Inhibition effect of {surfactant–substrate} aggregation on the rate of oxidation of reducing sugars by alkaline hexacyanoferrate(III)

The effect of cationic (cetyltrimethylammonium bromide, CTAB), anionic (sodium lauryl sulfate, NaLS), and nonionic (Brij‐35) surfactants on the rate of oxidation of some reducing sugars (xylose, glucose, and fructose) by alkaline hexacyanoferrate(III) has been studied in the temperature range from 35 to 50°C. The rate of oxidation is strongly inhibited in the presence of surfactant. The inhibition effect of surfactant on the rate of reaction has been observed below critical micelle concentration (CMC) of CTAB. In case of NaLS and Brij‐35, the inhibition effect was above CMC, at which the surfactant abruptly associates to form micelle. The kinetic data have been accounted for by the combination of surfactant molecule(s) with a substrate molecule in case of CTAB and distribution of substrate into micellar and aqueous pseudophase in case of NaLS and Brij‐35. The binding parameters (binding constants, partition coefficients, and free‐energy transfer from water to micelle) in case of NaLS and Brij‐35 have been evaluated with the help of Menger and Portnoy model reported for micellar inhibition. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 595–604, 2007     

Interaction of Polyacrylamide with Conventional Anionic and Gemini Anionic Surfactants

The interaction of polyacrylamide (PAM) with conventional anionic (sodium lauryl sulphate, NaLS) and gemini anionic (sodium salt of bis(1-dodecenyl succinimic acid), represented as NaBDS) surfactants has been studied in alkaline medium by electrical conductance and surface-tension measurements at 35⁰C in order to compare the behavior of two surfactants toward the polymer. The surface parameters and thermodynamic parameters have been evaluated and compared. The results indicate more readily interaction of anionic gemini surfactant with the polymer (PAM).     

Micellar catalysed chlorination of acetophenone by chloramine-T

The chlorination of acetophenone by chloramine-T cat has been catalysed by anionic micelle, sodium lauryl sulphate (NaLS). Though the order in cat is one, the order in acetophenone is fractional at lower concentration and becomes zero at higher concentration in the presence and absence of NaLS. This is probably due to the change in rate-determining step. At lower acetophenone concentration, the decomposition of enol-chlorinating species complex is rate-determining whereas at higher concentration, the formation of chlorinating species is rate determining. The graph ofk ₂ versus detergent concentration is sigmoidal and the positive co-operativityversus log[D] graph is 1.11, indicating possible interaction between micelle and substrate.     

Activity of α‐Chymotrypsin in Cationic and Nonionic Micellar Media: Ultraviolet and Fluorescence Spectroscopic Approach

α‐Chymotrypsin (α‐CT) activity was measured in aqueous buffer with the following alkyltriphenylphosphonium bromide surfactants in the series cetyl, tetradecyl, and dodecyl as a tail length. For the sake of comparison with mixed micellar investigation on activity of α‐CT, cationic cetyltriphenylphosphonium bromide (CTPB) and nonionic surfactant Triton X‐100, Brij‐56, Brij‐35, Tween 20, and Igepal Co‐210 have been used. The p‐nitrophenyl acetate (PNPA) hydrolysis rate was determined at the surfactant concentration of both cationic and mixed micellar systems by a UV–vis spectrophotometer. The catalytic reaction follows the Michaelis–Menten mechanism, and the catalytic efficiency (k_cat/K_M) was evaluated for both homogeneous and mixed‐micellar media. The maximum catalytic efficiency was observed at 5 mM concentration of CTPB, but the highest catalytic efficiency, 572 M^?1 s^?1, was measured in the presence of mixed micellar (7.5 mM CTPB + 2.5 mM Tween‐20). The fluorescence (FL) spectra showed the differences of α‐CT conformations in the presence of cationic surfactants. The FL results suggest that the influence of cationic surfactant on proteolysis arises from the interaction with the α‐CT. The binding constant, k_sv, of α‐CT with cationic aggregates was determined in the buffer using the Stern–Volmer equation by the fluorescence spectroscopic approach.     

