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The enzyme CYP1A2 is responsible for the metabolism of numerous antioxidants in the body, including caffeine, which is transformed into paraxanthine, its main primary metabolite. Both molecules are known for their antioxidant and pro-oxidant characteristics, and the paraxanthine-to-caffeine molar ratio is a widely accepted metric for CYP1A2 phenotyping, to optimize dose&ndash, response effects in individual patients. We developed a simple, cheap and fast electrochemical based method for the simultaneous quantification of paraxanthine and caffeine in human saliva, by differential pulse voltammetry, using an anodically pretreated glassy carbon electrode. Cyclic voltammetry experiments revealed for the first time that the oxidation of paraxanthine is diffusion controlled with an irreversible peak at ca. +1.24 V (vs. Ag/AgCl) in a 0.1 M H2SO4 solution, and that the mechanism occurs via the transfer of two electrons and two protons. The simultaneous quantification of paraxanthine and caffeine was demonstrated in 0.1 M H2SO4 and spiked human saliva samples. In the latter case, limits of detection of 2.89 &mu, M for paraxanthine and 5.80 &mu, M for caffeine were obtained, respectively. The sensor is reliable, providing a relative standard deviation within 7% (n = 6). Potential applicability of the sensing platform was demonstrated by running a small scale trial on five healthy volunteers, with simultaneous quantification by differential pulse voltammetry (DPV) of paraxanthine and caffeine in saliva samples collected at 1, 3 and 6 h postdose administration. The results were validated by ultra-high pressure liquid chromatography and shown to have a high correlation factor (r = 0.994).

The importance of sensing hydrogen peroxide (H2O2) is due to its ubiquity, being extensively used in industry and also being a biologically relevant side-product of several enzymatic processes. Electrochemical sensing is one of the most robust and simple methods for sensing H2O2 and the discovery of new electroactive materials, particularly at the nanoscale, represents a very hot topic of research. Here, we prove that upon appropriate integration of oxidized single-walled carbon nanohorns (ox-SWCNHs) into a per se moderate H2O2 sensor such as cerium dioxide (CeO2), the sensitivity toward H2O2 is enhanced by almost two orders of magnitude (from 0.4 to 160 μA cm−2 mM−1), on par with that of state-of-the-art metal or metal oxide-based sensors. The modified electrode is also very stable (82% response after 2 weeks of continuous use) and the results highly reproducible. The developed nanohybrid ox-SWCNHs@CeO2, characterized fully and whose average size is about 70 nm as measured by both TEM and AFM, was also tested in real case studies such as washing liquids and milk and was confirmed to be a robust and highly selective material, being not affected neither by the presence of complex matrices, nor by interferents in several organic substrates. The high recovery confirmed the excellent specificity and flexibility of this new electrocatalytic material. Fil: Bracamonte, Maria Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. University of Trieste; Italia Fil: Melchionna, Michele. University of Trieste; Italia Fil: Giuliani, Angela. University of Trieste; Italia Fil: Nasi, Lucía. CNR-IMEM Institute; Italia Fil: Tavagnacco, Claudio. University of Trieste; Italia Fil: Prato, Maurizio. University of Trieste; Italia. Carbon Nanobiotechnology Laboratory; España. BasqueFdnSci; España Fil: Fornasiero, Paolo. University of Trieste; Italia

The Haber-Bosch process for NH3 production leads to a considerable greenhouse gas release due to the remarkable use of fossil fuels. Therefore, there is an increasing interest in developing alternative and environmental friendly approaches. Among the possible solutions, the electrocatalytic conversion of N 2 has recently gained significant attention; on the other hand, not only scientific but also important technical aspects remain fundamental issues to be clarified. Particularly relevant is the need to improve the analytical protocols to ascertain that any detected NH 3 is actually produced from N 2 rather than from any external contaminations or partial decomposition of the catalyst itself. Here, a rotating ring-disc electrode (RRDE) setup is used for the first time to study the N 2 electroreduction process with the aim to recognize the product species formed at the disc and detected at the ring electrodes, respectively. We demonstrated that this experimental approach is effective to discern also a low-level ammonium concentration through monitoring the ammonia oxidation peak at the ring electrode for a fast and preliminary electrocatalytic performance evaluation and to prevent false positives. The versatility of the RRDE method employed as a fingerprint of new electrocatalyst candidates could allow to reserve time and cost.

The Oxygen Reduction Reaction (ORR) catalyzed by N-carbon electrocatalyst was investigated, focusing on the fundamental features for the selective H2O2 formation. The electrochemical characterization was primarily performed by the use of the Rotating Ring Disk Electrode (RRDE) tool in both hydrodynamic Linear Sweep Voltammetry (LSV) mode and by Chronoamperometry (CA) measurement. We rationalized the structure/activity relationship, reaching a new state-of-the-art in terms of current density for the H2O2 generation. The study also explored the performance in relation with the electrode deposit procedure that is of fundamental importance to achieve a suitable macroscopic electrode preparation. Furthermore, the electrode implementation in a polymer membrane static flow electrolyzer setup, was evaluated to understand how the material catalytic features such as current ranges and selectivity scale up from a classical three electrode system to a more realistic application-focused environment.

Electrocatalytic oxygen reduction (ORR) is an emerging synthetic strategy to prepare H

Electrocatalytic oxygen reduction (ORR) is an emerging synthetic strategy to prepare H2 O2 in a sustainable fashion. N-doped graphitic carbon with embedded cobalt nanoparticles was selected as an advanced material able to selectively trigger the ORR to form H2 O2 with a faradaic efficiency of almost 100 % at very positive applied potentials. The production of H2 O2 proceeded with high rates as calculated by bulk electrolysis (49 mmol g-1 h-1 ) and excellent current densities (≈-0.8 mA cm-2 at 0.5 V vs. reversible hydrogen electrode). The totally selective behavior depended on the combination of concomitant material features, such as the textural properties, the nature of the metal, the distribution of N moieties, the acidic environment, and the applied potential.

