Sodium Dodecyl Sulfate Monomers Research Articles

Moment analysis method for determination of rate constants of solute permeation across interface of spherical molecular aggregates by means of high-performance liquid chromatography

A moment analysis method was developed for the study of solute permeation at the interface of spherical molecular aggregates. At first, new moment equations were developed for determining the partition equilibrium constant (Kp) and permeation rate constants (kin and kout) of solutes from the first absolute (μ1A) and second central (μ2C) moments of elution peaks measured by using high-performance liquid chromatography (HPLC). Then, the method was applied to the analysis of mass transfer phenomena of three solutes, i.e., hydroquinone, resorcinol, and catechol, at the interface of sodium dodecylsulfate (SDS) micelles. HPLC data were measured by using an ODS column and an aqueous phosphate buffer solution (pH = 7.0) as the mobile phase solvent. Pulse response experiments were conducted while changing SDS concentration (5 - 20 mmol dm−3) in the mobile phase under the conditions that the surface of ODS stationary phase was dynamically coated by SDS monomers. In order to demonstrate the effectiveness of the moment analysis method using HPLC, the values of Kp, kin, and kout were determined for the three solutes as 35 - 69, 2.4 × 10−8 - 1.4 × 10−6 m s−1, and 7.0 × 10−10 - 2.1 × 10−8 m s−1, respectively. Their values increase with an increase in the hydrophobicity of the solutes. The method has some advantages for the study of interfacial solute permeation of molecular aggregates. For example, neither immobilization nor chemical modification of both solute molecules and molecular aggregates is required when elution peaks are measured by using HPLC. Interfacial solute permeation takes place in the mobile phase without any chemical reaction or physical action on molecular aggregates. The values of Kp, kin, and kout were analytically determined from those of μ1A and μ2C by using the moment equations. The results of this study must contribute to the dissemination of an opportunity for studying the interfacial solute permeation of molecular aggregates to many researchers because of extremely high versatility of HPLC.

Modifying interprotein interactions for controlling heat-induced protein gelation

Globular proteins undergo heat-induced denaturation and eventually gelation at significantly elevated temperatures. The present study provides pathways to control temperature-driven protein gelation, having potential applications in a wide range of fields, from medicine to cosmetics to the food industry. The sol-gel transitions have been directed via modifying interprotein (electrostatic and hydrophobic) interactions by complexation of protein with amphiphiles. The heat-induced gelation of bovine serum albumin protein (anionic) is prevented in the presence of anionic sodium dodecyl sulfate (SDS) surfactant without significantly altering its native conformation. The specific binding of SDS monomers on the oppositely charged sites of protein increases the electrostatic repulsion between protein molecules, thereby suppressing the protein gelation. On the other hand, incorporating nonionic decaoxyethylene $n\ensuremath{-}\mathrm{dodecylether}$ (${\mathrm{C}}_{12}{\mathrm{E}}_{10}$) surfactant along with ionic surfactant reverses this scenario, and the solution state of the bovine serum albumin-SDS system undergoes gelation. The preferential binding of SDS with ${\mathrm{C}}_{12}{\mathrm{E}}_{10}$ nonionic surfactant forms detached mixed micelles, resulting in the release of the SDS monomers from protein, hence reverting the SDS-induced prevention of protein gelation. The results are counterintuitive and explained based on the interplay of hydrophobic and electrostatic interactions among protein molecules, as probed by small-angle neutron scattering, dynamic light scattering, and rheology.

Mechanistic Evaluation of Antimicrobial Lipid Interactions with Tethered Lipid Bilayers by Electrochemical Impedance Spectroscopy

