Cylindrical Micelles Research Articles

An integral insight into pollen wall development: involvement of physical processes in exine ontogeny in Calycanthus floridus L., with an experimental approach.

We aimed to understand the underlying mechanisms of development in the sporopollenin-containing part of the pollen wall, the exine, one of the most complex cell walls in plants. Our hypothesis is that distinct physical processes, phase separation and micellar self-assembly, underpinexine development by taking the molecular building blocks, determined and synthesised by the genome, through several phase transitions. To test this hypothesis, we traced each stage of microspore development in Calycanthus floridus with transmission electron microscopy and then generated invitro experimental simulations corresponding to every developmental stage. The sequence of structures observed within the periplasmic space around developing microspores starts with spherical units, which are rearranged into columns to then form rod-like units (the young columellae) and, finally, white line centred endexine lamellae. Phase separation precedes each developmental stage. The set of experimental simulations, obtained as self-assembled micellar mesophases formed at the interface between lipid and water compartments, was the same: spherical micelles; columns of spherical micelles; cylindrical micelles; and laminate micelles, separated by gaps, resembling white-lined lamellae. Thus, patterns simulating structures observed at the main stages of exine development in C.floridus were obtained from invitro experiments, and hence purely physicochemical processes can construct exine-like patterns. This highlights the important part played by physical processes that are not under direct genomic control and share influence on the emerging ultrastructure with the genome during exine development. These findings suggest that a new approach to ontogenetic studies, including a consideration of physical factors, is required for a better understanding of developmental processes.

Oil-Tolerant Nonionic Worm-like Micellar Solution.

The goal of this work is to study the effect of crude oil on worm-like micelles and identify any oil-tolerant systems. A new class of nonionic surfactants was synthesized that forms viscous worm-like micelles under a wide range of temperature and salinity conditions. Aqueous stability, rheology, cryogenic transmission electron microscopy imaging, and dynamic-light-scattering measurements were performed to understand properties, shape, and size of the micelles formed using these surfactants under different temperatures and salinity conditions and in the presence of hydrocarbons. These micellar solutions maintained high viscosity in the presence of small amounts (up to 8 vol %) of crude oils and pure hydrocarbons. Similar experiments were performed with conventional surfactant systems that were known to form worm-like micelles; they did not show oil tolerance. Larger alkanes and viscous crude oils affect the viscosity and transformation of cylindrical micelles less. These new surfactants are useful for oil and gas operations such as hydraulic fracturing, conformance control, and mobility control as they form viscous worm-like micelles in the presence of small amounts of crude oils.

Selective incorporation of one of the isomers of a photoswitchable molecule in wormlike micelles

Understanding the physical and chemical mechanisms underlying the interactions between giant micelles and photoswitchable molecules is essential because it is not evident why some photoswitchable chromophores with apparently good potential to modify micellar systems' macroscopic properties have a poor performance on UV-irradiation. We report a mechanism that describes the trans-isomer's expulsion embedded in the wormlike micelles when it is transformed into the cis-isomer on UV-irradiation. Consequently, a small change in the rheological properties of the micellar solution is observed on UV-irradiation. As a model system, 4-(phenylazo)benzoate ion as the photoresponsive chromophore and giant cylindrical micelles made of N-Tetradecyl-N,N-Dimethyl-3-ammonio-1-PropaneSulfonate, and Sodium Dodecyl Sulfate, in saline water, are used. The trans-isomer chromophore incorporates into the micelles modifying the solution viscosity and viscoelastic spectra, which follows the Maxwell model at low and intermediate frequencies. However, the effect of UV-irradiation on rheological properties is not significant. Micro-rheological experiments are performed with diffusive wave spectroscopy to obtain high-frequency viscoelastic spectra to estimate the characteristic length scales of the wormlike micellar network with the embedded chromophore to understand its rheological behavior better. Detailed interaction between the chromophore and the micelles is obtained with 1H-NMR and 1H DOSY NMR experiments to determine the chromophore conformation into the micelles and diffusivity of the isomers.

