Interactions of monomeric and dimeric cationic surfactants with anionic polyelectrolytes: a fluorescence study

The interactions of conventional cationic, i.e. dodecyl-(DTAB), tetradecyl-(TTAB), and hexadecyltrimethylammonium bromides (HTAB), and dimeric cationic surfactants, i.e. dimethylene bis decyl-(10-2-10), and dodecyldimethylammonium bromides (12-2-12) with anionic polyelectrolytes, were studied by fluorescence measurements. The variation of I₁/I₃ ratio of the fluorescence of pyrene in aqueous solutions of polyelectrolytes was measured as a function of surfactant concentration. A three-step aggregation process involving the critical aggregation concentration (cac) and critical micelle concentration (cmc) was observed in each case. The cationic surfactants with lower hydrophobicity demonstrated higher degree of binding and vice versa.     

Critical aggregation concentration in mixed solutions of anionic polyelectrolytes and cationic surfactants

We have examined the polymer/surfactant interaction in mixed aqueous solutions of cationic surfactants and anionic polyelectrolytes combining various techniques: tensiometry, potentiometry with surfactant-selective electrodes, and viscosimetry. We have investigated the role of varying polymer charge density, polymer concentration, surfactant chain length, polymer backbone rigidity, and molecular weight on the critical aggregation concentration (Cac) of mixed polymer/surfactant systems. The Cac of these systems, estimated from tensiometry and potentiometry, is found to be in close agreement. Different Cac variations with polymer charge density and surfactant chain length were observed with polymers having persistence lengths either smaller or larger than surfactant micelle size, which might reflect a different type of molecular organization in the polymer/surfactant complexes. The surfactant concentration at which the viscosity starts to decrease sharply is different from the Cac and probably reflects the polymer chain shrinkage due to surfactant binding.     

Effect of mixing on the formation of complexes of hyperbranched cationic polyelectrolytes and anionic surfactants

The effect of different mixing protocols on the charged nature and size distribution of the aqueous complexes of hyperbranched poly(ethylene imine) (PEI) and sodium dodecyl sulfate (SDS) was investigated by electrophoretic mobility and dynamic light scattering measurements at different pH values, polyelectrolyte concentrations, and ionic strengths. It was found that at large excess of the surfactant a colloidal dispersion of individual PEI/SDS nanoparticles forms via an extremely rapid mixing of the components by means of a stop-flow apparatus. However, the application of a less efficient mixing method under the same experimental conditions might result in large clusters of the individual PEI/SDS particles as well as in a more extended precipitation regime compared with the results of stop-flow mixing protocol. The study revealed that the larger the charge density and concentration of the PEI, the more pronounced the effect of mixing becomes. It can be concluded that an efficient way to avoid precipitation in the solutions of oppositely charged polyelectrolytes and surfactants might be provided by extending the range of kinetically stable colloidal dispersion of polyelectrolyte/surfactant nanoparticles via the application of appropriate mixing protocols.     

The interaction of mixed surfactants with polyelectrolytes

The interactions between a linear polymer, sodium poly(2-acrylamide-2-methylpropane sulfonate), and two cationic surfactants, dodecylpyridinium chloride and tetradecylpyridinium chloride and their mixtures with different ratios, were studied by a potentiometric titration method using a surfactant-selective electrode. The ideal mixing/ideal cooperative binding model we had proposed previously was applied to successfully predict the binding isotherms of the mixed surfactant systems and the critical aggregation concentrations of the binding. The binding of surfactant mixtures to polymers is similar to the ideal mixed micelle formation and a sort of synergetic effect was found during the binding process. Received: 18 August 1998 Accepted in revised form: 6 November 1998     

Capillary electrophoresis method to determine siRNA complexation with cationic liposomes

Small interfering RNA (siRNA) inducing gene silencing has great potential to treat many human diseases. To ensure effective siRNA delivery, it must be complexed with an appropriate vector, generally nanoparticles. The nanoparticulate complex requires an optimal physiochemical characterization and the complexation efficiency has to be precisely determined. The methods usually used to measure complexation in gel electrophoresis and RiboGreen^® fluorescence‐based assay. However, those approaches are not automated and present some drawbacks such as the low throughput and the use of carcinogenic reagents. The aim of this study is to develop a new simple and fast method to accurately quantify the complexation efficiency. In this study, capillary electrophoresis (CE) was used to determine the siRNA complexation with cationic liposomes. The short‐end injection mode applied enabled siRNA detection in less than 5 min. Moreover, the CE technique offers many advantages compared with the other classical methods. It is automated, does not require sample preparation and expensive reagents. Moreover, no mutagenic risk is associated with the CE approach since no carcinogenic product is used. Finally, this methodology can also be extended for the characterization of other types of nanoparticles encapsulating siRNA, such as cationic polymeric nanoparticles.     

