title: Rational design of a nonbasic molecular receptor for selective NH4+/K+ complexation in the gas phase.
abstract: A new molecular receptor (1) for ammonium recognition has been designed and constructed by using only carbon atoms. This molecular receptor can co-exist in two different isoenergetic conformations but, upon complexation, the conformers are no longer isoenergetic, and a basket-shaped conformation becomes clearly more stable. The pre-organised tetrahedral structure of this basket-shaped molecule favours the complexation of ammonium ions by N-H⋅⋅⋅π interactions with the four phenyl groups of the host. A similar behaviour is not observed in a similar, but less pre-organised, reference molecule. ESI-MS competition experiments show that 1 is able to bind NH(4)(+) over K(+) selectively. This is the first example of a neutral molecular receptor that shows a remarkable NH(4)(+)/K(+) selectivity. DFT-calculations provide insight into the nature of host-guest interactions of both 1⋅NH(4)(+) and 1⋅K(+) complexes as well as in the mechanism involved in multiple cation-π interactions and the influence of these interactions on the conformational stability and the selective binding of the host.
authors.affiliation: Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, Spain.
authors.forename: Ainoa
authors.initials: A
authors.lastname: Rueda-Zubiaurre
authors.forename: Noelia
authors.initials: N
authors.lastname: Herrero-García
authors.forename: María
authors.initials: M
authors.lastname: del Rosario Torres
authors.forename: Israel
authors.initials: I
authors.lastname: Fernández
authors.forename: José
authors.initials: J
authors.lastname: Osío Barcina
mesh_terms: D001665:Binding Sites; D002412:Cations / Q000737:chemistry; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D004735:Energy Transfer; D007536:Isomerism; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D011188:Potassium / Q000737:chemistry*; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D013379:Substrate Specificity
chemical_list: D002412:Cations; D000644:Quaternary Ammonium Compounds; D011188:Potassium