Computational Investigations of a pH-Induced Structural Transition in a CTAB Solution with Toluic Acid

In this work, molecular dynamics simulations were performed to study the pH-induced structural transitions for a CTAB/p-toluic acid solution. Spherical and cylindrical micelles were obtained for aqueous surfactants at pH 2 and 7, respectively, which agrees well with the experimental observations. The structural properties of two different micelles were analyzed through the density distributions of components and the molecular orientations of CTA+ and toluic acid inside the micelles. It was found that the bonding interactions between CTA+ and toluic in spherical and cylindrical micelles are very different. Almost all the ionized toluic acid (PTA−) in the solution at pH 7 was solubilized into the micelles, and it was located in the CTA+ headgroups region. Additionally, the bonding between surfactant CTA+ and PTA− was very tight due to the electrostatic interactions. The PTA− that penetrated into the micelles effectively screened the electrostatic repulsion among the cationic headgroups, which is considered to be crucial for maintaining the cylindrical micellar shape. As the pH decreased, the carboxyl groups were protonated. The hydration ability of neutral carboxyl groups weakened, resulting in deeper penetration into the micelles. Meanwhile, their bonding interactions with surfactant headgroups also weakened. Accompanied by the strengthen of electrostatic repulsion among the positive headgroups, the cylindrical micelle was broken into spherical micelles. Our work provided an atomic-level insights into the mechanism of pH-induced structural transitions of a CTAB/p-toluic solution, which is expected to be useful for further understanding the aggregate behavior of mixed cationic surfactants and aromatic acids.

One-pot synthesis of oxidation-sensitive supramolecular gels and vesicles

Polypeptide-based nanoparticles offer unique advantages from a nanomedicine perspective such as biocompatibility, biodegradability and stimuli-responsive properties to (patho)physiological conditions. Conventionally, self-assembled polypeptide nanostructures are prepared by first synthesizing their constituent amphiphilic polypeptides followed by post-polymerization self-assembly. Herein, we describe the one-pot synthesis of oxidation-sensitive supramolecular micelles and vesicles. This was achieved by polymerization-induced self-assembly (PISA) of the N-carboxyanhydride (NCA) precursor of methionine using polyethylene oxide as stabilizing and hydrophilic block in dimethyl sulfoxide (DMSO). By adjusting the hydrophobic block length and concentration we obtained a range of morphologies from spherical to worm-like micelles, to vesicles. Remarkably, the secondary structure of polypeptides greatly influenced the final morphology of the assemblies. Surprisingly, worm-like micellar morphologies were obtained for a wide range of methionine block lengths and solid contents, with spherical micelles restricted to very short hydrophobic lengths. Worm-like micelles further assembled into oxidation-sensitive, self-standing gels in the reaction pot. Both vesicles and worm-like micelles obtained using this method demonstrated to degrade under controlled oxidant conditions which would expand their biomedical applications such as in sustained drug release or as cellular scaffolds in tissue engineering.

Dodecagonal quasicrystals of oil-swollen ionic surfactant micelles

A delicate balance of noncovalent interactions directs the hierarchical self-assembly of molecular amphiphiles into spherical micelles that pack into three-dimensional periodic arrays, which mimic intermetallic crystals. Herein, we report the discovery that adding water to a mixture of an ionic surfactant and n-decane induces aperiodic ordering of oil-swollen spherical micelles into previously unrecognized, aqueous lyotropic dodecagonal quasicrystals (DDQCs), which exhibit local 12-fold rotational symmetry and no long-range translational order. The emergence of these DDQCs at the nexus of dynamically arrested micellar glasses and a periodic Frank–Kasper (FK) σ phase approximant sensitively depends on the mixing order of molecular constituents in the assembly process and on sample thermal history. Addition of n-decane to mixtures of surfactant and water instead leads only to periodic FK A15 and σ approximants with no evidence for aperiodic order, while extended ambient temperature annealing of the DDQC also reveals its transformation into a σ phase. Thus, these lyotropic DDQCs are long-lived metastable morphologies, which nucleate and grow from a stochastic distribution of micelle sizes formed by abrupt segregation of varied amounts of oil into surfactant micelles on hydration. These findings indicate that molecular building block complexity is not a prerequisite for the formation of aperiodic supramolecular order, while also establishing the generic nature of quasicrystalline states across metal alloys and self-assembled micellar materials.

