Fethi Bedioui

Zeolite-encapsulated and clay-intercalated metal porphyrin, phthalocyanine and Schiff-base complexes as models for biomimetic oxidation catalysts: an overview

Abstract This paper reviews some important recent work on the design and characterization of zeolite-encapsulated and clay-intercalated metal-Schiff base, -porphyrin and-phthalocyanine complexes. After an introduction to the chemistry of clays and zeolites, the incorporation methods of these complexes within the mineral materials are discussed and an overview of their physicochemical characterization is reported. A large part of this paper is devoted to the reactivity of the zeolite- and clay-encapsulated complexes in biomimetic oxidation reactions.

N4-Macrocyclic Metal Complexes

Billion-Year-Old Oxygen Cathode that Actually Works: Respiratory Oxygen Reduction and Its Biomimetic Analogs.- Fundamental Aspects on the Catalytic Activity of Metallomacrocyclics for the Electrochemical Reduction of O2.- Oxygen Reduction in PEM Fuel Cell Conditions: Heat-Treated Non-Precious Metal-N4 Macrocycles and Beyond.- Biomimetic NOx Reductions by Heme Models and Proteins.- Electroreduction of CO2 Catalyzed by Metallomacrocyclics.- Supramolecular Porphyrins as Electrocatalysts.- Electrodes Modified with Monomeric M-N4 Catalysts for the Detection of Environmentally Important Molecules.- Electropolymerized Metalloporphyrin Metallophthalocyanine and Metal Schiff Base Complex Films: Applications to Biomimetic Electrocatalysis and Bioelectroanalysis.- Electron Transfer Processes of ?-Pyrrole Brominated Porphyrins: Structural vs. Electronic Effects.- Photoelectrochemical Reactions at Phthalocyanine Electrodes.- Organisation and Photoelectrochemical Reactivity of Water-Soluble Metalloporphyrins at the Liquid/Liquid Interface.- Theoretical Insights on the Chemical Reactivity of Metalloporphyrins Using Density Functional Theory.- Organized Multiporphyrinic Assemblies for Photoconduction and Electroconduction.- Vibrational Spectra and Surface-Enhanced Vibrational Spectra of Azamacrocycles.

Electrocatalytic oxidation of nitrite on a vitreous carbon electrode modified with cobalt phthalocyanine

The oxidation of nitrite on a vitreous carbon electrode modified with different surface concentrations of cobalt phthalocyanine (CoPc) was investigated using cyclic voltammetry and rotating disk electrode techniques. The voltammetric curves show well-defined anodic peak, which is indicative of the electrocatalytic oxidation of nitrite. The activity of the modified electrodes does not increase with the amount of CoPc adsorbed on the electrode in a wide range of surface coverages and the order of the electro-oxidation reaction is one in nitrite. Tafel plots obtained from rotating disk measurements give two linear regions of slopes of 0.071 and 0.14 V/decade, respectively. This was discussed in terms of a catalytic process and a mechanism is proposed.

Electro-oxidation of 2-mercaptoethanol on adsorbed monomeric and electropolymerized cobalt tetra-aminophthalocyanine films. Effect of film thickness

Abstract We have investigated the electrocatalytic activity of cobalt tetra-aminophthalocyanine (CoTAPc) for the one-electron oxidation of 2-mercaptoethanol (2-ME) using adsorbed monomeric CoTAPc and electropolymerized poly-CoTAPc films of different thickness on vitreous carbon electrode. Our results show that the activity of poly-CoTAPc increases slightly with the thickness of the film, while the activity of the adsorbed monomeric CoTAPc is still greatest. The trend in activities, analysed by cyclic voltammetry, is the same for the electro-oxidation of 2-ME and for the electroreduction of the corresponding disulphide. Tafel plots obtained from rotating disk measurement for adsorbed CoTAPc and poly-CoTAPc film modified electrodes show slopes close to RT/F (ca. 70 mV) at low polarisation potentials which increase gradually with potential to values close to 2RT/F (120 mV). This suggests that at low polarisation the rate-determining step is a chemical step (formation of a metal complex–thiol adduct) preceded by a fast electron-transfer step involving the CoTAPc. At higher polarisations the one electron oxidation of the adduct to give the thiyl radical becomes rate controlling. Even though monomeric CoTAPc adsorbed on glassy carbon presents higher activity for the electro-oxidation of 2-ME, the high stability of the electropolymerized poly-CoTAPc makes them more attractive for applications in the activation and/or the amperometric detection of thiols.

Oxidations catalyzed by zeolite ship-in-a-bottle complexes

Abstract A brief review of oxidation reactions catalyzed by zeolite ship-in-a-bottle complexes is presented. The encapsulation of V(O)SALEN (SALEN= bis(salicylaldehyde)ethylenediimine) in zeolite NaY via the flexible ligand method is described. V(O)SALEN-NaY was found to be an effective catalyst for the room temperature epoxidation of cyclohexene using t -butylhydroperoxide ( t -BOOH) as the oxidant. The preparation of zeolite NaX in the presence of RuF 16 Pc (F 16 Pc= perfluorophthalocyanine) also results in occluded metal complex. RuF 16 Pc-NaX has been shown to be an active catalyst for the room temperature oxidation of alkanes using t -BOOH as the oxidant.

