Self-assembly of nanostructured materials through irreversible covalent bond formation

Dual-Signal Chemical Exchange Saturation Transfer (Dusi-CEST): An Efficient Strategy for Visualizing Drug Delivery Monitoring in Living Cells

We report a dual-signal chemical exchange saturation transfer (Dusi-CEST) strategy for drug delivery and detection in living cells. The two signals can be detected by operators in complex environments. This strategy is demonstrated on a cucurbit[6]uril (CB[6]) nanoparticle probe, as an example. The CB[6] probe is equipped with two kinds of hydrophobic cavities: one is found inside CB[6] itself, whereas the other exists inside the nanoparticle. When the probe is dispersed in aqueous solution as part of a hyperpolarized 129Xe NMR experiment, two signals appear at two different chemical shifts (100 and 200 ppm). These two resonances correspond to the NMR signals of 129Xe in the two different cavities. Upon loading with hydrophobic drugs, such as paclitaxel, for intracellular drug delivery, the two resonances undergo significant changes upon drug loading and cargo release, giving rise to a metric enabling the assessment of drug delivery success. The simultaneous change of Dusi-CEST likes a mobile phone that can receive both LTE and Wi-Fi signals, which can help reduce the occurrence of false positives and false negatives in complex biological environments and help improve the accuracy and sensitivity of single-shot detection.

Light-driven self-assembly of spiropyran-functionalized covalent organic framework

Controlling the number of molecular switches and their relative positioning within porous materials is critical to their functionality and properties. The proximity of many molecular switches to one another can hinder or completely suppress their response. Herein, a synthetic strategy involving mixed linkers is used to control the distribution of spiropyran-functionalized linkers in a covalent organic framework (COF). The COF contains a spiropyran in each pore which exhibits excellent reversible photoswitching behavior to its merocyanine form in the solid state in response to UV/Vis light. The spiro-COF possesses an urchin-shaped morphology and exhibits a morphological transition to 2D nanosheets and vesicles in solution upon UV light irradiation. The merocyanine-equipped COFs are extremely stable and possess a more ordered structure with enhanced photoluminescence. This approach to modulating structural isomerization in the solid state is used to develop inkless printing media, while the photomediated polarity change is used for water harvesting applications.

Structural Quantification of the Surface-Confined Metal-Organic Precursors Simulated with the Lattice Monte Carlo Method

The diversity of surface-confined metal-organic precursor structures, which recently have been observed experimentally, poses a question of how the individual properties of a molecular building block determine those of the resulting superstructure. To answer this question, we use the Monte Carlo simulation technique to model the self-assembly of metal-organic precursors that precede the covalent polymerization of halogenated PAH isomers. For this purpose, a few representative examples of low-dimensional constructs were studied, and their basic structural features were quantified using such descriptors as the orientational order parameter, radial distribution function, and one- and two-dimensional structure factors. The obtained results demonstrated that the morphology of the precursor (and thus the subsequent polymer) could be effectively tuned by a suitable choice of molecular parameters, including size, shape, and intramolecular distribution of halogen substituents. Moreover, our theoretical investigations showed the effect of the main structural features of the precursors on the related indirect characteristics of these constructs. The results reported herein can be helpful in the custom designing and characterization of low-dimensional polymers with adjustable properties.

Hierarchical Materials from High Information Content Macromolecular Building Blocks: Construction, Dynamic Interventions, and Prediction

Hierarchical materials that exhibit order over multiple length scales are ubiquitous in nature. Because hierarchy gives rise to unique properties and functions, many have sought inspiration from nature when designing and fabricating hierarchical matter. More and more, however, nature's own high-information content building blocks, proteins, peptides, and peptidomimetics, are being coopted to build hierarchy because the information that determines structure, function, and interfacial interactions can be readily encoded in these versatile macromolecules. Here, we take stock of recent progress in the rational design and characterization of hierarchical materials produced from high-information content blocks with a focus on stimuli-responsive and "smart" architectures. We also review advances in the use of computational simulations and data-driven predictions to shed light on how the side chain chemistry and conformational flexibility of macromolecular blocks drive the emergence of order and the acquisition of hierarchy and also on how ionic, solvent, and surface effects influence the outcomes of assembly. Continued progress in the above areas will ultimately usher in an era where an understanding of designed interactions, surface effects, and solution conditions can be harnessed to achieve predictive materials synthesis across scale and drive emergent phenomena in the self-assembly and reconfiguration of high-information content building blocks.

