Self-aggregation and supramolecular structure investigations of Triton X-100 and SDP2S by NOESY and diffusion ordered NMR spectroscopy

The self-aggregation and supramolecular micellar structure of two surfactants in aqueous solution, the anionic surfactant SDP2S (sodium dodecyl dioxyethylene-2 sulfate) and the nonionic surfactant Triton X-100 (octylphenol-polyoxyethylene ether with 9.5 ethoxy groups), were investigated by NMR spectroscopy. The critical micellar concentration (CMC), the size, and shape of the aggregates were determined by diffusion ordered NMR spectroscopy (DOSY), while 2D NOESY NMR spectra were used to study the mutual spatial arrangement of surfactant molecules in the aggregated state. A nonlinear increase of the micellar hydrodynamic radius, indicating possible sphere-to-rod shape transition, was found for SDP2S at higher surfactant concentrations. Triton X-100 micelles were found to be almost spherical at low surfactant concentrations, but formation of ellipsoid shaped particles and/or micellar aggregation was observed at higher concentrations. The NOESY data show that at low concentration Triton X-100 forms a two-layer spherical structure in the micelles, with partially overlapping internal and external layers of Triton X-100 molecules and no distinct hydrophilic-hydrophobic boundary.     

Hydrophobic terminal group of surfactant initiating micellization as revealed by 1H NMR spectroscopy

The critical aggregation concentration (CAC) of four with three kinds of conventional surfactants, namely, two cationic surfactants [hexadecyltrimethyl ammonium bromide (CTAB) and tetradecyltrimethyl ammonium bromide (TTAB)], one anionic surfactant [sodium dodecyl sulfate (SDS)], and a nonionic surfactant [Triton X-100 (TX-100)], were determined by variation of ¹H chemical shifts with surfactant concentrations. Results show that the CAC values of protons at different positions of the same molecule are different, and those of the terminal methyl protons are the lowest, respectively, which suggests that the terminal groups of the alkyl chains aggregates first during micellization. Measurement of the transverse relaxation time (T₂) of different protons in SDS also show that the terminal methyl protons start to decrease with the increase in concentration first, which supports the above mentioned tendency.     

精密半微量滴定热量计的建立和胶束生成焓测定

为研究两亲分子自组合的弱相互作用,在LKB-8700精密量热系统的基础上设计和建立了精密半微量滴定热量计。实验数据的采集和处理由在线微机自动完成。利用本热量计测定量热基准物质三羟甲基氨基甲烷(Tris)和盐酸的反应热,实验结果与文献值一致,精度为±0.2%。对阴离子表面活性剂十二烷基硫酸钠(SDS),阳离子表面活性剂十二烷基三甲基溴化铵(DTAB)和非离子表面活性剂TritonX-100的胶束生成焓和临界胶束浓度(cmc)的测定结果也与文献报道值一致。     

Electrochemical surface plasmon resonance investigation of dodecyl sulfate adsorption to electroactive self-assembled monolayers via ion-pairing interactions

The redox-induced assembly of amphiphilic molecules and macromolecules at electrode surfaces is a potentially attractive means of electrochemically modulating the organization of materials and nanostructures on solid substrates via ion-pairing interactions or charge-transfer complexation. In this regard, we have investigated the potential-induced adsorption and aggregation of dodecyl sulfate, a common anionic surfactant, at a ferrocenylundecanethiolate (FcC11SAu) self-assembled monolayer (SAM)/aqueous solution interface by electrochemical surface plasmon resonance (ESPR) spectroscopy. The surfactant anions adsorb onto the electroactive SAM by specific ion-pairing interactions with the oxidized ferricinium species. The ferricinium charge density (QFc+) obtained by cyclic voltammetry and surface coverage measured by SPR indicate that the dodecyl sulfate forms an interdigitated monolayer, where half of the surfactant molecules have their sulfate headgroups paired to the surface and half have their headgroups exposed to the aqueous solution. The surface coverage of dodecyl sulfate was found to depend on both the ferricinium surface concentration and the surfactant aggregation state in solution. A maximum coverage of dodecyl sulfate on the ferricinium surface is obtained below the critical micelle concentration (cmc), in contrast to dodecyl sulfate adsorption to SAM surfaces of static positive charge. This marked difference in adsorption behavior is attributed to the dynamic generation of ferricinium by potential cycling and the specific nature of the ion-pairing interactions versus pure electrostatic ones. The results presented point to a new way of organizing molecules via electrical stimulus.     

