Sodium Dodecyl Sulfate System Research Articles

Choice of capillary electrophoresis systems for the impurity profiling of drugs

In order to develop a strategy for the impurity profiling of drugs, the possibilities of some capillary electrophoresis systems were investigated. A mixture containing a drug and some of its possible impurities has been used as a model problem. The test compounds were investigated by capillary zone electrophoresis (CZE) and by micellar electrokinetic chromatography (MEKC). The pH of the CZE buffer was varied, but the two stereoisomers could not be separated. Moreover, CZE is not suitable for neutral compounds. In MEKC, two different types of surfactants, sodium dodecyl sulphate (SDS) and cetyltrimethylammonium bromide (CTAB), have been used and the effect of type and concentration modifier on the separation and the elution window was studied. In the SDS system, both the resolution and the elution window could be increased considerably by the addition of modifier. The use of two MEKC systems of different selectivity seems to be a combination with high potential for the impurity profiling of drugs.

Study of the Polarity and Hydrogen-Bond Ability of Dodecyltrimethylammonium Bromide Micelles by the Kamlet−Taft Solvatochromic Comparison Method

We have studied the dipolarity/polarizability (π*), hydrogen-bond donor acidity (α), and hydrogen-bond acceptor basicity (β) of dodecyltrimethylammonium bromide (DTAB) micelles using the Kamlet−Taft solvatochromic comparison method. DTAB micelles were found to be quite polar (π* = 1.02), to have relatively strong hydrogen-bond donating ability (α = 0.700), and to have moderate hydrogen bond accepting ability (β = 0.486). These values are compared to the π*-, α-, and β-values of sodium dodecyl sulfate (SDS) micelles obtained in a previous solvatochromic study and are found to be qualitatively consistent with linear solvation energy relationship studies of both SDS and DTAB micellar systems. The chemical interpretation of these parameters and the nature of DTAB micelles which they reflect are discussed. By comparison to the solvatochromic parameters of representative pure solvents such as DMSO (π = 1.00), 2-propanol (α = 0.69), and ethylbenzoate (β = 0.43), it is evident that the micellar environments obser...

Conformation-Dependent Energy Transfer between Copolypeptide Carrying l-Ornithine and l-Tyrosine and Chlorophyll in Aqueous Sodium Dodecyl Sulfate Solution

Potentiometric and spectroscopic studies of a chlorophyll a (Chl)−copolypeptide of l-ornithine and l-tyrosine (poly(l-Orn, l-Tyr)) system in aqueous solutions of sodium dodecyl sulfate (SDS) were carried out. The cooperative binding of SDS to poly(l-Orn, l-Tyr) studied by the potentiometric measurement of the binding isotherm showed that coil to α-helix transition of the poly(l-Orn, l-Tyr)−SDS complex takes place with an increase in SDS concentration. An increase in the helix content of poly(l-Orn, l-Tyr)−SDS complex can be well interpreted in terms of the hydrophobic interaction among bound SDS ions. On the basis of theoretical analysis of the cooperative binding isotherm, it was concluded that the formation of a micelle-like cluster consisting of at least seven SDS ions is required for the stabilization of a surfactant-induced helical structure. Singlet excitation energy transfer between l-Tyr-containing copolypeptide and Chl was investigated with steady-state fluorescence spectroscopy, and the efficiency of energy transfer from l-Tyr to Chl was evaluated as a function of SDS concentration or the degree of binding of SDS ion to poly(l-Orn, l-Tyr). We also determined energy-transfer parameters such as critical transfer distance and effective mean distance between l-Tyr and Chl, based on the Förster theory. It was shown that the effective mean distance varies from 49 to 34 Å with an increse in SDS concentration or the degree of binding, and the effective local concentration of Chl acceptor is about 350 times larger than the analytical concentration (1.0 × 10-5 M); thus it can be concluded that Chl molecules are highly concentrated in poly(l-Orn, l-Tyr)−SDS complexes and Chl and l-Tyr are located close to each other. Resonance Raman spectra of the Chl−poly(l-Orn, l-Tyr)−SDS system indicated that the keto-carbonyl at the 9-position of Chl interacts with phenol side chain of l-Tyr in poly(l-Orn, l-Tyr) via hydrogen bond. Therefore, it is reasonable to assume the formation of Chl−poly(l-Orn, l-Tyr) complexes in the presence of SDS. The present results on quantum yields of Chl fluorescence and energy transfer indicate that Chl molecules are incorporated into poly(l-Orn, l-Tyr)−surfactant complexes accompanying conformational change from the random coil to α-helix, and then the conformation-dependent energy transfer effectively occurs from l-tyrosine residue to Chl in the Chl−copolypeptide−surfactant system.

