title: Biomimetic oxygen reduction by cofacial porphyrins at a liquid-liquid interface.
abstract: 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.
authors.affiliation: Department of Chemistry, Aalto University, P.O. Box 16100, 00076 Aalto, Finland.
authors.forename: Pekka
authors.initials: P
authors.lastname: Peljo
authors.forename: Lasse
authors.initials: L
authors.lastname: Murtomäki
authors.forename: Tanja
authors.initials: T
authors.lastname: Kallio
authors.forename: Hai-Jun
authors.initials: HJ
authors.lastname: Xu
authors.forename: Michel
authors.initials: M
authors.lastname: Meyer
authors.forename: Claude P
authors.initials: CP
authors.lastname: Gros
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Barbe
authors.forename: Hubert H
authors.initials: HH
authors.lastname: Girault
authors.forename: Kari
authors.initials: K
authors.lastname: Laasonen
authors.forename: Kyösti
authors.initials: K
authors.lastname: Kontturi
mesh_terms: D032701:Biomimetics / Q000379:methods*; D004566:Electrodes; D004579:Electron Transport; D005296:Ferrous Compounds / Q000737:chemistry; D006571:Heterocyclic Compounds / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D008958:Models, Molecular; D008968:Molecular Conformation; D010100:Oxygen / Q000737:chemistry*; D011166:Porphyrins / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D005296:Ferrous Compounds; D006571:Heterocyclic Compounds; D011166:Porphyrins; C050099:1,1'-dimethylferrocene; C063887:tetrathiafulvalene; D010100:Oxygen