Tautomerization equilibria in aqueous micellar solutions: a spectrophotometric and factor-analytical study

The keto-enol equilibria of benzoylacetone (BZA) as a model for 1,3-dicarbonyl compounds are studied in aqueous acid and cationic micellar solution. Evolving factor analysis (EFA), multivariate curve resolution-alternating least-squares (MCR-ALS), and rank annihilation factor analysis (RAFA) are used for complete resolving of measured spectrophotometric data. The acidity constants of the enolic, KaE, and ketonic, KaK, forms of BZA and also the tautomerization constant, Kt, and its related thermodynamic parameters have been determined by using EFA and MCR-ALS methods and spectral variation of BZA solutions in various pHs and temperatures. The concentration and spectral profiles of all species were calculated without any assumption about chemical models. The spectral variation of BZA solutions as a function of cationic micelle concentration sufficiently beyond its critical micelle concentration is analyzed according to the partition model for distribution between water and micellar pseudo-phase and RAFA. The outputs of using RAFA on measured rank deficient data are the spectrum of enolic form in the micellar pseudo-phase, free from contribution of the enolic form in the aqueous phase, the partition coefficient of enolic form, KdE, between the micelle and water phases, and the tautomerization constant in the micellar pseudo-phase, Ktm.     

Spectrophotometric determination of acidity and tautomeric constants and hydrogen bonding strength for a new Schiff base using hard modeling and multivariate curve resolution alternative least squares methods

The equilibria of a new Schiff base derived from 3,6-bis((aminoethyl)thio)pyridazine were studied spectrophotometrically with the aid of factor-analytical methods. Hard modeling program was used for determination of the acidity constants of the Schiff base in dimethylformamide (DMF)/water mixture (30:70 v/v). In this method acidity constant equations act as hard models and the score vectors obtained by decomposing of absorbance data matrix will be linear combinations of equilibrium concentrations of species that exist in the absorption matrix. Two rank annihilation factor analysis (TRAFA) was used as a standard method to investigate the accuracy of the method. The tautomerization constant, K_t, of the Schiff base solution in various DMF/water mixtures has also been determined using spectral variations of the Schiff base solutions in various volume ratios of water with the aid of evolving factor analysis (EFA) and multivariate curve resolution alternative least squares (MCR-ALS) methods. In addition the intramolecular hydrogen bonding strength and its related thermodynamic parameters have been determined using MCR-ALS and spectral variation of the Schiff base solutions in different temperatures.     

双子型阴离子表面活性剂的合成及浮选性能

分别以辛酰氯、癸酰氯、十二酰氯为原料,经加成、酰化及皂化等反应合成了3种双子型阴离子表面活性剂。产物结构经IR、1HNMR和13CNMR等波谱测试技术确定。25℃时测定了表面活性参数,结果表明随分子中疏水链增长,临界胶束浓度及表面张力均降低。目标化合物能一定程度增强油酸对胶磷矿中白云石的浮选能力。     

Kinetics of Fe(II) reduction of cis‐halogeno(dodecylamine) bis(ethylenediamine)‐ cobalt(III) complex ion in aqueous solutions

Kinetics of reduction of the surfactant complex ions, cis‐chloro/bromo (dodecylamine)bis(ethylenediamine)cobalt(III) by iron(II) in aqueous solution was studied at 303, 308, and 313 K by spectrophotometry method under pseudo‐first‐order conditions, using an excess of the reductant. The second‐order rate constant remains constant below critical micelle concentration (cmc), but increases with cobalt(III) concentration above cmc, and the presence of aggregation of the complex itself alters the reaction rate. The rate of reaction was not affected by the added [H⁺]. Variation of ionic strength (μ) influences the reaction rate. Activation and thermodynamic parameters have been computed. It is suggested that the reaction of Fe²⁺ (aq) with cobalt(III) complex proceeds by the inner‐sphere mechanism. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 98–105, 2006     

New fluorescence method for the determination of the critical micelle concentration by photosensitive monoazacryptand derivatives