Macrocycle-Surfaced Polymer Nanocapsules: An Emerging Paradigm for Biomedical Applications

In the recent decade, macrocycle-surfaced polymer nanocapsules have been developed and studied as potential drug carriers. In particular, a unique group of these nanocapsules were constructed from a covalently self-assembled polymer network based on several classic macrocycles including cucurbituril, pillararene, and calixarene. The unique structure of these nanocapsules consists of a liquid or solid core and a shell laced with macrocycles in which the macrocycles not only act as the shell matrix of the nanocapsules but also allow further facile, modular functionalization via host-guest interactions with guest-tagged molecules. More interestingly, when a responsive cross-linker was introduced between the macrocycles, the payload inside the nanocapsules could be selectively released in the presence of typical hallmarks of certain diseases, which is of great interest for biomedical applications. In this Topical Review, macrocycle-surfaced polymer nanocapsules derived from covalently self-assembled polymer networks are introduced systemically with a focus on the molecular design and biomedical applications.

Landscaping Covalent Organic Framework Nanomorphologies

The practical utilization of covalent organic frameworks (COFs) with manipulation at the atomic and molecular scale often demands their assembly on the nano-, meso-, and macroscale with precise control. Consequently, synthetic approaches that establish the ability to control the nucleation and growth of COF crystallites and their self-assembly to desired COF nanomorphologies have drawn substantial attention from researchers. On the basis of the dimensionality of the COF morphologies, we can categorize them into zero- (0-D), one- (1-D), two- (2-D), and three-dimensional (3-D) nanomorphologies. In this perspective, we summarize the reported synthetic strategies that enable precise control of the COF nanomorphologies' size, shape, and dimensionality and reveal the impact of the dimensionalities in their physicochemical properties and applications. The aim is to establish a synergistic optimization of the morphological dimensionality while keeping the micro- or mesoporosity, crystallinity, and chemical functionalities of the COFs in perspective. A detailed knowledge along the way should help us to enrich the performance of COFs in a variety of applications like catalysis, separation, sensing, drug delivery, energy storage, etc. We have discussed the interlinking between the COF nanomorphologies via the transmutation of the dimensionalities. Such dimensionality transmutation could lead to variation in their properties during the transition. Finally, the concept of constructing COF superstructures through the combination of two or more COF nanomorphologies has been explored, and it could bring up opportunities for developing next-generation innovative materials for multidisciplinary applications.

Nanomaterials: The New Antimicrobial Magic Bullet

Bacterial infections are a significant cause of mortality and morbidity worldwide, despite decades of use of numerous existing antibiotics and constant efforts by researchers to discover new antibiotics. The emergence of infections associated with antibiotic-resistant bacterial strains, has amplified the pressure to develop additional bactericidal therapies or new unorthodox approaches that can deal with antimicrobial resistance. Nanomaterial-based strategies, particularly those that do not rely on conventional small-molecule antibiotics, offer promise in part due to their ability to dodge existing mechanisms used by drug-resistant bacteria. Therefore, the use of nanomaterial-based formulations has attracted attention in the field of antibiotic therapy. In this Review, we highlight novel and emerging nanomaterial-based formulations along with details about the mechanisms by which nanoparticles can target bacterial infections and antimicrobial resistance. A detailed discussion about types and the activities of nanoparticles is presented, along with how they can be used as either delivery systems or as inherent antimicrobials, or a combination of both. Lastly, we highlight some toxicological concerns for the use of nanoparticles in antibiotic therapies.

Bioinspired photo-crosslinkable self-assembling peptides with pH-switchable "on-off" luminescence

