New methods for the detection of cyanide based on displacement of the glutathione ligand of glutathionylcobalamin by cyanide

<p>Glutathionylcobalamin (GSCbl) is a vitamin B₁₂ derivative that contains glutathione as the upper axial ligand to cobalt via a Co–S bond. In the present study, we discovered that cyanide reacted with GSCbl, generating cyanocobalamin (CNCbl) and reduced glutathione (GSH) via dicyanocobalamin (diCNCbl) intermediate. This reaction was induced specifically by the nucleophilic attack of cyanide anion displacing the glutathione ligand of GSCbl. Based on the reaction of GSCbl with cyanide, we developed new methods for the detection of cyanide. The reaction intermediate, violet-coloured diCNCbl, could be applied for naked eye detection of cyanide and the detection limit was estimated to be as low as 520 μg L⁻¹ (20 μM) at pH = 10.0. The reaction product, CNCbl, could be applied for a spectrophotometric quantitative determination of cyanide with a detection limit of 26 μg L⁻¹ (1.0 μM) at pH = 9.0 and a linear range of 26–520 μg L⁻¹ (1.0–50 μM). In addition, the other reaction product, GSH, could be applied for a fluorometric quantitative determination of cyanide with a detection limit of 31 μg L⁻¹ (1.2 μM) at pH = 9.0 and a linear range of 31–520 μg L⁻¹ (1.2–20 μM). These new GSCbl-based methods are simple, highly specific and sensitive with great applicability for the detection of cyanide in biological and non-biological samples.</p