Design, synthesis and evaluation of polymeric and surfactant 4-(dialkylamino)pyridines as hydrolase models

Shanghao Liu, Purdue University

Abstract

In the present study, a number of 4-(dialkylamino)pyridines (DAAP), both polymeric and surfactant, have been synthesized and evaluated as hydrolase models. A polysiloxane with DAAP groups integrated into the polymer backbone has been shown to be a highly selective transacylase. It very selectively transfers the acyl group from a p-nitrophenyl alkanoate to a long chain primary alcohol in the presence of excess methanol and water. A series of polyamides with DAAP groups integrated into the polymer backbone have been synthesized and characterized. Study of catalysis of hydrolysis of p-nitrophenyl alkanoates by these polymeric DAAP's has afforded the first direct evidence for involvement of an acylpyridinium ion in the hydrolysis pathway. Several anionic and neutral surfactant DAAP's have been prepared and evaluated as catalysts for hydrolysis of both cationic surfactant and lipophilic p-nitrophenyl alkanoates. Electrostatic interactions between the anionic catalysts and the cationic substrates have been found to play a variety of roles in promoting hydrolysis. The major discovery is that multi-molecular aggregates are formed from the anionic surfactant catalysts and the cationic surfactant substrates as a result of both hydrophobic and electrostatic interactions. And reaction of one catalyst molecule with one substrate molecule within a multi-molecular aggregate are promoted by other catalyst as well as substrate molecules within the same aggregate. As a result, the rate of hydrolysis observed for our best pair of catalyst and substrate is much higher than that observed previously with similar substrates. In connection with our study on surfactant DAAP's, a recent significant discovery has been re-examined. It was found that hexadecanoate ion aggregates instead of hydrolyzing a cationic surfactant amide. The basicity and catalytic activity of several structurally different DAAP's have also been evaluated in the presence of cationic micelles. It was found that cationic micelles markedly lower both the basicity and catalytic activity of the DAAP's. Therefore, the benefit of micellar catalysis comes at the expense of lowered activity of the functional groups. On the other hand, it was found that properly designed DAAP's may serve as excellent probes for characterization of the cationic surface.

Degree

Ph.D.

Advisors

Fife, Purdue University.

Subject Area

Organic chemistry

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