Tunable Fluorescence, Morphology, and Antibacterial Behaviors of Conjugated Oligomers via Host-Guest Supramolecular Self-Assembly.

Host-guest supramolecular self-assembly has become one facile but efficient way to regulate the optical properties of conjugated oligomers and construct promising photofunctional materials. Herein, we design two linear conjugated oligomers terminated with two or four pyridinium moieties, which show different 1:1 'head-to-tail' binding patterns with cucurbit[8]uril (CB[8]) to form host-guest supramolecules. After being encapsulated in the hydrophobic cavity of the CB[8] host, the fluorescence emission of the conjugated oligomers undergoes significant changes, resulting in tunable fluorescence color with enhanced quantum yields. Triggered by the aggregation of supramolecules, the regular or rigid binding modes lead to the formation of cuboids and spheroids in nanoscale, respectively. Due to the macrocyclic-confinement effect, the light-driven reactive oxygen species (ROS) production of the host-guest complex is increased significantly, thereby improving the photodynamic antibacterial performance toward Staphylococcus aureus (S. aureus).

Green Synthesis of Antimicrobial Peptide-Protected Silver Nanoclusters with Regulated Antibacterial Behavior.

The antibacterial system based on the silver element has been a very promising antibacterial material. However, the antibacterial activity of silver nanomaterials largely depends on their chemical composition and physical properties. Herein, we prepared ultrasmall silver nanoclusters by directly reducing silver ions with antimicrobial peptide in a green way. The positively charged peptide ligands drove the silver nanoclusters binding to bacteria by electrostatic attraction. Contrary to the large-sized silver nanomaterials, the ultrasmall silver nanoclusters were able to rapidly penetrate bacteria membranes via strong hydrophobic association, significantly promoting the generation of reactive oxygen species, and the subsequent high oxidative stress led to bacterial death. Moreover, the silver nanoclusters with antibacterial peptide ligand exhibited good stability, low cytotoxicity, and long-term antibacterial activity. Besides, synergistic enhancement of silver nanoclusters on antibacterial activity was observed. Therefore, the silver nanoclusters conjugated with the antimicrobial peptide can act as a synergistic antibacterial agent, in which their bio-interactions with bacteria have been regulated to achieve a rapid, long-lasting, and broad-spectrum antibacterial effect.

Protein-Assisted Molybdenum Disulfide as Biomimetic Nanozyme for Antibacterial Application.

Molybdenum-based nanomaterials with variable oxidation states can be developed as nanozyme catalysts. In this work, we developed a one-pot method for the preparation of molybdenum disulfide assisted by protein. Protamine was used as a cationic template to link molybdate anions and form complexes. During hydrothermal synthesis, protamine can affect the nucleation process of molybdenum disulfide and inhibit their aggregation, which facilitates the fabrication of small-sized molybdenum disulfide nanoparticles. Moreover, the abundant amino/guanidyl groups of protamine could both physically adsorb and chemically bond to molybdenum disulfide and further modulate the crystal structures. The optimized size and crystalline structure enabled a higher exposure of active sites, which enhanced the peroxidase-like activity of molybdenum disulfide/protamine nanocomposites. Meanwhile, the antibacterial activity of protamine was retained in the molybdenum disulfide/protamine nanocomposites, which could synergize with the peroxidase-like activity of molybdenum disulfide to kill bacteria. Therefore, the molybdenum disulfide/protamine nanocomposites are good candidates for antibacterial agents with lower chances of antimicrobial resistance. This study establishes an easy way to design artificial nanozymes by compounding suitable components.

Controllable Gold Nanocluster-Emulsion Interface for Direct Cell Penetration and Photothermal Killing.

In the view of their ability to be uptaken by cells, colloidal particles can exert diverse physiological effects and are promising vehicles for the intracellular delivery of biologically active substances. Given that the modulation of biomaterial interfaces greatly facilitates the prediction and control of the corresponding cellular responses, the interfacial behavior of hydrophobic dye-modified gold (Au) nanoclusters (Au NCs) is rationally designed to develop Au NC-containing emulsions and control their biointerfacial interactions with cell membranes. The observed biological performance is indicative of a physical penetration mechanism. The amphiphilic Au NCs decrease the interfacial energy of two immiscible liquids and hinder droplet coalescence to facilitate the formation of emulsions thermodynamically stabilized by dipole-dipole and hydrophobic interactions. Moreover, the amphiphilic Au NCs are localized on the emulsion droplet surface and form segregated interfacial microdomains that adapt to the membrane structure and facilitate the traverse of the emulsions across the cell membrane via direct penetration. Fast penetration coupled with excellent photophysical performance endows the emulsions with multifluorescence tracing and efficient photothermal killing capabilities. The successful change of the interaction mode between NCs and biological objects and the provision of a universal formulation to modulate biointerfacial interactions are expected to inspire new bioapplications.

