The aqueous supramolecular chemistry of crown ethers

This mini-review summarizes the seminal exploration of aqueous supramolecular chemistry of crown ether macrocycles. In history, most research of crown ethers were focusing on their supramolecular chemistry in organic phase or in gas phase. In sharp contrast, the recent research evidently reveal that crown ethers are very suitable for studying abroad range of the properties and applications of water interactions, from: high water-solubility, control of Hofmeister series, "structural water", and supramolecular adhesives. Key studies revealing more details about the properties of water and aqueous solutions are highlighted.

Toward more potent imidazopyridine inhibitors of Candida albicans Bdf1: Modeling the role of structural waters in selective ligand binding

Novel agents to treat invasive fungal infections are urgently needed because the small number of established targets in pathogenic fungi makes the existing drug repertoire particularly vulnerable to the emergence of resistant strains. Recently, we reported that Candida albicans Bdf1, a bromodomain and extra-terminal domain (BET) bromodomain with paired acetyl-lysine (AcK) binding sites (BD1 and BD2) is essential for fungal cell growth and that an imidazopyridine (1) binds to BD2 with selectivity versus both BD1 and human BET bromodomains. Bromodomain binding pockets contain a conserved array of structural waters. Molecular dynamics simulations now reveal that one water molecule is less tightly bound to BD2 than to BD1, explaining the site selectivity of 1. This insight is useful in the performance of ligand docking studies to guide design of more effective Bdf1 inhibitors, as illustrated by the design of 10 new imidazopyridine BD2 ligands 1a-j, for which experimental binding and site selectivity data are presented.

A High Potential Polyanion Cathode Material for Rechargeable Mg-Ion Batteries

The development of Mg-ion batteries is hindered by the lack of cathode materials that allow facile and reversible Mg²⁺ intercalation at high potential. Herein, the authors present a polyanion cathode material of K₂ (VO)₂ (HPO₄ )₂ (C₂ O₄ )⋅4.5H₂ O (KVPCH) for Mg-ion batteries. The inductive effect of polyanions ensures the high redox potential of the vanadium centers. In addition, the material contains structural water located between the layers. It helps with Mg²⁺ desolvation at the electrode-electrolyte interface and facilitates its diffusion in the structure, as confirmed by experimental analysis and theoretical calculations. Thanks to those factors, the KVPCH electrode presents excellent Mg storage capability at room temperature. It delivers 121 mAh g^-1 capacity at 1C with a high average discharge potential of 0.16 V versus Ag/Ag⁺ (3.2 V vs Mg/Mg²⁺ ). A capacity retention of 87% is realized after 1500 cycles at 5C. A rocking-chair Mg-ion full cell is also demonstrated with the KVPCH cathode and a MoO_x anode, which achieves 46 mAh g^-1 capacity (based on the total active material mass of two electrodes). This work would bring effective paths for the design of cathode materials for Mg-ion batteries.

Hydration-mediated G-protein-coupled receptor activation

Although G-protein–coupled receptors (GPCRs) control vast physiological pathways, their activation remains chemically and physically enigmatic. Our osmotic stress studies of the visual receptor rhodopsin have redefined the standard model of GPCR signaling by revealing the essential role of bulk water. We show results consistent with a large number of water molecules flooding the rhodopsin interior during activation to stabilize the effector binding conformation. These results suggest a model of GPCR activation in which the receptor becomes solvent-swollen upon formation of the active state. We thus demonstrate the mechanism whereby water acts as a powerful allosteric modulator of a pharmacologically important membrane protein family.

The Rhodopsin family of G-protein–coupled receptors (GPCRs) comprises the targets of nearly a third of all pharmaceuticals. Despite structural water present in GPCR X-ray structures, the physiological relevance of these solvent molecules to rhodopsin signaling remains unknown. Here, we show experimental results consistent with the idea that rhodopsin activation in lipid membranes is coupled to bulk water movements into the protein. To quantify hydration changes, we measured reversible shifting of the metarhodopsin equilibrium due to osmotic stress using an extensive series of polyethylene glycol (PEG) osmolytes. We discovered clear evidence that light activation entails a large influx of bulk water (∼80–100 molecules) into the protein, giving insight into GPCR activation mechanisms. Various size polymer osmolytes directly control rhodopsin activation, in which large solutes are excluded from rhodopsin and dehydrate the protein, favoring the inactive state. In contrast, small osmolytes initially forward shift the activation equilibrium until a quantifiable saturation point is reached, similar to gain-of-function protein mutations. For the limit of increasing osmolyte size, a universal response of rhodopsin to osmotic stress is observed, suggesting it adopts a dynamic, hydrated sponge-like state upon photoactivation. Our results demand a rethinking of the role of water dynamics in modulating various intermediates in the GPCR energy landscape. We propose that besides bound water, an influx of bulk water plays a necessary role in establishing the active GPCR conformation that mediates signaling.