Significant progress has been made in peptide self-assembly over the past two decades; however, the in situ cross-linking of self-assembling peptides yielding better performing nanomaterials is still in its infancy. Indeed, self-assembling peptides (SAPs), relying only on non-covalent interactions, are mechanically unstable and susceptible to solvent erosion, greatly hindering their practical application. Herein, drawing inspiration from the biological functions of tyrosine, we present a photo-cross-linking approach for the in situ cross-linking of a tyrosine-containing LDLK12 SAP. This method is based on the ruthenium-complex-catalyzed conversion of tyrosine to dityrosine upon light irradiation. We observed a stable formation of dityrosine cross-linking starting from 5 minutes, with a maximum peak after 1 hour of UV irradiation. Furthermore, the presence of a ruthenium complex among the assembled peptide bundles bestows unusual fluorescence intensity stability up to as high as 42 °C, compared to the bare ruthenium complex. Also, due to a direct deprotonation-protonation process between the ruthenium complex and SAP molecules, the fluorescence of the photo-cross-linked SAP is capable of exhibiting "off-on-off-on" luminescence switchable from acid to basic pH. Lastly, we showed that the photo-cross-linked hydrogel exhibited enhanced mechanical stability with a storage modulus of ∼26 kPa, due to the formation of a densely entangled fibrous network of SAP molecules through dityrosine linkages. As such, this ruthenium-mediated photo-cross-linked SAP hydrogel could be useful in the design of novel tyrosine containing SAP materials with intriguing potential for biomedical imaging, pH sensing, photonics, soft electronics, and bioprinting.

Amphiphilic Fullerene-BODIPY Photosensitizers for Targeted Photodynamic Therapy

Nanotheranostic tailor-made carriers are potent platforms for the treatment of cancer that propound a number of advantages over conventional agents for photodynamic therapy (PDT). Herein, four new heavy atom free amphiphilic glucose-BODIPY-fullerene dyads (14-17) endowed with carbohydrate units in the styryl units, which can also form nanomicelles (14-17NM) with Tween 80 for PDT are reported. Glucose-BODIPY-fullerene systems (14-17) and related nanomicelles (14-17NM) have been prepared to emcee efficient singlet oxygen generation upon light irradiation. In vitro anti-tumor effects of the compounds 14-17 and 14-17NM in the presence of light and in darkness have been investigated with K562 human chronic myelogenous leukemia suspension cells. Anti-tumor toxicity upon light irradiation was due to the formation of singlet oxygen and reactive oxygen species (ROS). This study may provide an accomplished example of efficient PDT applications based on nanovehicles fabricated with universal spin converter, fullerene, light harvesting unit, BODIPY dyes conjugated with targeting units to fight against cancer.

Biodegradable PCL-b-PLA Microspheres with Nanopores Prepared via RAFT Polymerization and UV Photodegradation of Poly(Methyl Vinyl Ketone) Blocks

Biodegradable triblock copolymers based on poly(ε-caprolactone) (PCL) and poly(lactic acid) (PLA) were synthesized via ring-opening polymerization of L-lactide followed by reversible addition–fragmentation chain-transfer (RAFT) polymerization of poly(methyl vinyl ketone) (PMVK) as a photodegradable block, and characterized by FT-IR and ¹H NMR spectroscopy for structural analyses, and by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) for their thermal properties. Porous, biodegradable PCL-b-PLA microspheres were fabricated via the oil/water (O/W) emulsion evaporation method, followed by photodegradation of PMVK blocks by UV irradiation. The macro-chain transfer agent (CTA) synthesized by reacting a carboxylic-acid-terminated CTA—S-1-dodecyl-S′-(a,a′-dimethyl-a′′-acetic acid)trithiocarbonate (DDMAT)—with a hydroxyl-terminated PCL-b-PLA block copolymer was used to synthesize well-defined triblock copolymers with methyl vinyl ketone via RAFT polymerization with controlled molecular weights and narrow polydispersity. Gel permeation chromatography traces indicated that the molecular weight of the triblock copolymer decreased with UV irradiation time because of the photodegradation of the PMVK blocks. The morphology of the microspheres before and after UV irradiation was investigated using SEM and videos of three-dimensional confocal laser microscopy, showing a change in their surface texture from smooth to rough, with high porosity owing to the photodegradation of the PMVK blocks to become porous templates.

Photoinduced Self-Assembly of Carbon Nitride Quantum Dots

The study of nanocrystal self-assembly into superlattices or superstructures is of great significance in nanoscience. Carbon nitride quantum dots (CNQDs), being a promising new group of nanomaterials, however, have hardly been explored in their self-organizing behavior. Here we report of a unique irradiation-triggered self-assembly and recrystallization phenomenon of crystalline CNQDs (c-CNQDs) terminated by abundant oxygen-containing groups. Unlike the conventional self-assembly of nanocrystals into ordered superstructures, the photoinduced self-assembly of c-CNQDs resembles a "click reaction" process of macromolecules, in which the activated -OH and -NH₂ functional groups along the perimeters initiate cross-linking of adjacent QDs through a photocatalytic effect. Our findings unveil fundamental physiochemical features of CNQDs and open up new possibilities of manipulating carbon nitride nanomaterials via controlled assembly. Prospects for potential applications are discussed as well.

