Surfactant Sodium Dodecyl Sulfate Micelles Research Articles

Manipulation of the thermo-rheological properties of stable Fe3O4 nanoparticles-embedded PCM nanoemulsions

Phase Change Material (PCM) nanoemulsions offer numerous benefits as thermal energy storage systems, including high energy storage capacity, rapid thermal response, enhanced stability, and easy integration into existing thermal management systems. This study focuses on producing nanoemulsions with fine droplets of commercial paraffin RT42, stabilized with the anionic surfactant sodium dodecyl sulfate (SDS) using the sonication method. The impact of formulation of PCM nanoemulsions on its thermophysical and rheological characterization has been investigated. The results indicated that the degree of supercooling declined from 12.8 °C to 8.6 °C as the PCM volume fraction varied from 10 to 45 vol%. This decrease was attributed to the enlargement of PCM droplet size from 110 to 164 nm while maintaining a constant PCM-to-surfactant ratio of 10:1. By incorporating Fe3O4 nanoparticles as a nucleating agent at two different concentrations of 1 and 4 %, the supercooling degree decreased from 10.2 °C to 8.2 °C when 4 % Fe3O4 nanoparticles were added. The samples exhibited remarkable stability throughout a period of one year of storage and under dynamic conditions, including 50 freeze-thaw cycles. Rheological investigations and the gelation mechanism through estimation of the attractive and repulsive interaction forces among droplets revealed that nanoemulsions with volume fractions ≥30 % transformed from fluid-like states to viscoelastic gels due to the depletion attractions caused by SDS micelles in the continuous phase. These findings contribute to a better understanding of the factors influencing the formation of viscoelastic PCM nanoemulsion gels and their potential applications across various fields.

Enhancing adsorption capacity of magnetic magnesium-aluminum layered double hydroxide by surface modification with sodium dodecyl sulfate for efficient removal of organic contaminants

A magnetic magnesium-aluminum layered double hydroxide (Mag-MgAl) was prepared, and its surface was modified using surfactant sodium dodecyl sulfate (SDS) and utilized as adsorbents for antibiotic ciprofloxacin (CIP) and dyes ponceau red (PR) and methylene blue (MB). Mag-MgAl/SDS demonstrated twice the adsorption capacity for CIP compared to Mag-MgAl, confirming that the surface modification by SDS aided the adsorption capacity. At pH 3.5, Mag-MgAl removed CIP and PR, attributed to electrostatic effect and hydrogen bonding, whereas it did not interact with MB. Conversely, Mag-MgAl/SDS successfully removed both MB and CIP, suggesting that SDS micelles acted as nanoreactors attracting cationic contaminants. The PR removal efficiency was low, possibly due to electrostatic repulsion. A binary dye system adsorption assessment was performed by mixing MB and PR aqueous solutions with Mag-MgAl and Mag-MgAl/SDS as selective adsorbents. Mag-MgAl removed around 80% of PR and 45% of MB, whereas Mag-MgAl/SDS removed less than 40% of PR and 80% of MB. SDS remains adsorbed on the surface of Mag-MgAl/SDS after the adsorption process of CIP, MB, or PR. The inversion in the affinity for the target molecules suggests that the surface of the composite can be adjusted to modulate the behavior of the adsorbent toward organic contaminants.

Structure of Cellulose Ether Affected by Ionic Surfactant and Solvent: A Small-Angle Neutron Scattering Investigation.

Polysaccharides and their derivatives are commonly used in pharmaceutical and agricultural formulations as rheology modifiers. Their performance is related to their conformation in solution, which in turn is affected by other ingredients present in the formulation. This study focuses on modulating the conformation of relatively rigid cellulose chains in aqueous solutions. In particular, we have investigated the nonionic cellulose derivative ethyl(hydroxyethyl)cellulose (EHEC) in water in the presence of the ionic surfactant sodium dodecyl sulfate (SDS) and/or ethanol acting as modulating agents. We have used small angle neutron scattering (SANS) with contrast variation to determine the EHEC chain conformation in the presence of (but not masked by) ethanol and SDS. In dilute and semidilute aqueous solutions, EHEC exhibits worm-like chain conformation due to the rigid cellulose backbone. Addition of ethanol does not impact the polymer conformation to a great extent. Addition of SDS alters the EHEC chain conformation, resulting in polyelectrolyte-like scattering behavior due to repulsive interactions between bound charged micelles which show similar structure as the free SDS micelles in solution (in the absence of polymers). Ethanol affects the polymer + surfactant system primarily by acting on the surfactant (bound on polymer) which, in turn, affects the polymer conformation. At higher ethanol concentrations (20 wt %), EHEC regains the worm-like chain conformation because of the detachment of the bound SDS micelles. To the best of our knowledge, this is the only study providing details on chain conformation of the rigid polymer EHEC in dilute or semidilute aqueous solutions in the presence of surfactant and alcohol and one of very few papers utilizing SANS for the characterization of polymer + surfactant + water + alcohol interactions. Such fundamental understanding of interactions and structure in multicomponent mixtures supports the design of industrial formulations.

