Doris Lexa

Characterization of the reduction steps of Fe(III) porphyrins

Abstract Polarographic studies have shown that Fe(III) porphyrins undergo successively three one-electron reduction steps in dimethylformamide. The first involves the Fe(III)/Fe(II) redox couple. The second step proceeds to a second reduction of the metal ion and is attributed to the Fe(II)/Fe(I)_couple. This new reduction state of iron porphyrins has been characterized by ESR spectra and by absorption spectra in various solvents. This compound is not axially liganded by strong nucleophilic bases but is sensitive to solvation, the lone electron being localised in the d z 2 orbital. The third reduction step is assumed to involve a reduction of the porphyrin π-electron system. All these results have been confirmed by chemical reductions in tetrahydrofuran.

Copper Complexes as Functional Models for Dopamine β-Hydroxylase – Stereospecific Oxygen Atom Transfer

The stereochemistry of oxygen atom transfer mediated by copper–oxygen species has been studied through a substrate binding ligand approach. Copper(II) [(IndPY2)Cu](CF3SO3)2 (2a) and copper(I) [(IndPY2)Cu]PF6 (5a) complexes were prepared and exposed to O2 in media of benzoin/NEt3/CH2Cl2 and CH2Cl2, respectively. In both cases, highly regio- and stereoselective oxygen atom transfer to the benzylic C–H bond of the indane ligand occurred. Using deuterium-labelled copper complexes 2b and 5b, we found that, in both cases, the oxygen atom transfer occurs with retention of configuration. The high deuterium kinetic isotope effects (7.6 and 11, respectively), determined by 13C-NMR spectroscopy, strongly suggest the intermediacy of two different copper–oxygen reactive species.

Porphyrins bound to Ru(bpy)2 clusters: electrocatalysis of sulfite

Abstract Mono-, di-, tri- and tetra-ruthenated porphyrins derived from phenyl/4-pyridyl mesosubstituted porphyrin and a trans di-ruthenated dipyridyl octaethylporphyrin have been synthesised. Coated on carbon electrodes, they have been tested as a sensor for sulfite using the oxidation wave of the Ru(II)/Ru(III) couples in hydroalcoholic solutions. At least two peripheral Ru are necessary to trigger the catalysis off. No major influence of the central metallic ions has been detected, but the Co (II) is coordinated by the sulfite.

Vitamin B12–transport protein interaction: electrochemistry of aquo- and glutathionyl-cobalamins adsorbed on carbon electrodes; role of the nucleotide chain

Abstract Several vitamin B12 derivatives (aquo, acetato, and glutathionyl cobalamins) adsorbed on an edge pyrolytic graphite electrode are studied in order to determine how their electrochemical behaviors are influenced by either the direct adsorption on the electrode material, or the adsorption in the presence of transport proteins, intrinsic factor (IF) and non-intrinsic factor (NIF). Comparison with the interfacial electrochemistry of the cobinamide demonstrates that, at neutral pH, the benzimidazole (Bzm) moiety is still coordinated to the Co(III) and Co(II) oxidized states of the adsorbed cobalamins. On the other hand, adsorption on pyrolytic graphite electrodes is shown to accelerate the kinetics for the reduction Co(III)/Co(II) when strong coordination by glutathione is involved compared to the results obtained in solution. The transport protein–cobalamin complexes are still reducible on the electrode. The potentials are not really changed for the IF complex while Co(II) is slightly more difficult to reduce in the case of the NIF complex.

Cobalt — bis(histidine methyl ester) deuteroporphyrine IX: A coenzyme B12 — related model

The synthesis of cobalt — bis (histidine methyl ester) deuteroporphyrine IX in which histidine residues are covalently bound to the propionic acid side chains of the porphyrin ring is described. Spectroscopic evidences of a coordination of histidines to the cobaltic ion are given. Two monoelectronic waves in cathodic range are found by polarographic study of this conpound in dimethylformamide. They are easily attributed to Co(III) — Co(II) and Co(II) — Co(I) reduction steps. The coordination state and the chemical reactivity of reduced species formed by electrolysis at each wave are characterized.