Effect of Cationic Micelle on the Kinetics of Oxidation of Citric Acid by N-Bromophthalimide in Acidic Medium

Kinetics of the oxidation of citric acid (CA) by N-bromophthalimide (NBP) has been studied in the presence of cationic surfactant cetyltrimethylammonium bromide (CTAB) at 35°C. The CMC value is lower than those given in the literature for aqueous solutions of CTAB without added electrolyte. The reaction is strongly catalyzed by cationic micelle, CTAB with a progressive increase in CTAB concentration the reaction rate increased, at higher concentration constancy in the rate constant was observed. The reaction follows first and fractional order kinetics in NBP and citric acid, respectively. The reaction follows inverse fractional order with respect to perchloric acid. The Arrhenius equation is found to be valid for the reaction. A detailed mechanism with the associated reaction kinetics is discussed. The catalytic role of CTAB micelles is discussed in terms of the Menger and Portnoy model.     

Kinetics of oxidation of iodide by vanadium (V): Catalysis by the water pools of CTAB reverse micelles

The kinetic study of the oxidation of iodide ion by V(V) has been carried out in the water pools of cetyl trimethyl ammonium bromide(CTAB) reverse micelles in a mixture of chloroform-hexane (3 : 2). The study of the effect of concentration of V(V) and I^? on rate show that the reaction obeys first order kinetics with each of the reactants. A plot of k′ (pseudo first order rate constant) versus [H⁺] is linear with a positive intercept at constant concentrations of iodide and bromide. The rate of the reaction is markedly increased in the reverse micellar medium compared to conventional aqueous medium under identical conditions. The pronounced acceleration in reverse micelles has been accounted for by the concentration effect in the water pool which have an effect on kinetics.     

Effect of Cationic Micellar Aggregates on the Kinetics of Dextrose Oxidation by N-Bromophthalimide

The effect of cationic micelles of Cetyltrimethyl ammonium bromide (CTAB) on the kinetics of oxidation of dextrose by N-Bromophthalimide were studied at 40°C. The reaction follows fractional-order and first order kinetics, with respect to [dextrose] and [NBP], respectively. CTAB strongly catalyze the reaction, and typical k_obs and [CTAB] profile was observed, that is, with a progressive increase in [CTAB], the reaction rate increased, reaches a maximum value then decreased. Results are treated quantitatively in terms of Berezin's Model, which is applicable to bimolecular micellar catalyzed reaction. There is a negative effect of mercuric acetate and phthalimide. The influence of salts on the reaction rates has also been seen. The activation parameters as well as other parameters were calculated and suitable mechanism consistent with the experimental findings has been proposed.     

CTAB对H2O2氧化抗坏血酸反应动力学的影响

H₂O₂氧化抗坏血酸H₂A的反应为一复杂过程,其过程可用下面可逆连续反应来描述:HA－＋H₂O₂ A,本文用热导式热量计研究了该复杂反应在25 ℃和pH=7的磷酸缓冲溶液(离子强度μ=0.1 mol•L^－1)以及在阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)存在下的反应动力学, 获得了不同CTAB浓度下该复杂反应的表观动力学参数k₁、k₂和k_－1.研究结果表明,表面活性剂CTAB单体分子对反应参数k_－1影响不大, 但却能催化第一步正向反应使k₁变大,而使k₂减小; 在临界胶束浓度cmc附近k₁达到最大值,随后又降低；低浓度胶束对k_-1影响不大,而使k₂增大；高浓度胶束则使k_-1增大而使k₂减小. 低浓度CTAB胶束对的活性影响不大, 而高浓度CTAB胶束将较显著地促进的歧化过程, 减缓的氧化过程. 胶束的静电效应、疏水效应和局部浓聚效应是影响上述反应的重要因素.     

