Kinetic studies on isotopic exchange between lutetium ion and its ethylenediaminetetraacetate

Abstract

The thermal exchange reaction between lutenium ion and its EDTA complex in aqueous solution was studied in a pH range of 4·0–6·0 and concentrations of Lutetium ion and complex of the order of 10 −3–10 −4 M. The rate was found to be proportional to [H +] 1·0–1·5 and [LuY] 1·0, and to be influenced slightly by the concentration of lutetium ion. Slight dependence on ionic strength was also observed in an ionic strength range of 0·02–0·2. Apparent activation energies 10·2 kcal mole −1 and 11·6 kcal mole −1 were obtained at pH 5·8 and 4·5, respectively. The rate of exchange in a pH value higher than 4·0 is expressed by: R mole 1. −1 min −1=k1[ LuY][ H +]+k′ 2[ LuY][ H +] 2+k′ 4[ LuY][ H +] 3+k 5[ LuY][ Lu 3+]+k′ 6[ LuY]x[ H +][ Lu 3+] where κ 1, κ′ 2, κ′ 4, κ 5 and τ' 6 are 14 mole −1 min −1, 1·5 × 10 6 1 2 mole −2 min −1, 4·2 × 10 10 1 3 mole −3 min −1, 2·2 × 10 −2 1 mole −1 min −1 and 7·5 × 10 3 1 2 mole −2 min −1 at 25°C in 0·01 M ammonium acetate buffer solution. Under the conditions studied the reaction via the protonation process is predominant and the bimolecular collision process is minor. Spontaneous dissociation process can be ignored.