Electrochemical nitric oxide microsensors: sensitivity and selectivity characterisation

In this study, we have prepared two nitric oxide (NO) microsensors using two combinations of nickel tetrasulfonated phthalocyanine (NiTSPc), o-phenylenediamine (o-PD) and Nafion® based layers to modify the surface of 8 μm diameter carbon fiber electrodes. We have compared the performances of the obtained composite microsensors (carbon/NiTSPc/Nafion®, and carbon/Nafion®/o-PD, respectively) in our home made operating conditions. We have developed the sessile drop contact angle measurement technique as well as the use of the electrochemical quartz crystal microbalance (EQCM), differential normal pulse voltammetry (DNPV) and differential normal pulse amperometry (DNPA) to correlate the hydrophobicity, mass deposit of the polymer coatings and the sensitivity of the examined microsensors. By comparing the permeability of the microsensors to various interfering analytes, such as L-arginine, ascorbate, nitrite, serotonine, dopamine, acetamidophenol, 4-met-catechol, epinephrine, norepinephrine, dopac and 5-hydroxyindol, we have discussed the molecular sieving exclusion of the deposited membranes in term of molecular weight cutoff (MWCO).

Nitric oxide production by endothelial cells: Comparison of three methods of quantification

Vascular endothelial cells have been found to produce a relaxant mediator, identified as nitric oxide (NO) and implicated in numerous physiological functions. Subsequently, there has been an intensive search for accurate and specific detection methods to measure biological NO production. In the present study, we compared three approaches to evaluate NO production, based respectively on the Griess reaction (that quantifies nitrites and nitrates after their reduction), on the hemoglobin reaction (that quantifies oxyhemoglobin to methemoglobin transformation by NO), and on the electrochemical NO detection with a porphyrinic micro-probe. Comparison was made both under standard conditions and biological conditions, through calibration curves and measurements of histamine-induced NO production by cultured human endothelial cells and its modulation by L-arginine and N(omega)-monomethyl-L-arginine. We demonstrated that these three methods differ in terms of sensitivity and selectivity. The hemoglobin reaction and nitrate measurements suffer from a lack of specificity. Nitrite determination by the Griess reaction was hardly suitable for kinetic studies but it remains useful for the evaluation of basal NO production. The electrochemical technique, although it does not allow measurement of basal NO production, is the only one to exhibit great sensitivity and specificity and to allow instantaneous and non destructive measurements. This study brings up the potential hazards and pitfalls that may be associated with the various methods.

Elaboration and use of nickel planar macrocyclic complex-based sensors for the direct electrochemical measurement of nitric oxide in biological media.

We describe here the electrochemical detection of nitric oxide, NO, in biological systems by using chemically modified ultramicro carbon electrodes. In the first part of the paper, the different steps involved in the electrochemical preparation and characterization of the nickel-based sensor are described. This is illustrated by the use of nickel(II) tetrasulfonated phthalocyanine complex. The second part of the paper describes two examples of the direct electrochemical measurement of NO production in human blood platelets and endothelial cells from umbilical cord vein.

The use of gold electrodes in the electrochemical detection of nitric oxide in aqueous solution

It was recently discovered that vascular endothelial cells could synthesize the free-radical gas nitric oxide (NO) [1,2] and since that discovery, it has been possible to demonstrate the considerable physiological importance of NO as for example in the control of human blood flow and pressure. Several works are now dealing with the understanding of the mechanism by which NO is synthesized [3]. As a matter of fact, it has appeared that measuring NO in biological models is very difficult because of its low stability and high fugacity. In a recent review Archer [4] has summarized the different NO measurement strategies reported in the literature. The most widely used techniques involve the ex-situ detection of NO by (i) electron paramagnetic resonance, (ii) spectrophotometry and (iii) chemiluminescence. New amperometric microelectrode probes are now developed to detect NO and the use of electrochemistry, as a potential way to do so is very promising. Indeed, ultramicroelectrode design and elaboration are now reaching very high levels of sophistication [5] contributing very actively to the promotion of the use of the electrochemical techniques for in vivo NO detection in intact tissues and from single cells. There are two amperometric methods reported in the literature for measuring NO in vitro and from tissues and single cells. The first method is based on the direct oxidation of NO on platinum electrode. Shibuki [6] reported the detection of NO by using a miniature Clark-type electrode. The electrode was designed by introducing a platinum wire within a pipette with a fire-polished 150-250 pm tip (with a thin chloroprene rubber seal) filled with an aqueous solution of 30 mM NaCl and 0.3 mM HCI. The platinum indicator electrode was placed as close as possible to

Electrochemistry of conducting polypyrrole films containing cobalt porphyrin: Part 2. New developments and inclusion of metallic aggregates in the coordination polymer

The electrochemical polymerization of a pyrrole-substituted cobalt porphyrin complex (i.e. 5-(3-(4-(1-pyrrolyl)butyl)phenoxy)-10,15,20-tritolylporphine cobalt) has been performed in acetonitrile + tetrabutylammonium tetrafluoroborate solution. The redox properties of the film were examined by cyclic voltammetry and chronoamperometry. The voltammograms of these films exhibited a reversible process for the Co(II)/Co(I) reaction at a formal potential of −0.90 V (vs. SCE). Using chronoamperometry, quantitative analysis of the curves allowed us to extract the diffusion coefficient D for the Co(II)/Co(I) step of the cobalt porphyrin film, D = 1.46×10−11cm2 s−1. The cobalt porphyrin content was estimated by cyclic voltammetry, and this shows that thick polymers act as insulators in the low potential range E < −1 V (vs. SCE). Electroreductive inclusion of Pt and Ag aggregates in these coordination polymers from K2PtCl4, H2PtCl6 and AgClO4 solutions was concluded. Evidence that metallic particles were included in the polymer films was provided by scanning electron microscopy coupled with X-ray fluorescence analysis.