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Anion removal from aqueous solutions remains a major challenge due to the strong hydration of anions. Here, we report the preparation of silica gel functionalized with covalently anchored bambusuril macrocycles. In aqueous solution, this material efficiently sorbs dicyanoaurate(I), the key anion in gold mining, even in the presence of competing dicyanoargentate(I) anions. We also examine the recyclability of the material and assess its stability in organic solvents, comparing its performance with that of a previously developed material containing noncovalently bound bambusuril.

The cover picture shows a fluorescent Cu‐Salphen host crystal structure interacting with an anion guest pink sphere that emits in the yellow‐green region represented by fireflies, as well as the counterparts linked to a polymer chain represented as a blue ribbon, which yields blue‐shifted hyperchromic cyan luminescence due to the protection from its coil conformation. They emerge from the UNESCO's World Heritage Site Central University City Campus of the National Autonomous University of Mexico. More information can be found in the Research Article by G. Zelada‐Guillén, M. V. Escárcega‐Bobadilla, and co‐workers.

This review intends to provide an overview on the role of halide anions in the development of the research area of asymmetric anion-binding organocatalysis. Key early elucidation studies with chloride as counter-anion confirmed this type of alternative activation, which was then exploited in several processes and contributed to the advance and consolidation of anion-binding catalysis as a field. Thus, the use of the halide in the catalyst–anion complex as both a mere counter-anion spectator or an active nucleophile has been depicted, along with the new trends toward additional noncovalent contacts within the HB-donor catalyst and supramolecular interactions to both the anion and the cationic reactive species.

Synthesis of the new scorpiand ligand L composed of a [9]aneN3 macrocyclic ring bearing a CH2CH2NHCH2-anthracene tail is reported. L forms both cation (Zn2+) and anion (phosphate, benzoate) complexes. In addition, the zinc complexes of L bind these anions. The equilibrium constants for ligand protonation and complex formation were determined in 0.1 M NaCl aqueous solution at 298.1 ± 0.1 K by means of potentiometric (pH-metric) titrations. pH Controlled coordination/detachment of the ligand tail to Zn2+ switch on and off the fluorescence emission from the anthracene fluorophore. Accordingly, L is able to sense Zn2+ in the pH range 6–10 down to nM concentrations of the metal ion. L can efficiently sense Zn2+ even in the presence of large excess of coordinating anions, such as cyanide, sulphide, phosphate and benzoate, despite their ability to bind the metal ion.

The CLC family of proteins are involved in a variety of physiological processes to control cellular chloride concentration. Two distinct classes of CLC proteins, Cl⁻ channels and Cl⁻/H⁺ antiporters, have been functionally and structurally investigated over the last several decades. Previous studies have suggested that the conformational heterogeneity of the critical glutamate residue, Gluₑₓ, could explain the transport cycle of CLC-type Cl⁻/H⁺ antiporters. However, the presence of multiple conformations (Up, Middle, and Down) of the Gluₑₓ has been suggested from combined structural snapshots of 2 different CLC antiporters: CLC-ec1 from Escherichia coli and cmCLC from a thermophilic red alga, Cyanidioschyzon merolae. Thus, we aimed to investigate further the heterogeneity of Gluₑₓ-conformations in CLC-ec1, the most deeply studied CLC antiporter, at both functional and structural levels. Here, we show that the crystal structures of the Gluₑₓ mutant E148D and wild-type CLC-ec1 with varying anion concentrations suggest a structural intermediate, the “Midlow” conformation. We also found that an extra anion can be located above the external Cl⁻-binding site in the E148D mutant when the anion concentration is high. Moreover, we observed that a carboxylate in solution can occupy either the external or central Cl⁻-binding site in the ungated E148A mutant using an anomalously detectable short carboxylic acid, bromoacetate. These results lend credibility to the idea that the Gluₑₓ can take at least 3 distinct conformational states during the transport cycle of a single CLC antiporter.

Ligands L1 and L2 are composed, respectively, by a diethylenetriamine or a dipropylenetriamine moiety linked at their extremities to anthracene units through methylene bridges and form stable 1:1 complexes with Zn(II), in which the metal is coordinated by all three nitrogens of the ligands. Zn(II) binding by L1 leads to a marked enhancement of the fluorescence emission, thanks to the inhibition of the photoinduced electron transfer (PET) process from the benzylic amine groups of the triamine sub-unit to the excited fluorophore, which normally quenches the emission of fluorescent polyamine receptors. Conversely, the emission of L2 is somewhat quenched by Zn(II) binding likely due—as also indicated by ab initio calculations and molecular dynamics simulations—to the formation of cation π quenching contacts between the metal and the anthracene moieties that overcome the effects of PET inhibition. The Zn(II) complexes of both ligands are able to bind ketoprofen (KP) in its anionic form, thanks to the formation of COO−—Zn(II) coordinative bonds, to form [KPZnL]+ and [(KP)2ZnL] (L = L1 or L2) ternary adducts. While KP binding to [ZnL2]2+ enhances the fluorophore emission, coordination of KP to [ZnL1]2+ slightly reduces the anthracene emission, due, once again, to the formation in the L1 ternary complexes of marked cation π contacts.

