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Hydrolysis of p‐nitrophenyl picolinate (PNPP) mediated by the micellar catalytic systems of two gemini cationic surfactants with different hydrophobic tail groups (ethanediyl‐1,2‐bis(dodecyldimethylammonium bromide) (12‐2‐12, 2Br - ), dimethylene‐1,2‐bis(cetyltrimethyl‐ammonium bromide) (16‐2‐16, 2Br - )) was investigated spectrophotometrically in the pH range of 7.0–9.0 and at 25°C. It is noteworthy that (1) two gemini surfactants showed catalytic effects on the hydrolysis of PNPP and gemini surfactant (16‐2‐16, 2Br - ) enhanced the hydrolytic reaction notably more than gemini surfactant (12‐2‐12, 2Br - ) micellar solutions under the same reaction conditions, which may be ascribed to the micelle effect and (2) the apparent rate constants ( k obsd ) of PNPP hydrolyses increased with increasing pH values of the reaction media. [ABSTRACT FROM AUTHOR]

The hydrolysis of p ‐nitrophenyl phosphate (NPP) catalyzed by metallomicelles formed from four asymmetry Cu II Ni II heterodinuclear oxamido‐bridged complexes, whose ligands contain different diamine groups, and nonionic surfactant Brij35 has been investigated quantitatively at the pH range of 6.0–10.5 and 25°C, respectively. The results indicated that the rates of catalytic hydrolysis of NPP by four complexes in Brij35 micellar solution were all largely enhanced under the experimental conditions. The order of effectiveness of the four complexes in Brij35 micellar solutions toward hydrolysis of NPP was found to be: complex I>complex II>complex III>complex IV. The different catalytic function of four complexes may be attributed to the different activation abilities of coordinated water molecules induced by different polarities of ligands, which has been discussed in detail. Meanwhile, kinetic studies show that the active species in the catalytic hydrolysis of NPP may be the aquo‐hydroxy form and that the mechanism of the reaction involves intramolecular nucleophilic attack of the nickel‐bound hydroxide ion on phosphoryl of NPP. The studies suggested that the metallomicelle containing Cu II Ni II heterodinuclear oxamido‐bridged complexes with two coordinated H 2 O molecules may be a potential catalyst for the hydrolysis of NPP. [ABSTRACT FROM AUTHOR]

Hydrolyses of p-nitrophenyl picolinate (PNPP) and p-nitrophenyl acetate (PNPA) mediated by the micellar catalytic systems of two types of cationic surfactants [cetyltrimethyhimmonium bromide (CTAB), Gemini dimethylene-1,2-bis(cetyltrimethylammonium bromide) (16-2-16, 2Br-)] were investigated spectrophotometrically in the pH range of 7.0-9.0 and 25°C. Also, the effects of several kinds of additives, such as ethanol, cyclodextrins (CDs), on the hydrolytic reactions of PNPP and PNPA were studied systematically. It is noteworthy that: (1) double chain Gemini surfactant micellar system enhanced the hydrolyses of carboxylic acid esters notably compared with single chain surfactant (CTAB) micellar solutions under the same reaction conditions; (2) the apparent rate constants (.kobsd) of PNPP and PNPA hydrolyses increased with the increasing in pH values of reaction media; (3) as additives, ethanol has effect on both PNPP and PNPA hydrolyses, and moreover, the kobsd for hydrolyses decreased with the increasing contents of ethanol (< 5%) at 25°C and pH 9.00; (4) the presence of CDs [α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), 7-cyclodextrin (7-CD)], as additives, showed different effects on PNPP and PNPA hydrolyses in different reaction systems. [ABSTRACT FROM AUTHOR]