Spectroscopic, conductivity and voltammetric investigations of interaction of sulfamethoxazole alone and in combination with trimethoprim with self-assembled structures

The demand and urgency of new drug design and discovery is facing new challenges in the wake of spread and persistence of serious global threat of antibiotic resistance. One of the major hurdles in the development of new drugs that are more aqueous soluble and passively diffusible is the paucity of knowledge regarding their physicochemical interactions with biological membranes. Being chemical-mimics of biomembranes, surfactant-based micellar systems present excellent pseudo-membrane models to study biophysical interactions of drugs with biological membranes in vitro. The present research focuses on physicochemical interaction of sulfamethoxazole (SMZ) alone and in combination with trimethoprim (TMP) with cationic surfactant cetyltrimethylammonium bromide (CTAB) and anionic surfactant sodium dodecyl sulfate (SDS). UV–visible spectroscopy, electrical conductivity and cyclic voltammetric techniques were employed to quantitate different drug-surfactant interaction parameters. UV–visible spectroscopic was used to evaluate critical micelle concentration (CMC) of CTAB and SDS in the presence of SMZ, TMP and their binary mixture in aqueous medium (pH 7.0). Differential absorption technique was used to determine partition coefficient (Kc ) and binding constant (Kb ) of SMZ and (SMZ + TMP) mixture with ionic micelles. Thermodynamic parameters of micellization such as and of CTAB and SDS in the presence SMZ and its mixed form with TMP were calculated in deionized water. Further, voltammetric investigations depict the strong binding of SMZ and its TMP mixture with CTAB micelles relative to SDS micelles.

Study on the Effects of Biologically Active Amino Acids on the Micellization of Anionic Surfactant Sodium Dodecyl Sulfate (SDS) at Different Temperatures

The micellar properties of the anionic surfactant, sodium dodecyl sulfate (SDS) are modified by the biologically active amino acids. Amino acids (AAs) have experienced a variety of interactions and are proposed to influence SDS micelles due to their nominated hydrophobic interactions. The present study determines the critical micellar concentration (CMC) of SDS in aqueous solutions as well as in amino aqueous solutions. Three amino acids (glutamic acid, histidine, and tryptophan) are considered here. The conductometric measurements were carried out using a wide range of SDS concentrations at different temperatures. Surface tension experiments have also been applied to estimate many surface parameters including surface excess concentration (Γmax), surface occupied area per surfactant molecule (Amin), surface tension at CMC (γcmc), surface pressure at CMC (Πcmc) and Gibbs free energy of adsorption (∆Gads°), enthalpy ∆Hm° and the critical packing parameter (CPP). Interestingly, CMC values of SDS in water and in aqueous amino acids estimated by the surface tension method are comparable with the corresponding values obtained by the conductance method. The thermodynamic parameters of SDS micellization were also evaluated in both presence and absence of AAs. The additives of AAs work to reduce the CMC values, as well as the SDS thermodynamic parameters. This reduction is highly dependent on the hydrophobicity of the AA side chain. Negative values of ∆Gm°, ∆Hm° elucidate that micellization of SDS in the presence of amino acids is thermodynamically spontaneous and exothermic. The outcomes here might be utilized for pharmaceutical applications to stabilize proteins and inhibit protein aggregation.

