Aroylthioureas: new organic ionophores for heavy-metal ion selective electrodes

Thiourea derivatives (46 aroylthioureas) having different substituents clos e to the sulfur atom were synthesized and their ionophore potential in ion selective electrodes (ISEs) was examined. Structural considerations were ta ken into account based on the corresponding heavy-metal ISE parameters, As ionophores, some 1-furoyl-3-substituted thioureas (series 2) gave the best results in Pb(ii), Hg(ii) and Cd(ii) ISEs. The strong intramolecular hydrog en bond in series 2 allows ligand interaction only through the C=S group. S ubstituents on the furan and phenyl rings give rise to low solubility in th e membrane plasticizer. 3-Alkyl substituted furoylthioureas improve solubil ity but enhance oxidative processes with chain length. New X-ray diffractio n (XRD) structures and theoretical DFT calculations were considered in the analysis of the substituent influence on the selectivity of ISEs. These new ionophores have advantages because of their stability, simple synthesis an d easy modification of the sulfur binding ability resulting from substituti on.