The search for a sustainable process for production of hydrogen peroxide (H2O2) is receiving a great attention in the last years in view of its possible use as a clean oxidant in the chemical industry or for decontamination of water streams. In this context, the electrochemical approach is particularly interesting, since it can use electricity produced from solar light through photovoltaic panels. H2O2 can be produced by selective 2-electron reduction of O2 from air, but the efficiency of this process is strongly limited by possible concomitant 4-electron reduction to H2O. Graphitic carbon materials have been reported as selective electrocatalysts in 2-electron O2 reduction, with recognized as active sites for the process. In this work, we present the preparation of high surface area graphitic carbons containing O and N as dopants, with optimal porosity and tunable composition depending on the molar ratio of the molecular precursors employed in the preparation. We observed that a tiny amount of N within the material can improve the selectivity to H2O2, without significant loss of performances. The addition of Cu nanoparticles deeply changes the selectivity of the systems, favoring the O2 reduction to H2O with a very low selectivity to H2O2.

The widespread industrial use of H2O2 has provoked great interest in the development of new and more efficient materials for its detection. Enzymatic electrochemical sensors have drawn particular attention, primarily because of their excellent selectivity. However, their high cost, instability, complex immobilization, and inherent tendency toward denaturation of the enzyme significantly limit their practical usefulness. Inspired by the powerful proton-catalyzed H2O2 reduction mechanism of peroxidases, we have developed a well-defined and densely functionalized carboxylic graphene derivative (graphene acid, GA) that serves as a proton source and conductive electrode for binding and detecting H2O2. An unprecedented H2O2 sensitivity of 525 μA cm–2 mM–1 is achieved by optimizing the balance between the carboxyl group content and scaffold conductivity of GA. Importantly, the GA sensor greatly outperforms all reported carbon-based H2O2 sensors and is superior to enzymatic ones because of its simple immobilization, low cost, and uncompromised sensitivity even after continuous operation for 7 days. In addition, GA-based sensing electrodes remain highly selective in the presence of interferents such as ascorbic acid, paracetamol, and glucose, as well as complex matrices such as milk. GA-based sensors thus have considerable potential for use in practical industrial sensing technologies.

Carbon nanotube (CNT)-modified surfaces unequivocally demonstrate their biocompatibility and ability to boost the electrical activity of neuronal cells cultured on them. Reasons for this effect are still under debate. However, the intimate contact at the membrane level between these thready nanostructures and cells, in combination with their unique electrical properties, seems to play an important role. The entire existing literature exploiting the effect of CNTs on modulating cellular behavior deals with cell cultures grown on purified multiwalled carbon nanotubes (MWNTs) deposited on a supporting surface via drop-casting or mechanical entrapment. Here, for the first time, it is demonstrated that CNTs directly grown on a supporting silicon surface by a chemical vapor deposition (CVD)-assisted technique have the same effect. It is shown that primary neuronal cells developed above a carpet of CVD CNTs form a healthy and functional network. The resulting neuronal network shows increased electrical activity when compared to a similar network developed on a control glass surface. The low cost and high versatility of the here presented CVD-based synthesis process, together with the possibility to create on supporting substrate patterns of any arbitrary shape of CNTs, open up new opportunities for brain-machine interfaces or neuroprosthetic devices.

Direct conversion of carbon dioxide to formic acid at thermodynamic equilibrium is an advantage of enzymatic catalysis, hardly replicated by synthetic analogs, but of high priority for carbon-neutral energy schemes. The bio-mimetic potential of totally inorganic Pd@TiO2 nanoparticles is envisioned herein in combination with Single Walled Carbon NanoHorns (SWCNHs). The high surface nano-carbon entanglement templates a wide distribution of "hard-soft" bimetallic sites where the small Pd nanoparticles (1.5 nm) are shielded within the TiO2 phase (Pd@TiO2), while being electrically wired to the electrode by the nanocarbon support. This hybrid electrocatalyst activates CO2 reduction to formic acid at near zero overpotential in the aqueous phase (onset potential at E < -0.05 V vs. RHE, pH = 7.4), while being able to evolve hydrogen via sequential formic acid dehydrogenation. The net result hints at a unique CO2 "circular catalysis" where formic acid versus H2 selectivity is addressable by flow-reactor technology. Fil: Melchionna, Michele. Università degli Studi di Trieste; Italia Fil: Bracamonte, Maria Victoria. Università degli Studi di Trieste; Italia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina Fil: Giuliani, Angela. Università degli Studi di Trieste; Italia Fil: Nasi, Lucia. Istituto Dei Materiali Per L'elettronica Ed Il Magnetismo; Italia Fil: Montini, Tiziano. Università degli Studi di Trieste; Italia Fil: Tavagnacco, Claudio. Università degli Studi di Trieste; Italia Fil: Bonchio, Marcella. Università di Padova; Italia Fil: Fornasiero, P. Università degli Studi di Trieste; Italia Fil: Prato, Maurizio. Università degli Studi di Trieste; Italia

Summary Electrochemical oxygen reduction (ORR) is a challenging approach for the sustainable production of hydrogen peroxide (H 2 O 2 ) and is also a reaction of relevance in fuel-cell applications. Here, we propose an outstanding metal-free electrocatalyst for the unexpectedly selective ORR to H 2 O 2 , consisting of graphitized N-doped single-wall carbon nanohorns (CNHs). The catalyst can operate at acidic pH to a faradic efficiency as high as 98%, but it also shows excellent performance at either physiological or alkaline pH. Moreover, the very positive onset potentials observed at all pH values investigated (+0.40 V, +0.53 V, and +0.71 V at pH 1.0, 7.4, and 13.0, respectively), good stability, and excellent reproducibility make this material a benchmark catalyst for ORR to H 2 O 2 . The outstanding activity arises from a combination of several factors, such as CNH-dependent facilitation of electron delivery, suitable porosity, and a favorable distribution of the types of N atoms.