Effect of Ionic Surfactants on the Adsorption of Quercus infectoria Natural Dye on Cotton Fiber: A Kinetic Study

The adsorption kinetics of Quercus infectoria natural dye on cotton in the absence and presence of the cationic (cetyl trimethyl ammonium bromide; CTAB) and anionic (sodium lauryl sulfate; NaLS) surfactants has been investigated at three temperatures, namely, 40°C, 50°C, and 60°C. On increasing the surfactant content in the surfactant-dye mixture, the initial rate of adsorption (h _i) and the adsorption capacity at equilibrium (q _e) were found to increase while pseudo-second-order rate constant (k ₂) was found to decrease. The retarding effect of surfactant on k ₂ was in order of CTAB > NaLS. The activation parameters for adsorption process have been evaluated in each case, and the mechanism of adsorption process has been discussed.     

Influence of Amine‐Based Cationic Gemini Surfactants on Catalytic Activity of α‐Chymotrypsin

The α‐chymotrypsin activity was tested in aqueous media with the presence of novel cationic amine–based gemini surfactant, with different spacer chain lengths and head group size, and also compared with the cationic cetyltrimethylammonium bromide (CTAB) and cetyltriphenylphosphonium bromide (CTPB) surfactants and aqueous buffer only. The p‐nitrophenyl acetate (PNPA) hydrolysis rate was monitored in the presence of the surfactant concentration at 30°C. Most of these gemini surfactants gave higher catalytic activity as compared to cationic CTAB and CTPB. The highest superactivity was measured in the presence of gemini 16‐12‐16, [dodecanediyl‐1,12‐bis(cetyldimethylammonium bromide)] surfactant at pH 7.5. The catalytic reaction follows the Michaelis–Menten mechanism. The catalytic rate constants, k_cat, show the same profile that the catalytic affinity; K_M being enhanced with increasing space chain length. The results are favorable for considering that the amine‐based gemini surfactant influences more than both the aqueous and cationic micellar media.     

Micellar effects upon electron transfer from ferrocenes

The oxidations of ferrocene (FcH) and n-butylferrocene (FcBu) by ferric salts (nitrate or bromide) are strongly inhibited by aqueous cetyltrimethylammonium bromide and nitrate (CTABr and CTANO₃, respectively). The kinetics of inhibition fit a model in which the substrates are distributed between water, and the micelles and binding constants K_s to the micelle can be estimated. The oxidations are strongly catalyzed by micelles of sodium lauryl sulfate (NaLS), and the kinetics can be fitted to a model in which the reaction rate depends upon the concentration of both reactants in the micellar pseudophase and the rate constants in that pseudophase, which for both substrates are very similar to those in water. Some added salts reduce the micellar catalysis by excluding ferric ions from the micelle. The oxidations of FcH and FcBu by ferricyanide ions are too fast to be followed in water, but they are inhibited by anionic micelles of NaLS. By analyzing the rate surfactant profiles using independently measured values of K_s the second-order rate constants in water have been estimated.     

Kinetics and mechanism of alkaline hydrolysis of 4‐nitrophthalimide in the absence and presence of cationic micelles

Pseudo‐first‐order rate constants (k_obs) for alkaline hydrolysis of 4‐nitrophthalimide (NPTH) decreased by nearly 8‐ and 6‐fold with the increase in the total concentration of cetyltrimethyl‐ammonium bromide ([CTABr]_T) from 0 to 0.02 M at 0.01 and 0.05 M NaOH, respectively. These observations are explained in terms of the pseudophase model and pseudophase ion‐exchange model of micelle. The increase in the contents of CH₃CN from 1 to 70% v/v and CH₃OH from 0 to 80% v/v in mixed aqueous solvents decreases k_obs by nearly 12‐ and 11‐fold, respectively. The values of k_obs increase by nearly 27% with the increase in the ionic strength from 0.03 to 3.0 M. The mechanism of alkaline hydrolysis of NPTH involves the reactions between HO^? and nonionized NPTH as well as between HO^? and ionized NPTH. The micellar inhibition of the rate of alkaline hydrolysis of NPTH is attributed to medium polarity effect. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 407–414, 2001     

