Structure Of Sodium Dodecyl Sulfate Research Articles

Co-assembly and Structure of Sodium Dodecylsulfate and other n-Alkyl Sulfates in Glycerol: n-Alkyl Sulfate-Glycerol Crystal Phase

Hypothesis.Following the observation of a microfibrillar phase in sodium dodecylsulfate (SDS)-glycerol mixtures, it is hypothesized that this phase is a crystalline structure containing SDS and glycerol, where the interaction between sulfate and glycerol layers mediates the co-assembly, which also could be universal for similar systems formed by n-alkyl sulfate homologues.Experiment.n-alkyl sulfate glycerol solutions were studied using a combination of optical microscopy, small- and wide-angle X-ray scattering (SAXS/WAXS). Time-resolved SAXS was employed to determine the phase formation in SDS-glycerol-water mixtures.Findings.The microfibrillar crystalline phase was reproduced in even-chained n-alkyl sulfates with a chain length between 12 and 18 carbon atoms, where the phase lamellar period increased uniformly with the alkyl chain length. Reconstruction of electron density profiles from the diffraction patterns allowed the lamellar structural motif of the phase, the glycerol location and stoichiometry to be determined. When SDS-glycerol-water mixtures with water concentration below 6 wt% are isothermally solidified at 20 °C, SDS-glycerol crystals and/or anhydrous SDS form, where the former is inhibited by the latter at higher water concentrations. The learnings from the SDS-glycerol phase formation allows new gels to be created, utilising the glycerol-sulfate motif generating microfibrils. This expands the knowledge of the applicable formulation space for SDS-water containing mixtures.

Degradation of textile wastewater by modified photo-Fenton process: Application of Co(II) adsorbed surfactant-modified alumina as heterogeneous catalyst

Fenton method is well recognized for organic pollutant degradation. However, traditional Fenton method has several drawbacks for practical application. In this regard different catalysts and modified Fenton processes are developed for better efficiency. In this study, a new catalyst is developed for methylene blue (MB) and methyl orange (MO) degradation under heterogeneous photo-Fenton process in presence of H2O2 and visible light. Finally, the catalyst was successfully applied for real textile wastewater degradation also. Here the as-prepared catalyst is the Co(II), which is adsorbed on the bilayer structure of sodium dodecyl sulfate (an anionic surfactant) formed on alumina support. The catalyst is designated as Co-SMA. The degradation characteristics of both the dyes are discussed. The MB, being a cationic dye, gets fully adsorbed on Co-SMA surface and the reaction proceeds on the solid surface with zero order kinetics. On the other hand, the degradation of MO follows first order kinetics because of its low adsorption. The efficiency of decolorization of real wastewater is found to be >92% in 60min time of reaction with 10gL−1 of Co-SMA, 37.9mM H2O2 and 10,010lx light intensity. Leaching of cobalt from Co-SMA is very less during the reaction which is advantageous for environmental applications.

Sodium Dodecyl Sulfate Adsorption onto Positively Charged Surfaces: Monolayer Formation With Opposing Headgroup Orientations

The adsorption and structure of sodium dodecyl sulfate (SDS) layers onto positively charged films have been monitored in situ with vibrational sum-frequency-generation (SFG) spectroscopy and surface plasmon resonance (SPR) sensing. Substrates with different charge densities and polarities used in these studies include CaF2 at different pH values as well as allylamine and heptylamine films deposited onto CaF2 and Au substrates by radio frequency glow discharge deposition. The SDS films were adsorbed from aqueous solutions ranging in concentration from 0.067 to 20 mM. In general the SFG spectra exhibited well resolved CH and OH peaks. However, at SDS concentrations between 1 and 8 mM the SFG CH and OH intensities decreased close to background levels. Combined data sets from molecular conformation, orientation, and order sensitive SFG with mass sensitive SPR suggest that the observed changes in SFG intensities above 0.2 mM are related to structural arrangements in the SDS layer. A model is proposed where the SFG intensity minimum between 1 and 8 mM is associated with a monolayer containing two headgroup orientations, one pointing toward the substrate and one pointing toward the solution phase. The SFG peaks observed at concentrations below 0.2 mM are dominated by the presence of adsorbed contaminants such as fatty alcohols (e.g., dodecanol), which are more surface active than SDS. As SDS solution concentration is increased above 1 mM SDS molecules are incorporated in the surface layer, with dodecanol continuing to be present in the surface layer for solution concentrations up to at least the critical micelle concentration.

