Sodium Dodecyl Sulfate Micelles Research Articles

Relationship between polymer-surfactant interaction and micellar solubilization revealed by NMR spectroscopy

Micellar solubilization is considered as a key factor affecting the recovery efficiency in chemically enhanced oil recovery (cEOR). However, it is poorly understood how polymers in surfactant-polymer (SP) flooding influences the micellar solubilization. Guar gum (GG) and hydroxyethyl cellulose (HEC) are two important and widely used polysaccharide polymers. In this work, the effect of GG and HEC on the solubilization of a crude oil model compound methyl benzoate (MB) in anionic sodium dodecyl sulfate (SDS) micelles and the underlying mechanism were explored at the molecular scale by NMR spectroscopy. GG and HEC slightly increased the MB solubility in SDS micelles but did not change the solubilization capacity. No correlation peak was observed to demonstrate the attractive interaction between polymer and SDS. After examination, there is weak electrostatic repulsion between HEC/GG and SDS, which made the polymer independent from SDS micelles and was unable to participate in the formation of micelles to alter micellar structure and solubilization behavior. Although the solubility of MB was slightly increased, this increase should originate from weak molecular interactions between polymers, surfactants and hydrophobic molecules, including hydrogen bonding, van der Waals forces and hydrophobic interactions, etc. In summary, without strong electrostatic attraction between polymer and surfactant, the solubilization of polymers and the solubilization of micelles proceed independently, resulting in that the solubilization capacity of SDS micelles was not improved.

Using Magnetic Micelles Combined with Carbon Fiber Ionization Mass Spectrometry for the Screening of Trace Triazine Herbicides from Aqueous Samples.

Triazine herbicides are commonly used in agriculture to eliminate weeds. However, they can persist in the environment. In this study, we explored a new method for detecting triazine herbicides in aqueous samples. We selected two triazine herbicides, namely, prometryn and ametryn, as model herbicides. To generate magnetic probes, we mixed aqueous Gd3+ with aqueous sodium dodecyl sulfate (SDS), which created magnetic probes made of Gd3+-SDS micelles. These probes showed a trapping capacity for the model herbicides. Results indicated that the trapping capacities of our magnetic probes for ametryn and prometryn were approximately 466 and 468 nmol mg-1, respectively. The dissociation constants of our probes toward ametryn and prometryn were 2.92 × 10-5 and 1.27 × 10-5, respectively. This is the first report that the developed magnetic probes can be used to trap triazine herbicides. For detection, we used carbon fiber ionization mass spectrometry (CFI-MS), which can be used to directly detect semi-volatiles from the samples in the condensed phase. Because of the semi-volatility of triazine herbicides, the herbicides trapped by the magnetic probes can be directly analyzed by CFI-MS without any elution steps. In addition, we also demonstrated the feasibility of using our approach for detecting triazine herbicides in lake water and drinking water.

Antiviral peptides inhibiting the main protease of SARS-CoV-2 investigated by computational screening and in vitro protease assay.

The main protease (Mpro) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) plays an important role in viral replication and transcription and received great attention as a vital target for drug/peptide development. Therapeutic agents such as small-molecule drugs or peptides that interact with the Cys-His present in the catalytic site of Mpro are an efficient way to inhibit the protease. Although several emergency-approved vaccines showed good efficacy and drastically dropped the infection rate, evolving variants are still infecting and killing millions of people globally. While a small-molecule drug (Paxlovid) received emergency approval, small-molecule drugs have low target specificity and higher toxicity. Besides small-molecule drugs, peptide therapeutics are thus gaining increasing popularity as they are easy to synthesize and highly selective and have limited side effects. In this study, we investigated the therapeutic value of 67 peptides targeting Mpro using molecular docking. Subsequently, molecular dynamics (MD) simulations were implemented on eight protein-peptide complexes to obtain molecular-level information on the interaction between these peptides and the Mpro active site, which revealed that temporin L, indolicidin, and lymphocytic choriomeningitis virus (LCMV) GP1 are the best candidates in terms of stability, interaction, and structural compactness. These peptides were synthesized using the solid-phase peptide synthesis protocol, purified by reversed-phase high-performance liquid chromatography (RP-HPLC), and authenticated by mass spectrometry (MS). The in vitro fluorometric Mpro activity assay was used to validate the computational results, where temporin L and indolicidin were observed to be very active against SARS-CoV-2 Mpro with IC50 values of 38.80 and 87.23 μM, respectively. A liquid chromatography-MS (LC-MS) assay was developed, and the IC50 value of temporin L was measured at 23.8 μM. The solution-state nuclear magnetic resonance (NMR) structure of temporin L was determined in the absence of sodium dodecyl sulfate (SDS) micelles and was compared to previous temporin structures. This combined investigation provides critical insights and assists us to further develop peptide inhibitors of SARS-CoV-2 Mpro through structural guided investigation.

