Complex formation. Data for solochrome Violet R. Part 6.—Some metal-dye-cysteine complexes

Abstract

The equilibrium constants for the reactions between the 1:1 chromium-Solochrome Violet R(2′-hydroxy-5′-sulphophenylazo-2-naphtholDH^–₂) complex (Cr^IIID) and L-cysteine hydrochloride (H₃L⁺) have been determined at 60, 75 and 90°C. At pH 4-5 the complex CrDHL is formed, in which the cysteine is coordinated to the chromium via the oxygen and nitrogen atoms. The stability constant (log K) is 5.66 at 60°C. Above pH 6 the complex CrDL^2–, in which the cysteine is co-ordinated through the sulphur and nitrogen atoms, is formed (log K= 8.28 at 60°C). For the corresponding Ni^II-dye-cysteine system (studied at 25°C) two complexes are also formed, but in this case the complex NiDHL (log K= 5.00) contains the cysteine coordinated through the oxygen and sulphur atoms. For NiDL (sulphur and nitrogen coordination) log K= 7.57.