There is extensive interest in developing real-time biosensing strategies to characterize the membrane-disruptive properties of antimicrobial lipids and surfactants. Currently used biosensing strategies mainly focus on tracking membrane morphological changes such as budding and tubule formation, while there is an outstanding need to develop a label-free biosensing strategy to directly evaluate the molecular-level mechanistic details by which antimicrobial lipids and surfactants disrupt lipid membranes. Herein, using electrochemical impedance spectroscopy (EIS), we conducted label-free biosensing measurements to track the real-time interactions between three representative compounds—glycerol monolaurate (GML), lauric acid (LA), and sodium dodecyl sulfate (SDS)—and a tethered bilayer lipid membrane (tBLM) platform. The EIS measurements verified that all three compounds are mainly active above their respective critical micelle concentration (CMC) values, while also revealing that GML induces irreversible membrane damage whereas the membrane-disruptive effects of LA are largely reversible. In addition, SDS micelles caused membrane solubilization, while SDS monomers still caused membrane defect formation, shedding light on how antimicrobial lipids and surfactants can be active in, not only micellar form, but also as monomers in some cases. These findings expand our mechanistic knowledge of how antimicrobial lipids and surfactants disrupt lipid membranes and demonstrate the analytical merits of utilizing the EIS sensing approach to comparatively evaluate membrane-disruptive antimicrobial compounds.

Effect of cations on surfactant induced membrane wetting during membrane distillation

Membrane wetting is regarded as challenges to the saline surfactant wastewater membrane distillation process, and the reason for wetting discrepancies under the assist of salt remains ambiguous. Herein, a comparative investigation was performed to reveal the mechanism of salt on sodium dodecyl sulfate (SDS) induced membrane wetting via the direct contact membrane distillation (DCMD) process. The results showed that different cations exhibited contrasting influences on membrane wetting. Compared to Na+, Mg2+ and Al3+, Ca2+ and K+ triggered significant flux increase. However, Ca2+ alleviated membrane wetting once feed temperature decreased. Feed solution characteristics indicated that Ca2+ and K+ significantly enhanced the Krafft point and hydrophobicity of micelles. Molecular dynamics simulation revealed the microcosmic interaction of Ca2+ and SDS, and verified that Ca2+ compressed the headgroup volume of SDS. By combining the critical packing parameter (CPP) of surfactants, dehydration of cations and micelle filtration experiments, it was concluded that the cations with weak hydration function in compressing the hydration layer of headgroups and facilitating the formation of more compact micelles that carry more SDS monomers, thus creating the transient adsorption of SDS in membrane pores and rapid membrane wetting. This study provides a new understanding of surfactant induced membrane wetting.

Cys-labeling kinetics of membrane protein GlpG: a role for specific SDS binding and micelle changes?

Empirically, α-helical membrane protein folding stability in surfactant micelles can be tuned by varying the mole fraction MFSDS of anionic (sodium dodecyl sulfate (SDS)) relative to nonionic (e.g., dodecyl maltoside (DDM)) surfactant, but we lack a satisfying physical explanation of this phenomenon. Cysteine labeling (CL) has thus far only been used to study the topology of membrane proteins, not their stability or folding behavior. Here, we use CL to investigate membrane protein folding in mixed DDM-SDS micelles. Labeling kinetics of the intramembrane protease GlpG are consistent with simple two-state unfolding-and-exchange rates for seven single-Cys GlpG variants over most of the explored MFSDS range, along with exchange from the native state at low MFSDS (which inconveniently precludes measurement of unfolding kinetics under native conditions). However, for two mutants, labeling rates decline with MFSDS at 0–0.2 MFSDS (i.e., native conditions). Thus, an increase in MFSDS seems to be a protective factor for these two positions, but not for the five others. We propose different scenarios to explain this and find the most plausible ones to involve preferential binding of SDS monomers to the site of CL (based on computational simulations) along with changes in size and shape of the mixed micelle with changing MFSDS (based on SAXS studies). These nonlinear impacts on protein stability highlights a multifaceted role for SDS in membrane protein denaturation, involving both direct interactions of monomeric SDS and changes in micelle size and shape along with the general effects on protein stability of changes in micelle composition.