A novel fluorescence method for the determination of the critical micelle concentration (cmc) is reported. The cmc values of nonionic and anionic surfactants were evaluated utilizing a photosensitive monoazacryptand-Ba2+ complex, whose fluorescence intensity is sensitively changed by environmental conditions based on the photoinduced electron transfer (PET) mechanism as a fluorescent probe (PET method). Based on a comparison of the cmc values obtained by the PET method versus those obtained by conventional fluorescence-based methods as well as the values reported in the literature, one can conclude that the PET method is useful for the cmc determination. In particular, the PET method was more effective for the cmc determination of nonionic surfactants with very low cmc values (< 10(-5) M) than any other fluorescence-based method. In the cases of anionic surfactants, the PET method revealed the formation of the premicellar aggregates comprised of surfactant molecules and fluorescent probes below the cmc. Moreover, the hydrophobicity around the monoazacryptand-Ba2+ complex incorporated into various nonionic surfactant micelles was evaluated by this PET method.     

Molecular mechanism and thermodynamics study of plasmid DNA and cationic surfactants interactions

The molecular mechanism and thermodynamics of the interactions between plasmid DNA and cationic surfactants were investigated by isothermal titration calorimetry (ITC), dynamic light scattering, surface tension measurements, and UV spectroscopy. The cationic surfactants studied include benzyldimethyldodecylammonium chloride, benzyldimethyltetradecylammonium chloride, cetylpyridinium chloride, and cetyltrimethylammonium chloride. The results indicate a critical aggregation concentration (cac) of a surfactant: above the cac the surfactant forms aggregates with plasmid DNA; below the cac, however, there is no detectable interaction between DNA and surfactant. Surfactants with longer hydrocarbon chains have smaller cac, indicating that hydrophobic interaction plays a key role in DNA-surfactant complexation. Moreover, an increase in ionic strength (I) increases the cac but decreases the critical micellization concentration (cmc). These opposite effects lead to a critical ionic strength (I(c)) at which cac = cmc; when I < I(c), cac < cmc; when I > I(c), DNA does not form complexes with surfactant micelles. In the interaction DNA exhibits a pseudophase property as the cac is a constant over a wide range of DNA concentrations. ITC data showed that the reaction is solely driven by entropy because both deltaH(o) (approximately 2-6 kJ mol(-1)) and deltaS(o) (approximately 70-110 J K(-1) mol(-1)) have positive values. In the complex, the molar ratio of DNA phosphate to surfactant is in the range of 0.63-1.05. The reaction forms sub-micrometer-sized primary particles; those aggregate at high surfactant concentrations. Taken together, the results led to an inference that there is no interaction between surfactant monomers and DNA molecules and demonstrated that DNA-cationic surfactant interactions are mediated by the hydrophobic interactions of surfactant molecules and counterion binding of DNA phosphates to the cationic surfactant aggregates.     

Diperiodatoargentate(III) Oxidation of D-Galactose in Absence and Presence of Anionic and Cationic Surfactants

Diperiodatoargentate(III) (DPA) was used as an oxidizing titrant in the spectrophotometric degradation of D-galactose for the first time. The kinetics is based on the reduction of silver(III) to silver(I) by D-galactose at specified experimental conditions. Effects of added [H⁺] and [periodate] have also been investigated. The premicellar environment of cetyltrimethylammonium bromide (CTAB) and sodiumdodecyl sulphate (SDS) strongly inhibits the reaction rate. The observed rate constant is strongly affected by [CTAB] and [SDS] changes for [surfactant] <cmc. Surfactant concentration range above the cmc does not influence the reaction rate. The monoperiodatoargentate(III) ions act as an active oxidant in comparison to that of DPA. A suitable mechanism involving a two-electron transfer from D-galactose to the silver(III) species has been proposed and hence a corresponding rate equation has been derived.     

Investigation of the Effect of Inclusion of Eriochrome Black T with β-Cyclodextrin on Its Complexation Reaction with Ca2+ and Mg2+ Using Rank Annihilation Factor Analysis

Rank annihilation factor analysis (RAFA) was used to investigate the effects of inclusion of eriochrome black T (EBT) on its complexation reaction with Ca²⁺ and Mg²⁺ at different pH values. Addition of β-cyclodextrin (β-CD) to Ca-EBT or Mg-EBT caused decomposition of the 1:1 metal complex and increase in EBT concentration in solution due to the formation of EBT-β-CD inclusion complex. In order to perform RAFA, concentration profiles were calculated by optimizing the value of the conditional stability constant and inclusion constant. The rank of original data matrix reduces by one by removing the information from the complex form (Ca-EBT or Mg-EBT). The performance of the method was evaluated by using synthetic data as well as experimental data and good results were obtained. The proposed method is capable of the simultaneous spectrophotometric determination of formation constant of a complex and the equilibrium constant of the competing reaction in solution.     