AIE-Active, Stimuli-Responsive Fluorescent 2D Block Copolymer Nanoplatelets Based on Corona Chain Compression.

Aggregation-induced emission (AIE) represents a powerful tool in nanoscience as a result of enhanced luminescence in the condensed state. Although AIEgenic materials have been utilized in a wide range of applications, well-defined self-assembled nanoparticles with tailorable and uniform dimensions and morphology remain challenging to access. Herein, we use the seeded growth, living crystallization-driven self-assembly (CDSA) method to prepare size-tunable and uniform AIE-active 2D nanoplatelets from amphiphilic block copolymer (BCP) precursors with a crystallizable core-forming block and a corona-forming block to which tetraphenylethene (TPE) groups were covalently grafted as AIE-active pendants. The nanoplatelets were formed as a result of a solvophobicity-induced 1D to 2D morphology preference change, which accompanied the seeded growth of a BCP with a quaternized corona-forming block bearing the TPE luminogen. The 2D nanoplatelets exhibited a solvent-responsive fluorescent emission, and examples with coronas containing homogeneously distributed AIE-active TPE groups and Hg(II)-capturing thymine units exhibited excellent performance as proof-of-concept "turn-on" sensors for Hg(II) detection with a rapid response, high selectivity, and a low detection limit (5-125 × 10-9 M, i.e., 1-25 ppb). The fluorescence intensity was found to be nonlinear with respect to analyte concentration and to increase with the area of the nanoplatelet. This behavior is consistent with a cooperative mechanism based on changes in the steric compression of the corona chains, which gives rise to a restriction of the intramolecular motion (RIM) effect.

Conjugated Molecule-Assisted Supramolecular Hydrogel with Enhanced Antibacterial and Antibiofouling Properties.

The hydrogel using natural and synthetic polymers to create a cross-linking network has drawn attention in diverse bioapplications. However, inhibition of bacterial infection is still a challenge for hydrogel's wide application. In this work, we reported a supramolecular hydrogel with a good antibacterial property built from conjugated molecules. The water-soluble molecular 4,7-bis[9,9-di(2-carboxy-ethyl)-fluoren-2-yl]-2,1,3-benzothiadiazole (OFBTCOOH) physically linked with monomers via hydrophobic interaction. The free-radical polymerized poly(N-acryloyl glycinamide) was hydrogen-bond cross-linked by dual amides in the side chains to form a hydrogel. An adjustable micro-network was obtained by increasing OFBTCOOH with evidence of enhanced intermolecular interaction. The successfully integrated OFBTCOOH could be excited upon light irradiation. The energy of triplet-state excitons of OFBTCOOH transferred to the ground-state oxygen to produce singlet oxygen, which endowed the hydrogel with the antibacterial property. Meanwhile, the superhydrophilic surface of the hydrogel can bind water molecules to form a stable hydration layer, which acted as barriers to resist protein and bacterial adsorption and achieve the anti-biofouling goal. The ease in introducing conjugated polyelectrolytes may provide a formulation to functionalize hydrogels via various physical interactions.

Conjugated Polymer-Functionalized Stretchable Supramolecular Hydrogels to Monitor and Control Cellular Behavior.

Natural extracellular matrix is formed by the assembly of small molecules and macromolecules into a hydrogel-like network that can mechanically support cells and involve in cellular processes. Here, we developed a fluorescent supramolecular hydrogel based on a conjugated oligomer OFBTCO2Na, which facilitated noncovalent assembly through hydrophobic interactions and hydrogen bonds in a molecular scale. The generated dense three-dimensional network endows the supramolecular hydrogel with stretchability and stability. Furthermore, fluorescent OFBTCO2Na in hydrogel acted as a donor, which can excite the acceptor dyes on cells encapsulated in hydrogel via the Förster resonance energy transfer (FRET) mechanism. Investigating the fluorescence signal responsiveness of hydrogel to dynamic mechanical stretching well reflected that enhanced stretching dictated the extent of connection between the cell and matrix, which enables effective FRET at a molecular level and allow spatiotemporally monitoring cell-matrix interactions at the three-dimensional network. Importantly, cells can sense stretch forces by their connection with a hydrogel matrix. The dynamic cell-matrix interaction can be conveniently employed to formulate cell morphology. Therefore, the fluorescent supramolecular hydrogel offers a suitable culture platform not only to investigate cell interactions on interfaces but also to regulate cell behavior at interfaces.