The thermodynamic parameters for the complexation reaction between Zn2+ and Hg2+ ions with the mixed amino-polypyridinic ligands tris[(2-pyridyl)methyl]amine (TPA) and 6,6-bis–bis (pyridylmethyl)aminomethyl]-2,2-bipyridine (BTPA) have been obtained in anhydrous dimethylsulfoxyde (DMSO) by using spectrophotometry, polarography, potentiometry and titration calorimetry. Complexes with stoichiometry 1:1 have been observed in all cases but Hg-TPA system, for which 1:2 complex is also formed. As found in water, both $$\Updelta G_{\rm{j}}^{\circ}$$ and $$\Updelta H_{\rm{j}}^{\circ}$$ become more favorable when going down along the group. From a comparison of data with those reported for other metal ions in DMSO (Co2+, Ag+, Cd2+) and in water as solvent, it is shown that TPA is more selective towards Hg2+ in water than in DMSO and that the selectivity of BTPA in DMSO is much higher towards Cd2+ and Hg2+ ions with respect to Zn2+.

Water is the most abundant, renewable source of hydrogen on our planet. Appropriate catalytic materials are needed to minimize the energy required to electrochemically split the water molecule, and electrode with high specific areas are sought to maximize the electrolyte/electrode interface. We use Carbon Nanotubes (CNTs) bundles as templates for water splitting electrodes fabrication. Appropriate catalyst materials are thermally evaporated on CNTs, to exploit both their good electrical conductivity and large specific area, while optimizing over-potential towards Hydrogen Evolving Reaction (HER) or Oxygen Evolving Reaction (OER) through the deposited catalysts. Electrodes morphology and surface chemistry are characterized, before and after electrolysis, by means of scanning electron microscopy and X-ray photoelectron spectroscopy. Our electrodes are able to perform water oxidation and water reduction near their thermo-dynamical limit. Performances of these electrodes, taking into account the extremely low loading mass of catalytic material (10−2 mg cm−2) with respect to other reported systems, are among the best HER and OER system reported so far. Finally, a working electrolyser, capable to operate at the interesting low voltage of a single AA battery (1.5 V) and output a stable current (>2.0 mA cm−2) for at least 20 h, is successfully assembled and tested. Fil: Cozzarini, Luca. Elettra Sincrotrone Trieste; Italia Fil: Bertolini, Gabriele. ETH Zurich; Suiza Fil: Suran Brunelli, Simone Tommaso. Elettra Sincrotrone Trieste; Italia Fil: Radivo, Andrea. Elettra Sincrotrone Trieste; Italia Fil: Bracamonte, Maria Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. University of Trieste; Italia Fil: Tavagnacco, Claudio. University of Trieste; Italia Fil: Goldoni, Andrea. Elettra Sincrotrone Trieste; Italia

The synthesis of functionalised carbon nanotubes as receptors for riboflavin (RBF) is reported. Carbon nanotubes, both single-walled and multi-walled, have been functionalised with 1,3,5-triazines and p-tolyl chains by aryl radical addition under microwave irradiation and the derivatives have been fully characterised by using a range of techniques. The interactions between riboflavin and the hybrids were analysed by using fluorescence and UV/Vis spectroscopic techniques. The results show that the attached functional groups minimise the p-p stacking interactions between riboflavin and the nanotube walls. Comparison of ptolyl groups with the triazine groups shows that the latter have stronger interactions with riboflavin because of the presence of hydrogen bonds. Moreover, the triazine derivatives follow the Stern–Volmer relationship and show a high association constant with riboflavin. In this way, artificial receptors in catalytic processes could be designed through specific control of the interaction between functionalised carbon nanotubes and riboflavin Fil: Lucío, María Isabel. Universita Degli Studi Di Trieste; Italia. Universidad de Castilla-la Mancha; España Fil: Pichler, Federica. Universidad de Castilla-la Mancha; España. Universita Degli Studi Di Trieste; Italia Fil: Ramírez, José Ramón. Universidad de Castilla-la Mancha; España Fil: de la Hoz, Antonio. Universidad de Castilla-la Mancha; España Fil: Sánchez Migallón, Ana. Universidad de Castilla-la Mancha; España Fil: Hadad, Caroline. Universita Degli Studi Di Trieste; Italia Fil: Quintana, Mildred. Universidad Autonoma de San Luis Potosi; Fil: Giulani, Angela. Universita Degli Studi Di Trieste; Italia Fil: Bracamonte, Maria Victoria. Universidad Nacional de Córdoba; Argentina. Universita Degli Studi Di Trieste; Italia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Fierro, Jose L.G.. Instituto de Catlisis y Petroleoqumica. Madrid; España Fil: Tavagnacco, Claudio. Universita Degli Studi Di Trieste; Italia Fil: Herrero, María Antonia. Universidad de Castilla-la Mancha; España Fil: Prato, Maurizio. Universita Degli Studi Di Trieste; Italia Fil: Vázquez, Ester. Universidad de Castilla-la Mancha; España

Substitution of the acetylacetonate ligands in [MO2(acac)2] (M = Mo or W) by 2-oxy-1-naphthaldehyde izonicotinoyl hydrazonate (NIH2−) or 3-methoxy-2-oxybenzaldehyde izonicotinoyl hydrazonate (VIH2−) gives rise to either zigzag chain polymers, [MO2(NIH)]n (1 and 2), square complexes [MO2(VIH)]4 (3 and 4), mononuclear complexes [MO2(VIH)(C2H5OH)] (5 and 6), or to polyoxomolybdate hybrid compounds [{; ; ; MoO2(HNIH)}; ; ; 2Mo6O19] (7) and [MoO2(HVIH)(H2O)]2Mo6O19 (8), depending on the reaction conditions. In all of these compounds the ligand is coordinated to the cis-MO22+ core via phenolic-oxygen, azomethine-nitrogen and enolic-oxygen atoms, while the remaining sixth coordination site is occupied either by the nitrogen atom of the izonicotinyl part, or by an oxygen atom from the solvent molecule, or by an oxygen atom from the hexanuclear anion. Crystal and molecular structures of the molybdenum(VI) compounds [MoO2(NIH)]n (1), [MoO2(VIH)]4 (3), [{; ; ; MoO2(HNIH)}; ; ; 2Mo6O19] (7) and [MoO2(HVIH)(H2O)]2Mo6O19 (8) were determined by the single crystal X-ray diffraction method. Dioxotungsten(VI) compounds [WO2(NIH)]n (2) and [WO2(VIH)]4 (4) were structurally characterized by the X-ray powder diffraction method. All of the investigated compounds were further characterized by elemental analysis, thermogravimetric analyses, cyclic voltammetry, FT-IR, UV-Vis and NMR spectroscopy.