A novel cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography method for the simultaneous determination of second-generation triazoles in human plasma

In this study, we introduce the first capillary electrophoresis method that combines cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography (CSEI-sweeping-MEKC) for the simultaneous and sensitive quantification of voriconazole (VRC), posaconazole (PSC), and isavuconazole (ISV) levels in human plasma. The sensitivity was remarkably improved, with a 5374-fold enhancement compared to the traditional MEKC method. We systematically optimized key parameters affecting sensitivity, resolution, and efficiency. The separation buffer included 100 mM NaH2PO4, 13 % acetonitrile, and 13 % tetrahydrofuran. This was followed by a high-conductivity buffer zone (1 psi, 50 s) of 100 mM NaH2PO4, an extended electrokinetic sample injection (10 kV, 600 s), and analyte sweeping with 100 mM sodium dodecyl sulfate micelles at −20 kV. Under these optimized conditions, the method allowed for an analytical run in 10 min and was validated for linearity (r ≥ 0.9997), precision (%RSD ≤ 8.8 %), and accuracy (%RE ≤ 2.20 %), delivering satisfactory results. The limit of detection was 2.55 ng/mL for ISV, 0.89 ng/mL for PSC, and 1.04 ng/mL for VRC. This method was successfully applied to analyze plasma samples from patients undergoing triazole antifungal treatment, demonstrating its feasibility for clinical testing.

A common pathway for detergent-assisted oligomerization of Aβ42

Amyloid beta (Aβ) aggregation is a slow process without seeding or assisted nucleation. Sodium dodecyl sulfate (SDS) micelles stabilize Aβ42 small oligomers (in the dimer to tetramer range); subsequent SDS removal leads to a 150-kD Aβ42 oligomer. Dodecylphosphorylcholine (DPC) micelles also stabilize an Aβ42 tetramer. Here we investigate the detergent-assisted oligomerization pathway by solid-state NMR spectroscopy and molecular dynamics simulations. SDS- and DPC-induced oligomers have the same structure, implying a common oligomerization pathway. An antiparallel β-sheet formed by the C-terminal region, the only stable structure in SDS and DPC micelles, is directly incorporated into the 150-kD oligomer. Three Gly residues (at positions 33, 37, and 38) create holes that are filled by the SDS and DPC hydrocarbon tails, thereby turning a potentially destabilizing feature into a stabilizing factor. These observations have implications for endogenous Aβ aggregation at cellular interfaces.

Stratification and film ripping induced by structural forces in granular micellar thin films