Effect of Surfactants and Ionic Strength on Dissociation of Hydrochlorides of Phenothiazine Derivatives

Abstract

A study of the effect of the anionic surfactant dodecyl sulfate, the cationic surfactant carbethoxypentadecyl trimethyl ammonium bromide (Septonex), nonionic surfactant p-octyl phenyl polyoxyethylene (Triton X-100), and a strong electrolyte (KBr) on the dissociation of the hydrochlorides of two derivatives of phenothiazine (diethazine and fluphenazine) was made. It was found that sodium dodecyl sulfate increases the pKa value, whereas Septonex and Triton X-100 decrease this value. The presence of KBr suppresses the effect of the surfactants. A new method for the potentiometric determination of fluphenazine in an aqueous medium was proposed.     

AGGREGATION CHARACTERISTICS OF LASER DYE RHODAMINE 6G IN AQUEOUS SURFACTANT SOLUTIONS

Abstract— –The role of surfactants as deaggregating agents for the laser dyes is investigated by spectrophotometry using Rhodamine 6G as a representative. A method to estimate the fraction of dye present as monomer, dimer and as a monomer-surfactant (monomer or micelle) complex is described. It is shown that among the surfactants, cetyl trimethyl ammonium bromide, Triton X-100, sodium lauryl sulfate (SLS) and potassium oleate, the anionic ones are the most effective in suppressing the aggregation of Rhodamine 6G. While the non-ionic surfactant is found to be effective only above its critical micellar concentration, the cationic surfactant has no effect on aggregation. The optimum concentration of SLS needed for suppression of dye-dimers is estimated.     

表面活性离子液体溴化N-十二烷基异喹啉与非离子表面活性剂Triton X-100在水溶液中的混合胶束

用等温滴定微量热法测定表面活性离子液体溴化N-十二烷基异喹啉([C₁₂iQuin]Br)与非离子表面活性剂Triton X-100混合物在水溶液中的临界胶束浓度。并以¹H核磁共振(NMR)和二维核Overhauser效应增强谱(2D NOESY)研究[C₁₂iQuin]Br与Triton X-100在混合胶束中的作用机理。研究结果显示：混合胶束中,Triton X-100分子的苯环定位于混合胶束的内核,聚氧乙烯链卷曲在异喹啉环周围。本文还应用规则溶液理论和浊点法对比研究了十二烷基三甲基溴化铵(DTAB)-Triton X-100混合胶束体系的相关性质。     

EXPERIMENTAL CHARACTERIZATION OF FLUOROCARBON-MODIFIED POLYACRYLAMIDE/SURFACTANT AQUEOUS SOLUTIONS

The interaction between surfactants and fluorocarbon-modified polyacrylamide (FC-PAM) in aqueous solutionswas evaluated by rheological means and fluorescence spectroscopy and was found to be strong regardless of the surfactant'snature. Two representative surfactants, anionic sodium dodecyl sulfate (SDS) and nonionic Triton X-100, were used. The origin of the interaction and its dependence on the surfactant concentration were discussed.     