Applicability of Positive Cooperativity Model of Enzyme Catalysis on Surfactant-Mediated Reaction of Pararosaniline Hydrochloride Carbocation with Hydroxide Ion

The reaction of hydroxide ion with stabilized pararosaniline hydrochloride carbocation was investigated in the presence of cationic micelles of cetyltrimethylammonium bromide (CTAB) and anionic micelles of sodium dodecyl sulfate (SDS). Pseudo-first-order kinetics were followed by the reaction system and rate constant depends on surfactant concentration. The reaction was strongly inhibited in the presence of SDS micelles whereas catalyzed in the presence of CTAB micelles. Micellar data were analyzed by applying positive cooperativity model of enzyme catalysis. The value of index of cooperativity (n) was greater than 1 for all reaction systems. Inhibitory and catalytic effect in the presence of micelles had been explained on the basis of hydrophobic and electrostatic interactions of various species present in the reaction systems. Presence of counterions in the reaction system inhibited the reaction rate.     

Kinetic study of oxidation of galactose by N-bromo phthalimide in the presence of cationic micelle in acidic medium

The kinetics of micellar catalyzed oxidation of galactose by N-bromophthalimide was studied in the presence of acidic medium at 308?K. The oxidation reaction exhibits first-order kinetics with respect to oxidant (N-bromophthalimide), fractional order with respect to substrate (galactose) and positive fractional order with respect to HClO₄ on the rate of reaction. The rate of the reaction increased with decreasing the dielectric constant of the medium. With a progressive increase in the concentration of CTAB, the rate of reaction increased and after reaching peak k _obs, decreased at higher concentrations of CTAB. There catalytic roles are best explained by Berezin??s model. The influence of salts on the reaction rate was also studied. The various activation parameters have been calculated. The rate constant and binding constant with the surfactant have also been evaluated. A suitable mechanism consistent with the experimental findings has been proposed.     

Micellae catalysis of the oxidation of 1,4-dihydro-nicotinamides by methylene blue part 2

The oxidation of 1-R-1,4-dihydronicotinamides (1a: R = benzyl, 1b:R = octyl, 1c:R = cetyl) by methylene blue has been studied in the presence of micelles of cetyltrimethylammonium bromide (CTAB), polyoxyethylene[23]lauryl ether (Brij^® 35) and sodium dodecylbenzenesulfonate (SDBS). In CTAB, a small rate enhancement was observed below the cmc, followed by a gradual decrease above the cmc. Brij 35 has little effect on the reaction rate. The rate vs. concentration profile in SDBS shows a very sharp maximum near the cmc for 1b and 1c, whereas a more moderate increase in rate is observed for 1a. The effects are analyzed in terms of the pseudophase model for micellar catalysis, and it appears that the observed rate enhancements can be completely ascribed to increments of the reactant concentration in the micellar pseudophase. Comparison with rate effects in sodium dodecylsulfate (SDS) micelles reveals that the reaction in SDBS micelles proceeds in a more polar environment. This provides kinetic evidence that the aryl moiety in SDBS allows a deeper penetration of water molecules into the micelle, thus giving rise to a more open surface for SDBS micelles than for SDS micelles.     

Kinetics of the H2O2-dependent ligninase-catalyzed oxidation of veratryl alcohol in the presence of cationic surfactant studied by spectrophotometric technique

The kinetics of ligninase-catalyzed oxidation of veratryl alcohol (VA) by H(2)O(2) in the aqueous medium containing cationic surfactant cetyltrimethylammonium bromide (CTAB) has been investigated using spectrophotometric technique. Steady-state kinetic studies at different concentrations of CTAB indicate that the reaction follows a ping pong mechanism and the mechanism always holds but the kinetic parameters vary with CTAB concentrations. CTAB is a weak inhibitor for ligninase; it lowers the maximum initial velocity. CTAB also causes the Michaelis constant of H(2)O(2) to decrease dramatically and that of VA to increase markedly. Based on the changes in kinetic parameters of the enzyme-catalyzed reaction at different CTAB concentrations (lower than, near to and larger than its critical micelle concentration) and the effects of the CTAB monomer and the micelles on the spectra of VA and its corresponding aldehyde, a conclusion could be made that modification of the enzymatic protein by the surfactant monomer should be responsible for the above-mentioned results.     

