Hierarchical self-assembly: well-defined supramolecular nanostructures and metallohydrogels via amphiphilic discrete organoplatinum(II) metallacycles

Block Co-PolyMOCs by Stepwise Self-Assembly

We report a stepwise assembly strategy for the integration of metal-organic cages (MOCs) into block copolymers (BCPs). This approach creates "block co-polyMOC" (BCPMOC) materials whose microscopic structures and mechanical properties are readily tunable by adjusting the size and geometry of the MOCs and the composition of the BCPs. In the first assembly step, BCPs functionalized with a pyridyl ligand on the chain end form star-shaped polymers triggered by metal-coordination-induced MOC assembly. The type of MOC junction employed precisely determines the number of arms for the star polymer. In the second step, microphase separation of the BCP is induced, physically cross-linking the star polymers and producing the desired BCPMOC networks in the bulk or gel state. We demonstrate that large spherical M12L24 MOCs, small paddlewheel M2L4 MOCs, or a mixture of both can be incorporated into BCPMOCs to provide materials with tailored branch functionality, phase separation, microdomain spacing, and mechanical properties. Given the synthetic and functional diversity of MOCs and BCPs, our method should enable access to BCPMOCs for a wide range of applications.

First report of charge-transfer induced heat-set hydrogel. Structural insights and remarkable properties

The remarkable ability of a charge-transfer (CT) complex prepared from a pyrene-based donor (Py-D) and a naphthalenediimide-based acceptor (NDI-A) led to the formation of a deep-violet in color, transparent hydrogel at room temperature (RT-gel). Simultaneously, the RT-gel was diluted beyond its critical gelator concentration (CGC) to obtain a transparent sol. Very interestingly, the resultant sol, on heating above 70 °C, transformed into a heat-set gel instantaneously with a hitherto unknown CGC value. Detailed studies revealed the smaller globular aggregates of the RT-gels fuse to form giant globules upon heating, which, in turn, resulted in heat-set gelation through further aggregation. The thermoresponsive property of Py-D alone and 1 : 1 Py-D : NDI-A CT complex was investigated in detail which revealed the hydrophobic collapse of the oxyethylene chains of the CT complex upon heating was mainly responsible for heat-set gelation. Thixotropy, injectability, as well as stimuli responsiveness of the RT-gels were also addressed. In contrast, heat-set gel did not show thixotropic behavior. The X-ray diffraction (XRD) patterns of the xerogel depicted lamellar packing of the CT stacks in the gel phase. Single crystal XRD studies further evidenced the 1 : 1 mixed CT stack formation in the lamellae and also ruled out orthogonal hydrogen bonding possibilities among the hydrazide unit in the CT gel although such interaction was observed in a single crystal of NDI-A alone. In addition, a Ag(+)-ion triggered metallogelation of NDI-A and nematic liquid-crystalline property of Py-D were also observed.

Thermodynamic-Driven Self-Assembly: Heterochiral Self-Sorting and Structural Reconfiguration in Gold(I)-Sulfido Cluster System

By employing chiral precursors, a new class of chiral gold(I)-sulfido clusters with unique structures has been constructed. Interestingly, pure enantiomers of the precursors are found to self-assemble into chiral hexa- and decanuclear clusters sequentially, while a racemic mixture of them has resulted in heterochiral self-sorting of an achiral meso decanuclear cluster. Chirality has determined not only the symmetry and structures but also the photophysical behaviors of these clusters. The racemic mixture of decanuclear clusters undergoes rearrangement and heterochiral self-sorting to give a meso decanuclear cluster. The thermodynamic-driven heterochiral self-sorting of gold(I) clusters provides a means to develop controlled self-assembly that may be of relevance to the understanding of chirality in nature.

