EFFECT OF POLYMER MICRODOMAINS ON THE CATALYZED ESTEROLYSIS OF HYDROPHOBIC PICOLINIC ESTERS

Hydrophobic microdomains are generated in aqueous solutions by intramo lecular coiling of poly(3-hexadecyl-1-vinylimidazolium bromide) (PC16V IB). The influence of the so produced microenvironments on the chemica l reactivity of water non-soluble reactants was studied by the followi ng kinetics of the hydrolysis of hydrophobic picolinic esters, catalys ed by hydrophobic benzimidazoles in the presence of Zn2+ ions or not. The results are compared with the rate constants obtained for cationic micellar systems prepared either from 3-hexadecyl-1-methylimidazolium bromide (HMIB), a model of polymer repeat unit, or from the conventio nal CTAB surfactant. The esterolytic activity of benzimidazoles, when alone, was similar in the presence of PC16VIB and HMIB, and it increas es with the alkyl chain length of the reactants. Compared with the CTA B medium, their strong esterolytic power is the highest ever reported for a benzimidazole ring. In the presence of Zn2+ ions, the observed d ifference between the reactivities was also striking due to either the lack of an additional catalytic effect (in the case of HMIB) or an in hibition phenomenon in the case of the polymer whereas it had been sho wn that a CTAB medium favoured the formation of a 2/1 active complex.