Determination of thermodynamic parameters of cadmium(II) association to glutathione using the fluorescent reagent FluoZin-1

A method was developed to determine the conditional association constants of cadmium(II) [Cd(II)] complexes based on the reagent FluoZin-1, which forms a fluorescent complex with Cd(II). A solution containing Cd(II) and FluoZin-1 was titrated with glutathione while determining fluorescence intensity of FluoZin-1 to estimate levels of free Cd(II). The results were analyzed with a nonlinear least-squares method using the Solver algorithm of Microsoft Excel to yield conditional association constants for 1:1 and 1:2 Cd(II)–glutathione complexes. The values obtained were consistent with those reported previously using isothermal titration calorimetry.