Viral-Capsid-Type Vesicle-Like Structures Assembled from M12L24 Metal-Organic Hybrid Nanocages

Nonaqueous Emulsion Polycondensation Enabled by a Self-Assembled Cage-like Surfactant

Nonaqueous emulsions are crucial for a range of applications based on water-sensitive systems such as controlled polymerizations requiring anhydrous reaction conditions and the stabilization of readily hydrolyzable reagents or pharmacologically active components. However, defined molecular surfactants to stabilize such nonaqueous emulsions are scarce. We introduce a self-assembled coordination cage, decorated with cholesterol functionalities, to serve as a molecular surfactant for various oil-in-oil emulsions of immiscible organic solvents. While the positively charged cage forms the amphiphile's polar moiety, the non-polar cholesterol appendices can bend in a common direction to stabilize the emulsion. Templated by the droplets, polycondensation reactions were carried out to produce microstructured polyurethane and polyurea materials of different particle sizes and morphologies. Further, the amphiphilic cage can encapsulate a guest molecule and the resulting host-guest assembly was also examined as a surfactant. In addition, the aggregation behavior of the amphiphilic cage in an aqueous medium was examined.

Balancing Ligand Flexibility versus Rigidity for the Stepwise Self-Assembly of M12 L24 via M6 L12 Metal-Organic Cages

Non-covalent interactions are important for directing protein folding across multiple intermediates and can even provide access to multiple stable structures with different properties and functions. Herein, we describe an approach for mimicking this behavior in the self-assembly of metal-organic cages. Two ligands, the bend angles of which are controlled by non-covalent interactions and one ligand lacking the above-mentioned interactions, were synthesized and used for self-assembly with Pd²⁺ . As these weak interactions are easily broken, the bend angles have a controlled flexibility giving access to M₂ (L1)₄ , M₆ (L2)₁₂ , and M₁₂ (L2)₂₄ cages. By controlling the self-assembly conditions this process can be directed in a stepwise fashion. Additionally, the multiple endohedral hydrogen-bonding sites on the ligand were found to play a role in the binding and discrimination of neutral guests.

Cu(II)-Metallacryptands Self-Assembled to Vesicular Aggregates Capable of Encapsulating and Transporting an Anticancer Drug Inside Cancer Cells

Crystallographically characterized M₂ L₄ type cationic Cu(II)-metallacryptands [MC(X)] derived from a series of bis-pyridyl-bis-urea ligands (L_X ; X = O, S, C) are self-assembled to single-layered vesicular aggregates in DMSO, DMSO/water, and DMSO/DMEM (biological media). One such vesicle is MC(O)-vesicle that is demonstrated to be able to load and release (pH responsive) an anticancer drug, namely doxorubicin hydrochloride (DOX). DOX-loaded MC(O)-vesicle is also successfully transported within MDA-MB-231 cells-a highly aggressive human breast cancer cell line. Such self-assembling behavior to form vesicular aggregates by metallacryptands (MCs) is hitherto unknown.

Design and Synthesis of ZnII -Coordination Polymers Anchored with NSAIDs: Metallovesicle Formation and Multi-drug Delivery

A series of coordination polymers synthesized from a bis-pyridyl linker, namely 4,4'-azopyridine (L), selected non-steroidal-anti-inflammatory drugs (NSAIDs), namely diclofenac (Dic), ibuprofen (Ibu), flurbiprofen (Flu), mefenamic acid (Mefe), and naproxen (Nap), and Zn(NO₃ )₂ were characterized by single crystal X-ray diffraction. One of the coordination polymers, namely CP3 derived from Flu, was able to form metallovesicles in DMSO, DMSO/H₂ O and DMSO/DMEM (biological media) as revealed by TEM, AFM and DLS. Metallovesicle formation by CP3 was further supported by loading a fluorescent dye, namely calcein, as well as an anti-cancer drug, doxorubicin hydrochloride (DOX), as revealed by UV-vis and emission spectra, and fluorescence microscopy. DOX-loaded metallovesicles of CP3 (DOX@CP3-vesicle) could be delivered in vitro to a highly aggressive human breast cancer cell line, namely MDA-MB-231, as revealed by MTT and cell migration assays, and also cell imaging performed under laser scanning confocal microscope (LSCM). Thus, a proof of concept for developing a multi-drug delivery system derived from a metallovesicle for delivering an anti-cancer drug to cancer cells is demonstrated for the first time.

Beyond Charge Balance: Counter-Cations in Polyoxometalate Chemistry

Polyoxometalates (POMs) are molecular metal-oxide anions applied in energy conversion and storage, manipulation of biomolecules, catalysis, as well as materials design and assembly. Although often overlooked, the interplay of intrinsically anionic POMs with organic and inorganic cations is crucial to control POM self-assembly, stabilization, solubility, and function. Beyond simple alkali metals and ammonium, chemically diverse cations including dendrimers, polyvalent metals, metal complexes, amphiphiles, and alkaloids allow tailoring properties for known applications, and those yet to be discovered. This review provides an overview of fundamental POM-cation interactions in solution, the resulting solid-state compounds, and behavior and properties that emerge from these POM-cation interactions. We will explore how application-inspired research has exploited cation-controlled design to discover new POM materials, which in turn has led to the quest for fundamental understanding of POM-cation interactions.