The Origins of Toroidal Micelles from a Liquid–Crystalline Triblock Copolymer†

Summary of main observation and conclusionIn this paper, we reported a systematic study on the formation mechanism of bent toroidal micelles from a triblock copolymer poly(acrylic acid)‐block‐(2‐cinnamoyloxylethyl methacrylate)‐block‐poly(perfluorooctylethyl methacrylate) (PAA‐b‐PCEMA‐b‐ PFMA) in the binary solvent mixture of methanol and α,α,α‐trifluorotoluene (MeOH/TFT) through a heating‐cooling procedure. It was found that the formation process of toroids was predominantly kinetic‐controlled, and can be influenced by the preparation protocol, solvent composition and stirring rate of the solutions. The toroids were formed via a complicated morphological transition process. At high temperature, the polymer formed bilayered vesicles with bumpy surface, while upon cooling, the vesicles broke and unfolded into bumpy platelet micelles, which subsequently perforated into toroidal and cylindrical micelles upon further cooling. Besides the distinct and unique bumpy vesicle and platelet structures, the transformation mechanisms from vesicular to platelet, and toroidal micelles are also very intriguing, and may provide new insights into the interconversion of micellar morphologies.

Effect of an alkyl spacer on the morphology and internalization of MUC1 aptamer-naphthalimide amphiphiles for targeting and imaging triple negative breast cancer cells.

Despite decades of research, there are few targeted treatment options available for triple negative breast cancer (TNBC), leaving chemotherapy, and radiation treatment regimes with poor response and high toxicity. Herein aptamer‐amphiphiles were synthesized which selectively bind to the mucin‐1 (MUC1) glycoprotein that is overexpressed in TNBC cells. These amphiphiles have a fluorescent tail (1,8‐naphthalimide or 4‐nitro‐1,8‐naphthalimide) which enables self‐assembly of the amphiphiles and allows for easy visualization without the requirement for further conjugation of a fluorophore. Interestingly, the length of the alkyl spacer (C4 or C12) between the aptamer and tail was shown to influence the morphology of the self‐assembled structure, and thus its ability to internalize into the TNBC cells. While both the MUC1 aptamer‐C4‐napthalimide spherical micelles and the MUC1 aptamer‐C12‐napthalimide long cylindrical micelles showed internalization into MDA‐MB‐468 TNBC cells but not the noncancerous MCF‐10A breast cells, the cylindrical micelles showed greatly enhanced internalization into the MDA‐MB‐468 cells. Similar patterns of enhanced binding and internalization were observed between the MUC1 aptamer‐C12‐napthalimide cylindrical micelles and SUM159 and MDA‐MB‐231 TNBC cells. The MUC1 aptamer cylindrical micelles were not toxic to the cells, and when used to deliver doxorubicin to the TNBC cells, were shown to be as cytotoxic as free doxorubicin. Moreover, a pharmacokinetic study in mice showed a prolonged systemic circulation time of the MUC1 aptamer cylindrical micelles. There was a 4.6‐fold increase in the elimination half‐life of the aptamer cylindrical micelles, and their clearance decreased 10‐fold compared to the MUC1 aptamer spherical micelles. Thus, the MUC1 aptamer‐C12‐napthalimide nanofibers represent a promising vehicle that could be used for easy visualization and targeted delivery of therapeutic loads to TNBC cells.

Self-assembly and viscosity changes of binary surfactant solutions: A molecular dynamics study

Hypothesis: Structure and self-assembly of surfactants in the solution shows a fundamental influence on its viscosity. Through molecular simulations using Martini force field, synergistic effects in aggregation as well as the viscosity changes of a binary ionic surfactant system can be modelled.Simulations: Coarse-grained molecular dynamics simulations are performed to model the SDS/CAPB binary surfactant solution, and both equilibrium and non-equilibrium methods are used to calculate the viscosity of the equilibrated micellar systems.Findings: Our simulation results indicate that the new version of the Martini force field can provide more reasonable self-assembly of surfactant, both single and binary system. Synergistic effects in micelle formation for SDS/CAPB have been successfully reproduced, that is, the formation of cylindrical micelles or even wormlike micelles at a lower concentration when compared with the pure system. Meanwhile, both equilibrium and non-equilibrium methods provide quantitatively comparable viscosity for each system. For pure micellar system, the viscosity linearly increases with the total concentration. Nevertheless, our simulation fails to capture the viscosity enhancement of the solution in corresponding with the formation of rodlike or wormlike micelles, and a full parameter optimization of force field is still necessary.