Cationic Reverse Micelles Create Water with Super Hydrogen‐Bond‐Donor Capacity for Enzymatic Catalysis: Hydrolysis of 2‐Naphthyl Acetate by α‐Chymotrypsin

Reverse micelles (RMs) are very good nanoreactors because they can create a unique microenvironment for carrying out a variety of chemical and biochemical reactions. The aim of the present work is to determine the influence of different RM interfaces on the hydrolysis of 2‐naphthyl acetate (2‐NA) by α‐chymotrypsin (α‐CT). The reaction was studied in water/benzyl‐n‐hexadecyldimethylammonium chloride (BHDC)/benzene RMs and, its efficiency compared with that observed in pure water and in sodium 1,4‐bis‐2‐ethylhexylsulfosuccinate (AOT) RMs. Thus, the hydrolysis rates of 2‐NA catalyzed by α‐CT were determined by spectroscopic measurements. In addition, the method used allows the joint evaluation of the substrate partition constant K_p between the organic and the micellar pseudophase and the kinetic parameters: catalytic rate constant k_cat, and the Michaelis constant K_M of the enzymatic reaction. The effect of the surfactant concentration on the kinetics parameters was determined at constant W₀=[H₂O]/[surfactant], and the variation of W₀ with surfactant constant concentration was investigated. The results show that the classical Michaelis–Menten mechanism is valid for α‐CT in all of the RMs systems studied and that the reaction takes place at both RM interfaces. Moreover, the catalytic efficiency values k_cat/K_M obtained in the RMs systems are higher than that reported in water. Furthermore, there is a remarkable increase in α‐CT efficiency in the cationic RMs in comparison with the anionic system, presumably due to the unique water properties found in these confined media. The results show that in cationic RMs the hydrogen‐bond donor capacity of water is enhanced due to its interaction with the cationic interface. Hence, entrapped water can be converted into “super‐water” for the enzymatic reaction studied in this work.     

Anionic gemini surfactant viz. sodium salt of bis(1-dodecenylsuccinamic acid); synthesis,surface properties and micellar effect on oxidation of reducing sugars by hexacyanoferrate(III)

An anionic gemini surfactant viz. sodium salt of bis(1-dodecenylsuccinamic acid) has been synthesized. Conductivity and surface tension measurements were performed in order to characterize the synthesized surfactant. The foaming power and contact angle have also been determined. Micellar effect of synthesized gemini surfactant on the rate of oxidation of reducing sugars (viz. glucose, fructose and xylose) by alkaline hexacyanoferrate(III) has been studied in the temperature range (40–60 °C). It has been observed that reducing sugar associates/binds with surfactant micelle to form mixed aggregate which is resistant to react with hexacyanoferrate(III). The binding parameters have also been evaluated using Menger and Portnoy model.     

L-半胱氨酸在SDS吸附胶束中的电化学催化氧化

The electrochemical oxidation of L-cysteine can be catalyzed by sodium dodecyl sulfate (SDS) admicelles. The catalytic efficiency increases hardly when SDS concentration is lower than the critical admicelle concentration (CAC) and increases rapidly when SDS concentration is between CAC and the critical micelle concentration (CMC), but decreases when SDS concentration is higher than CMC. Both results of rate constant k^0 and Gibbs free energy ΔG^ck accord with that of catalytic efficiency.     

