Evidence of a Stable Charge-Transfer Adduct Between 2-Mercaptoethanol and Cobalt-Polytetraaminophthalocyanine

Effect of the Substituents on the Ligand of Iron Phthalocyanines Adsorbed on Graphite Electrodes on Their Activity for the Electrooxidation of 2-Mercaptoethanol

“…These limitations seem to be a mixture of masstransport, chemical limitations or poisoning of the electrode surface due to the adsorption of an intermediate or product, which become more critical at higher overpotentials. This is in contrast to what is observed on cobalt phthalocyanines [47], but it is similar to the results obtained on poly-Cotetraaminophthalocyanine [20].…”

“…Figure 3 also shows, as expected, that electron-withdrawing groups shift redox potentials to more positive values and the opposite is true for electron-donating groups, compared to À H in FePc. This Figure also indicates that the groups on the periphery of the phthalocyanine ligand modulate the electron density on the Fe center, which is crucial for the electrocatalytic process, since this should affect the binding properties of the Fe center towards the thiol [7,20]. Figure 4 shows the potentiodynamic response of the bare OPG and of the OPG electrode modified with four different iron phthalocyanines in the presence of 3 Â 10 À 3 M 2-mercaptoethanol (R-SH) in the electrolyte.…”

“…A possible explanation for this observation is that the activity of the modified electrode decreases, as the potential is made more positive. This can be attributed to an adsorbed product or intermediate of the reaction, which blocks the active sites [20]. Another explanation is that the electrode loses its activity due to the oxidation of Fe (II) to the Fe (III) in the adsorbed phthalocyanine.…”

Metallophthalocyanine-based molecular materials as catalysts for electrochemical reactions

“…In some cases, this interaction can be so strong that the catalytic process is inhibited as the active sites are blocked by the reacting molecules bound to the active sites in the phthalocyanine. Indeed, in the case of polymeric tetraaminocobalt phthalocyanine poly-4␤(NH 2 )CoPc deposited on transparent indium tin oxide (ITO) electrodes, there is in situ evidence that an adduct is formed between this molecule and 2-mercaptoethanol (2-ME) [292,329]. This adduct, if it is labile, could be a precursor in the electrocatalytic process of oxidation of thiols.…”

“…Metallophthalocyanines and related complexes exhibit catalytic activity for the electrochemical oxidation of a great variety of thiols [14,21,100,274,[284][285][286][287][290][291][292][321][322][323][324][325][326][327][328][329][330][331][332][333][334][335][336][337][338] and for the reduction of the corresponding disulfides [100]. These "molecular phthalocyanine electrodes" act by lowering the overpotential of oxidation or reduction of the target molecules [14].…”