Template-Free Self-Assembly of Two-Dimensional Polymers into Nano/Microstructured Materials

In the past few decades, enormous efforts have been made to synthesize covalent polymer nano/microstructured materials with specific morphologies, due to the relationship between their structures and functions. Up to now, the formation of most of these structures often requires either templates or preorganization in order to construct a specific structure before, and then the subsequent removal of previous templates to form a desired structure, on account of the lack of “self-error-correcting” properties of reversible interactions in polymers. The above processes are time-consuming and tedious. A template-free, self-assembled strategy as a “bottom-up” route to fabricate well-defined nano/microstructures remains a challenge. Herein, we introduce the recent progress in template-free, self-assembled nano/microstructures formed by covalent two-dimensional (2D) polymers, such as polymer capsules, polymer films, polymer tubes and polymer rings.

Chemical kinetic mechanisms and scaling of two-dimensional polymers via irreversible solution-phase reactions

Two-dimensional (2D) polymers are extended networks of multi-functional repeating units that are covalently linked together but confined to a single plane. The past decade has witnessed a surge in interest and effort toward producing and utilizing 2D polymers. However, facile synthesis schemes suitable for mass production are yet to be realized. In addition, unifying theories to describe the 2D polymerization process, such as those for linear polymers, have not yet been established. Herein, we perform a chemical kinetic simulation to study the recent synthesis of 2D polymers in homogeneous solution with irreversible chemistry. We show that reaction sites for polymerization in 2D always scale unfavorably compared to 3D, growing as molecular weight to the 1/2 power vs 2/3 power for 3D. However, certain mechanisms can effectively suppress out-of-plane defect formation and subsequent 3D growth. We consider two such mechanisms, which we call bond-planarity and templated autocatalysis. In the first, although single bonds can easily rotate out-of-plane to render polymerization in 3D, some double-bond linkages prefer a planar configuration. In the second mechanism, stacked 2D plates may act as van der Waals templates for each other to enhance growth, which leads to an autocatalysis. When linkage reactions possess a 1000:1 selectivity (γ) for staying in plane vs rotating, solution-synthesized 2D polymers can have comparable size and yield with those synthesized from confined polymerization on a surface. Autocatalysis could achieve similar effects when self-templating accelerates 2D growth by a factor β of 10⁶. A combined strategy relaxes the requirement of both mechanisms by over one order of magnitude. We map the dependence of molecular weight and yield for the 2D polymer on the reaction parameters, allowing experimental results to be used to estimate β and γ. Our calculations show for the first time from theory the feasibility of producing two-dimensional polymers from irreversible polymerization in solution.

Supramolecular nanomedicine for selective cancer therapy via sequential responsiveness to reactive oxygen species and glutathione

Cancer cells are generally immersed in an oxidative stress environment with a high intracellular reduction level. Thus, nanocarriers with sequential responsiveness to oxidative and reductive species, matching the traits of high oxidation in the tumor tissue microenvironment and high reduction potential inside cancer cells, are highly desired for specific cancer therapy. Herein, we report a supramolecular nanomedicine comprised of a reduction-responsive nanoparticle (NP) core whose surface was modified by an oxidation-responsive polyethylene glycol (PEG) derivative via strong host-guest interactions. In this delicate design, the PEGylation of NPs not only reduced their immunogenicity and extended systemic circulation, but also enabled oxidation-responsive de-PEGylation in the tumor tissues and subsequent intracellular payload release in response to glutathione (GSH) inside tumor cells. As a proof of concept, this supramolecular nanomedicine exhibited specific chemotherapeutic effects against cancer in vitro and in vivo with a decent safety profile.

ROS-initiated chemiluminescence-driven payload release from macrocycle-based Azo-containing polymer nanocapsules

Reactive oxygen species (ROS) overproduction is involved in many pathological processes, particularly in inflammatory diseases. Therefore, ROS-responsive nanocarriers for specific drug release have been highly sought after. Herein we developed a ROS-responsive drug delivery system based on covalently self-assembled polymer nanocapsules (Azo-NCs) formed via crosslinking macrocyclic cucurbit[6]urils by a photo-sensitive azobenzene derivative (Azo). Luminol, a chemiluminescent molecule activatable by ROS, was co-loaded into Azo-NCs together with a therapeutic payload. When exposed to high ROS concentration that is typically encountered in inflammatory cells or tissues, the ROS-initiated blue chemiluminescence of luminol drives photoisomerization of the Azo groups within Azo-NCs, leading to Azo-NCs' surface transformation and distortion of the nanostructure, and subsequent payload release. As a proof-of-concept, ROS-responsive payload release from luminol-loaded Azo-NCs in inflammatory cells and zebrafish was demonstrated, showing promising anti-inflammatory effects in vitro and in vivo.

