Superoxide dismutase mimetic activity of cytokinin-copper(II) complexes

Dissociation constants of cytokinins, derivatives of purine which form complexes with cupric ion, were determined by spectrophotometry and the stability constants of their copper complexes by pH titration. The values found for kinetin were 3.76, 9.96, 7.8, and 15.3 for pK1, pK2, logk1, and log beta 2, respectively, and those for 6-benzylaminopurine were, in the same order, 3.90, 9.84, 8.3, and 15.9. The copper(II) complexes with kinetin and 6-benzylaminopurine had superoxide dismutase mimetic activity, and the reaction rate constants with superoxide, which were determined by polarography, were 2.3 X 10(-7) M-1 s-1 for kinetin and 1.5 X 10(-7) M-1 s-1 for 6-benzylaminopurine at pH 9.8 and 25 degrees C.