Unusual Structures of Interpolyelectrolyte Complexes: Vesicles and Perforated Vesicles

Abstract

By means of computer simulation and analytical theory, we first demonstrated that the interpolyelectrolyte complexes in dilute solution can spontaneously form hollow spherical particles with thin continuous shells (vesicles) or with porous shells (perforated vesicles) if the polyions forming the complex differ in their affinity for the solvent. The solvent was considered good for the nonionic groups of one macroion and its quality was varied for the nonionic groups of the other macroion. It was found that if the electrostatic interactions are weak compared to the attraction induced by the hydrophobicity of the monomer units, the complex in poor solvent tends to form “dense core–loose shell” structures of different shapes. The strong electrostatic interactions favor the formation of the layered, the hollow, and the filled structured morphologies with the strongly segregated macroions. Vesicles with perforated walls were distinguished as the intermediate between the vesicular and the structured solid morphologies. The order parameter based on the spherical harmonics expansion was introduced to calculate the pore distribution in the perforated vesicles depending on the solvent quality. The conditions of the core–shell and hollow vesicular-like morphologies formation were determined theoretically via the calculations of their free energy. The results of the simulation and theoretical approaches are in good agreement.

Hierarchical Shape-Specified Model Polymer Nanoparticles via Copolymer Sequence Control

“…Realization of controlled assembly of synthetic molecules comparable to that achieved in biological macromolecules has been a long-term goal of polymer science . Efforts in this direction have predominantly relied upon a balance between long-ranged interactions , and short-ranged solvation forces or have employed multi-molecular assembly. − In biological macromolecules, on the other hand, fine control of repeat unit sequence , in single or small numbers of molecules, can enable targeted self-assembly into a hierarchy of nanostructures with controlled shape and size. Recent work has hinted that this type of single-molecule assembly may offer unique opportunities in molecular design, − for example in yielding nanostructures with well-defined multicompartment catalytic sites and in controlling molecular blood circulation times, degradation rates, and drug loading capacities. , Indeed, the efficacy of sequence in mediating single-molecule assembly of biomacromolecules suggests that this route could enable transformational new synthetic molecules for use in applications such as advanced catalysis, molecular sequestration, drug delivery, and sensing …”

“…Indeed, incorporation of charges into a polymer chain can yield a range of single-molecule structures, from coils to necklaces, to cylinders, as solvent quality is varied . Introduction of other relatively long-ranged (screened-electrostatic-like) interactions for single-molecule assembly can yield a variety of structures including cylinders, necklaces, spherical globule-like vesicles, and multi-layered vesicles. ,− These shapes have been realized in experiment via assembly of amphiphilic homopolymers in selective solvents. ,, Inclusion of paired chains of opposite charge can yield even more complex structures including perforated vesicles, identified in other works as stomatosomes. , …”

Unusual Nanostructured Morphologies Enabled by Interpolyelectrolyte Complexation of Polyions Bearing Incompatible Nonionic Segments

“…It should be mentioned that necklace-type PECs found in our work are similar to the ones predicted for PECs from block copolymers with a polyelectrolyte short block and oppositely charged long-linear homopolymers. 25 Unusual vesicular conformations of symmetric PECs found via computer simulations have recently been reported; 56 however, the effect of the PEC asymmetry is explored here for the first time.…”

Stable Vesicles Formed by a Single Polyelectrolyte in Salt Solutions

“…For the vesicle formed by a homogeneous PE, our results show that the cavity is at the center of the vesicle to more effectively increase the average distance between charged segments. This is different from the recent computer simulation on interpolyelectrolyte complexes where perforated vesicles with pores near the surface can be formed. , The existence of vesicle as a equilibrium structure is beyond the well-accepted framework of the globule to pearl-necklace transition in explaining the conformational behavior of a single PE.…”

“…In biology, vesicles also widely exist within and outside cells, governing a variety of functions of the human body . Almost all the vesicles previously reported are formed by the self-assembly of multiple amphiphilic molecules, such as phospholipids, block copolymers, , interpolyelectrolyte complexes, , and mixtures of surfactants, where the compositions of hydrophilic and hydrophobic components have to be carefully controlled to tune the curvatures of the inner and outer surfaces. Due to the nature of the multimolecular self-assembly, these vesicles usually are not thermodynamically stable but kinetically trapped.…”