Bis(methylphenylglyoximate)cobalt(III) complexes exist both as cis and trans isomers due to the asymmetry of the equatorial ligand, and, when the axial ligands are different, the trans isomer is chiral. The reaction of racemic trans-[CH3Co(mpgH)2py] (1) with either 3- or 4-pyridylboronic acid affords dimeric units arranged on a crystallographic symmetry center such that the pyridyl nitrogen of one moiety coordinates to the Co atom of the symmetry-related unit. In principle, three structurally different dimeric species (two homodimers and one heterodimer) can be obtained. Time-resolved 1H NMR spectra of a 1:1 mixture of racemic 1 and either 3- or 4-pyridylboronic acid in CDCl3/CD3OD show that the reaction does not converge toward a unique species in solution. Nevertheless, X-ray structures show that the heterochiral dimers are the only products that crystallize from the reaction mixture. The nature of the dioximate side groups does not affect the geometry of the dimeric arrangements assembled by 4-pyridylboronic acid (“molecular box”). On the contrary, the geometry of the species assembled by 3-pyridylboronic acid varies from the “molecular parallelogram” obtained from the bis(dimethylglyoximates) to the highly squeezed “molecular box” obtained from bis(methylphenylglyoximates). Cyclic voltammetry studies show that the metal centers in the dimeric species do not interact with each other and undergo a simultaneous redox process. However, depending on the geometry of the systems, the redox process involves a single four-electron reduction for 3 and 5 or two consecutive two-electron reduction steps for 4 and 6. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

The electrochemical oxidation of a Hg electrode in the presence of thiopyrimidine derivatives has been investigated in a collection of organic solvents using voltammetric and polarographic techniques. Remarkable adsorption phenomena control the electrochemical process, which in all cases gives rise to a Hg(I) complex. The Laviron adsorption model is found to describe well the polarographic adsorption wave. Some correlations between adsorption parameters and solvent properties have also been observed and discussed.Key words: polarography, voltammetry, thiopyrimidine, solvent effect, adsorption.

Bovine heart cytochrome c was studied through cyclic voltammetry in mixed water–organic solvent solutions under different conditions of temperature and the thermodynamic properties Δ S ° rc and Δ H ° rc calculated by the dependence of E ° by temperature. The effect of the organic fraction of the solvent on the E ° values of the native cyt c was found to be determined mainly by the decrease in dielectric constant of the medium. Specific interactions on the protein surface do not seem to play a remarkable role. The thermodynamic properties changes induced by the organic fraction have been interpreted tentatively in terms of solvation properties of cytochrome c and structural features of the protein environment.

The development of new electrocatalysts for the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) at physiological pH is critical for several fields, including fuel cells and biological applications. Herein, the assembly of an electrode based on carboxyl-functionalised hydrophilic multiwalled carbon nanotubes (MWCNTs) filled with Fe phases and their excellent performance as electrocatalysts for ORR and HER at physiological pH are reported. The encapsulated Fe dramatically enhances the catalytic activity, and the graphitic shells play a double role of efficiently mediating the electron transfer to O2 and H2O reactants and providing a cocoon that prevents uncontrolled Fe oxidation or leaching.

A series of electronically tuned trans- [CoIII(chel)(CH2Cl)]2 complexes, where chel is a salen derivative (salen = 2, 2′- ethylenebis(nitrilomethylidene)diphenol) containing either two or four methyl substituents in different positions, has been synthesized and characterized, both in solution and in the solid state. These complexes undergo an intramolecular cyclization reaction in methanolic solution to form the corresponding cis β organometallic derivative containing a seven-membered metallacycle, by replacement of the Cl atom of the axial CH2Cl by the salen phenolate oxygen. The cyclization rate increases on going from two to four methyl substituents in the chelate, in agreement with the electrochemical data that evidence a general shift toward more negative values with an increase in the number of methyl substituents. The cyclization rate is also affected by the substituent position, and both electrochemical and kinetic data evidence a remarkable influence of the methyls on the −C═N– groups of the chelate. The X-ray structures of cyclized complexes, [CoIII(chelCH2)(py)(H2O)]+, show a dependence of the conformation of the seven-membered metallacycle on the different positions of substituents in the chelate. In fact, in the complex having methyls on the −C═N– groups, the conformation is characterized by having the methylene carbon atom significantly displaced (ca. 1.26 Å) from the aromatic ring plane, whereas in the complex lacking methyl groups in those positions, the atoms of the Ph–O–CH2 fragment are coplanar. The standard Gibbs energies obtained by quantum chemical calculation reveal that the different conformations observed in the solid state are mainly the result of the energetically unfavorable setup of the methyls on the −C═N– groups and of the energetically favorable displacement of the CH2 group out of plane of the aromatic ring. 1H NMR data suggest that the different conformations of the metallacycle are, at least partially, retained in solution.

Preparations of [Rh(Hdmg) 2 (H 2 O) 2 ]ClO 4 ( 1 ) (Hdmg=dimethylgyoximate) from [Rh(H 2 O) 6 ](ClO 4 ) 3 and dimethylglyoxime and of [Rh(Hdmg) 2 (PPh 3 ) 2 ]ClO 4 ( 2 ) from 1 and PPh 3 are described. 1 crystallizes in the space group with a =14.910(3), b =6.058(1), c =18.617(4), A, β =107.649(8)°, Z =4. The structure was refined up to R =0.021 for 1849 reflections. The IR and NMR spectra and electrochemical behavior of 1 and 2 are discussed and compared with other rhodoximes. Three polarographic and CV processed can be detected for 2 , the first two, respectively to Rh(II) and Rh(I), being followed by fast reactions.