Single-Layered Chiral Nanosheets with Dual Chiral Void Spaces for Highly Efficient Enantiomer Absorption

Although considerable effort in recent years has been devoted to the development of two-dimensional nanostructures, single-layered chiral sheet structures with a lateral assembly of discrete clusters remain elusive. Here, we report single-layered chiral 2D sheet structures with dual chiral void spaces in which discrete clusters of planar aromatic segments are arranged with in-plane AB order in aqueous methanol solution. The chirality of the sheet is induced by the slipped-cofacial stacks of rectangular plate-like aromatic segments in the discrete clusters which are arranged laterally with up and down packing, resulting in dual chiral void spaces. The chiral nanosheets function as superfast enantiomer separation nanomaterials, which rapidly absorb a single enantiomer from a racemic mixture with greater than 99 % ee.

Nanoassembled Peptide Biosensors for Rapid Detection of Matrilysin Cancer Biomarker

Early detection of cancer is likely to be one of the most effective means of reducing the cancer mortality rate. Hence, simple and ultra-quick methods for noninvasive detection of early-stage tumors are highly sought-after. In this study, a nanobiosensing platform with a rapid response time of nearly 30 s is introduced for the detection of matrilysin-the salivary gland cancer biomarker-with a limit of detection as low as 30 nm. This sensing platform is based on matrilysin-digestible peptides that bridge gold nanoparticle (AuNPs) cores (≈30-50 nm) and carbon quantum dot (CDs) satellites (≈9 nm). A stepwise synthesis procedure is used for self-assembly of AuNP-peptide-CDs, ensuring their long-term stability. The AuNP-peptide-CDs produce ideal optical signals, with noticeable fluorescence quenching effects. Upon peptide cleavage by matrilysin, CDs leave the surface of AuNPs, resulting in ultra-fast detectable violet and visible fluorescent signals.

Morphological Transformation between Orthogonal Dynamic Covalent Self-Assembly of Imine-Boroxine Hybrid Polymer Nanocapsules and Thin Films via Linker Exchange

Orthogonal dynamic covalent self-assembly is used as a facile method for constructing polymer hollow nanocapsules (NCs) and thin films. The bifunctional precursor 4-formylphenylboronic acid is symmetrically installed with a boronic acid group for the boroxine linkage, and an aldehyde group for the Schiff base reaction which can react with twofold symmetry linkers ethylenediamine and para phenylenediamine to attain polymer NCs and nanosheets. Owing to the reversibility of the imine linkages, the mutual morphological transformation between polymer NCs and thin films via an amine-imine-exchange strategy is successfully achieved. Multiple reversible covalent bonds allow the control the release of the load in polymer NCs using different techniques. This may be useful for designing stimulus-responsive smart materials.

Covalent co-assembly between resilin-like polypeptide and peptide amphiphile into hydrogels with controlled nanostructure and improved mechanical properties

Covalent co-assembly holds great promise for the fabrication of hydrogels with controllable nanostructure, versatile chemical composition, and enhanced mechanical properties given its relative simplicity, high efficiency, and bond stability. This report describes our approach to designing functional multicomponent hydrogels based on photo-induced chemical interactions between an acrylamide-functionalized resilin-like polypeptide (RLP) and a peptide amphiphile (PA). Circular dichroism (CD) spectroscopy, electron microscopy, and amplitude sweep rheology were used to demonstrate that the co-assembled hydrogel systems acquired distinct structural conformations, tunable nanostructures, and enhanced elasticity in a PA concentration-dependent manner. We envisage the use of these materials in numerous biomedical applications such as controlled drug release systems, microfluidic devices, and scaffolds for tissue engineering.

Solving the COF trilemma: towards crystalline, stable and functional covalent organic frameworks

Strategies in covalent organic frameworks and adjacent fields are highlighted for designing stable, ordered and functional materials.

