Tuesday, 9 February 2010

Covalent Catalysis (Pemangkinan Kovalen)

Muat turun Slide Kuliah (Download Lecture Slides)

Covalent catalysis is another form of catalysis that is important in many enzymatic catalysis. In the beginning of the topic, hydrolysis of p-nitrophenyl acetate by chymotrypsin has been discussed. There are three possible reasons to the rapid initial reaction rate: (a) product inhibition, (b) conformation change and (c) product releasing and intermediate formation. 

The similar reaction has been performed in the presence of o-(N,N-dimethylaminomethyl) benzyl alcohol to mimic chymotrypsin. From the results, it is quite clear that covalent bonding was formed by nucleophilic attack to electron sink of carbonyl group. Perhaps, the nucleophilic attack was enhanced by the adjacent amino group that "deprotonating" the hydroxyl group. The intermediate is the key point to deduce the formation of covalent bonding between the catalyst and the substrate as well as producing the main product (p-nitrophenol).

There are a couple of examples of such activity: decarboxylation of acetoacetate and stereoselective nucleophilic attack to an alkene.

Hopefully, the discussion will help to understand the nucleophilic catalysis.

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