Hierarchical design of a polymeric nanovehicle for efficient tumor regression and imaging

Effective delivery of therapeutics to disease sites significantly contributes to drug efficacy, toxicity and clearance. Here we designed a hierarchical polymeric nanoparticle structure for anti-cancer chemotherapy delivery by utilizing state-of-the-art polymer chemistry and co-assembly techniques. This novel structural design combines the most desired merits for drug delivery in a single particle, including a long in vivo circulation time, inhibited non-specific cell uptake, enhanced tumor cell internalization, pH-controlled drug release and simultaneous imaging. This co-assembled nanoparticle showed exceptional stability in complex biological media. Benefiting from the synergistic effects of zwitterionic and multivalent galactose polymers, drug-loaded nanoparticles were selectively internalized by cancer cells rather than normal tissue cells. In addition, the pH-responsive core retained their cargo within their polymeric coating through hydrophobic interaction and released it under slightly acidic conditions. In vivo pharmacokinetic studies in mice showed minimal uptake of nanoparticles by the mononuclear phagocyte system and excellent blood circulation half-lives of 14.4 h. As a result, tumor growth was completely inhibited and no damage was observed for normal organ tissues. This newly developed drug nanovehicle has great potential in cancer therapy, and the hierarchical design principle should provide valuable information for the development of the next generation of drug delivery systems.

Highly branched and loop-rich gels via formation of metal-organic cages linked by polymers

Gels formed via metal-ligand coordination typically have very low branch functionality, f, as they consist of ∼2-3 polymer chains linked to single metal ions that serve as junctions. Thus, these materials are very soft and unable to withstand network defects such as dangling ends and loops. We report here a new class of gels assembled from polymeric ligands and metal-organic cages (MOCs) as junctions. The resulting 'polyMOC' gels are precisely tunable and may feature increased branch functionality. We show two examples of such polyMOCs: a gel with a low f based on a M2L4 paddlewheel cluster junction and a compositionally isomeric one of higher f based on a M12L24 cage. The latter features large shear moduli, but also a very large number of elastically inactive loop defects that we subsequently exchanged for functional ligands, with no impact on the gel's shear modulus. Such a ligand substitution is not possible in gels of low f, including the M2L4-based polyMOC.

Construction and luminescence property of a highly ordered 2D self-assembled amphiphilic bidentate organoplatinum(ii) complex

A red luminescent film was constructed by self-assembly of 1-Pt from methanol. The film on a substrate, exhibiting multi-stimuli responsiveness, was further obtained.

AIE-caused luminescence of a thermally-responsive supramolecular organogel

A two-stage-assembly of a supramolecular gel (B-gel) can emit brilliant blue light due to the strong AIEE effect depending on the multiple hydrogen-bonding and coordination bonds between gelator L and Cd²⁺.

Carbohydrates in Supramolecular Chemistry

Carbohydrates are involved in a variety of biological processes. The ability of sugars to form a large number of hydrogen bonds has made them important components for supramolecular chemistry. We discuss recent advances in the use of carbohydrates in supramolecular chemistry and reveal that carbohydrates are useful building blocks for the stabilization of complex architectures. Systems are presented according to the scaffold that supports the glyco-conjugate: organic macrocycles, dendrimers, nanomaterials, and polymers are considered. Glyco-conjugates can form host-guest complexes, and can self-assemble by using carbohydrate-carbohydrate interactions and other weak interactions such as π-π interactions. Finally, complex supramolecular architectures based on carbohydrate-protein interactions are discussed.

A Suite of Tetraphenylethylene-Based Discrete Organoplatinum(II) Metallacycles: Controllable Structure and Stoichiometry, Aggregation-Induced Emission, and Nitroaromatics Sensing

Materials that organize multiple functionally active sites, especially those with aggregation-induced emission (AIE) properties, are of growing interest due to their widespread applications. Despite promising early architectures, the fabrication and preparation of multiple AIEgens, such as multiple tetraphenylethylene (multi-TPE) units, in a single entity remain a big challenge due to the tedious covalent synthetic procedures often accompanying such preparations. Coordination-driven self-assembly is an alternative synthetic methodology with the potential to deliver multi-TPE architectures with light-emitting characteristics. Herein, we report the preparation of a new family of discrete multi-TPE metallacycles in which two pendant phenyl rings of the TPE units remain unused as a structural element, representing novel AIE-active metal-organic materials based on supramolecular coordination complex platforms. These metallacycles possess relatively high molar absorption coefficients but weak fluorescent emission under dilute conditions because of the ability of the untethered phenyl rings to undergo torsional motion as a non-radiative decay pathway. Upon molecular aggregation, the multi-TPE metallacycles show AIE-activity with markedly enhanced quantum yields. Moreover, on account of their AIE characteristics in the condensed state and ability to interact with electron-deficient substrates, the photophysics of these metallacycles is sensitive to the presence of nitroaromatics, motivating their use as sensors. This work represents a unification of themes including molecular self-assembly, AIE, and fluorescence sensing and establishes structure-property-application relationships of multi-TPE scaffolds. The fundamental knowledge obtained from the current research facilitates progress in the field of metal-organic materials, metal-coordination-induced emission, and fluorescent sensing.

