Shape Of Micelles Research Articles

Self-aggregation of cationic gemini surfactants with amide groups in the spacer and variable alkyl chain length

AbstractSynthesis, aggregation parameters and antimicrobial activity of novel cationic gemini surfactants with two amide groups in gemini spacer structure and a variable number of carbon atoms in alkyl tails ranging from 12 to 15 are reported. The critical micelle concentration of gemini surfactants was determined using surface tension and electrical conductivity methods. The cmc values were found in the range 0.83 to 0.06 mM. The interfacial area, micelle ionisation degree and the Gibbs free energy per molecule and alkyl chain were calculated from the surface tension and conductivity curves. Particle size analysis using the dynamic light scattering method confirmed the formation of small spherical micelles 6–7 nm large in size for gemini surfactants with 12 and 13 carbon atoms in the alkyl chain. A large size above 50 nm was found for the aggregates composed of long-chain gemini molecules with 14 and 15 carbon atoms. The zeta potential of gemini surfactants shows a continuous increase with the increasing alkyl chain length. Micelle aggregation number of gemini surfactants correlates well with the hydrodynamic size data. Small aggregation number values were found for short-chain gemini molecules with 12 and 13 carbon atoms in the alkyl chain. Long-chain gemini molecules with 14 and 15 carbon atoms exhibit aggregate growth represented by an increase in the aggregation number values while maintaining the spherical or spheroidal shape of micelles. The investigations of antimicrobial activity against Gram-positive bacteria, Gram-negative bacteria and yeast indicate the increasing antimicrobial efficiency towards the short-chain surfactant with 12 carbon atoms in the alkyl chain. A possible cut-off effect presence is proposed to explain the dependence of antimicrobial activity on the surfactant alkyl tail length.

Insights into the self-assembly of water reverse micelles and solubilization process in liquid and supercritical solvents: A molecular dynamics study

This article reports on a full-atomic classical molecular dynamics simulation investigating the self-assembly process of reverse micelles in carbon tetrachloride and supercritical carbon dioxide (scCO2). The study explores the impact of solvent type, surfactant structure (sodium dodecyl sulfate and sodium bis(3,5,5-trimethyl-1-hexyl) sulfosuccinate), water/surfactant ratio, and surfactant concentration on the self-assembly, size, and shape of reverse micelles. The results indicate that at low water/surfactant ratios in scCO2, irregularly shaped reverse micelles are formed, whereas spherical micelles form as the water/surfactant ratio increases. In scCO2, there is always a small fraction of free water molecules present, whereas in CCl4, all water molecules are surrounded by surfactants. The distribution of head groups of di-chain surfactants over the surface of micelles is observed to occur in groups of several surfactants, forming salt bridges through sodium cations. The solubilization of methyl orange by reverse micelles in pure scCO2 and scCO2 modified with ethanol has also been investigated. The study reveals that the hydrophilic part of the solute is located in the water core of the micelle, while the tail is positioned in the hydrophobic crown. Moreover, the presence of ethanol increases the number of reverse micelles compared to the system without ethanol. Ethanol molecules primarily reside on the surface of the water core, forming stable hydrogen bonds with surfactants, as well as shorter-lived hydrogen bonds with water molecules.

Chemical Feedback in Templated Reaction-Assembly of Polyelectrolyte Complex Micelles: A Molecular Simulation Study of the Kinetics and Clustering.

The chemical feedback between building blocks in templated polymerization of diblock copolymers and their consecutive micellization was studied for the first time by means of coarse-grained molecular dynamics simulations. Using a stochastic polymerization model, we were able to reproduce the experimental findings on the effect of chemical feedback on the polymerization rates at low and high solution concentrations. The size and shape of micelles were computed using a newly developed software in Python conjugated with graph theory. In full agreement with the experiments, our simulations revealed that micelles formed by the templated micellization are more spherical and have a lower radius of gyration than those formed by the traditional two-step micellization method. The advantage of molecular simulation over the traditional kinetic models is that with the simulation, one studies in detail the heterogeneous polymerization in the presence of the oppositely charged template while also accounting for the incompatibility between reacted species, which significantly influences the reaction process.

