Anion Recognition through Multivalent C-H Hydrogen Bonds: Anion-Induced Foldamer Formation and Transport across Phospholipid Membranes

Recognition of anion-water clusters by peptide-based supramolecular capsules

The biological and technological importance of anion-mediated processes has made the development of improved methods for the selective recognition of anions one of the most relevant research topics today. The hydration sphere of anions plays an important role in the functions performed by anions by forming a variety of cluster complexes. Here we describe a supramolecular capsule that recognizes hydrated anion clusters. These clusters are most likely composed of three ions that form hydrated C3 symmetry complexes that are entrapped within the supramolecular capsule of the same symmetry. The capsule is made of self-assembled α,γ-cyclic peptide containing amino acid with by five-membered rings and equipped with a tris(triazolylethyl)amine cap. To recognise the hydrated anion clusters, the hexapeptide capsule must disassemble to entrap them between its two subunits.

Probing and evaluating transmembrane chloride ion transport in double walled trifluorophenyl/phthalimide extended calix[4]pyrrole-based supramolecular receptors

Therapeutic applications have sparked increased interest in the use of synthetic anion receptors for ion transport across lipid membranes. In this context, the construction of synthetic transmembrane transporters for the physiologically important chloride ion is currently of enormous interest. As a result, considerable effort is being devoted to the design and synthesis of artificial transmembrane chloride ion transporters. However, only inadequate progress has been made in developing macrocyclic chloride ion transporters using the fundamental principles of supramolecular chemistry, and hence this field entails fostering investigations. In this investigation, the synthesis of two new double walled trifluorophenyl/phthalimide extended calix[4]pyrrole (C4P) receptors (3 and 7) has been successfully reported. 1H-NMR titration and HRMS studies confirmed the 1 : 1 binding stoichiometry of the chloride ion with these receptors in the solution phase (only receptor 3b was studied by 1H-NMR). Regarding ion transport of 3b and 7, when studied in the HPTS-based vesicular system, 3b showed better activity with an EC50 value of 0.39 μM. The detailed ion transport studies on 3b have revealed that ion transport occurs through the Cl-/NO3- antiport mode.

Remote control of anion binding by CH-based receptors

We show that the substitution of tetra(benzimidazole)resorcin[4]arenes with electron withdrawing groups on the upper rim enhances anion binding at the opposite edge by more than three orders of magnitude. Moreover, selective anion binding at either the OH/NH or CH binding sites is demonstrated.

The paradigm for exceptional iodine capture by nonporous amorphous electron-deficient cyclophanes

Nuclear power emerges as a beacon of hope in tackling the energy crisis. However, the emission of radioactive iodine originating from nuclear waste and accidents poses a serious danger to nature and human well-being. Therefore, it becomes imperative to urgently develop suitable adsorbents capable of iodine capture and long-term storage. It's generally recognized that achieving high iodine capture efficiency necessitates the presence of electron-rich pores/cavities that facilitate charge-transfer (CT) interactions, as well as effective sorption sites capable of engaging in lone pair interactions with iodine. In this study, an unprecedented iodine capture paradigm by nonporous amorphous electron-deficient tetracationic cycloalkanes in vapor and aqueous solutions is revealed, overturning preconceived notions of iodine trapping materials. A newly reported tetracationic cyclophane, BPy-Box4+, exhibited an exceptional iodine vapor sorption capacity of 3.99 g g-1, remarkable iodine removal efficiency in aqueous media, and outstanding reusability. The iodine capture mechanism is unambiguously elucidated by theoretical calculations and the single-crystal structures of cyclophanes with a gradual increase in iodine content, underlining the vital role of host-guest (1:1 or 1:2) interactions for the enhanced iodine capture. The current study demonstrates a new paradigm for enhanced iodine capture by nonporous amorphous electron-deficient cyclophanes through host-guest complexation.

A chloride-responsive molecular switch: driving ion transport and empowering antibacterial properties

A molecular switch was developed to recognize and transport Cl- across lipid bilayers. The XRD-crystal structure and NOESY NMR spectra of a potent 4-aminoquinazoline analogue confirmed Cl--induced conformation changes. Systematic biophysical studies revealed that the quinazoline moiety forms cooperative interactions of H+ and Cl- ions with the thiourea moiety, resulting in the transport of H+/Cl- across the membranes. A pH-dependent analysis revealed that the transport of Cl- by the potent compound increased in an acidic environment. The potent compound could also transport H+/Cl- across Gram-positive bacteria, leading to antibacterial activities.