Controlling the Interaction between Fluorescent Gold Nanoclusters and Biointerfaces for Rapid Discrimination of Fungal Pathogens.

Nondestructive detection and discrimination of fungal pathogens is essential for rapid and precise treatment, which further effectively prevents antifungal resistance from overused drugs. In this work, fluorescent gold nanoclusters served as the basis for discriminating Candida species. Varied on surface ligands, these gold nanoclusters demonstrated different optical properties as a result of the perturbation effects of ligands. The biointerface interaction between the surface ligands of gold nanoclusters and the cell walls of Candida species can be constructed, and their restriction on ligands perturbation effect produced enhanced fluorescence signals. Owing to the variation of the cell wall composition, cells of different Candida species demonstrated different degrees of association with the gold nanoclusters, leading to discriminable amounts of fluorescence enhancements. The reverse signal response from these gold nanoclusters gives rise to a synergistic and effective assay that allows identification of Candida species.

Distribution control enables efficient reduced-dimensional perovskite LEDs.

Light-emitting diodes (LEDs) based on perovskite quantum dots have shown external quantum efficiencies (EQEs) of over 23% and narrowband emission, but suffer from limited operating stability1. Reduced-dimensional perovskites (RDPs) consisting of quantum wells (QWs) separated by organic intercalating cations show high exciton binding energies and have the potential to increase the stability and the photoluminescence quantum yield2,3. However, until now, RDP-based LEDs have exhibited lower EQEs and inferior colour purities4-6. We posit that the presence of variably confined QWs may contribute to non-radiative recombination losses and broadened emission. Here we report bright RDPs with a more monodispersed QW thickness distribution, achieved through the use of a bifunctional molecular additive that simultaneously controls the RDP polydispersity while passivating the perovskite QW surfaces. We synthesize a fluorinated triphenylphosphine oxide additive that hydrogen bonds with the organic cations, controlling their diffusion during RDP film deposition and suppressing the formation of low-thickness QWs. The phosphine oxide moiety passivates the perovskite grain boundaries via coordination bonding with unsaturated sites, which suppresses defect formation. This results in compact, smooth and uniform RDP thin films with narrowband emission and high photoluminescence quantum yield. This enables LEDs with an EQE of 25.6% with an average of 22.1 ±1.2% over 40 devices, and an operating half-life of two hours at an initial luminance of 7,200 candela per metre squared, indicating tenfold-enhanced operating stability relative to the best-known perovskite LEDs with an EQE exceeding 20%1,4-6.

Fluorescence "Turn-On" Enzyme-Responsive Supra-Amphiphile Fabricated by Host-Guest Recognition between γ-Cyclodextrin and a Tetraphenylethylene-Sodium Glycyrrhetinate Conjugate.

A novel fluorescence "turn-on" enzyme-responsive supra-amphiphile is developed based on the host-guest recognition between γ-cyclodextrin (γ-CD) and an amphiphilic tetraphenylethene-sodium glycyrrhetinate conjugate (TPE-SGA). The covalent amphiphile TPE-SGA displayed strong fluorescence in aqueous solution owing to the aggregation-induced emission. Upon addition of γ-CD, the fluorescence of TPE-SGA was effectively turned off due to the host-guest recognition with γ-CD prohibiting the aggregation of TPE-SGA in aqueous solution. The as-formed nonfluorescent supra-amphiphile (TPE-SGA/γ-CD) inherited the α-amylase-responsive property of γ-CD. In the presence of α-amylase, the fluorescence of the supra-amphiphile was gradually turned on owing to the hydrolysis of γ-CD, and the fluorescence intensity linearly correlated to the activity of α-amylase. This study enriches the field of supra-amphiphile on the basis of cyclodextrin-based host-guest chemistry and provides a novel strategy to construct fluorescence turn-on functioned self-assemblies. It is anticipated that the fluorescence turn-on supra-amphiphile has potential applications in biological analysis and diagnosis of pancreatic diseases.

Dendritic Micelles with Controlled Branching and Sensor Applications.