Revealing foam stability for cationic and zwitterionic triethylsilyl-containing surfactants

A fundamental understanding of surfactant structure–property–performance relationships will inform the design of next-generation alternatives to perfluoroalkyl substances (PFAS) in aqueous film-forming foams. This manuscript describes the synthesis, solution properties, and foam stability of novel triethylsilyl-containing surfactants, which elucidated the influence of the hydrophilic head group on critical micelle concentration (CMC), surface tension, and foam stability. Photocatalyzed hydrosilylation of triethylsilane and N,N-dimethyl allylamine yielded N,N-dimethyl-3-(triethylsilyl)propane-1-amine. Subsequent functionalization with either propane sultone or bromoethane afforded zwitterionic sulfobetaine surfactant, 3-(dimethyl(3-(triethylsilyl)propyl)ammonio)propane-1-sulfonate (TESDMAPS) and cationic quaternary ammonium surfactant, and N-ethyl-N,N-dimethyl-3-(triethylsilyl)propane-1-ammonium bromide (TESDMABr), respectively. Dynamic light scattering and cryo-transmission electron microscopy (TEM) characterized micelle size and shape in solutions above the CMC. Surface tensiometer analysis determined minimum TESDMAPS and TESDMABr solution surface tensions of 37.7 and 35.9 mN/m, respectively. Molecular dynamics simulations related this decrease in surface tension to a larger average interfacial area of 88 Å2 per TESDMABr molecule compared to 66 Å2 per TESDMAPS molecule. Steady-shear rheological measurements showed consistent exponential viscosity-scaling relationships between TESDMAPS and TESDMABr solutions ≤ 30 wt. %. Above this concentration, TESDMAPS displayed solution viscosities greater than TESDMABr, and a mixture of surfactants provided an intermediate concentration dependent viscosity scaling. Dynamic foam analysis revealed TESDMABr foams displayed longer 25% foam drainage times than TESDMAPS. The oscillatory rheology of TESDMABr solutions demonstrated solid-like solution behavior at low shear rates. Finally, polarized light-imaging rheology highlighted the formation of birefringent structures in TESDMABr solutions under shear. For the first time, this work relates solution viscoelasticity from shear-induced surfactant assembly to foam stability with implications on fluorine-free, next-generation, fire-fighting foams.

Characterisation of the apparent aqueous solubility enhancement of testosterone analogues in micelles of dodecyl-chained surfactants with different headgroups

The solubilisation capacities of the micelles formed by a range of surfactants possessing a dodecyl (C12) hydrocarbon ‘tail’ and a variety of hydrophilic ‘headgroups’ have been studied for a range of hydrophobic steroids (testosterone (T) and its propionate (TP) and enanthate (TE) esters). The solubilisation studies were performed at ambient temperature, with drug concentration monitored (over 48–72 h) by UV absorbance. The various surfactant systems were characterised in terms of their physicochemical properties, including their surface tension, critical micelle concentration, viscosity, and density. Results show that while the apparent aqueous solubility of the poorly water-soluble steroids increases upon solubilisation within the surfactant micelles, the extent of this increase varies with the nature of the hydrophilic headgroup and the hydrophobicity of the drug. Specifically, changing the surfactant headgroup from non-ionic to zwitterionic, then to ionic, results in a marked increase in solubility of the two least hydrophobic steroids, testosterone and testosterone propionate, suggesting rather counter-intuitively that these steroidal drugs tend to associate to a greater extent with micelles formed by surfactants with more hydrophilic/charged head groups. The more hydrophobic steroid, TE, was solubilised to the greatest extent, being predominantly solubilised within the micelle core. In this case, the influence of surfactant head group on TE solubilisation was less obvious, with surfactants containing ionic and zwitterionic head groups exhibiting high levels of solubilisation. The physicochemical properties that had most influence on solubilisation of the testosterone analogues, as evaluated using multiple linear regression, were micelle shape for T and TP, and critical micelle concentration for TE. Through the findings of this comparative study, the essential molecular descriptors of optimal solubilisation for improved drug delivery and the loci of solubilisation of the testosterone analogues have been identified.