Phase Diagram for Ideal Diblock-Copolymer Micelles Compared to Polymerization-Induced Self Assembly.

In this work we constructed a detailed phase diagram for the solutions of ideal diblock-copolymers and compared such diagram with that obtained during polymerization-induced self-assembly (PISA); a wide range of polymer concentrations as well as chain compositions was studied. As the length of the solvophobic block nB increases (the length of the solvophilic block nA was fixed), the transition from spherical micelles to cylinders and further to vesicles (lamellae) occurs. We observed a rather wide transition region between the spherical and cylindrical morphology in which the system contains a mixture of spheres and short cylinders, which appear to be in dynamic equilibrium; the transition between the cylinders and vesicles was found to be rather sharp. Next, upon increasing the polymer concentration in the system, the transition region between the spheres and cylinders shifts towards lower nB/nA values; a similar shift but with less magnitude was observed for the transition between the cylinders and vesicles. Such behavior was attributed to the increased number of contacts between the micelles at higher polymer volume concentrations. We also found that the width of the stability region of the cylindrical micelles for small polymer volume concentrations is in good quantitative agreement with the predictions of analytical theory. The obtained phase diagram for PISA was similar to the case of presynthesized diblock copolymer; however, the positions of the transition lines for PISA are slightly shifted towards higher nB/nA values in comparison to the presynthesized diblock copolymers, which is more pronounced for the case of the cylinders-to-vesicles transition. We believe that the reason for such behavior is the polydispersity of the core-forming blocks: The presence of the short and long blocks being located at the micelle interface and in its center, respectively, helps to reduce the entropy losses due to the insoluble block stretching, which leads to the increased stability of more curved micelles.

Pollen wall development in Hydrangea bretschneiderii Dippel. (Hydrangeaceae): advanced interpretation through physical input, with in vitro experimental verification.

We aimed to unravel the underlying mechanisms of pollen wall development in Hydrangea bretschneiderii. For this, we tested our hypothesis that distinct physical processes, phase separation and micellar self-assembly, underpinned exine development by taking the substances, determined by the genome, through several phase transitions. We traced each developmental stage with TEM; then, we obtained in vitro simulations corresponding to those stages. The main steps of exine ontogeny observed in the microspore periplasmic space were initiated with phase separation, resulting in the conversion of homogeneous contents to heterogeneous two-layered state of the material. After each step of phase, separation self-assembly picked up the initiative and took the substances through the sequence of micellar mesophases which were the base for all the exine structures. These mesophases are as follows: spherical micelles, transforming first into columns, and then to cylindrical micelles which turn to columellae after initial sporopollenin accumulation. The tectum appeared along the interface of the phase separated material. After the tetrad disintegration and the next phase separation, laminate mesophase appeared being the base for the endexine lamellae. Then, a new step of phase separation at aperture sites brought the appearance of a granular endexine layer; the latter became intermixed finally with lamellae. This gives, together with experimental simulation, strong evidence that the genome "shifts a part of work" on exine formation onto physical processes, and the latter are an inherent mechanism of evolution.

Growth and Termination of Cylindrical Micelles via Liquid-Crystallization-Driven Self-Assembly

Growth and termination of cylindrical micelles with cholesteric liquid crystal (LC) cores (seeds) were achieved experimentally, following the simulation studies of liquid-crystallization-driven sel...

Computer simulations of comb-like macromolecules with responsive diblock copolymer side chains

Comb-like macromolecules having diblock copolymer side chains with inner (grafted to the backbone) responsive block and outer soluble block were studied using dissipative particle dynamics simulations. Like for thermoresponsive polymers, responsiveness of the inner block means variation of its solubility upon changing of external conditions leading to variation of the solvent quality. The collapse of single copolymers (regime of infinite dilution) and their self-assembly in solution were examined. The effects of grafting density and the composition of the side chains were considered. The results reveal three distinct regimes which are characterized by the different balance of interactions between solvophilic and solvophobic groups and by the number of intramolecular clusters in the single macromolecules. The solvent quality, at which the transition between the regimes occurs, depends on the molecular architecture. In the case of macromolecular ensemble, the increase in the grafting density not only requires poorer solvent to induce intermolecular aggregation but also changes the shape of the aggregates (micelles). Namely, the grafted macromolecules can form the continuous or branched cluster, as well as cylindrical micelles. In turn, the change of the side chain composition strongly influences the stability of the solution: the longer the responsive block, the sooner the macromolecules precipitate upon the block collapse.