Adsorption and Micellization Properties of Novel Heterodouble‐Chained N‐Acyltaurate Surfactants

A set of heterodouble‐chained N‐acyltaurate surfactants (abbreviated as m+nP‐T, where m and n were carbon numbers of alkyl chain; P was phenyl; T was taurate) were synthesized. The novel amphiphiles contained sodium taurine as hydrophilic moiety and two different hydrocarbon chains as hydrophobic moiety. One was a long alkyl chain, and the other had an aromatic residue. Their surface properties were determined by Wilhelmy‐plate method, and micellization properties were investigated by fluorescence spectra of extrinsic probe and intrinsic probe. It was found that these surfactants showed some aberrant properties. It was difficult to obtain the equilibrium surface tension and critical micelle concentration (cmc) for the surfactants with two long chains. Pyrene was solubilized in micelle at concentration above cmc, and the fluorescent intensity ratio of the first vibronic peak (373 nm) to the third vibronic peak (383 nm) of pyrene decreased gradually. The aggregation number N, characterized by quenching the phenoxyl residue with methyl viologen (MV²⁺) as the extrinsic quencher, gradually increased with increasing surfactant concentration. These indicated that more and more molecules packed in a micelle with increasing concentration.     

Removal of cadmium ions using micellar-enhanced ultrafiltration with mixed anionic-nonionic surfactants

Micellar-enhanced ultrafiltration (MEUF) was used to remove cadmium ions from wastewater efficiently. In this study the nonionic surfactants polyoxyethyleneglycol dodecyl ether (Brij35) and polyoxyethylene octyl phenyl ether (TritonX-100) were for micellar-enhanced ultrafiltration to lower the dosage of the anionic surfactant sodium dodecyl sulfate (SDS). The surfactant critical micelle concentration (CMC) and the degree of micelle counterion binding were investigated. The effects of nonionic surfactant addition on the efficiency of cadmium removal, the residual quantities of surfactant, the permeate flux and the secondary membrane resistance were investigated. A comparison between MEUF with SDS and MEUF with mixed anionic–nonionic surfactants was undertaken. The results show that the addition of Brij35 or TritonX-100 reduced the CMC of SDS and the degree of counterion binding for the micelles. Due to these variations the Cd²⁺ rejection efficiency was at a maximum when the Brij35:SDS and the TritonX-100:SDS molar ratio was 0.5. The Cd²⁺ rejection efficiency in MEUF with SDS is higher than for MEUF with mixed surfactants when the total dose of surfactant is constant. The permeate flux of MEUF with SDS is higher than that for MEUF with mixed surfactants while the secondary resistance of MEUF with SDS is less than that of MEUF with mixed surfactants.     

全氟壬烯氧基苯磺酸钠与烷基季铵盐的相互作用

通过六氟丙烯三聚体(全氟壬烯)氧基苯磺酸钠(C₉F₁₇OC₆H₄SO₃Na, OBS)与阳离子碳氢表面活性剂C_nNR[C_nH_2n+1N(CH₃)₃Br, C_nNM, n=8, 10和C_nH_2n+1N(CH₂CH₃)₃Br, C_nNE, n=8, 10, 12]复配, 研究了OBS与C_nNR的摩尔比、 C_nNR疏水链长及C_nNR亲水基团大小对此类阴、 阳离子碳氟-碳氢表面活性剂混合体系的临界胶束浓度(cmc)、 最低表面张力(γ_cmc)、 总饱和吸附量(Γ_tm)及极限分子面积(A_min)的影响. 结果表明, 通过与C_nNR复配, OBS的cmc和γ_cmc均大幅下降, 达到了全面增效的结果. 不同摩尔比的OBS-C₈NE混合体系中, 摩尔比为1:1时表面活性最好, cmc和γ_cmc均最小; 偏离等摩尔比时, OBS过量时混合体系的cmc小于C₈NE过量时混合体系的cmc, 但γ_cmc相差不大. 与单体系相比, OBS-C₈NE混合体系的Γ_tm明显增大、 A_min明显变小. OBS与不同疏水链长的C_nNE复配时, cmc的变化规律为C₈NE>C₁₀NE>C₁₂NE, 表明C_nNE疏水链长的增加能降低混合体系的cmc. 通过比较C_nNM和C_nNE(n=8, 10)的表面活性发现, 改变混合体系中C_nNR的亲水基团大小对混合体系的表面活性无明显影响.     

