Interaction of Calix[4]arene and Aliphatic Amines: A Combined NMR, Spectrophotometric and Conductimetric Investigation

[摘要] Calixarenes are molecular receptors having a cavity defined by benzene rings and an acidic hydroxylic moiety, able to form complexes with metal ions, anions and neutral molecules.1 In acetonitrile, calixarenes react with amines via proton transfer forming salts, that, as proposed by Gutsche, would exist as an equilibrium between exo and endo-calix complexes, in the same manner that calixarenes interact with soft metal cations and fullerenes,2 even at low concentrations, such as that used in spectrophotometric titrations.3,4In solid state,5 the exo-calix structure of the salt formed by calix[4]arene and piperidine does not show interactions between ammonium ion and the calixarene cavity, and the interaction between ions occurs only through one hydrogen bond between N+-H and O- of calix[4]arene. Coulombic interactions have a major role for structures of ammonium-calixarene salts carrying acid groups.6De Namor et al.7,8studying the reactions involving p-tert-butylcalix[n]arenes (n= 6, 8) and amines in nitrobenzene and benzonitrile, observed that the salts formed exist as an equilibrium between free ions and ion pairs, and determined the values of proton transfer and association equilibrium constants. In these solvents, the formation of free ions was not detected when p-tert-butylcalix[4]arene was employed, but it was not determined whether the cause would be an exclusive ion pairing or the lack of proton transfer. A review by De Namor et al.9 includes a compilation of the results described in the literature. In this paper, we report the results obtained for the equilibrium constants of the system aliphatic amines and calix[4]arene, in acetonitrile, which allow the evaluation of the role of the cavity and phenolic oxygens without the interference of groups on para position. The substituents on para position prevent the solvation and a guest immersed in the cavity to suffer interactions with external molecules. In the

[学科分类] 化学（综合）

[关键词] calixarenes;supramolecular chemistry;interactions of amines