Heavy metal complexation by N-acyl(thio)urea-functionalized cavitands: synthesis, extraction and potentiometric studies

The synthesis and binding properties of resorcinarene-based cavitands functionalized with N-acylthiourea moieties towards different cations are described. Extraction studies with metal (Pb2+, Cu2+, Ag+, Hg2+, Cd2+, Eu3+, Fe3+, K+, Na+, and Ca2+) picrates and the incorporation in ion selective electrodes (ISEs), show that there is more than a 40% increase of the Ag+ extraction for N-acylthiourea ionophores (2, 3, and 8) in comparison with N-benzoyl-N′-benzylthiourea (9). Ionophore 8, which has a C3 chain between the platform and the ionophore, extracts two times more Cu2+ than the more rigid one (2). Stoichiometry studies showed for ligand 2 a ligand/metal ratio of 1:1, while for model compound 9 a ratio of 1:2 was found. Potentiometric studies of electrodes revealed that cavitands 2, 3, and 8 induce a significantly different selectivity pattern compared to the cation-exchanger used, as well as model compound 9. Especially, a considerable enhancement of the selectivity towards Ag+ and Pb2+ over K+, Ca2+, and Na2+ ions was observed.