Micellar catalysis on the redox reaction of glycolic acid with chromium(VI)

Chromium(VI) oxidation of glycolic acid in the absence and presence of cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPB) followed the same mechanism as shown by kinetic study. The reaction followed second‐order kinetics, first‐order in each reactant. The oxidation is strongly catalyzed by manganese(II) and cationic micelles of CTAB or CPB. The catalytic effect of micelles can be fitted to a model in which the reaction rate depends upon the concentration of both reactants in the micellar pseudophase. Some added inorganic salts (NaCl, NaBr, NaNO₃, and Na₂SO₄) reduce the micellar catalysis by excluding glycolic acid from the reaction site. The reactivity of glycolic acid towards chromium(VI) has been discussed and also compared with those obtained previously for the reaction between chromium(VI) and the reductants oxalic and lactic acids. On the basis of the observed results, probable mechanisms have been proposed. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 377–386, 2001     

Kinetics and mechanism of oxidation reaction of lactose by N-bromophthalimide: Micelles used as a catalyst

The kinetics and mechanism of the oxidation of lactose by N-bromophthalimide in the absence and presence of cetyltrimethylammonium bromide and sodium dodecyl sulfate micelles was investigated in the presence of sulfuric acid medium. Under pseudo-first-order conditions reaction rate agreed with a first-, fractional- and negative fractional-order kinetics in N-bromophthalimide, lactose and sulfuric acid, respectively. In the presence of additives, the critical micellar concentration values were lower than those given in the literature. The catalytic role of cationic micelles was explained by the Berezin model. The anionic micelles showed slightly inhibitory effect. The influence of salts, phthalimide and mercuric acetate on the reaction rate was also studied. Using the kinetic data, the rate constant, binding constants, and corresponding activation parameters were evaluated. A possible reaction mechanism, which is based on the kinetic results and the product analysis, is proposed.     

Micelle Catalyzed Oxidation of D-Mannose by Cerium (IV) in Sulfuric Acid

Kinetics of D-mannose oxidation by cerium (IV) was studied in a sulfuric acid medium at 40°C both in absence and presence of ionic micelles. In both cases, the rate of the reaction was first-order in D-mannose and cerium (IV), which decreased with increasing [H₂SO₄]. This suggested that the redox reaction followed the same mechanism. The reaction proceeded through formation of an intermediate complex, which was proved by kinetic method. The complex underwent slow unimolecular decomposition to a free radical that reacted with cerium (IV) to afford the product. The catalytic role of cationic cetyltrimethylammonium bromide (CTAB) micelles was best explained by the Menger-Portnoy model. The study of the effect of CTAB also indicated that a negatively charged species was the reactive form of cerium (IV). From the kinetic data, micelle-cerium (IV) binding and rate constants in micellar medium were evaluated. The anionic micelle of sodium dodecyl sulfate plays no catalytic role. The oxidation has the rate expression: -d[Ce(IV)]=k1Kc1[D-mannose][Ce(IV)]dt Different activation parameters for micelle catalyzed and uncatalyzed paths were also calculated and discussed.     

Catalytic effect of CTAB reverse micelles on the kinetics of dissociation of bis(2,4,6–tripyridyl-s-triazine) iron(II)

The kinetics of dissociation of bis(2,4,6–tripyridyl-s-triazine) iron(II), ([Fe(TPTZ)₂]²⁺) has been studied in CTAB/chloroform/hexane reverse micellar medium. In the absence of acid, the reaction is immeasurably slow and does not go to completion in conventional aqueous medium but is markedly accelerated and takes place with a rate constant equal to 55.3 × 10^?3 s^?1 and goes to completion in reverse micelles. The significant increase in rate is attributed to the special properties of the water pool in the reverse micelles like low dielectric constant, nucleophilic effect of Br^- ion, and favorable partitioning of TPTZ in the organic phase. The rate of the reaction decreases with increase in W (=[H₂O]/[CTAB]) at constant CTAB concentration and remains constant with increase in CTAB at fixed W. The results are compared with other closely related systems.     

