Meng Xiangguang

Catalytic Hydrolyses of Carboxylic Acid Esters in the Presence of Gemini Surfactant

Hydrolyses of p‐nitrophenyl picolinate (PNPP) and p‐nitrophenyl acetate (PNPA) mediated by the micellar catalytic systems of two types of cationic surfactants [cetyltrimethylammonium 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 (k obsd) 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 k obsd 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), γ‐cyclodextrin (γ‐CD)], as additives, showed different effects on PNPP and PNPA hydrolyses in different reaction systems.

Metallomicellar Catalysis: Phosphodiester Hydrolysis Catalyzed by Cu(II), Zn(II), Ni(II), and Co(II) Complexes of Chelating Pyridyl Donor Ligands in CTAB Micellar Solution

The syntheses of two alkanol‐pyridyl ligands, 6‐(n‐dodecyloxymethyl) ‐2‐(hydro‐xymethyl)pyridine (1) and 6‐(methyloxymethyl)‐2‐(hydroxymethyl)pyridine(2), are reported. Metallomicellar systems made of complexes of these ligands with Cu(II), Zn(II), Ni(II), and Co(II) in the presence of surfactant CTAB are efficient catalyzers in the hydrolysis of bis(p‐nitrophenyl)phosphate (BNPP). The experimental results indicate that 2∶1 ligand:metal ion complexes in CTAB micellar solution are the active species for the catalytic hydrolysis of BNPP. The ternary complex kinetic model for metallomicellar catalysis was employed to treat the results to obtain the relative kinetic and thermodynamic parameters. The results predicted the reasonability of such kinetic models.

Hydrolysis of p‐Nitrophenyl Picolinate Catalyzed by Gemini Surfactants with Different Hydrophobic Tail Groups

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.

CATALASE MIMIC WITH Fe (II) METALLOMICELLE

Abstract The effect of Fe (II) metallomicelle as a model of catalase, which was formed by adding surfactants (CTAB, SDS, LSS, Brij35) in Fe (II) -trien complex of molar ratios 1: 500 on the decomposition of hydrogen peroxide was investigated at 20°C and 30°C in pH 10 using KI-color and UV Spectrophotometry. A kinetic model for metallomicellar catalysis was proposed. The association constant of the ternary complex K and the rate constant of the decomposition of hydrogen peroxide k3 were obtained. The results indicate that the metallomicelles making up of Fe (II) metal complex and cationic or nonionic surfactants have obvious catalysis on the decomposition of hydrogen peroxide, but the metallomicelles making up of Fe (II) metal complex and anionic or zwitterionic surfactants have inhibition on this reaction.

Phosphate Monoester Cleavage with Dinuclear Zinc(II) and Copper(II) Macrocyclic Complexes in Micellar Solution

Homodinuclear and heterodinuclear Zn(II) and Cu(II) complexes derived from macrocyclic ligand (1) have been kinetically examined as catalysts for the hydrolysis of phosphomonoester p‐nitrophenyl phosphate (pNPP) in Brij35 micellar solutions. Kinetic data indicated that the aquo‐hydroxy form of the dinuclear complex was the active species and the metal‐coordinated hydroxide nucleophile attacked the substrate in the hydrolysis reaction in a fashion of intramolecule nucleophilic reaction. Two oxygens of pNPP associated with the two metal centers of the dinuclear complex, and in this case the metal ions exerted a double Lewis acid effect. Different structure requirements of metal ions and nucleophilicity of M‐OH species determined the activity sequence of the three dinuclear complexes. The rigid and compact geometry of these complexes hindered their catalytic effects in the hydrolysis of phosphodiester bis(p‐nitrophenyl) phosphate (BNPP).

Metallomicellar Catalytic Hydrolysis of NPP by CuIINiII Heterodinuclear Complexes Containing Diamine Groups in Brij35 Micellar Solution

The hydrolysis of p‐nitrophenyl phosphate (NPP) catalyzed by metallomicelles formed from four asymmetry CuIINiII 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 CuIINiII heterodinuclear oxamido‐bridged complexes with two coordinated H2O molecules may be a potential catalyst for the hydrolysis of NPP.

The effect of mixed micelles of surfactants on the alkaline hydrolysis of dimethylformamide

ABSTRACT The alkaline hydrolysis of dimethylformamide has been studied at 40°C In mixed micelles of surfactants (CTAB—Brij35, SD6 — Brij35, CTAB — BHMI, SDS —BHMI, Brtj35—BHMI) and functional molecule 1—benzyl—2—hydroxymethylimidazole (BHMI) solutions with analog thermogram method of thermokinetics. The kinetic parameters km In micellar pseudophase, rate constant ke in functional molecular solution, and the association constant of reactant with micelle Ki, with functional molecule K, have been calculated from kinetic equations of mixed micellar catalysis in the case of [S]>[M]. The results indicate that all the researched systems exhibit catalytic effect on the reaction. Polarity and local concentration effect were employed to explain these phenomena. A mechanism of catalysis of BHMI and mixed micelles of a surfactant and BHMI was proposed.