A comparative study and behaviour of a series of cationic surfactants towards the degree of the basic hydrolysis of p-nitrophenyl acetate.
The surfactant effect of cationic micelles of Dodecyl, tetradecyl and hexadecyl trimethyl ammonium bromide, Cetyl pyridinium bromide, Cetyl dimethyl ethyl ammonium bromide and benzalkonium chloride on the hydrolysis of p-nitrophenyl acetate (PNPA), was studied. The effect of cationic surfactants was within concentration range of 1 x 10(-6) M - 1 x 10(-1) M, with the exception of benzalkonium chloride, where the concentration effect was investigated between 1 x 10(-6) M - 3 x 10(-1) M. All cationic micelles increased the rate of hydrolysis of PNPA upto their concentration of 1 x 10(-2) M and then the rate decreased while benzalkonium chloride showed this maximum at 5 x 10(-2) M. Orientation and adsorption of substrate at the micelle surface are put forwarded to explain this catalytic behaviour. An attempt has also been made to interpret the influence of cationic micelles on the basis of ion exchange model.
Hassan
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Department of Pharmaceutics, Faculty of Pharmacy, University of Karachi, Karachi-75270, Pakistan.
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