Although micelles derived from the solution self-assembly of amphiphilic molecules and polymers have been prepared with a wide variety of shapes, examples with well-defined branched structures have remained elusive. We describe a divergent, directed self-assembly approach to low dispersity dendritic micelles with a high degree of structural perfection and tailorable branch numbers and generations. We use block copolymer amphiphiles as precursors and a crystallization-driven seeded growth approach whereby the termini of fiber-like micelles function as branching sites. Different dendrimeric generations are accessible by adjusting the ratio of added unimers to pre-existing seed micelles where the branch positions are determined by the reduced coronal chain grafting density on the surface of the micelle crystalline core. We demonstrate the spatially defined decoration of the assemblies with emissive nanoparticles and utility of the resulting hybrids as fluorescent sensors for anions where the dendritic architecture enables ultrahigh sensitivity.

Efficient Fenton Degradation of Perylene Diimide Dye Promoted by a Catalytic Amount of Cucurbit[8]uril.

Herein, we propose a new method for promoting the degradation of a perylene diimide (PDI) dye, through a Fenton reaction with cucurbit[8]uril (CB[8]) as a supramolecular catalyst. The CB[8] can encapsulate the hydrophobic moiety of the PDI dye and inhibit its aggregation in aqueous solutions, thus increasing the collision frequency between the PDI and oxidants to accelerate the reaction. As a result, the encapsulated PDI molecule is preferentially degraded, followed by freeing the cavity of CB[8] and enabling it to encapsulate another PDI molecule to realize a catalytic cycle. Hence, a catalytic amount of CB[8] is sufficient to accelerate the the Fenton degradation. It is anticipated that this work will extend the realm of supramolecular catalysis systems and enrich the field of degradation of polycyclic aromatic dyes.

pH/ROS Dual-Responsive Supramolecular Vesicles Fabricated by Carboxylated Pillar[6]arene-Based Host-Guest Recognition and Phenylboronic Acid Pinacol Ester Derivative.

The pH and reactive oxygen species (ROS) dual-responsive supramolecular vesicle utilizing a novel host-guest molecular recognition between a phenylboronic acid pinacol ester derivative carrying long alkyl chain (PBEC12A) and carboxylated pillar[6]arene (CP[6]) is developed. The host-guest complexation between CP[6] and PBEC12A was first studied in aqueous solution. PBEC12A was encapsulated within CP[6] forming a stable host-guest complex with a binding constant as high as 106 M-1 order of magnitude. The driving force behind such a host-guest recognition was the combination of electrostatic interaction and hydrophobic effect. Then, the self-assembly of the supra-amphiphiles of PBEC12A-CP[6] host-guest complexes was investigated in aqueous solution through high-resolution transmission electron microscope and dynamic light scattering. It was found that the supra-amphiphiles self-assembled into supramolecular vesicles and the size of the self-assembled supramolecular vesicles could be tuned from 25 to 200 nm by varying the ratio of CP[6] to PBEC12A. To demonstrate the pH- and ROS-responsive properties of the self-assembled vesicles, the supramolecular vesicles self-assembled from PBEC12A/CP[6] (5:1) were utilized. The Nile Red loading and release studies demonstrated that the supramolecular vesicles possessed good pH/ROS dual-responsive properties. This study enriches the field of supra-amphiphile based on noncovalent interactions. It is anticipated that the pH/ROS dual-responsive supramolecular vesicles have potential applications in drug-delivery systems because both the stimuli are in close relation with specific microenvironments of tumors and relevant diseases of the human body.

Chloride Insertion-Immobilization Enables Bright, Narrowband, and Stable Blue-Emitting Perovskite Diodes.

Metal halide perovskites show promise for light-emitting diodes (LEDs) owing to their facile manufacture and excellent optoelectronic performance, including high color purity and spectral stability, especially in the green region. However, for blue perovskite LEDs, the emission spectrum line width is broadened to over 25 nm by the coexistence of multiple reduced-dimensional perovskite domains, and the spectral stability is poor, with an undesirable shift (over 7 nm) toward longer wavelengths under operating conditions, degradation that occurs due to phase separation when mixed halides are employed. Here we demonstrate chloride insertion-immobilization, a strategy that enables blue perovskite LEDs, the first to exhibit narrowband (line width of 18 nm) and spectrally stable (no wavelength shift) performance. We prepare bromide-based perovskites and then employ organic chlorides for dynamic treatment, inserting and in situ immobilizing chlorides to blue-shift and stabilize the emission. We achieve sky-blue LEDs with a record luminance over 5100 cd/m2 at 489 nm, and an operating half-life of 51 min at 1500 cd/m2. By device structure optimization, we further realize an improved EQE of 5.2% at 479 nm and an operating half-life of 90 min at 100 cd/m2.

Host-Guest Interactions between Oxaliplatin and Cucurbit[7]uril/Cucurbit[7]uril Derivatives under Pseudo-Physiological Conditions.

