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Oxygen reduction catalyzed by cofacial metalloporphyrins at the 1,2-dichlorobenzene-water interface was studied with two lipophilic electron donors of similar driving force, 1,1'-dimethylferrocene (DMFc) and tetrathiafulvalene (TTF). The reaction produces mainly water and some hydrogen peroxide, but the mediator has a significant effect on the selectivity, as DMFc and the porphyrins themselves catalyze the decomposition and the further reduction of hydrogen peroxide. Density functional theory calculations indicate that the biscobaltporphyrin, 4,5-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]-9,9-dimethylxanthene, Co(2)(DPX), actually catalyzes oxygen reduction to hydrogen peroxide when oxygen is bound on the "exo" side ("dock-on") of the catalyst, while four-electron reduction takes place with oxygen bound on the "endo" side ("dock-in") of the molecule. These results can be explained by a "dock-on/dock-in" mechanism. The next step for improving bioinspired oxygen reduction catalysts would be blocking the "dock-on" path to achieve selective four-electron reduction of molecular oxygen.

Enterobactin mediates iron uptake in Escherichia coli and related bacteria. The structure of the neutral protonated ferric enterobactin complex Fe[H 3 enterobactin] has been the source of some controversy in the literature. The coordination chemistry of the new model ligands tris[(2-hydroxybenzoyl)-2-aminoethyl]-amine (TRENSAM) and tris[(2-hydroxy-3-methoxybenzoyl)-2-aminoethyl]amine (TREN(3M)SAM) demonstrate the previously proposed tris-salicylate mode of binding for ferric enterobactin; they form 1:1 metal-ligand complexes with Fe 3+ and Al 3+ that bind the metals through tris-salicylato coordination (i.e., the chelate is a six-membered metallocycle with the phenolic and amide oxygens binding the metal center). The ferric and aluminum complexes of TRENSAM are isostructural and crystallize in the monoclinic space group P2 1 /c. The ferric and aluminum complexes of TREN(3M)SAM are nearly isostructural and crystallize in the triclinic space group P1 h, with the same salicylate mode of bonding as the TRENSAM complexes. The TRENSAM ligand and its metal complexes have been investigated by NMR, potentiometric, and spectrophotometric techniques, and the results of these experiments are compared to Fe[H 3 enterobactin] and a biomimetic analogue Fe[H 3 MECAM] (which supports growth of E. coli). The properties of Fe[TRENSAM] and Fe[TREN(3M)-SAM] represent an iron release pathway for synthetic analogues of enterobactin that are not susceptible to the degradative pathway usual for enterobactin.