“…The NH signal is shifted slightly downfield as compared to the pure host III due to an interaction with maleic acid, the same behavior that was also observed in titration experiments. The overall picture reflects the formation of a host−guest adduct between macrocycle II and maleic acid and is quite similar to the spectra obtained for other similar host−guest systems. − No host−guest cross-peaks were registered in dilute solutions (5 mM) in nuclear Overhauser effect (NOE) difference experiments. 10 NOESY spectrum of 20 mM solution of 1:1 maleic acid and II in CD 3 CN.…”
A series of 14-, 15-, and 16-membered nickel(II) cyclidene macrocycles appended with 2-aminoethyl(2-pyridine) receptors I-III, respectively, were prepared and characterized by X-ray crystallography and NMR techniques. The 14- and 15-membered macrocycles I and II exist in a planar or extended Z-configuration, whereas the 16-membered macrocycle III was saddle shaped and had two asymmetric configurations in the unit cell (IIIa in a "capped" configuration and IIIb in an "open" configuration). Variable-temperature (1)H NMR studies of III in CD(3)CN were conducted (25-65 degrees C), and at room temperature, the interconversion between capping and uncapping is slow on the NMR time scale, resulting in a broad spectrum, whereas at 65 degrees C, interconversion was fast. (1)H NMR binding studies indicated I-III bind unsaturated dicarboxylic acids in a 1:1 stoichiometry with binding constants approaching 400 M(-)(1) in CD(3)CN, and the binding strength was dependent on the shape of the macrocyclic cyclidene platforms, whereas monocarboxylic acids were not bound. Generally, the planar 14-membered cyclidene I bound diacids the weakest and the 16-membered cyclidene III bound diacids the strongest. The presence of nuclear Overhauser effect spectrometry cross peaks in a 20 mM solution of 1:1 II-maleic acid indicates that the binding mode is ditopic with the guest being encapsulated by the aminoethylpyridine arms above the macrocyclic framework.
“…The NH signal is shifted slightly downfield as compared to the pure host III due to an interaction with maleic acid, the same behavior that was also observed in titration experiments. The overall picture reflects the formation of a host−guest adduct between macrocycle II and maleic acid and is quite similar to the spectra obtained for other similar host−guest systems. − No host−guest cross-peaks were registered in dilute solutions (5 mM) in nuclear Overhauser effect (NOE) difference experiments. 10 NOESY spectrum of 20 mM solution of 1:1 maleic acid and II in CD 3 CN.…”
A series of 14-, 15-, and 16-membered nickel(II) cyclidene macrocycles appended with 2-aminoethyl(2-pyridine) receptors I-III, respectively, were prepared and characterized by X-ray crystallography and NMR techniques. The 14- and 15-membered macrocycles I and II exist in a planar or extended Z-configuration, whereas the 16-membered macrocycle III was saddle shaped and had two asymmetric configurations in the unit cell (IIIa in a "capped" configuration and IIIb in an "open" configuration). Variable-temperature (1)H NMR studies of III in CD(3)CN were conducted (25-65 degrees C), and at room temperature, the interconversion between capping and uncapping is slow on the NMR time scale, resulting in a broad spectrum, whereas at 65 degrees C, interconversion was fast. (1)H NMR binding studies indicated I-III bind unsaturated dicarboxylic acids in a 1:1 stoichiometry with binding constants approaching 400 M(-)(1) in CD(3)CN, and the binding strength was dependent on the shape of the macrocyclic cyclidene platforms, whereas monocarboxylic acids were not bound. Generally, the planar 14-membered cyclidene I bound diacids the weakest and the 16-membered cyclidene III bound diacids the strongest. The presence of nuclear Overhauser effect spectrometry cross peaks in a 20 mM solution of 1:1 II-maleic acid indicates that the binding mode is ditopic with the guest being encapsulated by the aminoethylpyridine arms above the macrocyclic framework.
“…164 ) bind ammonium ions by their aromatic moieties. The turn structure induced by the amino acid sequence leads to a sandwich complex of the guest between both π-systems as confirmed by 2D NMR ROESY experiments [ 744 ]. The peptide 232 bound several quaternary ammonium salts in CDCl 3 with the highest binding constants for benzyltrimethylammonium chloride and N -butylpyridinium chloride with association constants of 580 M −1 and 1000 M −1 , respectively.…”
SummaryAmmonium ions are ubiquitous in chemistry and molecular biology. Considerable efforts have been undertaken to develop synthetic receptors for their selective molecular recognition. The type of host compounds for organic ammonium ion binding span a wide range from crown ethers to calixarenes to metal complexes. Typical intermolecular interactions are hydrogen bonds, electrostatic and cation–π interactions, hydrophobic interactions or reversible covalent bond formation. In this review we discuss the different classes of synthetic receptors for organic ammonium ion recognition and illustrate the scope and limitations of each class with selected examples from the recent literature. The molecular recognition of ammonium ions in amino acids is included and the enantioselective binding of chiral ammonium ions by synthetic receptors is also covered. In our conclusion we compare the strengths and weaknesses of the different types of ammonium ion receptors which may help to select the best approach for specific applications.
“…Cation−π interactions play a fundamental role in the formation of complexes between quats and natural or artificial receptors . The latter include cyclophanes, − cryptophanes, calixarenes, and acyclic receptors endowed with aromatic subunits. 5a,, …”
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