Cucurbit[8]uril-based supramolecular nanocapsules with a multienzyme-cascade antioxidative effect

A supramolecular nanocapsule was constructed by the ternary host-guest complexation of azobenzene (Azo) and methylviologen (MV) to cucurbit[8]uril (CB[8]) and the subsequent self-assembly. The supramolecular nanocapsule with both glutathione peroxidase (GPx) and superoxide dismutase (SOD) activities can mimic the intracellular enzymatic reactive oxygen species (ROS) defense system.

Constructing antibacterial polymer nanocapsules based on pyridine quaternary ammonium salt

Excessive use of antibiotics accelerates the development and spread of drug-resistant strains, which is a huge challenge for the field of medical health worldwide. Quaternary ammonium salt polymers are considered to be membrane-active bactericidal groups with vast potential to control bacterial infections and inhibit drug resistance. Herein, we report on the creative synthesis and characterization of novel antimicrobial polymer nanocapsules based on pyridine quaternary ammonium salt. The antimicrobial polymer nanocapsules were formed by reaction of C₃ symmetrical rigid monomer 2,4,6‑tris(4‑pyridyl)‑1,3,5‑triazine (TPT) and a flexible linker 1,2‑dibromoethane. The polymer nanocapsule was constructed as a cationic hollow sphere composed of a two-dimensional sheet whose main chain was formed by the pyridine quaternary ammonium salt, and a part of the bromide ion was adsorbed on the sphere. This hollow nanocapsule was characterized in detail by DLS, SEM, TEM, AFM, EDS and EA. When the cationic polymer nanocapsules are close to the Gram-negative Escherichia coli, the negatively charged phospholipid molecules in the bacterial membrane are attracted to the cationic surface and lead to rupture of cells. SEM confirmed the breakage of Escherichia coli membranes. The minimum inhibitory concentration was found to be 0.04 mg/mL, and the minimum bactericidal concentration was 0.1 mg/mL. Our experiments demonstrated that the adsorption of negatively charged phospholipid molecules on the surface of the pyridine quaternary ammonium salt polymer can kill Gram-negative bacteria without inserting quaternary ammonium salt hydrophobic groups into the cell membrane.

Deciphering and Controlling Structural and Functional Parameters of the Shells in Vesicle-Templated Polymer Nanocapsules

Vesicle-templated nanocapsules are prepared by polymerization of hydrophobic acrylic monomers and cross-linkers in the hydrophobic interior of self-assembled bilayers. Understanding the mechanism of capsule formation and the influence of synthetic parameters on the structural features and functional performance of nanocapsules is critical for the rational design of functional nanodevices, an emerging trend of application of the nanocapsule platform. This study investigated the relationship between basic parameters of the formulation and synthesis of nanocapsules and structural and functional characteristics of the resulting structures. Variations in the monomer/surfactant ratio, temperature of polymerization, and the molar fraction of the free-radical initiators were investigated with a multipronged approach, including shell thickness measurements using small-angle neutron scattering, evaluation of the structural integrity of nanocapsules with scanning electron microscopy, and determination of the retention of entrapped molecules using absorbance and fluorescence spectroscopy. Surprisingly, the thickness of the shells did not correlate with the monomer/surfactant ratio, supporting the hypothesis of substantial stabilization of the surfactant bilayer with loaded monomers. Decreasing the temperature of polymerization had no effect on the spherical structure of nanocapsules but resulted in progressively lower retention of entrapped molecules, suggesting that a spherical skeleton of nanocapsule forms rapidly, followed by filling the gaps to create the structure without pinholes. Lower content of initiators resulted in slower reactions, outlining the baseline conditions for practical synthetic protocols. Taken together, these findings provide insights into the formation of nanocapsules and offer methods for controlling the properties of nanocapsules in viable synthetic methods.

Supramolecular nanostructures constructed by rod-coil molecular isomers: effect of rod sequences on molecular assembly

