Discrete and Discontinuous Increase in the Micellar Aggregation Number: Effects of the Alkyl Chain Length on Platonic Micelles

Polymer Micelles Composed of Molecular-Bottlebrush-Based Surfactants: Precisely Controlling Aggregation Number Corresponding to Polyhedral Structures

Over the past few decades, there has been remarkable progress in the construction of self-assemblies in the field of supramolecular chemistry, such as micelles with precisely controlled and refined structures. One promising approach represents the previously proposed concept of Platonic micelles, in which the aggregation number (N_agg ) is discretized in accordance with vertexes of regular polyhedra (i.e., Platonic solids), i.e., 4, 6, 8, 12, and 20 units. Herein, attempt is made to construct Platonic polymer micelles using rigid and persistent architecture of molecular-bottlebrush-based surfactant (MBS). The structure of MBS micelles is carefully elucidated using small-angle X-ray and light scattering and analytical centrifugation measurements. This study shows that the N_agg of MBS micelles is consistent with one of the Platonic numbers when N_agg is intentionally set in the range of 4-20. In addition, some of the MBS micelles demonstrate a discontinuous change in N_agg , when the salt concentration is changed, which is an important factor in controlling micellar N_agg . This is one of the characteristic aggregation behaviors of Platonic micelles in surfactant systems, which strongly indicates the formation of Platonic micelles from macromolecular surfactants.

Asymmetric flow field-flow fractionation as a multifunctional technique for the characterization of polymeric nanocarriers

The importance of polymeric nanocarriers in the field of drug delivery is ever-increasing, and the accurate characterization of their properties is paramount to understand and predict their behavior. Asymmetric flow field-flow fractionation (AF4) is a fractionation technique that has gained considerable attention for its gentle separation conditions, broad working range, and versatility. AF4 can be hyphenated to a plurality of concentration and size detectors, thus permitting the analysis of the multifunctionality of nanomaterials. Despite this potential, the practical information that can be retrieved by AF4 and its possible applications are still rather unfamiliar to the pharmaceutical scientist. This review was conceived as a primer that clearly states the "do's and don'ts" about AF4 applied to the characterization of polymeric nanocarriers. Aside from size characterization, AF4 can be beneficial during formulation optimization, for drug loading and drug release determination and for the study of interactions among biomaterials. It will focus mainly on the advances made in the last 5 years, as well as indicating the problematics on the consensus, which have not been reached yet. Methodological recommendations for several case studies will be also included.

Structural Polymorphism of Resorcinarene Assemblies

In 1997, a study based on X-ray crystallography revealed that resorcinarenes adopt a hexameric capsule-like structure. The function of resorcinarenes has been discussed on the basis of this structure; however, our recent study showed that the hexamer may be only one of resorcinarenes' polymorphic members. Here, we present the solvent dependence of the aggregation number of C-undecylresorcinarene in water-saturated toluene and chloroform using small-angle neutron and X-ray scattering and analytical ultracentrifugation measurements. We found that a new octamer was formed in toluene where the eight resorcinarene units were placed at the vertices of a regular cube; this contrasts to the previous structure in chloroform, namely, a hexamer with the six resorcinarenes located at the vertices of a regular octahedron that has a cavity inside where chloroform molecules are pooled.

Bis-Thioether-Containing Lipid Chains in Cationic Amphiphiles: Physicochemical Properties and Applications in Gene Delivery

Cationic amphiphiles featuring two thioether functions in each lipid chain of bicatenar cationic amphiphiles are reported here for the first time. The physicochemical properties and transfection abilities of these new amphiphiles were compared with those of already reported analogues featuring either (i) saturated, (ii) unsaturated or (iii) mono-thioether containing lipid chains. The homogeneity of the series of new compounds allowed to clearly underscore the effect of bis-thioether containing lipid chains. This study shows that besides previous strategies based on unsaturation or ramification, the incorporation of two thioether functions per lipid chain constitutes an original complementary alternative to tune the supramolecular properties of amphiphilic compounds. The potential of this strategy was evaluated in the context of gene delivery and report that two cationic amphiphiles (i. e. 4 a and 4 b) can be proposed as new efficient transfection reagents.

Monodisperse micelles composed of poly(ethylene glycol) attached surfactants: platonic nature in a macromolecular aggregate

Among the many studies on micelles, dating back more than 100 years, we first found a series of monodisperse micelles: spherical micelles made from calix[4]arene surfactants exhibited monodispersity in aggregation number (Nagg) with values of 4, 6, 8, 12, and 20. We named these Platonic micelles because these values coincided with the face numbers of the Platonic solids. The preferred Nagg values were explained in relation to the mathematical Tammes problem: how to obtain the best coverage of a sphere surface with multiple identical circles. In this paper, we synthesized poly(ethylene glycol)-attached surfactants and carried out small-angle X-ray scattering (SAXS) and analytical ultracentrifugation (AUC) to determine the Nagg. We found that these polymeric surfactants also formed monodispersed micelles and Nagg discontinuously increased from 20 to 24, and then 32 with increasing the alkyl carbon numbers from 9 to 11 continuously. The determined Nagg was greater than 20 and the Platonic solid numbers. We assumed that the preferred Nagg values could be explained in relation to the Tammes problem as well.