Fabrication and Antifungal Activity of Cellulose Acetate-Based Fibers Encapsulating Natural Neem Seed Oil

Due to an attempt to increase the economic value of Thai neem (Azadirachta indica A. Juss. var. siamensis Valeton) as well as a concern on biosafety and environmental friendliness of a material that can be used for shelf-life extension of foods and perishable crops, this work was conducted to evaluate the antifungal property of NSO (NSO) and to fabricate and investigate the antifungal activity of NSO encapsulated in bio-based fibrous films. Natural cold-pressed NSO was first stabilized in micelles structure of sodium dodecyl sulfate (SDS) and then embedded in a composite matrix of cellulose acetate (CA) and poly (ethylene oxide) (PEO) via needleless electrospinning technique. The effects of SDS and NSO ratios in the electrospinning solution on the micelles size distribution, which in turn influenced the morphology of the e-spun fibers and payload of the encapsulated NSO, were investigated. Morphology of the fiber samples was examined via scanning electron microscopy (SEM). Fibrous films were selected to test for their in vivo antifungal property with wounded-inoculated and healthy tomatoes; Alternaria alternata was chosen as a tested fungus. As indicated by SEM images, an average fiber diameter was 900 nm. The results also showed that as the NSO ratio increased, the fibers tended to exhibit rice-grain-on-string microstructure. Electrospun fibrous film containing 50% NSO exhibited antifungal effect on wounded-inoculated tomatoes at a utilized weight ratio of the film to tomato of 125 mg film/1 kg tomato (in a 100% relative humidity controlled closed chamber).

Probing Carbon Nanotube–Surfactant Interactions with Two-Dimensional DOSY NMR

Two-dimensional diffusion ordered spectroscopy (2D DOSY) NMR was used to probe the micellar structure of sodium dodecyl sulfate (SDS) and sodium cholate (SC) in aqueous solutions with and without semiconducting and metallic single-walled carbon nanotubes (SWCNTs). The solutions contain SDS and SC at weight ratios of 1:4 and 3:2, the ratios commonly used to isolate semiconducting and metallic SWCNTs through density gradient ultracentrifugation (DGU). These results show that the coverage of surfactant on the semiconducting and metallic SWCNTs is nearly identical in the 1:4 surfactant mixture, and a lower degree of bundling is responsible for the greater buoyancy of semiconducting SWCNTs. In the 3:2 surfactant mixture, the metallic SWCNTs are only encapsulated in SC while the semiconducting SWCNTs remain encapsulated in a poorly packed two-surfactant micelle, leading to a large buoyant density difference between the electronic species. This work provides insight into future directions to increase the purity of semiconducting and metallic SWCNTs sorted through DGU and demonstrates the utility of 2D DOSY NMR in probing SWCNT-surfactant complexes.

Molecular Dynamics Simulation of Effect of Salt on the Compromise of Hydrophilic and Hydrophobic Interactions in Sodium Dodecyl Sulfate Micelle Solutions

The presence of salt has a profound effect on the size, shape and structure of sodium dodecyl sulfate (SDS) micelles. There have been a great number of experiments on SDS micelles in the presence and absence of salt to study this complex problem. Unfortunately, it is not clear yet how electrolyte ions influence the structure of micelles. By describing the compromise between dominant mechanisms, a simplified atomic model of SDS in presence of salt has been developed and the molecular dynamics (MD) simulations of two series of systems with different concentrations of salt and charges of ion have been performed. Polydispersity of micelle size is founded at relatively high concentration of SDS and low charge of cation. Although the counter-ion pairs with head groups are formed, the transition of micelle shape is not observed because the charge of cation is not enough to neutralize the polar of micelle surface.