Interactions between adsorbed layers of cationic gemini surfactants

The forces acting between glass and between mica surfaces in the presence of two cationic gemini surfactants, 1,4 diDDAB (1,4-butyl-bis(dimethyldodecylammonium bromide)) and 1,12 diDDAB (1,12-dodecyl-bis(dimethyldodecylammonium bromide)), have been investigated below the critical micelle concentration (cmc) of the surfactants using two different surface force techniques. In both cases, it was found that a recharging of the surfaces occurred at a surfactant concentration of about 0.1 x cmc, and at all surfactant concentrations investigated repulsive double-layer forces dominated the interaction at large separations. At smaller separations, attractive forces, or regions of separation with (close to) constant force, were observed. This was interpreted as being due to desorption and rearrangement in the adsorbed layer induced by the proximity of a second surface. Analysis of the decay length of the repulsive double-layer force showed that the majority of the gemini surfactants were fully dissociated. However, the degree of ion pair formation, between a gemini surfactant and a bromide counterion, increased with increasing surfactant concentration and was larger for the gemini surfactant with a shorter spacer length.     

Effects of Surfactants on Hydride Transfer from Methylene Blue Leucodye to 2,5-Dihydroxyl-1,4-benzoquinone in Aqueous Solution

The effects of monomeric surfactants on the hydride transfer from (one electron oxidation of) methylene blue leucodye to (by) 2,5-dihydroxy-1,4-benzoquinone in aqueous solution were investigated at 25°C using a stopped-flow spectrometer. The results indicated that cationic, anionic, and zwitterionic surfactants inhibited the reaction while nonionic surfactant showed no appreciable effect on the reaction. These observations are rationalized by electrostatic factors between surfactant monomer (or micelle) and reactant with charge or the charge transfer complex of the hydride transfer reaction. Above the cmc, the effects are treated quantitatively using a kinetic model.     

甘氨酸酯衍生物双子季铵盐表面活性剂

双子表面活性剂;合成;甘氨酸酯衍生物双子季铵盐表面活性剂     

Micellar catalysis in the oxidation of acetophenones by Ce(IV)

Rate of oxidation of acetophenones by Ce(IV) in aqueous acetic acid 80:20 (v/v) either slows down or remains constant over a range of cetyltrimethyl ammonium bromide (CTAB) concentration exceeding the cmc value. The rate is then found to increase sharply as the surfactant concentration increases with no sign of reaching a maximum or constant value. From Fluorescence quenching, binding constant for p-nitro acetophenone has been evaluated. The rate data have been rationalized on the basis of a reaction between the acetophenones situated on the micelle surface and active Ce(IV) species in the bulk aqueous phase.     

Adsorption of ionic surfactants at an expanding air-water interface

A quantitative model for the kinetics of adsorption of ionic surfactants to an expanding liquid surface is presented for surfactant concentrations below and above the critical micelle concentration (cmc). For surfactant concentrations below the cmc, the electrostatic double layer is accounted for explicitly in the adsorption isotherm. An overflowing cylinder (OFC) was used to create nonequilibrium liquid surfaces under steady-state conditions. Experimental measurements of the surface excess for solutions of cationic surfactants CH3(CH2)n-1N+(CH3)3 Br- (CnTAB, n = 12, 14, 16) and the anionic fluorocarbon surfactant sodium bis(1H,1H-nonafluoropentyl)-2-sulfosuccinate (di-CF4) in the OFC are in excellent agreement with the theoretical predictions for diffusion-controlled adsorption for all concentrations studied below the cmc. For surfactant concentrations above cmc, the diffusion ofmicelles and monomers are handled separately under the assumption of fast micellar breakdown. This simplified model gives excellent agreement for the system C14TAB + 0.1 M NaBr above the cmc. Agreement between theory and experiment for C16TAB + 0.1 M NaBr is less good. A plausible explanation for the discrepancy is that micellar breakdown is no longer fast on the time scale of the OFC (ca. 0.1 s).     

