title: Conformational features and recognition properties of a conformationally blocked calix[7]arene derivative.
abstract: The shaping of a calix[7]arene macrocycle into cone-like structure 3, through exhaustive alkylation of doubly bridged calix[7]arene derivative 2 with bulky groups, has been investigated. Conformational details about the structure adopted by calix[7]arene derivative 3 in solution have been obtained by using chemical shift surface maps, as previously reported by our group. Thus, chemical shift contour plots indicated that 3 adopted a cone-shaped structure in solution analogous to that adopted by the known p-tert-butylcalix[7]arene heptacarboxylic acid derivative 4. Interestingly, the X-ray structure of derivative 3 showed a high degree of similarity to the theoretical structure, which confirmed the validity of the contour plots method. The preorganized calix[7]arene host 3 showed interesting recognition abilities toward both organic and alkali cations. In fact, an unprecedented endo-cavity complexation of linear and branched alkyl ammonium cations with a larger calix[7]arene host was evidenced. A comparable affinity for branched tBuNH(3)(+) and linear nBuNH(3)(+) guests was observed.
authors.affiliation: Dipartimento di Chimica e Biologia, Università degli Studi di Salerno, Via Ponte don Melillo, 84084 Fisciano, Italy. cgaeta@unisa.it
authors.forename: Carmine
authors.initials: C
authors.lastname: Gaeta
authors.forename: Carmen
authors.initials: C
authors.lastname: Talotta
authors.forename: Francesco
authors.initials: F
authors.lastname: Farina
authors.forename: Gaetano
authors.initials: G
authors.lastname: Campi
authors.forename: Mercedes
authors.initials: M
authors.lastname: Camalli
authors.forename: Placido
authors.initials: P
authors.lastname: Neri