Molecular Dynamics Study on the Aggregation Behavior of Triton X Micelles with Different PEO Chain Lengths in Aqueous Solution.

The aggregation structure of Triton X (TX) amphiphilic molecules in aqueous solution plays an important role in determining the various properties and applications of surfactant solutions. In this paper, the properties of micelles formed by TX-5, TX-114, and TX-100 molecules with different poly(ethylene oxide) (PEO) chain lengths in TX series of nonionic surfactants were studied via molecular dynamics (MD) simulation. The structural characteristics of three micelles were analyzed at the molecular level, including the shape and size of micelles, the solvent accessible surface area, the radial distribution function, the micelle configuration, and the hydration numbers. With the increase of PEO chain length, the micelle size and solvent accessible surface area also increase. The distribution probability of the polar head oxygen atoms on the surface of the TX-100 micelle is higher than that in the TX-5 or TX-114 micelle. In particular, the tail quaternary carbon atoms in the hydrophobic region are mainly located at the micelle exterior. For TX-5, TX-114, and TX-100 micelles, the interactions between micelles and water molecules are also quite different. These structures and comparisons at the molecular level contribute to the further understanding of the aggregation and applications of TX series surfactants.

PECULIARITIES OF STRUCTURAL PHASE TRANSITIONS IN A SELF-ORGANIZING AOT/WATER/ISOPROPYL MYRISTATE SYSTEM UPON INTRODUCTION OF L-LYSINE

New biocompatible microemulsion and liquid-crystalline sodium bis(2-ethylhexyl) sulfosuccinate (AOT)/water/isopropyl myristate systems have been obtained for the delivery of drugs and physiologically active substances. A combination of dynamic light scattering and X-ray diffraction methods has been used to determine their structural and size characteristics. The Primus and SasView software packages have been employed to simulate the shape and arrangement of particles as depending on AOT content. It has been shown that, as the concentration of the surfactant increases, the shape of micelles varies from spherical to cylindrical, and, at high concentrations, a structural phase transition occurs with the formation of a liquid-crystalline phase. The influence of a model bioactive compound, L-lysine, on the size and structure of the system has been studied. It has been revealed that the addition of the amino acids to the samples leads to an increase in the microemulsion droplet size, and, in the case of the liquid-crystalline phase, to the disintegration of the hexagonal packing into individual cylinders. The results obtained can be useful for the analysis of the mechanisms of L-lysine release from the AOT/water/isopropyl myristate transport system.

Micelle Formation in Aqueous Solutions of the Cholesterol-Based Detergent Chobimalt Studied by Small-Angle Scattering.

The structure and interaction parameters of the water-soluble cholesterol-based surfactant, Chobimalt, are investigated by small-angle neutron and X-ray scattering techniques. The obtained data are analyzed by a model-independent approach applying the inverse Fourier transformation procedure as well as considering a model fitting procedure, using a core-shell form factor and hard-sphere structure factor. The analysis reveals the formation of the polydisperse spherical or moderately elongated ellipsoidal shapes of the Chobimalt micelles with the hard sphere interaction in the studied concentration range 0.17-6.88 mM. The aggregation numbers are estimated from the micelle geometry observed by small-angle scattering and are found to be in the range of 200-300. The low pH of the solution does not have a noticeable effect on the structure of the Chobimalt micelles. The critical micelle concentrations of the synthetic surfactant Chobimalt in water and in H2O-HCl solutions were obtained according to fluorescence measurements as ~3 μM and ~2.5 μM, respectively. In-depth knowledge of the basic structural properties of the detergent micelles is necessary for further applications in bioscience and biotechnology.

