Single-Chain Conjugated Polymer Guests Confined inside Metal-Organic Frameworks (MOFs): Boosting the Detection and Degradation of a Sulfur Mustard Simulant.

Real-time detection and effective degradation of toxic gases have attracted considerable attention in environmental monitoring and human health. Here, we demonstrate a solvent-assisted dynamic assembly strategy to strongly enhance the detection and degradation performance for 2-chloroethyl ethyl sulfide (CEES, as a sulfur mustard simulant) via confinement of a conjugated polymer in metal-organic frameworks (MOFs). The conjugated polymer poly(9,9-di-n-octylfluorene-altbenzothiadiazole) (F8BT) is infiltrated into one-dimensional nanochannels of the Zr-based topological MOF NU-1000 in a single-chain manner, which is caused by the nanoconfinement effect and the steric hindrance between 9,9-dioctylfluorene units and benzothiadiazole units. The obtained F8BT⊂NU-1000 composites provide a high specific surface area and abundant active sites. Based on the cooperative effect of F8BT and NU-1000, rapid and sensitive detection of CEES has been achieved. Moreover, the F8BT⊂NU-1000 composites can selectively oxidize CEES into 2-chloroethyl ethyl sulfoxide (CEESO) under mild photooxidation conditions. Overall, this study opens a new avenue for the fabrication of conjugated polymer/MOF hybrid materials that show great potential for the sensitive detection and effective removal of hazardous chemicals.

Tunable Chirality of Self-Assembled Dipeptides Mediated by Bipyridine Derivative.

Supramolecular peptide assemblies have been widely used for the development of biomedical, catalytical, and optical materials with chiral nanostructures in view of the intrinsic chirality of peptides. However, the assembly pathway and chiral transformation behavior of various peptides remain largely elusive especially for the transient assemblies under out-of-equilibrium conditions. Herein, the N-fluorenylmethoxycarbonyl-protected phenylalanine-tyrosine dipeptide (Fmoc-FY) was used as a peptide assembly platform, which showed that the assembly proceeds multistep evolution. The original spheres caused by liquid-liquid phase separation (LLPS) can nucleate and elongate into the formation of right-handed helices which were metastable and easily converted into microribbons. Interestingly, a bipyridine derivative can be introduced to effectively control the assembly pathway and induce the formation of thermodynamically stable right-handed or left-handed helices at different stoichiometric ratios. In addition, the chiral assembly can also be regulated by ultrasound or enzyme catalysis. This minimalistic system not only broadens the nucleation-elongation mechanisms of protein aggregates but also promotes the controllable design and development of chiral biomaterials.

Highly sensitively detection of amine vapors released during shrimp spoilage by fluorescent molecules locked in covalent organic frameworks.

The fluorescent sensors allow sensitive detection of amine vapors for assessing the safety and quality of seafood products. However, high diffusion resistance and insufficient recognition sites usually limit the sensitivity of the sensors. Here, we employed an emulsion-confined assembly strategy to uniform encapsulate fluorescent molecules perylene diimide (PDI) molecules into covalent organic frameworks (COFs) to achieve ultrasensitive detection of amine vapors. The detection mechanism is based on the photoinduced electron transfer from amine to the excited PDI. This method exhibits a broad linear detection range from 8 ppb to 800 ppm and the limit of detection reaches as low as 1.2 ppb. The real-time detection of the amine vapors produced during shrimp spoilage is successfully achieved with excellent performance. This provides a versatile method for the on-demand synthesis of functional materials with high fluorescence properties for the development of chemical sensors via encapsulating different fluorescent molecules into COFs.

Controlled Supramolecular Self-Assembly Pathways by Intramolecular Rotation of D-A Molecular System toward the Signal Differentiation Detection of Toxic Vapors.

Revealing the structural evolution mechanisms of supramolecular self-assembly can facilitate the exploitation of new self-assembly pathways and various functional materials. Here, this work reports a unique intramolecular rotation-induced structural evolution of supramolecular assemblies from a metastable state to a thermodynamically stable state using a twisting D-A molecule. These self-assemblies are applied to the signal differentiation detection of toxic dimethylsulfide (DMS) vapors. The F161 BT monomer of the inactive state is trapped in off-pathway metastable nanospheres, which can disassemble and induce the transformation of the F161 BT monomer into an active state by crossing the energy barrier. Subsequently, the active monomer goes through the processes of nucleation and elongation, forming thermodynamically stable on-pathway microribbons. Adding seeds can accelerate the molecular conformational transformation, generating microribbons with controlled lengths. Opposite fluorescent responses are obtained when exposing the two aggregates to the DMS vapors, allowing the sensitive detection of DMS with enhanced selectivity, which offers tremendous potential in practical applications.