Hierarchical Self-Assembly of Poly(d-glucose carbonate) Amphiphilic Block Copolymers in Mixed Solvents

We report the fibril formation of poly(d-glucose carbonate) (PGC)-based amphiphilic diblock copolymers using solution assembly. Unlike conventional cylindrical micelles constructed from amphiphilic block copolymers (BCPs) with coil-like blocks, the assembled PGC fibrils exhibit thin, ribbon-like features due to significant stiffness and hydrophobicity of the PGC BCP backbone that result in a unique polymer chain packing. A tetrahydrofuran/H2O solvent mixture was used to create a solvent quality gradient during which a hierarchical assembly pathway was observed with fibril precursor nanoparticles that linked together into fibrils. These initial precursors were soft, patchy nanoparticles caused by the phase-segregated hydrophilic block of the PGC diblock copolymer. With aging, the patchy nanoparticles underwent unidirectional attachment through hydrophobic association to transform into uniform fibril structures. Transmission electron microscopy, interpretation of the small-angle neutron scattering measurements fit with analytical models, and genetic algorithm-based reverse engineering of structure confirmed the presence of initial particle precursors, intermediate stages during growth, and the fully matured fibrils. The results suggest that unconventional backbone chemistry-based molecules reveal unique effects of chain stiffness and hydrophobicity on block copolymer solution assembly when using glucose-based polycarbonates.

Molecular structure of maltoside surfactants controls micelle formation and rheological behavior

HypothesisThe anomeric configuration (α or β) of n-hexadecyl-d-maltopyranoside (C16G2) has been shown to affect the morphology of the micelle, from elongated for α-C16G2 to worm-like micelles for β-C16G2. The entanglement of worm-like micelles often leads to strong modifications of the rheological behavior of the system and, as such, the anomeric configuration of C16G2 could also provide the possibility of controlling this. Furthermore, mixing these surfactants are hypothesized to result in mixed micelles allowing to finely tune the rheology of a system containing these sustainable surfactants. ExperimentsThe rheology of α- and β-C16G2, and mixtures of those, was determined by rotational and oscillatory rheology at different temperatures and surfactant concentrations. Micelle structure and composition for these systems were characterized using contrast variation small-angle neutron scattering and small-angle X-ray scattering. The results from these were connected in order to elaborate a molecular understanding of the rheological response of the system. FindingsThe self-assembly of these surfactants have been found to result in different rheological properties. β-C16G2 show a high viscosity with a non-Newtonian viscoelastic behavior, which was linked to the formation of worm-like micelles. In contrast, α-C16G2 self-assembled into short cylindrical micelles, resulting in a Newtonian fluid with low viscosity. Furthermore, mixtures of these two surfactants lead to systems with intermediate rheological properties as a result of the formation of micelles with intermediate morphology to those of the pure anomers. These results also show that the rheological properties of the system can be tuned to change the micelle morphology, which in turn depends on the anomeric configuration of the surfactant. Also, surfactant concentration, temperature of the system, and micelle composition for surfactant mixtures provide control over the rheological properties of the system in a wide temperature range. Therefore, these results open new possibilities in the development of sustainable excipients for formulation technology, where the characteristics of the system can be easily tailored through geometric variations in the monomer structure whilst maintaining the chemical composition of the system.

