Polyoxometalates Macroions: From Self-Recognition to Functional Materials

Large, hydrophilic polyoxoanions with high solubility in water and/or other polar solvents demonstrate unique solution behavior by self-assembling into single layer, hollow, spherical blackberry -like structures, which are obviously different from small, simple ions. These macroions cannot be treated as insoluble colloidal suspensions either because they form stable real solutions . These inorganic macroions demonstrate some features usually Pobelieved to belong only to complex biological molecules, such as the self-recognition, chiral recognition, and chiral selection in dilute solutions. Highly negatively-charged molecular rods with almost identical structures were observed to self-assemble into their individual `blackberry\u27 structures, demonstrating tiny differences (e.g. charge, charge distribution, and organic ligands) could lead to self-recognition behavior. Chiral recognition behavior was understood by studying the self-assembly process in the racemic mixture solutions. Moreover, chiral organic molecules (lactic acid and tartaric acid) can be used to selectively inhibit the self-assembly process of one of the enantiomers. Meanwhile, polyoxometalate-based organic-inorganic hybrid materials demonstrate amphiphilic properties by self-assembling into vesicles and reverse vesicles in polar and non-polar solvents, respectively, and form catalytic emulsions in biphasic environments. Designed hybrid molecules can be programed to different devices with applications in fluorescence, photo-electronic conversion, molecular switch, and catalyst

Unprecedented halide‐ion binding and catalytic activity of nanoscale anionic metal oxide clusters

One halide ion (X−) can bind on the surface of nanoscale Anderson‐type polyoxometalate (POMs) clusters [(n‐C4H9)4N]3{AlMo6O18(OH)3[(OCH2)3CCH3]}, and form stable complexes in solution with binding constant K=1.53×103. Single‐crystal structural analysis showed that this binding behavior occurs through multiple hydrogen bonding between X− and three hydroxy groups on the uncapped side of the cluster. This supramolecular interaction in the cluster systems means that their catalytic activities, evaluated from the oxidation of alcohols to aldehydes, can be switched upon the introduction of halide ions and water molecules. The halide ions work as inhibitors by blocking the active sites of the clusters while they can be re‐activated by the addition of water

Role of Protein Charge Density on Hepatitis B Virus Capsid Formation

The role of electrostatic interactions in the viral capsid assembly process was studied by comparing the assembly process of a truncated hepatitis B virus capsid protein Cp149 with its mutant protein D2N/D4N, which has the same conformational structure but four fewer charges per dimer. The capsid protein self-assembly was investigated under a wide range of protein surface charge densities by changing the protein concentration, buffer pH, and solution ionic strength. Lowering the protein charge density favored the capsid formation. However, lowering charge beyond a certain point resulted in capsid aggregation and precipitation. Interestingly, both the wild-type and D2N/D4N mutant displayed identical assembly profiles when their charge densities matched each other. These results indicated that the charge density was optimized by nature to ensure an efficient and effective capsid proliferation under the physiological pH and ionic strength

The dynamical signature and scaling of supramolecular assemblies

We present a brief overview of current investigations on the dynamics of supramolecular assemblies, with the focus on applying broadband dielectric spectroscopy (BDS) combined with different techniques. The dielectric methods have significant advantages in probing the dynamical signature and scaling of supra-structures. We summarize various mechanisms describing supramolecular dynamics, which could produce a relaxation governed by supramolecular association slower than the glass-transition-related structural relaxation. Next, we also discuss the relaxation dynamics in phase-separated supramolecular assemblies and supramolecular assembly under nanoconfinement, for controlling bonus macroscopic performances. This perspective emphasizes the idea that the relaxational response of supramolecular assemblies is generic to some extent. It does not necessarily depend on the chemistry of associations, but could reflect supra-materials’ behaviors determined by their molecular architectures

Editorial: Emerging polyoxometalates with biological, biomedical, and health applications

Editorial on the Research Topic: Emerging polyoxometalates with biological, biomedical, and health applications.MA received Portuguese national funds from FCT—Foundation for Science and Technology through projects UIDB/04326/2020 and LA/P/0101/2020.Peer reviewe

The coupling of rotational and translational dynamics for rapid diffusion of nanorods in macromolecular networks

Abstract The rod-like viruses show anomalously rapid diffusion in bio-tissue networks originated from the rotation-facilitated transportation; however, the experimental investigation of the correlation of the rotational and translational dynamics is still in blank. Herein, typical rod-like and spherical gold nanoparticles (NPs) are dispersed in the classical Tetra-PEG gels, respectively, as model systems for light scattering studies. The contributions from translational and rotational diffusive dynamics, and network fluctuation dynamics can be well-resolved and the stretch exponent of rotational dynamics at 0.25 is proven to be the fingerprint for the coupled rotational and translational dynamics of nanorods. The rotation facilitated re-orientation finally leads to the fast transportation of nanorods. The discoveries are confirmed to be valid for rod-like biomacromolecule systems by studying the diffusive dynamics of Tobacco mosaic virus in gels. The work can be inspiring for the development of protocols to prevent infection of microorganism and regulate the transportation of nano-medicines

Self-Assembly of Subnanometer-Scaled Polyhedral Oligomeric Silsesquioxane (POSS) Macroions in Dilute Solution

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

Spontaneous Self-Assembly of γ-Cyclodextrins in Dilute Solutions with Tunable Sizes and Thermodynamic Stability

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

Adsorption, Ordering, and Local Environments of Surfactant-Encapsulated Polyoxometalate Ions Probed at the Air–Water Interface

The continued development and application of surfactant-encapsulated polyoxometalates (SEPs) relies on understanding the ordering and organization of species at their interface and how these are impacted by the various local environments to which they are exposed. Here, we report on the equilibrium properties of two common SEPs adsorbed to the air–water interface and probed with surface-specific vibrational sum-frequency generation (SFG) spectroscopy. These results reveal clear shifts in vibrational band positions, the magnitude of which scales with the charge of the SEP core, which is indicative of a static field effect on the surfactant coating and the associated local chemical environment. This static field also induces ordering in surrounding water molecules that is mediated by charge screening via the surface-bound surfactants. From these SFG measurements, we are able to show that Mo₁₃₂-based SEPs are more polar than Mo₇₂V₃₀ SEPs. Disorder in the surfactant chain packing at the highly curved SEP surfaces is attributed to large conic volumes that can be sampled without interactions with neighboring chains. Measurements of adsorption isotherms yield free energies of adsorption to the air–water interface of −46.8 ± 0.4 and −44.8 ± 1.2 kJ/mol for the Mo₁₃₂ and Mo₇₂V₃₀ SEPs, respectively, indicating a strong propensity for the fluid surface. The influence of intermolecular interactions on the surface adsorption energies is discussed