Schiff base nanoarchitectonics for supramolecular assembly of dipeptide as drug carriers.

Development of peptide-based supramolecular materials with hierarchical morphology and tunable guest loading displays broad potential as drug carrier in view of biocompatibility and biodegradability. Herein, we report a facile Schiff base nanoarchitectonic for supramolecular assembly of diphenylalanine (FF) metastable gel. The addition of trace glutaraldehyde (GA)/H2O solution induces the Schiff base reaction between GA and FF accompanying by phase transition from gel to solution. FF nanoparticles and hierarchical beaded nanofibers with autofluorescence properties can be constructed by regulating the competitive assembly between FF-H2O and FF-GA oligomer. Moreover, various guest molecules with different hydrophilic and hydrophobic properties can be easily loaded into such assembled particles and its release can be triggered under weak alkaline conditions, which show the potential application of the assembled FF system as drug carriers.

Viscosity-Based Flow Sensor on Paper for Quantitative and Label-Free Detection of α-Amylase and Its Inhibitor.

α-Amylase (AMS) in human serum is a critical biomarker for the early diagnosis of pancreatic damage. In addition, the inhibition of α-amylase has long been thought to decrease the occurrence of diabetes. Thus, it is critical to construct a facile and convenient method for the determination of AMS and its inhibitor. In this study, we demonstrate a novel amylase sensor based on translating the viscosity change of the aqueous solution into the difference of the water diffusion length on a pH paper strip. AMS can be quantitatively detected by measuring the viscosity change of the amylopectin solution in the presence of AMS with different concentrations. The paper-based AMS sensor has a very high sensitivity with a detection limit of 0.017 U/mL and also shows excellent specificity. In addition, the inhibitory effect of acarbose on AMS is demonstrated with the IC50 value determined to be 21.66 ± 1.13 µg/mL. Furthermore, it is also evaluated for the detection of AMS in human serum samples of healthy people and acute pancreatitis patients. The difference in amylase levels between the two groups is unambiguously distinguished. Overall, this study provides a very simple, cost-effective, equipment-free, high-throughput, and label-free method for rapid and quantitative detection of α-amylase and may have significant applications in the diagnosis of acute pancreatitis and the screening of AMS inhibitors.

Highly Photostable and Luminescent Donor-Acceptor Molecules for Ultrasensitive Detection of Sulfur Mustard.

Real-time, high signal intensity, and prolonged detection is challenging because of the rarity of fluorophores with both high photostability and luminescence efficiency. In this work, new donor-acceptor (D-A) molecules for overcoming these limitations are reported. A hybridized local and an intramolecular charge-transfer excited state is demonstrated to afford high photoluminescence efficiency of these D-A molecules in solution (≈100%). The twisted molecular structure and bulky alkyl chains effectively suppress π-π and dipole-dipole interactions, enabling high luminescence efficiency of 1 and 2 in the solid state (≈94% and 100%). Furthermore, two D-A aggregates exhibit high photostability as evidenced by 4% and 8% of the fluorescence decreasing after 6 h of continuous irradiation in air, which is in sharp contrast to ≈95% of fluorescence decreasing in a reference compound. Importantly, with these molecules, ultrasensitive detection of sulfur mustard (SM) with a record limit of 10 ppb and selective detection of SM in complex matrices are achieved.

A pendant droplet-based sensor for the detection of acetylcholinesterase and its inhibitors.

In this work, a pendant droplet-based sensor is developed for the rapid and label-free detection of acetylcholinesterase (AChE) and its inhibitors. The detection limit of AChE reaches 0.17 mU mL-1. The pIC50 values of AChE inhibitors such as neostigmine, rivastigmine and galantamine are determined to be 0.45 µM, 0.64 µM and 4.93 µM, respectively.

Co-assembled Supramolecular Gel of Dipeptide and Pyridine Derivatives with Controlled Chirality.