On the complexation of proteins and polyelectrolytes

Both natural and synthetic polyelectrolytes form strong complexes with a variety of proteins. One peculiar phenomenon is that association can take place even when the protein and the polyelectrolyte carry the same charge. This has been interpreted as if the ion-dipole interaction can overcome the repulsive ion-ion interaction. On the basis of Monte Carlo simulations and perturbation theory, we propose a different explanation for the association, namely, charge regulation. We have investigated three different protein-polymer complexes and found that the induced ionization of amino acid residues due to the polyelectrolyte leads to a surprisingly strong attractive interaction between the protein and the polymer. The extra attraction from this charge-induced charge interaction can be several kT and is for the three cases studied here, lysozyme, alpha-lactalbumin, and beta-lactoglobulin, of the same magnitude or stronger than the ion-dipole interaction. The magnitude of the induced charge is governed by a response function, the protein charge capacitance Z2-Z2. This fluctuation term can easily be calculated in a simulation or measured in a titration experiment.     

Interaction of cellulose-based cationic polyelectrolytes with mucin

Mucoadhesivity of water-soluble polymers is an important factor, when testing their suitability for controlled drug delivery systems. For this purpose, the interaction of new cationic cellulose polyelectrolytes with lyophilized mucin was investigated by means of turbidimetric titration, microscopy and measurement of zeta potential and particle size changes in the system. Results show that the cellulose derivatives interact with mucin. This interaction became stronger if cellulose macromolecules contained positively charged groups and an electrostatic interaction with the negatively charged mucin particles occurred. Under certain conditions flocculation of mucin particles by the cellulose polyelectrolyte was observed.     

Synthesis and polymerization of tail-type cationic polymerizable surfactants and hydrophobic counter-anion induced association of polyelectrolytes

A series of tail-type cationic surface-active monomers with the cationic charge at the -end (1; ST-C_m-AB, m=5, 7, and 9, where ST is a styrenic group, C_m the alkylene chain at the 4-position of styrene, and AB is alkyltrimethylammonium bromide) have been synthesized as a novel cationic polymerizable surfactant. Their fundamental physicochemical properties such as critical micelle concentration (cmc) and weight-average aggregation number of the micelle (N_w(agg)) have been characterized in water at 25 °C by static light-scattering measurements. The cmc values determined for the tail-type surfactant monomers are two-orders of magnitude smaller than those of the corresponding head-type cationic surfactant monomers (2; ST-C₁-AC-C_m). The N_w(agg) of ST-C_m-AB is 68 for m=5, 156 for m=7, and 413 for m=9. Free-radical homopolymerization of ST-C₇-AB proceeds very rapidly in water as a result of organization in the micelle to afford the corresponding amphiphilic cationic polyelectrolyte with M_w=3.63×10⁶ and 23 nm hydrodynamic radius at 25 °C. Emulsion copolymerization of styrene with ST-C_m-AB also proceeds rapidly to afford very stable cationic polystyrene latex particles of 30–60 nm diameter. The amphiphilic cationic polyelectrolyte of poly(ST-C₇-AB) is likely to assume a compact conformation with high segment density in 0.1 mol L^–1 NaCl in water. Addition of hydrophobic aromatic counter-anions with an weak acid group, for example potassium hydrogen phthalate (PHK) and sodium salicylate, to a salt-free aqueous solution of poly(ST-C₇-AB) induces intermolecular aggregation and increases the solution viscosity substantially, often producing gels and precipitation at high polymer concentration.     

Interactions of hydrophobically modified polyelectrolytes with nonionic surfactants

Interactions of surfactants with hydrophobically modified polyelectrolytes in aqueous solutions are important in several applications such as detergency, cosmetics, food, and paints. Complexes formed in these systems raise some fundamental questions about the polymer-surfactant interactions that control their behavior. In this work, the interactions of a nonionic surfactant, penta-ethyleneglycol mono n-dodecyl ether (C(12)EO(5)), with a hydrophobically modified anionic polymer, poly(maleic acid/octyl vinyl ether) (PMAOVE), in aqueous solutions were studied using surface tension, viscosity, electron paramagnetic resonance (EPR) spectroscopy, light scattering, and fluorescence spectroscopic techniques. When the nonionic surfactant C(12)EO(5) was added to aqueous solutions of the anionic polymer PMAOVE, it was incorporated into the hydrophobic nanodomains of PMAOVE far below the the critical micelle concentration (cmc) of the surfactant. Two inflection points were observed corresponding to the critical complexation concentration (formation of mixed micelles composed of C(12)EO(5) and the octyl chains of PMAOVE) and the saturation concentration (saturation of the polymer with C(12)EO(5) molecules). Above the saturation concentration, the coexistence of pure C(12)EO(5) micelles and mixed micelles of PMAOVE and C(12)EO(5) was observed. Such a coexistence of complexes has major implications in their performance in colloidal processes.     

