Thermodynamic studies on complexation of dopamine with gadolinium(III) in water-ethanol system

The stability constant for complexation of gadolinium(III) with dopamine in mixed solvent systems of ethanol + water and free-energy changes have been determined spectro-photometrically with a temperature variation method in 0.2 mol dm− 3 sodium chloride as ionic medium employed at [(15, 25 and 35 ± 0.1) °C] at pH ranges of ~ 5 to ~ 7.5 with a high ratio of ligand to metal. The effect of solvent systems on protonation and complexation are discussed. Linear relationships are observed by plotting log K versus 1/D, where K and D are the stability and dielectric constants, respectively.