Molecular interactions of sodium laureth sulfate with N-alkyl-1,3-propanediamine in aqueous solutions, based on potentiometric and photometric data

The role of Coulomb and hydrophobic interactions in association and aggregation in binary solutions of anionic surfactant sodium laureth sulfate and cationic surfactant N-alkyl-1,3-propanediamine is established from the concentration dependences of the pH of the solutions. It is shown that the development of the processes is initiated by the Coulomb interaction of oppositely charged sodium laureth sulfate and N-alkyl-1,3-propanediamine molecules and enhanced by the hydrophobic interaction between the hydrocarbon tails of neutral associates of the surfactant molecules.     

Structure of DNA-cationic surfactant complexes at hydrophobically modified and hydrophilic silica surfaces as revealed by neutron reflectometry

In this article, we discuss the structure and composition of mixed DNA-cationic surfactant adsorption layers on both hydrophobic and hydrophilic solid surfaces. We have focused on the effects of the bulk concentrations, the surfactant chain length, and the type of solid surface on the interfacial layer structure (the location, coverage, and conformation of the DNA and surfactant molecules). Neutron reflectometry is the technique of choice for revealing the surface layer structure by means of selective deuteration. We start by studying the interfacial complexation of DNA with dodecyltrimethylammonium bromide (DTAB) and hexadecyltrimethylammonium bromide (CTAB) on hydrophobic surfaces, where we show that DNA molecules are located on top of a self-assembled surfactant monolayer, with the thickness of the DNA layer and the surfactant-DNA ratio determined by the surface coverage of the underlying cationic layer. The surface coverages of surfactant and DNA are determined by the bulk concentration of the surfactant relative to its critical micelle concentration (cmc). The structure of the interfacial layer is not affected by the choice of cationic surfactant studied. However, to obtain similar interfacial structures, a higher concentration in relation to its cmc is required for the more soluble DTAB surfactant with a shorter alkyl chain than for CTAB. Our results suggest that the DNA molecules will spontaneously form a relatively dense, thin layer on top of a surfactant monolayer (hydrophobic surface) or a layer of admicelles (hydrophilic surface) as long as the surface concentration of surfactant is great enough to ensure a high interfacial charge density. These findings have implications for bioanalytical and nanotechnology applications, which require the deposition of DNA layers with well-controlled structure and composition.     

Effect of terbium(III) chloride on the micellization properties of sodium decyl- and dodecyl-sulfate solutions

The effect of TbCl3 on the aggregation processes of the anionic surfactants sodium decyl sulfate (SDeS) and sodium dodecyl sulfate (SDS) has been investigated. Electrical conductivity data, combined with Tb(III) luminescence measurements suggest that the formation of micelles involving TbCl3 and SDS occurs at concentrations below the critical micelle concentration (cmc) of the pure surfactants; the formation of these mixed aggregates was also monitored by light scattering, which indicates that the addition of TbCl3 to surfactant concentration at values below the pure surfactant cmc results in a much greater light scattering than that found with pure sodium alkylsulfate surfactant micelles. This phenomenon is dependent upon the alkyl chain length of the surfactant. With Tb(III)/DS-, complexes are formed with a cation/anion binding ratio varying from 3 to 6, which depends upon the initial concentration of Tb(III). This suggests that the majority of the cation hydration water molecules can be exchanged by the anionic surfactant. When the carbon chain length decreases, interactions between surfactant and Tb(III) also decrease, alterations in conductivity and fluorescence data are not so significant and, consequently, no binding ratio can be detected even if existing. The surfactant micellization is dependent on the presence of electrolyte in solution with apparent cmc being lower than the corresponding cmc value of pure SDS.     

Adsorption behavior of hydrophobin and hydrophobin/surfactant mixtures at the solid-solution interface

