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Abstract: The ozonation of d-glucose-1-13C, 2-13C, and 6-13C was carried out at pH 2.5 in a semi-batch reactor at room temperature. The products present in the liquid phase were analyzed by GC–MS, HPAEC-PAD, and 13C NMR spectroscopy. Common oxidation products of glucose have also been submitted to identical ozonation conditions. For the first time, a pentaric acid was identified and its formation quantitatively correlated to the loss of C-6 of glucose in the form of carbon dioxide. Potential mechanisms for the formation of this pentaric acid are discussed. The well-accepted pathway involving the anomeric position in glucose, gluconic acid, arabinose, and carbon dioxide is reinvestigated. The origin of small molecules such as tartaric, erythronic, and oxalic acids is clarified. Finally, new reaction pathways and tentative mechanisms consistent with the formation of ketoaldonic acids and smaller acids are proposed. [Copyright &y& Elsevier]

Abstract: A series of heterobinuclear cofacial porphyrin–corrole dyads containing a Co(IV) corrole linked by one of four different spacers in a face-to-face arrangement with an Fe(III) or Mn(III) porphyrin have been examined as catalysts for the electroreduction of O2 to H2O and/or H2O2 when adsorbed on the surface of a graphite electrode in air-saturated aqueous solutions containing 1M HClO4. The examined compounds are represented as (PCY)MIIIClCoIVCl where P is a porphyrin dianion, C is a corrole trianion and Y is a biphenylene (B), 9,9-dimethylxanthene (X), dibenzofuran (O) or anthracene (A) spacer. The catalytic behavior of the seven investigated dyads in the two heterobimetallic (PCY)MClCoCl series of catalysts is compared on one hand to what was previously reported for related dyads with a single Co(III) corrole macrocycle linked to a free-base porphyrin with the same set of linking bridges, (PCY)H2Co, and on the other hand to dicobalt porphyrin–corrole dyads of the form (PCY)Co2 which were shown to efficiently electrocatalyze the four electron reduction of O2 at a graphite electrode in acid media. Comparisons between the four series of porphyrin–corrole dyads, (PCY)Co2, (PCY)H2Co, (PCY)FeClCoCl and (PCY)MnClCoCl, show that in all cases the biscobalt dyads catalyze O2 electroreduction at potentials more positive by an average 110mV as compared to the related series of compounds containing a Co(III) or Co(IV) corrole macrocycle linked to a free-base metalloporphyrin or a metalloporphyrin with an Fe(III) or Mn(III) central metal ion. The data indicates that the E 1/2 values where electrocatalysis is initiated is related to the initial site of electron transfer, which is the Co(III)/Co(II) porphyrin reduction process in the case of (PCY)Co2 and the Co(IV)/Co(III) corrole reduction in the case of (PCY)MnClCoCl, (PCY)FeClCoCl and (PCY)H2Co. The overall data also suggests that the catalytically active form of the biscobalt dyad in (PCY)Co2 contains a Co(II) porphyrin and a Co(IV) corrole. [Copyright &y& Elsevier]