Latest ArticlesA water-soluble macrocycle that bears four carboxylate anions has been designed and prepared, which forms a rectangular cavity that can efficiently encapsulate discrete electron-deficient aromatic compounds, including berberine and palmatine. This macrocycle is revealed to be highly biocompatible and able to inhibit the bitter taste of the two drugs.
Protein recognition using host-guest recognition approach is of great interest but has been limited mainly to the protein N-terminal residues. Here, we site-specific incorporated two novel non-canonical amino acids containing supramolecular guest motifs into protein via an expanded genetic code. Through Staudinger reduction reactions, the encoded unnatural residues on protein becoming activated and can be specifically recognized by cucurbit[7]uril (CB[7]) and cucurbit[8]uril (CB[8]). We demonstrated that enzyme containing guest amino acid incorporated near the active site can be reversibly regulated by CB[7] recognition, and CB[8] recognition induces protein dimerization. These amino acids will make useful addition to the supramolecular toolbox for protein targeting using molecular recognition approaches.
Molecular weaving is a powerful approach to make molecularly woven materials that have showed unprecedented characteristics and properties intrinsically distinct to those of non-woven materials. We here report a facile and efficient approach for the synthesis of 2D woven supramolecular polymers by differentiated self-assembly through orthogonal noncovalent interactions. Importantly, the difference in binding strength of two orthogonal noncovalent interactions can be used to control the process of molecular weaving. Consequently, single-layered 2D woven supramolecular polymers were synthesized and fully characterized by various techniques. This study demonstrates a controllable method for molecular weaving, and will significantly hasten the development of molecularly woven materials.
Microcystins (MCs), a family of cyclic heptapeptide cyanotoxins, exists in aquatic environment where cyanobacterial bloom happens, which will accumulate in aquatic organisms and transfer through the food chain to higher trophic levels, posing a health risk to both animals and human bodies. Among various MCs, Microcystin-LR (MC-LR) is worthiest studied for its strong toxicity, ubiquity and widespread. Here in this work, iminodiacetic acid (IDA) decorated magnetic mesoporous silica (mSiO2) nanocomposites (Fe3O4@mSiO2-IDA) were facilely synthesized which possessed the merits of large surface area (188.21 m2/g), accessible porosity (2.66 nm), excellent hydrophilicity and rapid responsiveness to magnetic field. Then the composites were successfully employed to the removal process of Microcystin-LR in real water samples followed by Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis, achieving the removal efficiency above 92.5% even after ten recycles of the composites. It provided a potential method for removing MC-LR in aqueous environment with high effectiveness, lower costs and less secondary contamination.
Imine bonds are among the most explored building motifs in dynamic chemistry, polymers, and materials, and yet, their acid-resistance remains a longstanding issue. Herein we demonstrate a concept of internal protecting groups for improving the kinetic stability of dynamic imine bonds and polymers. Systematic examination of structure-reactivity relationship of a series of aldehydes/imines bearing a neighboring carboxyl allowed uncovering of required structural features for dynamically masking imine bonds with cyclic structures. Mechanistic studies indicated that noncovalent interactions along with sterics control the ring-chain equilibrium and the stability of imine bonds. The incorporation of internal protecting groups into imine polymers further enabled their controlled stability in acidic media. Moreover, a combination of dynamic covalent network and coordination supramolecular network provided a facile means for the modulation of luminescent and mechanical properties of polymers. The strategies and results reported should be beneficial to molecular assemblies, dynamic polymers, biological delivery, and intelligent materials.
Sulfydryl-contained (-SH) substances including hydrogen sulfide (H2S), cysteine (Cys), homocysteine (Hcy) and glutathione (GSH) play crucial roles in living systems, and their variations are closely associated with various diseases. Herein, we developed a near-infrared intramolecular charge transfer (ICT) based fluorescent probe Y-NBD, achieving detection of Cys/Hcy and H2S with different fluorescent signals (green-red for Cys/Hcy, red for H2S), large Stokes shifts (~100/105 nm or 191 nm) and high signal-background-ratio, but not responding to GSH. Y-NBD was successfully applied to image exogenous/endogenous Cys/Hcy and H2S in various living cancer cells (HeLa, A549, and HepG2) and in zebrafish. It not only visualized the transformation pathway of several thiols in HepG2 cells but also verified that the intestine is the main site for the activation and metabolism of Y-NBD in zebrafish, as well as realized to evaluate the degree of drug-induced liver injury. This work provides a promising tool for imaging Cys/Hcy and H2S in living systems and shows great potency in evaluating drug-induced liver injury and its treatment.
