A chiral endohedral Pd12Ala24 metal-organic cage (MOC) incorporating enantiomeric tert-butyloxycarbonylalanine (Boc-Ala) ligands is synthesized as a model system of a chiral macrocation containing internal chiral centers away from the surface of the MOC. The endohedral chiral geometry leads to the interaction between these chiral centers inside the MOCs far away from other chiral components such as chiral counterions in solution. The consequence is that the chiral recognition (two MOC enantiomers self-assemble individually in their mixed solution) and chiral discrimination (self-assembly favors one enantiomer over the other) previously observed in the self-assembly of MOCs carrying exohedral chiral centers become weaker or completely disappear in the current MOC solutions, demonstrating that the effective electrostatic interaction in a short range is critical for the chiral recognition behavior of macromolecules during their self-assembly. Different small chiral species in solution (e.g., arabinose, lactate, tartrate, and gamma-cyclodextrin) show various capabilities on the chiral recognition and discrimination of endohedral Pd12Ala24 MOCs during the self-assembly, based on the size and charge of these species.

Blackberry structure is a type of universal, stable, porous, single layered, hollow, spherical supramolecular structure with sizes from tens to hundreds of nanometers self-assembled by various macroions (1–6 nm-size) in dilute solutions of water or other polar solvents. This self-assembly process is driven by counterion-mediated attraction, and merely requires ions to be large enough and moderately charged. The blackberry structures possess important features including their spontaneous and reversible self-assembly with tunable assembly sizes, capability of selectively segregating counterions, permeability to small counterions and molecules, self-recognition, as well as chiral recognition and selection. Considering such simple requirements for the self-assembly process and the mentioned features, and the availability of various macroions on the prebiotic earth, we will discuss about the possible role of blackberry structures as a compartmentalizing system in the origin of life concentrating the precursors and preparing proper conditions for the reaction to synthesize building blocks of early lives. We also speculate that they could have played a key role in the evolution of homochiral biological systems by intensifying the small enantiomeric imbalance, that might have existed on the prebiotic Earth.

We present seven rare-earth derivants of mixed-polyoxoniobates, which behave as weak acids with good stability and high proton release capacity.

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.

The self-assembly of chiral Pd12L24 metal-organic cages (MOCs) based on hydrophobic amino acids, including alanine (Ala), valine (Val), and leucine (Leu), into single-layered hollow spherical blackberry-type structures is triggered by nitrates through counterion-mediated attraction. In addition to nitrates, anionic N-(tert-butoxycarbonyl) (Boc)-protected Ala, Val, and Leu were used as chiral counterions during the self-assembly of DMOCs. Previously, we showed that L-Ala suppresses the selfassembly process of D-Pd12Ala24 but has no effect on L-Pd12Ala24, i.e., chiral discrimination. Here, we indicate when the amino acid used as the chiral counterion has a bulkier side group than the amino acid in the MOC structure, no chiral discrimination exists; otherwise, chiral discrimination exists. For example, Ala can induce chiral discrimination in all chiral MOCs, whereas Leu can induce chiral discrimination only in Pd12Leu24. Moreover, chiral anionic D- and L-alanine-based surfactants have no chiral discrimination, indicating that bulkier chiral counterions with more hydropohobic side groups can erase chiral discrimination.

We report herein that dendron-shaped macromolecules ABn 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.

Molecular metal-organic cages (MOCs) are constructed via coordination among diverse ligands and metal acceptors with great control over the size, shape, cavity, and composition. Their unique and complex molecular structures make different types of intermolecular interactions, including electrostatic, hydrophobic, hydrogen bonding, van der Waals, π-π and host-guest interactions etc., possible to co-exist in MOC solution. The cooperative or competitive interplay of multiple attractive forces is the driving force leading to exciting and rich solution self-assembly behavior of the MOCs into various supramolecular structures, such as micelles, fibers, nanosheets, nanocubes, nanorods, and blackberry structures. Extensive efforts have been made for gaining better understanding on the formation of these higher ordered structures and designing supramolecular structures with desired properties and functions. In this review, we try to sort out the self-assembly behaviors in MOC solutions from literature based on the type of physical forces involved.

