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The aim of this work is to study four types of modification of a glassy carbon electrode by Fe(III)-tetrakis(p-tetraaminophenyl)porphyrin and determine the influence of the method of immobilization of the complex on glassy carbon in electrocatalytic properties for the sulfite and hydrogensulfite oxidation in ethanol–water. The first modification was deposition of a drop of solution containing the porphyrin on a glassy carbon electrode and evaporation of the solvent (dry-drop method). The second method was immersion of the electrode at 54°C in a solution of dimethylformamide containing the porphyrin for 2 h. The third method consisted of the same heating treatment but after formation of a chemical bond of 4-aminopyridine on the glassy carbon surface, which acts as an axial ligand for the first layer of porphyrin. The fourth method involves electropolymerization of the porphyrin on the electrode surface. Important differences in stability, the potential where the oxidation wave begins and selectivity of the...

A modified synthetic route for the complexes [Cu(II)5,7,12,14-tetramethyldinaphtho [b,i][1,4,8,11]tetraaza[14]annulene], [Cu(II)tmdnTAA], and [Cu(II) 5,7,12,14-tetramethyl-6,13-dichloro-dinaphtho[b,i][1,4,8,11]tetraaza[14]annulene], [Cu(II)dCltmdnTAA], is presented in this work. The electrochemical characterization of both complexes and their precursors, [bis(2,4-pentanedionato)copper(II)], [Cu(II)(acac)2] and [bis(3-chloro-2,4-pentanedionato)copper(II)], [Cu(II)(3-Cl-acac)2], respectively, under nitrogen and carbon dioxide is also presented. The voltammetric response of [Cu(II)(acac)2] and [Cu(II)(3-Cl-acac)2] are different compared to [Cu(II)tmdnTAA] and [Cu(II)dCltmdnTAA] under nitrogen. Precursors show the reduction of Cu(I) to Cu(0) and the tetraazadinaphtho[14]annulene complexes do not. The chlorine substituted complex has a lower reduction potential than the unsubstituted homologue under nitrogen atmosphere. However, the contrary response is obtained in the presence of carbon dioxide: the unsubstit...

Three glass electrodes covered with Co-cobaltite/SnO2:F (to obtain conducting glass electrodes) modified with p-Ni-tetraaminophenylporphyrin are described. In one electrode the porphyrin was absorbed on the electrode surface at room temperature, in another the porphyrin was electropolymerized on the electrode surface by cyclic voltammetry, and in the third the bare electrode was immersed in DMF containing the porphyrin and refluxed 6 h at 150°C. The three electrodes were tested as electrocatalysts for the oxidation of hydrazine and as potentiometric sensors of this chemical. The electrode modified by refluxing showed good electrocatalytic behavior as well as a linear relationship between its open circuit potential and the concentration of hydrazine in a concentration range from 0.16 to 12 µM, with fast response. These characteristics indicate that the conducting glass electrode of Co-cobaltite/SnO2:F covered with p-Ni-tetraaminophenylporphyrin by the reflux method is a good potentiometric sensor of hydraz...

5,15‐Bis(veratryl)porphyrin (1), 5,10,15‐tris(veratryl)porphyrin (2), and 5,10,15,20‐tetrakis(veratryl)porphyrin (3), C36H30N4O4, C44H38N4O6, and C52H46N4O8 were synthesized by an acid‐catalyzed, one‐pot reaction of meso‐dipyrromethane, 3,4‐di‐OCH3‐benzaldehyde (veratraldehyde), and trifluoroacetic acid (TFA). These three different products were obtained as a result of scrambling reactions. The molecular structures have been characterized by elemental analysis, ESI mass spectra, 1D and 2D NMR techniques (1H and 13C), and UV‐visible spectroscopy.

The electro-reduction of carbon dioxide was studied by using a glassy carbon electrode modified with Co(II)-tetrabenzoporphyrin as adsorbed layers or as a supramolecular system. In order to obtain the supramolecular electrode, 4-aminopyridine was chemically bonded to the electrodic surface. On this surface, a first layer of porphyrins was anchored by the pyridine as a fifth ligand. Packed on the first layer of porphyrins, a supramolecular system is formed. The electrode modified with physically adsorbed layers of porphyrins does not show catalytic response toward the electroreduction of CO2. However, the supramolecular electrode is very stable and shows a high catalytic response.

The electrochemical reduction of carbon dioxide using hexa-aza-macrocycles derived from the condensation of 1,10-phenanthroline and its Co(II) complex as an electrocatalyst dissolved in dimethylformamide has been studied by cyclic voltammetry and UV-visible spectroscopy. The ligand does not show catalytic activity and only generates hydrogen when it is reduced under carbon dioxide. The cobalt complex shows electrocatalytic activity toward the reduction of carbon dioxide, generating carbon monoxide and formic acid. Cyclic voltammetry and UV-visible spectroscopy show that the active site for the reduction is the metal center in oxidation state (I), although the reduced cobalt center alone is not enough to promote reduction of the carbon dioxide. Electrolysis at controlled potential shows that only at potentials corresponding to reduction of the ligand (second reduction) does carbon dioxide reduction occur. Cobalt(I) probably reacts with CO2 forming a non-isolated intermediate which, when reduced, gives CO a...

The electro-oxidation of 2-mercaptoethanol by poly-Co-tetraaminophthalocyanine (p-Co-TAPc) and poly-metal-free-tetraaminophthalocyanine (p-H2TAPc), absorbed on electrode surfaces has been investigated by UV-visible spectroelectrochemistry and electrochemical techniques. In the case of p-CoTAPc, an irreversible oxidation wave is obtained by cyclic voitammetry, whereas p-H2PcTA practically does not show activity. The foot of the oxidation, as the open circuit potential measurements indicate that the responsible redox couple is Co(II)/Co(I). The p-CoTAPc modified-electrode loses its activity after a first potential cycle. UV-visible spectroelectrochemical measurements show a charge transfer band (metal to ligand) for the p-CoTAPc between Q and Soret bands when negative potentials are applied and Co(I) is obtained. The presence of 2-mercaptoethanol promotes the appearance of the charge transfer band at open circuit potential and retain this band even at potentials as positive as +0.2V where normally ...