Ubiquitin forms conventional decorated micelle structures with sodium dodecyl sulfate at saturation

The anionic surfactant sodium dodecyl sulfate (SDS) interacts strongly with most globular proteins and denatures and unfolds them. While scattering studies using X-rays and neutrons have shown that this denaturation generally leads to protein-decorated SDS micelles, a different SDS-decorated polypeptide model has recently been suggested for complexes between SDS and Ubiquitin (UBI), in which individual SDS molecules are distributed on a partially stretched protein. To resolve this apparent discrepancy, we have investigated the SDS-UBI system by a number of complementary techniques. Small-angle X-ray scattering (SAXS) provides the overall structure of the SDS-UBI complexes, Tyr fluorescence and circular dichroism follow changes in tertiary and secondary structure, and isothermal titration calorimetry determines the stoichiometries of complexes and the amount of free SDS as a function of [SDS]. At low [SDS], UBI preserves its folded structure but dimerizes to a small extent. At 4 SDS per UBI, a complex is formed with two UBI and a small shared SDS cluster with 8 SDS molecules. In these complexes UBI preserves most of its native fold. At 10–12 SDS per UBI, which remains below the critical micelle concentration under our conditions, UBI-covered SDS micelles form with four UBIs around a core of 40 SDSs. This implies a protein-assisted micellization and an associated unfolding of UBI involving a change from mainly β-strands to mainly α-helical secondary structure. As [SDS] is increased, the complex gradually changes so that finally only one UBI covers one micelle with a similar number of SDS molecules at SDS saturation. Thus, we conclude that SDS unfolds UBI by mechanisms very similar to those observed for other globular proteins, leading to a protein-decorated SDS micelle rather than an SDS-decorated unfolded polypeptide chain.

Association between Nonionic Amphiphilic Polymer and Ionic Surfactant in Aqueous Solutions: Effect of Polymer Hydrophobicity and Micellization.

The interaction in aqueous solutions of surfactants with amphiphilic polymers can be more complex than the surfactant interactions with homopolymers. Interactions between the common ionic surfactant sodium dodecyl sulfate (SDS) and nonionic amphiphilic polymers of the poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO-PPO-PEO) type have been probed utilizing a variety of experimental techniques. The polymer amphiphiles studied here are Pluronic F127 (EO100PO65EO100) and Pluronic P123 (EO19PO69EO19), having the same length PPO block but different length PEO blocks and, accordingly, very different critical micellization concentrations (CMC). With increasing surfactant concentration in aqueous solutions of fixed polymer content, SDS interacts with unassociated PEO-PPO-PEO molecules to first form SDS-rich SDS/Pluronic assemblies and then free SDS micelles. SDS interacts with micellized PEO-PPO-PEO to form Pluronic-rich SDS/Pluronic assemblies, which upon further increase in surfactant concentration, break down and transition into SDS-rich SDS/Pluronic assemblies, followed by free SDS micelle formation. The SDS-rich SDS/Pluronic assemblies exhibit polyelectrolyte characteristics. The interactions and mode of association between nonionic macromolecular amphiphiles and short-chain ionic amphiphiles are affected by the polymer hydrophobicity and its concentration in the aqueous solution. For example, SDS binds to Pluronic F127 micelles at much lower concentrations (~0.01 mM) when compared to Pluronic P123 micelles (~1 mM). The critical association concentration (CAC) values of SDS in aqueous PEO-PPO-PEO solutions are much lower than CAC in aqueous PEO homopolymer solutions.

Enhanced micellization of Gemini surfactants using diphenhydramine hydrochloride as an organic counterion

Micellization of the Gemini surfactant sodium dilauramidoglutamide lysine (SDGL) in the presence of an antihistamine drug, diphenhydramine hydrochloride (DPC) was investigated. The anionic surfactant sodium dodecyl sulfate (SDS) was used for comparison. DPC significantly decreased the critical micelle concentration (cmc) of both SDGL and SDS in aqueous media and increasing the DPC concentration decreased the pyrene excimer/monomer polarity ratio in SDGL micelles but increased it in SDS micelles, suggesting that SDGL and SDS micelles have different shapes. The counterion binding and binding constant values reveal that SDGL micelles interact more strongly with DPC than SDS micelles. Thus, DPC, as an organic counterion, can enhance surfactant micellization. The evaluation of the solubility of a poorly water-soluble drug (clotrimazole) in SDGL and SDS micelles containing DPC revealed that the drug was more soluble in SDS micelles than SDGL micelles, indicating that the cmc and the shape and size of micelles are essential factors for controlling drug solubilization.

Inhibition of Escherichia coli O157:H7 and Salmonella enterica Isolates on Spinach Leaf Surfaces Using Eugenol-Loaded Surfactant Micelles.