The adsorption of surface-active protein hydrophobin, HFBII, and HFBII/surfactant mixtures at the solid-solution interface has been studied by neutron reflectivity, NR. At the hydrophilic silicon surface, HFBII adsorbs reversibly in the form of a bilayer at the interface. HFBII adsorption dominates the coadsorption of HFBII with cationic and anionic surfactants hexadecyltrimethyl ammonium bromide, CTAB, and sodium dodecyl sulfate, SDS, at concentrations below the critical micellar concentration, cmc, of conventional cosurfactants. For surfactant concentrations above the cmc, HFBII/surfactant solution complex formation dominates and there is little HFBII adsorption. Above the cmc, CTAB replaces HFBII at the interface, but for SDS, there is no affinity for the anionic silicon surface hence there is no resultant adsorption. HFBII adsorbs onto a hydrophobic surface (established by an octadecyl trimethyl silane, OTS, layer on silicon) irreversibly as a monolayer, similar to what is observed at the air-water interface but with a different orientation at the interface. Below the cmc, SDS and CTAB have little impact upon the adsorbed layer of HFBII. For concentrations above the cmc, conventional surfactants (CTAB and SDS) displace most of the HFBII at the interface. For nonionic surfactant C(12)E(6), the pattern of adsorption is slightly different, and although some coadsorption at the interface takes place, C(12)E(6) has little impact on the HFBII adsorption.     

In situ AFM studies on self-assembled monolayers of adsorbed surfactant molecules on well-defined H-terminated Si(111) surfaces in aqueous solutions

The formation of self-assembled monolayers (SAMs) of adsorbed cationic or anionic surfactant molecules on atomically flat H-terminated Si(111) surfaces in aqueous solutions was investigated by in situ AFM measurements, using octyl trimethylammonium chloride (C8TAC), dodecyl trimethylammonium chloride (C12TAC), octadecyl trimethylammonium chloride (C18TAC)) sodium dodecyl sulfate (STS), and sodium tetradecyl sulfate (SDS). The adsorbed surfactant layer with well-ordered molecular arrangement was formed when the Si(111) surface was in contact with 1.0x10(-4) M C18TAC, whereas a slightly roughened layer was formed for 1.0x10(-4) M C8TAC and C12TAC. On the other hand, the addition of alcohols to solutions of 1.0x10(-4) M C8TAC, C12TAC, or SDS improved the molecular arrangement in the adsorbed surfactant layer. Similarly, the addition of a salt, KCl, also improved the molecular arrangement for both the cationic and anionic surfactant layers. Moreover, the adsorbed surfactant layer with a well-ordered structure was formed in a solution of mixed cationic (C12TAC) and anionic (SDS) surfactants, though each surfactant alone did not form the well-ordered layer. These results were all explained by taking into account electrostatic repulsion between ionic head groups of adsorbed surfactant molecules as well as hydrophobic interaction between their alkyl chains, which increases with the increasing chain length, together with the increase in the hydrophobic interaction or the decrease in the electrostatic repulsion by incorporating alcohol molecules into the adsorbed surfactant layer, the decrease in the electrostatic repulsion by increasing the concentration of counterions, and the decrease in the electrostatic repulsion by alternate arrangement of cationic and anionic surfactant molecules. The present results have revealed various factors to form the well-ordered adsorbed surfactant layers on the H-Si(111) surface, which have a possibility of realizing the third generation surfaces with flexible structures and functions easily adaptable to circumstances.     

The effect of surfactants on the dissociation constants of phenothiazine derivatives Alkalimetric determination of diethazine and chlorpromazine

The effect of a cationic, an anionic and a non-ionic surfactant on the acid-base equilibria of the phenothiazine derivatives, diethazine hydrochloride and chlorpromazine hydrochloride, has been studied. It has been found that the presence of cationic and non-ionic surfactants strongly enhances the dissociation of the two derivatives, whereas the anionic surfactant decreases the dissociation constant. These effects are in agreement with a theory based on a pseudophase, ion-exchange model of micelles. From the dissociation-constant values as a function of the surfactant concentration, the binding constants for diethazine and chlorpromazine with the surfactants Septonex and sodium dodecylsulphate have been calculated. The ability of cationic surfactants to solubilize the free bases of the phenothiazine derivatives and to increase their dissociation constants has been utilized to develop a new method for alkalimetric determination of the derivatives in a micellar medium. The method has been applied to determination of the content of the active component in pharmaceutical preparations.     