Dynamic and thermodynamic aspects of polymer‐surfactant interactions: The SDS‐PVP‐water system

AbstractThe water‐PVP (polyvinylpyrrolidone)‐SDS (sodium dodecylsulfate) system has been investigated by ultrasonic relaxation measurements. In water‐PVP mixtures the relaxation time is independent on the polymer content, whereas in water‐SDS solutions it decreases on increasing the amount of surfactant in micellar form. In the ternary water‐PVP‐SDS systems, at fixed PVP content, three different regions have been observed on increasing the amount of SDS: namely, at very low surfactant content the relaxation time, τ, increases then remains nearly constant and finally decreases. The above behaviour has been ascribed to surfactant binding onto the polymer and to micelle formation, respectively. By analysing the dependence of relaxation time(s) on composition, it was possible to divide the investigated region in three domains (i.e. non interaction region, polymer‐surfactant interaction region and micellar region). A phase diagram for the above system was drawn according to the experimental kinetic results. From the data obtained by ultrasonic relaxation experiments the number of SDS molecules bound to PVP, (m), was evaluated and the Gibbs energy of binding, [ΔGbind/<m>], calculated.

Polymer−Surfactant Interactions: An Ultrasonic Relaxation Study

Polymer−surfactant interactions in water−polyvinylpyrrolidone−sodium dodecylsulfate systems have been investigated, at 25 °C, by ultrasonic relaxation methods as a function of polymer and surfactant concentration. At fixed polymer content, three regions, characterized by significant differences in their kinetic behavior, have been observed. In the first region the relaxation time increases with the surfactant content, in the second it is nearly constant, and in the third region it decreases with increasing surfactant concentration. Such behavior has been ascribed to the binding of the surfactant aggregates on the polymer backbone and to micelle formation above the saturation threshold. To account for the reported behavior, a kinetic model has been developed from the theory of ultrasonic relaxation in micellar solutions. Some thermodynamic quantities related to polymer−surfactant interactions, i.e. the Gibbs energy of binding per monomer, ΔGbind/〈m〉, where 〈m〉 is the number of monomers in polymer-bound micelles, and the volume change of binding of the surfactant to the polymer, ΔVbind, have been obtained from the data analysis.

Influence of Cationic Polyelectrolytes on Structure Formation in Lamellar Liquid Crystalline Systems

The influence of cationic polyelectrolytes, poly[(diallyldimethylammonium chloride)-co-(N-methyl-N-vinylacetamide)] (poly(DADMAC-co-NMVA)) of different charge density in contrast to that of a noncharged polymer, poly(N-methyl-N-vinylacetamide) (polyNMVA), on the lamellar liquid crystalline system sodium dodecyl sulfate (SDS)/decanol/water was investigated by means of microscopy observation between crossed polarizers, by small angle X-ray diffraction, and by rheology. The lamellar liquid crystal remained stable in all investigated formulations. The results depended on the charge density as well as the concentration of the incorporated polymer. For the polymer with the highest charge two lamellar structures existed concurrently. In excess of a certain concentration the highest charged polymer adsorbed flat onto the SDS-decanol bilayer as shown by its changed interlayer spacing, whereas at lower concentration the polymer did not have a discernible effect on the X-ray diffraction pattern. The results obtained for mixtures of the lowest charged polymer are in accordance with a loop adsorption of the polymer onto the SDS−decanol bilayer. Incorporation of the noncharged polymer did not lead to such adsorption structures and a conclusion of the importance of electrostatic interactions depending on the charge density of the polymer is reasonable. The results obtained by SAXS measurements were supported by the results of rheological measurements.