Structure and physico‐chemical properties in mixed aqueous solution of sodium alkylcarboxylate‐alkyltrimethylammonium bromide

The physico‐chemical properties of organized assemblies (micelle or vesicle) from sodium alkylcarboxylate ‐ alkyltrimethyl ‐ammonium bromide mixture have been investigated systematically. In different mixed cationc‐anionic surfactant systems, micelles and vesicles can coexist or be transformed into each other on different conditions. The experimental results are explained prelimilarily from the viewpoint of molecular packing geometry. The solubilization of organic compound in the mixed surfactant system was also studied in detail.     

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     

Kinetics of the acid hydrolysis of isoproturon in the absence and presence of sodium lauryl sulfate micelles

Kinetics of the hydrolysis of isoproturon by hydrochloric acid has been studied spectrophotometrically in the absence and the presence of anionic sodium lauryl sulfate (NaLS) micelles. The anionic micelle was found to increase the rate of reaction. The reaction followed first-order kinetics with respect to isoproturon and was linearly dependent upon [HCl]. In both aqueous and micellar pseudophases, the reaction was started with the protonation of the amino group of isoproturon followed by attack of water to yield phenylcarbamic acid and the corresponding amine, thus obeying the addition–elimination mechanism. The surfactant decreased the activation entropy. The binding constant in consistence with the rate constants was evaluated on the basis of pseudophase ion-exchange model. The added salts (NaCl and KCl) decreased the rate of reaction due to the exclusion of H⁺ from micellar surfaces.     

Interfacial and Thermodynamic Properties of Anionic‐Nonionic Mixed Surfactant System: Influence of Hydrophobic Chain Length of the Nonionic Surfactant

The influence of hydrophobic chain length in nonionic surfactants on interfacial and thermodynamics properties of a binary anionic‐nonionic mixed surfactant was investigated. In this study, nonionic surfactants lauric‐monoethanolamide (C₁₂ MEA) and myrisitic‐monoethanolamide (C₁₄ MEA) were mixed with an anionic surfactant, α‐olefin sulfonate (AOS). The critical micelle concentration (cmc), maximum surface excess (Γ_max), and minimum area per molecule (A_min) were obtained from surface tension isotherms at various temperatures. The thermodynamic parameters of micellization and adsorption were also computed. Micellar aggregation number (N_agg), micropolarity, and binding constant (K_sv) of pure and mixed surfactant system was calculated by fluorescence measurements. Rubingh's method was applied to calculate interaction parameters for the mixed surfactant systems.     

Nonionic Micellar Catalyzed Oxidation of Vitamins by Chloramine-T in HClO4 Medium: A Kinetic Study

The kinetics of oxidation of vitamin B₁ (thiamine hydrochloride) and vitamin B₆ (pyridoxine hydrochloride) by chloramine-T (CAT) in perchloric acid medium and in presence of a non ionic surfactant (Triton x-100) have been investigated. A catalytic effect of the nonionic micelle on the rate of oxidation has been observed and rate is found to be proportional to 7lcub;k′ + k″ [Triton x-100]}, where k′ and k″ are the rate constants in absence and presence of surfactant, respectively. The rate shows a first-order, a fractional order and a zero order dependence on [Chloramine-T]_o, [Vitamin]_o and [H⁺]₀, respectively in absence as well as in presence of surfactant. A mechanism involving association/binding between the oxidant and the surfactant micelle, which is supported by spectrophotometric evidence has been proposed. The binding parameters have also been evaluated using a pseudo-phase kinetic model.     