Experimental and in silico investigation on the interaction of indomethacin with bovine serum albumin: Effect of sodium dodecyl sulfate surfactant monomers on the binding

This paper describes the interaction of indomethacin with bovine serum albumin (BSA) using experimental and computational approaches. Inner filter effect (IFE) had significantly impacted the fluorescence results as uncorrected data shown the considerable involvement of tyrosine residues which became very low after correcting the data with the former, thus, only the tryptophan residues were found to be associated with fluorescence quenching. Analyses of the corrected data suggested that there was 1:1 strong binding between BSA and indomethacin that taken place via static quenching mechanism. The binding was exothermic in nature and energetically favorable with ordering of the system. The binding of indomethacin remained almost unchanged in presence of low amount of sodium dodecyl sulfate (SDS) surfactants monomers while it significantly diminished when the concentration of SDS monomers increased. Low concentrations of indomethacin didn’t affect the secondary structure of BSA, however, high concentrations led to the partial unfolding of the protein. Molecular docking along with molecular dynamics simulation results explained that this drug molecule occupied new binding site with strong binding affinity of −8.35 kcal/mol, which is oriented in the interface between domain 1 and domain 2. The interaction was facilitated by both hydrophobic forces as well as hydrogen bonding.

Investigation the effect of sodium carboxymethylcellulose as polycounterion on cetirizine hydrochloride–sodium dodecyl sulphate mixed micelle

The aim of this research was to investigate the binding properties of sodium carboxymethylcellulose (NaCMCu) as polycounterions on mixed micelles of drug surfactants. Mixed micellization behavior of cetirizine hydrochloride (CTZ) and sodium dodecyl sulphate (SDS) was investigated in the absence and presence of NaCMCu using electrical conductivity, surface tension, fluorescence measurements, dynamic light scattering and UV measurements. The critical micelle concentration (CMC) in the aqueous and NaCMCu medium of CTZ + SDS mixed micelle was lower than the single micelle of CTZ and SDS. The presence of electrostatic interaction between NaCMCu and CTZ + SDS could increase the stability of mixed micelle from αSDS 1.0–0.0. The results showed that CTZ + SDS monomers could bind to the NaCMCu chains and form free mixed micelles in the solution, whereas no SDS / NaCMCu micelle-like complexes were found due to repulsive interaction. NaCMCu significantly decreased the CMC of CTZ. The values of counterion binding (B) from Corrin–Harkins approach and binding constant (Kb) indicated that the CTZ micelles bound to electrostatic interaction by –COO¯ ions of NaCMCu. UV absorbance data given a significant parameter, mean ion occupancy per micelle (i0) which estimated the occupancy per micelle of polycounterions for αSDS 1.0–0.0. However, the turbidity data and micellar size showed that the amount of NaCMCu increased, and the mixed micellar size also increased. Eventually, this system demonstrated that polyelectrolyte was used as an organic counterion to improve the micellar properties of amphiphilic drugs for the formulation of pharmaceutical medicinal products.

Molecular Modeling Investigation of the Interaction between Humicola insolens Cutinase and SDS Surfactant Suggests a Mechanism for Enzyme Inactivation.

One of the largest commercial applications of enzymes and surfactants is as main components in modern detergents. The high concentration of surfactant compounds usually present in detergents can, however, negatively affect the enzymatic activity. To remedy this drawback, it is of great importance to characterize the interaction between the enzyme and the surfactant molecules at an atomistic resolution. The protein enzyme cutinase from the thermophilic and saprophytic fungus called Humicola insolens (HiC) is a promising candidate for use in detergents thanks to its hydrolase activity targeting mostly biopolyesters (e.g., cutin). HiC is, however, inhibited by low concentrations of sodium dodecyl sulfate (SDS), an ubiquitous surfactant. In this work, we investigate the interaction between HiC and SDS using molecular dynamics simulations. Simulations of HiC dissolved in different aqueous concentrations of SDS show the interaction between HiC and SDS monomers, as well as the formation and dynamics of SDS micelles on the surface of the enzyme. These results suggest a mechanism of cutinase inhibition by SDS, which involves the nucleation of aggregates of SDS molecules on hydrophobic patches on the cutinase surface. Notably, a primary binding site for monomeric SDS is identified near the active site of HiC constituting a possible nucleation point for micelles and leading to the blockage of the entrance to the enzymatic site. Detailed analysis of the simulations allow us to suggest a set of residues from the SDS binding site on HiC to probe as engineered mutations aimed at reducing SDS binding to HiC, thereby decreasing SDS inhibition of HiC.

