A Self-Assembled Cage with Endohedral Acid Groups both Catalyzes Substitution Reactions and Controls Their Molecularity |
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Authors: | Paul M Bogie Lauren R Holloway Courtney Ngai Tabitha F Miller Divine K Grewal Prof Richard J Hooley |
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Institution: | Department of Chemistry, University of California–Riverside, Riverside, CA, 92521 USA |
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Abstract: | A self-assembled Fe4L6 cage complex internally decorated with acid functions is capable of accelerating the thioetherification of activated alcohols, ethers and amines by up to 1000-fold. No product inhibition is seen, and effective supramolecular catalysis can occur with as little as 5 % cage. The substrates are bound in the host with up to micromolar affinities, whereas the products show binding that is an order of magnitude weaker. Most importantly, the cage host alters the molecularity of the reaction: whereas the reaction catalyzed by simple acids is a unimolecular, SN1-type substitution process, the rate of the host-mediated process is dependent on the concentration of nucleophile. The molecularity of the cage-catalyzed reaction is substrate-dependent, and can be up to bimolecular. In addition, the catalysis can be prevented by a large excess of nucleophile, where substrate inhibition dominates, and the use of tritylated anilines as substrates causes a negative feedback loop, whereby the liberated product destroys the catalyst and stops the reaction. |
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Keywords: | catalysis enzyme models molecular recognition self-assembly supramolecular chemistry |
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