Sugar-based carboxamidoquinoline conjugate for sensing Cu2+ and Au3+ ions in water through different binding modes and real application

A simple water-soluble carboxamidoquinoline derivative of glucofuranose 1 exhibited reversible selectivity toward Cu2+ and Au3+ ions in different binding modes. Sensor 1 is an example of a dual sensor for identifying copper and gold ions in the water medium. Sensor 1 exhibited excellent selection ability and sensitivity for Cu2+ and Au3+ ions rather than several metal ions and anions with a wide pH range (5-10). The association constants for both ions were determined to be 3.58 × 104 M-1 and 1.84 × 104 M-1, respectively. The 1:1 binding chemistry of the complexes was verified from the Job method and again validated through mass spectra. Sensor 1 can detect Cu2+ and Au3+ ions at very low concentrations, such as 0.014 μM for Cu2+ and 0.058 μM for Au3+. The different sensing strategies of sensor 1 towards Cu2+ and Au3+ were manifested from the photophysical properties of sensor 2 with metal ions, FT-IR spectra, and theoretical (DFT) observations. The useful relevance of the sensor for Cu2+ and Au3+ ions was tested in different water samples.

Nontoxic Artificial Chloride Channel Formation in Epithelial Cells by Isophthalic Acid-Based Small Molecules

Artificial channels capable of facilitating the transport of Cl^- ions across cell membranes while being nontoxic to the cells are rare. Such synthetic ion channels can mimic the functions of membrane transport proteins and, therefore, have the potential to treat channelopathies by replacing defective ion channels. Here we report isophthalic acid-based structurally simple molecules 1 a and 2 a, which self-assemble to render supramolecular nanochannels that allow selective transport of Cl^- ions. As evident from the single-crystal X-ray diffraction analysis, the self-assembly is governed by intermolecular hydrogen bonding and π-π stacking interactions. The MD simulation studies for both 1 a and 2 a confirmed the formation of stable Cl^- channel assembly in the lipid membrane and Cl^- transport through them. The MQAE assay showed the efficacy of the compounds in delivering Cl^- ions into cells, and the MTT assays proved that the compounds are nontoxic to cells even at a concentration of 100 μM.

Progress and prospects toward supramolecular bioactive ion transporters

The majority of cellular physiological processes depend on natural ion channels, which are pore-forming membrane-embedded proteins that let ions flow across the cell membranes selectively. This selective movement of ions across the membranes balances the osmolality within and outside the cell. However, mutations in the genes that encode essential membrane transport proteins or structural reorganisation of these proteins can cause life-threatening diseases like cystic fibrosis. Artificial ion transport systems have opened up a way to replace dysfunctional natural ion channels to cure such diseases through channel replacement therapy. Moreover, recent research has also demonstrated the ability of these systems to kill cancer cells, reigniting interest in the field among scientists. Our contributions to the recent progress in the design and development of artificial chloride ion transporters and their effect on biological systems have been discussed in this review. This review would provide current vistas and future directions toward the development of novel ion transporters with improved biocompatibility and desired anti-cancer properties. Additionally, it strongly emphasises stimuli-responsive ion transport systems, which are crucial for obtaining target-specificity and may speed up the application of these systems in clinical therapeutics.

Multistate Redox-Switchable Ion Transport Using Chalcogen-Bonding Anionophores

Synthetic supramolecular transmembrane anionophores have emerged as promising anticancer chemotherapeutics. However, key to their targeted application is achieving spatiotemporally controlled activity. Herein, we report a series of chalcogen-bonding diaryl tellurium-based transporters in which their anion binding potency and anionophoric activity are controlled through reversible redox cycling between Te oxidation states. This unprecedented in situ reversible multistate switching allows for switching between ON and OFF anion transport and is crucially achieved with biomimetic chemical redox couples.

A Benzimidazolium-Based Organic Cage with Antimicrobial Activity

Considering the wide interest in (benz)imidazolium-based drugs, we here report our study on a benzimidazolium-based organic cage as potential antimicrobial and antifungal agent. Cytotoxicity studies on a human derived cell line, SH-SY5Y, showed that the cage is not cytotoxic at all at the investigated concentrations. Anion binding studies demonstrated that the cage can bind anions (chloride and nitrate, in particular) both in organic solvent and 20%v D2O/CD3CN mixture. The cage was also tested as anionophore, showing a weak but measurable transport of chloride and nitrate across LUVs vesicles. Nonetheless, the compounds have antimicrobial activity towards Staphylococcus aureus (Gram-positive bacteria). This is probably the first organic cage studied as anionophore and antimicrobial agent.

Chloride Transport across Liposomes and Cells by Nontoxic 3-(1H-1,2,3-Triazol-1-yl)benzamides

Synthetic anion transmembrane transporters are adding new aspirations for treating channelopathies by replacing defective ion channels. The availability of such suitable candidates is still infrequent due to the associated toxicity. Here, we report 3-(1H-1,2,3-triazol-1-yl)benzamides as transmembrane anion carriers, nontoxic to cells. The selective and electrogenic chloride transport activity was established by fluorescence and ion selective electrode-based assays. MQAE assay confirmed the chloride uptake into the cells by the nontoxic compounds.