HypothesisInteractions across incredibly thin layers of fluids, known as thin films, underpin many important processes involving colloids, such as wetting-dewetting phenomena. Often in these systems, thin films are composed of complex fluids that contain dispersed components, such as spherical micelles, giving rise to oscillatory structural forces due to preferential layering under confinement. Modelling of thin film dynamics involving Derjaguin-Landau-Verwey-Overbeek (DLVO) type forces has been widely reported using the Stokes-Reynolds-Young-Laplace (SRYL) model, and we hypothesize that this theory can be extended to a concentrated micellar system by including an oscillatory structural force term in the disjoining pressure. ExperimentsWe study the drainage behaviour of thin films comprising sodium dodecyl sulfate (SDS) micelles across a range of concentrations and interaction conditions between an air bubble and a mica disk using a custom-built dual-wave interferometry apparatus. FindingsEarly-stage film behaviour is dominated by hydrodynamics, which can be well reproduced by the SRYL model. However, experimental profiles drain significantly faster than predicted, transitioning into a structural force dominated phase characterised by four types of film ripping instabilities that we term ‘waving’, ‘ridging’, ‘webbing’, and ‘hole-sheeting’. These instabilities were mapped according to SDS concentration and approach velocity, providing insight into the interplay between structural forces and hydrodynamic conditions.

Ultrafast spectroscopic studies on the interaction of reactive oxygen species with a probe impregnated in nanoscopic and microscopic matrix formulation

Reactive oxygen species (ROS) plays important role to maintain homeostasis in living bodies. Here we have studied interaction of ROS generated from hydrogen peroxide (H2O2) with a well-known spectroscopic probe Rose Bengal (RB) encapsulated in nanoscopic sodium dodecyl sulphate (SDS) micelles in aqueous medium and entrapped in microscopic nylon 66 solid matrix generated using electrospinning technique. A detailed spectroscopic characterization of ROS with SDS encapsulated RB (RB-SDS) shows efficient interaction compared to that in bulk medium. The time resolved analysis on the probe based on femtosecond resolved 2D-spectrum time images collected from streak camera reveal the simultaneous existence of an ultrafast electron (∼6 ps) and a hole transfer mechanism (∼93 ps) resulting from generation of hydroxyl radicals through photobleaching of the probe in presence of H2O2. Based on the spectroscopic and time resolved studies of RB in bulk and in restricted (SDS) medium, we have further translated it for the development of an in-field prototype device which utilizes RB as a ROS sensor impregnated in a nylon thin film. The microscopic nylon solid matrix characterized by scanning electron microscope (SEM) shows porous structure for holding sample containing ROS. Our study quantitatively measures the amount of ROS by using RB embedded microfiber membrane. Thus, our developed prototype device based on RB embedded on the nylon matrix would be beneficial for the potential use in quantification of ROS in extracellular fluids and food materials.

Cork granules for remediation of soils contaminated with lindane

This work aims to assess the effectiveness of an integrated approach combining surfactant-assisted soil washing (SASW) and cork granules for removing lindane from contaminated soil. It focuses on the evaluation of cork granules (raw and regranulated) as natural sorbents for lindane and on the feasibility of the combination of this physical treatment with surfactant-enhanced soil washing to face the remediation of soil polluted with this hazardous pesticide. The results demonstrate that cork can efficiently retain lindane contained in aqueous solutions and dispersions consisting of mixtures of lindane and sodium dodecylsulfate (SDS) surfactant. Performance improves when using regranulated cork because of its higher affinity for nonpolar species. For lower concentrations of lindane and without surfactant, the raw cork granules presented a sorption capacity of 3.02 mg g− 1, while the regranulated cork presented 6.52 mg g−1. When using a much higher concentration of lindane and SDS, the capacities were 1.90 and 8.21 mg g−1 for raw and regranulated cork, respectively. As well, soil washing with SDS can separate efficiently lindane from spiked soil. It was also observed that the integration of both treatments was feasible, but not as efficient as initially expected. It exhibited a non-expected antagonistic effect caused by the entrapping of the lindane into SDS micelles, which makes it not readily available for sorption. Hence, the higher the amount of SDS the lower the lindane retained by the cork. If the aim is to eliminate lindane with cork specifically, the use of low concentrations of SDS in the combined treatment is encouraged, resulting in an uptake capacity for lindane of 80% from the soil. However, better overall results are achieved when higher concentrations of SDS are used where about 91% of lindane was removed from the soil remaining mainly in the liquid phase. Dichlorination caused by interaction with hydroxyl ions is also observed, being less important in the case of using cork because it attains operation at mild conditions. The results demonstrate that the integration of processes in soil remediation does not always yield expected outcomes and they enhance the knowledge about environmental technologies and their interactions.

