Search for: All records

Hydrogen bonding is crucial in biological systems but challenging to replicate in synthetic receptors operating in water due to solvent competition. This minireview highlights recent advances in the design of synthetic hydrogen-bonding receptors that function effectively in water. By employing strategies like hydrophobicityassisted hydrogen bonding, charge-assisted interactions, and dynamic covalent chemistry, researchers have developed effective approaches to synthesizing hydrogen-bonding receptors with enhanced affinity and selectivity for hydrophilic substrates. These innovations not only overcome the traditional hurdles of aqueous molecular recognition but also open new avenues in environmental monitoring, biomedical diagnostics, and materials science. The progress underscores the potential of these receptors to drive significant advancements in molecular recognition within aqueous media. 

Hydrogen bonding is prevalent in biological systems, dictating a myriad of life-sustaining functions in aqueous environments. Leveraging hydrogen bonding for molecular recognition in water encounters significant challenges in synthetic receptors on account of the hydration of their functional groups. Herein, we introduce a water-soluble hydrogen bonding cage, synthesized via a dynamic approach, exhibiting remarkable affinities and selectivities for strongly hydrated anions, including sulfate and oxalate, in water. We illustrate the use of charge-assisted hydrogen bonding in amide-type synthetic receptors, offering a general molecular design principle that applies to a wide range of amide receptors for molecular recognition in water. This strategy not only revalidates the functions of hydrogen bonding but also facilitates the effective recognition of hydrophilic anions in water. We further demonstrate an unconventional catalytic mechanism through the encapsulation of the anionic oxalate substrate by the cationic cage, which effectively inverts the charges associated with the substrate and overcomes electrostatic repulsions to facilitate its oxidation by the anionic MnO4–. Technical applications using this receptor are envisioned across various technical applications, including anion sensing, separation, catalysis, medical interventions, and molecular nanotechnology. 

The complex distribution of functional groups in carbohydrates, coupled with their strong solvation in water, makes them challenging targets for synthetic receptors. Despite extensive research into various molecular frameworks, most synthetic carbohydrate receptors have exhibited low affinities, and their interactions with sugars in aqueous environments remain poorly understood. In this work, we present a simple pyridinium-based hydrogen-bonding receptor derived from a subtle structural modification of a well-known tetralactam macrocycle. This small structural change resulted in a dramatic enhancement of glucose binding affinity, increasing from 56 M−1 to 3001 M−1. Remarkably, the performance of our synthetic lectin surpasses that of the natural lectin, concanavalin A, by over fivefold. X-ray crystallography of the macrocycle–glucose complex reveals a distinctive hydrogen bonding pattern, which allows for a larger surface overlap between the receptor and glucose, contributing to the enhanced affinity. Furthermore, this receptor possesses allosteric binding sites, which involve chloride binding and trigger receptor aggregation. This unique allosteric process reveals the critical role of structural flexibility in this hydrogen-bonding receptor for the effective recognition of sugars. We also demonstrate the potential of this synthetic lectin as a highly sensitive glucose sensor in aqueous solutions. 

Abstract Achieving selective molecular recognition of hydrophilic anions in water remains a formidable challenge due to the competitive nature of water and the high hydration energies of target anions such as sulfate. Here, we report the design, synthesis, and characterization of a simple dicationic tetralactam macrocycle (BPTL²⁺·2Cl⁻) capable of binding highly hydrated anions in water via charge‐assisted hydrogen bonding. Structural, spectroscopic, thermodynamic, and computational studies reveal that BPTL²⁺ exhibits a strong binding affinity for sulfate (K_a = 2892 M⁻¹), driven primarily by entropic gain from water release and reinforced by electrostatic and hydrogen bonding interactions. Single‐crystal X‐ray diffraction and DFT‐optimized structures confirm the formation of directional [N─H•••O] and [C─H•••O] hydrogen bonds. Comparative studies with a control macrocycle (6Na⁺•HCTL⁶⁻) that has a charge‐neutral binding cavity underscore the essential role of cationic charge in overcoming desolvation enthalpic penalties. The receptor displays anti‐Hofmeister selectivity, preferentially binding more hydrophilic anions. This work provides fundamental insights into the mechanisms of anion recognition in water. It establishes charge‐assisted hydrogen bonding as a powerful strategy for developing next‐generation receptors for sensing, separation, sequestration, transport, and catalysis in aqueous environments. 

A binary mixture of mesoporous silica nanoparticles plus organic polyammonium additive (dye or drug) is cleanly converted upon mild heating into hollow nanoparticles. The remodeled nanoparticle shell is an organized nanoscale assembly of globular additive/silica subunits and cancer cell assays show that a loaded drug additive is bioavailable. 

Abstract We report that the direct macrocyclization of naphthalene monomers bearing ethyl ester functional groups delivers prism[5]arene derivatives, which can be deprotected to yield water‐soluble prism[5]arenes (H1andH3).¹H NMR spectroscopy showed that dicationic guests bind with the hydrophobic cores buried inside the anisotropic magnetically shielding cavity. Isothermal titration calorimetry measurements showed thatH1andH3are high‐affinity hosts in PBS‐buffered water with K_avalues exceeding 10⁹ M⁻¹for a select guest. The complexation events are driven by the non‐classical hydrophobic effect, CH⋅⋅⋅π interactions, and electrostatic interactions. HostH1displays somewhat higher affinity toward a common guest than pillar[6]arene bearing carboxylic acid functional groups but is significantly less potent than pillar[6]arene bearing sulfate groups.H1andH3should be considered alongside other high affinity hosts for a variety of chemical and biological applications.