It is commonly considered that amyloid-ß (Aß) fibrils are heavily involved in the neurological diseases. Establishing an external model based on the core recognition motif (diphenylalanine, FF) of Aß would be of significance in understanding the assembly and disassembly of Aß fibrils in living system. Herein, supramolecular gels with structure transition from amyloid-like ß-sheet to different supramolecular helices were obtained through the co-assembly of a N-fluorenylmethoxycarbonyl-protected L-FF (L-FmocFF) with achiral pyridine derivatives. It is found that the different stacking modes (H- or J-aggregates) of additives and the microenvironment of chiral carbon play vital roles for the selectively chiral transfer or amplification of L-FmocFF. The dynamic process of helix formation was also captured. This work provides a convenient co-assembly way to explore the structure basis of Aß fibrils with a controlled chirality.

Long-Range Exciton Migration in Coassemblies: Achieving High Photostability without Disrupting the Electron Donation of Fluorene Oligomers.

In this work, photostable coassemblies from a nonphotostable fluorene oligomer (the energy donor) and a photostable oligomer (the energy acceptor) are fabricated. Long-range exciton migration over a net distance of about 370 energy-donor molecules to energy acceptors is demonstrated in such coassemblies. The fast and long energy migration allows harvesting of the excitation energy of energy donors by embedding a small number of energy acceptors for photostability enhancement. Importantly, embedding a small number of energy acceptors in coassemblies causes a negligible negative influence on the electron donation of energy donors that are desired in practical applications. The advantages of the coassemblies fabricated, that is, high photostability without disrupting the electron donation of energy donors, are well illustrated in fluorescence detection of trace explosives where prolonged working life and improved detection capacity are achieved.

Light-Driven Crawling of Molecular Crystals by Phase-Dependent Transient Elastic Lattice Deformation.

The light-driven crawling of a molecular crystal that can form three phases, (α, ß, and γ) is presented. Laser irradiation of the molecular crystal can generate phase-dependent transient elastic lattice deformation. The resulting elastic lattice deformation that follows scanning irradiation of a laser can actuate the different phases of molecular crystal to move with different velocity and direction. Because the γ phase has a large Young's modulus (ca. 26 GPa), a force of 0.1 µN can be generated under one laser spot. The generated force is sufficient to actuate the γ-formed molecular crystals in a wide dimensional range to move longitudinally at a velocity of about 60 µm min-1 , which is two orders of magnitude faster than the α and ß phases.

Sensitive Fluorescence Detection of Phthalates by Suppressing the Intramolecular Motion of Nitrophenyl Groups in Porous Crystalline Ribbons.

A novel, highly sensitive fluorescence sensor for phthalates is developed by introducing nitrophenyl groups to a trifluorene molecule that can form porous crystalline ribbons. On the basis of single-crystalline analysis and theoretical calculations, we demonstrate that phthalate molecules can diffuse into the caves of crystalline ribbons and effectively suppress the rotation of nitrophenyl groups via noncovalent interactions to enhance the emission. Because of this novel response mechanism, fluorescence detection of phthalates with high sensitivity (the limit of detection of widely used di(2-ethylhexyl) phthalate (DEHP) is 0.03 ppb) and rapid reversible turn-on responses is achieved. Sensitive detection of phthalates released from commercial polyvinyl chloride (PVC) products further illustrate the utility of such a sensor in in situ and real-world applications.

Emergent Self-Assembly Pathways to Multidimensional Hierarchical Assemblies using a Hetero-Seeding Approach.

The controlled formation of complex and functional 1-, 2-, and 3D hierarchical assemblies from molecular building blocks represents a key current challenge. Herein, we report the use of a seeded growth approach for a series of perylenediimide-based molecules (PDIs 1-4) to access otherwise inaccessible self-assembly pathways that yield complex hierarchical structures. The key to the new approach is to use hetero-seeds which possess a different composition and morphology from that of the molecular building block. For example, a nanotube seed (from PDI 3) and a microribbon seed (from PDI 4) were found to initiate different self-assembly pathways for PDI 1, which normally assembles to yield nanocoils. This led to the formation of unprecedented 3D scroll-like and scarf-like hierarchical nanostructures, respectively. Also, the hetero-seeds from PDI 3 initiate hidden self-assembly pathways of PDI 2 to generate 1D tubular heterojunctions. Significantly, this new strategy offers new opportunities to create emergent and functional hierarchical and complex structures from small molecule precursors.