Role of Counterion Condensation in the Self-Assembly of SDS Surfactants at the Water−Graphite Interface

The aggregate structure of sodium dodecyl sulfate (SDS) adsorbed at the graphite-water interface has been studied with the aid of molecular dynamics (MD) simulations. As expected, our results show that adsorbed SDS yields hemi-cylindrical micelles. The hemi-cylindrical aggregates in our simulations closely resemble all structural and morphological details provided by previous solution atomic force microscopy (AFM) experiments. More interestingly, our data indicate that SDS head groups do not provide a complete shield to the hydrophobic tails. Instead, we found regions in which the hydrophobic tails are exposed to the aqueous solution. By conducting a parametric study for SDS-like nonionic surfactants we show that electrostatic interactions between SDS head groups and counterions are responsible for the unexpected result. Our interpretation is corroborated by density profiles, analysis of the coordination states, and mean square displacement data for both the adsorbed SDS surfactants and the counterions in solution. Counterion condensation appears to be a physical phenomenon that could be exploited to direct the assembly of advanced nanostructured materials.

Ultraviolet emission from layered nanocomposites of Zn(OH)2 and sodium dodecyl sulfate prepared by laser ablation in liquid

We investigated the optical properties of Zn nanocomposites with the lamellar structure of sodium dodecyl sulfate (SDS) molecules prepared by laser ablation in an SDS aqueous solution. The absorption band of the nanocomposites was found at the same wavelength as that of ZnO (370nm). The peak positions of the nanocomposites in the photoluminescence and excitation spectra were almost the same as those of ZnO. This coincidence implies that the ZnO electronic structure was partially formed in the nanocomposites. Two structural possibilities were discussed for the nanocomposites.

Computer simulation studies of surfactant monolayer mixtures at the water/oil interface: charge distribution effects

Charge distribution effects on polar head groups for a mixture of amphiphilic molecules at the water/oil interface were studied. For this purpose a model which allowed us to investigate the charge effects exclusively was created. As a molecular model we used the structure of sodium dodecyl sulfate. Then we prepared molecules with the same molecular structure but with different charge distributions in order to have one cationic and one nonionic molecule. So, in this way, we were able to focus only in the charge effects. The monolayer mixtures were composed of anionic/nonionic and cationic/nonionic surfactants. Simulations of these systems show that the location of the different surfactants at the interface is determined by the interaction and the charge distribution of the molecules. Due to the difference in the charge distribution of the surfactant monolayers, the water molecules present distinct orientations in the mixture. Finally, it was found that the electrostatic potential difference across the interface depended on the interactions (charge distribution) of the anionic, cationic, and nonionic molecules in the mixture.

Electrophoretic mobility of Alzheimer’s amyloid-β peptides in urea–sodium dodecyl sulfate–polyacrylamide gel electrophoresis

The 43-amino acid Alzheimer’s amyloid-β peptide (Aβ peptide) retains a predominantly α-helix and β-strand structure in sodium dodecyl sulfate (SDS) solution. This conformer has a high tendency to aggregate during conventional SDS–polyacrylamide gel electrophoresis (PAGE). Both the secondary structure and the proclivity for aggregation are obviated by the use of urea–SDS–PAGE: In 8 M urea—with or without SDS—the Aβ peptide becomes 100% random coil and remains monomeric. However, during electrophoresis in this medium, the peptide and its truncated variants do not obey the law of mass/mobility relationship that most proteins—including Aβ peptides—follow in conventional SDS–PAGE. Rather, the smaller carboxy-terminally truncated peptides migrate slower than the larger full-length peptide, while the amino terminally truncated peptide does migrate faster than the full-length Aβ peptide. Thus, despite their small size (2–4 kDa) and minor differences between their lengths, the Aβ peptides display a wide separation in this low-porosity (12% acrylamide) gel. We found that this unusual electrophoretic mobility in 8 M urea is due to the fact that the quantity of [ 35S]SDS bound to the Aβ peptides, instead of being proportional to the total number of amino acids, is rather proportional to the sum of the hydrophobicity consensus indices of the constituent amino acids. It is then their hydrophobicity and, hence, the net negative charges contributed by the peptide-bound SDS that plays a major role in determining the mobility of Aβ peptides in 8 M urea–SDS–PAGE. The high selectivity of the 8 M urea–SDS–PAGE method allowed us to detect the presence of hitherto unknown Aβ peptide variants that were secreted in the conditioned medium by cultured HeLa cells.