The reaction of RhCl 3 ·3H 2 O with Hdamo and PPh 3 (Hdamo = diacetyl monoxime = C 4 H 7 NO), both in the absence ( 1 ) and in the presence of HClO 4 ( 2 ) afforded the complex Rh(damo)(PPh 3 ) 2 Cl 2 . The reaction of the acidic water/ethanolic solution of [Rh(H 2 O) 6 ] 3+ with Hdamo and PPh 3 ( 3 ) gave the mixture of the isomers of the compound [Rh(damo) 2 (PPh 3 ) 2 ]ClO 4 ( 3A and 3B ). A similar mixture of isomers was formed when [Rh(H 2 O) 6 ] 3+ reacted with H 2 dopn (H 2 dopn = 3,9-dimethyl-4,8-diazaundeca-3,8-diene-2,10-dione dioxime) and PPh 3 ( 4 ). Two isomers ( 4A = 3B ) and [Rh cis -(damo) 2 cis -(PPh 3 ) 2 ]ClO 4 ·CHCl 3 ( 4B ) have been isolated. All the compounds were characterized by elemental analysis NMR and IR spectroscopy. Single-crystal X-ray diffraction studies were carried out on the complex 4B . In this compound the coordination environment around rhodium(III) is pseudooctahedral composed of two cis -oxime nitrogen atoms [av. RhN = 2.031(3) A], two trans -oxime oxygen atoms [av. RhO = 2.026(2) A] and two cis -phosphine phosphorus atoms [av. RhP = 2.403(1) A].

Thermodynamic parameters of complex formation between d(10) metal ions, such as Zn(2+), Cd(2+), Hg(2+) and Ag(+), and the macrocyclic thioether 1,4,7-trithiacyclononane ([9]AneS3) or the monodentate diethylsulfide (Et(2)S), in acetonitrile (AN) at 298.15 K, were studied by a systematic methodology including potentiometry, calorimetry and polarography. [9]AneS3 is able to form complexes with all the target cations, Et(2)S only reacts with Hg(2+) and Ag(+). Mononuclear ML(j) (j = 1, 2) complexes are formed with all the metal ions investigated, where the affinity order is Hg(2+)Ag(+)Cd(2+) ≈ Zn(2+) when L = [9]AneS3 and Hg(2+)Ag(+) when L = Et(2)S. Enthalpy and entropy values are generally negative, as a consequence of both metal ion interactions with neutral ligands, the reagents' loss of degrees of freedom and the release of solvating molecules. DFT calculations on the complexes formed with [9]AneS3 in vacuum and in AN are also carried out, to correlate experimental and theoretical thermodynamic values and to highlight the interplay between the direct metal-thioether interaction and the solvation effects. Trends obtained for the stability constants and enthalpies of the 1 : 1 and 1 : 2 complexes in solvent well reproduce the experimental ones for all the divalent metal ion complexes with [9]AneS3 and indicate the release of 3 AN molecules in the formation of each consecutive octahedral complex. In addition, calculated and experimental values for Ag(+) complex formation in solution suggest that in AgL(2) species [9]AneS3 ligands are not both tridentate.

A new series of inorganic and organometallic cobalt Schiff base complexes containing the tetradentate ligand {[Z-Tyr(3-Ac)-OMe] 2 en} derived from the condensation of two equivalents of protected 3-acetyl- l -tyrosine with one equivalent of ethylenediamine has been synthesized. As the amino acids have l configuration, the resulting ligand is chiral. The complexes have been characterized by 1 H and 13 C NMR, ESI-MS spectrometry and UV–Vis spectroscopy. The UV–Vis spectra recorded in CH 2 Cl 2 show an absorption band at about 650 nm, characteristic of penta-coordinated alkylcobalt(III)(salen), but an evident deviation from the Lambert Beer law in the concentration range 0.20–2.0 × 10 −3 M suggests some kind of association in this solvent. In coordinating solvent the complexes are hexa-coordinated. The equilibrium constants for pyridine ligation in CH 3 OH decrease with increasing electron-donor power of the axial alkyl group. Cyclic voltammetry studies indicate that after the reduction RCo(III)/RCo(II), the complexes decompose giving a Co(I) species that is stable on the CV time scale and can be reoxidized to Co(II) and Co(III) species. Both the E pa and the E pc values show that the peak potentials are shifted to more negative values with increasing inductive effect of the axial alkyl group.

The electrochemical behaviour of 4,6-dimethyl-2-thiopyrimidine (LH) and 4,6-dimethyl-1-phenyl-2-thiopyrimidine (LΦ) and their protonated forms was investigated in dimethylformamide on Hg electrodes. Adsorption processes affect the oxidation mechanism of both the compounds and the formation of Hg(I) complexes was observed. The electrochemical reduction of LH provides an example of the so-called “father—son reaction” but this kind of mechanism cannot occur with LΦ. Only in the species LH is a proton present which can be abstracted by the product of the first electron transfer LH · − while LΦ can be protonated by the solvent. However, in the presence of strong acids, for both molecules LH and LΦ the formation of the dimer from the radical anion obtained in the first electron transfer is kinetically preferred to the father—son reaction.

Unfolding turns immobilized cytochrome c into a His-His ligated form endowed with catalytic activity towards O(2), which is absent in the native protein. Dioxygen could be used by naturally occurring unfolded cytochrome c as a substrate for the production of partially reduced oxygen species (PROS) contributing to the cell oxidative stress.

The electron transfer (ET) process of progressively unfolded bovine cytochrome c immobilized on different self-assembled monolayers (SAMs) was investigated. Insight is gained on the role of the SAM surface on the functionality of the partially unfolded and non-native forms of the adsorbed protein. Direct electrochemical measurements were performed on cytochrome c adsorbed on mercaptopyridine (MP) and mixed 11-mercapto-1-undecanoic acid/11-mercapto-1-undecanol (MUA/MU) at varying temperature, in the presence of urea as unfolding agent. Under strongly unfolding conditions, a non-native form of cytochrome c , in which the methionine ligand is replaced by a histidine, was observed on both MP and MUA/MU SAMs. The E °′ of the native form, in which the haem is axially coordinated by methionine and histidine, slightly shifts to negative values upon increasing urea concentration. However, the non-native bis-histidinate species shows a much lower E °′ value (by approximately 0.4 V) which is by far enthalpic in origin and largely determined by axial ligand swapping. Analysis of the reduction enthalpies and entropies and of the ET rate constants indicate that the nature of the SAM (hydrophilic or anionic) results in changes in the conformational rearrangement of the cytochrome c under unfolding conditions.