Interaction of the low-molecular weight salts with cationic polyelectrolytes

The interaction of several mono-, di-, and trivalent anions with cationic polyelectrolytes having different contents in N,N-dimethyl-2-hydroxypropylen ammonium chloride units (polymer A) or tertiary amine N-atoms and PEG (polymer PEGA) in the main chain was studied by viscosimetric and conductometric measurements. Both methods have shown a stronger interaction for tri- and bi- than for univalent counterions. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2571–2581, 1997     

Novel method for the estimation of the binding isotherms of ionic surfactants on oppositely charged polyelectrolytes

One of the most important characteristics of the polyelectrolyte/surfactant interaction is the binding isotherm of the surfactant because it provides basic thermodynamic information about the binding mechanism. However, the amount of the surfactant bound to the polymer may crucially affect the surface properties of these systems via changing the thermodynamic activity of the components. Therefore, a knowledge of the binding isotherms can also be useful in tuning the efficiency of commercial products. However, the determination of these isotherms is still subject to significant experimental difficulties. In this letter, we offer a novel method for the estimation of binding isotherms based on electrokinetic measurements. The technique provides a simple and quick way to estimate the bound amount of surfactant that might be useful in both fundamental and industrial research. In principle, the proposed method could also be extended to the determination of the binding isotherms of small ligands on biomacromolecules.     

Supramolecular systems based on cationic surfactants: an influence of hydrotropic salts and oppositely charged polyelectrolytes

Russian Chemical Bulletin - For cationic surfactant 4-aza-1-dodecyl-1-azoniabicyclo[2.2.2]octane bromide (DABCO-16), a significant decrease in the critical micelle concentration (CMC) is shown in...     

曙红Y分光光度法测定阳离子表面活性剂及其机理研究

在弱酸性的HCl-NaAc缓冲介质中,阳离子表面活性剂(CS)与曙红Y(EY)染料反应,形成离子缔合物,溶液颜色发生明显改变,最大褪色波长分别在514 nm(EY-CPB体系)、516 nm(EY-CTAB体系),同时在548 nm(CPB体系)、544 nm(CTAB体系)处有吸收峰,在褪色波长处阳离子表面活性剂的浓度与褪色程度呈良好线性关系,从而建立测定阳离子表面活性剂的光度法。在最大褪色波长处,CPB体系、CTAB体系中CS的浓度在0~4.79×10-5mol/L、0~2.90×10-5mol/L范围内遵守比尔定律,表观摩尔吸光系数为2.94×104、2.86×104L.mol-1.cm-1,检出限为8.97×10-7mol/L、7.87×10-7mol/L。若用双波长叠加,表观摩尔吸光系数达5.58×104、5.20×104L.mol-1.cm-1,检出限为5.87×10-7、6.25×10-7mol/L。方法适用于水样中CS的测定。本文还用密度泛函理论对反应机理进行了探讨。     

Surfactant polymer interactions between strongly interacting cationic surfactants and anionic polyelectrolytes from conductivity and turbidity measurements

The interactions between oppositely charged surfactant/polymer mixtures have been studied using conductivity and turbidity measurements. The dependence of aggregation phenomenon on the chain length and head group modifications of conventional cationic surfactants, i.e., hexadecyl- (HTAB), tetradecyl- (TTAB), and dodecyltrimethylammonium bromides (DTAB) and dimeric cationic surfactants, i.e., decyl- (DeDGB) and dodecyldimethylgemini bromides (DDGB), is investigated. It was observed that cationic surfactants induce cooperative binding with anionic polyelectrolytes at critical aggregation concentration (cac). The cac values are considerably lower than the critical micelle concentration (cmc) values for the same surfactant. After the complete complexation, free micelles are formed at the apparent critical micelle concentration (acmc), which is slightly higher in aqueous polyelectrolyte than in pure water. Among the conventional and dimeric cationic surfactants, DTAB and DeDGB, respectively, have been found to have least interactions with oppositely charged polyelectrolytes.     

