Receptors For Anion Recognition Research Articles

Preorganized Homochiral Pyrrole-Based Receptors That Display Enantioselective Anion Binding.

Herein, a new scaffold for anion recognition based on a tripodal tris(pyrrolamide) motif is presented. The receptors were able to bind to a variety of anions with high affinity. Using density functional theory methods, the three-dimensional geometry of the receptor-anion complex was calculated. These calculations show that the receptors bind anions via a preorganized cavity of amide and pyrrole hydrogen bond donor groups. Based on these findings, homochiral tris(pyrrolamide) receptors were prepared, which produced as much as a 1.6-fold greater affinity for (S)-(+)-mandelate over (R)-(-)-mandelate, demonstrating the ability to differentiate between these enantiomeric anions. The interaction of (S)-(+)-mandelate and (R)-(-)-mandelate within the homochiral receptor was examined by solution NMR spectroscopy and density functional theory calculations. These findings indicate that the preorganized positioning of the pyrrole groups and subsequent sterics allows to differentiate between the stereoisomeric anions.

ChemInform Abstract: Di‐ and Tricationic Organic Salts: An Overview of Their Properties and Applications

AbstractReview: 104 refs + subrefs

Di‐ and Tricationic Organic Salts: An Overview of Their Properties and Applications

AbstractDuring recent years growing interest has been devoted to the synthesis and applications of polycationic organic salts. Among them, di‐ and tricationic organic salts can be considered the natural evolution of monocationic ones. These last have given rise to the large class of ionic liquids. In the cases of di‐ and tricationic organic salts, the potential to change their structural features simply by varying the properties either of the charged heads or of the spacers separating them provides the opportunity to obtain materials suitable for different applications. This review article highlights recent progress in the study of the properties of di‐ and tricationic organic salts, as well as in some of their uses as solvent systems, receptors for anion recognition, ionic liquid crystals, low‐molecular‐weight gelators, additives for dye‐sensitized solar cells, and so on.

Pyridyl- and benzimidazole-based ruthenium(iii) complex for selective chloride recognition through fluorescence spectroscopy

Three ruthenium(II) and (III) metal complexes of the compositions ([Ru(1)(Cl)(PPh3)]+ (4), ([Ru(2)(Cl)(PPh3)]+ (5) and ([Ru(3)(Cl)(H2O)]2+ (6) have been synthesized from oligodentate pyridyl-(1) and benzimidazole ligands (2–3) and structurally characterized. Our investigations revealed that if the coordination sphere of the metal ion carries a strong coordinating PPh3 ligand (complexes 4 and 5), the framework was not suitable for anion binding at all. However, when coordination of solvent (H2O) to the metal centre occurred instead (complex 6), a receptor for anion recognition through fluorescence spectroscopy could be generated. This allowed us to develop a sensor for the selective recognition of chloride over several other anions. In order to screen potential applications, the sensor was tested for the determination of chloride concentration in a series of four commercially available oral rehydration salts, giving excellent agreement with the values reported by the corresponding manufacturer. The detection limit was established to be 5 μM.

Anion Recognition by a Macrobicycle Based on a Tetraoxadiaza Macrocycle and an Isophthalamide Head Unit

A macrobicycle formed by a tetraoxadiaza macrocycle containing a dibenzofuran (DBF) spacer and an isophthalamide head unit, named DBF-bz, was used as receptor for anion recognition. The molecular structure of DBF-bz was established in solution by NMR and ESI-MS spectroscopies and in single crystal by X-ray diffraction analysis. The X-ray structure showed a water molecule encapsulated into the macrobicyclic cavity by four hydrogen bonds, two of them involving the two N-H amide binding sites and the oxygen of the water molecule (N-H...O hydrogen bonds) and the other two (O-H...N) involving the amine groups as hydrogen bonding acceptors. (1)H NMR temperature dependence studies demonstrated that the same structure exists in solution. The ability of this ditopic receptor to recognize alkali halide salts was evaluated by extraction studies followed by (1)H NMR and ESI-MS spectroscopies. The macrobicycle showed a capacity to extract halide salts from aqueous solutions into organic phases. The binding ability of this macrobicycle for halides was also quantitatively investigated using (1)H NMR titrations in CDCl(3) (and DMSO-d(6)) solution, and in acidic D(2)O solution. The largest binding association constant was found for the chloride anion and the completely protonated receptor. The results suggest that the diammonium-diamide unit of the receptor strongly bind the anionic substrate via multiple N-H...Cl(-) hydrogen bonds and electrostatic interactions. The binding trend follows the order Cl(-) > Br(-) > I(-) approximately F(-) established from the best fit between the size of the anion and the cavity size of the protonated macrobicycle. Molecular dynamics (MD) simulations of the DBF-bz in CHCl(3) solution allowed a detailed insight into the structural and binding properties of the receptor.