Removal of Cd(Ⅱ) by micellar enhanced ultrafiltration: Role of SDS behaviors on membrane with low concentration

Surfactant monomers tend to adsorb and aggregate on membrane, which plays a crucial role in removal of metal ions by micellar enhanced ultrafiltration (MEUF) at low concentration level. In this paper, MEUF of cadmium(Ⅱ) (Cd(Ⅱ)) with low sodium dodecyl sulfate (SDS) concentration was studied. Ultrafiltration performance was evaluated in terms of rejection ratios of Cd(Ⅱ) and SDS and relative flux of membranes. The results showed that almost 90% of Cd(Ⅱ) were removed by MEUF when SDS concentration was merely 4 mmol/L. This indicates that reducing the dosage of anionic surfactant in removal of metal ions by MEUF is possible. The retention rates of SDS ranged from 20% to 60%. Relative flux dramatically declined when SDS concentration increased from 0.4 mmol/L to 4 mmol/L. In addition, SDS behaviors on membrane during ultrafiltration were analyzed based on Zhu and Gu's adsorption model and Hermia's blocking models. When large amounts of monomeric SDS existed in the bulk solution, SDS monomers adsorbed on membrane and aggregated into hemimicelles. With SDS concentration gradually increasing, standard pore blocking and cake filtration occurred because SDS hemimicelles deposited on membrane. Cd(Ⅱ) rejection was related to the fouling layer formed by deposition of SDS on membrane.

Molecular insights into sodium dodecyl sulphate mediated control of size for silver nanoparticles

A specific condition directing the formation of silver nanoparticles (AgNPs) with narrow size-distribution in aqueous sodium dodecyl sulphate (SDS) solutions, using trisodium citrate (TSC) is investigated. The peculiar control in distribution of size for AgNPs in presence of 35 mM (~1 wt%) aqueous SDS solution as stabilizing agent is evident. Water penetration through packed PTFE powder and dynamic surface tension measurements demonstrate formation of stable aggregates at the given condition and accordingly reduced numbers of free SDS monomers diffusing to the growing AgNP interface. The smaller size of AgNPs was also confirmed by TEM images, which illustrates mixed morphologies for the nanoparticles in an aggregated state. The NMR experiments reveal strong hydrophobic interactions between the alkyl chains of SDS molecules adsorbed on AgNPs. These results also indicate that TSC is molecularly distributed in bulk phase without binding to the SDS micellar aggregates. A plausible molecular mechanism is proposed based on diffusion of Ag+ ions to the growing AgNP surface along with SDS monomers and submicellar aggregates, subsequently forming bigger size AgNPs. The narrow distribution of size for AgNP in presence of 35 mM SDS is arguably driven by the capping of stable SDS micelles or monomers around growing nuclei and restricted number of SDS monomers and submicellar aggregates responsible for supply of Ag+ at the growing AgNP nuclei.

Effect of the sodium dodecyl sulfate/monomer ratio on the network structure of hydrophobic association hydrogels with adjustable mechanical properties

ABSTRACTThe study of gel‐network structure is not as extensive as the study of the application of hydrogels. However, the distribution of the inner structure is crucial for designing hydrogels with tunable mechanical properties to meet certain kinds of demands. In this study, a series of hydrophobic association hydrogels (HA‐gels) were synthesized by free‐radical micellar copolymerization in a sodium dodecyl sulfate (SDS) surfactant solution. The hydrophobic monomer was palmityl alcohol poly(oxyethylene acrylate) (AEO–AC), which is an ecofriendly alternative to the traditional octyl phenol poly(oxyethylene acrylate). Interestingly, we found that the molar ratio [or ratio point (R)] of SDS to AEO–AC played a key role in tuning the mechanical properties. All series HA‐gels denominated a similar down–up–down tendency with increasing R, and the best R is 3. This result was consistent with the microscopic network structure number of the hydrophobic monomer (NH = 21–24), and this indicated that each hydrophobic monomer associated three SDS monomers in its internal networks. The resulting AEO–AC–acrylamide gels exhibited the best mechanical strength (yield maximum broken stress = 218 kPa) and the maximum effective crosslink density. Moreover, the relationship between the network structure and the mechanical properties of the HA‐gels was investigated with various Rs. Two different interaction effects of distribution between SDS and AEO–AC are discussed in detail. The HA‐gels exhibited self‐healing properties and maintained their shape in water over 160 days. The results indicate that changing R is an effective method for tuning the mechanical properties of HA‐gels as a type of prospective biomedical material. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45196.

