skip to main content


Search for: All records

Award ID contains: 1904397

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. Abstract

    Inorganic salts usually demonstrate simple phasal behaviors in dilute aqueous solution mainly involving soluble (homogeneous) and insoluble (macrophase separation) scenarios. Herein, we report the discovery of complex phase behavior involving multiple phase transitions of clear solution – macrophase separation – gelation – solution – macrophase separation in the dilute aqueous solutions of a structurally well-defined molecular cluster [Mo7O24]6−macroanions with the continuous addition of Fe3+. No chemical reaction was involved. The transitions are closely related to the strong electrostatic interaction between [Mo7O24]6−and their Fe3+counterions, the counterion-mediated attraction and the consequent charge inversion, leading to the formation of linear/branched supramolecular structures, as confirmed by experimental results and molecular dynamics simulations. The rich phase behavior demonstrated by the inorganic cluster [Mo7O24]6−expands our understanding of nanoscale ions in solution.

     
    more » « less
  2. Abstract

    A unique trend in the binding affinity between cationic metal−organic cages (MOCs) and external counteranions in aqueous media was observed. Similar to many macroions, two MOCs, sharing similar structures but carrying different number of charges, self‐assembled into hollow spherical single‐layered blackberry‐type structures through counterion‐mediated attraction. Dynamic and static light scattering and isothermal titration calorimetry measurements confirm the stronger interactions among less charged MOCs and counteranions than that of highly charged MOCs, leading to larger assembly sizes. DOSY NMR measurements suggest the significance of thick hydration shells of highly charged MOCs, inhibiting the MOC‐counterion binding and weakening the interaction between them. This study demonstrates that the greater role played by hydration shell on ion‐pair formation comparing with charge density of MOCs.

     
    more » « less
  3. Abstract

    Three sets of polyoxometalate (POM)‐based amphiphilic hybrid macromolecules with different rigidity in their organic tails are used as models to understand the effect of molecular rigidity on their possible self‐recognition feature during self‐assembly processes. Self‐recognition is achieved in the mixed solution of two structurally similar, sphere‐rigid T‐shape‐linked oligofluorene(TOF4) rod amphiphiles, with the hydrophilic clusters being Anderson (Anderson‐TOF4) and Dawson (Dawson‐TOF4), respectively. Anderson‐TOF4is observed to self‐assemble into onion‐like multilayer structures and Dawson‐TOF4forms multilayer vesicles. The self‐assembly is controlled by the interdigitation of hydrophobic rods and the counterion‐mediated attraction among charged hydrophilic inorganic clusters. When the hydrophobic blocks are less rigid, e.g., partially rigid polystyrene and fully flexible alkyl chains, self‐recognition is not observed, attributing to the flexible conformation of hydrophobic molecules in the solvophobic domain. This study reveals that the self‐recognition among amphiphiles can be achieved by the geometrical limitation of the supramolecular structure due to the rigidity of solvophobic domains.

     
    more » « less
  4. Abstract

    We report a feasible method to control self‐recognition during the self‐assembly of a hydrophilic macroion, phosphate‐functionalized γ‐cyclodextrin (γ‐CD‐P), though host‐guest interactions. We confirmed that γ‐CD‐P can form a host‐guest complex with a super‐chaotropic anion, namely the B12F122−borate cluster, by using NMR spectroscopy and isothermal titration calorimetry. The loaded γ‐CD‐P, which has a higher charge density, can be distinguished from the uncomplexed γ‐CD‐P, leading to self‐sorting behavior during the self‐assembly process, confirmed by the formation of two types of individual supramolecular structures (Rhof ca. 57 nm and 18 nm, determined by light scattering) instead of hybrid structures in mixed dilute solution. This self‐recognition behavior is accounted for by the difference in intermolecular electrostatic interactions arising from the loading.

     
    more » « less
  5. Abstract

    The accurate distribution of countercations (Rb+and Sr2+) around a rigid, spherical, 2.9‐nm size polyoxometalate cluster, {Mo132}42−, is determined by anomalous small‐angle X‐ray scattering. Both Rb+and Sr2+ions lead to shorter diffuse lengths for {Mo132} than prediction. Most Rb+ions are closely associated with {Mo132} by staying near the skeleton of {Mo132} or in the Stern layer, whereas more Sr2+ions loosely associate with {Mo132} in the diffuse layer. The stronger affinity of Rb+ions towards {Mo132} than that of Sr2+ions explains the anomalous lower critical coagulation concentration of {Mo132} with Rb+compared to Sr2+. The anomalous behavior of {Mo132} can be attributed to majority of negative charges being located at the inner surface of its cavity. The longer anion–cation distance weakens the Coulomb interaction, making the enthalpy change owing to the breakage of hydration layers of cations more important in regulating the counterion–{Mo132} interaction.

     
    more » « less
  6. We report herein that dendron-shaped macromolecules AB n crystallize into well-ordered pyramid-like structures from mixed solvents, instead of spherical motifs with curved structures, as found in the bulk. The design of the asymmetric molecular architecture and the choice of mixed solvents are applied as strategies to manipulate the crystallization process. In mixed solvents, the solvent selection for the Janus macromolecule and the existence of dominant crystalline clusters contribute to the formation of flat nanosheets. Whereas during solvent evaporation, the bulkiness of the asymmetric macromolecules easily creates defects within 2D nanosheets which lead to their spiral growth through screw dislocation. The size of the nanosheets and the growth into 2D nanosheets or 3D pyramidal structures can be regulated by the solvent ratio and solvent compositions. Moreover, macromolecules of higher asymmetry generate polycrystals of lower orderliness, probably due to higher localized stress. 
    more » « less