Thermochromic Hydrogels with Opaque-Transparent Gradient Transition for Switchable Window and Temperature Monitor.

In recent years, the thermochromic hydrogel was acted as suitable sandwiching material to adjust light transmission. However, to accurately control the thermochromic temperature in a wide range still was a significant challenge. Here, a simple method was explored to prepare hydrogels with gradient opaque-transparent transition thermochromic temperature from 5 °C to 53 °C, which was regulated by the aggregation state of sodium dodecyl sulfate micelles by adding potassium tartrate hemihydrate and cations. Using Li+ , Na+ , and K+ as cations, the accuracy was controlled at 1 °C. Moreover, the transmittance of the hydrogel was not changed when the thermochromic temperature was adjusted. As a result, an intelligent window was fabricated by utilizing thermochromic hydrogel as a sandwiching layer into the outer glass layers, which could effectively and stably regulate the visible and infrared light. The temperature monitors/detectors were also designed, which showed excellent temperature monitoring/detecting ability. Therefore, this low-cost, high-efficient, large-scale prepared thermochromic hydrogel provided more potential for intelligent temperature devices.

Surfactants interaction with sulfathiazole: Spectroscopic, conductometric, and thermodynamic approach

Taking into the account the advantages of surfactant micelles as drug carrier, the interaction of sulfathiazole (STZ) with three types of surfactants, namely, cationic cetyltrimethylammonium bromide (CTAB), anionic sodium dodecyl sulfate (SDS), and non-ionic t-octylphenoxypolyethoxyethanol (TX-100) has been studied by using UV–visible spectroscope and conductivity measurements. The critical micelle concentration (CMC), degree of ionization (α), counter ion binding constant (β), free energy change of micellization (ΔG0m), relative solubility (St/S0), STZ-surfactant interaction constant (θ), approximate number (n) of STZ molecules incorporated per micelle, heat capacity (ΔC0m), and transfer of thermodynamic parameters were calculated and discussed for both the systems. The CMC values of CTAB and SDS were found to decrease in presence of increasing STZ concentrations. The values of counter ions dissociation were also found to be dependent of temperature. The ΔG0m values are obtained to be negative of both systems. A comparison of the binding constants (KC) calculated from the Kawamura equation indicated that the solubilization tendency of STZ with CTAB is much higher than that with SDS micelles. However, this interaction was weak since no significant change in the micellization phenomenon was observed with TX-100 under our experimental conditions.

Optimization and Enhancement of the Peroxidase-like Activity of Hemin in Aqueous Solutions of Sodium Dodecylsulfate.

