Temperature effects in cyanolysis using elemental sulfur

As part of our studies directed at new treatments for cyanide poisoning we examined the effect of temperature on both the non-catalyzed and the albumin-catalyzed reactions of cyanide with a colloidal suspension of elemental sulfur (CSES). Using saturated sulfur solutions prepared in two solvents, pyridine (PY) and methyl cellosolve (MC), the reactions were studied at 15.0, 25.0, 30.0 and 37.5 degrees C. For all the cyanolysis reactions (non-catalyzed and albumin-catalyzed) there is an enhancement of reaction rate when the organic solvent for the sulfur is MC. Irrespective of the solvent for the CSES, the non-catalyzed reactions gave linear Arrhenius plots (PY, correlation coefficient = 0.998; MC, correlation coefficient = 0.997). In each case the entropy of activation was positive (14.1 cal K-1 mol-1 for PY and 56.4 cal K-1 mol-1 for MC). In contrast with these results the albumin-catalyzed reactions generated non-linear Arrhenius plots and negative entropies of activation. Non-linear plots were observed with the three albumins studied: human serum albumin, heat-shock bovine serum albumin and fatty acid-free bovine serum albumin. The non-linear plots are the result of a more complex reaction sequence than a simple cyanolysis reaction.