Investigation on the basic hydrolysis of crystal violet in mixed reverse micelles formed with AOT and nonionic surfactants

 The kinetics and thermodynamics of the basic hydrolysis of crystal violet (CV) in mixed reverse micelles formed with anionic surfactant AOT and nonionic surfactants have been investigated. It was found that the mixed reverse micelles had inhibitory effects on CV hydrolysis compared with the normal aqueous solution, and the equilibrium constant K of the reaction in mixed reverse micellar systems is smaller than that in pure water. The influence of water content and surfactant composition in reverse micelles on the second-order rate constant k ₁ of the positive reaction, on the first-order rate constant k _-1 of the reverse reaction, as well as on the equilibrium constant K of the reaction has been studied, and the results obtained were interpreted in terms of the nature of surfactants and the properties of microenvironment where the reaction took place. Received: 24 October 1997 Accepted: 18 March 1998     

Micellar effects upon the basic hydrolysis of 2,7-bis(diethylamino)phenazoxonium chloride

The effect of cationic and anionic surfactants on the reaction of Basic Blue 3 (2,7-bis(diethylamino)phenazoxonium chloride, 1) with hydroxide ion has been studied. Cetyltrimethylammonium bromide (CTAB), cetyl and tetradecyltrimethylammonium chloride (CTAC and MTAC) enhance the rate of basic hydrolysis whereas sodium dodecyl sulfate (SDS) has an inhibitory effect. The extent of micellar catalysis is reduced by the addition of organic solvents. The results have been analyzed on the basis of the pseudophase ion-exchange model [1–3].     

Hydrolysis of bis(4-nitrophenyl) ethyl phosphate in micellar solutions of dicationic surfactants

The effect of dicationic surfactants on the hydrolysis of bis(4-nitrophenyl) ethyl phosphate in a borate buffer is studied. The presence of long-chain surfactants results in a significant (up to 50-fold) increase in the observed rate constant (k _obs) of the process. The catalytic effect of micelles increases with increasing alkyl chain length due to the strengthening of binding of the reagents by micelles. The presence of two cationic centers in the surfactant molecule enhances the catalytic properties of micelles. The dependence ofk _obs of hydrolysis of the substrate on the borate buffer concentration is studied. Alkaline hydrolysis is more sensitive to the added surfactant than the reaction involving borate ions.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1576–1580, September, 1994.     

Effect of self‐assemblies of various surfactants in their single and mixed states on the BZ oscillatory reaction

Micelles of different surfactants are well known to affect chemical equilibria and reactivities by selectively sequestering the reagent substrates through electrostatic and hydrophobic interactions. In this article, the effects of micelles of various surfactants on different parameters of the Ce(IV)‐catalyzed Belousov–Zhabotinsky (BZ) oscillatory reaction at 35°C in nonstirred closed conditions are studied by employing spectrophotometry and tensiometry. Surfactants used in this study are the cationics hexadecyltrimethylammonium bromide (CTAB) and pentamethylene‐1,5‐bis(N‐hexadecyl‐N,N‐dimethylammonium)bromide gemini (Gemini), anionic sodium dodecylbenzene sulfonate (SDBS), and nonionic Brij58, whereas the binary surfactant systems used are cationic–nonionic CTAB+Brij58 and anionic–nonionic SDBS+Brij58. The results revealed that the induction period shows a definite variation with increasing concentration of different surfactants above their critical micelle concentration (cmc). The amplitudes of oscillation and absorbance maxima and minima are enhanced in the presence of micelles of CTAB and Gemini surfactants, whereas micelles of SDBS and Brij58 have almost no effect on the nature of the oscillations. However, mixed micelles of CTAB+Brij58 and SDBS+Brij58 binary mixtures show a quite different effect on the overall behavior of the oscillations. The enhanced effect of CTAB and Gemini surfactants on the overall nature of oscillations has been attributed to the positive charge on the surface of their micelles and to some extent on the presence of nitrogen in their head group. The effect of mixed binary micelles may be attributed to their synergistic nature. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 659–668, 2010     

Effects of emulsifier charge and concentration on pancreatic lipolysis. 1. In the absence of bile salts

An in vitro study is performed with sunflower oil-in-water emulsions to clarify the effects of type of used emulsifier, its concentration, and reaction time on the degree of oil lipolysis, α. Anionic, nonionic, and cationic surfactants are studied as emulsifiers. For all systems, three regions are observed when surfactant concentration is scaled with the critical micelle concentration, C(S)/cmc: (1) At C(S) < cmc, α ≈ 0.5 after 30 min and increases up to 0.9 after 4 h. (2) At C(S) ≈ 3 × cmc, α ≈ 0.15 after 30 min and increases steeply up to 0.9 after 2 h for the cationic and nonionic surfactants, whereas it remains around 0.2 for the anionic surfactants. (3) At C(S) above certain threshold value, α = 0 for all studied surfactants, for reaction time up to 8 h. Additional experiments show that the lipase hydrolyzes molecularly soluble substrate (tributirin) at C(S) > cmc, which is a proof that these surfactants do not denature or block the enzyme active center. Thus, we conclude that the mechanism of enzyme inhibition by these surfactants is the formation of a dense adsorption layer on an oil drop surface, which displaces the lipase from direct contact with the triglycerides.     