Modulating properties of aqueous sodium dodecyl sulfate by adding hydrophobic ionic liquid

Altering and modifying important physicochemical properties of aqueous surfactant solutions is highly desirable as far as potential applications of such systems are concerned. Changes in the properties of aqueous solutions of a common anionic surfactant sodium dodecyl sulfate (SDS) are assessed in the presence of a common and popular 'hydrophobic' ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF(6)). Upon addition of up to approximately 0.10 wt% bmimPF(6), a dramatic decrease in critical micelle concentration (cmc) is accompanied by an increase in the degree of counterion dissociation (alpha) and micellar aggregation number (N(agg)) indicating micellar growth. However, in the range 0.10 wt% < or = bmimPF(6) 2.00 wt%, relatively gradual decrease in alpha and N(agg) is observed along with no change in cmc. Significantly decreased microfluidity of the aqueous SDS solutions on addition of bmimPF(6) is indicated by a fluorescence microviscosity probe 1,3-bis-(1-pyrenyl)propane which suggests partitioning of bmimPF(6) into the SDS micellar phase. Behavior of solvatochromic fluorescence probes, pyrene, pyrene-1-carboxaldehyde, and 2-(p-toluidino)naphthalene-6-sulfonate, confirms interaction, and possible complexation, between IL bmimPF(6) and anionic micellar surface. Increased solubility of bmimPF(6) with increasing SDS concentration further confirms SDS-bmimPF(6) interactions. Presence of strong electrostatic attraction between bmim(+) and anionic micellar surface is proposed to be the most dominant reason for these observations. All-in-all, unique role of a hydrophobic ionic liquid bmimPF(6) in modifying the properties of aqueous anionic sodium dodecyl sulfate is demonstrated.     

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.     

基于光纤折射率传感原理的表面活性剂临界胶束浓度测定方法

提出并研究了一种新颖的基于光纤折射率传感原理的表面活性剂临界胶束浓度(cmc)测定方法.应用此方法测定有代表性的阴离子表面活性剂十二烷基硫酸钠(SDS)与阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)在25℃下的cmc分别为8.05×10-3和9.11×10-4mol·L-1,与文献值比较,结果相当吻合.从而证实了本方法的准确性.进一步研究了各种条件对测量表面活性剂cmc的影响,结果表明温度和无机盐NaCl的加入对本方法测量的准确性影响小,证明了本方法对测试环境的要求不苛刻,适用性好.最后对本方法进行了重复性和稳定性测试,相对标准偏差(RSD)为0.17%,与预期符合,效果良好.     

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.     

Sorption of a fluorescent whitening agent (Tinopal CBS) onto modified cellulose fibers in the presence of surfactants and salt

The combined effect of salt (10 mmol L(-1)) and surfactants on the sorption of the fluorescent brightener 4,4'-distyrylbiphenyl sodium sulfonate (Tinopal CBS) onto modified cellulose fibers was studied. Sorption efficiencies with both cationic and anionic surfactants were evaluated. Emission spectroscopy was used for quantitative analysis since Tinopal has an intense fluorescence. The sorption efficiency of the brightener is greater for solutions containing a cationic surfactant (DTAC) below the critical micelle concentration (cmc), while for an anionic surfactant (SDS) above its cmc the efficiency is greater. The profile of the sorption isotherms were interpreted in terms of the evolution of surfactant aggregation at the fiber/solution interface. Salt influences the efficiency of the Tinopal sorption on the modified cellulose fibers either because it decreases the cmc of the surfactants or because the ions screen the surface charges of the fiber which decreases the electrostatic interaction among the charged headgroup of the surfactant and the charged fiber surface.     

Interactions between zwitterionic and conventional anionic and cationic surfactants

Critical micelle concentration (cmc) values have been determined for the mixed zwitterionic/anionic surfactant systems of N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (ZW3-12)/sodium dodecyl sulfate (SDS), N-dodecyl-N,N-(dimethylammonio)butyrate (DDMAB)/SDS, N-octyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (ZW3-08)/sodium octyl sulfate (SOS), and the zwitterionic/cationic systems of ZW3-12/dodecyltrimethylammonium bromide (DTAB), DDMAB/DTAB. Conductivity studies and nuclear magnetic resonance (NMR) spectroscopy were the methods employed for cmc determinations. The degree of nonideality of the interaction in the micelle (beta(m)), for each system, was determined according to Rubingh's nonideal solution theory. Evidence was found for the existence of strong interactions between zwitterionic and anionic surfactants in each of the zwitterionic/anionic systems. The ZW3-08/SOS and DDMAB/SDS systems behaved synergistically at all mole fractions studied while the ZW3-12/SDS system exhibited synergistic behavior above mole fractions of 0.30. Greater negative deviations from ideal behavior were demonstrated in the DDMAB/SDS system than in the other two zwitterionic/anionic systems. The zwitterionic/cationic systems of ZW3-12/DTAB and ZW3-08/OTAB displayed only slight deviations from ideal behavior, therefore indicating near ideal mixing.     