Influence of enzymatic cross-linking on the apparent viscosity and molecular characteristics of casein micelles at neutral and acidic pH

Individual caseins represent almost 80% of the protein in milk, they are organized as protein assemblies called casein micelle (CM). The micelle is a heat-resistant structure, but it becomes dissociated in acidic environments. Microbial transglutaminase (mTGase) promotes the stability of the CM under acidic environments by catalyzing the formation of covalent cross-links. However, no quantitative data are available concerning the structure of the CM at pH 3.0 as a function of the progress of the enzymatically induced cross-linking reaction, measured through a polymerization degree (DP). This study aims to provide information on the cross-linked CM structure at acidic pH (3.0) and neutral pH (7.0) according to their DP and correlate these changes with the viscosity of the dispersions. The size, the molar mass, the apparent density, and the molecular shape of the casein micelle (CM-0%) and cross-linked CM at three cross-linking degrees (TG-41%, TG-51%, TG-56%) were determined using Asymmetrical-Flow-Field-Flow-Fractionation coupled with light scattering techniques. At pH 7.0, the cross-linked CM depicts an increase in the apparent density and a spherical shape due to intra-molecular cross-linking. At pH 3.0, the loss of the colloidal calcium phosphate (CCP) leads to a change in the shape and the density, decreasing the viscosity of the CM dispersions. A master curve describing the evolution of apparent viscosity as a function of DP suggests that DP is the key parameter to tune the viscosity of acidified casein dispersions and predicts structural changes.

The correlation between the micelle morphology of surface-active ionic liquids with self-assembly and thermodynamic characteristics: coarse-grained MD simulation and experiment.

Surface-active ionic liquids (SAILs) show great promise as novel green solvents due to their low vapor pressure, high thermal stability, high electrical conductivity, and bio-friendly nature to replace traditional volatile organic solvents in industrial processes. In the present work, the combination of coarse-grained (CG) molecular dynamics (MD) simulations with conductivity measurements was employed to explain the correlation between the micelle morphology and physicochemical and thermodynamic properties of self-assembly. A homologous series of SAIL molecules, 1-n-alkyl-3-methylimidazolium bromide [Cnmim][Br] (n = 4, 6, 8, 10, and 12), were chosen at various concentrations to shed light on this issue. Simultaneously two factors of concentration and alkyl chain length affected the morphology to control the physical and thermodynamic features. Moreover, the nature of the headgroup for two SAILs with the longest alkyl chain was assessed by shifting from imidazolium into ammonium. First, the critical micelle concentration (CMC), the degree of counterion dissociation of micelles, and the standard Gibbs energy of micellization of SAILs were determined using conductivity data. The micelle morphology such as the aggregation number, micelle radius, and moment of inertia was computed before, around, and after the CMC by MD simulation. Simulated results in accordance with the experimental measurements provide a quantitative understanding of the micellar properties. Increasing the alkyl chain length was associated with a non-spherical bigger micelle while the ammonium-based surfactant with a lower repulsion between neighboring monomers in micelles induced bigger and more spherical aggregates. Raising the SAIL concentration did not considerably influence the sphericity of the micelle except for the SAIL with the longest tail. The umbrella sampling method calculated the potential of mean force (PMF) for pulling a monomer of SAIL from a pre-assembled micelle into the solution. The dissociation energy of a SAIL monomer from a micelle increased with the tail length or with shifting into the ammonium head group and was substantially influenced by micelle morphology. Comparison between a sphere micelle with an oval one demonstrated that the dissociation of a SAIL monomer from a non-spherical shape needed a higher amount of energy. An improved understanding of how the shape of the SAIL micelles controls the physicochemical properties and stability helps to extend their application to different chemical processes.