We described the guest-induced synthesis of a rectangular host derived from methylaquacobaloxime CH3Co(dmgH)2H2O and 4,4′-biphenyldiboronic acid containing 4,4′-bipyridine (bipy) molecule as guest. The assembly, monitored by a time dependent 1H NMR experiment, showed that the guest thermodynamically drives the organization of the host. The structural characterization of the complex evidenced a centrosymmetric rectangular box having two biphenyldiboronate units and a central 4,4′-bipyridine spacer connecting the cobaloxime units (1). The spacers have coplanar rings, being negligible the tilt angle around the central C–C bond. The molecular structure of 1 and of the dinuclear complex [CH3Co(dmgH)2]2(bipy) indicates close comparable intermetallic distance for the rigid bipy bridge and a coplanar arrangement of the cobaloxime moieties that facilitates the formation of the molecular box. The other tested ditopic ligands L (α,α′-diamino-p-xylene and 1,6-diaminohexane) used in this study allowed only a partial assembly. These derivatives and the related dinuclear complexes [CH3Co(dmgH)2]2(L), which were synthesized with the aim to obtain further insights about the formation of the molecular boxes, were also characterized by X-ray structural analysis. The structures of [CH3Co(dmgH)2]2(L), beside the expected flexibility of L, indicate not facing cobaloxime moieties. CV measurements suggest the formation of dinuclear non organometallic Co(II) and Co(I) species after the first reduction for all the dinuclear compounds that are stable in solution. For 1 no electronic coupling is shown, in spite of coplanar conformation of the 4,4′-bipyridine rings.

We have studied the effect of urea-induced unfolding on the electron transfer process of yeast iso-1-cytochrome c and its mutant K72AK73AK79A adsorbed on electrodes coated by mixed 11-mercapto-1-undecanoic acid/11-mercapto-1-undecanol self-assembled monolayers. Electrochemical measurements, complemented by surface enhanced resonance Raman studies, indicate two distinct states of the adsorbed proteins that mainly differ with respect to the ligation pattern of the haem. The native state, in which the haem is axially coordinated by Met80 and His18, displays a reduction potential that slightly shifts to negative values with increasing urea concentration. At urea concentrations higher than 6 M, a second state prevails in which the Met80 ligand is replaced by an additional histidine residue. This structural change in the haem pocket is associated with an approximately 0.4 V shift of the reduction potential to negative values. These two states were found for both the wild-type protein and the mutant in which lysine residues 72, 73 and 79 had been substituted by alanines. The analysis of the reduction potentials, the reaction enthalpies and entropies as well as the rate constants indicates that these three lysine residues have an important effect on stabilising the protein structure in the adsorbed state and facilitating the electron transfer dynamics. © 2010 SBIC.

The thermodynamics of the electron transfer (ET) process for beef heart and yeast cytochromes c and the Lys72Ala/Lys73Ala/Lys79Ala mutant of the latter species subjected to progressive urea-induced unfolding was determined electrochemically. The results indicate the presence of at least three protein forms which were assigned to a low-temperature and a high-temperature His-Met intermediate species and a bis-histidinate form (although the presence of a His-Lys form cannot be excluded). The much lower E°' value of the bis-histidinate conformer as compared to His-Met ligated species is largely determined by the enthalpic contribution induced by axial ligand substitution. The biphasic E°' versus T profile for the His-Met species is due to a difference in reduction entropy between the conformers at low and high temperatures. Enthalpy-entropy compensation phenomena for the reduction reaction at varying urea concentration for all the forms of the investigated cytochromes c were addressed and discussed. © 2009 Springer Science+Business Media B.V.

The interaction between molecular oxygen and the metal atom in two Co(II) complexes with bis(diacetylmonoxime-imino)propane-1,3 ( A ) and with the related ligand obtained from cobaloxime by substitution of both the O-H ⋯ O bridges with the -BF 2 -group ( B ) is investigated using electrochemical and spectroelectrochemical techniques. Notwithstanding the stability of the Co(II) complex B in air, the results suggest the formation of a dioxygen adduct as an unstable intermediate in the electrocatalytic reduction of molecular oxygen in the presence of either A or B . Furthermore, the oxygenation ratio at a given p O 2 appears to be quite different for the homogeneous reaction of A in the Co(II) oxidation state in bulk as compared with either the electrogenerated Co(II) (from complex A ) on the electrode surface or the Co(II) complex B .

The results of an investigation of the electrochemical behaviour in dimethyl sulphoxide (DMSO) and aqueous solution of the two new halogen-DMSO complexes Na[ trans -RuCl 4 (DMSO) 2 ] (I) and mer -RuCl 3 (DMSO) 3 (II) are presented. Both complexes give trans -RuCl 2 (DMSO) 4 upon bulk one-electron reduction of their DMSO solutions. In DMSO solution, complex II equilibrates with a less easily reducible isomer differing in the mode of binding of one DMSO ligand. This equilibrium, together with the homogeneous chemical reactions following the heterogeneous mono-electronic reduction of II, was estimated quantitatively by means of cyclic voltammetry. Cyclic voltammetry of I in aqueous medium shows the occurrence of an H 2 O/DMSO exchange reaction following its one-electron reduction at a Pt microelectrode. The complete scheme of the reactions which characterize the bulk electrolysis behaviour of the two complexes in aqueous medium is also reported.