Polymers in lyotropic liquid crystalline systems

The influence of oppositely charged polyelectrolytes and copolymers of different charge density and polyanion-polycation mixtures on the preordered lamellar liquid crystalline system sodium dodecylsulfate decanol water due to Coulombic interactions with special accentuation of aggregation and adsorption phenomena was examined. Small-angle X-ray results and rheological investigations are discussed with regard to changes in the interlayer spacing after introducing the polymers at various concentrations. The liquid crystalline phase was maintained, but the preformed lamellar structure was modified via penetration of the macromolecules between the hydrocarbon chains of the surfactant molecules. In the case of the polycation, strong Coulombic interactions cause a so-called “frozen” structure, whereas for the copolymers with decreasing charge density a “loop” conformation becomes possible, resulting in significantly increased interlayer spacings. Polyanions and polyanion-polycation mixtures showed phenomena of phase separation.

Mixed Micelles of Sodium Dodecyl Sulfate and Sodium Cholate: Micellar Electrokinetic Capillary Chromatography and Nuclear Magnetic Resonance Spectroscopy

Physicochemical properties of a mixed micellar system of sodium dodecyl sulfate (SDS) and sodium cholate (SC) were investigated. The micelle−micelle and micelle−buffer interactions in an SDS/SC/[(1,1-dimethyl-2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid buffer system for separations by micellar electrokinetic capillary chromatography (MEKC) were studied by capillary electrophoresis (CE) and nuclear magnetic resonance (NMR) techniques. A mixed micellar system of SDS and SC can effectively be used for the separation by MEKC of highly hydrophobic compounds like corticosteroids. Marked differences in distribution coefficients of the corticosteroids were observed when the micellar phase was changed from the highly hydrophobic SDS to the less hydrophobic SC. Measurements of critical micelle concentration were made by CE and conductometric titration. The mixed micellar system was further characterized by NMR methods. NMR-based self-diffusion measurements and NMR relaxation measurements showed that SC affe...

Determination of saikosaponins by micellar electrokinetic capillary chromatography

In this study, we examine the feasibility of determining saikosaponins a, b1, b2, c and d, i.e., the bioactive components in Bupleuri Radix, using the micellar electrokinetic capillary chromatography technique. Results obtained from using different anion surfactants, bile salt or sodium dodecyl sulfate (SDS), are also compared. By using bile salt as a pseudostationary phase, the baseline separation of saikosaponins is observed; however, the detection limit is unfavorable. Whereas the baseline resolution of saikosaponins is achieved after adding γ-cyclodextrin in the SDS running buffer. In addition, another separating method is developed with the mixed micellar system of SDS and Brij 35 containing γ-cyclodextrin. The contents of saikosaponins in traditional Chinese medicinal prescriptions, such as Sheau Chair Hwu Tang, Bupleuri Radix plant and Chair Hwu San are analyzed by one of the above methods. The entire separation can be completed within 9 min by these methods. The R.S.D. values of the migration times are all below 1%. Moreover, the detection limits of saikosaponins vary from 7 to 33 μg/ml.

Thermodynamic properties of micellization of sodium dodecyl sulfate in binary mixtures of ethylene glycol with water

Micellar properties of sodium dodecyl sulfate (SDS) in aqueous mixtures of ethylene glycol (EG) were determined using techniques such as conductivity, density, EMF, surface tension, viscosity, ultrasonic velocity, and spectroscopy (fluorescence). The effective degree of disssociation of micelles (α) was determined using three different methods. Thermodynamics of micellization were obtained from the temperature dependence of critical micelle concentrations (cmc) values. The difference in Gibbs energies of micellization [Formula: see text] of SDS, between water and mixed solvent systems, was calculated to evaluate the influence of cosolvent on the micellization process. Surfactant aggregation numbers (Ns) obtained from static fluorescence quenching methods indicated a decrease in the aggregation numbers with increasing concentration of ethylene glycol in the binary solvent mixtures. In addition, the micropolarity of the micellar interior was determined from the pyreneI1/I3 ratios. These values were consistent with a decrease in the micropolarity surrounding the probe molecule as the EG content in the solvent mixture was increased. Key words: thermodynamics, micellization, aggregation numbers, ultrasonic velocity, degree of dissociation.

