Journal
COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS
Volume 168, Issue 3, Pages 241-250Publisher
ELSEVIER
DOI: 10.1016/S0927-7757(99)00454-9
Keywords
micellar catalysis; kinetics; ninhydrin; aspartic acid; cetyltrimethylammonium bromide; cetylpyridinium bromide
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Cationic micelles of cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPB) increase the pseudo-first-order rate constant for the addition-elimination type interaction between aspartic acid and ninhydrin leading to the formation of purple colored diketohydrindylidenediketohydrindamine (DYDA). The rate enhancements have been treated in terms of concentration of both the reactants at the micellar surface and the related micelle-substrate, and micelle-ninhydrin association constants (K-S and K-N), second-order rate constants (k(m)') and activation parameters have been evaluated. The presence of inorganic salts (NaCl, NaBr, Na2SO4) does not reveal any detectable effect on the rate constants. On the other hand, the observed data with organic salts (NaBenz, NaSal, NaTos) show an increase in the rate followed by a decrease. The role of the hydrophilic side chain of aspartic acid (HOOCH2C-) is also discussed. (C) 2000 Elsevier Science B.V. All rights reserved.
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