The Microscopic Structure-Property Relationship of Metal-Organic Polyhedron Nanocomposites

Monodispersed hairy nanocomposites with typical 2 nm (isophthalic acid)₂₄ Cu₂₄ metal-organic polyhedra (MOP) as a core protected by 24 polymer chains with controlled narrow molecular weight distribution has been probed by imaging and scattering studies for the heterogeneity of polymers in the nanocomposites and the confinement effect the MOPs imposing on anchored polymers. Typical confined-extending surrounded by one entanglement area is proposed to describe the physical states of the polymer chains. This model dictates the counterintuitive thermal and rheological properties and prohibited solvent exchange properties of the nanocomposites, whilst those polymer chain states are tunable and deterministic based on their component inputs. From the relationship between the structure and behavior of the MOP nanocomposites, a MOP-composited thermoplastic elastomer was obtained, providing practical solutions to improve mechanical/rheological performances and processabilities of inorganic MOPs.

Self-Assembly of Spherical Organic Molecules to Form Hollow Vesicular Structures in Water for Encapsulation of an Anticancer Drug and Its Release

Developing hierarchical supramolecular structures is important for better understanding of various biological functions and possibly generating new materials for biomedical applications. Herein, we report the first examples of functional vesicles derived from cationic spherical organic molecules (C₁ -C₃ ) which were readily synthesized by reacting a C₃ -symmetric tris-benzimmidazole derivative (possessing a 1,3,5-ethyl substituted aromatic core) with 1,3,5-substituted tris-bromomethyl benzene derivatives. Vesicle formation by C₁ -C₃ was probed by high-resolution microscopy (TEM and AFM), dynamic light scattering (DLS) and fluorescence microscopic imaging of calcein-loaded vesicles. One of the vesicles [Vesicle(C₃ )] displayed the ability to load the anticancer drug doxorubicin (DOX). The drug was subsequently released from DOX@Vesicle(C₃ ) in a stimuli-responsive manner in presence of the well-known vesicle destroyer Triton X-100, as revealed by in vitro cell migration assay carried out on a highly aggressive human breast cancer cell line (MDA-MB-231).

Hierarchical Assembly of an Interlocked M8 L16 Container

The self-assembly of eight PdII cations and sixteen phenanthrene-derived bridging ligands with 60° bite angles yielded a novel M8 L16 metallosupramolecular architecture composed of two interlocked D4h -symmetric barrel-shaped containers. Mass spectrometry, NMR spectroscopy, and X-ray analysis revealed this self-assembled structure to be a very large "Hopf link" catenane featuring channel-like cavities, which are occupied by NO3- anions. The importance of the anions as catenation templates became imminent when we observed the nitrate-triggered structural rearrangement of a mixture of M3 L6 and M4 L8 assemblies formed in the presence of BF4- anions into the same interlocked molecule. Furthermore, the densely packed structure of the M8 L16 catenane was exploited in the preparation of a hexyloxy-functionalized analogue, which further self-assembled into vesicle-like aggregates in a reversible manner.

Face and edge directed self-assembly of Pd12 tetrahedral nano-cages and their self-sorting

Reactions of a cis-blocked Pd(ii) 90° acceptor [cis-(tmeda)Pd(NO3)2] (M) with 1,4-di(1H-tetrazol-5-yl)benzene (H2L1 ) and [1,3,5-tri(1H-tetrazol-5-yl)benzene] (H3L2 ) in 1 : 1 and 3 : 2 molar ratios respectively, yielded soft metallogels G1 and G2 [tmeda = N,N,N',N'-tetramethylethane-1,2-diamine]. Post-metalation of the gels G1 and G2 with M yielded highly water-soluble edge and face directed self-assembled Pd12 tetrahedral nano-cages T1 and T2, respectively. Such facile conversion of Pd(ii) gels to discrete tetrahedral metallocages is unprecedented. Moreover, distinct self-sorting of these two tetrahedral cages of similar sizes was observed in the self-assembly of M with a mixture of H2L1 and H3L2 in aqueous medium. The edge directed tetrahedral cage (T1) was successfully used to perform Michael reactions of a series of water insoluble nitro-olefins assisted by encapsulation into the cage in aqueous medium.

Multifunctional single-layered vesicles derived from Cu(ii)-metal–organic-polyhedra

Multifunctional vesicles derived from Cu(ii) metal–organic polyhedra (MOP) displayed the ability to encapsulate and release anti-cancer drug doxorubicin for the first time.

Evolution of actinyl peroxide clusters U28 in dilute electrolyte solution: exploring the transition from simple ions to macroionic assemblies

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)4(3-) 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.