Study on Dimerization of Diaqua(ethylenediamine)platinum(II) by Means of Ion-pair High-performance Liquid Chromatography

Abstract

The dimerization of diaqua(ethylenediamine)platinum(II) (DAEP) was investigated by means of ion-pair high-performance liquid chromatography. The experiments were carried out under the conditions of pH 2.50∼10.00 at an ionic strength of μ=0.01 containing 2.5×10^-3 mol⋅dm-3 of DAEP. The optimum HPLC conditions were as follows: column, Nucleosile 5 C18 (4.6 mm in diameter, 15 cm in length); eluent, acetonitrile: 0.1 mol⋅dm^-3 tartaric acid: sodium dodecyl sulfate =100 cm³: 100 cm³: 0.5 g; flow rate, 0.91 cm³⋅min^-1; detection, UV 260 nm. Two peaks appeared in the chromatograms, in which one peak (a)corresponded to DAEP. As the dimerization proceeded, another peak (b) corresponding to μ-p-hydroxo-bis[ethylenediamineplatinum(II)](D²⁺) appeared and grew gradually, while peak (a) fell down. After the equilibrium was attained, the ratio of the peak height of (a) to (b) was constant. The dimerization proceeded in the range of pH 4.90∼8.50, where DAEP, aqua(ethylenediamine)hydroxoplatinum(II) (AEHP) and ethylenediaminedihydroxoplatinum(II) (EDHP) were present. However, no dimerization occurred in lower or higher pH ranges, in which AEHP was in a negligible amount. Thus, the dimerization was found to proceed by the following equations.