Ultrasensitive Detection of Sulfur Mustard via Differential Noncovalent Interactions.

In this work, we fabricate two types of hierarchical microspheres, i.e., one coassembled from two fluorene-based oligomers (1 and 2) and one self-assembled from a fluorene-based oligomer (1), for ultrasensitive and selective detection of trace sulfur mustard (SM) vapor. On the basis of distinct fluorescence responses of 1-2 coassembled and individual 1 hierarchical microspheres that originate from differential noncovalent interactions between analytes and these sensors, SM vapor can be ultrasensitively detected (30 ppb) and easily discriminated from various sulfides and other potential interferents. Our work that utilizes differential noncovalent interactions to give sensitive and selective fluorescence response patterns represents a new detection approach for SM and other hazardous chemicals.

Kinetic Control of a Self-Assembly Pathway towards Hidden Chiral Microcoils.

Manipulating the self-assembly pathway is essentially important in the supramolecular synthesis of organic nano- and microarchitectures. Herein, we design a series of photoisomerizable chiral molecules, and realize precise control over pathway complexity with external light stimuli. The hidden single-handed microcoils, rather than the straight microribbons through spontaneous assembly, are obtained through a kinetically controlled pathway. The competition between molecular interactions in metastable photostationary intermediates gives rise to a variety of molecular packing and thereby the possibility of chirality transfer from molecules to supramolecular assemblies.

Fabrication of Biocompatible, Luminescent Supramolecular Structures and Their Applications in the Detection of Dopamine.

Supramolecular materials assembled by amide-functionalized surface active ionic liquid, N-dodecyl- N'-acetamido imidazolium bromide ([C12ImCONH2]Br), and europium-containing polyoxometalates (Eu-POM) were fabricated in aqueous solution by a one-step method via ionic self-assembly strategy. The [C12ImCONH2]Br/Eu-POM supramolecular structures exhibit favorable fluorescence properties and represent a 15-fold increase in quantum yield (∼13.68%) compared to Eu-POM. Besides, more fluorescence was quenched obviously with the increasing concentration of dopamine (DA) (within the range of 0-100 µM), based on which DA monitoring could be achieved. The detection limit was identified to be 0.1 µM. The supramolecular nanoparticles are highly specific for the detection of DA. In addition, the hybrid assemblies display not only low cytotoxicity but also excellent biocompatibility to MC3T3-E1 cells. As a result, as-prepared supramolecular materials with these superior properties show the promising application in some fields such as biochemistry and biomedical science.

Plumbagin prevents osteoarthritis in human chondrocytes through Nrf-2 activation.

Osteoarthritis (OA) is an inflammatory disorder dealing with the focal degradation of articular cartilage. Oxidative stress and inflammation are the major events in OA. The present study aimed at identifying the mechanism of the potent antioxidant, plumbagin, in protecting against hydrogen peroxide (H2O2)­induced chondrocyte oxidative stress and inflammatory signaling. Oxidative stress was determined by measuring reactive oxygen species, lipid peroxidation, non­enzymic (glutathione; GSH) and enzymic antioxidant activities (GSH, glutathione S­transferase, glutathione peroxidase, superoxide dismutase, catalase). Expression levels of nuclear factor (erythroid­derived 2)­like 2 (Nrf­2), heme oxygenase 1 (HO­1), NAD(P)H:quinone oxidoreductase 1 (NQO­1), nuclear factor­κB (NF­κB), cyclooxygenase­2 (COX­2) and inducible NO synthase (iNOS) were determined by western blot analysis. Pro­inflammatory cytokine expression levels were assessed using ELISA. Results from reactive oxygen species generation, lipid peroxidation content and antioxidant enzyme activities demonstrated that plumbagin significantly inhibited oxidative stress status in H2O2­induced chondrocytes. In addition, plumbagin modulated transcription factors involved in redox and inflammation regulation, including NF­κB and Nrf­2, by nuclear expression. plumbagin enhanced antioxidant status by increasing the expression levels of Nrf­2 target genes, including HO­1 and NQO­1. An anti­inflammatory effect against chondrocyte­induced inflammation was demonstrated by downregulating COX­2, iNOS and pro­inflammatory cytokine expression levels (tumor necrosis factor­α, interleukin (IL)­6 and IL­8). The present study identified strong evidence for a protective role of plumbagin against H2O2-induced oxidative stress and inflammation in chondrocytes by modulating redox signaling transcription factors.