Loading of Vesicles into Soft Amphiphilic Nanotubes using Osmosis

The facile assembly of higher-order nanoarchitectures from simple building blocks is demonstrated by the loading of vesicles into soft amphiphilic nanotubes using osmosis. The nanotubes are constructed from rigid interdigitated bilayers which are capped with vesicles comprising phospholipid-based flexible bilayers. When a hyperosmotic gradient is applied to these vesicle-capped nanotubes, the closed system loses water and the more flexible vesicle bilayer is pulled inwards. This leads to inclusion of vesicles inside the nanotubes without affecting the tube structure, showing controlled reorganization of the self-assembled multicomponent system upon a simple osmotic stimulus.

Characterization of Metallosupramolecular Polymers by Top-Down Multidimensional Mass Spectrometry Methods

Top-down multidimensional mass spectrometry, interfacing electrospray ionization (ESI) with ion mobility mass spectrometry (IM-MS), and energy resolved (gradient) tandem mass spectrometry (gMS(2) ) are employed to characterize the stoichiometries, architectures, and intrinsic stabilities of coordinatively bound supramolecular polymers containing terpyridine functionalized ligands. As a soft ionization method, ESI prevents or minimizes unwanted assembly destruction. The IM dimension affords separation of the supramolecular ions by charge and collision cross-section (a function of size and shape). The mobility separated ions are subsequently identified by their mass-to-charge-ratios and isotope patterns in the orthogonal MS dimension. Finally, the gMS(2) dimension reveals bond breaking proclivities and disintegration pathways of the assemblies. The described methodology does not require high sample purity due to the dispersive nature of the IM and MS steps. Its utility is demonstrated with the comprehensive analysis of bisterpyridine-based metallomacrocycle mixtures and a tristerpyridine based complex with 3-D nanosphere-like architecture.

Directional supracolloidal self-assembly via dynamic covalent bonds and metal coordination

An emerging strategy towards the sophistication of supramolecular nanomaterials is the use of supracolloidal self-assembly, in which micelles or colloids are used as building blocks. Binding directionality can produce nanostructures with attractive properties. Herein, we present a new directional supracolloidal self-assembly by virtue of dynamic covalent bonds and metal coordination in water. Conjugation of a ligand precursor to a water-soluble block copolymer through dynamic covalent bonds leads to the dehydration and micellization of the functionalized polymer. Reversible reaction facilitates the permeation of metal ions into core-shell interfaces. Conversely, metal-coordination promotes reaction over the interfaces. Cu(ii)-coordination occurs overwhelmingly inside each isolated micelle. However, Zn(ii)-coordination induced a directional self-assembly whose nanostructures evolve stepwise from nanorods, nanowires, necklaces, and finally to supracolloidal networks scaling-up to several tens of micrometres. Post-reactions of simultaneous dynamic covalent bond conversion and Zn(ii)-coordination over the core-shell interfaces endow these supracolloidal networks with a huge specific surface area for hydrophobic dative metal centres accessible to substrates in water. Water-soluble shells play important roles in directional supracolloidal assembly and in the stabilization of nanostructures. Thus the directional self-assembly provides a versatile platform to produce metallo-hybridized nanomaterials that are promising as enzyme-inspired aqueous catalysts.