Superactivity of peroxidase solubilized in reversed micellar systems

Vaccinium mirtyllus peroxidase solubilized in reversed micelles was used for the oxidation of guaiacol. Some relevant parameters for the enzymatic activity, such as pH,w _o (molar ratio water/surfactant), surfactant type and concentration, and cosurfactant concentration, were investigated. The peroxidase showed higher activities in reversed micelles than in aqueous solution. The stability of the peroxidase in reversed micelles was also studied, namely, the effect ofw _o and temperature on enzyme deactivation. The peroxidase displayed higher stabilities in CTAB/hexanol in isooctane reversed micelles, with halflife times higher than 500 h.     

Studies on bio-antioxidants II. An ESR study on the antioxidant efficiency of ascorbyl palmitate in micelles

The kinetics for the reaction of ascorbyl palmitate and 4-hydroxy-TEMPO, 4-methoxy-TEMPO or 4-hexanoyloxy-TEMPO in CTAB and SDS micelles was studied by ESR spectroscopy. It was found that the behavior of ascorbyl palmitate is remarkably different from ascorbic acid in their antioxidant activity in micelles. The predominant factors governing the activity in micelles involve the lipophilicity of the antioxidant and the oxidant, the charge type of the substrates and the concentration of the surfactant. As high as 2 × 10⁴ fold rate variation was observed by changing the lipophilicity of the antioxidant and the microenvironment of the reaction medium.     

Effect of surfactant micelles on the kinetics of oxidation of D‐fructose by cerium(IV) in sulfuric acid medium

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 K_s 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     

Exploitation of reversed micelles as a medium in mimetic peroxidase-catalyzed fluorogenic reaction between hydrogen peroxide and l-tyrosine

The peroxidase activity of mimetic enzyme, iron tetrasulfonatophthalocyanine (FeTSPc), was characterized in reversed micelles of hexadecyltrimethylammonium bromide (CTAB) formed in n-heptane-n-pentanol solution (2:1, V:V). The assay is based on its catalytic effect on the oxidation reaction of l-tyrosine (l-tyr) by hydrogen peroxide. The influences of environmental factors, such as the water content, CTAB concentration and pH, on the peroxidase activity of FeTSPc were investigated. It was observed that the reaction rate was distinctly enhanced in CTAB reversed micelles as compared with the rate in aqueous solution. Under optimum conditions, application of the FeTSPc-catalyzed fluorescence system in reversed micelles to the determination of H(2)O(2) and FeTSPc led to a highly sensitive system compared with that in aqueous solution, permitting detection limits of 5x10(-9) mol l(-1) H(2)O(2) and 2.3x10(-9) mol l(-1) FeTSPc. The advantages and limitations of employing the reversed micellar media in such mimetic peroxidase-catalyzed fluorescent detection schemes were discussed.     

Regulatory role of surfactants in the kinetics of glucose oxidase-catalyzed oxidation ofd-glucose by ferrocenium andn-butylferrocenium ions