Study of mixtures of n-dodecyl-beta-D-maltoside with anionic, cationic, and nonionic surfactant in aqueous solutions using surface tension and fluorescence techniques

Surfactants of practical interest are invariably mixtures of different types. In this study, mixtures of sugar-based n-dodecyl-beta-D-maltoside with cationic dodecyltrimethylammonium bromide, anionic sodium dodecylsulfate, and nonionic pentaethyleneglycol monododecyl ether in solution, with and without supporting electrolyte, have been studied using surface tension and fluorescence spectroscopic techniques. Interaction parameters and mole fraction of components in mixed micelles were calculated using regular solution theory. The magnitude of interactions between n-dodecyl-beta-D-maltoside and other surfactants followed the order anionic/nonionic > cationic/nonionic > nonionic/nonionic mixtures. Since all surfactants have the same hydrophobic groups, strengths of interactions are attributed to the structures of hydrophilic headgroups. Electrolyte reduced synergism between n-dodecyl-beta-D-maltoside and ionic surfactant due to charge neutralization. Industrial sugar-based surfactant, dodecyl polyglucoside, yielded results similar to that with dodecyl maltoside, implying that tested commercial alkyl polyglucosides are similar to the pure laboratory samples in synergistic interactions with other surfactants. Fluorescence study not only supported the cmc results using tensiometry, but showed that interfaces of all the above mixed micelle/solution interfaces are mildly hydrophobic. Based on these results, an attempt is made to discover the nature of interactions to be a combination of intermolecular potential energies and free energy due to packing of surfactant molecules in micelles.     

Mixed micellar properties of cationic trimeric-type quaternary ammonium salts and anionic sodium n-octyl sulfate surfactants

The properties of quaternary ammonium salt-type cationic trimeric surfactants (m-2-m-2-m, m represents the carbon atom number in alkyl chain lengths of 8, 10, and 12) and oppositely charged anionic monomeric surfactant, sodium n-octyl sulfate (SOS), were characterized by employing several techniques such as static surface tension, fluorescence spectroscopy, and dynamic light-scattering measurements. The critical micelle concentrations (cmc) of m-2-m-2-m were much lower than those of the corresponding dimeric and monomeric surfactants, and decreased with increasing chain length. The addition of SOS to m-2-m-2-m solutions resulted in a further decrease of the cmc. The mixed surfactants showed higher efficiencies in lowering the surface tension than the individual surfactants. The fluorescence measurements suggested the formation of mixed micelles with a hydrophobic environment in the solutions even at lower concentrations. The dynamic light-scattering study indicated the presence of two different kinds of aggregates with different hydrodynamic diameters. The larger one was attributed to the mixed micelle of m-2-m-2-m and SOS. These results indicated a decline of the electrostatic repulsion between cationic head groups through the incorporation of anionic surfactant into the mixed surfactants.     

Specific interactions of poly(4-vinyl phenol) gel with cationic and anionic surfactants

Binding behaviors of ionic surfactants (decyl- and dodecyltrimethylammonium bromide (C(10)TAB, C(12)TAB), sodium decane sulfonate (SDeSo), and sodium dodecyl sulfate (SDS)) to poly(4-vinyl phenol) (P4VPh) gel were investigated to elucidate a specific swelling behavior that has been found for P4VPh gel in aqueous solutions of tetraalkylammonium salts. With increasing cationic surfactant concentration, P4VPh gel significantly deswelled and then remarkably reswelled at a concentration somewhat below the respective cmc values. On the other hand, in the case of the anionic surfactants, the gel only showed a marked swelling at a concentration just below the respective cmc values. A similar charge-specific behavior of the surfactants was also found for the P4VPh dispersion system studied with a UV-vis spectroscopy; namely, in the cationic surfactant-P4VPh systems, the turbidity of the dispersion first increased with increasing the surfactant concentration and then decreased. This result suggests that aggregation of P4VPh particles first occurred and finally the particles were solubilized. A red shift followed by a blue shift observed for a pi-pi absorption of phenol at around 278 nm was also consistent with the aggregation-solubilization behavior. In the anionic surfactant-P4VPh system, however, only solubilization of the polymer particle was observed, and the UV peak only showed a blue shift. All these results in the gel and the dispersion systems strongly suggest that the cation-pi interaction is involved in the binding of the cationic surfactants to P4VPh.     