The Polarographic Behaviour of Bromate Ions in Buffered and Unbuffered Solutions and the Effect of Surface Active Substances

The polarographic behaviour of bromate ions in buffered and unbuffered solutions has been studied in the absence and presence of cationic, anionic and nonionic surfactants. The mechanism for the reduction in acid media is discussed. The adsorption effects of electrochemically inactive surfactants on the polarographic waves of BrO₃^? has been investigated. The values of the kinetic parameters for the electrode reaction at different pH values have been computed.     

Micellar catalyzed hydrolysis of mono-2,3-dichloroaniline phosphate

The kinetics of micellar catalyzed hydrolysis of mono-2,3-dichloroaniline phosphate in the presence of different surfactants has been studied at 303?K. The rate of reaction has been found to be first order with respect to both [substrate] and [HCl]. The cationic micelles of cetylpyridinium chloride (CPC), anionic micelles of di-octyl sodium sulphosuccinate (AOT), and non-ionic micelles of polyoxyethylene sorbitan monooleate (Tween 80) enhanced the rate of reaction to a maximum value and after that the increase in concentration of surfactant decreased the reaction rate. The applicability of different kinetic models has been tested to explain the observed micellar effects. The various thermodynamic activation parameters (E_a, ΔH^≠, ΔS^≠, ΔG^≠) have been evaluated. The added salts viz. KCl, KNO₃, K₂SO₄ enhanced the rate of reaction in the presence of CPC, AOT, and Tween 80 micelles. The kinetic parameters were determined from the rate (surfactant) profile and a suitable mechanism consistent with the experimental finding has been proposed.     

Micellar effects of cation-active surfactants on the reaction of (o-aminomethyl)phenols with ethylp-nitrophenyl chloromethylphosphonate

The reaction of (o-aminomethyl)phenols with ethylp-nitrophenyl chloromethylphosphonate in aqueous micellar solutions of cation-active surfactants has been studied. The effect of the structure of the surfactant and the nucleophile, pH of the medium, and temperature on the reaction rate in the micellar phase has been investigated. The rate constants in micelles are much higher than those in water.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2065–2068, December, 1993.     

光引发的甘油三乙酯反应的振荡

在(30±0.1)℃条件下,以1对5W节能灯(电子荧光灯)为光源,设计出以甘油三乙酯为底物,环已烷水混合体系的Beluosov-Zhabotinskii振荡反应,并研究了改变光源、有机溶剂、各组分浓度以及加入各类表面活性剂形成O/W型乳液后,各种因素对此类光引发振荡反应的影响。实验表明,能够引发反应产生振荡的光源范围是较大的,通过光谱实验,分解实验和元素分析说明了环已烷在此反应中基本是惰性,并通过机理模型的计算,初步讨论了光照使原单调反应产生振荡的原因。     

Micellar effect on the reaction of picolinic acid catalyzed chromium(VI) oxidation of dimethyl sulfoxide in aqueous acidic media: A kinetic study

The kinetics and mechanism of picolinic acid (PA) catalyzed oxidation of dimethyl sulfoxide (DMSO) to dimethyl sulfone by chromium(VI) in both aqueous H₂SO₄ and HClO₄ media have been studied in the absence and presence of surfactants at different temperatures. Cr(VI)–PA complex formed in preequilibrium steps is the active oxidant that experiences the nucleophilic attack by DMSO to form a positively charged intermediate ternary complex. Within the proposed ternary complex, an oxygen transfer or a ligand coupling or both occurs to generate the product, dimethyl sulfone. Cr(VI) is ultimately converted to Cr(III)–PA complex. Under the experimental conditions, the process shows a first‐order dependence on each of the reactants (i.e., [Cr(VI)]_T, [PA]_T, [DMSO]_T, and [H⁺]). HCrO₄⁻ has been found kinetically active. The reaction is catalyzed by sodium dodecyl sulfate (SDS, a representative anionic surfactant) monotonically, while cetylpyridinium chloride (CPC, a representative cationic surfactant) retards the reaction continuously. The observed micellar effects have been explained by considering the hydrophobic and electrostatic interaction between the surfactants and reactants. A pseudo‐phase ion exchange (PIE) model has been applied to explain the micellar effect. The Piszkiewicz cooperative model has been applied to determine the kinetic parameters, and it indicates the existence of catalytically productive submicellar aggregates. Because of this reactant‐promoted micellization of the surfactant before or below the cmc value, the present systems do not show any discontinuity at the respective reported cmc values of the surfactants. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 173–181, 2001     

