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

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• 作者：Nicolas Bernier ; Slvia Carvalho ; Feng Li ; Rita Delgado ; Vtor Flix
• 刊名：Journal of Organic Chemistry
• 出版年：2009
• 出版时间：July 3, 2009
• 年：2009
• 卷：74
• 期：13
• 页码：4819-4827
• 全文大小：330K
• 年卷期：v.74,no.13(July 3, 2009)
• ISSN：1520-6904

文摘

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. ¹H 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 ¹H 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 ¹H NMR titrations in CDCl₃ (and DMSO-d₆) solution, and in acidic D₂O 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⁻ ≈ 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 CHCl₃ solution allowed a detailed insight into the structural and binding properties of the receptor.