树枝聚醚改性聚丙烯酰胺和阴离子表面活性剂的缔合行为

采用粘度法、荧光探针技术和^1H NMR驰豫和自扩散方法，研究了树枝聚醚疏 水改性丙烯酰胺共聚物(PDAM)和十二烷基硫酸钠(SDS)在水溶液中的相互作用．这 种共聚物含有少量的树枝聚醚，具有疏水性，容易和SDS发生相互作用，在表面活 性剂浓度远低于临界胶束浓度(cmc)的情况下，生成混合胶束状聚集体．它们的缔 合行为和溶液性质明显地取决于表面活性剂的浓度，随着聚合物溶液中加入SDS， 溶液粘度发生急剧变化，并在较低的表面活性剂浓度处出现很大的最高点．荧光和 ^1H NMR测定结果表明，这是由于在不同SDS浓度范围内，PDAM/SDS形成的聚集体结 构不同的缘故．     

Micellar catalysis on the electron transfer reactions of iron(III)-polypyridyl complexes with organic sulfides-importance of hydrophobic interactions

The oxidation of organic sulfides with iron(III)-polypyridyl complexes [Fe(NN)3]3+ proceeds through an electron transfer mechanism and an increase in the methanol content in the methanol-water mixture favors the reaction. The reaction is catalyzed by both the anionic surfactant, sodium dodecyl sulfate (SDS) and the cationic surfactant, cetyltrimethylammonium bromide (CTAB). The micellar catalysis in the presence of SDS is accounted for in terms of strong binding of the cationic oxidant with the anionic surfactant and the development of positive charge on sulfur center of substrate in the transition state. The micellar catalysis observed on the reaction involving a trication, [Fe(NN)3]3+, in the presence of CTAB indicates the importance of hydrophobic interaction between the micelle and hydrophobic ligand of [Fe(NN)3]3+. The micellar catalysis is explained in terms of a pseudophase ion exchange model.     

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。     

Aggregation Number of Ionic Surfactants and its Application for Alkyltrimethyl Ammonium Bromides and Sodium Tetradecyl Sulfate by Potentiometric Technique

A potentiometric technique based on surfactant ion selective electrode has been used for various cationic and anionic surfactants. The data obtained contain m ₁ (surfactant monomer concentration); m ₂ (free counterion concentration) and α (degree of dissociation of micelle) were used for determination of aggregation number at and above cmc (critical micelle concentration). Data fitting show a relationship between aggregation number with such parameters. The correlation equation obtained shows that size of ionic micelle vary sharply after cmc. Also, the equation obtained shows size of micelle growth with increase in counterion concentration.     

Flow injection spectrophotometric determination of anionic surfactants using methyl orange as chromogenic reagent

A flow injection(FI) spectrophotometric method for the determination of anionic surfactants was developed on the basis of the competition for the cationic surfactant cetyl pyridine (CP+) chloride between the acidic dye methyl orange (MO) and anionic surfactants. In a pH 5.0 medium the cation of cetyl pyridine (CP+) reacts with dissociated methyl orange (MO-) to form an ion-associate complex, causing a blue shift of lambda(max) from 465 nm for MO- to 358 nm for the CP+ x MO- associate. The MO- in the ion-associate complex can be quantitatively substituted by such anionic surfactants as sodium dodecyl benzene sulfonate (DBS) or sodium lauryl sulfate (LS), leading to an increase in the absorbance measured at 465 nm. This increased absorbance value is proportional to the concentration of anionic surfactants. Various chemical and physical parameters for the FI spectrophotometric method were optimized, and interference-free levels were examined. At the optimized conditions, Beer's law was obeyed in the range 1.4 approximately 25 mg/L sodium DBS for an injected sample volume of 180 microL, and a detection limit of 0.22 mg/L for sodium DBS was achieved at a sampling rate of 90 h(-1). Eleven determinations of a 16 mg/L sodium DBS solution gave a RSD of 0.4%. The proposed method has successfully been applied to the determination of anionic surfactant concentration in waste water and in detergents.