Iron porphyrins play several important roles in present-day living systems and probably already existed in very early life forms. Hemin (= ferric protoporphyrin IX = ferric heme b), for example, is the prosthetic group at the active site of heme peroxidases, catalyzing the oxidation of a number of different types of reducing substrates after hemin is first oxidized by hydrogen peroxide as the oxidizing substrate of the enzyme. The active site of heme peroxidases consists of a hydrophobic pocket in which hemin is embedded noncovalently and kept in place through coordination of the iron atom to a proximal histidine side chain of the protein. It is this partially hydrophobic local environment of the enzyme which determines the efficiency with which the sequential reactions of the oxidizing and reducing substrates proceed at the active site. Free hemin, which has been separated from the protein moiety of heme peroxidases, is known to aggregate in an aqueous solution and exhibits low catalytic activity. Based on previous reports on the use of surfactant micelles to solubilize free hemin in a nonaggregated state, the peroxidase-like activity of hemin in the presence of sodium dodecyl sulfate (SDS) at concentrations below and above the critical concentration for SDS micelle formation (critical micellization concentration (cmc)) was systematically investigated. In most experiments, 3,3',5,5'-tetramethylbenzidine (TMB) was applied as a reducing substrate at pH = 7.2. The presence of SDS clearly had a positive effect on the reaction in terms of initial reaction rate and reaction yield, even at concentrations below the cmc. The highest activity correlated with the cmc value, as demonstrated for reactions at three different HEPES concentrations. The 4-(2-hydroxyethyl)-1-piperazineethanesulfonate salt (HEPES) served as a pH buffer substance and also had an accelerating effect on the reaction. At the cmc, the addition of l-histidine (l-His) resulted in a further concentration-dependent increase in the peroxidase-like activity of hemin until a maximal effect was reached at an optimal l-His concentration, probably corresponding to an ideal mono-l-His ligation to hemin. Some of the results obtained can be understood on the basis of molecular dynamics simulations, which indicated the existence of intermolecular interactions between hemin and HEPES and between hemin and SDS. Preliminary experiments with SDS/dodecanol vesicles at pH = 7.2 showed that in the presence of the vesicles, hemin exhibited similar peroxidase-like activity as in the case of SDS micelles. This supports the hypothesis that micelle- or vesicle-associated ferric or ferrous iron porphyrins may have played a role as primitive catalysts in membranous prebiotic compartment systems before cellular life emerged.

Decoupling of the Confused Complex in Oxidation of 3,3',5,5'-Tetramethylbenzidine for the Reliable Chromogenic Bioassay.

Regulation of the reaction pathways is a perennial theme in the field of chemistry. As a typical chromogenic substrate, 3,3',5,5'-tetramethylbenzidine (TMB) generally undertakes one-electron oxidation, but the product (TMBox1) is essentially a confused complex and is unstable, which significantly hampers the clinic chromogenic bioassays for more than 50 years. Herein, we report that sodium dodecyl sulfate (SDS)-based micelles could drive the direct two-electron oxidation of TMB to the final stable TMBox2. Rather than activation of H2O2 oxidant in the one-electron TMB oxidation by common natural peroxidase, activation of the TMB substrate by SDS micelles decoupled the thermodynamically favorable complex between TMBox2 with unreacted TMB, leading to an unusual direct two-electron oxidation pathway. Mechanism studies demonstrated that the complementary spatial and electrostatic isolation effects, caused by the confined hydrophobic cavities and negatively charged outer surfaces of SDS micelles, were crucial. Further cascading with glucose oxidase, as a proof-of-concept application, allowed glucose to be more reliably measured, even in a broader range of concentrations without any conventional strong acid termination.

Effect of molar ratio and alkyl chain length on the aggregation behavior of imidazolium-based ionic liquid surfactants/SDS systems

In our previous publication (https://doi.org/10.1016/j.jcis.2019.04.023), the volumes and concentrations of syringe and sample cell in Isothermal titration calorimetry (ITC) limit the molar ratios and concentrations during the titration process. The molar ratios and concentrations of sodium dodecylsulfate (SDS) are almost higher than those of the ionic liquids (ILs) throughout the titration process. From the perspective of SDS molar ratios and concentrations, when the molar ratios and concentrations of the imidazolium-based ILs exceed those of SDS, the research remains unexplored. This aspect of the research has been consistently neglected, yet it is crucial for a fundamental understanding of self-assembly structure transitions. For these mixed systems, the phase behavior, zero-shear viscosity, and dynamic viscoelasticity of the system do not increase with the increasing carbon chain length of imidazolium ILs. The variation in carbon chain length exhibits an optimal value (1-octyl-3-methylimidazolium chloride ([OMIM]Cl)/SDS system), which may be related to the balance between the electrostatic attraction among headgroups and the hydrophobic interactions among hydrophobic chains. To enhance a deeper comprehension of the variations in macroscopic properties across the entire range of mole ratios, enthalpy changes and cryogenic Transmission Electron Microscopy (cryo-TEM) were employed to study the mixed systems. When 100.0 mM imidazolium-based ILs were titrated into 12.5 mM SDS solution, the titration curves consistently exhibited a plateau. During this plateau, SDS micelles undergo disassembly and reassemble into vesicle structures of different sizes. The formation of vesicles is a continuous process until the imidazolium ILs is completely consumed. We propose a straightforward and feasible method to determine the molecular ratios of surfactants responsible for constructing vesicle structures in different alkyl chain lengths systems by fitting the enthalpy changes at different stages. Through this approach, the molecular ratios of SDS and 1-Hexyl-3-methylimidazolium chloride ([HMIM]Cl), 1-Octyl-3-methylimidazolium chloride ([OMIM]Cl), and 1-Dodecyl-3-methylimidazolium chloride ([DMIM]Cl) in the vesicle structures are 1:1, 4:5 and 7:10, respectively.

