Danièle Limosin

Poly(pyrrole-manganese porphyrin): A catalytic electrode material as a model system for olefin epoxidation and drug metabolism with molecular oxygen

Abstract The oxidative electropolymerization of three pyrrole-substituted manganese tetraphenylporphyrins can be used to coat Pt or C electrodes with polymeric films able to catalyse the epoxidation of cyclo-octene and stilbene with molecular oxygen. Cross-linked polymers prepared from monomers containing two or three pyrrole groups, and thus having a better polymerizability, present a lower activity than the polymeric films synthesized from the monomer containing only one pyrrole moiety. Confinement of the catalyst on the electrode surface markedly improves its stability compared with that of homogeneous electrocatalytic systems. This catalytic electrode material has been successfully applied to the preparation of oxidized metabolites of a drug.

Poly(pyrrole-metallotetraphenylporphyrin)-modified electrodes: Part 2

Abstract The preparation of poly(pyrrole-metallotetraphenylporphyrin) films (metal = Ni(II), Zn(II), Co(II) and Cu(II)) has been achieved in CH 2 Cl 2 + 0.1 M BU 4 NClO 4 (TBAP) by anodic electropolymerization of the corresponding monomers in which the macrocycle is linked to a pyrrole group by an alkyl chain. The redox properties of these modified electrodes have been investigated by cyclic voltammetry. Their voltammograms display the regular electroactivity of the porphyrin derivatives; however, the reversible slow process Co(II)/Co(III) is exhibited only at a low sweep rate (ν = 0.005 V s −1 . The free porphyrin base cannot be electropolymerized even in acidic conditions.

Electro-oxidative oligomerization of 1,5-diaminonaphthalene in acetonitrile medium

Abstract New electroactive oligomer films of 1,5-diaminonaphthalene have been prepared on platinum and carbon graphite electrodes in acetonitrile solution by potential sweep electrolysis and controlled potential electrolysis. The films were electroactive in aqueous acidic solutions with a formal redox potential of ca. 0.33 V vs. SCE in 1 M HCl solution. Cyclic voltammetry, controlled potential electrolysis, SEM, FT-IR spectroscopy, 1 H NMR, conductivity measurements and gel permeation chromatography were used to characterize the oligomeric film.

Complexes of ligands providing endogenous bridges. Part 4. Copper(II) complexes of macrocyclic Schiff bases derived from 2,6-diacetylpyridine and 1,n-diamino-n′-hydroxyalkanes (n,n′= 3,2; 4,2; and 5,3): synthesis, properties, and structures

The synthesis, physicochemical properties, and X-ray crystal and molecular structures of three dinuclear copper (II)complexes of tetraimine Schiff-base macrocycles derived from 2,6-diacetylpyridine and 1,n-diamino-n′-hydroxyalkanes (n,n′= 3,2; 4,2; and 5,3) are reported. The complex derived from a 20-membered macrocycle has present a single endogenous alkoxy bridge and so can serve as a speculative model for the dicopper(II) site in oxyhaemocyanin. As the ring size is increased this bridge is lost and is replaced by an unusually short hydrogen bond between the protonated and deprotonated hydroxyl groups.

Monoelectronic reduction of 1-alkyl-3,5-di(alkylcarbamoyl)pyridinium ions as a model of the NAD+/ NADH system : obtaining 1,4-dihydropyridines

In an aqueous medium the compounds studied have the same electrochemical properties as the biological ion NAD+, and are reducible on several electrode materials. On mercury, at −1.1 V vs. SCE, a potential which corresponds to the first monoelectronic charge transfer, dimers are obtained as major products. On platinum in the same conditions, 1,4-dihydropyridine is formed preferentially. In this case, the analysis of voltamperometric curves and the products of macroscale electrolyses at various concentrations seem to corroborate the interference of a chemical reaction between radical adsorbed species and hydrogen atoms.

Heteroditopic ligands containing a 2,2 ′ -bipyridine and a 2,2 ′ :6 ′ ,2″ -Terpyridine moiety and their ruthenium tris(bipyridine)-like complexes

Abstract Two novel heteroditopic ligands in which the bidentate 2,2 ′ -bipyridine (bpy) ligand is covalently linked to one or two 2,2 ′ :6 ′ ,2″-terpyridine (terpy) terdentate ligands have been prepared and characterized. The synthesis and the physico-chemical features of their corresponding complexes in which the bpy site is complexed by a ruthenium moiety are also reported.

Electrochemical behaviour of 1-alkyl-3,5-di(alkylcarbamoyl)pyridinium ions as a model of the NAD+/NADH system in aqueous solution

Abstract Electrochemical studies of the title compounds show that these two series may be considered as models of the NAD + /NADH system. The pyridinium salts are reducible in two mono-electronic waves, with half-wave potentials at about −0.65 and −1.4 V/SCE. The reduction of N -benzyl compounds leads to the formation of dimers when the electrolyses are carried out on mercury at −1 V, and of dihydroderivatives at −1.7 V. On the other hand, reduction of N -methyl compounds on a platinum electrode at −1 V gave the dihydroderivatives directly, which is in accordance with the existence of a disproportionation equilibrium. In either case the yield in hydrogenated compound may reach 95 to 100%.

Structural and electrochemical studies of dicopper complexes of a binucleating ligand involving sulfides and benzimidazoles

Abstract The reaction of malondialdehyde with mercaptoacetic acid furnishes a tetraacid which upon condensation with 1,2-diaminobenzene gives the tetrathioethertetrabenzimidazole binucleating ligand (L). One copper(I) and three copper(II) complexes of this ligand have been isolated. The latter are not stable in solution where they are reduced by the solvent or the ligand itself. An investigation of the structures of the compounds by EXAFS and XANES techniques has shown that in the copper(I) complex the metal is in an N 2 S environment of T-shaped geometry. The copper(II) derivatives are square pyramidal and there is no sulfur atom in the tetragonal plane. This situation is in agreement with the absence of magnetic interaction between the two copper(II) ions in the oxidized compounds. All complexes exchange electrons at high potentials of the Cu(I)/Cu(II) couple in the range 0.2–0.6 V sec .

STRUCTURE OF THE DIMERS OBTAINED FROM THE REDUCTION OF 1-BENZYL-3,5-BIS(DIALKYLCARBAMOYL)PYRIDINIUM IONS : MODELS OF NAD

In aqueous media the one-electron reduction of the title compounds on a mercury pool generally gives rise to three dimers, which are distinguishable by HPL chromatography. From spectroscopic analyses it has been possible to propose a structure for these conformers and their stability has been studied. Two conformers are unstable, yielding the third conformer. A mechanism is proposed for this transformation.

Dicopper complexes of a new binucleating ligand involving sulphides and benzimidazoles

The new binucleating ligand (1) is able to achieve high stabilization of the copper(I) ion and to mediate interaction between the two copper sites; this leads to the isolation of dicopper(II), mixed-valence, and dicopper(I) derivatives depending on reaction conditions.