A polyoxometalate-based supramolecular chemosensor for rapid detection of hydrogen sulfide with dual signals.

Hydrogen sulfide (H2S) has been verified as an important biological mediator in human physiological activities, but its rapid and accurate detection is remaining a challenge. Based on our early work, Eu-containing polyoxometalate/ionic liquid-type gemini surfactant hybrid nanoparticles fabricated by EuW10O36·32H2O (Eu-POM) and 1,2-bis(3-hexadecylimidazolium-1-yl) ethane bromide ([C16-2-C16im]Br2) via ionic self-assembly (ISA) strategy, we modified the hybrids with copper (II) ion and used them as a novel turn-off supramolecular fluorescence probe for H2S immediate response. Although copper (II) ions can cause decrease of the fluorescence intensity, the probe with moderate amount of copper (II) still has a high performance in emission property. The copper (II) ion-modified supramolecular sensor (CSS) shows dual signals in the fluorescence intensity and absorbance for H2S detection, and the detection limit is about1.25µM. Furthermore, CSS displays high selectivity for H2S in the presence of other anions and species (e.g. Cl-, Br-, I-, SO42-, SO32-, S2O32-, AC-, H2O2, HCO3-, l-cysteine, homocysteine and l-glutathione), and also have potential for preferential imaging in vivo. Besides, the fluorescence quenching mechanism of CSS in the presence of H2S was explored. CuS generated by the reaction between Cu2+ and H2S was testified to act as a quencher, and the nonradiative resonance energy transfer mechanism was speculated to be responsible for fluorescence quenching. It is anticipated that the as-prepared CSS will be used as an efficient chemosensor for the rapid detection of H2S, which is critical for the diagnosis of some diseases, e.g. Alzhermer's disease, Down's syndrome, and diabetes, etc.

Multi-stimuli Responsive Supramolecular Structures Based on Azobenzene Surfactant-Encapsulated Polyoxometalate.

Multi-stimuli responsive materials have attracted intense attention as extensive application prospect in many fields, yet achievement of multi-stimuli responsiveness remains a challenge. Herein, we report a tri-stimuli responsive supramolecular structure fabricated by a cationic surfactant, 4-ethyl-4'-(trimethylaminohexyloxy) azobenzene bromide (ETAB), and anionic Eu-containing polyoxometalates (Eu-POM), based on an ionic self-assembly (ISA) strategy. Following different responsive mechanisms, the resultant ETAB/Eu-POM supramolecular materials are responsive to UV light, pH, and Cu(2+), respectively. The response to UV irradiation is based on the configuration change of azobenzene molecules. The response to H(+) can be attributed to the formation of a hydrogen bond W-O···H···O-H among Eu-POM, H(+), and H2O, which blocks the energy transfer pathway from O → W, while the coordination interaction between Cu(2+) and Oc (bridged oxygen of two octahedra sharing an edge in the Eu-POM molecule) causes the response to Cu(2+). The multi-stimuli responsive characteristics for the ETAB/Eu-POM supramolecular structures maybe provide a potential application in ultraviolet detection, optical storage devices, and chemical substance sensors, etc.

A Terrestrial Microbial Fuel Cell for Powering a Single-Hop Wireless Sensor Network.

Microbial fuel cells (MFCs) are envisioned as one of the most promising alternative renewable energy sources because they can generate electric current continuously while treating waste. Terrestrial Microbial Fuel Cells (TMFCs) can be inoculated and work on the use of soil, which further extends the application areas of MFCs. Energy supply, as a primary influential factor determining the lifetime of Wireless Sensor Network (WSN) nodes, remains an open challenge in sensor networks. In theory, sensor nodes powered by MFCs have an eternal life. However, low power density and high internal resistance of MFCs are two pronounced problems in their operation. A single-hop WSN powered by a TMFC experimental setup was designed and experimented with. Power generation performance of the proposed TMFC, the relationships between the performance of the power generation and the environment temperature, the water content of the soil by weight were measured by experiments. Results show that the TMFC can achieve good power generation performance under special environmental conditions. Furthermore, the experiments with sensor data acquisition and wireless transmission of the TMFC powering WSN were carried out. We demonstrate that the obtained experimental results validate the feasibility of TMFCs powering WSNs.