Evidence for the formation of acylated or phosphorylated monoperoxyphthalates in the catalytic esterolytic reactions in cationic surfactant aggregates

Abstract

Monoperoxyphthalate (MPP) was solubilized in three different aqueous cationic surfactant aggregates composed of (i) a micellar cetyltrimethylammonium chloride (CTACl) solution; (ii) an oil-in-water (O/W) microemulsion (ME) stabilized by CTACl, and a cosurfactant, tert-butyl alcohol, and (iii) a vesicular medium composed of dispersions of dihexadecyldimethylammonium chloride (DHDAC). At pH 8.5 and 25 °C, each of these formulations was used to cleave p-nitrophenyl diphenyl phosphate (PNPDPP). The aggregate and the maximum pseudo-first-order rate constants ([MPP] = 4 × 10^-5 M, and [PNPDPP] = 1 × 10^-5 M) for the PNPDPP cleavages are the following: buffer alone, 0.00034 s^-1; micelle: 0.024 s^-1; ME: 0.0048 s^-1; and vesicle: 0.025 s^-1. Importantly all the catalytic formulations showed 'turnover' behavior in the presence of excess substrates. By the combined use of ¹H- and ³¹P-NMR spectrometry and synthesis, it was possible to provide evidence for the formation of acylated or phosphorylated monoperoxypthalates in the catalytic hydrolyses in cationic surfactant aggregates.