Catalysis concerted

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 site are properly aligned with the substrate so that concerted catalysis may occur. Mutarotation of tetramethyl glucose is frequently cited as an example of bifunctional catalysis. Lowry and... 

Both mechanisms give expressions for koh8 which are consistent with the observed pH-rate profiles. Morawetz et a/.255 256 have reported schemes in which both a carboxyl group and a carboxylate ion participate in hydrolysis, and a similar mechanism of concerted catalysis has been proposed for the hydrolysis of o-carboxyphthalanilic acid256 which exhibits a bell-shaped pH-rate profile. 

As with the additions to carbonyl carbon, there is the possibility here of concerted catalysis through a transition state 34, with an acid and a base simultaneously attacking. Early evidence was found by Dawson and Spivey, who... 

Key words. Recognition, hydrogen bonding, molecular clefts, convergent functionality, concerted catalysis, stereoelectronic effects. 

Perhaps the greatest advantage of the new systems is a consequence of their rigidity. This provides an opportunity to place both electrophilic and nucleophilic centers on a single substrate. This notion was first suggested by Swain [28] as ideal for concerted catalysis (Scheme 14), but flexible structures are unable to prevent intramolecular reactions of the catalytic acid-base pairs. We are pursuing these notions with suitable spacers and functional groups and will report on developments in due course. 

A bell-shaped rate profile as a function of pH is characteristic of acid-base concerted catalysis. 

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