Differential-pulse polarographic investigation of L- and DL-5-hydroxytryptophan in the presence of copper(II) ions

Abstract

The complexes of L- and DL-5-hydroxytryptophan have been investigated by differential-pulse polarography, in Britton–Robinson buffer in the pH range 5.0–10.3, ionic strength l= 0.2 mol dm^–3, at room temperature. It has been established that the formation of the ML⁺ and ML₂ complexes occurs. By applying Lingane's method, the over-all stability constant logβ₂ was 15.91 at pH 9.30. The stability constant of the ML⁺ complex, logβ₁, was determined to be 8.30 at pH 5.0 by Leden's method. No differences were found in stability constant values between L- and DL-5-hydroxytryptophan–Cu^II complexes at pH values above 9.0. Some differences were obtained in the qualitative results at pH values below 9.0.