Studies on Secondary Coordination Sphere Effects in Metal and Enzyme Catalysis
In metal catalysts and enzymes, the primary coordination sphere of the metal and/or substrate determines basic reactivity. The secondary coordination sphere tunes the reactivity through weaker interactions and therefore usually presents the best handle for optimizing artificial enzymes and metal catalysts. We studied an artificial metalloenzyme system and found that the enzyme improves activity through a pi-stacking interaction in the secondary coordination sphere. The dynamics of this interaction altered reactivity among different mutants. In a natural enzyme, we found that the electric field generated solely by the primary and secondary coordination spheres was sufficient to reproduce experimental energy surfaces. We also studied a redox-active bimetallic system, finding that the redox potential could be tuned by simple electrostatics in the secondary coordination sphere if the primary coordination sphere was rigid.