FLUORESCENCE PROBE FOR MICROENVIRONMENTS: A NEW PROBE FOR MICELLE SOLVENT PARAMETERS AND PREMICELLAR AGGREGATES

Abstract— A previous study on the electronic spectroscopy of p -N,N-dialkylaminobenzylidenemalononitrile, 1, has been extended to a larger variety of organic solvents and to micelles of ionic and nonionic surfactants. By comparing the fluorescence emission (λ_F and φ_∫) of 1 in micelles and in homogeneous organic solvents, the effective polarity and the microviscosity of the micellar environments of potassium dodecanoate, sodium dodecyl sulfate, cetyltrimethylammonium bromide and Triton X-100 micelles have been determined to be 40, 40, 36 and 28, respectively and 23, 31, 34 and 28 cP, respectively. These results indicate that the fluorescence probe is located in the micelle–water interface of a micelle and this region of a micelle is polar and viscous. 1 has also been studied in different surfactants with varying surfactant concentrations. The φ_∫ of 1, a microviscosity gauge for micellar aggregates, remains unchanged at the critical micelle concentrations of various surfactants, but decreases at much lower surfactant concentrations. This is attributable to the formation of premicellar aggregates of surfactant molecules below their critical micelle concentrations.     

表面活性剂中DNA构象变化的研究

以荧光探针法研究了表面活性剂与小牛胸腺DNA的相互作用，结果表明：阳离子表面活性剂主要通过静电引力和疏水方式与DNA作用；阴离子表面活性剂与DNA之间存在静电排斥力，两者之间的相互作用不太明显；而非离子表面活性剂与DNA的相互作用类似于有机溶剂对DNA的影响，即通过溶液的极性、粘度和介电常数来影响DNA的构象，表面活性剂使得DNA构象发生较大的变化，预示了它可能使DNA的生物功能发生较大的变化。     

Interaction between casein and sodium dodecyl sulfate

The interaction of the anionic surfactant sodium dodecyl sulfate (SDS) with 2.0 mg/ml casein was first investigated using isothermal titration calorimetry (ITC), dynamic light scattering (DLS), and fluorescence spectra. ITC results show that individual SDS molecules first bind to casein micelles by the hydrophobic interaction. The micelle-like SDS aggregate is formed on the casein chains when SDS concentration reaches the critical aggregation concentration (c1), which is far below the critical micellar concentration (cmc) of SDS in the absence of casein. With the further increase of SDS concentration to the saturate binding concentration c2, SDS molecules no longer bind to the casein chains, and free SDS micelles coexist with casein micelles bound with SDS aggregates in the system. DLS results show that the addition of SDS leads to an increase in the hydrodynamic radius of casein micelles with bound surfactant at SDS concentration higher than 4 mM, and also an increase in the casein monomer molecule (or submicelles) at SDS concentration higher than 10 mM. Fluorometric results suggest the addition of SDS leads to some changes in the binding process of hydrophobic probes to casein micelles.     

Phenomenon observed at the onset of micellization using static light scattering

A phenomenon was observed near the critical micelle concentration (cmc) of surfactants using static light scattering. This consists of an unexpected peak in light scattering as the concentration varies between zero and above the cmc. This work studied three different surfactants: the two ionic surfactants hexadecyltrimethylammonium bromide (CTABr) and sodium dodecyl sulfate (SDS) and the nonionic surfactant Triton X-100. Peaks were observed for all three under different conditions such as varying ionic strengths and different concentration paths. These peaks are real, are reproducible, and appear to have static properties.     

Wetting and adsorption: II. Adsorption of Triton X-100 and Triton X-305 onto carbon black from water and cyclohexane solutions

The adsorption isotherms of nonionic surfactants Triton X-100 and Triton X-305 from water and cyclohexane on carbon black have been determined at 15 and 30°C. The Langmuir-type and BET-type isotherms are obtained for adsorption of Triton X-100 and Triton X-305 from water and cyclohexane respectively. Both the contact angles of water for graphite/water/air and graphite/water/cyclohexane decrease monotonously with increasing surfactant concentration. From these results, it is proposed that the adsorption of Triton X-100 and Triton X-305 on carbon black or graphite from water is monolayer. For the adsorption from cyclohexane solutions, the ethyleneoxide group of the surfactant molecules may be adsorbed onto the polar spot at the surface of carbon black, and the hydrophobic group of adsorbed molecules may direct toward the liquid phase or attaches to the nonpolar surface region around the polar spot. As the concentration increases, the ethylene oxide groups of the adsorbed molecules can be aggregated with each other via polar interactions to form hemi-reversed micelle.     

