Density functional study of molecular recognition and reactivity of thiourea derivatives used in sensors for heavy metal polluting cations

The geometry and electronic structure of four thiourea derivatives, 1,3-dip henylthiourea, 1-furoyl-3-phenylthiourea, 1-furoyl-3-bencyl-3-phenylthioure a, and 1-furoyl-3-hydroxyethylthiourea, were determined by means of the DGa uss program, which is a density functional theory based method. Calculation s performed were of the all-electron type at the local spin density level o f theory. Orbital basis sets of DZVP2 quality were used for the H, C, N, O, and S atoms. The frontier molecular orbitals were characterized. They acco unt for the observed selectivity of these molecules toward the following ca tions: Pb2+, Hg2+, Cd2+, Ag+, Cu2+, Ni2+, Zn2+, and Mn2+. Moreover, the loc alization of the highest occupied molecular orbital coupled with a high neg ative charge over the sulfur center accounts for the softness of the active sulfur site. Indeed, a metal-sulfur interaction is mainly responsible for the observed electrochemical behaviors in ion-selective electrodes toward t he different cations. These results agree with the estimated softness repor ted previously for these cations. Our calculations explain the observed dif ferences of reactivity for these neutral carriers through their interaction s with heavy metal cations. (C) 2000 John Wiley & Sons, Inc.