The effect of micelles of different surfactants (cationic, anionic, and neutral) on the kinetics of the glucose oxidase-catalyzed reduction of ferrocenium cations RFc⁺ (R=H, Buⁿ) byd-glucose was studied by spectrophotometry. In micellar media of Triton X-100 and sodium dodecyl sulfate (SDS), the Michaelis dependence of the reaction rate on the HFc⁺ concentration is observed, while this dependence has an extreme character in cationic micelles of cetyltrimethylammonium bromide (CTAB). The nature and concentration of surfactants of all types have a slight effect on the rate of reduction of HFc⁺. The level of enzymatic activity is approximately equal in the case of Triton X-100 and CTAB and is considerably lower in the SDS micelles. On going from HFc⁺ to BuⁿFc⁺, the reaction rate is maximum in the cationic CTAB micelles, the anionic SDS micelles exhibit almost no activity, and the activity has an intermediate value in neutral micelles of Triton X-100. The conditions are presented under which the micellar medium controls the catalytic activity of glucose oxidase with respect to ferrocenium cations. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1795–1801, October, 1997.     

Effect of ionic micellar medium on kinetics and mechanism of oxidation of bovine serum albumin: A pulse radiolysis study

Effect of protein–micelle interaction on bovine serum albumin (BSA) oxidation by trichloromethyl peroxyl radical (CCl₃O₂^·) in anionic sodium dodecyl sulfate (SDS) and cationic cetyltrimethyl ammonium bromide (CTAB) micellar media has been studied using nanosecond pulse radiolysis technique. Viscosity measurement and light scattering studies have suggested that SDS and CTAB micelles produce BSA–micelle aggregates of different sizes and polydispersity. Oxidation kinetics and transients have been affected both by anionic SDS and cationic CTAB micelles but in a different manner. Tryptophanyl-CCl₃O₂^· adduct radical to tyrosyl radical transformation in BSA has been observed in anionic SDS micelles but not in cationic CTAB micelles. Similar studies have also been done with tryptophan and tyrosine amino acids, which undergo oxidation in BSA. The study suggests that Coulombic and hydrophobic interactions between micelles and protein affect the structure of the protein to shield its functional amino acids, like tryptophan and tyrosine, to neutral oxidizing radical.     

Kinetics of the alkaline hydrolysis of isoproturon in CTAB and NaLS micelles

Kinetics of the alkaline hydrolysis of isoproturon has been studied in the absence and presence of cetyltrimethylammonium bromide (CTAB) and sodium lauryl sulfate (NaLS) micelles. CTAB micelles were found to enhance the rate of reaction, while NaLS micelles inhibited the reaction rate. The reaction obeyed first‐order kinetics in [isoproturon] and was linearly dependent on [NaOH] at lower concentration. The rate of reaction became independent at higher [NaOH]. At lower [NaOH] the reaction proceeded via formation of hydroxide ion addition complex, while at higher [NaOH] the reaction occurred via deprotonation of ? NH? , leading to the formation of isocyanate. The values of k_w, k_m, and K_s were determined by considering the pseudophase ion exchange model. The activation parameters have also been reported. The effect of added salts (NaCl and KNO₃) on the reaction rate has also been studied. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 39: 39–45, 2007     

Micellar effects of a triazole-based cationic gemini surfactant on the rate of a nucleophilic aromatic substitution reaction

The reaction between 2,4-dinitrochlorobenzene (DNCB) and hydroxide ion was studied spectrophotometrically at 25 °C in micelles of a triazole-based cationic gemini surfactant 18-triazole-18 or micelles of the conventional cationic surfactant CTAB. Both CTAB and 18-triazole-18 accelerated this nucleophilic aromatic substitution reaction. The binding constant of the substrate to the micelle, K _S, for 18-triazole-18 (K _S=335 M⁻¹) was found to be much larger than that for CTAB (85 M⁻¹) by fitting the kinetic results with pseudophase ion-exchange (PIE) model, which suggests that DNCB binds with gemini micelles more easily than it does with CTAB micelles. It was also found that 18-triazole-18 catalytic system was in accordance with PIE model at surfactant concentrations below ca. 0.5 mM, above which the increase of viscosity and the change of micelle size with increased surfactant concentration may remarkably influence the reaction. This was quite different from the reaction catalyzed by micelles of the conventional surfactant CTAB.