Spinach and other leafy green vegetables have been linked to foodborne disease outbreaks of Escherichia coli O157:H7 and Salmonella enterica around the globe. In this study, the antimicrobial activities of surfactant micelles formed from the anionic surfactant sodium dodecyl sulfate (SDS), SDS micelle-loaded eugenol (1.0% eugenol), 1.0% free eugenol, 200 ppm free chlorine, and sterile water were tested against the human pathogens E. coli O157:H7 and Salmonella Saintpaul, and naturally occurring microorganisms, on spinach leaf surfaces during storage at 5 °C over 10 days. Spinach samples were immersed in antimicrobial treatment solution for 2.0 min at 25 °C, after which treatment solutions were drained off and samples were either subjected to analysis or prepared for refrigerated storage. Whereas empty SDS micelles produced moderate reductions in counts of both pathogens (2.1–3.2 log10 CFU/cm2), free and micelle-entrapped eugenol treatments reduced pathogens by >5.0 log10 CFU/cm2 to below the limit of detection (<0.5 log10 CFU/cm2). Micelle-loaded eugenol produced the greatest numerical reductions in naturally contaminating aerobic bacteria, Enterobacteriaceae, and fungi, though these reductions did not differ statistically from reductions achieved by un-encapsulated eugenol and 200 ppm chlorine. Micelles-loaded eugenol could be used as a novel antimicrobial technology to decontaminate fresh spinach from microbial pathogens.

How copper ions and membrane environment influence the structure of the human and chicken tandem repeats domain?

Prion proteins (PrPs) from different species have the enormous ability to anchor copper ions. The N-terminal domain of human prion protein (hPrP) contains four tandem repeats of the –PHGGGWGQ– octapeptide sequence. This octarepeat domain can bind up to four Cu2+ ions. Similarly to hPrP, chicken prion protein (chPrP) is able to interact with Cu2+ through the tandem hexapeptide -HNPGYP- region (residues 53–94). In this work, we focused on the human octapeptide repeat (human Octa4, hPrP60–91) (Ac-PHGGGWGQPHGGGWGQPHGGGWGQPHGGGWGQ-NH2) and chicken hexapeptide repeat (chicken Hexa4, chPrP54–77) (Ac-HNPGYPHNPGYPHNPGYPHNPGYP-NH2) prion protein fragments. Due to the fact that PrP is a membrane-anchored glycoprotein and its unstructured and flexible N-terminal domain may interact with the lipid bilayer, our studies were carried out in presence of the surfactant sodium dodecyl sulfate (SDS) mimicking the membrane environment in vitro. The main objective of this work was to understand the effects of copper ion on the structural rearrangements of the human and chicken N-terminal repeat domain. The obtained results provide a fundamental first step in describing the thermodynamic (potentiometric titrations) and structural properties of Cu(II) binding (UV–Vis, NMR, CD spectroscopy) to both human Octa4 and chicken Hexa4 repeats in both a DMSO/water and SDS micelle environment. Interestingly, in SDS environment, both ligands indicate different copper coordination modes, which results of the conformational changes in micelle environment. Our results strongly support that copper binding mode strongly depends on the protein backbone structure. Moreover, we focused on previously obtained results for amyloidogenic human and chicken fragments in membrane mimicking environment.

Effect of ionic strength on crude emulsification and EOR potential of micellar flood for oil recovery applications in high saline environment

Micellar flooding is one of the chemical oil recovery techniques in which micelle action emulsifies the crude oil to be mobilized in form of emulsion from a subsurface porous media. However, the subsurface conditions such as high ionic strength and temperature are challenges to the successful use of micellar flood owing to the deterioration of micelle action suggesting no crude emulsification. The ionic compounds dissociate into different ions that may further affect micelle action via loss in viscosity and pressure drop, increased water cut, and mobility contrast between micellar flood and displaced oil. Thus, investigation leading to the successful use of micellar flood, context to crude emulsion, in extreme salinity and temperature is vital to extend the use of chemical methods in new reservoirs. In this work, a typical surfactant sodium dodecyl sulfate (SDS) solution with critical micelle concentration (0.8 wt%) was tested to emulsify a fresh crude oil in the presence of varying ionic strength (0–4 wt%, NaCl/CaCl2 and temperature (40–98 °C). The efficacy of SDS micelles to produce crude emulsion significantly reduced with increasing salt concentration as reported through microscopic, rheological, and flooding experiments, particularly for divalent salt (CaCl2) than monovalent salt (NaCl). The increase in temperature (>40 °C) further curtailed the growth of crude emulsion, mainly due to enhanced droplet coalescence; thus the use of micellar flood is critical in a reservoir enriched with high salinity and high temperature. Salinity effect on emulsion viscosity is reported through rheological measurements. The study highlighted important aspects of surfactant flooding and is a forward step towards the use of SDS based micellar flood at complex reservoir conditions.

