Solubility increase of colloidal zinc hydroxide as revealed by isothermal titration calorimetry

•Association between zinc (II) and dipicolylamine was studied by ITC.•Increasing heat release was observed as the titration proceeded.•Thermodynamics of the association was discussed.•The increasing heat release was ascribed to solubility increase of colloidal Zn(OH)2.

In this study, association between zinc (II) and dipicolylamine was studied by isothermal titration calorimetry. At neutral of weakly alkaline conditions, with zinc (II) in cell and dipicolylamine in syringe, increasing heat release was observed as the titration proceeded. Considering the equilibrium between Zn2+ and Zn(OH)2 at these conditions, the increasing heat release is ascribed to the increasing solubilization of colloidal Zn(OH)2 followed by neutralization of OH- by the buffer. Though quantitative determination of the increase in solubility is not accomplished, to the best of our knowledge, this is the first report about solubility increase of colloidal zinc hydroxide using calorimetric method.