Abstract
The breath reaction, which is the four-electron reduction of oxygen to water, should be studied so as to clarify life mechanisms and also produce novel catalysts. In the human body, the breath enzyme, cytochrome oxidase, is the primary agent for four-electron reduction of oxygen to water under atmospheric pressure at mild temperature in ca. pH 7 solution. Structural analysis of this enzyme and mimicking of catalytic reactions has been pursued extensively.
Metalloporphyrins were frequently used as catalysts to promote the reaction. Monomeric metalloporphyrins such as cobalt and iron, permit only two-electron reduction of oxygen to hydrogen peroxide. Multi-nuclear porphyrins such as dimeric porphyrin, tetranuclear ruthenated porphyrin and polymeric metalloporphyrin were used in this study to bring about efficient multi-electron transfer to oxygen for the preferential four-electron reduction of oxygen. Activity only under strong acidic atmosphere has so far been noted.
Oxygen oxidation promoted by 4-electron transfer is essential for many chemical reactions. Synthesis based on 4-electron reduction oxygen and facilitated by a metal catalyst is presently being studied. The catalyst for the 4-electron reduction of oxygen should provide a convenient means for molecular conversion under mild aerobic conditions.