Volumetric determination of reverse micelle structural properties and the validity of commonplace approximations

Molecular volumes within reverse micelles are important in determining many aggregate properties. Molecular volumes also depend upon differences in molecular environment and thereby might also be capable of detecting changes in molecular structure and interactions within an aggregate. However, approximations are typically used in their place along with approximations of aggregate radius, aggregation number, surfactant tail length, and reverse micelle shape particularly for Aerosol OT systems. Consequently, volumetric measurements have not been thoroughly tested as a measure of aggregate properties. Volumetric methods do not require the commonly used approximations. Therefore, comparison with previous approaches will demonstrate volumetric measurements’ utility in measuring aggregate structural properties and provide a useful assessment of the applicability of these commonplace approximations. Partial molar volumes of water and surfactant, evaporation rate, and reverse micelle radius are measured over the w0 = 0–40 range for water/Aerosol OT/isooctane solutions. These results are used to calculate how aggregation number, surfactant layer thickness, head group area, and water droplet structure change with aggregate radius. Volumetric measurements reveal a surfactant layer structural transition at w0 = 5, an aggregate shape change at w0 = 25, and reproduced the general trends in structural properties. Important variations from approximated methods are noted. Molecular volume and aggregate radius approximations were found valid in many but not all situations. However, approximations of aggregation number and tail length created important miscalculations of some properties when treating reverse micelles as spherical. It was found that consideration of an ellipsoidal reverse micelle shape for w0 < 10 could account for previously identified changes in surfactant layer thickness and head group area that were based on a spherical geometry.

Anti-Proliferative Potential of Quercetin Loaded Polymeric Mixed Micelles on Rat C6 and Human U87MG Glioma Cells.

Quercetin (Qu) is a natural flavonoid present in many commonly consumed food items and is also identified as a potential anticancer agent. The present study evaluates the Qu-loaded polymeric mixed micelles (Qu-PMMs) against C6 and U87MG glioma cell lines. The Box–Behnken Design (BBD) was employed to study the influence of independent variables such as Soluplus, Vitamin-E polyethyleneglycol-1000 succinate (E-TPGS), and poloxamer 407 concentrations on dependent variables including particle size (PS), polydispersity index (PDI), and percentage entrapment efficiency (%EE) of the prepared Qu-PMMs. The Qu-PMMs were further characterized by Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), and were assessed for in vitro drug release, effect on cell viability, migration, cellular uptake, and apoptosis assays. The PS, PDI, and % EE of the optimized PMMs were 107.16 ± 1.06 nm, 0.236 ± 0.053, and 77.46 ± 1.94%, respectively. The FTIR and XRD revealed that the Qu was completely entrapped inside the PMMs. The SEM analysis confirmed the spherical shape of micelles. The in vitro cell viability study showed that the Qu-PMMs had 1.7 times higher cytotoxicity against C6 and U87MG cells than Qu pure drug (Qu-PD). Furthermore, Qu-PMMs demonstrated superior cellular uptake, inhibited migration, and induced apoptosis when tested against C6 and U87MG cells than pure Qu. Thus, the polymeric mixed micelle (PMMs) enhanced the therapeutic effect of Qu and can be considered an effective therapeutic strategy to treat Glioma.

Industrial block copolymer surfactants: Diversity of associative forms and interaction with carbon nanomaterial

