Abstract
The influence of two cationic micellar systems on the absorption and fluorescence spectra and on the acid-base equilibria of indole and indole-2-, 3-, 4- and 5-carboxylic acid are studied. Indole-2- and indole-4-carboxylic acid on the one hand, and the 3- and 5-substituted derivatives on the other, show similar values of p K COOH in the micellar media of hexadecyltrimethylammonium bromide and benzyldimethylhexadecylammonium chloride. The same equilibrium in the excited state shows a decrease in the acid character of the 4- and 5-carboxylic derivatives. In the excited state, all the compounds show two equilibria associated with protonation of the heterocyclic ring and deprotonation of pyrrolidine nitrogen. The p K a1 ∗ and p K a3 ∗ values of indole and carboxylic acid derivatives are influenced by the nature of the medium, the position of the carboxyl group and the nature of the hydrocarbon chain of the surfactant.
Published Version
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