On the Thermodynamics of Reverse Micelles: Effect of Water on Micellization

Water may be involved in reverse micelle formation either in the form of a hydration shell or as a solubilisate. Both cases have been analyzed within the framework of a theory based on the mass action law and the definition of the critical micelle concentration (CMC) via the constant of this law. In the first case, it is supposed that a surfactant is primordially hydrated, and water is a priori incorporated into the surfactant. Its amount is determined from the volume of the hydrated core of a micelle, while the aggregation number of the surfactant is calculated from the packing conditions for spherical, cylindrical, and platelike micelles. The CMC is, in turn, found from its dependence on the aggregation number, with this dependence being determined by the general theory. In the second case, water is taken into account as a separate component of a micelle, but in the form of a solubilisate (hydration water is, as before, introduced into the chemical formula of the surfactant). Here, the CMC appears to depend on not only the overall concentration of water (with no regard to its hydration form), but also on the value of the critical degree of water micellization. The effect of water on micellization has been analyzed at both its preset chemical potential and its constant amount. All versions of the theory lead to the conclusion that CMC decreases with an increase in water content, thereby confirming the prediction put forward by Eicke and Christen (Eicke, H-F. and Christen, H., Helv. Chim. Acta, 1978, vol. 61, p. 2258).

A General Approach to Describing Fast Relaxation with Regard to Specific Features of Micellar Models

It has been shown that, when passing from the Becker–Doring finite-difference equations to the differential kinetic equation for the function of aggregate distribution over aggregation numbers, the value of the error in the calculation of the times of fast relaxation in a micellar solution is primarily determined by the approximation used for the behavior of the aggregation work in the vicinity of the minimum of the work. The approach developed in this study on the basis of the perturbation theory enables one to take into account the features of a specific micellar model and, in particular, the possible essential asymmetry of the aggregation work in the vicinity of its minimum already in the principal order. The values of some characteristic times of fast relaxation obtained in terms of the proposed approach show a markedly improved accuracy (in the sense of the closeness to “exact” solutions) as compared with recently obtained results at all considered concentrations. This approach is undoubtedly advantageous in the simplicity of its application, universality, and the feasibility to use it for spherical normal and reverse micelles, as well as for cylindrical micelles. Therewith, the complexity of the method is independent of the explicit specification of employed aggregation work and attachment coefficient as functions of aggregation number.

Effect of hydrocarbon chain length of aliphatic solvents on the reverse self-assembly of lecithin and monovalent ion mixtures

Surfactants are used as organogelators, which form surfactant-based gels in nonpolar solvents. One of the well-known surfactants that form organogels is lecithin, which self-assembles into reverse spherical micelles in nonpolar solvents. When inorganic salts are added to lecithin solutions, the reverse spherical micelles transform into long reverse cylindrical micelles, giving rise to organogels. Although previous studies have shown that the addition of inorganic salts to lecithin solutions can induce the gel formation, the solvent effects on the gel formation have not been mapped out in detail. In this study, we systematically investigated the effects of hydrocarbon chain length of alkanes on the self-assembly of lecithin and monovalent ion mixtures. Our findings showed that LiCl, LiBr, LiI, NaBr, NaI, and KI salts formed organogels in the presence of lecithin, whereas NaCl and KBr formed viscoelastic solutions with lecithin. More importantly, with an increase in the hydrocarbon chain length of alkanes, the lecithin/salt mixtures formed gels more efficiently. The gel formation is closely related to the length of the reverse cylindrical micelles, as confirmed by small-angle X-ray scattering analysis. In addition, the length of the cylinders is affected by the interactions between the lecithin head groups and ions, as evidenced by Fourier transform infrared spectroscopy.

Synthesis of a Cylindrical Micelle from Hydrophilic Polymers Connected with a Single Supramolecular Structure-Directing Unit

This article reports the facile synthesis of a cylindrical micelle from mostly hydrophilic polymers by a specific molecular interaction among a hydrophobic single supramolecular structure-directing...

Analytical modeling of micelle growth. 3. Electrostatic free energy of ionic wormlike micelles – Effects of activity coefficients and spatially confined electric double layers

Hypotheses: To correctly predict the aggregation number and size of wormlike micelles from ionic surfactants, the molecular-thermodynamic theory has to calculate the free energy per molecule in the micelle with accuracy better than 0.01 kT, which is a serious challenge. The problem could be solved if the effects of mutual confinement of micelle counterion atmospheres, as well as the effects of counterion binding, surface curvature and ionic interactions in the electric double layer (EDL), are accurately described.Theory: The electric field is calculated using an appropriate cell model, which takes into account the aforementioned effects. Expressions for the activity coefficients have been used, which vary across the EDL and describe the electrostatic, hard sphere, and specific interactions between the ions. New approach for fast numerical calculation of the electrostatic free energy is developed.Findings: The numerical results demonstrate the variation of quantities characterizing the EDL of cylindrical and spherical micelles with the rise of electrolyte concentration. The effect of activity coefficients leads to higher values of the free energy per surfactant molecule in the micelle as compared with the case of neglected ionic interactions. The results are essential for the correct prediction of the size of wormlike micelles from ionic surfactants. This study can be extended to mixed micelles of ionic and nonionic surfactants for interpretation of the observed synergistic effects.

