Binding Study of Ionizable Calix[4]-1,3-Crowns-5,6 Nano-baskets by Differential Pulse Voltammetry

Abstract

Four proton di-ionizable diacid conformers of cone 25,27-di(carboxymethoxy)calix[4]arene-crown-5, 1,3-alternate 25,27-di[carboxymethoxy]-calix[4]arene-crown-5, cone 25,27-bis[carboxymethoxy]calix[4]arene-crown-6 and 1,3-alternate 25,27-di[carboxymethoxy]-calix[4]arene-crown-6 were synthesized and their binding abilities toward alkali and alkaline earth metals as well as some lanthanides were studied by means of differential pulse voltammetry. The novelty of this study was investigation of those nano-baskets by voltammetric behavior of two acidic moieties in each scaffold during complexation of the crown ether ring. Their voltammetric behavior was closely related to the complex formation by entrapment of the cation into the crown ether cavity and ion-dipole interaction between cation and acidic moieties in calixcrowns. The results revealed the selective changes in voltammetric behavior of synthesized scaffolds toward the cations. Moreover, the position of crown ether in 1,3-alternate instead of cone enhanced the domain of binding ability to more cations. Furthermore, it was shown that those carboxylic acid moieties, which were far from the crown ether ring in the 1,3-alternate, were not affected by encapsulated cations in the coordination space of crown ether and showed no voltammetric response.