Analytical Sciences

Thermodynamics of Complexation between Thiourea-based Receptor and Acetate in Water/Acetonitrile Mixture

Takaya SUZUKI,* Yuuta SHIBUYA,* Takaya SATO,** Seiichi NISHIZAWA,** Itaru SATO,* and Akira YAMAGUCHI*

*College of Science, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512, Japan
**Department of Chemistry, Graduate School of Science, Tohoku University, Aoba, Sendai 980-8578, Japan

A thiourea-based receptor has been extensively studied for selective anion recognition for reasons of its strong hydrogen bond donor ability. In the present study, the thermodynamics of complexation between a thiourea-based receptor and acetate was examined in a water/acetonitrile mixture. The receptor used in this study was N,N′-bis(p-nitrophenyl)thiourea (BNPTU). UV/vis spectroscopic titration and isothermal titration calorimetry (ITC) experiments clearly revealed endothermic and entropy-driven complexation of BNPTU with acetate in water/acetonitrile mixtures. Since the endothermic peaks found in water/acetonitrile mixtures were about three times greater than those in acetonitrile, it appears that preferential hydration of both receptor and acetate was responsible for the endothermic and entropy-driven complexation reaction. The thermodynamic properties found in this study have the potential to contribute to the design of a thiourea-based anion receptor.

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