Novel fluorescent probe as aggregation predictor and micro-polarity reporter for micelles and mixed micelles

Aggregational behaviour of micelles sodium dodecyl sulphate (SDS and Triton X-100, TX-100 both in pure and mixed form) and micelle like aggregates such as polymer-surfactant system [polymer poly(vinyl pyrrolidone), PVP]-SDS have been studied by using fluorescence characteristics of a newly synthesized probe. The critical micelle concentration (CMC) values determined at various surfactant compositions are lower than the ideal values indicating a synergistic effect. The value of the interaction parameter for the surfactant mixture has been determined which agrees well with the value calculated according to molecular thermodynamic theory. The total aggregation number of surfactant in mixed micelle shows a drastic variation in the SDS mole fraction range 0 < or = alpha1 < or = 0.3 and beyond the range it remains practically constant. Molar-based partition coefficients for the dye between the micellar and aqueous phase have been determined and a non-linear variation is obtained for the mixed micellar system. Variations of micro-polarity in the mixed micellar region have been investigated as a function of surfactant composition and results have been explained in terms of a suitable realistic model.     

A Study on the Location and Aggregation of Tetrahydrophenylporphyrin with a Single Hexadecyl Chain in Triton X-100 Micelle

The location and aggregation of 5,10,15-tris(4-hydroxyphenyl)-20-(hexadecyloxyphenyl)porphyrin (P) in nonionic polyoxyethylene (9.5) octylphenol (Triton X-100) micelle solutions were studied by means of UV–Vis and fluorescence spectra. P forms premicelle surfactant–porphyrin aggregates when the surfactant concentration is below and approaching the CMC. In Triton X-100 micelle solutions, different types of H-aggregates of P were formed when the concentration of P is higher than 3.9×10^-6?mol?dm^-3. As the bulk pH is changed, a transfer process for the porphyrin moiety in Triton X-100 micelle occurs. In neutral Triton X-100 micelle solutions, P may be located at the inner layer of the micelle; in basic conditions, the porphyrin moiety may transfer to the outer surface of the micelle. The kinetic study of porphyrin complexed with Cu(II) in Triton X-100 micelle solutions shows that the metalation rate could be controlled by changing the pH.     

Magnetic Relaxation Probing of the State of Diheptyl Dithiophosphate Ions in Water and Aqueous Triton X-100 Solutions

The nuclear magnetic relaxation was used to study the state of diheptyl dithiophosphoric acid (D7DTP, L₇) anions in water and aqueous solutions of the nonionic surfactant, Ttiton X-100, at 298 K in the presence of paramagnetic probes, Mn²⁺ions. It was found that increase in the spin-lattice relaxation rate of water protons is caused by formation of simple and mixed (with surfactant) aggregates of D7DTP. Unlike the Mn²⁺–sodium dodecyl sulfate –Triton X-100 system, studied previously an influence of a probe concentration was found at surfactant concentration close to the CMC. It was suggested that two types of mixed species containing diheptyl dithiophosphate ions, Mn(II), and nonionic surfactant can be formed: micellar aggregates, {Mn(L₇)₂(TX)}, and polynuclear associates, [Mn _x (L₇) _y (tx) _z ]. The associates likely contain surfactant in the form of monomers (tx).     

Daunomycin binding to detergent micelles: a model system for evaluating the hydrophobic contribution to drug-DNA interactions