血红蛋白过氧化物模拟酶胶束催化显色体系

在胶束Tween80介质中，研究了以血红蛋白（hemoglobin,Hb)作为过氧化物模拟酶、隐性亮绿（recessive brilliant green,RGB)为氢供体底物、溶解氧为受氢体的酶催化反应特性。在pH5.64(NH4)2HPO4-KH2PO4缓冲溶液中，利用模拟酶对溶解氧作为受氢体催化RBG氧化生成亮绿（brilliant green,BG)而拟定了测定Hb含量的新方法。讨论了胶束介质对酶体系催化反应的影响及酶催化反应的可能机理。     

Thermodynamic study of the thermal denaturation of a globular protein in the presence of different ligands

By means of difference UV-Vis spectra, the thermal denaturation of catalase has been studied in the presence of different surfactants: sodium perfluorooctanoate, sodium octanoate and sodium dodecanoate. These results indicate that hydrogenated surfactants play two opposite roles in the folding and stability of catalase, they act as a structure stabiliser at a low molar concentrations (enhancing T _m) and as a destabilizer at a higher concentrations (diminishing T _m). Meanwhile sodium perfluorooctanoate enhances T _m in the whole concentration range. An approach for the determination of the heat capacity, enthalpy and entropy has been made, finding that for the three studied surfactants, at all concentrations, the enthalpy term dominates the entropy term.     

表面活性剂形成的微环境对SOD和水杨酸铜配合物 SOD样活性的影响

合成水杨酸铜配合物,用X射线衍射测定了它的结构,并用改进的NBT法研究了它和SOD在pH=7.8磷酸缓冲液、表面活性剂CTAB、TX-100形成效团、层状液晶中的SOD样活性。结果表明,在不同微环境中SOD和水杨酸铜配合物的SOD样活性顺序是：在pH=7.8磷酸缓冲液中＞在CTAB胶团中＞在CTAB层状液晶中;在TX-100有序组合体中＞在CTAB有序组合体中。加入少量三氯化镨(PrCl3)也能抑制NBT的还原。而且,PrCr3对NBT的抑制作用与Cu(Ⅱ)配合物的抑制作用是叠加的。     

Micellar Effect on the Reaction of Chromium(VI) Oxidation of L‐Sorbose in the Presence and Absence of Picolinic Acid in Aqueous Acid Media: A Kinetic Study

The kinetics and mechanism of chromic acid oxidation of L‐sorbose in the presence and absence of picolinic acid (PA) have been studied under the conditions, [L‐sorbose]_T » [PA]_T » [Cr(VI)]_T, at different temperatures. In the absence of PA, the monomeric chromic acid undergoes esterification with the substrate followed by the acid catalysed redox decomposition of the Cr(VI)‐substrate ester through glycol splitting to formaldehyde and the lactone of C₅‐aldonic acid and Cr(IV) which subsequently participates in the faster reactions. In the presence of PA, the Cr(VI)‐PA complex produced in a pre‐equilibrium step experiences a nucleophilic attack by the substrate to produce a ternary complex which decomposes through glycol splitting giving rise to the organic products and Cr(IV)‐PA complex. Both the uncatalysed and PA‐catalysed paths show the first‐order dependence on [L‐sorbose]_T and [Cr(VI)]_T. The PA‐catalysed path is first‐order in [PA]_T and it shows a fractional order in [H⁺]. The uncatalysed path shows a second‐order dependence on [H⁺]. In the presence of the surfactants like N‐cetylpyridinium chloride (CPC, a cationic surfactant) and sodium dodecyl sulfate (SDS, an anionic sulfate), the reaction orders remain unchanged. CPC has been found to inhibit both the uncatalysed and PA‐catalysed paths while SDS shows the rate accelerating effect for both the uncatalysed and PA‐catalysed paths. The observed micellar effects have been rationalised by considering the distribution of the reactants between the micellar and aqueous phases in terms of the proposed reaction mechanism.     

AOT/Triton X-100混合反胶束体系中假丝酵母脂肪酶催化蓖麻油水解的活性

研究了二(2-乙基己基)琥珀酸磺酸钠(AOT)/Triton X-100混合反胶束体系中假丝酵母脂肪酶(candida rugosa lipase)催化蓖麻油水解的反应. 考察了Triton X-100占总表面活性剂的摩尔分数(x(Triton X-100))、水与总体表面活性剂的摩尔比(ω0)、pH值、反应温度以及底物蓖麻油的浓度等因素对酶活性的影响. 研究结果表明, 加入非离子表面活性剂Triton X-100可以使假丝酵母脂肪酶的活性得到显著提高, 但是当底物蓖麻油的浓度大于0.24 mol·L-1时, 会对假丝酵母脂肪酶产生抑制作用.     

