1362017-23-9Relevant academic research and scientific papers
Conformational features and recognition properties of a conformationally blocked calix[7]arene derivative
Gaeta, Carmine,Talotta, Carmen,Farina, Francesco,Campi, Gaetano,Camalli, Mercedes,Neri, Placido
experimental part, p. 1219 - 1230 (2012/03/26)
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 tBuNH3+ and linear nBuNH3+ guests was observed. Pursuing the weak: The first example of a completely rigidified calix[7]arene derivative (see figure) shows interesting recognition abilities toward cationic guests. In particular, an endo-calix complexation of alkylammonium guests was observed when they are coupled to the "superweak" tetrakis[3,5-bis(trifluoromethyl) phenyl]borate anion. Copyright