Weak Influence of Divalent Ions on Anionic Surfactant Surface-Aggregation

The aggregated structure of sodium dodecyl sulfate (SDS) adsorbed to the graphite−solution interface has been determined in the presence of the divalent ions: Mg2+, Mn2+, and Ca2+. Divalent ions are expected to alter the electrostatic interactions between charged headgroups and thus to cause changes from the structure formed with monovalent ions. However, atomic force microscopy reveals that the adsorbed structures are long (μm) and thin (∼5 nm) and thus very similar in appearance to those observed in the presence of only monovalent counterions. Energetic considerations suggest that under most conditions the aggregates are hemicylinders, although not necessarily of constant curvature. When Mn2+ is added at constant low SDS concentration, the narrow dimension of the structure (the period) decreases linearly with solution Debye length down to a limiting period of about 5 nm. When Mg2+ is added at constant low SDS concentration, the period decreases slightly and then remains roughly constant. This suggests that the aggregate diameter increases. For both of these ions, force measurements suggests that there is a transition from a thin layer to a thicker layer as the divalent ion is added. At surfactant concentrations several times greater than the critical micelle concentration, the addition of divalent ions has no observable effect on the adsorption. We did not observe a transition to a flat layer at any of the conditions examined.

Organization of Sodium Dodecyl Sulfate at the Graphite−Solution Interface

The aggregated structure of sodium dodecyl sulfate (SDS) adsorbed to the graphite−solution interface has been determined. Atomic force microscopy reveals that SDS adsorbs in periodic structures when the solution concentration is in the range 2.8−81 mM. Using previously obtained adsorption isotherms, we deduce that these structures are hemicylindrical, but we are not able to determine their length. The long axes of the hemicylinders lie parallel in grains which typically extend over (500 nm)2 to (1000 nm)2, but the grain size can be reduced by adsorption of other species from solution. Two basic types of grain boundaries have been identified: broad boundaries, where the periodicity of both grains continue into the boundary for several periods, and narrow boundaries, where one or both of the hemicylindrical arrays terminate within a short distance. The period within each grain decreases when the concentration of SDS or the concentration of added NaCl is increased and approaches the diameter of bulk micelle...

Conformational studies of human [15-2-aminohexanoic acid]little gastrin in sodium dodecyl sulfate micelles by proton NMR

Human little gastrin is a 17 amino acid peptide that adopts a random conformation in water and an ordered structure in sodium dodecyl sulfate (SDS) micelles as well as in trifluoroethanol (TFE). The circular dichroism spectra in these two media have the same shape, indicative of a similar preferred conformation [Mammi, S., Mammi, N. J., Foffani, M. T., Peggion, E., Moroder, L., & Wünsch, E. (1987) Biopolymers 26, S1-S10]. We describe here the assignment of the proton NMR resonances and the conformational analysis of [Ahx15]little gastrin in SDS micelles. Two-dimensional correlation techniques form the basis for the assignment. The conformational analysis utilized NOE's, NH to C alpha H coupling constants, and the temperature coefficients of the amide chemical shifts. The NMR data indicate a helical structure in the N-terminal portion of the peptide. These results are compared with the conformation that we recently proposed for a minigastrin analogue (fragment 5-17 of [Ahx15]little gastrin) in TFE.

