Cleavage of phosphate diesters mediated by Zn(II) complex in Gemini surfactant micelles

The cleavage of 2-hydroxypropyl p  -nitrophenyl phosphate (HPNP) catalyzed by the Zn(II)–biap (biap: N,NN,N-bis(2-ethyl-5-methylimidazole-4-ylmethyl)aminopropane) complex has been investigated spectrophotometrically in a micellar solution of cationic Gemini surfactant 16-2-16 [bis(hexadecyldimethylammonium)ethane bromide] and CTAB (hexadecyltrimethylammonium bromide) at 25±0.1°C. The experimental results reveal that a higher rate of acceleration (about 2016-fold) of HPNP cleavage promoted by the Zn(II)–biap complex has been observed in the 16-2-16 micellar solution in comparison with the background rate (k0k0) of HPNP spontaneous cleavage at 25 °C. Reaction rates of HPNP cleavage in CTAB micellar solutions are only about 40% of that in Gemini 16-2-16 micelles under comparable conditions. In addition, the cleavage rates of HPNP in Gemini micelles and in CTAB micelles are respectively 29.5 times and 12 times faster than that in aqueous buffer. Especially, a “sandwich absorptive mode” has been proposed to explain the acceleration of HPNP cleavage in a cationic micellar solution.

Metal-promoted cleavage of 2-hydroxypropyl p-nitrophenyl phosphate (HPNP) in Gemini 16-2-16 micelles has firstly been evaluated. A 29.5- and 2.5-fold kinetic advantages in Gemini 16-2-16 micelles have respectively been observed in comparison with in pure buffer and CTAB micelles.Figure optionsDownload as PowerPoint slide