A TIME DEPENDENT STUDY FOR THE FORMATION OF ULTRASMALL Cs-AlMCM-41 HOLLOW NANOSPHERES

Monitoring of the formation of ultrasmall Cs-AlMCM-41 nanospheres under hydrothermal condition has been performed. It showed that when the CTABr surfactant, silica and alumina were mixed, homogenization of raw materials was first taking place, where CTABr molecules first interacted with the inorganic species via self-assembly into helical rod-like micelles. Hydrolysis, condensation and polymerization of silica and alumina precursors were then initiated. In addition, the Cs+ cation also participated during the formation of MCM-41 structure where it counterbalanced the negative charge of the aluminosilicate surface. After 14 h, the aluminosilicate oligomers were produced and fully enclosed the spherical micelles. Further increasing the hydrothermal treatment to 24 h onwards, polycondensation silanol siloxane would take place leading to the emergence of well-defined and highly ordered MCM-41 structure. This study came up with a clear picture on the formation of Cs-AlMCM-41 hollow nanospheres in cationic-surfactant-templated. This suggested that similar studies for other mesoporous materials such as MCM-48 and MCM-50 under different conditions and approaches could also be explored

Drug-dependent morphological transitions in spherical and worm-like polymeric micelles define stability and pharmacological performance of micellar drugs

Significant advances in physicochemical properties of polymeric micelles enable optimization of therapeutic drug efficacy, supporting nanomedicine manufacturing and clinical translation. Yet, the effect of micelle morphology on pharmacological efficacy has not been adequately addressed. We addressed this gap by assessing pharmacological efficacy of polymeric micelles with spherical and wormlike morphologies. We observed that poly(2 oxazoline) based polymeric micelles can be elongated over time from a spherical structure to wormlike structure, with elongation influenced by several conditions, including the amount and type of drug loaded into the micelles. We further evaluated the role of different morphologies of olaparib micelles on pharmacological performance against a triple negative breast cancer tumor (TNBC) model. Spherical micelles accumulated rapidly in the tumor tissue while retaining large amounts of drug; wormlike micelles accumulated more slowly and only upon releasing significant amounts of drug. These findings suggest that the dynamic character of the drug micelle structure and the micelle morphology play a critical role in pharmacological performance, and that spherical micelles are better suited for systemic delivery of anticancer drugs to tumors when drugs are loosely associated with the polymeric micelles.

Unravelling a Novel Sol-Gel Transition Mechanism in Polymer Self-Assemblies: An Order-Order Transition Based on Specific Molecular Interactions Between Hydrophilic and Hydrophobic Polymer Blocks

Using a wide range of state-of-the art analytical techniques and molecular dynamics simulation, a novel mechanism for macromolecular interactions are described. Distinct interactions between the hydrophilic and hydrophobic blocks in amphiphilic triblock copolymers lead to an order-order transition from spherical micelles to worm-like micelles upon cooling the aqueous polymer solutions below room temperature. Macroscopically, this this leads to reversible gelation. This novel mechanism represent a novel building block to better understand polymer self-assembly.<br>

Unravelling a Novel Sol-Gel Transition Mechanism in Polymer Self-Assemblies: An Order-Order Transition Based on Specific Molecular Interactions Between Hydrophilic and Hydrophobic Polymer Blocks

Using a wide range of state-of-the art analytical techniques and molecular dynamics simulation, a novel mechanism for macromolecular interactions are described. Distinct interactions between the hydrophilic and hydrophobic blocks in amphiphilic triblock copolymers lead to an order-order transition from spherical micelles to worm-like micelles upon cooling the aqueous polymer solutions below room temperature. Macroscopically, this this leads to reversible gelation. This novel mechanism represent a novel building block to better understand polymer self-assembly.<br>