Miscibility of sodium dodecyl sulfate and sodium decyl sulfate in the adsorbed film and micelle

The interfacial tension of the aqueous solution of sodium dodecyl sulfate (SDS) and sodium decyl sulfate (SDeS) mixture against hexane was measured as a function of the total molality and composition of the surfactant mixture at 298.15 K under atmospheric pressure. The compositions of adsorbed film and micelle were evaluated numerically by applying the thermodynamic relations to the experimental results. These results were shown in the form of the phase diagrams of adsorption and micelle formation and compared with those of the aqueous solution of sodium perfluorooctanoate (SPFO) and SDeS mixture. It was found that the diagrams of SDS and SDeS system have swollen cigar shapes and are quite different from those of SPFO and SDeS system which show non-ideal mixing both in the adsorbed film and micelle. This finding was attributed to the fact that the interaction between fluorocarbon and hydrocarbon chains is weaker than that between hydrocarbon chains.

Quantitative structure-activity relationships studies with micellar electrokinetic chromatography influence of surfactant type and mixed micelles on estimation of hydrophobicity and bioavailability

Applications of micellar electrokinetic chromatography (MEKC) in quantitative structure-activity relationships (QSAR) were studied. First, quantitative structure-retention relationships (QSRR), which describe the correlation between logarithm of capacity factor (log k′) in MEKC and logarithm of distribution coefficient between 1-octanol and water (log P ow), were investigated for 60 aromatic compounds and 9 corticosteroids using three different anionic surfactants [e.g., sodium dodecyl sulfate (SDS), sodium cholate (SC), and lithium perfluorooctane sulfonate (LiPFOS)], one cationic surfactant (C 14TAB), and mixed anionic micellar systems. Linear solvation energy relationships (LSER) and solvatochromic parameters were used to shed light on the different log k′ vs. log P ow relationships for the various surfactants. It was concluded that hydrogen bonding interactions have a great influence on retention behavior in MEKC and its relationship with hydrophobicity. Interestingly, bile salt surfactants (e.g., SC) and mixed bile salt micellar systems provide better correlations for log k′ vs. log P ow than SDS and/or SDS with buffer additives (e.g., ß-cyclodextrin, urea, and acetonitrile). Using SC micelles, only one line was adequate to describe the relationship between retention in MEKC and hydrophobicity for a group of 60 aromatic compounds. The existence of higher correlation for the SC system was attributed to a similar hydrogen bonding pattern between SC micelles and 1-octanol. In the SDS system, however, three lines were recognized for the congeneric subgroups of compounds. This is due to the hydrogen bond donor (HBD) characteristics of SDS micelles that selectively differentiate between the solutes with different hydrogen bond acceptor (HBA) strength, thus demonstrating that retention is not solely based on hydrophobicity. A similar result was observed for a C 14TAB-MEKC system, however, the HBA characteristics of C 14TAB selectively differentiates between the solutes with different HBD strength. In addition, quantitative retention-activity relationships in MEKC were also investigated for 9 corticosteroids. Two types of biological activities [small intestinal absorption in the rat (log A/NA) and protein binding to human serum albumin (log B/F)] were examined in this work. High correlations were observed between bioactivity and log k′ in MEKC using bile salt surfactants and mixed bile salt systems.

Porous polymeric membranes by bicontinuous microemulsion polymerization: effect of anionic and cationic surfactants

Porous polymeric membranes made by polymerizing bicontinuous microemulsions stabilized with anionic sodium dodecyl sulfate (SDS) and cationic dodecyltrimethylammonium bromide (DTAB) as surface-active agents were investigated. The morphology, swelling and permeability characteristics of the membranes were found to be highly dependent on the surfactant concentration in both SDS and DTAB systems. The pore size of the DTAB system decreases on increasing the DTAB concentration, while the reverse trend was observed for the SDS system until its concentration exceeded 10 wt%. The membrane prepared using SDS was found to have a larger pore size in the range of 100 nm to 3 μm as compared to that of DTAB, which is less than 100 nm. In addition, the variation of SDS concentration led to a continuous change in the shape of particle aggregates of the membranes while it appeared to remain in globular form for the DTAB system. The remarkable differences between the membranes prepared using SDS and DTAB are discussed in terms of their different monolayer flexibilities.

