Micellar inhibited hydrolysis of esters-evaluation of binding constant and cooperativity index.

The inhibition in the rate of hydrolysis of four esters, by the anionic micelles of sodium laurylsulphate has been explained by a binding model. It provides the critical micelle concentration under reaction conditions. Kinetic data suggest that more than 90% of the substrate is micelle-bound at 0.010 M concentration of the anionic micelle and the binding constants obtained agree with those of other systems studied elsewhere. The marked inhibition in the comicellar phase and the cationic micellar phase of sodium Iaurylsulphate, cetyldimethylbenzylammonium chloride or cetyltrimethylammonium bromide, has been explained by using the same pseudo model and the binding constant, K and the fraction of substrate held at the comicellar surface, F , indicates greater binding at the comicellar surface. The cooperativity treatment has been extended to micelle-inhibited reactions and the proposed model has been tested with literature data as well as in the present work. The cooperativity index value ranges from 0.59 to 1.51, and a value less than unity indicates negative cooperativity. [ABSTRACT FROM AUTHOR]