In four series of strictly related organocobalt complexes, derived from cobaloximes by replacement of the O…H…O with O…-BF2…O and/or (CH2)3 groups, the trends of 59Co-NMR shielding and electrochemical data are discussed. A largely parallel behaviour of the plots of E1/2(I) values for the first Co(III)/Co(II) electron transfer vs. the 59Co chemical shifts reflects the similar sensitivity of the two parameters to a change in electron affinity of the central metal ion due to a variation of the organic group R. E1/2(II) values for the second Co(II)/CO(I) electron transfer are less sensitive to the change of R, but the trend of the plot vs. δ(59Co) is still parallel in the four series. Consistent deviations from a roughly linear dependence of E1/2(I) on pKa of the hydrocarbon acid corresponding to R, on Taft constant s* and on 59Co shielding are noticed for the isopropyl derivatives and attributed to a steric effect. This was confirmed in a series of RCo(DMG)pyridine complexes in which 59Co shielding decreases steadily with increasing steric parameter Es (Taft) of the alkyl group. There is experimental evidence from X-ray data that δ(59Co) decreases with an increase of the CoC bond length, illustrating steric hindrance in alkyl coordination to be responsible for the decreased shielding of the 59Co nucleus. The relative displacements of the graphic displays for the different series reflect the effect of changes in electron affinity of the redox center, due to the equatorial ligand, which, in turn, is caused by variations in the electron-withdrawing power due to the introduction of the BF2 group and by the change from −2 to −1 valence of the (CH2)3-capped ligands.

Recently LaNi1–xFexO3 materials have been indicated as good candidates for cathodes for intermediate temperature solid oxide fuel cells (IT-SOFCs), and LaNi0.6Fe0.4O3 (LNF) showed the highest specific conductivity in the LaNi1–xFexO3 series. Here we report the results of our investigation on the performances of LNF, synthesized by the coprecipitation method. A detailed local structure analysis, performed using X-ray absorption near edge spectroscopy (XANES ) and extended X-ray absorption fine structure (EXAFS) techniques, indicated that both Fe and Ni are in the (III) oxidation state with coordination numbers of ∼6, suggesting the absence of appreciable amount of oxygen vacancies. The fresh LNF material was used as a precursor for LNF–YSZ (yttria-stabilized zirconia) and LNF–SDC (samaria-doped ceria) electrodes. In the case of the LNF–YSZ nanocomposite, even a short (5 h) treatment at 1000 °C induced a strong reaction between the cathode components, leading to the formation of an undesirable La2Zr2O7 insu...

Recently LaNi 1− x Fe x O 3 materials have been suggested as good candidates for cathodes for Intermediate Temperature Solid Oxide Fuel Cells. The electrical conductivity and the morphology of LaNi 0.6 Fe 0.4 O 3 samples have been studied as a function of preparation route and calcination temperature. The conductivity, mainly electronic, strongly depends on the densification of the material, which is influenced by the preparation procedure. DFT calculations indicate that the conduction bands of LaNi 0.6 Fe 0.4 O 3 are mainly made up of Fe and Ni 3d states and that there is a small bandwidth (2.3 eV) around the Fermi level. Moreover, a small polaron mechanism for the electronic conduction in this material is suggested by the simulations. Three different preparation methods have been investigated: the glycine–nitrate process, the gel–citrate complexation route and the coprecipitation route. The glycine–nitrate synthesis produces non-homogenous LaNi 0.6 Fe 0.4 O 3 materials. Good specific conductivity is obtained only after high temperature treatments that homogenise and sinter the material. The gel–citrate complexation route leads to homogenous LaNi 0.6 Fe 0.4 O 3 samples, which however are resistant to sinterization/densification. Finally, homogenous LaNi 0.6 Fe 0.4 O 3 is obtained with coprecipitation synthesis. This synthesis is particularly promising since the morphology of the obtained precipitate favours the sinterization at low temperatures. These temperatures are low enough to prevent the undesirable reaction with ZrO 2 -based electrolyte.

The formation of Cd(II) and Co(II) complexes with N-methylethylenediamine (men) has been studied at 298 K in dimethylsulfoxide (dmso) in an ionic medium set to 0.1 mol dm−3 with Et4NClO4 in anaerobic conditions by means of potentiometric, UV–Vis, calorimetric and FT-IR technique. Mononuclear MLj (M=Cd, Co; j=1–3) complexes are formed in exothermic reactions, whereas the entropy changes oppose the complexes formation. The results are discussed in terms of different basicities and steric requirements and the whole of the thermodynamic data reported till now for the two ions with a number of diamines are summarized to visualize the selectivity of the ligands. The dioxygen uptake of Co(men)2 species has also been studied by means of UV–Vis and EPR techniques. The kinetic parameters and stability constants obtained for the formation of the superoxo and μ-peroxo species are discussed in terms of solvent effect and steric hindrance due to methyl group. Cyclic voltammetry was used to confirm the stability constant for the Co(dmen)2 (dmen=N,N′-dimethylethylenediamine) superoxo adduct formation but was not successful to investigate this Co(men)2–O2 system.

The electrochemical reduction of a series of thio- and oxopyrimidine derivatives has been investigated in organic solvents on mercury electrodes. In all cases the electrochemical process gave a dimeric species as the major product. The overall reduction mechanism is the same for oxo and thio derivatives, and is found to be dependent only on the nature of the ring nitrogen substituent. A ‘father–son reaction’ is observed when hydrogen is bound to the ring nitrogen atom: the radical anion obtained from the first electron transfer draws out the nitrogen proton of a non-reduced molecule and this then dimerizes. In the presence of a protonating agent as well as for the N-substituted derivatives, the ‘father–son reaction’ is not observed. Theoretical calculations have been performed to gain insight into the proposed mechanisms: the LUMO energy and the vertical electron affinity show a linear correlation with the reduction potentials. Analysis of the theoretical parameters has allowed step-by-step determination of the electrochemical reduction process. The manner in which solvent properties influence electrochemical behaviour has been examined, and the role of the acceptor number (AN) has been discussed.