• Upon copolymer micellization alteration of micelle shape and hydrodynamic size takes place. • Hypothesis about the double-stage nature of copolymer micellization was proposed. • Diversity of associative forms of MWCNT-block copolymer complexation was revealed. • Interaction of block copolymers can results in liquid crystal structuring. In this work, we studied self-association/micellization of several block copolymers based on PEO and PPO blocks – two poloxamers and reverse-sequential poloxamine in aqueous solutions and dispersions of multi-walled carbon nanotubes (MWCNTs). To study this process the number of NMR experiments was used, such as self-diffusion measurements and spectral analysis including alterations of chemical shift and resonance line width. The absence of strictly defined critical micelle concentration, when micelles of constant size start forming, was found. The obtained results proved that amphiphilic copolymers alter micelle shape and hydrodynamic size upon the growth of polymer concentration. The hypothesis about the double-stage nature of copolymer molecules association/micellization has been proposed. At the first stage the polymers hydrophobic blocks connect into cord-like associates/micelles and then these associates join into spherical micelles or liquid-crystalline domains. The transmission electron microscopy of block copolymers revealed a variety of their associative forms. The interaction peculiarities of various associates for different block copolymers with MWCNTs were considered. In poloxamers/MWCNTs dispersions the central hydrophobic blocks of poloxamers can be adsorbed on the hydrophobic surface of MWCNTs, isolating a part of the nanotube surface, thereby preventing their sticking. For the X-shaped diproxamine another mechanism of interaction with carbon surface was proposed, which makes it possible to explain the opposite NMR effects in the presence of MWCNTs. The transmission electron microscopy revealed a variety of associative forms of block copolymers studied.

Polycation Architecture Affects Complexation and Delivery of Short Antisense Oligonucleotides: Micelleplexes Outperform Polyplexes.

Herein, we examine the complexation and biological delivery of a short single-stranded antisense oligonucleotide (ASO) payload with four polymer derivatives that form two architectural variants (polyplexes and micelleplexes): a homopolymer poly(2-dimethylaminoethyl methacrylate) (D), a diblock polymer poly(ethylene glycol)methylether methacrylate-block-poly(2-dimethylaminoethyl methacrylate) (ObD), and two micelle-forming variants, poly(2-dimethylaminoethyl methacrylate)-block-poly(n-butyl methacrylate) (DB) and poly(ethylene glycol)methylether methacrylate-block-poly(2-dimethylaminoethyl methacrylate)-block-poly(n-butyl methacrylate) (ObDB). Both polyplexes and micelleplexes complexed ASOs, and the incorporation of an Ob brush enhances colloidal stability. Micellplexes are templated by the size and shape of the unloaded micelle and that micelle-ASO complexation is not sensitive to formulation/mixing order, allowing ease, versatility, and reproducibility in packaging short oligonucleotides. The DB micelleplexes promoted the largest gene silencing, internalization, and tolerable toxicity while the ObDB micelleplexes displayed enhanced colloidal stability and highly efficient payload trafficking despite having lower cellular uptake. Overall, this work demonstrates that cationic micelles are superior delivery vehicles for ASOs denoting the importance of vehicle architecture in biological performance.

Analytical modeling of micelle growth. 5. Molecular thermodynamics of micelles from zwitterionic surfactants

HypothesisThe critical micelle concentration, aggregation number, shape and length of spherocylindrical micelles in solutions of zwitterionic surfactants can be predicted by knowing the molecular parameters and surfactant concentrations. This can be achieved by upgrading the quantitative molecular thermodynamic model with expressions for the electrostatic interaction energy between the zwitterionic dipoles and micellar hydrophobic cores of spherical and cylindrical shapes. TheoryThe correct prediction of the mean micellar aggregation numbers requires precise calculations of the free energy per molecule in the micelles. New analytical expressions for the dipole electrostatic interaction energy are derived based on the exact solutions of the electrostatic problem for a single charge close to a boundary of spherical and cylindrical dielectric media. The obtained general theory is valid for arbitrary ratios between dielectric constants, radii of spheres and cylinders, positions, and orientations of dipoles. FindingsThe detailed numerical results show quantitatively the effects of the micelle curvature and dielectric properties of the continuum media on the decrease of the dipole electrostatic interaction energy. Excellent agreement was achieved between the theoretical predictions and experimental data for the critical micelle concentration, size and aggregation number of zwitterionic surfactant micelles. This study can be extended to mixed micelles of zwitterionic and ionic surfactants in the presence of salt to interpret and predict the synergistic effect on the rheology of solutions.