Influence of Microheterogeneous Environments of Sodium Dodecyl Sulfate on the Kinetics of Oxidation of l-Serine by Chloro and Chlorohydroxo Complexes of Gold(III).

The oxidation of l-serine by chloro and chlorohydroxo complexes of gold(III) was spectrophotometrically investigated in acidic buffer media in the absence and presence of the anionic surfactant sodium dodecyl sulfate (SDS). The oxidation rate decreases with increase in either [H+] or [Cl-]. Gold(III) complex species react with the zwitterionic form of serine to yield acetaldehyde (principal reaction product) through oxidative decarboxylation and subsequent deamination processes. A reaction pathway involving one electron transfer from serine to Au(III) followed by homolytic cleavage of α-C-C bond with the concomitant formation of iminic cation intermediate has been proposed where Au(III) is initially reduced to Au(II). The surfactant in the submicellar region exhibits a catalytic effect on the reaction rate at [SDS] ≤ 4 mM; however, in the postmicellar region an inhibitory effect was prominent at [SDS] ≥ 4 mM. The catalytic effect below the critical micelle concentration (cmc) may be attributable to the electrostatic attraction between serine and SDS that, in turn, enhances the nucleophilicity of the carboxylate ion of the amino acid. The inhibition effect beyond cmc has been explained by considering the distribution of the reactant species between the aqueous and the micellar pseudophases that restricts the close association of the reactant species. The thermodynamic parameters Δ H0 and Δ S0 associated with the binding between serine and SDS micelle were calculated to be -14.4 ± 2 kJ mol-1 and -6.3 ± 0.5 J K-1 mol-1, respectively. Water structure rearrangement and micelle-substrate binding play instrumental roles during the transfer of the reactant species from aqueous to micellar pseudophase.

Supramolecular assemblies involving calix[4]resorcinol and surfactant with pH-induced morphology transition for drug encapsulation

The present investigations concern the mixed aggregation of anionic surfactant sodium dodecyl sulfate (SDS) and aminomethylated calix[4]resorcinol (ACR) with ethylsulfonate groups on the lower rim. The interaction between these compounds was investigated by DOSY NMR, tensiometry, conductometry, dynamic and electrophoretic light scattering, atomic force microscopy and drug solubilization. The mixed supramolecular systems based on ACR and SDS can be derived due to pH-switchable properties. Supramolecular assembly took place in acidic medium which caused protonation of the amine groups of ACR and thereby the interaction of charged species in solution. Remarkably, the globular SDS micelles were observed to transform into rod-like micelles in the presence of ACR at lower pH, which can be used to encapsulate the hydrophobic guest molecules.

Effects of nonionic surfactant and salts on the interactions between oppositely charged star-shaped copolymer and ionic surfactant in aqueous solutions

The interaction between star-shaped copolymer poly(2-(dimethylamino)ethyl methacrylate-b-2-(2-methoxyethoxy)ethyl methacrylate) (CDPDPM) and anionic surfactant sodium dodecyl sulfate (SDS) in aqueous solutions are investigated by using fluorescence and dynamic light scattering (DLS) techniques. The effects of nonionic surfactant dodecyl β-D-maltopyranoside (C12G2) and salts including inorganic salt ammonium bromide (NH4Br) and organic salt tetra-n-butylammonium bromide (Bu4NBr) on the interaction between CDPDPM and SDS have been explored systematically. The results have suggested that SDS molecules can bind on CDPDPM by electrostatic interaction between the positively charged CDPDPM and negatively charged SDS and thus weaken the binding ability of CDPDPM to water molecules. CDPDPM exhibits temperature-responsive aggregation behavior in aqueous solution gradually with the increase of SDS concentration and the lower critical solution temperature (LCST) decreases correspondingly. The introduction of nonionic surfactant C12G2 changes the interaction between CDPDPM and SDS significantly by participate the formation of complexes and the stability of the CDPDPM/SDS complexes declines leading to the chance of forming larger complexes is deprived at higher temperature. The addition of NH4Br to the CDPDPM/SDS system can retard the binding of SDS on the polymer chains because of electrostatic shielding. Correspondingly, LCST is higher and the formed aggregates are smaller. For CDPDPM/Bu4NBr/SDS system, the phenomenon is similar to that of the CDPDPM/C12G2/SDS system. This should be attributed to the nature of Bu4N+, possesses not only positive charges but also certain hydrophobicity, and thus Bu4N+ has the ability to participate and facilitate the formation of SDS micelles. Obviously, the LCST of the mixed system can be tailored by adjusting the system composition on purpose.