Dual fluorescence enhancement of loratidine by photoinduced electron transfer blocking and micellization: Application to the development of novel highly sensitive microwell spectrofluorimetric assay for analysis of dosage forms and urine samples

This study describes the enhancement of the weak native fluorescence of loratadine (LOR) by dual strategy via photoinduced electron transfer (PET) blocking followed by micellization into sodium dodecyl sulfate micelles. The enhanced fluorescence was employed as a basis for the development of a novel microwell spectrofluorimetric assay (MW-SFA) for the determination of LOR in its pharmaceutical dosage forms and urine samples. The assay was conducted in 96-microwell assay plates, and the enhanced fluorescence signals were measured by a microplate reader at 290 and 435 nm for excitation and emission, respectively. The optimum conditions of the assay were established, calibration curve was generated, and the linear regression equation was computed. The relation between the fluorescence signals and LOR concentrations was linear with good determination coefficients (0.9992) in the range of 10 – 2000 ng mL−1. The assay limits of detection and quantitation were 4.1 and 12.5 ng mL−1, respectively. The precision was satisfactory, with values of relative standard deviation not exceeding 1.68%, and the assay’s accuracy was ≥ 99.1%. The proposed was successfully applied to the analysis of LOR in its pharmaceutical dosage forms with acceptable accuracy and precision. The label claims were 99.3 – 100.5% (±0.95 – 1.59%). Statistical analysis comparing the results of the proposed assay with those obtained by a reported pre-validated assay revealed no significant difference between both methods in terms of the accuracy and precision at the 95% confidence level. The assay was also applied to the analysis of urine samples containing LOR with accuracy ≥ 98.24%. The greenness of the proposed assay was confirmed by three efficient metric tools. In overall conclusion, the proposed assay is characterized by high sensitivity, procedure simplicity, and high throughput, enabling the simultaneous analysis of many samples in a short time. Therefore, it is a valuable tool for rapid routine application in pharmaceutical quality control units and clinical laboratories for the determination of LOR.

Interaction of sodium alginate biopolymer with sodium dodecyl sulfate in aqueous medium and different additive solutions at several temperatures

Interactions between sodium dodecyl sulfate (SDS) and sodium alginate (NaAlg) in aq. salts/hydrotrope (HDT) media have been investigated using conductivity method with changing the micellar parameters (e.g., critical micelles concentration (CMC), extent of micelle ionization (α), and bound counterions (β)) and thermodynamics of the micellization of SDS + NaAlg mixtures. CMC values and α were assessed from the plots of conductivity versus [SDS]. The micellization of SDS + NaAlg was enhanced in aq. electrolyte and aq. HDTs media. The formation of SDS + NaAlg micelles was found to happen delayed with an increase in temperature in water and aq. 10% (w/w) glycerol (GLY) solution, while in other employed solvents, micelle creation was observed to favor with an upsurge of working temperature. Thermodynamics of SDS + NaAlg mixtures were computed from temperature dependency of CMC. The values of ΔG 0 m were found negative for all the experiments, thereby, examined. The values of Δ H m 0 in the micellization of SDS + NaAlg mixtures in H2O, H2O + sodium acetate (NaOAc), H2O + sodium benzoate (NaBenz), and H2O + 4-amino benzoic acid (4-ABA) media were observed positive, and, hence, the process was endothermic in these solvents. Micellization of SDS + NaAlg was exothermic in 10% (w/w) glycerol (GLY) solutions at all temperatures and in H2O + NaCl at 298.15 and 303.15 K. The values of Δ H m 0 and Δ S m 0 for SDS + NaAlg show that the hydrophobic, van der Waals and exothermic interactions are the driving forces between SDS and NaAlg in electrolytes and HDT media.

