Induced Fit in a Molecular Pac-Man

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Science  04 Feb 2000:
Vol. 287, Issue 5454, pp. 769
DOI: 10.1126/science.287.5454.769b

Many fundamental oxidation-reduction (“redox”) reactions require the transfer of several electrons. In biological systems, such multielectron redox reactions are often catalyzed by enzymes that contain multiple metal atoms. Chemists are devising biomimetic synthetic systems to understand the underlying mechanisms and to develop new catalysts. For example, molecules consisting of two porphyrin units linked by a spacer—cofacial bisporphyrins—can catalyze reactions such as the direct reduction of oxygen to water.

J. P. Collman suggested in the mid-1980s that some cofacial bisporphyrins may show a “Pac-Man”-like flexibility that would allow their binding pocket to accommodate reaction intermediates during catalysis in a manner similar to “induced fit” in enzyme catalysis. Now, Deng et al. have synthesized cofacial bisporphyrins linked by a rigid dibenzofuran pillar and show that the molecules can open and close their binding pockets with a “bite” of more than 4 angstroms in the presence of suitable ligands. The authors have recently used the biscobalt(II) derivative of the dibenzofuran platform to catalyze the electrochemical four-electron reduction of oxygen to water.—JU

J. Am. Chem. Soc.122, 410 (2000).

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