Micelle Dynamic Reconstruction to Effectively Modulate the Transmission of Smart Windows.

Micelles are extremely dynamic equilibrium aggregates. The size and shape of micelles are subject to appreciable structural fluctuations with the introduction of foreign ions, temperature, etc. The highly dynamic character has for a long time hugely attracted the interest of researchers to investigate the mechanism of micellar structure change and the dependence of their optical properties on the structure change. Herein, taking the most common sodium dodecyl sulfate (SDS) as an example, the aggregation behavior of SDS with excess K+ and the effect of temperature on the K+/SDS mixed system were detailed and systematically investigated by combining with molecular dynamics simulations and experiments. The addition of K+ leads to a reconfiguration of the original micelle structure, resulting in a significant change in micelle size from the nanoscale up to the microscale. And simultaneously, temperature can induce a dynamic process of conjugation/deconjugation of K+/SDS micelles in the mixed solution, which is manifested macroscopically by the change of transmittance. Finally, a temperature-responsive smart gel was prepared by introducing K+/SDS into a polyacrylamide (PAM) gel, which showed an excellent tunable performance in transmittance (ΔT550 nm = 60.1%, ΔT808 nm = 42.72%). The designed smart window shows potential applications in room temperature control (Δt = 4.1 °C) and excellent stability over the course of 50 cycles.

A Review of Polymeric Micelles and Their Applications.

Self-assembly of amphiphilic polymers with hydrophilic and hydrophobic units results in micelles (polymeric nanoparticles), where polymer concentrations are above critical micelle concentrations (CMCs). Recently, micelles with metal nanoparticles (MNPs) have been utilized in many bio-applications because of their excellent biocompatibility, pharmacokinetics, adhesion to biosurfaces, targetability, and longevity. The size of the micelles is in the range of 10 to 100 nm, and different shapes of micelles have been developed for applications. Micelles have been focused recently on bio-applications because of their unique properties, size, shape, and biocompatibility, which enhance drug loading and target release in a controlled manner. This review focused on how CMC has been calculated using various techniques. Further, micelle importance is explained briefly, different types and shapes of micelles are discussed, and further extensions for the application of micelles are addressed. In the summary and outlook, points that need focus in future research on micelles are discussed. This will help researchers in the development of micelles for different applications.

Unraveling the Role of Charge Patterning in the Micellar Structure of Sequence-Defined Amphiphilic Peptoid Oligomers by Molecular Dynamics Simulations.

Electrostatic interactions play a significant role in regulating biological systems and have received increasing attention due to their usefulness in designing advanced stimulus-responsive materials. Polypeptoids are highly tunable N-substituted peptidomimetic polymers that lack backbone hydrogen bonding and chirality. Therefore, polypeptoids are suitable systems to study the effect of noncovalent interactions of substituents without complications of backbone intramolecular and intermolecular hydrogen bonding. In this study, all-atom molecular dynamics (MD) simulations were performed on micelles formed by a series of sequence-defined ionic polypeptoid block copolymers consisting of a hydrophobic segment and a hydrophilic segment in an aqueous solution. By combining the results from MD simulations and experimental small-angle neutron scattering data, further insights were gained into the internal structure of the formed polypeptoid micelles, which is not always directly accessible from experiments. In addition, information was gained into the physics of the noncovalent interactions responsible for the self-assembly of weakly charged polypeptoids in an aqueous solution. While the aggregation number is governed by electrostatic repulsion of the negatively charged carboxylate (COO–) substituents on the polypeptoid chain within the micelle, MD simulations indicate that the position of the charge on singly charged chains mediates the shape of the micelle through the charge–dipole interactions between the COO– substituent and the surrounding water. Therefore, the polypeptoid micelles formed from the single-charged series offer the possibility for tailorable micelle shapes. In contrast, the polypeptoid micelles formed from the triple-charged series are characterized by more pronounced electrostatic repulsion that competes with more significant charge–sodium interactions, making it difficult to predict the shape of the micelles. This work has helped further develop design principles for the shape and structure of self-assembled micelles by controlling the position of charged moieties on the backbone of polypeptoid block copolymers.