Kinetics of Malachite Green Fading in Water‐ethanol‐1‐propanol Ternary Mixtures

The rate constant of malachite green (MG⁺) alkaline fading was measured in water‐ethanol‐1‐propanol ternary mixtures. This reaction was studied under pseudo‐first‐order conditions at 283‐303 K. It was observed that the reaction rate constant increases in the presence of different weight percentages of ethanol and 1‐propanol. The fundamental rate constants of MG⁺ fading in these solutions were obtained by SESMORTAC model. In each series of experiments, concentration of one alcohol was kept constant and the concentration of the second one was changed. It was observed that at constant concentration of one alcohol and variable concentrations of the second one, with increase in temperature, k₁ values increase and this indicates that presence of ethanol (or 1‐propanol) increases dissolution of 1‐propanol (or ethanol) in the activated complex formed in these solutions. Also, in each zone, fundamental rate constants of reaction at each certain temperature change as k₂ » k₁ » k_?1.     

Kinetic characterization of a transient reaction by degeneration of the precursor mechanism: Application to the synthesis of 3,4‐diazabicyclo[4.3.0]‐ non‐2‐ene

The rate of the oxidation of N‐amino‐3‐azabicyclo[3.3.0]octane by chloramine has been studied by GC and HPLC between pH 10.5 and 13.5. The second‐order reaction exhibits specific acid catalysis. The formation of N,N′‐azo‐3‐azabicyclo[3.3.0]octane or 3,4‐diazabicyclo[4.3.0]non‐2‐ene is pH, concentration, and temperature dependent. In alkaline media, the exclusive formation of 3,4‐diazabicyclo[4.3.0]non‐2‐ene is observed. Kinetic studies show that the oxidation of N‐amino‐3‐azabicyclo[3.3.0]octane by chloramine is a multistep process with the initial formation of a diazene‐type intermediate, which is converted by hydroxide ions into 3,4‐diazabicyclo[4.3.0]non‐2‐ene. Because it was not possible to follow the rate of change of the intermediate concentration, to determine the kinetics of 3,4‐diazabicyclo[4.3.0]non‐2‐ene formation, a procedure based on the degeneration of the precursor process was adopted. An appropriate mathematical treatment allowed a quantitative interpretation of all the phenomena observed over the given pH interval. The activation parameters were determined. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 327–338, 2006     

Effect of Alcohols on the CMC and Thermodynamic Functions of Anionic Surfactants in DMF/Long‐Chain Alcohol Using Microcalorimetric Method

The critical micelle concentration (CMC) of two kinds of anionic surfactant (including sodium laurate (SLA) and sodium dodecyl sulfate (SDS)) in mixed alcohol and N, N‐dimethyl formamide solvent (DMF) were investigated through measuring power‐time curves by titration microcalorimetry. From data of the lowest point and the area of the power‐time curves, their CMC and ΔH _m ⁰ can be obtained. According to standard thermodynamic equations, ΔG _m ⁰ and ΔS _m ⁰ also can be calculated. For different surfactant, the influences of the carbon number and the concentration of alcohol on the CMC and standard thermodynamic functions are different in DMF polar medium. These thermodynamic functions for micelle formation can be further interpreted.     

Kinetics and mechanism of oxidation of neutral α ‐amino acids by sodium N‐chloro‐p‐toluenesulfonamide in acid medium

Kinetics of oxidation of α ‐amino acids, glycine, valine, alanine, and phenylalanine, by sodium N‐chloro‐p‐toluenesulfonamide or chloramine‐T (CAT) has been investigated in HClO₄ medium at 30°C. The rate shows first‐order dependence on both CAT and amino acid concentrations and an inverse first‐order on [H⁺]. The variation of ionic strength and the addition of p‐toluenesulfonamide and Cl^? ion had no effect on the reaction rate. Decrease of dielectric constant of the medium by increasing the MeOH content decreased the rate. Rate studies in D₂O medium showed the inverse solvent‐isotope effect of k_D2O/k_H2O=0.50. Proton‐inventory studies were carried out using H₂O–D₂O mixtures. The activation parameters have been computed. The proposed mechanism and the derived rate law are consistent with the observed kinetic data. An isokinetic relationship is observed with β=323 K, indicating enthalpy as a controlling factor. The rate of oxidation increases in the following order: Gly < Val < Phe < Ala. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 49–55, 2002