Multifunctional Catalysis and Simple Models

Another fundamental idea that has been invoked to explain enzymatic catalysis is that such reactions utilize bifunctional or multifunctional catalysis. That is, several functional groups in the active center are properly aligned with the substrate so that concerted catalysis may occur. 

One of the earliest examples (71) in solution chemistry is the study of the rate of mutarotation of 0-tetramethyl-D-glucose in the presence of a-pyri-done. A 10 M solution of a-pyridone was 7000 times more effective than an equivalent concentration of phenol and pyridine. 

A concerted mechanism was proposed where the catalyst acts as a base and an acid simultaneously  

A key feature of enzyme catalysis is observed regeneration of the catalyst (via the reversible pathway). 2-Aminophenol, which is both a stronger acid and base than a-pyridone, is not as potent a catalyst. In the presence of 2-aminophenol a concerted mechanism of catalysis is not possible. 

Another classical example (72) of multifunctional catalysis is the hydrolysis of the monosuccinate ester of hexachlorophene  

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