Self-Assembly Process of Dodecanuclear Pt(II)-Linked Cyclic Hexagon

The self-assembly process of a Pt(II)-linked hexagonal macrocycle consisting of six linear dinuclear Pt(II) units and six organic ditopic bent ligands was investigated. The process was monitored by (1)H NMR, and the intermediates in the self-assembly were analyzed by the n-k analysis. It was found that a 1:2 complex of a dinuclear Pt(II) unit and an organic ditopic ligand was exclusively observed as an intermediate with a certain lifetime and that the reaction of the 1:2 complex is the rate-determining step in the supramolecular macrocycle formation. The key 1:2 complex was unambiguously characterized by (1)H and DOSY NMR and ESI-TOF mass measurement.

Gemini supra-amphiphiles with finely-controlled self-assemblies

Novel gemini supra-amphiphiles, [Mim-4-Mim][DBS](2) and [Mim-4-Mim][DS](2), were facilely constructed. A slight variation of building blocks can effectively modulate the driving forces for the fabrication of gemini supra-amphiphiles, thus leading to the fine control of subsequent self-assemblies. [Mim-4-Mim][DS](2), constructed via electrostatic attraction, tends to form micelles and hexagonal liquid crystals. Rich lamellar structures, including unilamellar and multilamellar vesicles, planar bilayers, and lamellar liquid crystals can be formed by [Mim-4-Mim][DBS](2), which is constructed through electrostatic and π-π stacking interactions. With increasing temperatures, [Mim-4-Mim][DBS](2) exhibits interesting phase separation in the L(a) phase, behaving like common nonionic surfactants. The cross-linking between vesicles, where the "bola-type" [Mim-4-Mim](2+) cations act as the bridges, was found to promote the elongation of aggregates until the occurrence of phase separation.

Recent advances in the construction of fluorescent metallocycles and metallocages via coordination-driven self-assembly

During the last few years, the construction of fluorescent metallocycles and metallocages has attracted considerable attention because of their wide applications in fluorescence detection of metal ions, anions, or small molecules, mimicking complicated natural photo-processes, and preparing photoelectric devices, etc. This perspective focuses on the recent advances in the construction of a variety of fluorescent metallocycles and metallocages via coordination-driven self-assembly. In addition, the fluorescence properties and the applications of these organometallic architectures have also been discussed.

Well-defined nano-sunflowers formed by self-assembly of a rod-coil amphiphile in water and their morphology transformation based on a water-soluble pillar[5]arene

Well-defined nano-sunflowers were constructed by self-assembling a rod-coil amphiphile in water, and their morphologies transformed by addition of a water soluble pillar[5]arene and Ag2O were also investigated.

Luminescent platinum(ii) complexes with self-assembly and anti-cancer properties: hydrogel, pH dependent emission color and sustained-release properties under physiological conditions

Luminescent platinum(ii) complexes show anti-cancer and pH-dependent self-assembly and sustained-release properties under physiological conditions.

Supramolecular interactions are of paramount importance in biology and chemistry, and can be used to develop new vehicles for drug delivery. Recently, there is a surge of interest on self-assembled functional supramolecular structures driven by intermolecular metal–metal interactions in cellular conditions. Herein we report a series of luminescent Pt(ii) complexes [Pt(C^N^N^pyr)(C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> NR)]⁺ [HC^N^N^pyr = 2-phenyl-6-(1H-pyrazol-3-yl)-pyridine)] containing pincer type ligands having pyrazole moieties. These Pt(ii) complexes exert potent cytotoxicity to a panel of cancer cell lines including primary bladder cancer cells and display strong phosphorescence that is highly sensitive to the local environment. The self-assembly of these complexes is significantly affected by pH of the solution medium. Based on TEM, SEM, ESI-MS, absorption and emission spectroscopy, and fluorescence microscopy together with cell based assays, [Pt(C^N^N^pyr)(C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> NR)]⁺ complexes were observed to self-assemble into orange phosphorescent polymeric aggregates driven by intermolecular Pt(ii)–Pt(ii) and ligand–ligand interactions in a low-pH physiological medium. Importantly, the intracellular assembly and dis-assembly of [Pt(C^N^N^pyr)(C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> NR)]⁺ are accompanied by change of emission color from orange to green. These [Pt(C^N^N^pyr)(C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> NR)]⁺ complexes accumulated in the lysosomes of cancer cells, increased the lysosomal membrane permeability and induced cell death. One of these platinum(ii) complexes formed hydrogels which displayed pH-responsive and sustained release properties, leading to low-pH-stimulated and time-dependent cytotoxicity towards cancer cells. These hydrogels can function as vehicles to deliver anti-cancer agent cargo, such as the bioactive natural products studied in this work.