Compared with conventional drug delivery systems (DDSs), DDSs based on host-guest interactions possess unique advantages, such as high selectivity, tunable binding ability, and controllable release of drugs. It is important to study the host-guest interactions between the carrier and drug under physiological conditions for constructing DDSs. In this work, we have studied the host-guest interaction between cucurbit[7]uril (CB[7]) and oxaliplatin (OxPt), a clinical antitumor drug, in the cell culture medium. The results show that amino acids such as phenylalanine in the 1640 culture medium can partially occupy the cavity of CB[7], which leads to the decrease of enthalpy changes of the host-guest interaction between OxPt and CB[7]. In addition, inorganic salts such as NaCl in the medium reduce the enthalpy change and increase the entropy change of the binding because of the preorganization of the portal of CB[7] and sodium cation. As a result, the binding constant of CB[7] with OxPt in the 1640 culture medium is 1/20 of that in pure water. When CB[7] is modified at the terminal of star-type PEG to construct the star-PEGylated CB[7], it is shown that the molecular weight and topological structure of the PEG polymer backbone exhibit little effect on the host-guest interactions between CB[7] and OxPt. This study enriches the host-guest chemistry of cucurbiturils and may provide guidance for constructing novel DDSs based on host-guest interactions with high loading and releasing efficiency.

Supramolecularly Catalyzed Polymerization: From Consecutive Dimerization to Polymerization.

Herein, we propose a new method for promoting covalent polymerization by supramolecular catalysts. To this end, we employed cucurbit[8]uril (CB[8]) as a supramolecular catalyst, and successfully prepared polyelectrolytes in an aqueous solution by taking advantage of the CB[8]-enhanced photodimerization of Brooker merocyanine moieties. Interestingly, 10 mol % CB[8] is enough to effectively catalyze this polymerization, because CB[8] can be spontaneously replaced by terminal groups from photodimerized products. In addition, the molecular weights of the obtained polyelectrolytes can be varied by the irradiation time or the monomer. By combining supramolecular catalysis and polymer chemistry, this line of research may enrich the methodology of polymerization and open up new horizons for supramolecular polymer chemistry.

Supramolecular catalyst functions in catalytic amount: cucurbit[8]uril accelerates the photodimerization of Brooker's merocyanine.

Supramolecular catalysis aims to modulate chemical reactions on both selectivity and rate by taking advantage of supramolecular chemistry. However, due to the effect of product inhibition, supramolecular catalysts are usually added in stoichiometric amounts. Herein, we report a supramolecular catalysis system in which 1% of the supramolecular catalyst, cucurbit[8]uril, is able to significantly accelerate the photodimerization of Brooker's merocyanine. This catalytic process is realized in a cyclic manner because the photodimerized product can be spontaneously replaced by monomeric reactants via competitive host-guest complexation. Thus, a catalytic amount of cucurbit[8]uril is sufficient to accomplish photodimerization within 10 min. This line of research will enrich the field of supramolecular catalysis and allow the development of more efficient catalytic systems.

An Amylase-Responsive Bolaform Supra-Amphiphile.

An amylase-responsive bolaform supra-amphiphile was constructed by the complexation between ß-cyclodextrin and a bolaform covalent amphiphile on the basis of host-guest interaction. The bolaform covalent amphiphile could self-assemble in solution, forming sheet-like aggregates and displaying weak fluorescence because of aggregation-induced quenching. The addition of ß-cyclodextrin led to the formation of the bolaform supra-amphiphile, prohibiting the aggregation of the bolaform covalent amphiphile and accompanying with the significant recovery of fluorescence. Upon the addition of α-amylase, with the degradation ß-cyclodextrin, the fluorescence of the supra-amphiphile would quench gradually and significantly, and the quenching rate linearly correlated to the concentration of α-amylase. This study enriches the field of supra-amphiphiles on the basis of noncovalent interactions, and moreover, it may provide a facile way to estimate the activity of α-amylase.

Controllable Supramolecular Polymerization Promoted by Host-Enhanced Photodimerization.

In this letter, we report a new method of controllable supramolecular polymerization, taking advantage of host-enhanced photodimerization. The low-molecular-weight supramolecular oligomers were formed by noncovalent complexation between cucurbit[8]urils (CB[8]) and the bifunctional monomers (DBN) with Brooker's merocyanine moiety (MOED) on either end. Interestingly, when irradiated with UV light, the supramolecular oligomers could transform into supramolecular polymers with high molecular weight. The molecular weight of supramolecular polymers could be controlled by varying the irradiation time. It is highly anticipated that this work can enrich the methods on the modulation of supramolecular polymerization.