Macromolecular design of new cationic polyelectrolytes

Methods were elaborated for the synthesis of new monomers, derivatives of diallylguanidine and macromers, which contain fragments of polytetrahydrofuran and diallylic nitrogencontaining end groups (diallylamine, alkyldiallylammonium, diallylguanidine both in base and acetate forms). Alkylation of a macromer with a diallylamine end group was carried out with methyl iodide in various organic solvents. The possibility of synthesis of diallylguanidine acetate homopolymer as well as its statistical copolymer with diallyldimethylammonium chloride was shown. For the first time, block copolymers based on synthesized macromers were obtained.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1976–1982, November, 1994.The work was supported in part by the Russian Foundation For Basic Research (project code 94-03-08924a).     

Size exclusion chromatography of cationic polyelectrolytes

Molecular weight distributions of the cationic polyelectrolyte poly(2-trimethylammonium ethyl methacrylate chloride) were determined via size exclusion chromatography (SEC) for a very broad molecular weight range ($\text{7.7 × 10}{}^3\text{?}\text{M}{}_{\mathrm{<mtext>w</mtext>}}\text{? 1.1 × 10}{}_7$). Non-size exclusion effects (ion inclusion, ion exclusion, adsorption) were controlled by special surface treatment of the stationary phase (DMAE-Fractosil^R, E. Merck) and by proper selection of the mobile phase. A non-linear effective molecular weight calibration procedure was applied to account for the high polydispersity of the polyelectrolyte standard polymers. $\text{M}{}_{\mathrm{w}}$ data from SEC experiments agree with results from light scattering, and the molecular weight distributions obtained from SEC and sedimentation velocity analysis compare well.     

Interactions of temperature-responsive anionic polyelectrolytes with a cationic surfactant

The interactions of temperature-responsive copolymers of sodium 2-acrylamido-2-methyl-1-propanesulfonate (AMPS) and N-isopropylacrylamide (NIPAM) with a cationic surfactant, dodecyltrimethylammonium chloride (DTAC), have been studied. The content of AMPS in the copolymers ranged from 1.1 to 9.6 mol%. The surface activity was higher for the polymers with lower AMPS content. It was found that DTAC undergoes association with the polymer chain, forming mixed polymer-surfactant micelles. The values of cac for the polymers were found in fluorescence studies using pyrene as the fluorescent probe. They were in the range 0.9-3.6x10(-3) M and were lower for polymers with higher AMPS content. An increase in DTAC concentration up to about its cmc results in a decrease of the LCST (lower critical solution temperature) of the copolymers, while further increase above the cmc results in an increase of the LCST. The minimum value of LCST in the presence of the surfactant is lower than the LCST of NIPAM homopolymer.     

Spectrophotometric determination of cationic surfactants with benzothiaxolyldiazoaminoazobenzene

A novel spectrophotometric method for the determination of cationic surfactants (CS) by using a new reagent benzothiaxolyldiazoaminoazobenzene (BTDAB) is developed. In 0.06-0.10 M sodium hydroxide, CS such as cetyltrimethylammonium bromide (CTMAB) and cetylpyrdinium chloride (CPC) react with BTDAB to form a violet-red 1:2 (CS:BTDAB) ion association complex in the presence of Triton X-100. This ion associate exhibits an absorption maximum at 580 nm with an apparent molar absorptivity of 4.1×10⁴ l mol⁻¹ cm⁻¹. Beer’s law is obeyed for CTMAB or CPC in the concentration range 0-100 μg per 25 ml of solution. The proposed method based on the above colour reaction is simple and rapid, and there is no use of toxic organic solvents. It has been applied to the determination of trace CS in industrial wastewater with satisfactory results.     

Surface complexation of DNA with a cationic surfactant

We have studied the surface complexation of DNA with a cationic surfactant (DTAB) using a combination of methods: dynamic surface tension, ellipsometry and Brewster angle microscopy. Below the surfactant critical aggregation concentration (cac), complexation occurs only at the surface, and the results are consistent with neutralization of the surfactant charges by the free polymer ions. Above the cac, surfactant starts to bind cooperatively to DNA in the bulk, and adsorption of the preformed hydrophobic surfactant DNA aggregate is now possible, leading to thick surface layers. At still higher concentrations of surfactant (still below saturation of binding in the bulk), there is decrease in adsorption due to competition with bulk aggregates. Finally, as surfactant concentration is increased still further, bulk aggregates become less soluble and large amounts are adsorbed, forming a surface layer, which is solid-like and brittle.