The electrochemistry of dioxygen reduction in the presence of a model molecule of biological significance, 4,6-dimethyl-2-thiopyrimidine (LH) was studied in dimethylformamide at a glassy carbon (GC) electrode. The first, mono-electronic, reduction step took place under kinetic control of charge transfer or of the following chemical reactions, or both, depending on the time scale of the experiment, leading to a complicated pattern of events. A father–son reaction step and other cross protonation reactions could explain the detailed results obtained from the electrochemical investigation. The involvement of LH in the dioxygen reduction path was indicated by the presence of a new cathodic peak in cyclic voltammetry, which did not pertain to the voltammetric behavior of either species, and was shifted by ca. 70 mV from that due to the O 2 /O 2 − reduction in the absence of LH. The experimental results could be consistently interpreted by assigning the new peak to the O 2 /O 2 − coupled with a fast protonation of O 2 − by LH, and explaining the amount of the displacement by the rate of the protonation reaction.

The electrochemical behavior of dioxygen in the presence of adenine in dimethylformamide solution on the Hg electrode is studied. Evidence for the activation of O 2 is given by the shift of 150 mV towards more positive values of the one-electron reduction, accompanied by the autooxidation of adenine, while the adsorption of O 2 is shown by the characteristics of a polarographic pre-wave and voltammetric peak. The activation of O 2 is attributed to the interaction with adenine co-adsorbed on the Hg electrode.

Polarographic and voltammetric evidences are reported for the production of intermediates superoxo [Rh]OO and hydroperoxo [Rh]OOH derivatives at the electrode surface, in the reduction of dioxygen in the presence of rhodium bis(dimethylglyoximato) chloro triphenylphosphine, [ClRh(III)(DMG)2(PPh3)] (I), in the absence and in the presence of protons in non-aqueous solvents. In the latter case the electrocatalytic reduction of dioxygen is observed. From the trends of the concentrations of dioxygen vs the rhodium complexes, a mechanism for the electrochemical process is proposed. The molar ratio of dioxygen to the rhodium complex when the latter is completely consumed for the formation of the adduct, as compared with the 1:1 stoichiometric ratio determined by the Hill plot, together with the influence of the electrode material, suggests that the reduction of dioxygen involves adsorbed species.

Rh(Hdmg)2(PPh3)Cl (Hdmg=monoanion of dimethylglyoxime) undergoes reduction with zinc amalgam to give the tetranuclear bimetallic compound [Rh(Hdmg)(ClZndmg)(PPh3)]2, characterized by elemental analysis, electronic, IR and NMR spectroscopy and X-ray crystallography. It crystallizes in the triclinic space group P1 with: a=14.262(4), b=14.675(4), c=14.698(4) A, α=82.15(4), β=87.57(4), γ=65.89(3)°, Z=2. The structure was refined up to R=0.13 for 4704 reflections. The molecule consists of two [Rh(dmg)(Hdmg)(PPh3)] subunits linked by an [Rh(II)(II)] bond of length equal to 2.852(3) A and by two Zn ions bridging the oxygens of the equatorial ligands. The binding with zinc relieves the equivalence among the atoms of each subunit.

Publisher Summary Transition metal complexes are widely used as models, either of oxygen carriers or of catalysts for biological and industrial oxidations. The key factors determining the oxygen carrying or the catalytic properties are the thermodynamic and kinetic features of the reaction of molecular oxygen with the metal center, which, in the case of oxygen carriers yields a relatively stable oxygen adduct, while, in the case of catalytic oxidations, the actual mechanism and the nature of the interaction between molecular oxygen and the metal center in a transition metal complex are much more elusive. This interaction is the key step also in the electrocatalytic reduction of molecular oxygen in the presence o f transition metals or transition metal complexes, taking place in the bulk of the solution or at the electrode surface, respectively. Catalytic efficiency, though demanding high reactivity of the product of the interaction between molecular oxygen and the transition metal complex, obviously does not require substantial amounts of this product which is actually the very reactive intermediate. The problem thus is to provide evidence for the coupling of the reduction of the transition metal complex with the reaction with molecular oxygen, yielding the active intermediate, and for possible formation of an unstable oxygen adduct, undergoing fast reactions.

This paper clarifies the adsorption mechanism of 1-[(2S)-3-mercapto-2-methyl-1-oxopropyl]-L-proline (CPT) on DME. Some characteristic features of CPT adsorption, previously followed by cyclic voltammetry (CV), have been investigated to give more precise information about some electrochemical constants by alternating current polarography (ACP). The first harmonic ACP was considered a suitable tool for obtaining electrochemical parameters of surface-confined reactions. The entity and sign of the molecular interaction parameter (g), the thermodynamic constant of adsorption (Kads), the extrapolated apparent electron rate constant (Kextsh), the saturation concentration (Co), maximum surface density (Γt)etc. have been determined. The values of some of these electrochemical parameters, found in a previous paper, were confirmed.

Heterogeneous electron transfer rate constants were determined as a function of electrode potential for one-electron oxidation in acetonitrile (AN) at O °C of a series of organocobaloximes [R-Co(DH)2L] bearing widely different organic groups. Reaction entropies were determined by voltammetric half-wave potential (Er 1 2 ) measurements in a non-isothermal cell. The electron transfer coefficients and reorganization parameters were calculated following the Marcus theory. The reaction free energies relative to a reference couple ΔG∘ are linearly correlated with the polar Taft constant of the organic substituent R. The steric effects on ΔG∘ are shown by the correlation of Er sol1 2 with the CoC bond distance. Assuming constancy of double layer effects along the series in the given solution composition, the trends of the apparent rate constants kapp were considered in order to evaluate the effects of the nature of the organic ligand on the activation energy ΔG‡ of the electron transfer. The steric effects on ΔG‡ are pointed out i.a. by consideration of the relationship between ΔG‡ and ΔG∘.

The electrochemical reduction of alkylcobaloximes at the dropping mercury electrode involves an initial one electron transfer process to give a radical anion with the cobalt in the CoII formal oxidation state. The CoC bond cleavage in the radical anion is an homolytic process yielding the CoI cobaloxime and competing with a second electron transfer. The nature of the organic group and of the solvent coordinated in the trans position to the Co atom influences the thermodynamics of the electron transfer and the stability of the radical anion. Electronic and steric effects on the thermodynamics of the first electron transfer can be distinguished. These effects have only a small influence on the kinetics of the first electron transfer.