Developing and Validating a Set of All-Atom Potential Models for Sodium Dodecyl Sulfate.

We present a set of novel all-atom potential models for sodium dodecyl sulfate (SDS), developed within the framework of the widely used OPLS-AA and General AMBER force fields. The choice of the parameters for the models is made by rigorously following the methodology of the used force fields to ensure full compatibility with the models for other compounds. For the GAFF model, extensive quantum-chemical computations are performed to obtain reliable Boltzmann-averaged atomic point charges, and the latter are compared with the single-conformation charges. For representation of the hydrocarbon tail, we use recently published improved parameters that correctly reproduce the properties of lipids and long alkanes. The models are validated on the basis of correct reproduction of the main properties of micelles (size, degree of counterion binding) as well as diffusion coefficient of the SDS monomer. As an extended test, a simulation of a micelle with a high aggregation number (382) and unnatural initial shape is performed, and a restructuring to the correct shape is observed. This proves the suitability of the developed models for simulations of concentrated SDS solutions containing large micelles and also emphasizes importance of hydrocarbon tail parameters for the micelle properties. Finally, the developed DS- models are tested in combination with several common Na+ and water models. Their effect on the properties of SDS micelles is discussed, and suitable combinations are determined.

Solubility enhancement of dioxins and PCBs by surfactant monomers and micelles quantified with polymer depletion techniques

Partitioning of super-hydrophobic organic contaminants (SHOCs) to dissolved or colloidal materials such as surfactants can alter their behaviour by enhancing apparent aqueous solubility. Relevant partition constants are, however, challenging to quantify with reasonable accuracy. Partition constants to colloidal surfactants can be measured by introducing a polymer (PDMS) as third phase with known PDMS-water partition constant in combination with the mass balance approach. We quantified partition constants of PCBs and PCDDs (log KOW 5.8–8.3) between water and sodium dodecyl sulphate monomers (KMO) and micelles (KMI). A refined, recently introduced swelling-based polymer loading technique allowed highly precise (4.5–10% RSD) and fast (<24 h) loading of SHOCs into PDMS, and due to the miniaturisation of batch systems equilibrium was reached in <5 days for KMI and <3 weeks for KMO. SHOC losses to experimental surfaces were substantial (8–26%) in monomer solutions, but had a low impact on KMO (0.10–0.16 log units). Log KMO for PCDDs (4.0–5.2) were approximately 2.6 log units lower than respective log KMI, which ranged from 5.2 to 7.0 for PCDDs and 6.6–7.5 for PCBs. The linear relationship between log KMI and log KOW was consistent with more polar and moderately hydrophobic compounds. Apparent solubility increased with increasing hydrophobicity and was highest in micelle solutions. However, this solubility enhancement was also considerable in monomer solutions, up to 200 times for OCDD. Given the pervasive presence of surfactant monomers in typical field scenarios, these data suggest that low surfactant concentrations may be effective long-term facilitators for subsurface transport of SHOCs.

Effect of 1-Butyl-3-methylimidazolium Halide on the Relative Stability between Sodium Dodecyl Sulfate Micelles and Sodium Dodecyl Sulfate-Poly(ethylene oxide) Nanoaggregates.

