engleski

Calix[4]arenes bearing urea moieties - investigation of supramolecular behaviour

Calixarenes are a useful family of compounds that can bind cationic, anionic, and neutral species, when properly functionalised at upper and/or lower rim. Although (thio)urea-derivatives of calixarenes are known for three decades, their applicability for selective binding or transport of biologically important species is still widely unexplored. Receptors M1 and M2, which belong to this compound class, have been recently investigated as anion binders. Thermodynamics of their complexation with various anions (Cl–, HSO4–, H2PO4–, benzoate, and hydrogen pyrophosphate) was studied in acetonitrile. Complexes of 1:1 stoichiometry were observed with all examined anions except H2PO4– and hydrogen pyrophosphate which also formed 2:1 complexes (anion:receptor). Due to the larger number of urea groups in M2, the anion binding equilibrium constants for this receptor were proven to be significantly higher than those for hybrid amide- urea analogue M1. In this work the supramolecular behaviour of these two calix[4]arenes was characterized in more detail. Firstly, the cation binding abilities of M1 and M2 were examined focusing on alkali and alkaline earth metal cations using several experimental methods (NMR, ITC, UV/Vis). Further on, the ability of M1 and M2 to act as ion-pair receptors was investigated. Structural features of the complexes were elucidated by means of NMR spectroscopy and the cooperative effect of binding two oppositely charged species was evaluated and discussed from the thermodynamic point of view.

calix[4]arene ; anion-binding ; ion-pair receptor ; thermodynamics ; NMR

nije evidentirano