Fluorescence Analysis of Single and Mixed Micelle Systems of SDS and DTAB

Structural features of the single and mixed micellar systems of sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) were characterized using the fluorescence probe 6-propionyl-2-(dimethylamino)naphthalene (Prodan). In particular, our investigations capitalized on the spectral sensitivity of Prodan to its environment as well as the extensive solubility of Prodan in solvents of varying polarity and/or hydrophobicity to effectively use a three-mode factor analysis technique to resolve the coincident emission from Prodan in multiple microenvironments of single and mixed micelle systems. Our investigations reveal parameters of Prodan fluorescence that reflect the relative polarities of the surfaces of SDS and DTAB micellar cores, the permeability of the SDS micelle interface, and the heterogeneity of SDS−DTAB mixed micellar systems. In particular, we observe a strong affinity of Prodan for both SDS and DTAB micelles at the water−surfactant interface with the emission λmax of Prodan consistent with greater water accessibility in the SDS interfacial region. Reduction in SDS head-group repulsion upon the addition of both an alkali metal series of counterions (Li+ → Na+ → K+) and a tetrasubstituted ammonium series of counterions (NH4+ → N(CH3)4+ → N(CH3CH2)4+ → N(CH3CH2CH2CH2)4+) appears to induce a more nonpolar environment for Prodan. Each one-phase and two-phase region of the dilute aqueous binary SDS−DTAB pseudoternary diagram is identified by distinct Prodan λmax values. Evidence is presented for the presence of SDS−DTAB mixed micelle systems.

Chiral separation of naphthalene-2,3-dialdehyde labelled peptides by cyclodextrin-modified electrokinetic chromatography.

The chiral separation of several dipeptide enantiomers, derivatized by naphthalene-2,3-dialdehyde (NDA), was achieved by use of cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC). The dipeptides contained one or two chiral centers. In the case of several dipeptides containing two chiral centers, all four of the optical isomers could be separated and baseline resolved in less than 15 min with 20 mM gamma-CD and 50 mM sodium dodecyl sulphate (SDS) in the background electrolyte. The order of elution of these derivatized dipeptides was explained by considering important chemical equilibria in the SDS, CD and peptide system. Additionally, the influence of geometric location of the chiral center, the structure of the side-chain and the effect of CD concentration on the resolution are discussed.

Chemical Selectivity in Micellar Electrokinetic Chromatography: Characterization of Solute-Micelle Interactions for Classification of Surfactants

The influence of surfactant type on migration behavior and chemical selectivity in micellar electrokinetic chromatography (MEKC) is investigated through linear solvation energy relationships (LSER) and functional group selectivities. In LSER modeling, solutes' capacity factors are correlated with their structural descriptors such as size, dipolarity, and hydrogen-bonding abilities. Using the LSER methodology, useful information about the nature of solute interactions with different types of surfactant aggregates can be obtained since capacity factor in MEKC is directly related to solute distribution between the bulk aqueous solvent and micelles. High correlations were observed for different LSER models of migration behavior in MEKC for a group of 60 uncharged aromatic compounds of non-hydrogen bonding (NHB), hydrogen-bonding acceptor (HBA) bases, and hydrogen-bonding donor (HBD) acids. In two anionic, hydrocarbon micellar systems of sodium dodecyl sulfate (SDS) and sodium cholate (SC), retention is primarily influenced by the size of molecules and their hydrogen bond accepting basicity. Their dipolarity/polarizability and hydrogen bond donating acidity play minor roles. Capacity factors of solutes in SDS and SC systems increase with their size and decrease for stronger hydrogen bond acceptor bases. These results are similar to those observed for other systems where hydrophobic interactions play a major role, e.g., solute distribution in the 1-octanol-water solvent system or retention in reversed phase LC. In MEKC with an anionic fluorocarbon surfactant, lithium perfluorooctanesulfonate (LiPFOS), however, size and solute HBD acidity are the two predominant factors. The LSER results indicate that compounds find the SDS micellar environments slightly less cohesive (i.e., more apolar) than the SC micelles, while the LiPFOS micelles are the most cohesive among the three surfactant aggregates and 1-octanol provides the least cohesive environment. The fluorocarbon micelles of LiPFOS, on the other hand, are the strongest hydrogen bond donor acids, followed by SDS, SC, and 1-octanol, respectively. The SC micelles have the most hydrogen bond acceptor basic characteristics, followed by 1-octanol, SDS, and LiPFOS micelles. It can be concluded that selectivity differences between these surfactant types in MEKC is primarily due to hydrogen-bonding interactions rather than the dipolar interactions. Comparing the perfluorinated and the hydrocarbon surfactants, even solute size can play a role in selective migration patterns. In addition, information from polar and hydrophobic group selectivities confirm the LSER conclusions about the underlying interactions that control migration behavior and chemical selectivity in MEKC.(ABSTRACT TRUNCATED AT 400 WORDS)

