retained with log reduction values (LRV) of 4 and 3.5, respectively. Transmembrane pressure did not in¯uence the levels of bacterial passage signi®cantly. Pore size effects were investigated with track-etched membranes (Poretics TM : Osmonics, Minnetonka MN) with nominal pore sizes of 0.2, 0.1 and 0.05 mm. The LRV of 0.2 mm membranes for SW8 and secondary ef¯uent cells was 3 and 1.5, respectively (total counts). Both membranes with pore sizes smaller than 0.2 mm acted similarly, they still transmitted secondary ef¯uent cells with LRV 2 log higher than 0.2 mm membranes, but for SW8 only 50% higher. In contrast to total count results, removal of bacteria was 100% with all membranes when assessed by cultureable counts, i.e. numbers of bacterial colonies recovered on R2A agar plates. Transmitted bacteria failed to grow on standard basal microbiology media most probably because they were injured during passage through the membranes to the extent that recovery in laboratory media did not occur. However, tests with CTC, an indicator of cell viability, indicated that approximately half of the cells of SW8 which passed the membranes had what appeared to be functional electron transfer chains in their membranes. All membranes had a pore size distribution which included pores larger than the nominal value. Field emission scanning electron microscopy (FESEM) provided evidence for entrapment of bacteria within the membrane matrix. # 0376-7388/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. P I I : S 0 3 7 6 -7 3 8 8 ( 9 8 ) 0 0 2 5 1 -8