Spontaneous and Selective Macrocyclization in Nitroaldol Reaction Systems.

Through a dynamic polymerization and self-sorting process, a range of lowellane macrocycles have been efficiently generated in nitroaldol systems composed of aromatic dialdehydes and aliphatic or aromatic dinitroalkanes. All identified macrocycles show a composition of two repeating units, resulting in tetra-ß-nitroalcohols of different structures. The effects of the building block structure on the macrocyclization process have been demonstrated, and the influence from the solvent has been explored. In general, the formation of the lowellanes was amplified in response to phase-change effects, although solution-phase structures were, in some cases, favored.

Small-molecule activators of a bacterial signaling pathway inhibit virulence.

The Burkholderia genus encompasses multiple human pathogens, including potential bioterrorism agents, that are often extensively antibiotic resistant. The FixLJ pathway in Burkholderia is a two-component system that regulates virulence. Previous work showed that fixLJ mutations arising during chronic infection confer increased virulence while decreasing the activity of the FixLJ pathway. We hypothesized that small-molecule activators of the FixLJ pathway could serve as anti-virulence therapies. Here, we developed a high-throughput assay that screened over 28,000 compounds and identified 11 that could specifically active the FixLJ pathway. Eight of these compounds, denoted Burkholderia Fix Activator (BFA) 1-8, inhibited the intracellular survival of Burkholderia in THP-1-dervived macrophages in a fixLJ-dependent manner without significant toxicity. One of the compounds, BFA1, inhibited the intracellular survival in macrophages of multiple Burkholderia species. Predictive modeling of the interaction of BFA1 with Burkholderia FixL suggests that BFA1 binds to the putative ATP/ADP binding pocket in the kinase domain, indicating a potential mechanism for pathway activation. These results indicate that small-molecule FixLJ pathway activators are promising anti-virulence agents for Burkholderia and define a new paradigm for antibacterial therapeutic discovery.

Self-Healable, Regenerable, and Degradable Dynamic Covalent Nitroalcohol Organogels.

Dynamic covalent gels are synthesized from an aromatic trialdehyde and α,ω-dinitroalkanes via the nitroaldol reaction in organic solvents. The gelation process can be fine-tuned by changing the starting nitroalkanes, solvents, feed concentration, catalyst loading, or reaction temperature. The resulting organogels demonstrate good structural integrity and excellent self-healing ability. Intact xerogels are produced upon drying, without damaging the network, and the solvent-free network can recover its gel form in the presence of an organic solvent. Furthermore, the crosslinked dynameric gel depolymerize to small molecules in response to excess nitromethane.

Polymerization, Stimuli-induced Depolymerization, and Precipitation-driven Macrocyclization in a Nitroaldol Reaction System.

Dynamic covalent polymers of different topology have been synthesized from an aromatic dialdehyde and α,ω-dinitroalkanes via the nitroaldol reaction. All dinitroalkanes yielded dynamers with the dialdehyde, where the length of the dinitroalkane chain played a vital role in determining the structure of the final products. For longer dinitroalkanes, linear dynamers were produced, where the degree of polymerization reached a plateau at higher feed concentrations. In the reactions involving 1,4-dinitrobutane and 1,5-dinitropentane, specific macrocycles were formed through depolymerization of the linear chains, further driven by precipitation. At lower temperature, the same systemic self-sorting effect was also observed for the 1,6-dinitrohexane-based dynamers. Moreover, the dynamers showed a clear adaptive behavior, displaying depolymerization and rearrangement of the dynamer chains in response to alternative building blocks as external stimuli.

Efficient removal of bisphenol-A from water and wastewater by Fe2O3-modified graphene oxide.