Temperature dependence of second critical micelle concentration of dodecyldimethylbenzylammonium bromide in aqueous solution

The specific conductivity of dodecyldimethylbenzylammonium bromide (C12BBr) in aqueous solutions, in the temperature range of 15 to 40 °C, has been measured as a function of molality. The two breaks which were found on the conductivity against molality plots were attributed to the critical micelle concentration, cmc, and second critical micelle concentration, 2^nd cmc, respectively. The ratio of the slopes, S, of the three linear fragments on the plots, S2/S1 and S3/S1, was attributed to the degree of ionization of the micelles at cmc and 2^nd cmc respectively. It was shown that the values of the 2^nd cmc estimated above 27 °C are only apparent due to thermal disintegration of the micelles. In the temperature range of 15 to 27 °C, the values of the 2^nd cmc increase gradually and the plot of the 2^nd cmc against temperature is concave. The ratio of 2^nd cmc/cmc for C12BBr at 25 °C amounts to 15 and appears to be high compared to the literature values for other surfactants. For comparative purposes the cmc and 2^nd cmc values were also estimated conductometrically for decyldimethylbenzylammonium bromide (C10BBr) at 25 °C. The 2^nd cmc value for this surfactant is higher compared to the value for the C12 homologue by a factor of 2.6.The standard Gibbs free energies of micellization at cmc and at the 2^nd cmc were estimated from the experimental data for both surfactants at 25 °C.     

Kinetics of the Micellar Effects on the Alkaline Hydrolysis of 2-Chloro-quinoxaline in Acetonitrile-Water Mixtures at 35°C

Pseudo-first-order reaction rate for alkaline hydrolysis of 2-chloroquinoxaline (2-CQX) is carried out in acetonitrile (AN)-water (H₂O) mixtures at 35°C. Cationic surfactants as dodecyltrimethylammonium bromide (DOTAB) and an anionic surfactant as sodium dodecylsulphate (SDS) are used above their critical micelle concentration (cmc) to study the effect of micelles on reaction rate. When increasing the percentage of volume of AN, the rate profiles with DOTAB are shown to slightly increase with increasing surfactant concentration, while that with SDS are found to smoothly decrease. The micellar effect is explained in terms of a modified pseudo-phase ion exchange model. The binding constant (K_S) between 2-CQX and DOTAB as micelle showed a decrease by increasing percentage of volume of AN, while that with SDS increased. The counterion micellar coverage degrees (β) are found to be 0.55 and 0.85 with DOTAB and SDS systems, respectively, at all range of volume percentage of AN. Finally, the calculated ratio between rate constants in water to that in the micelle region k_w/k_M at different volume percentage of AN indicated that DOTAB enhances the reaction rate while SDS inhibits it.      

两相催化体系中双子表面活性剂对1-十二烯氢甲酰化反应的助催化作用

合成了几种具有刚性连接基团的双子表面活性剂,研究了它们在Rh-TPPTS体系中催化长链烯烃氢甲酰化反应中的助催化作用.结果表明,在水/有机两相催化体系中,新型双子表面活性剂的助催化作用比单链表面活性剂CTAB更好,在较低的表面活性剂浓度下能得到较高的反应转化率.这归因于此类表面活性剂有较低的cmc,降低界面张力的能力和对1-十二烯的增溶能力比CTAB更强.     

混合胶束中Gemini阳离子表面活性剂14-s-14与常规表面活性剂的协同作用:连接臂及反离子效应(英文)

The mixed micelle formation of binary cationic 14-s-14 gemini with conventional single chain surfactants was studied by conductivity measurements.The critical micelle concentration(cmc) and the degree of counterion binding values(g) of the binary systems were determined.The results were analyzed by applying regular solution theory(RST) to calculate micellar compositions(X),activity coefficients(f1,f2),and the interaction parameters(β).The synergistic interactions of all the investigated cationic gemini+conventional surfactant combinations were found to be dependent upon the length of hydrophobic spacer of the gemini surfactant.The excess Gibbs free energy of mixing was evaluated,and it indicated relatively more stable mixed micelles for the binary combinations.