Solution Structures of Anionic-Amphoteric Surfactant Mixtures near the Two-Phase Region at Fixed pH.

We examine the solution structures in a mixed surfactant system of sodium dodecyl sulfate (SDS) and N,N-dimethyldodecylamine N-oxide (DDAO) in water, on both sides of the two-phase boundary, employing dynamic light scattering, small-angle neutron scattering, and Fourier transform infrared spectroscopy. The precipitate phase boundary was accessed by lowering pH to 8, from its floating pH 9.5 value, and was experimentally approached from the monomeric and micellar regions in three ways: at fixed DDAO or SDS concentrations and at a fixed (70:30) SDS:DDAO molar ratio. We characterize the size, shape, and interactions of micelles, which elongate approaching the boundary, leading to the formation of disk-like aggregates within the biphasic region, coexisting with micelles and monomers. Our data, from both monomeric and micellar solutions, indicate that the two phase structures formed are largely pathway-independent, with dimensions influenced by both pH and mixed surfactant composition. Precipitation occurs at intermediate stoichiometries with a similar SDS:DDAO ratio, whereas asymmetric stoichiometries form a re-entrant transition, returning to the mixed micelle phase. Overall, our findings demonstrate the effect of stoichiometry and solution pH on the synergistic interaction of mixed surfactants and their impact on phase equilibrium and associated micellar and two-phase structures.

Synthesis and characterizations of sugar-glass nanoparticles mediated protein delivery system for tissue engineering application

The present work focuses on the synthesis and characterization of a sugar-glass nanoparticle (SGnP) based reservoir type protein delivery system pertinent to tissue engineering applications. The SGnP nanocarriers were prepared via inverse micelle of sodium bis(2-ethylhexyl) sulfosuccinate based on an anionic surfactant and subsequent flash-freezing technique. Initially, a total of five different grades of protein-free SGnPs have been prepared to examine the effects of systematic changes in starting concentrations of the aqueous phase, organic solvent, the molar ratio of water, and surfactant in controlling the size, shape, and uniformity of micelles. Evidently, the Fourier transform infrared (FTIR) and scanning electron microscope (SEM) results confirmed that the SGnP can be successfully prepared. Subsequently, SGnP based protein depot has been validated using bovine serum albumin (BSA), horseradish peroxidase (HRP) and growth and differentiation factor-5 (GDF-5). The particle size, morphology, protein encapsulation efficiency and in vitro release kinetics were assessed using SEM, FTIR, UV–visible spectroscopy and Bradford protein assays. Excellent encapsulation efficiency (93%–94%) and sustained release behaviour of BSA (∼22% protein release after 14 d) and GDF-5 proteins (∼29% protein release after 30 d) were exhibited by the optimal grades of SGnP constructs with an average particle size of 266 nm and 93 nm, respectively. Furthermore, FTIR, differential scanning calorimeter (DSC), polyacrylamide gel electrophoresis (PAGE) and NATIVE-PAGE studies results confirm successful encapsulation, stability and preserving the structural integrity of proteins placed into the core of the SGnP constructs. Evidently, a very high (93%) residual HRP enzyme activity signifies the capability of our SGnP system to protect the encapsulated proteins from process-related stresses. In vitro cytotoxicity and fluorescence cell morphology analyses using human adipose-derived mesenchymal stem cells affirmed good cytocompatibility of protein encapsulated SGnP. Overall, the study findings indicate SGnP nanocarrier-mediated protein delivery systems as a promising approach complementary to conventional techniques in tissue engineering and therapeutic applications.