It is well-known that ionic liquids (ILs) alter the properties of aqueous systems containing only surfactants. However, the effect of ILs on polymer-surfactant systems is still unknown. Here, the effect of 1-butyl-3-methylimidazolium bromide (bmimBr) and chloride (bmimCl) on the micellization of sodium dodecyl sulfate (SDS) and its interaction with poly(ethylene oxide) (PEO) was evaluated using conductimetry, fluorimetry, and isothermal titration calorimetry. The ILs decreased the critical micellar concentration (cmc) of the surfactant, stabilizing the SDS micelles. A second critical concentration (c2thc) was verified at high SDS concentrations, due to the micelle size decrease. The stability of PEO/SDS aggregates was also affected by ILs, and the critical aggregation concentration (cac) of SDS increased. Integral aggregation enthalpy changed from -0.72 in water to 2.16 kJ mol(-1) in 4.00 mM bmimBr. IL anions did not affect the SDS micellization or the beginning of PEO/SDS aggregation. Nevertheless, when chloride was replaced with bromide, the amount of SDS bound to the polymer increased. At 100.0 mM IL, the PEO-SDS interaction vanished. We suggest that the effect of ILs comes from participating in the structure of the formed aggregates, interacting with the SDS monomers at the core/interface of the micelles, and promoting preferential solvation of the polymer.

Studies on the anticancer drug mitoxantrone–DNA–sodium dodecyl sulfate system

The interaction of anticancer drug mitoxantrone with sodium dodecyl sulfate (SDS) in the presence of two fixed DNA concentrations (1.75×10−5M, when electrostatic binding of positively charged mitoxantrone at negatively charged DNA prevails and 1.50×10−4M, when mitoxantrone molecules intercalate between DNA base pairs) was investigated by UV–Visible absorption spectroscopy.For both DNA concentrations, the spectral results indicate two processes: process I in premicellar SDS concentration assigned to electrostatic interaction between positively charged mitoxantrone and negatively charged SDS monomers, and process II in micellar SDS concentration when the surfactant micelles are formed and mitoxantrone is encapsulated in micelles as monomer. Absorption and circular dichroism spectroscopy, and thermal denaturation studies evidenced the exclusion of intercalated mitoxantrone from DNA and further their encapsulation in SDS micelles.The values of the total binding free energies show that the interaction of (mitoxantrone–DNA)complex with SDS is favored in the presence of low DNA concentration (−15.96kcal/mol), when drug molecules are electrostatically bound to DNA, than in the presence of high DNA concentration (−10.62kcal/mol) when drug molecules are intercalated between base pairs of DNA. This difference in the total binding free energies can be attributed to the cost of the deintercalation process of mitoxantrone from DNA.

Expanding the separation capability of sequential injection chromatography: Determination of melamine in milk exploiting micellar medium and on-line sample preparation

Silica, C8 and C18 monolithic column were the only option for separation on a sequential injection chromatography (SIC) system due its low-pressure operation. Therewith, the separation of molecules poorly retained by this stationary phase was a difficult task. This work presents the first use of micellar chromatography on a SIC system, with the applicability demonstrated by the determination of melamine in milk. The mobile phase was composed by aqueous sodium dodecyl sulfate (SDS) solution and propanol (92.5:7.5). The adsorption of SDS monomers on the C18 stationary phase modified its chromatographic properties, enabling satisfactory melamine separation from the milk components. The sample pretreatment procedure was on-line implemented by dilution of the sample with SDS using a multiposition valve. Calibration equations obtained from melamine solutions prepared in different types of milk and water presented similar sensitivity, indicating absence of matrix effects. A linear response was observed within 2.0 and 6.0mgL−1 of melamine with a detection limit estimated at 0.6mgL−1 and coefficients of variation at 2.9% (n=6). The procedure was suitable for fast determination of melamine below the limits established by FDA and WHO (2.5mgL−1), with minimized reagent consumption. Results for different milk samples agreed with those obtained by high performance liquid chromatography at the 95% confidence level.

Poly(amidoamine) and Poly(propyleneimine) Dendrimers Show Distinct Binding Behaviors with Sodium Dodecyl Sulfate: Insights from SAXS and NMR Analysis

