[15]aneN(4)S: Synthesis, Thermodynamic Studies and Potential Applications in Chelation Therapy

The purpose of this work was to synthesize and characterize the thiatetraaza macrocycle 1-thia-4,7,10,13-tetraazacyclopentadecane ([15]aneN(4)S). Its acid-base behaviour was studied by potentiometry at 25 °C and ionic strength 0.10 M in KNO(3). The protonation sequence of this ligand was investigated by (1)H-NMR titration that also allowed the determination of protonation constants in D(2)O. Binding studies of [15]aneN(4)S with Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+) and Pb(2+) metal ions were further performed under the same experimental conditions. The results demonstrated that this compound has a higher selectivity and thermodynamic stability for Hg(2+) and Cu(2+), followed by Ni(2+). The UV-visible-near IR spectroscopies and magnetic moment data for the Co(II) and Ni(II) complexes indicated a tetragonal distorted coordination geometry for both metal centres. The value of magnetic moment and the X-band EPR spectra of the Cu(II) complex are consistent with a distorted square pyramidal geometry.