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CTAB Micelles (ctab + micelle)
Selected AbstractsMetallomicelle catalysis: Hydrolysis of p -nitrophenyl picolinate induced by Schiff base Co(II) complexes in a Gemini surfactant micellar solutionINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 12 2007Weidong Jiang Two Schiff base cobalt(II) complexes containing crowned substituents have been synthesized and employed to promote the hydrolysis of p -nitrophenyl picolinate (PNPP) in a buffered micellar solution formed by a cationic Gemini surfactant, bis(hexadecyldimethylammonium)hexane bromide (G(hex)C16, 2Br,) over a pH range of 6.50,8.50. In comparison, the reactivity of PNPP hydrolysis catalyzed by the same catalysts in the other micellar system, formed by a conventional single-chain analogue, that is, hexadecyltrimethylammonium bromide (CTAB), has also been evaluated under a selected condition. The results clearly reveal that the two metallomicelles made of the aforementioned Co(II) complexes and the G(hex)C16 are both efficient for catalyzing PNPP hydrolysis with about 3 orders of magnitude in rate acceleration compared with the background rate of PNPP spontaneous hydrolysis. Moreover, the rates of PNPP hydrolysis catalyzed by the two cobalt(II) complexes in G(hex)C16 micelles are about 2 times higher than in CTAB micelles, correspondingly. In addition, observations show that steric hindrance of substituents of the two complexes is also one of the major influencing factors in the PNPP hydrolytic reaction. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 672,680, 2007 [source] Micellar and salt effects on the interaction of [Cu(II)-Gly-Gly]+ with ninhydrinINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2007Mohd. Akram The effect of cationic micelles of cetyltrimethylammonium bromide (CTAB) on the kinetics of interaction of copper dipeptide complex [Cu(II)-Gly-Gly]+ with ninhydrin has been studied spectrophotometrically at 70°C and pH 5.0. The reaction follows first- and fractional-order kinetics, respectively, in complex and ninhydrin. The reaction is catalyzed by CTAB micelles, and the maximum rate enhancement is about twofold. The results obtained in the micellar medium are treated quantitatively in terms of the kinetic pseudophase and Piszkiewicz models. The rate constants (kobs or k,), micellar-binding constants (kS for [Cu(II)-Gly-Gly]+, kN for ninhydrin), and index of cooperativity (n) have been evaluated. A mechanism is proposed in accordance with the experimental results. The influence of different inorganic (NaCl, NaBr, Na2SO4) and organic (NaBenz, NaSal) salts on the reaction rate has also been seen, and it is found that tightly bound/incorporated counterions are the most effective. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 556,564, 2007 [source] Effect of surfactant micelles on the kinetics of oxidation of D -fructose by cerium(IV) in sulfuric acid mediumINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2006Kabir-ud-Din Kinetics of the oxidation of D -fructose by cerium(IV) has been investigated both in the absence and presence of surfactants (cetyltrimethylammonium bromide, CTAB, and sodium dodecyl sulfate, SDS) in sulfuric acid medium. The reaction exhibits first-order kinetics each in [cerium(IV)] and [D -fructose] and inverse first order in [H2SO4]. The Arrhenius equation is found to be valid for the reaction between 30,50°C. A detailed mechanism with the associated reaction kinetics is presented and discussed. While SDS has no effect, CTAB increases the reaction rate with the same kinetic behavior in its presence. The catalytic role of CTAB micelles is discussed in terms of the pseudophase model proposed by Menger and Portnoy. The association constant Ks that equals to 286 mol,1 dm3 is found for the association of cerium(IV) with the positive head group of CTAB micelles. The effect of inorganic electrolytes (Na2SO4, NaNO3, NaCl) has also been studied and discussed. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 18,25, 2006 [source] Oxidation and chemiluminescence of catechol by hydrogen peroxide in the presence of Co(II) ions and CTAB micellesLUMINESCENCE: THE JOURNAL OF BIOLOGICAL AND CHEMICAL LUMINESCENCE, Issue 5 2007Jan Lasovsky Abstract The oxidation of catechol in neutral and slightly alkaline aqueous solutions (pH 7,9.6) by excess hydrogen peroxide (0.002,0.09 mol/L) in the presence of Co(II) (2.10,7,2.10,5 mol/L) is accompanied by abrupt formation of red purple colouration, which is subsequently decolourized within 1 h. The electron spectra of the reaction mixture are characterized by a broad band covering the whole visible range (400,700 nm), with maximum at 485 nm. The reaction is initiated by catechol oxidation to its semiquinone radical and further to 1,2-benzoquinone. By nucleophilic addition of hydrogen peroxide into the p -position of benzoquinone C=O groups, hydroperoxide intermediates are formed, which decompose to hydroxylated 1,4-benzoquinones. It was confirmed by MS spectroscopy that monohydroxy-, dihydroxy- and tetrahydroxy-1,4-benzoquinone are formed as intermediate products. As final products of catechol decomposition, muconic acid, its hydroxy- and dihydroxy-derivatives and crotonic acid were identified. In the micellar environment of hexadecyltrimethylammonium bromide the decomposition rate of catechol is three times faster, due to micellar catalysis, and is accompanied by chemiluminescence (CL) emission, with maxima at 500 and 640 nm and a quantum yield of 1 × 10,4. The CL of catechol can be further sensitized by a factor of 8 (maximum) with the aid of intramicellar energy transfer to fluorescein. Copyright © 2007 John Wiley & Sons, Ltd. [source] | ||||||||||