Coil-rod-coil molecules, composed of flexible oligoether chains and conjugated rod blocks, have a well-known ability to produce various nanostructures in bulk and in aqueous solution. Herein we report the synthesis and self-assembly of coil-rod-coil molecules based on the sequence of the rod building block and the type of oligoether coil chain. These molecules consist of conjugated rod segments, which are composed of biphenyl, terphenyl, and acetylenic bonds, with chiral oligoether chains as flexible coil segments. The experimental results imply that the sequence of the rod segments markedly influences the self-assembled nanostructures of coil-rod-coil molecules in the bulk state, and that the type of coil chain strongly affects the morphology of the supramolecular nanoassemblies of these molecules in aqueous solution. In the bulk state, molecules 1a and 1b, which contain biphenyl units connected to the end of the coil segments self-organize into a hexagonal perforated lamellar phase, and oblique columnar and body-centred tetragonal structures, respectively. However, molecules 2a and 2b bearing terphenyl units linked to the end of the coil segments self-assemble into lamellar, hexagonal perforated lamellar and hexagonal columnar structures. In aqueous solution, rod-coil molecular isomers with linear chiral oligoether chains self-assemble into helical nanofibres of various lengths. Meanwhile, isomers with chiral oligoether dendron chains self-organize into sheet-like nanoribbons of different sizes.

Facile Preparation of Cucurbit[6]uril-Based Polymer Nanocapsules for Targeted Photodynamic Therapy

Covalently self-assembled polymer nanocapsules (NCs) based on cucurbit[6]uril have been previously prepared and their applications in payload delivery and bioimaging have been demonstrated, showing significant potentials. However, the preparation of these NCs often requires laborious and tedious multistep reactions, including a low-yield conversion of perhydroxycucurbit[6]uril to perallyloxycucurbit[6]uril, subsequent photopolymerization of perallyloxycucurbit[6]uril with dithiol linkers, and two additional steps of treatment to remove disulfide loops and create cationic sulfoniums. Herein, we report a novel, facile approach leading to cucurbit[6]uril-based polymer NCs via direct alkylation of perhydroxycucurbit[6]uril with a ditopic linker, thereby saving significant time and efforts, which may lead to significant expansion in investigations of these unique materials in various applications, particularly biomedical sciences. As a proof of concept, we have further demonstrated that a photosensitive therapeutic payload, such as chlorin e6, may get encapsulated inside the NCs for improved, targeted photodynamic therapy against cancer cells.

Exfoliating a CdII -Purine Framework: Conversion of Nanosheets-to-Nanofibers and Studies of Elastic and Capacitive Properties

Layered bulk crystals are amenable to exfoliation to yield 2D nanosheets through isolation and intercalation processes, which could be further converted to 1D nanoscale structures. The latter inherit gross morphological and physical properties associated with the precursor structures. Herein, we report three purine-based crystal structures 1, 2, and 3, where 3 is obtained by a single-crystal-to-single-crystal transformation from 2 and is a conformational polymorph of 1. Next, we describe the sonication-assisted liquid exfoliation of 1, a Cd^II -purine coordination framework, into nanosheets and nanofibers in a solvent-dependent process. The exfoliation was carefully studied at low temperatures to ascertain this unique conversion. This work also features the determination of the Young's modulus and surface potential of the bioinspired Cd^II -based nanostructures by using amplitude modulation-frequency modulation atomic force microscopy and Kelvin probe force microscopy, respectively, revealing their interesting elastic and capacitive properties for their possible use in electronics and energy devices. Electron impedance spectroscopy measurements further established a higher value of capacitance for the exfoliated Cd^II framework as compared to the ligand alone.

Constructing Artificial Light-Harvesting Systems by Covalent Alignment of Aggregation-Induced Emission Molecules

The characteristics of chloroplasts harvesting solar energy and conducting energy transfer have inspired chemists to mimic similar processes. However, accurate manipulation to gain regularly displayed antenna chromophores in mimicking chloroplasts is a great challenge. Herein, a rational design is presented that combines orderly arranged chromophores with aggregation-induced emission (AIE) to develop artificial light-harvesting systems. Tetraphenyl ethylene (TPE) molecules, which exhibited strong AIE properties, are considered as building blocks to fabricate high emissive 2D nanosheets and nanovesicles, respectively. Furthermore, the well-aligned TPE molecules are also developed as donor chromophores in light-harvesting processes. After subsequent surface modification by porphyrin molecules as acceptor chromophores, an efficient light-harvesting system has been integrally constructed. This study demonstrates a novel strategy to utilize AIE feature to mimic chloroplasts process in nature.