Insights Into Molecular Interaction of Antitumor Drug Mitoxantrone With Anionic Surfactant Sodium Dodecyl Sulfate at Different Temperatures

AbstractA study of the interaction of antitumor drug mitoxantrone with anionic surfactant sodium dodecyl sulfate (SDS) has been carried out by UV–Vis absorption spectroscopy at submicellar and micellar surfactant concentrations, pH 7.4 and 10, and over a temperature range of 293.15–323.15 K. The variation of the monomer drug absorbance as a function of SDS concentration indicates, at pH 7.4 and all investigated temperatures, two definite processes: process I in the submicellar range, attributed to the electrostatic interaction between mitoxantrone and SDS monomers; and process II in the micellar range, when the drug is incorporated into SDS micelles in monomer form. At pH 10, the results have indicated only the process II at micellar SDS concentrations. The monomer absorbance changes occurring as a result of the interactions between mitoxantrone and SDS were rationalized in terms of binding constant, micelle/water partition coefficient, and the corresponding thermodynamic parameters for binding and partitioning processes. Thermodynamic parameters indicate that at pH 7.4 both binding process of mitoxantrone to SDS and partition process of mitoxantrone between micellar and bulk aqueous phases are spontaneous and enthalpy controlled, while at pH 10 both processes are spontaneous and entropy controlled.

Self- and co-assembly of amphiphilic gradient polyelectrolyte in aqueous solution: Interaction with oppositely charged ionic surfactant

Association behavior of the biocompatible amphiphilic cationic gradient polyelectrolyte poly[(2-methyl-2-oxazoline)-grad-(2-phenyl-2-oxazoline)-mod-(ethylene imine)] (HPPhMeOx) prepared by partial hydrolysis of the gradient copolymer poly[(2-methyl-2-oxazoline)-grad-(2-phenyl-2-oxazoline)] and the interaction of HPPhMeOx with the anionic surfactant sodium dodecyl sulfate (SDS) in aqueous solutions were investigated by scattering techniques (SANS, DLS) and by atomic force microscopy. SANS measurements revealed that large particles with the hydrodynamic radius of ca. 500nm observed in HPPhMeOx aqueous solutions by DLS are formed by a network of physically crosslinked compact hydrophobic domains with the mean radius of ca. 10nm. Upon addition of sodium dodecyl sulfate (SDS), the size of the domains increases at low amounts of the added SDS due to hydrophobic interaction of the single surfactant ions with the aggregates. Further addition of SDS leads to the formation of the co-assembled polyelectrolyte–surfactant complex manifested in SANS by the presence of the correlation peak from the densely packed SDS micelles as well as by partial disruption of the domains.