Bipyridine hydrogel for selective and visible detection and absorption of Cd(2+)

Herein, we report for the first time the use of bipyridine-based hydrogel for selective and visible detection and absorption of Cd(2+). At low concentrations, hydrogelator 1 was applied for selective detection of Cd(2+) in vitro and in living cells with high sensitivity. In the absence of metal ions, 1 is nonfluorescent at 470 nm. Upon addition of metal ions, 1 selectively coordinates to Cd(2+), causing an 86-fold increase of fluorescence intensity at 470 nm via the chelation enhanced fluorescence (CHEF) effect, as revealed by first-principles simulations. At 1.5 wt% and pH 5.5, 1 self-assembles into nanofibers to form hydrogel Gel I. Since Cd(2+) could actively participate in the hydrogelation and promote the self-assembly, we also successfully applied Gel I for visible detection and absorption of Cd(2+). With these excellent properties, Gel I is expected to be explored as one type of versatile biomaterial for not only environmental monitoring but also for pollution treatment in the near future.

Controlled topologies and self-assembly behaviors of oligomeric supra-amphiphiles

Fine control of the topology and self-assembly behavior of oligomeric supra-amphiphiles was achieved by switching hydrogen bonding “on” and “off”.

Self-assembly of benzothiadiazole-functionalized dinuclear platinum acetylide bolaamphiphiles for bio-imaging application

Benzothiadiazole-functionalized dinuclear platinum(ii) acetylide bolaamphiphiles have been demonstrated to form nanoparticles in protic solvents, serving as novel fluorescent labels for bio-imaging applications with good biocompatibility and sufficient stability.

Macrocyclic amphiphiles

This review describes recent results in the investigation of macrocyclic amphiphiles, which are classified based on different macrocyclic frameworks including cyclodextrins, calixarenes, cucurbiturils, pillararenes, and other macrocycles involved.

Co-assembly of two types of complementary dendritic units into amphiphilic supramolecular complexes capable of hosting guest molecules

Novel amphiphilic supramolecular complexes with two types of complementary dendritic units could encapsulate hydrophilic guests with excellent aggregating encapsulation performances.

A pH-responsive amphiphilic supramolecular graft copolymer constructed by crown ether based molecular recognition

Based on the bis(m-phenylene)-32-crown-10/paraquat molecular recognition motif in water, we have successfully prepared an amphiphilic supramolecular graft copolymer by the combination of modified hydrophilic poly(ethylene oxide) and hydrophobic polystyrene. It could self-assemble into pH-responsive bilayer vesicles in water.

A novel supramolecular polymer gel constructed by crosslinking pillar[5]arene-based supramolecular polymers through metal–ligand interactions

A novel heteroditopic A–B monomer was synthesized and used to construct linear supramolecular polymers utilizing pillar[5]arene-based host–guest interactions. Upon addition of Cu²⁺ ions, a supramolecular polymer gel formed through metal–ligand interactions.

A supramolecular ladder polymer prepared by hydrogen bonding-mediated self-assembly of a metallomacrocycle

A defect-free supramolecular ladder polymer was prepared by H-bond-mediated self-assembly of a metallocycle 1 as determined by NMR, viscometry and dynamic laser light scattering studies.

Well-defined supramolecular polymers based on orthogonal hydrogen-bonding and host–guest interactions

Two architecturally controlled supramolecular polymers have been fabricated via the concurrent integration of orthogonal non-covalent recognition motifs, demonstrating significant chain topological-dependent supramolecular polymerization behaviors.

Creation of hollow microtubular iron oxalate dihydrate induced by a metallo-supramolecular micelle based on the self-assembly of potassium ferrioxalate and sodium dodecyl sulphate

A novel metallo-supramolecular micelle PF–SDS–SM was formed at room temperature through the self-assembly of potassium ferrioxalate and sodium dodecyl sulphate.