We investigate the interactions of generation 3 (G3) poly(amidoamine) (PAMAM) and G3 poly(propylenimine) (PPI) dendrimers with sodium dodecyl sulfate (SDS) in aqueous solution. Size and structure of the dendrimer-SDS aggregates as a function of SDS/dendrimer molar ratio were revealed by SAXS and NMR. G3 PAMAM has a relatively open and dense-core structure, while G3 PPI with the same number of surface amine groups possesses a compact and uniform structure. Upon addition of SDS, much more SDS monomers were encapsulated in the interior of PPI rather than in PAMAM. More significant size increase in PAMAM-SDS aggregate is observed at low SDS concentrations, due to the binding of SDS on PAMAM surface and further assembly into larger supramolecular structures. Both noncooperative and cooperative binding of SDS on G3 PPI surface are observed, while only noncooperative binding is proposed on G3 PAMAM, due to its open surface and large surface group distance. The size of the PPI-SDS complex is larger than that of PAMAM-SDS at higher SDS concentrations. Within the investigated SDS concentrations, SDS exhibits much stronger interactions with G3 PPI than with G3 PAMAM. These results provide new insights into dendrimer-surfactant interactions and explain why PPI is much more cytotoxic than PAMAM.

Effect of SDS and CTAB on Derivatives of Antimicrobial Peptides Arenicin and LL-37

Abstract The interaction of two antimicrobial peptides (AMPs) with amphiphiles was investigated. In addition, the influence of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) solutions, both below and above the critical micelle concentration (cmc), was investigated by circular dichroism (CD) spectroscopy. The AMPs we used were from two different classes: C/S-Ar-1, from a lugworm, and LL-20, a fragment of human LL-37. Cationic CTAB did not influence the AMPs, independent of the amphiphile aggregation state. However, anionic SDS had a clear effect on the secondary structure of the peptides. In the case of C/S-Ar-1, no difference was observed in the CD spectra below or above the cmc (change to β-sheet). In contrast, SDS monomers led to an aggregation of LL-20 and SDS micelles changed the secondary structure of the peptides from unstructured to α-helical.

Coarse-grained molecular dynamics simulation of self-assembly of polyacrylamide and sodium dodecylsulfate in aqueous solution

Coarse-grained molecular dynamics simulations have been performed to study the self-assembly of polymer, polyacrylamide (PAM) and surfactant, sodium dodecylsulfate (SDS) in aqueous solution. Our simulations revealed that PAM curled into clusters in the absence of SDS, while it was stretched if SDS was added. For the SDS–PAM complexes, the aggregate formation process can be divided into three stages: firstly, PAM quickly absorbs some SDS monomers until the radius of gyration (Rg) of polymer reaches a minimum; then, PAM stretches and the Rg of PAM increases due to more and more adsorbed SDS; ultimately, the commonly accepted “necklace” structure is formed with PAM located at the interface of the hydrophobic and hydrophilic regions of the SDS micelle. The main driving force for the association was hydrophobic interactions between the polymer backbone and the surfactant hydrophobic tails. As the concentration of SDS increased, the Rg of PAM increased up to a maximum, indicating the polymer was saturated with surfactant.

Anomalous Solubilization Behavior of Dimyristoylphosphatidyl-choline Liposomes Induced by Sodium Dodecyl Sulfate Micelles

The solubilization dynamics of dimyristoylphosphatidylcholine (DMPC) liposomes, as induced by sodium dodecyl sulfate (SDS), were investigated; this investigation was motivated by several types of atypical behavior that were observed in the solubilization in this system. The liposomes and surfactants were mixed in a microchip, and the solubilization reaction of each liposome was observed using a microscope. We found that solubilization occurred not only via a uniform dissolution of the liposome membrane, but also via a dissolution involving the rapid motion of the liposome, or via active emission of protrusions from the liposome surface. We statistically analyzed the distribution of these patterns and considered hypotheses accounting for the solubilization mechanism based on the results. When the SDS concentration was lower than the critical micelle concentration (CMC), the SDS monomers entered the liposome membrane, and mixed micelles were emitted. When the SDS concentration was higher than the CMC, the SDS micelles directly attacked the liposome membrane, and many SDS molecules were taken up; this caused instability, and atypical solubilization patterns were triggered. The size dependence of the solubilization patterns was also investigated. When the particle size was smaller, the SDS molecules were found to be homogeneously dispersed throughout the whole membrane, which dissolved uniformly. In contrast, when the particle size was larger, the density of SDS molecules increased locally, instability was induced, and atypical dissolution patterns were often observed.