The behavior in dilute solution of phosphate-functionalized γ-cyclodextrin macroanions with eight charges on the rim was explored. The hydrophilic macroions in mixed solvents show strong attraction between each other, mediated by the counterions, and consequently self-assemble into blackberry-type hollow spherical structures. Time-resolved laser light scattering (LLS) measurements at high temperature ruled out the possibility of hydrogen bonding as the main driving force in the self-assembly and indicated the good thermodynamic stability of assemblies regulated by the charge. The transition from single macroions to blackberries can be tuned by adjusting the content of organic solvent. The sizes of blackberries vary with the charge density of γ-cyclodextrin by adjusting pH. It is the first report that pure cyclodextrins can generate supramolecular structures by themselves in dilute solution. The unique solution behavior of macroions provides a new opportunity to assemble cyclodextrin into functional materials and devices.

Two Keplerate-type macroions, [Mo^VI₇₂Fe^III₃₀O₂₅₂- (CH₃COO)₁₂{Mo₂O₇(H₂O)}₂{H₂Mo₂O₈(H₂O)}(H₂O)₉₁]⋅ca. 150 H₂O= {Mo₇₂Fe₃₀} and [{Na(H₂O)₁₂}⊂{Mo^VI₇₂Cr^III₃₀O₂₅₂(CH₃COO)₁₉- (H₂O)₉₄}]⋅ca. 120 H₂O={Mo₇₂Cr₃₀}, with identical size and shape but different charge density, can self-assemble into spherical “blackberry”-like structures in aqueous solution by means of electrostatic interactions. These two macroanions can self-recognize each other and self-assemble into two separate types of homogeneous blackberries in their mixed dilute aqueous solution, in which they carry −7 and −5 net charges, respectively. Either adjusting the solution pH or raising temperature is expected to make the self-recognition more difficult, by making the charge densities of the two clusters closer, or by decreasing the activation energy barrier for the blackberry formation, respectively. Amazingly, the self-recognition behavior remains, as confirmed by dynamic and static light scattering, TEM, and energy dispersive spectroscopy techniques. The results prove that the self-recognition behavior of the macroions due to the long-range electrostatic interaction is universal and can be achieved when only minimum differences exist between two types of macroanions.

The self-assembly of semiglobular, positively charged poly(propyleneimine) (PPI) dendrimers with small monovalent counterions (e.g., Cl⁻) in water/acetone mixtures was investigated. We showed that PPI dendrimers can assemble into hollow, spherical, single-layered blackberry-type structures mediated by the presence of monovalent counterions. The effects on the assembly of changing the solvent polarity and adjusting the pH were further investigated to confirm the presence of electrostatic interactions and hydrogen bonding as the driving forces. Results showed that PPI dendrimers form stable, hollow spheres in 5–20 % v/v acetone/water and that the size of the spheres decreases monotonically as the solvent polarity and/or the charge on the dendrimers (i.e., lower solution pH) increases. This is the first example to show that small monovalent counterions can trigger attraction among PPI dendrimers (or broadly defined polyelectrolytes) that is strong enough to bring them together to form large, stable supramolecular assemblies, which indicates that these organic macroions have similar solution behavior to more-well-defined inorganic molecular macroions.

Three diblock copolymers, each consisting of a relatively polar polyoxometalate-containing block and a nonpolar polythiophene block, were studied for their solution self-assembly behavior. Hollow spherical vesicular structures have been observed; their formation is driven by solvophobic–solvophilic interactions. The size of the vesicles can be controlled by varying the polarity of the solvent. Regular vesicles seem to form when the solvent combination is relatively polar, while reverse vesicles form when the solvent is relatively nonpolar.

Both positively and negatively charged polyhedral oligomeric silsesquioxane (POSS) electrolytes were observed to self-assemble into blackberry-type supramolecular structures in water/acetone mixed solvents, driven by the counterion-mediated attraction. Laser light-scattering studies reveal that the sizes of the blackberry structures increase with increasing acetone content, which suggests a charge-regulated process. Studies on two oppositely charged POSS macroions with identical charges and similar sizes show the discrepancy between positively and negatively charged POSS macroions, which is related to counterions, ionic domains of macroions, and the water-bridged hydrogen bonding between monomers. These POSS ions further decrease the lower size limit of macroions that can self-assemble in polar solvents reported to date. The new phenomena were observed in the self-assembly process of POSS macroions relative to other macroion systems.

Actinyl peroxide clusters, a unique class of uranyl-containing nanoclusters discovered in recent years, are crucial intermediates between the (UO₂)²⁺ aqua-ion monomer and bulk uranyl minerals. Herein, two actinyl polyoxometalate nanoclusters of Cs₁₅[(Ta(O₂)₄)Cs₄K₁₂(UO₂(O₂)_1.5)₂₈]⋅20 H₂O (CsKU₂₈) and Na₆K₉[(Ta(O₂)₄)Rb₄Na₁₂(UO₂(O₂)_1.5)₂₈]⋅20 H₂O (RbNaU₂₈) were synthesized by incorporating a central Ta(O₂)₄³⁻ anion that templates a hollow shell of 28 uranyl peroxide polyhedra. When dissolved in aqueous solutions with additional electrolytes, those 1.8 nm-size macroanions self-assembled into spherical, hollow, blackberry-type supramolecular structures, as was characterized by laser-light scattering (LLS) and TEM techniques. These clusters are the smallest macroions reported to date that form blackberry structures in solution, therefore, can be treated as valuable models for investigating the transition from simple ions to macroions. Kinetic studies showed an unusually long lag phase in the initial self-assembly process, which is followed by a rapid formation of the blackberry structures in solution. The small cluster size and high surface-charge density are essential in regulating the supramolecular structure formation, as was shown from the high activation energy barrier of 51.2±2 kJ mol⁻¹. Different countercations were introduced into the system to investigate the effect of ion binding to the length of the lag phase. The current research provides yet another scale of self-assembly of uranyl peroxide complexes in aqueous media.

An inorganic–organic hybrid surfactant with a hexavanadate cluster as the polar head group was designed and observed to assemble into micelle structures, which further spontaneously coagulate into a 1D anisotropic structure in aqueous solutions. Such a hierarchical self-assembly process is driven by the cooperation of varied noncovalent interactions, including hydrophobic, electrostatic, and hydrogen-bonding interactions. The hydrophobic interaction drives the quick formation of the micelle structure; electrostatic interactions involving counterions leads to the further coagulation of the micelles into larger assemblies. This process is similar to the crystallization process, but the specific counterions and the directional hydrogen bonding lead to the 1D growth of the final assemblies. Since most of the hexavanadates are exposed to the surface, the 1D assembly with nanoscale thickness is a highly efficient heterogeneous catalyst for the oxidation of organic sulfides with appreciable recyclability.