A partial exploration of the potential energy surfaces of SCN and HSCN: implications for the enzyme-mediated detoxification of cyanide.

Cyanide (CN) is considered to be a terrorist chemical weapon due to its ready availability in multi-kilogram quantities and multi-modal means of intoxication. The body uses the sulfur transferase enzyme rhodanese to detoxify cyanide via conversion of cyanide to thiocyanate. This paper explores the potential energy surfaces for the conversion of cyanide anion and hydrogen cyanide to thiocyanate anion and thiocyanic acid, respectively. The potential energy surface for the conversion of cyanide anion to thiocyanate shows that the formation of thiocyanate (SCN) is vastly preferred to formation of its isomer SNC. However, the potential energy surface for the conversion of hydrogen cyanide to thiocyanic acid reveals that the formation of HSCN and HNCS would be relatively equal. The failure for analytical methods to detect HNCS is rationalized by the observation that deprotonation of either HNCS or HSCN leads to the same thiocyanate anion.