Complexation Study of Bis-Thiourea Compound with Aluminium Ion as Ionophore for Development of Potentiometric Ion Sensor

Thiourea compounds have been applied as ionophores for mercury, cadmium, copper, lead, and iron(III) in the field of chemical sensor. However, thiourea compound as aluminium ionophore has not yet been sufficiently explored. In this work, a new thiourea compound, 1,1'-limethylazanediyl)bis(ethane-2,1-diyl)]bis[3-(naplztlzalen-1-yl)tlziourea] had been synthesized and characterized by using 1H, 13C-nuclear magnetic resonance spectroscopy, Fourier-transform infrared spectroscopy and mass spectrometry. To assess and confirm the suitability of ACH compound as aluminum ionophore, complexation study of ACH ligand with aluminum ion in different solvent compositions of H2O-EtOH via spectrofluorimetic method had been carried out. Among the five types of solvent mixtures, the study indicated that only the solvent mixture of 25%H2O-75%EtOH showed the formation of complex. The stoichiometric ratio formed between ACH ligand and Al3+ ions was 3:1 with the formula of Al(ACH)(3)](3+) and the pK(a) value was 5.10 +/- 0.01. The structure optimization of the complex ion [ACH-Al](3+) in the ratio of 1:1 was also conducted by using the density functional theory calculation. Both of the sulfur atoms in the functional group of bis-thiourea were found to be the main active sites for the complexation process and the ACH ligand showed a partial cavity geometry to coordinate with Al3+ ion. The low negative value of the binding energy [ACH-Al](3+), -5.560 x 10(6) kJ/mol also showed that the complex ion formed was strong and stable. In conclusion, ACH compound was suitable as a new aluminum ionophore for potentiometric ion sensor.