Calculation of the molecular exchanging energy of binary surfactants system on the surface monolayer of aqueous solution

By using the binary anionic/cationic surfactants system CH3(CH2)nOSO_3/CH3(CH2)nN (CH3)3 as an ex-ample, the molecular exchanging energy (ε) of adsorption on the surface monolayer of aqueous solu-tion has been studied. ε can be obtained with two methods. One is from the relationship between ε and the molecule interaction parameter (β). This relationship is founded by considering that the adsorption of mixed surfactants on the surface monolayer of solution satisfies the dimensional crystal model condition under which β can be obtained by testing the surface tension of solution. The other is directly from the molecular structure of surfactants with the Lennard-Jones formula. The results for the studied system show that these two methods coincide well.     

三氮烯试剂的结构与性能关系的研究

为建立三氮烯试剂结构与性能的关系, 我们研究了在非离子型表面活性剂TritonX-100存在下, 上述试剂亚氨基氢的酸性离解常数及镉(II)与上述试剂的显色反应。研究结果表明: (1)三氮烯试剂亚氨基氢的酸性离解常数遵循Hammett方程式, 其反应常数ρ=2.23; (2)试剂的亚氨基氢的酸性离解常数(pKa)与试剂和镉(II)显色反应的最佳酸度(pH最佳)之间的经验关系式为pH最佳=pKa-(1.70±0.20)。     

Surface activity and redox behavior of nonionic surfactants containing an anthraquinone group as the redox-active site

Two new nonionic surfactants, α-anthraquinonyloxyhexyl-ω-hydroxy-oligo(ethylene oxide) (ACPEG) and α-anthraquinonyl-ω-hydroxy-oligo(ethylene oxide) (APEG), were synthesized. The fundamental interfacial behavior of these surfactants at the air/water interface has been investigated by means of surface tensiometry to provide an insight into the relationship between the structure of the hydrophobic moiety and the surfactant properties, with specific emphasis on the anthraquinone linkage. Aggregation numbers of the surfactants have been determined from static light scattering measurements. At a constant hydration of the ethylene oxide chain, the increase in the hydrophobic chain length in ACPEG raises its hydrophobic interaction and results in enhanced aggregation and significant variation in the interfacial and micellization properties compared to APEG. The electrochemical behavior of the surfactants has also been studied in 0.16 M NaCl aqueous solutions and in 0.1 M tetrabutylammonium perchlorate acetonitrile solutions at the interface of a glassy carbon electrode. A difference in the extent of aggregation has a pronounced effect on the cyclic voltammetric behavior of the surfactants in aqueous solution. In organic media, on the other hand, the redox process depends only on the molecular geometry of the monomeric species. A comparison of the electrochemical responses in the two phases has been made to explain the distinctive features of the redox properties of the surfactants. Received: 30 May 1999 Accepted in revised form: 29 June 1999     

Mechanistic aspects of oxidation of dextrose by N-bromophthalimide in acidic medium: a micellar kinetic study

Kinetic investigations of oxidation of dextrose by N-bromophthalimide (NBP) in acidic medium in the presence of mercuric(II) acetate as a scavenger have been studied. In both the absence and presence of surfactants, the oxidation kinetics of dextrose by NBP shows a first-order dependence on NBP, fractional order on dextrose, and negative fractional order dependence on sulfuric acid. The determined stoichiometric ratio was 1:1 (dextrose:NBP). The variation of Hg(OAC)₂ and phthalimide (reaction product) have an insignificant effect on reaction rate. Effects of surfactants, added acrylonitrile, added salts, and solvent composition variation have been studied. Activation parameters for the reaction have been evaluated from Arrhenius plot by studying the reaction at different temperature. The rate law has been derived on the basis of obtained data. A plausible mechanism has been proposed from the results of kinetic studies, reaction stoichiometry and product analysis. The role of anionic and non-ionic micelle was best explained by the Berezin’s model.     

Comparative study of the cationic surfactants and their influence on the alkaline hydrolysis of acetylsalicylic acid

A kinetic study of the reaction of acetylsalicylic acid (aspirin) with sodium hydroxide has been studied in the presence of some conventional and novel cationic surfactants. The pseudo‐first‐order rate constant increases with the surfactant concentration initially and then decreases. In comparison to conventional cationic surfactants, i.e., cetyltrimethylammonium bromide and cetylpyridinium bromide, novel alkyldiethylethanolammonium bromide (R = C₁₆) surfactant accelerated the alkaline hydrolysis significantly. The pseudophase ion‐exchange model has been applied to fit the experimental results. Activation parameters have also been evaluated. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 43: 1–8, 2011