Anionic species are one of the most common pollutants in residual and freshwaters. The presence of anthropogenic anions in water drastically increases the toxicity to living beings. Here, we report the preparation of a new optical active material based on tri(tosylamino)phthalocyanines grafted to ferromagnetic silica nanoparticles for anion detection and removal. The new unsymmetrical phthalocyanines (Pcs) proved to be excellent chemosensors for several anions (AcO−, Br−, Cl−, CN−, F−, H2PO4−, HSO4−, NO2−, NO3−, and OH−) in dimethyl sulfoxide (DMSO). Furthermore, the Pcs were grafted onto magnetic nanoparticles. The resulting novel hybrid material showed selectivity and sensitivity towards CN−, F−, and OH− anions in DMSO with limit of detection (LoD) of ≈4.0 µM. In water, the new hybrid chemosensor demonstrated selectivity and sensitivity for CN− and OH− anions with LoD of ≈0.2 µM. The new hybrids are easily recovered using a magnet, allowing recyclability and reusability, after acidic treatment, without losing the sensing proprieties.

We describe the synthesis, crystallographic characterization of a new Cu−Salphen compound and its use as a host Lewis‐acid against guest anions in two versions: a) free molecule, b) copolymerized with methyl methacrylate:n‐butyl acrylate (1 : 4‐wt.) as protective co‐monomers. Higher contents in Cu−Salphen yielded larger and more homogeneous polymer sizes. Polymer size together with glass transitions, heat capacity, thermal degradation, guest‐saturation degrees and host‐guest species distribution profiles from spectrophotometric titrations explained growths of up to 630‐fold in K11 and 180000‐fold in K12 for the host's binding site attributable to a solvophobic protection from the macromolecular structure. Spectrofluorimetry revealed blue‐shifted×13–16 larger luminescence for Cu−Salphen in the polymers (λem=488–498 nm) than that of the non‐polymerized counterpart (λem=510–543 nm) and “turn‐on” blue‐shifted enhanced fluorescence upon guest association. We propose a cooperative incorporation of the guests occurring from the outer medium toward internally protected binding site pockets in the random coil polymer conformations. One‐color cached light beacons. Fluorescence performance of a new Cu−Salphen coordination compound showed blue‐shifted turn‐on one‐order of magnitude higher luminescence when protected by copolymerization to acrylic monomers in chains of different sizes. Higher light emission levels and up to five‐orders of magnitude larger association constants were possible upon host‐guest binding for the polymerized metal complex, after internalization of anion guests into the protective polymer random coils.

The dual-host strategy offers a straightforward approach to ion separation, yet the nature of cooperative interactions between receptor-complexed cations and anions remains poorly understood. In this study, we utilize 18-crown-6 as a cation receptor and a tripodal hexaurea receptor L as an anion receptor to extract cesium salts (chloride, nitrate, carbonate, sulfate, and phosphate) from the solid phase into chloroform. Remarkably, Cs 3 PO 4 exhibits the highest extraction efficiency, driven by strong cooperative interactions involving ion-dipole coordination between Cs + and carbonyl (C=O) groups, as well as direct ion-pairing interactions between 18-crown-6-complexed Cs + and hexaurea-bound PO 4 3− . Single-crystal structural analysis corroborates these interactions, shedding light on the underlying mechanisms and providing valuable guidance for the rational design of advanced dual-host systems for selective ion separation.

The synthesis of a new RuII complex, in which the metal is coordinated by two 1,10-phenanthroline ligands and a 2,2′-bipyridyl unit linked, via methylene bridges in its 4 and 4′ positions, to two 1,4,7,10-tetraazacyclododecane (cyclen) macrocycles ([Ru(phen)2L]2+) is reported. Protonation and ZnII binding by [Ru(phen)2L]2+ have been analyzed by potentiometric titration, evidencing the formation of mixed hetero-binuclear and hetero-trinuclear ZnII/RuII complexes. These complexes were tested as bis-phenol A (BPA) binders. Only the dizinc complex with [Ru(phen)2L]2+ is able to bind BPA in aqueous solution, affording a remarkably stable Zn2[Ru(phen)2L]BPA(H−2)4+ adduct at neutral pH, in which BPA is bound in its doubly deprotonated form to the two ZnII ions. BPA binding was found to quench the luminescence emission of the RuII(phen)2bipy core. Although the quenching effect is modest, this study demonstrates that appropriately designed dizinc complexes can be used for binding and optical sensing of BPA in water.