Lactic acid-functionalized chiral fullerene (C60) molecules are used as models to understand chiral selection in macroionic solutions involving chiral macroions, chiral counterions, and/or chiral co-ions. With the addition of Zn2+ cations, the C-60 macroions exhibit slow self-assembly behavior into hollow, spherical, blackberry-type structures, as confirmed by laser light scattering (LLS), transmission electron microscopy (TEM), and atomic force microscopy (AFM) techniques. Chiral counterions with high charge density show no selection to the chirality of AC(60) macroions (LAC(60) and DAC(60)) during their self-assembly process, while obvious chiral discrimination between the assemblies of LAC(60) and DAC(60) is observed when chiral counterions with low charge density are present. Compared with chiral counterions, chiral co-ions show weaker effects on chiral selection with larger amounts needed to trigger the chiral discrimination between LAC(60) and DAC(60). However, they can induce a higher degree of discrimination when abundant chiral co-ions are present in solution. Furthermore, the self-assembly of chiral AC(60) macroions is fully suppressed by adding significant amounts of neutral molecules with opposite chirality. Thermodynamic parameters from isothermal titration calorimetry (ITC) reveal that chiral selection is controlled by the ion pairing and the destruction of solvent shells between ions, and meanwhile originates from the delicate balance between electrostatic interaction and molecular chirality.

The role of chiral counterions on the attraction and self-assembly of chiral Pd12L24 metal organic cages (MOCs) with NO3- being the original counterion is studied by laser light scattering and isothermal titration calorimetry. Nitrates can trigger the self-assembly of macrocationic Pd12L24 into hollow spherical blackberry-type supramolecular structures via counterion-mediated attraction. Although chiral counteranions, such as N-(tert-butoxycarbonyl)-alanine (Boc-Ala), have weaker interaction with the MOCs compared to NO3-, they can induce different assembly behaviors between two enantiomeric MOCs by inhibiting the MOC-nitrate binding and weakening the interaction between them. The d-counterions are capable of selectively suppressing and slowing down the assembly of l-MOCs and also considerably decreasing their assembly size due to the much weaker MOC-nitrate interaction. The same scenario is observed for l-counterions when interacting with the d-MOCs. This study unveils the role of weakly associated chiral counterions on the central chiral macroions, especially their supramolecular structure formation, and provides additional evidence on the mechanism of the homochirality phenomenon.

We report cation-binding behaviors of two {P4Ta6}-type polyoxometalate (POM) clusters withcis-andtrans-subunit geometry in aqueous solution. Two types of divalent cations, Sr(2+)and Pb2+, possess different binding affinities and sites when interacting with {P4Ta6}. Sr(2+)ions only form solvent-share ion-pairs with {P4Ta6}, whereas Pb(2+)ions form contact-ion pairs, selectively interacting with the phosphate groups at different locations and subsequently induce the aggregation of {P4Ta6}, confirmed by isothermal titration calorimetry (ITC), NMR, and small-angle X-ray scattering (SAXS) techniques. Despite Sr(2+)and Pb(2+)possessing similar ionic sizes and hydration energies, Pb(2+)ions with stronger coordination capability result in a closer association with the clusters, eventually to selective interaction that depends on the chelating effect, charge density, and the acidity of phosphate groups at specific sites.

ABSTRACTThe reactive compatibilization of blends consisting polypropylene (PP) and thermoplastic starch (TPS) (70/30) with different portions of PP‐grafted maleic anhydride (PP‐g‐MA) is carried out by melt mixing. The esterification reaction between the starch hydroxyl and the PP‐g‐MA groups proved by the FTIR leads to a compatibility improvement. The dynamic rheological properties, morphology, elongation at break, and the impact strength of the blends were studied. The SEM images show that increasing the compatibilizer concentration reduces the dispersed TPS droplet size. The generalized Zener model states that an elastic interface is established (minimum α value) and enables us to predict the dynamic rheological properties of our blends in a longer frequency range to where the current experimental limitation exists. The modified Cross model is implemented to confirm better adhesion between phases when 20 wt % PP‐g‐MA is used (minimum ac value). The increase in the dynamic viscoelastic moduli at concentrations up to 20 wt % and the observed plateau at the elongation at break point at this concentration confirmed that this concentration is the optimum for the maximum stress transfer. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48742.

ABSTRACT In this work, polypropylene/thermoplastic starch (PP/TPS) with and without halloysite nanotubes (HNTs) was prepared via melt mixing in order to obtain environmentally friendly plastics. PP‐grafted maleic anhydride (PP‐ g ‐MA) was used to improve the compatibility among the highly incompatible polymers. The mechanical characterization showed a reduction in the tensile properties of the polymer when TPS increased; however, HNT successfully compensated for some of the observed losses. The results from the thermogravimetric analysis (TGA) indicated that HNT is an efficient reinforcement for the thermal stability improvement. TPS caused an increase in the storage modulus ( G ′) and the complex viscosity (η*) which marks a change in the viscoelastic properties of the system. The scanning electron microscope (SEM) images showed the effective plasticization of starch and better dispersion of TPS in the presence of HNT. Some samples were also buried in the soil to measure their sustainability after their lifetime lapse. The results indicated that TPS improves the biodegradability of the PP/TPS system. PP considerably lowered the moisture uptake of TPS; nevertheless, HNT caused a slight increase in the moisture absorption. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135 , 45740.