Chiral alcohols and amines are important structural units widely existing in pharmaceuticals, agrochemicals, and food additives. Dynamic kinetic resolution (DKR) is an efficient strategy to deliver optically active alcohols and amines from their racemates. For the development of DKR method, racemization catalyst plays as a crucial element with the requirement of compatibility with the kinetic resolution (KR) system. In this paper, recent advance in the catalytic racemization of secondary alcohols and amines is summarized based on different types of racemizing intermediates, which are redox racemization via ketone/imine intermediates, racemization via radical intermediates, and racemization via carbocation intermediates. Enzymatic racemization of secondary alcohols and amines is also enclosed.
Molecular recognition in water, the biological solvent, always receives significant research focus in supramolecular chemistry. The mechanisms of molecular recognition in water is key to comprehending biological processes at the molecular level. Over the past five decades, supramolecular chemists have developed a vast array of synthetic receptors with highly diverse structures and recognition properties. Among them, cyclophanes represent an important family of macrocyclic receptors that have been extensively explored. The aromatic moieties in cyclophanes not only facilitate chemical modifications to impart water solubility but also enable forming hydrophobic cavities for guest inclusion in aqueous environments. Pioneered by Koga et al., who reported the first inclusion complex of cyclophanes in water and solid state, numerous water-soluble cyclophanes, including derivatives of blue box, calixarenes, resorcinarenes, pillararenes, octopusarenes, biphenarenes, coronarenes, and naphthotubes, etc., have been synthesized and subjected to investigation of the recognition capabilities in aqueous solutions. This review provides an overview of cyclophane receptors designed to bind organic guests in water. We categorize them into two classes based on the modifications made to their hydrophobic cavities: those with "exo-functionalized hydrophobic cavities" and those with "endo-functionalized hydrophobic cavities". We introduce their distinctive features and discuss strategies to enhance recognition affinity and selectivity. This review aims to inspire the development of novel synthetic receptors with intriguing properties and foster practical applications of cyclophanes.
Covalent organic polymer (COP) thin film-based memristors have generated intensive research interest, but the studies are still in their infancy. Herein, by controlling the content of hydroxyl groups in the aldehyde monomer, Py-COP thin films with different electronic push-pull effects were fabricated bearing distinct memory performances, where the films were prepared by the solid-liquid interface method on the ITO substrates and further fabricated as memory devices with ITO/Py-COPs/Ag architectures. The Py-COP-1-based memory device only exhibited binary memory behavior with an ON/OFF ratio of 1:101.87. In contrast, the device based on Py-COP-2 demonstrated ternary memory behavior with an ON/OFF ratio of 1:100.6: 103.1 and a ternary yield of 55%. The ternary memory mechanism of the ITO/Py-COP-2/Ag memory device is most likely due to the combination of the trapping of charge carriers and conductive filaments. Interestingly, the Py-COPs-based devices can successfully emulate the synaptic potentiation/depression behavior, clarifying the programmability of these devices in neuromorphic systems. These results suggest that the electronic properties of COPs can be precisely tuned at the molecular level, which provides a promising route for designing multi-level memory devices.
Due to the various pH liquid environment in nature, the pH-responsive lubricating hydrogel is widely investigated and developed for tissue interface substitute. However, the applied liquid environment will lead to poor mechanical property and weaken the pH-responsive capability. In this work, a carbon dots-enhanced pH-responsive lubricating hydrogel is developed by combining a pH-responsive section of dynamic PVA-borax network into a PAAm covalent polymer network. The formed hydrogel presents a partial gel-sol transition under controlled pH environments. At low pH environments (< 6.0), the formed lubricating layer originated from dynamic disassembly of PVA-borax hydrogel, and brings the lubricating properties on the hydrogel surface. Moreover, the mechanical strength and lubrication properties are well promoted by introducing the carbon dots into the hydrogel, the blue sol layer can be observed more visually under the fluorescence microscope. The pH-response also exhibits well reversibility. The prepared hydrogel broadens the idea for designing pH-responsive soft materials for soft lubricating actuator or robot.
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