Spontaneous Formation and Fusion of Raspberry Vesicle Self-Assembled from Star Block Terpolymers in Aqueous Solution

The spontaneous formation and fusion of raspberry vesicles was studied using the dissipative particle dynamics (DPD) method. The vesicles were formed through the self-assembly of amphiphilic E12O6F2 star terpolymers in selective solvent. E and F blocks are solvophobic and the O block is solvophilic. The shortest F block plays a major role in the formation of raspberry vesicles. Distinct vesicle formation mechanisms were observed at different polymer concentrations. At higher concentrations, vesicles form via the bending and closure of an oblate F-bump-E bilayer. At lower concentrations, the formation pathway contains: the initial formation of a vesicle with a core, the combination of such vesicles into cylindrical micelles, and the bending of the cylindrical micelles to form a hollow vesicle. In addition, raspberry vesicle fusion is regulated by F bumps through the continuous coalescence of them from apposed vesicle membranes. The contact area bends, followed by the formation of a fusion pore and a tilted inner layer. As the pore sealed, the hemifusion structure appears, which further restructures to form a vesicle. Our results provide guidance on understanding the dynamic processes of complex vesicles and biological membrane fusion.

Selective solvent conditions influence sequence development and supramolecular assembly in step-growth copolymerization

Sequence control in synthetic copolymers remains a tantalizing objective in polymer science due to the influence of sequence on material properties and self-organization. A greater understanding of sequence development throughout the polymerization process will aid the design of simple, generalizable methods to control sequence and tune supramolecular assembly. In previous simulations of solution-based step-growth copolymerizations, we have shown that weak, non-bonding attractions between monomers of the same type can produce a microphase separation among the lengthening nascent oligomers and thereby alter sequence. This work explores the phenomenon further, examining how effective attractive interactions, mediated by a solvent selective for one of the reacting species, impact the development of sequence and the supramolecular assembly in a simple A-B copolymerization. We find that as the effective attractions between monomers increase, an emergent self-organization of the reactants causes a shift in reaction kinetics and sequence development. When the solvent-mediated interactions are selective enough, the simple mixture of A and B monomers oligomerize and self-assemble into structures characteristic of amphiphilic copolymers. The composition and morphology of these structures and the sequences of their chains are sensitive to the relative balance of affinities between the comonomer species. Our results demonstrate the impact of differing A-B monomer-solvent affinities on sequence development in solution-based copolymerizations and are of consequence to the informed design of synthetic methods for sequence controlled amphiphilic copolymers and their aggregates.