Variation in nitroxide probe chain flexibility within sodium dodecyl sulfate hemimicelles

Three nitroxide spin probes (5-, 12-, and 16-doxylstearic acid) were used to investigate the structure of sodium dodecyl sulfate (SDS) micelles and the interfacial layer between water and alumina formed by SDS (hemimicelles of SDS). It was found that whereas the rotational correlation times of the three probes differ in SDS micelles, the effective microviscosities of the probes are the same. In contrast, the microviscosity within the SDS hemimicelles varies according to the distance from the alumina surface: the nitroxide sees a more ordered environment as it is placed closer to the alumina. This represents the first report of variations in flexibility (microviscosity) within a hemimicelle. The science of the water-solid interfacial layer formed by adsorbed long-chain surfactants on solids has been studied extensively for its value in the fields of enhanced oil recovery,2 fl~tation,~ detergen~y,~ l ~brication,~ and microelectronics.6 Considerable experimental evidence is consistent with the postulate that such surfactants form localized aggregates (termed hemimicelles) on the solid surface.’ The evidence for hemimicelles has generally been indirect, and hemimicelle structure and dynamics have been inferred from measurements of bulk properties using such techniques as adsorption isotherms, {potentials, particle wettability, and heats of adsorption.8 Recently we reported the use of two types of molecular probes for use in spectroscopic investigations of the hemimicelle microstructure formed by sodium dodecyl sulfate (SDS) adsorbed on alumina. The first involved studies of pyrene and dinaphthylpropane fl~orescence,~ while the second involved the spin probe 16-doxylstearic acid (l), a stable nitroxide radical, for use with ESR spectroscopy.i0 The carboxylate functionality of this latter probe adsorbs on the positively charged alumina surface. Our results indicated that at pH 6.5 this probe aggregates mostly by itself on the surface at low SDS concentrations and forms cohemimicelles with the SDS at higher SDS concentrations. The relative anisotropy observed in an ESR spectrum is directly related to the rotational mobility of the probe, a term that can be correlated with the probe’s microviscosity.” Using this correlation, we were able to deduce that the environment within the SDS hemimicelle is relatively viscous. In both these studies of the microenvironment of the SDS hemimicelle, the data reported represent a single probe position within the hemimicelle (or a time average of many depths from the surface). Spin probes have been used extensively to study the microviscosity and micropolarity of membranes, multilayers, and micelles.12 In particular, doxylstearic acid spin probes have been useful in determining these parameters for different probe depths within phospholipid bilayers and micelles. Such studies have provided information on the orientation of the probes within the systems as well as information on the microenvironmental differences within the bilayer or micelle. In this communication, we wish to report the use of three doxylstearic acid derivatives, 16-, 12-, and 5-doxylstearic acids (1, 2, and 3, respectively) in

The importance of coulombic interactions for the induction of beta structure in lysine oligomers by sodium dodecyl sulfate.

AbstractCircular dichroism spectra have been obtained for tri(L‐lysine), tetra(L‐lysine), and penta(L‐lysine) in aqueous sodium dodecyl sulfate at 25°C. None of the oligomers are affected significantly by sodium dodecyl sulfate at detergent concentrations exceeding 0.01 M. Literature results show that the high‐molecular‐weight polymer forms a β strucure under these conditions. At detergent concentrations near 3.5 × 10−4 M the penta(L‐lysine), but not the smaller oligomers, undergoes a conformational change. Its circular dichroism under these conditions is essentially identical to that observed with poly(L‐lysine) when it forms a β structure in sodium dodecyl sulfate. Solutions of the penta(L‐lysine), which exhibit this modified circular dichroism, are also turbid, leading to the conclusion that the oligomer has formed an intermolecular β structure. When these experiments are conducted in the presence of 0.1 M sodium hydroxide, the sodium dodecyl sulfate produces neither turbidity nor a modified circular dichroism spectrum. These observations provide compelling evidence that Coulombic interaction between the anionic detergent head and the cationic lysyl amino groups is essential for the conformational change induced in penta(L‐lysine) by sodium dodecyl sulfate.