The delivery of sensitive food bioactive ingredients: Absorption mechanisms, influencing factors, encapsulation techniques and evaluation models

Food-sourced bioactive compounds have drawn much attention due to their health benefits such as anti-oxidant, anti-cancer, anti-diabetes and cardiovascular disease-preventing functions. However, the poor solubility, low stability and limited bioavailability of sensitive bioactive compounds greatly limited their application in food industry. Therefore, numbers of carriers were developed for improving their dispersibility, stability and bioavailability. This review addresses the digestion and absorption mechanisms of bioactive compounds in epithelial cells based on several well-known in vitro and in vivo models. Factors such as environmental stimuli, stomach conditions and mucus barrier influencing the utilization efficacy of the bioactive compounds are discussed. Delivery systems with enhanced utilization efficacy, such as complex coacervates, cross-linked polysaccharides, self-assembled micro-/nano-particles and Pickering emulsions are compared. It is a comprehensive multidisciplinary review which provides useful guidelines for application of bioactive compounds in food industry.

Self-assembly of stimuli-responsive imine-linked calix[4]arene nanocapsules for targeted camptothecin delivery

Here we report template-free synthesis of imine-linked calix[4]arene hollow nanocapsules and their utility in the effective delivery of a poorly soluble cancer drug into tumor cells.

Supramolecular polymer nanocapsules by enzymatic covalent condensation: biocompatible and biodegradable drug-delivery systems for chemo-photothermal anticancer therapy

Supramolecular polymer nanocapsules were constructed by enzymatic covalent condensation and they acted as drug-delivery systems for chemo-photothermal anticancer therapy.

An ultrathin iron-porphyrin based nanocapsule with high peroxidase-like activity for highly sensitive glucose detection

For the first time, an ultrathin iron-porphyrin based polymer nanocapsule with multiple peroxidase-like catalytic centers was constructed by covalently assembling iron-porphyrin monomers; this nanocapsule with a single molecule thickness shell acted as a highly efficient artificial enzyme for mimicking peroxidase. On the basis of the peroxidase-like activity of Fe-TPyP based nanocapsules (Fe-TPyP NCs), a highly sensitive colorimetric sensor for glucose determination was fabricated, the limit of detection was found to be as low as 0.098 μM. This study provided a novel strategy for developing artificial enzymes based on covalently assembled nanostructures. Furthermore, the colorimetric sensor for glucose determination showed potential applications in biomedicine and biology.

Porphyrin Boxes

In order to fabricate efficient molecular photonic devices, it has been a long-held aspiration for chemists to understand and mimic natural light-harvesting complexes where a rapid and efficient transfer of excitation energy between chlorophyll pigments is observed. Synthetic porphyrins are attractive building blocks in this regard because of their rigid and planar geometry, high thermal and electronic stability, high molar extinction, small and tunable band gap, and tweakable optical as well as redox behavior. Owing to these fascinating properties, various types of porphyrin-based architectures have been reported utilizing both covalent and noncovalent approaches. However, it still remains a challenge to construct chemically robust, well-defined three-dimensional porphyrin cages which can be easily synthesized and yet suitable for useful applications both in solution as well as in solid state. Working on this idea, we recently synthesized box-shaped organic cages, which we called porphyrin boxes, by making use of dynamic covalent chemistry of imine condensation reaction between 4-connecting, square-shaped, tetraformylporphyrin and 3-connecting, triangular-shaped, triamine molecules. Various presynthetic, as well as postsynthetic modifications, can be carried out on porphyrin boxes including a variation of the alkyl chain length in their 3-connecting subunit, chemical functionalization, and metalation of the porphyrin core. This can remarkably tune their inherent properties, e.g., solubility, window size, volume, and polarity of the internal void. The porphyrin boxes can therefore be considered as a significant addition to the family of multiporphyrin-based architectures, and because of their chemical stability and shape persistency, the applications of porphyrin boxes expand beyond the photophysical properties of an artificial light-harvesting complex. Consequently, they have been exploited as porous organic cages, where their gas adsorption properties have been investigated. By incorporating them in a lipid bilayer membrane, an iodide selective synthetic ion channel has also been demonstrated. Further, we have explored electrocatalytic reduction of carbon dioxide using Fe(III) metalated porphyrin boxes. Additionally, the precise size and ease of metalation of porphyrin boxes allowed us to utilize them as premade building blocks for creating coordination-based hierarchical superstructures. Considering these developments, it may be worth combining the photophysical properties of porphyrin with the shape-persistent porous nature of porphyrin boxes to explore other novel applications. This Account summarizes our recent work on porphyrin boxes, starting with their design, structural features, and applications in different fields. We also try to provide scientific insight into the future opportunities that these amazing boxes have in store for exploring the still uncharted challenging domains in the field of supramolecular chemistry in a confined space.