The interaction of daunomycin with sodium dodecyl sulfate and Triton X-100 micelles was investigated as a model for the hydrophobic contribution to the free energy of DNA intercalation reactions. Measurements of visible absorbance, fluorescence lifetime, steady-state fluorescence emission intensity, and fluorescence anisotropy indicate that the anthraquinone ring partitions into the hydrophobic micelle interior. Fluorescence quenching experiments using both steady-state and lifetime measurements demonstrate reduced accessibility of daunomycin in sodium dodecyl sulfate micelles to the anionic quencher iodide and to the neutral quencher acrylamide. Quenching of daunomycin fluorescence by iodide in Triton X-100 micelles was similar to that seen with free daunomycin. Studies of the energetics of the interaction of daunomycin with micelles by fluorescence and absorbance titration methods and by isothermal titration calorimetry in the presence of excess micelles revealed that association with sodium dodecyl sulfate and Triton X-100 micelles is driven by a large negative enthalpy. Association of the drug with both types of micelles also has a favorable entropic contribution, which is larger in magnitude for Triton X-100 micelles than for sodium dodecyl sulfate micelles. The thermodynamic profile for the interaction of daunomycin with both types of micelles is characteristic of the "nonclassical" hydrophobic effect. The enthalpy for the interaction of daunomycin with sodium dodecyl sulfate micelles increases nonlinearly with temperature, indicating a positive (and temperature dependent) heat capacity change. The binding isotherm for daunomycin association with sodium dodecyl sulfate micelles was cooperative, with a Hill coefficient of 1.6. The cooperative behavior and the positive heat capacity change suggest that the drug alters micelle size or imposes order on the hydrocarbon interior of the micelle.     

Partitioning behavior of silica in the Triton X-100/dextran/water aqueous biphasic system

The partitioning behavior of silica particles was investigated in the Triton X-100/dextran/water system. It was found that both electrostatic effects and interactions between phase-component species and the solid surface played important roles in determining the distribution of solids. Silica partition was highly pH-dependent, which was interpreted in terms of the pH dependence of the Triton X-100/SiO(2) interaction and the weak acidity of dextran. The presence of sodium dodecyl sulfate (SDS) moved the particles from the top surfactant-rich phase to the interface and the bottom phase, while dodecyltrimethylammonium bromide (DTAB) had the opposite effect. These trends are attributable to the electrostatic interaction between the charged mixed micelles in the top phase and the particles and to the fact that the ionic surfactants modified the adsorption density of the nonionic surfactant on silica.     

Micellization and synergistic interaction of binary surfactant mixtures based on sodium nonylphenol polyoxyethylene ether sulfate

Mixed micelle formation and synergistic interactions of binary surfactant combinations of sodium nonylphenol polyoxyethylene ether sulfate (NPES) with typical surfactants such as sodium dodecyl sulfate (SDS), Triton X-100 (TX100), cetyl trimethyl ammonium bromide (CTAB), and sodium bis(2-ethylhexyl) sulfosuccinate (AOT) at 25 degrees C in the presence of NaCl have been investigated. The critical micelle concentration of the binary mixtures has been quantitatively estimated by steady-state fluorescence measurements. The micellar characteristics such as composition, activity coefficients, and mutual interaction parameters have been estimated following different theoretical treatments. Investigation on the micellization and synergistic interaction of NPES with four kinds of surfactants showed that the behavior of the binary mixture deviated from the ideal state. The analysis revealed that the interaction parameter values (beta) varied with variation of solvent composition. Besides the strong electrostatic attraction between the oppositely charged surfactant NPES-CTAB mixture, the interaction between NPES and SDS also showed far more deviation from ideal behavior than that of TX100 and AOT. The reason for the synergism is also discussed and the results show that an ionic and a nonionic surfactant character existed concurrently in NPES due to the combination of a sulfate group and polyoxyethylene as a hydrophilic moiety. Zeta potential and diffusion coefficient measurements of micelles confirmed the synergistic interaction between the binary surfactants.     

Surfactant aggregation within room-temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

On the basis of the response of solvatochromic probes [Reichardt's betaine dye, pyrene, and 1,3-bis(1-pyrenyl)propane], we have investigated the aggregation behavior of common anionic, cationic, and nonionic surfactants when solubilized within a low-viscosity room-temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (emimTf2N). We observed possible aggregate formation by all nonionic surfactants included in the study (Brij-35, Brij-700, Tween-20, and Triton X-100), while no aggregation was observed for the cationic surfactant cetyltrimethylammonium bromide. The anionic surfactant sodium dodecyl sulfate does not appear to solubilize within emimTf2N at ambient conditions.