| STUDY |
A manganese porphyrin epoxidation catalyst, when placed in the cavity formed by the directed assembly of zinc porphyrin molecules, acts as an artificial enzyme. "We have replicated the topology that nature intended for a metalloenzyme: an active metal site encapsulated by a cavity that protects the active center, defines the size/shape selectivity, and allows substrate binding. The cavity protects the catalyst but is large enough to allow substrate molecules to reach the catalyst. The increased stability allows the catalyst to last longer, with the lifetime increasing from 10 minutes to more than three hours. The bare manganese porphyrin generally loses its activity after 50 cycles, but in the supramolecular structure, one catalyst reached turnover numbers as high as 21,000. The selectivity of the catalyst can be tuned by adding up to two ligands, which change the size of the cavity. The resulting size selectivity allows significant differentiation between substrates, even those that are similar to one another
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