Analysis of dansyl amino acids in feedstuffs and skin by micellar electrokinetic capillary chromatography

Micellar electrokinetic capillary chromatography (MECC) using sodium dodecyl sulphate (SDS) and sodium cholate have been used for analyses of 30 dansylated (Dns) amino acids. The influences of sample preparation, Dns/amino acid ratio, sample solvent composition, and separation conditions including voltage, temperature, pH and buffer composition were investigated. Complete separations of acidic and neutral amino acids were obtained within 45 min in the SDS system. The efficiency expressed as number of theoretical plates for the applied capillary 0.52 m long were between 210 000 and 343 000, and the repeatability was very good with relative standard deviations on relative migration times between 0.09 and 0.70% and on relative normalised peak areas (RNPAs) between 0.85 and 3.41%. The linearity studies gave correlation coefficients between 0.9957 and 0.9993 for RNPAs against concentration. Detection limits were between 3 and 6 fmol or approximately 2 pg of each amino acid. Basic amino acids were separated in a MECC system using sodium cholate. Procedures and problems using Dns derivatisation for amino acids analysed by the MECC methods are described. Finally, examples of analyses of hydrolysates of real complex samples show, that this method can be applied to determine the amino acid composition of proteins in feedstuffs and skin.

Small-angle X-ray scattering of systems with inhomogeneous particles

Stabilization procedures are used to deduce the distance distribution function p(r) for the specific case of inhomogeneous particles where the scattering curve I(q) is dominated by a peak resulting from the particle form factor. The system sodium dodecyl sulfate (SLS)/water micellar solution is studied by small-angle X-ray scattering for low concentrations (up to 9 wt% of SLS). Subsequent computation of the electron-density distribution ρ(r) from the function p(r) confirms the existence of micellar anisometry, which is also deduced from Dmax values. The modelling of ρ(r) by two- and three-step functions is discussed; both give reasonable agreement with the p(r) function.

Microstructure and thermodynamics of a lamellar phase with disrupted surfactant bilayers

Abstract Intrinsic structural defects in the lamellar (Lα) phase of the system sodium dodecyl sulphate (SDS)/decanol/water are studied by a combination of NMR 2H quadrupole splittings of α-deuteriated SDS and small angle X-ray scattering (SAXS). The focus is on the variation of the density and size of the defects with the bilayer composition (decanol/SDS mol ratio 0.46–2.5), the bilayer volume fraction (0.27–0.64), and the temperature (20–40°C). It is found that bilayer defects are promoted by a small decanol/SDS ratio in the bilayers and by a low bilayer volume fraction, i.e. the same factors that drive the progression of phases towards microstructures with more highly curved interfaces. Variations of the extent of defects in the Lα phase reflect variations of the number of defects rather than changes of their size. The data are consistent with either slit defects (slit width ∼ 10 A) or pore defects (diameter ∼ 25 A). In either case, the interface separation across the defect is considerably smaller than...

Effect of Additives on the Clouding Behavior of an Ethylene Oxide-Propylene Oxide Block Copolymer in Aqueous Solution

Abstract Phase behavior of an ethylene oxide-propylene oxide block copolymeric surfactant Pluronic L-64 (MW = 2900, % PEO = 40) in the presence of various additives was studied from cloud point (CP) and phenol index measurements. Electrolytes with different sizes and polarizabilities of anions and cations showed an increase/decrease in cloud point; the effect of salts is discussed in terms of “salting in” and “salting out” and follows the Hofmeister series. The effect of various nonelectrolytes, viz., hydroxy compounds and amides, on the CP of L-64 was examined and discussed in terms of their influence on water structure. Ionic surfactant, viz., sodium dodecyl sulfate (SDS), increased the CP of L-64 which could be decreased drastically in the presence of small amounts of electrolytes. The clouding behavior of a mixed L-64 + SDS system in the absence/presence of salt is discussed primarily in terms of electrical charge on the micelle surface. The polyelectrolyte-like nature of the L- 64 + SDS complex is sh...