A comprehensive assessment of interfacial and bulk properties of sodium dodecylsulfate via addition of competitive Hofmeister ions in presence of Cosolvent: A combined experimental and theoretical study

The synergistic interaction of sodium dodecyl sulphate (SDS) and added electrolyte in presence of cosolvent is investigated by determining the critical micelle concentration of SDS. The present system is carried out with two different types of counterions from Hofmeister series where Hofmeister chaotropic ion i.e. NH4+ is attracted more towards the negatively charged chaotropic dodecyl sulphate headgroup of SDS than the kosmotropic ion. To understand the thermodynamic behavior of SDS micelle, counterion binding constant values are measured using the well-established Corrin-Harkins or modified Corrin-Harkins equations. Various assessments of aggregation and adsorption phenomena of SDS micelle are established from both experimental and theoretical concepts. The exchange of counterion i.e. Na+ ion by NH4+ ions can occur at a particular electrolyte concentration where SDS micelle leads to the formation of ammonium dodecyl sulphate (AmDS) in the present cosolvent media. Therefore, the Hofmeister chaotropic ion (NH4+) is found to be a competitive ion. In addition to that, solvophobicity of the cosolvent mixture is another important parameter which could influence SDS micellization differently.

A molecularly informed field-theoretic study of the complexation of polycation PDADMA with mixed micelles of sodium dodecyl sulfate and ethoxylated surfactants.

The self-assembly and phase separation of mixtures of polyelectrolytes and surfactants are important to a range of applications, from formulating personal care products to drug encapsulation. In contrast to systems of oppositely charged polyelectrolytes, in polyelectrolyte-surfactant systems the surfactants micellize into structures that are highly responsive to solution conditions. In this work, we examine how the morphology of micelles and degree of polyelectrolyte adsorption dynamically change upon varying the mixing ratio of charged and neutral surfactants. Specifically, we consider a solution of the cationic polyelectrolyte polydiallyldimethylammonium, anionic surfactant sodium dodecyl sulfate, neutral ethoxylated surfactants (C[Formula: see text]EO[Formula: see text]), sodium chloride salt, and water. To capture the chemical specificity of these species, we leverage recent developments in constructing molecularly informed field theories via coarse-graining from all-atom simulations. Our results show how changing the surfactant mixing ratios and the identity of the nonionic surfactant modulates micelle size and surface charge, and as a result dictates the degree of polyelectrolyte adsorption. These results are in semi-quantitative agreement with experimental observations on the same system.

(Invited) Kinetics of SWCNT Coating Displacement By ssDNA Depends on SWCNT Structure

