ArticleFluorinated Bambusurils as Highly Effective and Selective Transmembrane Cl À /HCO 3 À Antiporters Synthetic anion receptors can be used to transport ions across membranes. In this work, bambusuril macrocycles are demonstrated to be very efficient in exchanging chloride and bicarbonate ions, whereas exchange with nitrate is much slower. This is explained by the anion binding properties of the receptor. The high rates of transport by these bambusurils and mechanistic insight provided here represent an advancement toward the future therapeutic applications of synthetic anion carriers.

The simultaneous synthesis of a molecular nine-crossing composite knot that contains three trefoil tangles of the same handedness and a [Formula: see text] link (a type of cyclic [3]catenane topologically constrained to always have at least three twists within the links) is reported. Both compounds contain high degrees of topological writhe (w = 9), a structural feature of supercoiled DNA. The entwined products are generated from the cyclization of a hexameric Fe(II) circular helicate by ring-closing olefin metathesis, with the mixture of topological isomers formed as a result of different ligand connectivity patterns. The metal-coordinated composite knot was isolated by crystallization, the topology unambiguously proven by tandem mass spectrometry, with X-ray crystallography confirming that the 324-atom loop crosses itself nine times with matching handedness (all Δ or all Λ) at every metal centre within each molecule. Controlling the connectivity of the ligand end groups on circular metal helicate scaffolds provides an effective synthetic strategy for the stereoselective synthesis of composite knots and other complex molecular topologies.

The host-guest complexes of C-propyl-2-bromoresorcinarene with pyridine N-oxide, 3-methylpyridine N-oxide, quinoline N-oxide and isoquinoline N-oxide are studied using single crystal X-ray crystallography and 1 H NMR spectroscopy. The C-propyl-2-bromoresorcinarene forms endo-complexes with the aromatic N-oxides in the solid-state when crystallised from either methanol or acetone. In solution, the endo-complexes were observed only in methanol-d4. In DMSO the solvent itself is a good guest, and crystallization provides only solvate endo-complexes. The C-propyl-2-bromoresorcinarene shows remarkable flexibility when crystallised from either methanol or acetone, and packs into onedimensional self-included chains. Of special note, crystallizing C-propyl-2bromoresorcinarene with 3-methylpyridine N-oxide from acetone results in a 2:2 dimeric capsular assembly organized through both C−H•••πhost and N−O•••(H−O)host interactions.

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