Bisphenol-A (BPA) has been widely used as a plasticizer in modern society and persistently released into aquatic environments. Herein, a novel Fe2O3-graphene oxide (GO) hybrid containing 22.8% of GO was prepared to enhance BPA removal from contaminated water and wastewater. This hybrid material afforded outstanding BPA adsorption capacities of 3293.9 mg g-1 under optimized conditions, which led to 1.9 times and 1.2 times of BPA removal as compared to GO and reduced GO (rGO), respectively. In addition, Fe2O3-GO showed higher thermal stability, greater solid/liquid separation performance, and better anti-fouling performance. Moreover, the coexistence of natural or effluent organic matter caused 6.7-16.8% decline in BPA adsorption capacity of Fe2O3-GO, which was lower than those of GO and rGO (11.8-39.4%). Further characterization experiments revealed that BPA removal by Fe2O3-GO was enhanced because of the formation of Lewis acid-base (AB) interactions between the active sites on Fe2O3 (Lewis base) and BPA anions (Lewis acid). The existence of the AB interaction is beneficial for practical application considering the low environmental concentrations of BPA in water and wastewater. Besides, the distinctly lowered GO content of the hybrid saved 77.2% of the adsorbent cost. In conclusion, this study demonstrated the potential of Fe2O3-GO as a novel material for the treatment of BPA-contaminated water and wastewater.

Dynamic Covalent Polymers for Biomedical Applications.

The rapid development of supramolecular polymer chemistry and constitutional dynamic chemistry over the last decades has made tremendous impact on the emergence of dynamic covalent polymers. These materials are formed through reversible covalent bonds, endowing them with adaptive and responsive features that have resulted in high interest throughout the community. Owing to their intriguing properties, such as self-healing, shape-memory effects, recyclability, degradability, stimuli-responsiveness, etc., the materials have found multiple uses in a wide range of areas. Of special interest is their increasing use for biomedical applications, and many examples have been demonstrated in recent years. These materials have thus been used for the recognition and sensing of biologically active compounds, for the modulation of enzyme activity, for gene delivery, and as materials for cell culture, delivery, and wound-dressing. In this review, some of these endeavors are discussed, highlighting the many advantages and unique properties of dynamic covalent polymers for use in biology and biomedicine.

Preparation of κ-carrageenan/graphene oxide gel beads and their efficient adsorption for methylene blue.

A series of environmental-friendly adsorbents, κ-carrageenan/graphene oxide gel beads (κ-Car/GO GBs), were synthesized from κ-carrageenan and graphene oxide via a simple method. The composition and morphology of these gel bead adsorbents were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, scanning electron microscopy, etc. The adsorption ability of κ-Car/GO GBs was investigated by measuring the removal of methylene blue (MB) from aqueous solutions. The effects of the initial dye concentration, adsorption time, temperature and pH value were evaluated. The results of the adsorption experiments were consistent with the Langmuir model, while the adsorption kinetic data were fit with a pseudo-second-order model. The maximum adsorption capacity of κ-Car/GO GBs for MB is 658.4mg/g at 25°C, which barely declined even after five cycles. Hence, the κ-Car/GO GBs are outstanding adsorbents with high adsorption capacity and excellent regeneration ability. Furthermore, the gel bead adsorbents could be easily separated from aqueous solutions after adsorption using a simple filtration method.

Natural polysaccharides-modified graphene oxide for adsorption of organic dyes from aqueous solutions.

Three polysaccharide- graphene oxide composite materials (PS-GO) were synthesized from graphene oxide (GO) and natural polysaccharides, which compounds were tested for removal of organic dyes from aqueous solutions. These adsorbents were characterized by Fourier transform infrared spectroscopy (FT-IR), Raman spectrometer, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), N2 adsorption-desorption isotherms and UV-vis spectrum. The adsorption properties of PS-GO towards four organic dyes were investigated along with measured effects on adsorption by initial concentration, temperature, contact time and pH value. Resulting adsorption isotherms, thermodynamics and kinetics were analyzed systematically. In these tests, PS-GO composite materials were found to be more efficient than as-prepared GO as adsorbents for the removal of both cationic and anionic organic dyes.