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    Molecular Electrocatalysis for Oxygen Reduction by Cobalt Porphyrins Adsorbed at Liquid/Liquid Interfaces
    (AMER CHEMICAL SOC, 2010) Su, Bin; Hatay, İmren; Trojanek, Antonin; Samec, Zdenek; Khoury, Tony; Gros, Claude P.; Barbe, Jean-Michel; Daina, Antoine; Carrupt, Pierre-Alain; Girault, Hubert H.
    Molecular electrocatalysis for oxygen reduction at a polarized water/1,2-dichloroethane (DCE) interface was studied, involving aqueous protons, ferrocene (Fc) in DCE and amphiphilic cobalt porphyrin catalysts adsorbed at the interface. The catalyst, (2,8,13,17-tetraethyl-3,7,12,18-tetramethyl-5-p-aminophenylporphyrin) cobalt(II) (CoAP), functions like conventional cobalt porphyrins, activating 02 via coordination by the formation of a superoxide structure. Furthermore, due to the hydrophilic nature of the aminophenyl group, CoAP has a strong affinity for the water/DCE interface as evidenced by lipophilicity mapping calculations and surface tension measurements, facilitating the protonation of the CoAP-O(2) complex and its reduction by ferrocene. The reaction is electrocatalytic as its rate depends on the applied Galvani potential difference between the two phases.
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    Oxygen Reduction Catalyzed by a Fluorinated Tetraphenylporphyrin Free Base at Liquid/Liquid Interfaces
    (Amer Chemical Soc, 2010) Hatay, İmren; Su, Bin; Mendez, Manuel A.; Corminboeuf, Clemence; Khoury, Tony; Gros, Claude P.; Bourdillon, Melanie; Meyer, Michel; Barbe, Jean-Michel; Ersöz, Mustafa; Zális, Stanislav; Samec, Zdenek; Girault, Hubert H.
    The diprotonated form of a fluorinated free base porphyrin, namely 5-(p-aminophenyl)-10,15,20-tris(pentafluorophenyl)porphyrin (H(2)FAP), can catalyze the reduction of oxygen by a weak electron donor, namely ferrocene (Fc). At a water/1,2-dichloroethane interface, the interfacial formation of H(4)FAP(2+) is observed by UV-vis spectroscopy and ion-transfer voltammetry, due to the double protonation of H(2)FAP at the imino nitrogen atoms in the tetrapyrrole ring. H(4)FAP(2+) is shown to bind oxygen, and the complex in the organic phase can easily be reduced by Fc to produce hydrogen peroxide as studied by two-phase reactions with the Galvani potential difference between the two phases being controlled by the partition of a common ion. Spectrophotometric measurements performed in 1,2-dichloroethane solutions clearly evidence that reduction of oxygen by Fc catalyzed by H(4)FAP(2+) only occurs in the presence of the tetrakis(pentafluorophenyl)borate (TB(-)) counteranion in the organic phase. Finally, ab initio computations support the catalytic activation of H(4)FAP(2+) on oxygen.
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    Proton-Coupled Oxygen Reduction at Liquid-Liquid Interfaces Catalyzed by Cobalt Porphine
    (AMER CHEMICAL SOC, 2009) Hatay, Imren; Su, Bin; Li, Fei; Mendez, Manuel Alejandro; Khoury, Tony; Gros, Claude P.; Barbe, Jean-Michel
    Cobalt porphine (COP) dissolved in the organic phase of a biphasic system is used to catalyze O-2 reduction by an electron donor, ferrocene (Fc). Using voltammetry at the interface between two immiscible electrolyte solutions (ITIES), it is possible to drive this catalytic reduction at the interface as a function of the applied potential difference, where aqueous protons and organic electron donors combine to reduce O-2. The current signal observed corresponds to a proton-coupled electron transfer (PCET) reaction, as no current and no reaction can be observed in the absence of either the aqueous acid, COP, c, or O-2.