Effect of aliphatic solvents on the reverse self-assembly of lecithin and calcium chloride mixtures

Reverse spherical micelles are formed by self-assembly of lecithin molecules in nonpolar solvents. They are transformed into reverse cylindrical micelles when inorganic salts such as CaCl2 are added to lecithin solutions. When the reverse cylindrical micelles are long enough to be entangled, the solution viscosity increases significantly, forming organogels. In this study, we investigate the effects of aliphatic solvents on the reverse self-assembly of lecithin and CaCl2 mixtures. When the hydrocarbon chain length of the aliphatic solvents increases, the viscosities of lecithin and CaCl2 mixtures increase. In addition, for the same hydrocarbon chain length, mixtures in alkanes have higher viscosities than those in alkenes. Small-angle X-ray scattering (SAXS) results suggest that the viscosities of the mixtures are correlated with the length of the reverse cylindrical micelles. Herein, Fourier transform infrared spectroscopy was used to investigate the interactions between lecithin headgroups and CaCl2, which play a significant role in forming the reverse cylindrical micelles.

Spontaneous Self-Assembly of Thermoresponsive Vesicles Using a Zwitterionic and an Anionic Surfactant.

Spontaneous formation of vesicles from the self-assembly of two specific surfactants, one zwitterionic (oleyl amidopropyl betaine, OAPB) and the other anionic (Aerosol-OT, AOT), is explored in water using small-angle scattering techniques. Two factors were found to be critical in the formation of vesicles: surfactant ratio, as AOT concentrations less than equimolar with OAPB result in cylindrical micelles or mixtures of micellar structures, and salt concentration, whereby increasing the amount of NaCl promotes vesicle formation by reducing headgroup repulsions. Small-angle neutron scattering measurements reveal that the vesicles are approximately 30-40 nm in diameter, depending on sample composition. Small-angle X-ray scattering measurements suggest preferential partitioning of OAPB molecules on the vesicle inner layer to support vesicular packing. Heating the vesicles to physiological temperature (37 °C) causes them to collapse into smaller ellipsoidal micelles (2-3 nm), with higher salt concentrations (≥10 mM) inhibiting this transition. These aggregates could serve as responsive carriers for loading or unloading of aqueous cargoes such as drugs and pharmaceuticals, with temperature changes serving as a simple release/uptake mechanism.

Mechanism for Transition of Reverse Cylindrical Micelles to Spherical Micelles Induced by Diverse Alcohols.

Herein, the effects of various alcohols on lecithin/CaCl2 organogels are investigated. Mixtures of lecithin and CaCl2 form reverse cylindrical micelles, resulting in optically transparent organogels. The addition of various alcohols to a mixture of lecithin and CaCl2 induces a decrease in viscosity through which reverse cylindrical micelles are transformed into spherical micelles (or short cylindrical micelles). Long-hydrocarbon-chain alcohols decrease the viscosity of lecithin/CaCl2 mixtures more efficiently. Hydrogen bonding and hydrocarbon chain interactions between lecithin and alcohol play important roles in the morphological transition. More importantly, isothermal titration calorimetry was conducted to obtain thermodynamic variables such as the enthalpy, equilibrium constant, Gibbs free energy, entropy, and stoichiometry of the associated molecules observed in the transition. It was found that the transition is an entropically driven process, in which the endothermic and exothermic behaviors were observed depending on the hydrocarbon chain length in the alcohol. In addition, the enthalpy for the association of the alcohol with lecithin showed a linear relationship depending on the hydrocarbon chain length, in which the magnitude of hydrogen bonding and hydrocarbon chain interactions was obtained quantitatively. To the best of our knowledge, this is the first study reporting the thermodynamic properties of the morphological transition observed in a reverse self-assembly process.