Separation Study of Eight Isoflavones by MEKC with Different Surfactants

Isoflavones are a very important group of natural products. This study investigated the separation of eight isoflavones, namely ononin, daidzin, genistin, biochanin A, formononetin, puerarin, genistein, and daidzein, from pueraria by micellar electrokinetic chromatography (MEKC) with different surfactants. The following micellar systems of MEKC were systematically compared for the analysis of these isoflavones: (1) a single surfactant comprising the anionic surfactant sodium dodecyl sulfate (SDS), the cationic surfactant hexadecyltrimethylammonium bromide, the neutral surfactant polyoxyethylene sorbitan monolaurate (Tween 20), and the ionic liquid-type surfactant (also a cationic surfactant) 1-dodecyl-3-methylimidazolium tetrafluoroborate (C12MIMBF4); (2) different single surfactants with 1-butyl-3-methylimidazolium tetrafluoroborate (BMImBF4) as an additive (modifier); and (3) mixed micelles of SDS + Tween 20 and C12MIMBF4 + Tween 20. Both SDS with BMImBF4 as additive and mixed micelles of SDS + Tween 20 had the highest separation efficiency for the eight investigated compounds. Furthermore, the SDS with BMImBF4 as additive was more stable (good repeatability of retention time and peak shape of analytes) than mixed micelles of SDS + Tween 20, which may be the result of a stabilizing effect of BMImBF4. Therefore, the final analytical conditions were 15 mM SDS added with 50 mM BMImBF4 in 30 mM sodium tetraborate (STB, pH 9.5) as running buffer; applied voltage, 20 kV; injection, 50 mbar for 5 s; cartridge temperature, 25 °C; compounds were detected at 260 nm. The developed method was fully validated (limit of detection, limit of quantification, intraday precision, inter-day precision, and recovery) and successfully applied to determine the eight analytes in three Radix Puerariae samples. The present study indicated that SDS with ionic liquids as additive in MEKC was suitable for the analysis of isoflavones.

Determination of micelle aggregation numbers of alkyltrimethylammonium bromide and sodium dodecyl sulfate surfactants using time-resolved fluorescence quenching

Abstract The time-resolved fluorescence quenching method was applied to determine the micelle aggregation number of cationic single-chain surfactants dodecyltrimethylammonium bromide (DTAB), cetyltrimethylammonium bromide (CTAB) and anionic surfactant sodium dodecyl sulfate (SDS). The concentration dependence of micelle aggregation number was found to be linear for all investigated surfactants in the concentration range 2‒15 × the value of critical micelle concentration of the respective surfactant. The values of micelle aggregation number were found in the range 30‒77. Different trends in the linear concentration dependence of micelle aggregation number were observed for cationic surfactants and for the anionic surfactant SDS. A small slope value was found for cationic surfactants, while the SDS micelle aggregation number concentration dependence showed significantly a larger slope value. The aggregation number increase with the increasing SDS concentration results in the micellar growth. Results from a simple analysis based on computer models of cationic and anionic surfactant molecules with dodecyl chains supports, the formation of intramicellar hydrogen bonding between surfactant molecules in SDS micelle shell.

Impact of SDS surfactant on the interactions of Cu(2+) ions with the amyloidogenic region of human prion protein.

Prion diseases, known as Transmissible Spongiform Encephalopathies (TSEs), are a group of fatal neuronal, and to some extent infectious disorders, associated with a pathogenic protein agent called prion protein (PrP). The human prion protein (hPrP) fragment encompassing the 91-127 region, also known as the amyloidogenic domain, comprises two copper-binding sites corresponding to His-96 and His-111 residues that act as anchors for Cu(2+) binding. In this work, we investigated Cu(2+) interaction with hPrP91-127 in the presence of the anionic surfactant sodium dodecyl sulfate (SDS), which induces a partial α-helix folding of the peptide. Our data indicate that the Cu(2+) coordination ability of the amyloidogenic fragment in the presence of SDS micelles is significantly different to that observed in aqueous solution. This is mainly due to the fact that SDS micelles strongly stabilize the formation of the α-helical structure of the peptide backbone, which is well conserved also upon Cu(2+) binding, contrary to the random coil conformation mainly assumed by hPrP91-127 in aqueous solutions. Potentiometric and spectroscopic studies clearly indicate that in the case of SDS containing solutions, Cu(2+) ions coordinate simultaneously to both imidazoles, while in the case of water solutions, metal ion coordination involves only a single His side chain, which individually acts as an independent Cu(2+) anchoring site.

Investigation of nanoscale structures by small-angle X-ray scattering in a radiochromic dosimeter

This study examines the nanoscale structures in a radiochromic dosimeter that was based on leuco-malachite-green dye and the surfactant sodium dodecyl sulfate (SDS) suspended in a gelatin matrix. Small-angle X-ray scattering was used to investigate the structures of a range of compositions of the dosimeter. When omitting gelatin, ellipsoidal micelles of SDS were formed with a core radius near 15 A, an eccentricity of 1.6, and a head-group shell thickness near 7 A. Gelatin significantly changed the micelles to a cylindrical shape with around three times lower core radius and four times larger shell thickness, which shows that the gelatin is present in the shell and the outer part of the core. Insight into the detailed structure might help to improve the dosimeter performance and increase the dose response to clinically relevant dose levels.