Reduced Intercalation Energy Barrier by Rich Structural Water in Spinel ZnMn2O4 for High-Rate Zinc-Ion Batteries

Aqueous zinc-ion batteries are considered promising next-generation systems for large-scale energy storage due to low cost, environmental friendliness, and high reversibility of the Zn anode. However, the interfacial charge-transfer resistance for the insertion of divalent Zn²⁺ into cathode materials is normally high, which limits the kinetics of Zn²⁺ transfer at the cathode/electrolyte interface. This study reveals the presence of rich structural water in spinel ZnMn₂O₄ (ZnMn₂O₄·0.94H₂O, denoted as ZMO), synthesized by a scalable and low-temperature process, significantly overcoming the great interfacial charge-transfer resistance. ZMO exhibits excellent electrochemical performance toward Zn storage, that is, high capacity (230 and 101 mA h g^-1 at 0.5 and 8 A g^-1), high specific energy/specific power (329 W h kg^-1/706 W kg^-1 and 134 W h kg^-1/11,160 W kg^-1), and stable cycle retention (75% after 2000 cycles at 4 A g^-1) can be achieved. On the contrary, the controlled sample ZMO-450 with deficient structural water, prepared by post-heat treatment of ZMO at 450 °C, demonstrates limited discharge capacity (45 and 15 mA h g^-1 at 0.5 and 8 A g^-1). As examined by electrochemical impedance spectroscopy, rich structural water in ZMO effectively reduces the activation energy barrier upon Zn²⁺ insertion, rendering fast interfacial kinetics for Zn storage. Benefiting from rich structural water in ZMO, the involvement of Zn²⁺ during the charge/discharge process exhibits good reversibility, as characterized by X-ray diffraction and X-ray photoelectron spectroscopy.

Rational Design and Bulk Synthesis of Water-Containing Supramolecular Polymers

The utilization of structural water in chemical self-assembly has not only effectively eliminated the negative influences of solvents from solutions or gels but has also provided new insight into the fabrication of new materials in bulk. However, up to now, supramolecular polymerization triggered by structural water has been dominated more by serendipity than rational design. After carefully analyzing the chemical structures of artificial monomers and gaining a deep understanding of the water-triggered assembly process, we report herein the bulk formation of polymeric materials from water and low-molecular weight monomers by rational design instead of serendipity.

Pore-modulating toxins exploit inherent slow inactivation to block K+ channels

Voltage-dependent potassium channels (K_vs) gate in response to changes in electrical membrane potential by coupling a voltage-sensing module with a K⁺-selective pore. Animal toxins targeting K_vs are classified as pore blockers, which physically plug the ion conduction pathway, or as gating modifiers, which disrupt voltage sensor movements. A third group of toxins blocks K⁺ conduction by an unknown mechanism via binding to the channel turrets. Here, we show that Conkunitzin-S1 (Cs1), a peptide toxin isolated from cone snail venom, binds at the turrets of K_v1.2 and targets a network of hydrogen bonds that govern water access to the peripheral cavities that surround the central pore. The resulting ectopic water flow triggers an asymmetric collapse of the pore by a process resembling that of inherent slow inactivation. Pore modulation by animal toxins exposes the peripheral cavity of K⁺ channels as a novel pharmacological target and provides a rational framework for drug design.

Water-Lubricated Intercalation in V2 O5 ·nH2 O for High-Capacity and High-Rate Aqueous Rechargeable Zinc Batteries

Low-cost, environment-friendly aqueous Zn batteries have great potential for large-scale energy storage, but the intercalation of zinc ions in the cathode materials is challenging and complex. Herein, the critical role of structural H₂ O on Zn²⁺ intercalation into bilayer V₂ O₅ ·nH₂ O is demonstrated. The results suggest that the H₂ O-solvated Zn²⁺ possesses largely reduced effective charge and thus reduced electrostatic interactions with the V₂ O₅ framework, effectively promoting its diffusion. Benefited from the "lubricating" effect, the aqueous Zn battery shows a specific energy of ≈144 Wh kg^-1 at 0.3 A g^-1 . Meanwhile, it can maintain an energy density of 90 Wh kg^-1 at a high power density of 6.4 kW kg^-1 (based on the cathode and 200% Zn anode), making it a promising candidate for high-performance, low-cost, safe, and environment-friendly energy-storage devices.

AquaBridge: A novel method for systematic search of structural water molecules within the protein active sites

We have developed a novel method for calculation of the water bridges that can be formed in the active sites of proteins in the absence or in the presence of small-molecule ligands. We tested its efficiency on a representative set of human ATP-binding proteins, and show that the docking accuracy of ligands can be substantially improved when water bridges are included in the modeling of protein-ligand interactions. Our analysis of binding pocket hydration can be a useful addition to the in silico approaches of Drug Design.