Non-covalent hybrids formed by suspending single-wall carbon nanotubes (SWCNTs) in single-stranded DNA (ssDNA) present novel phenomena and suggest potential applications in biomedicine and nanotube sorting. Although the structures of these hybrids have been simulated using molecular dynamics calculations, much more experimental research is needed to understand their properties. In this study, selective interactions between SWCNTs and ssDNA are probed by measuring the kinetics by which ssDNA displaces SDS (sodium dodecyl sulfate) coatings on the nanotube surfaces. We used samples initially suspended in a low concentration of SDS to allow the coating displacement to occur and to suppress formation of free SDS micelles. The displacement process was monitored by time-dependent measurements of SWCNT fluorescence intensities and wavelengths. Our experiments showed very smooth decreases in fluorescence intensity and red-shifts in fluorescence wavelengths during the displacement process. Through a series of measurements, we found that ssDNA sequences with repeated guanine (G) and thymine (T) bases showed systematic patterns in the coating displacement kinetics. One result is that SDS displacement depends strongly on oligo length, with (GT)3 showing an initial rate constant 500 times greater than that of (GT)20. For shorter oligos in the (GT) n series, we observe an inverse dependence of initial rate constant on SWCNT diameter, with SDS displacement from (6,5) more than twice as fast as from (8,7). However, this diameter dependence is not present for (GT) n oligos with n greater than 6. We also find a distinct and systematic dependence of initial rate constant on nanotube chiral angle for (GT)5 and (GT)6. This effect gives a factor of ~3 difference between (9,1) and (6,5) despite their identical diameters. We empirically find these initial rate constants to vary as (SWCNT diameter)-4(cos 3θ)-y with y = -1/2 for (GT)5 and -1 for (GT)6. In addition, the full displacement kinetic traces are well fitted by double exponential kinetics, with rate constants and amplitudes dependent on SWCNT diameter. A two-step kinetic model for the displacement process will be presented to account for these findings.

Analytical Quality by Design-Compliant Development of a Cyclodextrin-Modified Micellar ElectroKinetic Chromatography Method for the Determination of Trimecaine and Its Impurities.

In 2022, the International Council for Harmonisation released draft guidelines Q2(R2) and Q14, intending to specify the development and validation activities that should be carried out during the lifespan of an analytical technique addressed to assess the quality of medicinal products. In the present study, these recommendations were implemented in Capillary Electrophoresis method development for the quality control of a drug product containing trimecaine, by applying Analytical Quality by Design. According to the Analytical Target Profile, the procedure should be able to simultaneously quantify trimecaine and its four impurities, with specified analytical performances. The selected operative mode was Micellar ElectroKinetic Chromatography employing sodium dodecyl sulfate micelles supplemented with dimethyl-β-cyclodextrin, in a phosphate-borate buffer. The Knowledge Space was investigated through a screening matrix encompassing the composition of the background electrolyte and the instrumental settings. The Critical Method Attributes were identified as analysis time, efficiency, and critical resolution values. Response Surface Methodology and Monte Carlo Simulations allowed the definition of the Method Operable Design Region: 21-26 mM phosphate-borate buffer pH 9.50-9.77; 65.0 mM sodium dodecyl sulfate; 0.25-1.29% v/v n-butanol; 21-26 mM dimethyl-β-cyclodextrin; temperature, 22 °C; voltage, 23-29 kV. The method was validated and applied to ampoules drug products.

Rheological and mechanical properties of hydroxypropyl methylcellulose-based hydrogels and cryogels controlled by AOT and SDS micelles

HypothesisThe type and concentration of surfactants affect the rheological behavior of hydroxypropyl methylcellulose (HPMC) chains in hydrogels, influencing the microstructure and mechanical properties of HPMC cryogels. ExperimentsHydrogels and cryogels containing HPMC, AOT (bis (2-ethylhexyl) sodium sulfosuccinate or dioctyl sulfosuccinate salt sodium, two C8 chains and sulfosuccinate head group), SDS (sodium dodecyl sulfate, one C12 chain and sulfate head group), and sodium sulfate (salt, no hydrophobic chain) at different concentrations were investigated using small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM), rheological measurements, and compressive tests. FindingsSDS micelles bound to the HPMC chains building “bead necklaces”, increasing considerably the storage modulus G’ values of the hydrogels and the compressive modulus E values of the corresponding cryogels. The dangling SDS micelles promoted multiple junction points among the HPMC chains. AOT micelles and HPMC chains did not form “bead necklaces”. Although AOT increased the G’ values of the hydrogels, the resulting cryogels were softer than pure HPMC cryogels. The AOT micelles are probably embedded between HPMC chains. The AOT short double chains rendered softness and low friction to the cryogel cell walls. Therefore, this work demonstrated that the structure of the surfactant tail can tune the rheological behavior of HPMC hydrogels and hence the microstructure of the resulting cryogels.